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GEO2322 - The Cryosphere, Larsen B Ice Shelf, image, Major, Major, Least…

- - - - Defined as the balance between inputs and outputs which can be defined at a location or across the entire ice system
      - Can be defined over multiple time scales (seasonally, annually etc.)
      - Controlled by differences in proportion of accumulation and ablation of ice into the cryosphere
      - Ablation
        
        Ablation focuses on basal melt and calving (melt water from below glaciers and large chunks being lost and minimalist, as well as surface melt and accumulation
        
        Accumulation
        
        Density (kg m-3)
        
        Snow: 50 - 300, low density, high void content
        
        Firn: 400-830, Compacted snow, survived a melt season
        
        Ice: 830 - 917, Air passages cut off
        
        To turn ice volume into SLE, we need to know the density, which helps to derive from satellite data
        
        Ablation is a function of energy balance (energy deficit or surplus at glacier surface)
        
        Qm = Qs + Ql + Qh + Qe
        
        Qm = energy available to melt ice
        
        Qs = net solar (shortwave) radiation
        
        Ql = net longwave (emitted) radiation
        
        Qh = sensible heat transfer (exchange with atmosphere)
        
        Qe = latent heat (absorbed/released during phase changes)
        
        Influence of Surface (Debris) cover
        
        Albedo
        
        Surface energy balance and ablation greatly influenced by supraglacial debris cover
        
        Typical albedos (radiation reflected):
        
        clean ice (34-51%)
        
        dirty ice (15-25%)
        
        debris covered ice (10-15%)
        
        Thin debris = increased absorption and re-radiation = increased ablation
        
        Thick debris = decreased conduction = increased protection = decreased ablation
        
        How much of the sun's radiation is reflected by the surface?
        
        Ablation
        
        If you cover ice with lots of debris – it actually insulates it.
        
        Cryoconite holes
        
        Sediment carried by the wind
        
        Creates a depression
        
        Micro-organisms colonise
        
        Further darken the ice sheet surface
        
        'Black and Bloom' and darkening occuring in Greenland
        
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        Calving
        
        'Dry' Calving
        
        Ice breaking off glaciers in steep mountain environments
        
        No melt involved, hence dry
        
        'Wet' calving (glacier or ice sheet finishes in the water, and parts break off into the water) is a function of:
        
        Water depth
        
        Water temperature
        
        Water salinity
        
        Tidal variation
        
        Glacier crevassing
        
        Presence of surface meltwater
        
        Freeze-thaw
        
        Surface meltwater ponds in crevasses this may exacerbate calving weathering
        
        Important for thinking about ice shelves
        
        Basal Melt
        
        Ice Shelf Basal Melting
        
        Warm’ ocean water eroding base of floating ice
        
        Causes grounding line to retreat
        
        Grounded Ice Subglacial melting
        
        Geothermal heat flux
        
        Melting on the base of the ice where it is in contact with the warm bedrock (mm/yr)
        
        Ice velocity (frictional heating)
        
        Small amounts of melt, but important in ice flow
        
        Antarctica has melting underneath due to contact with water, although Greenland does have this a little bit too
      - Mass balance as a whole system is the net Mass balance (which is the contribution of all of these smaller factors into one)
      - Ice Sheet Balance
        
        Accumulation = Ablation
        
        MASS IS BALANCED
        
        There is a balance between amount of water in ice and amount of water in ocean
        
        THIS IS A KEY IDEA
        
        Accumulation > Ablation
        
        POSITIVE MASS BALANCE
        
        Accumulation < Ablation
        
        NEGATIVE MASS BALANCE
        
        This water is going somewhere and will always end up in the oceans
        
        Glaciers will grow at lower temperatures -and/or greater snowfall
        
        And glaciers will shrink at higher temperatures and/or less snowfall
        
        BUT increased temperatures can be offset by an increase in snowfall
        
        Is increased snowfall high enough to combat an increase in ablation
        
        What kind of time scale is this ablation occuring on and how does this correlate to the timescale that snowfall is accumulating?
        
        In any one year for a whole glacial system:
        
        Mass Balance over Time
        
        Generally, in the winter there is a positive mass balance as there is increased snowfall and in summer there is a negative mass balance as increased temperatures lead to increased ablation
        
        Surface mass balance is (mostly) positive across Antarctica
        
        Ablation is largely from ice shelf melting and calving
        
        Its okay to also have an area with negative mass balance, this is not unhealthy. Seasonality is most likely the main cause of this negative net balance
        
        Although, Greenland does have a slighlty more negative mass balance
      - IPCC SROCC p4-16
      - Can be defined at a location or defined as a whole system
        
        Depends on what spatial scale we are looking at
        
        Can be better to look at it hollisticaly
        
        Location based surface mass balance
        
        Expected to see high ablation rates along the margin where sea level is the closest and high accumulation rates within the interior
        
        Surface Mass Balance is defined in mm “water equivalent per year in a given area (m square for example. Water equivalent eradicates the different densities in the accumulation and the ablation zone.
        
        If you melted a m squared of ice, how deep would it be? How much water would it make? This is useful as a m squared of ice would make more water than a m squared of snow
        
        Takes account for different densities
        
        Here we can see the surface mass balance on the Greenland Ice sheet
        
        We expect positive mass balance in the accumulation zones in the centre for a healthy glacier system
        
        And negative mass balance in the ablation zones, outside margin of the ice sheet
        
        This doesn't tell us the overall net mass balance of the Greenland Ice Sheet
        
        Assessing local mass balance changes over time to investigate spatial variation - Modelled surface mass balance trend (1958–2007) in kg m2, Ettema et al., 2009
        
        Modelled approach to estimating surfacemass balance trends
        
        Looking over time where is there changes in the mass balance signal
        
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        This study predicts that there will be thinning of the ice sheets in the the purple areas of the periphery
        
        There are spatial structures to this thinning, it wont thin the same everywhere, some places will thin more than others
        
        There are areas that are expected to thicken, particularly in the centre
        
        As a whole system
        
        Zone based mass balance
        
        Accumulation zone
        
        Accumulation > Ablation (+ve MB)
        
        Ablation zone
        
        Ablation > Accumulation (-ve MB)
        
        Antarctica (Marine Terminating)
        
        Ablation is not just on the surface but is also experiencing melt into the water
        
        Greenland (Land terminating)
        
        Simpler, just affected by snowfall and surface ablation
        
        The Equilibrium Line Altitude (ELA) divides the accumulation and ablation zones, it acts as a boundary between the two
        
        Must consider this when looking at changing mass of glaciers
        
        This is the point where net mass balance = 0
      - Cogley et al. 2011
        
        Net Mass Balance of all these things is resulting to contribution to sea level
        
        Net Mass Balance will tell you overall whether that cryospheric feature is contributing to sea level rise or is accumulating water instead
        
        Interglacial to Glacial, sea level falls as cryosphere grows
      - Mass Balance Components
        
        Accumulation (inputs)
        
        Snowfall
        
        Wind-blown drift
        
        Avalanches
        
        Condensation (rime)
        
        Freezing rain or external water
        
        Ablation (outputs)
        
        Calving (wet/dry)
        
        Melting
        
        Wind-blown drift
        
        Avalanches
        
        Evaporation/sublimation
      - Mass Balance Gradients
        
        ◦ increase in mass balance with altitude
        
        ◦ Steep gradients = high acc. & abl. rates (e.g. moist, mid-latitudes such as Norway)
        
        ◦ Shallow gradients = low acc. & abl. rates (e.g. arid, polar latitudes such as Arctic Canada)
        
        ◦ the higher the gradient, the faster the flow
    - - Ice Flow
        
        Provides dynamic link between accumulation and ablation subsystems
        
        Ice discharge: volume of ice passing through the equilibrium line during the balance year (m3/year). Flow rate dependent on magnitude of input and output.
        
        Factors that control ice flow
        
        Mass balance (rate of accumulation and ablation)
        
        Ice (&valley) geometry (thickness, steepness)
        
        Ice properties (temperature, density)
        
        Ice Internal Deformation
        
        Ice can be considered a fluid, though it is actually a solid
        
        => It flows via deformation of ice crystals
        
        Ice Temperature
        
        Ice flow velocity is a function of temperature
        
        Ice can be different temperatures, it can be near melting – or super frozen.
        
        Warm ice deforms more readily than cold ice
        
        Ice temperature varies with depth
        
        o Surface air temp. controls ice temp. at the surface
        
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        Temperature Regime of Glaciers
        
        Warm Based
        
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        Polythermal
        
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        Cold Based
        
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        Bedrock conditions (hard, soft, frozen or thawed bed)
        
        Basal Sliding
        
        Subglacial water may cause the separation of ice from its bed and cause it to ‘float’ if it is at sufficient pressure:
        
        Hydraulic jacking
        
        Hard Bedrock Sliding
        
        Where ice is not frozen at the base, basal sliding can occur
        
        Seasonal variations in velocity observed
        
        ◦ E.g. Gornergletscher, summer velocity is 20-80 % higher than the average (Weertman, 1964)
        
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        Enhanced Basal Sliding
        
        Due to stress concentration when ice encounters an obstacle
        
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        Regelation (pressure melting)
        
        Pressure forces ice to melt and re-freeze on the other side of the obstacle
        
        Factors controlling sliding:
        
        ◦ bed roughness
        
        ◦ quantity & distribution of water at bed
        
        ◦ amount of debris embedded in base of glacier
        
        Sediment Deformation
        
        ◦ Ice is often underlain by soft sediments rather than hard bedrock
        
        ◦ This can deform allowing ice to flow very fast
        
        ◦ Depends on water content of sediment
        
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        Subglacial hydrology
        
        Subglacial Hydrology
        
        Hard bed theory
        
        Water ‘drowns’ roughness (Weertman, 1964)
        
        Decouples the ice from the bed (Lliboutry, 1968)
        
        Soft bed theory (different role of water)
        
        Ice sliding facilitated by deformation of subglacial sediment (Blankenship et al., 1986)
        
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        Surging Glaciers
        
        Cyclic glacier flow instability
        
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        Water in sediments
        
        Ice stream cyclicity
        
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        High water content
        
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        Deform under the stress exerted by the ice
        
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        (Tulaczyk et al., 2000a)
        
        Terminal environment (land, sea, ice shelf, sea ice)
        
        Terminal environment
        
        Tidewater Glaciers
        
        Glaciers that terminate into the sea (and discharge icebergs into the ocean)
        
        Occur in:
        
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        Proposed “tidewater glacier cycle” (e.g. Vieli, 2015, Meier and Post, 1987, Post, 1975)
        
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        Marine Ice Sheet Instability
        
        Marine Ice Sheet Instability Hypothesis (MISIH)
        
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        Bed below sea level
        
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        Retreating of Grounding Line
        
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        If you remove and ice shelf quickly, no matter whether the slope is pro/retrograde.
        
        Stress and Strain
        
        ‘Stress’ is a measure of how hard a material is pushed or pulled as a result of external forces.
        
        All stresses consist of two equal and opposite tractions
        
        Normal stresses
        
        act at right angles (normal) to a surface
        
        Shear stresses
        
        act parallel to a surface
        
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        Driving Stress
        
        Stress therefore increases with thickness
        Normal stresses increase from 0 at the surface to maximum at the bed
        
        Driving stress ()
        
        = ρigH tan(α)
        
         ρigH α
        
        ρi = ice density (~900 kg m-3)
        
        g = gravity (9.81 m sec-2)
        
        H = ice thickness
        
        α = surface slope
        
        Ice flow is driven by gravity (gravitational driving stress – golden syrup spreading under its own weight) – the more mass the faster it spreads.
        
        ‘Strain’ is a measure of the amount of deformation that occurs as a result of the stress.
        
        Stress Balance
        
        The Shallow Ice Approximation (SIA)
        
        Considered gravitational driving stress and basal drag as the only factors influencing ice dynamics.
        
        Simplified glacier modelling method, assuming that ice sheets are mainly split up by basal sheer stress, meaning its not necessary to consider other forces
        
        Basal sheer stress is the forces that pushes a glacier or ice sheet along its base (primary result of gravity)
        
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        Shallow Shelf Approximation
        
        Basal drag neglected
        
        Longitudinal stresses & lateral shear stresses important
      - Ice Mass Response to Climate
        
        'Steady-state' equilibrium
        
        Assumes that by default, glacier is in equilibrium* But…if perturbed by external (or internal) drivers e.g. change in temperature/accumulation
        
        Glacier will adjust over a period of time to reach a new ‘steady-state’ it will advance or retreat to a new position frontal
        
        *inputs = outputs (mass balance = 0) so glacier is ‘in balance’ and unchanging over time
        
        ELA: Equilibrium Line Altitude
        
        • It is the boundary between the accumulation zone (area of net mass gain) and the ablation zone (area of net mass loss)
        
        • Important theoretical concept when considering the changing mass of glaciers (mass balance)
        
        • Changes in climate affect both accumulation and ablation – causing the ELA to move up or down.
        
        Although climate variability exists!
        
        Ice & Landscape
        
        Warm-based ice advance causes erosion & leaves erosional features
        
        Warm-based ice retreat produces deposition & obscures erosional features
        
        Cold-based ice preserves underlying surfaces
        
        Importance for future ice sheet change
        
        Increased ice velocity
        
        Leads to enhanced delivery of ice to the ablation zone
        
        => becomes out of balance with climate
        
        => increased mass loss
        
        Leads to thinner ice
        
        => lower elevations & higher air temperatures
        
        => increased likelihood of ice floatation
        
        Greenland Ice Sheet
        
        Focus on – site 4:
        
        d) Blue line: velocity
        
        e) Blue line: temperature
        
        We can see decadal slowdown of a land-terminating sector of the Greenland Ice Sheet despite warming
        
        Change in ocean forcing is still a factor is terminating glaciers
        
        Variability in the meltwater supply is more important than the amount of water
        
        Consider efficiency of the water system
        (Schoof, 2010)
      - Subglacial Water/Drainage Systems
        
        Channelised Systems
        
        Water is confined to narrow conduits
        
        Efficient pathways allowing rapid flow through well connected networks
        
        Channelised systems: drainage is carried by a few channels (type 4).
        
        Water Pressure
        
        As discharge increases, pressure decreases
        
        Localised contact with the ice
        
        Decreased pressure & localized contact means reduced ice flow
        
        At high discharge, channels form
        
        Distributed systems
        
        Extend over large areas of the bed
        
        Less efficient
        
        Distributed systems: drainage takes place over much of the bed (type 1, 2, 5, 6 and 7)
        
        Water pressure
        
        Increased discharge means increased pressure
        
        Widespread contact with the ice
        
        Increased pressure means increased ice flow
        
        Drainage System Elements
        
        Bulk movement with deforming till;
        
        Darcian porewater flow (permeability, hydraulic gradient);
        
        Pipe flow;
        
        Dendritic network;
        
        Linked cavity system;
        
        Braided canal network;
        
        Thin film at the ice-rock interface.
        
        These are constantly undergoing spatial and temporal changes – link to ice dynamics
  - - - Sliding, and therefore significant erosion can only occur where the ice is at the pressure melting point
        Cold-based ice tends to protect underlying stratum
    - - Abrasion
      - Plucking (also known as Quarrying)
        
        Extended abrasion processes enlarges cracks
        
        Leads to isolation of fragments and rock fracture
        
        Strongly influenced by pre-existing joints within bedrock
        
        Regelation mechanism of sliding important
        
        (With added pressure, ice can melt at lower points (ice skating melting ice) – this is called regelation)
      - Boulton (1979)
    - - Evidence of scoring by particles embedded in glacier
      - • Direct evidence of abrasion
      - • And therefore sliding at the bed
      - May widen down glacier due to progressive ‘blunting’ of embedded particle which can be used to derive ice-flow direction
      - Striae (singular: striation) are scratches incised into bedrock or clast surfaces
    - - There are many ways that debris can travel through glacial systems
      - Depends on glacier configuration and conditions
      - Debris may undergo several cycles of ‘modification’ between source and deposition
      - Due to ice/water/wind/gravity etc
      - Leads to very large variability in form and appearance!
      - Transport pathways
        
        Supraglacial debris entrainment
        
        Ice Caps
        
        Nunataks, Volcanic ash (e.g. Iceland)
        
        Ice Sheets
        
        Nunataks (exposed rocky peaks or ridges that protrude through an ice sheet or glacier)
        
        Valley Glaciers
        
        Valley sides and headwalls
        
        Subglacial debris entrainment
        
        Basal ice can be very different from the rest of the glacier due to ‘freeze-on’ (regelation)
        
        Can have a very high (>75%) debris content
        
        Has implications for:
        
        Ice motion, as debris content changes the rheology (i.e. how it deforms under driving stress)
        
        Rates of subglacial erosion
        
        Debris can be transported large distance, beyond the glacier margins (e.g. ice-rafted)
    - - Whalebacks and rock drumlins
        
        Elongate, approximately symmetrical, smoothed bedrock bumps
      - Crag and tails
        
        Produced by ice streaming around an obstacle
      - Roches Moutonnees
        
        Assymetric bedrock bumps with abraded up-ice (stoss) sides and quarried down-ice (lee) sides
      - Channels
        
        Ice marginal channels and proglacial channels
      - Glacial troughs
        
        Steep sided, flat-bottomed
        
        distinguished from fluvial troughs:
        
        ◦ ~80% larger in CSA, and ~30 % deeper (Amerson (2008))
        
        ◦ May contain overdeepenings
        
        Erosion in the main trough is greater than that in tributary glacier
        
        This creates hanging valleys
      - Cirques
        
        Also known as corries or coires in Scotland, and cwms in Wales
        
        Hollow, open downstream, but bounded upstream by a steep headwall
        
        Gently sloping floor or overdeepened basin
        
        Adjoining cirques separated by an Arete
        
        Most characteristic form of glacial erosion in mountains
    - - Glacifluvial deposits (secondary)
      - Gravitational Mass Movement (secondary)
      - Glacigenic deposits (primary)
        
        Key glacigenic landform: Moraines
        
        Why are they important?
        
        Indicate the specific marginal processes at work
        
        Powerful tool for reconstructing changes in behaviour
        
        Patterns of advance and retreat – history of movement
        
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        Different moraine types have different characteristic morphologies, formational mechanisms and result from different glacier behaviour
        
        There are three different types of moraines
        
        Dump moraines
        
        • Ridges formed of supraglacial and subglacial material that accumulates at a stationary glacier front that has steep margins, and is then deposited by slump and flow processes
        
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        • Common to temperate glacier systems
        
        • Frontal and lateral examples; often latero-frontal
        
        • Depositional-constructional features
        
        • Material is not deformed (as in glaciotectonic moraines)
        
        • If the glacier front is stable/in place – it means that the glacier system is in equilibrium
        
        Ablation moraines
        
        Ablation moraine is supraglacial material that is present on the surface of a pro-glacial stranded/detached ice block that subsequently melts
        
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        Ablation moraines formation
        
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        Glaciotectonic moraines (annual push moraines)
        
        Glaciotectonism
        
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        Inferring glacier behaviour from moraine type
        
        Dump Moraines
        
        Stationary margin: supraglacial sediment, frontal deposition
        
        Ablation Moraines
        
        Detached or stagnating ice margin: hummocky terrain
        
        Glaciotectonic
        
        Steady ice recession, seasonal, limited deformation, climate proxy?
    - - Non-aligned – no relation to ice flow
        
        SSSSS
      - Transverse – oriented perpendicular to flow
        
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        Ribbed moraines
      - Longitudinal – oriented with ice flow
        
        Drumlins
        
        Mega-scale glacial lineation
        
        We will consider as a single family of bedforms related to ice sheets
      - Transverse bedforms: Ribbed Moraines
        
        Till-formed ribs generated transverse to flow
        
        Often found in ‘core areas of glaciation’, near ice divides, ice flow slow
        
        Have zero elongation (i.e. no stretching along flow)
        
        Very regular spacing, 100s m wide, 100s-1000s m long, 10s m high
        
        Close link to drumlins (sometimes drumlinised)
        
        Longitudinal bedforms: Drumlins
        
        Stubby evolving to elongated
        
        ‘Basket of eggs’ topography
        
        Blunt stoss, tapered lee
        
        Bedform points down-flow
        
        Found under tracks of outlet glaciers, ice streams, retreating glaciers
        
        >58,000 drumlins in the UK and Ireland
        
        Show flow pattern of British Ice Sheet
        
        Long debate about whether drumlins are depositional or erosional landforms.
        
        Bedforms in the direction of ice flow – much more common than transverse bedforms
        
        Longitudinal bedforms: Mega-scale glacial lineations
        
        Drumlins often grade into more elongate MSGLs
        
        Long, elongated groove-ridge bedforms
        
        Exceptionally parallel
        
        6-10’s kms long, 5-15 m high
        
        Always found with deformation till – soft sediments, deforming bed
        
        Swarms over vast areas, typically in troughs but sometimes over flat plains
        
        Mark out past ice stream tracks
  - - - When water moves through the hydrological cycle, different isotopes of Oxygen are preferred due to their isotopic lightness, and the ratios of O18 to O16 in marine sediment can help us to reconstruct glacial and interglacial periods.
      - Timescales of glaciation and deglaciation are different – glacial periods can take a long time to form – but can end very quickly due to strong positive feedbacks.
    - - Astronomers since ancient Greeks observed gradual, progressive changes in Earth’s orbit
        
        Rantanen et al. 2022
      - Later attributed to gravitational forces exerted on Earth from other planets and moon
      - Defined 3 major orbital parameters: Eccentricity (Shape), Obliquity (Tilt) and Precession (Wobble)
        
        Eccentricity (S) = 100 ka
        
        Obliquity (T) = 40 ka
        
        Precession (W) - 20 ka
      - Developed theories that explained ice ages
      - Change in incoming radiation as a result of Milankovitch cycles is actually quite small
        
        Ice ages are caused by the feedbacks to this change in incoming radiation (polar amplification)
        
        So how does this cause ice ages?
        
        Positive feedback mechanisms:
        
        Ice/albedo feedback
        
        Ice/elevation feedback
        
        Cloud feedbacks
        
        Lapse rate feedback
        
        Ice / ocean feedbacks
      - Milankovitch said that the key to ice ages is summer insolation in high northern latitudes. This is due to a decreased albedo causing major melting of the cryosphere in the Northern Hemisphere – causing fluxes of freshwater and freezing causing an ice age.
        
        Northern and Southern Hemisphere
        
        Southern
        
        South Pole
        
        Land mass => less ice / albedo +ve feedback
        Ice shelves => more ice shelf melting / sea ice – ve feedback?
        
        Hemisphere
        
        Less land mass & Antarctic Ocean
        
        Northern
        
        North Pole
        
        Ocean => more ice / albedo +ve feedback
        
        Hemisphere
        
        More land mass & Greenland Ice sheet
    - - Positive feedback caused by orbital forcing affecting polar regions and ice cover.
        
        Coined by Manabe and Stouffer – 1980
        
        They expected polar amplification to be stronger in the Northern Hemisphere than the Southern Hemisphere – less potential for ice/albedo feedback in S.hem due to sea ice distribution.
        
        Warming in the Arctic is regional, with local amplification being higher than it is in surrounding regions.
      - Cloud / sea ice feedbacks
        
        In non-summer months (positive feedback)
        
        Decreased sea ice cover
        
        Greater cloud cover
        
        Less longwave radiation escapes
        
        Warmer
        
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        Cloud optical depth (negative feedback)
        
        Climate warms
        
        Fraction of liquid water in clouds increases
        
        Higher cloud albedo
        
        Increased reflection of incoming radiation
        
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      - Negative Polar Feedbacks
        
        Ice shelf melting / sea ice
        
        Ocean Warming
        
        Ice shelf melting
        
        Freshwater release
        
        Sea ice expansion
        
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        Glacial Isostatic Adjustment
        
        Less Ice Thickness
        
        Bed uplift
        
        Shallower grounding line
        
        Stabilising effect
        
        e.g. Whitehouse et al. (2019)
      - Marine Ice Sheet Instability
        
        Retreat of grounding line
        
        → Greater ice thickness at grounding line
        
        → Greater discharge of ice
        
        → Grounding line retreat into deeper ocean
        
        → Greater ice thickness at grounding line
        
        → Greater discharge of ice
    - - Positive feedback amplifies a change, leading to an increase in the output
        
        Change in the same direction as the original change
      - While negative feedback reduces a change, leading to a decrease in the output and a return towards a stable state.
        
        Change in the opposite direction as the original change
      - Climate Feedback Examples
        
        Positive
        
        Increased temperatures
        
        Increased evaporation
        
        Increased water vapour
        
        Increased trapping of outgoing radiation
        
        Increased temperatures
        
        Negative
        
        Increased temperatures
        
        Increased evaporation
        
        Increased water vapour
        
        Increased clouds
        
        Decreased incoming radiation
        
        Decreased temperatures
        
        Lapse rate feedback
        
        Stable stratification of atmosphere in Arctic
        
        This restricts mixing between the lower and free troposphere
        
        Tells you how the temperature changes as the atmosphere changes
        
        Warming at earth surface of more than warming at the top of atmosphere
        
        Less longwave radiation lost
        
        Deep ocean / thermohaline circulation
        
        Deep water formation
        
        Cold water is denser
        
        Evaporation by dry polar air
        
        Only water is evaporated, leaving salt behind
        
        The water left behind is more saline, and therefore denser
        
        Sea ice formation
        
        Sea freezes to form sea ice
        
        Salt is not incorporated into sea ice
        
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        Thermohaline Circulation
        
        Warm surface waters flow north and cool
        
        This has led to the creation of the North Atlantic Deep Water (NADW)
        
        Impact of freshwater flux on thermohaline circulation
        
        Influx of fresh water would disrupt thermohaline circulation
        
        Greenland is losing mass, both from surface melting & dynamic thinning
        
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        This effects the AMOC (Atlantic Meridional Ocean Current) that could have large effects on climate and huge human impacts – especially in areas around the UK and Europe. It regulates the climate of the UK – and keeps it so humid for its latitude.
      - Ice/albedo feedback (positive)
        
        Amplification of temperature trend due to feedbacks involving sea ice & snow cover. On fresh snow 75-90% of incoming radiation is reflected back.
        
        Increase albedo
        
        => more incoming radiation reflected back => greater potential for temperature lowering
        
        => Glaciation
        
        This can apply in the formation of an ice age. When there is less insolation and lower temperature, more snow falls and more radiation is reflected back. This causes less melting – and increased accumulation allowing for the build-up of large areas of permanent albedo – growing ice sheets and sea ice.
        
        Sea ice is the top of the ocean freezing and snowfall is freshwater accumulating on top of glaciers. Less sea ice also causes lower albedo.
        
        Ice shelfs can also lower albedo when the collapse as there is more melting and lowering area of available albedo.
        
        Seen in the collapse of the Larsen Ice Shelf in 2002 (NW Antarctica)
        
        Decrease albedo
        
        => less incoming radiation reflected back => greater potential for temperature rise
        
        => Deglaciation
        
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        Albedo Values
        
        Reflectivity of the surface (% incoming radiation reflected)
        
        Fresh Snow: 75-90 %
        
        Sea Ice: 30-40 %
        
        Land: < 30 %
        
        Road: 5-10%
        
        Water: 2-4%
        
        (From Smithson et al.)
      - Ice/elevation feedback (positive)
        
        Ice sheets have ice thicknesses of 1000s metres
        
        => adds elevation to ice sheet locality
        
        => alters local & global climate
        
        Temperature cools with elevation => less melt
        
        Snowfall increases with elevation (cold air holds less moisture) => more accumulation
        
        => Mass balance becomes more positive
        
        => Ice sheet grows
      - Feedbacks and sea level change
        
        Allows formerly marine regions to be glaciated
        
        => more sea level fall
        
        => more land for glaciation
        
        => ice sheet grows more & albedo feedback
        
        Increases elevation of high topography
        
        => elevation feedback
  - - - The IMBIE Team 2019
        Rignot and Thomas measured mass using volume, but this measurement in missing density. The IMBIE team recreated this by using satellite imaging and different units (tonnes per year which is a mass)
        
        Did this for the Greenland and Antarctic ice sheets
        
        Greenland lost 3,800 billion tonnes of ice between 1992 and 2018, causing mean sea level to rise by 10.6 +- 0.9mm
        
        IMBIE team uses tonnes per year
        
        'Although the ice sheet was close to a state of balance in the 1990s, annual losses have risen since then, peaking at 335 +- 62 billion tonnes per year in 2011' This is the net loss
      - One of the first attempts to create a budget of a polar ice sheet
        
        Creating a way of accounting for the inputs and outputs of the ice dynamics
      - There is no universally accepted way of determining mass balance, no standardised units
      - This paper used km cubed per year, measuring mass gains and losses using a volume calculations
        
        Need to turn the volume calculations into mass values
        
        This requires density values
      - Must also focus on uncertainties
    - - Decrease in mass balance in coastal areas
      - Small increase in the centre
      - Does not counteract decrease in coastal areas
      - Hence will have a –ve overall mass balance
      - => system not in balance
      - => net loss in overall mass balance
    - - commonly appear asynchronous to climatic forcing
        seem to be strongly influenced by basal topography
    - - e.g. Vellinga &
        Wood (2002)
      - Temperature change 20-30 years after thermohaline shutdown (from global climate model)
    - - Sea level in the Quaternary
        
        **Eustatic sea level change**: global average sea-level fluctuates with global ice volume.
        
        This is **closely correlated with the glacial-interglacial cycle**
        
        **Sea level at LGM 120/125m lower** than present
      - Quaternary Ice Sheets
        
        Europe (British, Scandinvian)
        
        North American (Laurentide, Cordilleran)
        
        Russia (Barents, Kara)
        
        Greenland
        
        This was a period of increased global ice volume, and therefore lower sea levels
      - British Ice Sheet
        
        Maximum extent of British-Irish Ice sheet during Devensian glacial period
        
        LGM was around 21,000 years ago
        
        Covered Scotland, Ireland, Wales and Northern England
        
        800,000km cubed and 1.5m thick
        
        One third of the size of modern Greenland
        
        Significant pressure system over ice
      - Glacial Deposition
        
        1.) Glacigenic deposits - Primary
        
        2.) Glacifluvial deposits – Secondary (Not in situ – modified after primary deposits)
        
        a. Seasonal abundance in meltwater makes sediment deposited from flowing water very common– especially in temperate regions
        
        b. They are some of the easiest deposits to identify due to high degree of sorting due its high energy fluvial transport
        
        i. These can also be seen in crossbedding (cross-laminated facies) where the sediment is laid diagonally due to the strong flow of water (characterised of shallow fast flowing water) during deposition and the presence of plane bed deposits.
        
        3.) Gravitational Mass Movement – Secondary
        
        a. Steep unstable slopes extremely common in glacial environments
        
        i. Slides (Layer of rock parallel to slope), Slumps (Creating cascading rock steps), Rockfalls (Fractured rock falling off of cliffs), Flows (Seen mostly in sandy sediments, especially when wet)
      - Fall deposits: Debris Flow
        
        **Caused by flash floods or GLOFs**
        
        **Homogenizes sediments**: ‘cement mixer’
        
        **Diamict (poorly sorted) deposits hard to distinguish from subglacial tills**
        
        Individual deposits form lobate sheets cm to m thick, covering (up to) >1000 m2.
        
        Sequences of deposits from multiple events can be > 10 m thick and > 10 000 m2.
      - Effect of transport on debris
        
        Active vs Passive (Boulton, 1978)
        
        Passive Transport – 'high-level transport'
        
        Supraglacial and englacially transported particles transported with little or no modification
        
        Active Transport – in basal transport zone
        
        Sediment transported in the basal tractive zone
        
        Abrasion and crushing progressively modifies particles
        
        Glaciofluvial Transport
        
        Suspended load
        
        For a given water flow, grains settle at a rate proportional to diameter
        
        Generally finer than sand
        
        Bedload
        
        Larger particles roll/slide across stream bed
        
        Sorting
        
        High energy can transport smaller and larger particles, but low energy can only transport smaller particles
        
        Glaciers can transport larger sediments, so when looking a t past environments – the more sorted something is, the less likely it is a primary glacigenic sediment.
        
        Matrix-supported diamict – finer sediment surrounding larger sediment deposits (large boulders or cobbles surrounded by sands, silts etc)
        
        Clast Morphology
        
        Bedding? Parallel beds?
        
        Imbrication? Alignment of clasts – used to indicate ice/water flow directions, clast supported, matric supported or non-imbricated?
        
        Matrix supported diamict
        
        Unconformable – missing/ irregular pattern?? This can represent a large time gap in the geological record
        
        We believe that these deposits (Upper Cliff) may have been deposited through solifluction. We can see this process occurs on Mars. It is a periglacial head deposit – which can be seen all over North Devon.
        
        Glacial and fluvial transport imprint distinctive signature on the morphology of clasts
        
        Shape (relative dimensions of height, width, depth)
        
        Roundness (degree of curvature of clast edges)
        
        Texture (character of the clast surface)
        
        Wear patterns (nature and orientation of erosion)
        
        Sediment Fabric
      - Interpreting stratigraphy in the field
        
        When looking through the field photos, pay attention to:
        
        Sediment appearance
        
        Fabric
        
        E.g. cross-bedding/imbrication/faulting/folding.
        
        Contacts between units
        
        ‘conformable’ = continuous deposition
        
        ‘unconformable’ = erosion = missing sediments (& time!)
      - Unconformities
        
        Distinct boundary in orientation of sediment bedding
        
        Or…boundary between sedimentary and metamorphic/igneous rocks
        
        ‘Missing’ rocks
        
        Represents a large time gap in the geological record!
      - Pink Boulder
        
        Pink granite boulder that is thought to be a glacial erratic
        
        We think it was more than one glacial period that brought this deposit to Saunton. We believe that the only glacial period that had a far enough extent to bring this boulder down was around 400,000 years ago in the Anglian glacial period.
        
        We can use our understanding of uniformitarianism to understand and reconstruct the glacial landscapes that we see today.
    - - There are strong links between sea ice and albedo, with decreased sea ice leading to decreased albedo with less solar radiation being reflected back - and more being absorbed into the Earth
        
        We can also see large extents of sea ice loss
      - So what is sea ice?
        
        Frozen sea water: ~ metres thick
        
        'Frazil' ice, not meteoric ice
        
        How does it form
        
        Small needle-like ice crystals called frazil form
        
        Salt doesn’t freeze – so sea ice largely fresh water
        
        Sheets of sea ice form when frazil crystals float to the surface, accumulate and bond together
        
        Difference in process & make up depending on ocean conditions
        
        Grease ice vs pancake ice
      - Sea Ice Features
        
        'First year' and Multi-year' Ice
        
        When the ice first forms it is called ‘first year ice’ and when this doesn’t freeze in the warmer months and begins to accumulate again in the next cold period, it is classed as ‘multi-year ice’.
        
        Due to the compression of ice acting against itself, a process of compression forming pressure ridges forms dips in the ice. A shearing process occurs when fast moving ice and drift pack ice collides within the ‘shear zone’. Tides in the sea can also create fractures.
        
        Distribution of multi-year Ice
        
        From this graph we can see that over time, there is less sea ice coverage, but also less multi-year ice.
        
        This means that the majority is first year ice which is easy to melt and break away making it much more vulnerable.
        Sea ice can be talked about as ‘coverage extent’ or sea ice ‘area’.
        
        Remember that in either hemisphere, the seasons are swapped. Arctic winter is Sep-March and Antarctic summer is Sep-March.
        
        Leads
        
        Linear Cracks
        
        Polynas
        
        Open ocean
        
        Warm water upwelling
        
        Coastal polynyas
        
        Wind driven
      - Arctic Sea Ice
        
        Spatially, there is a large difference in sea ice across different regions of the Arctic.
        
        Here we can see two graphs to show the monthly deviations of sea ice extents in two different regions in the Arctic
        
        Here we can see that in March in the Arctic, there is a a relatively high extent of sea ice, which decreases by September
        
        From this graph we can see that all years since 2012 have been out of the interquartile range for sea ice extent (lower) due to warmer ocean waters in the regions and higher atmospheric temperatures leading to increasing melting and decreasing in amount of ocean freezing.
        
        Causes of sea ice change
        
        Long Term Trend
        
        Ice / albedo feedback is key contributor
        
        Loss of multiyear ice
        
        Warm, moist air intrusions
        
        Short Term Variability
        
        Climate oscillations (e.g. North Atlantic Oscillations)
        
        Antarctic Sea Ice
        
        Antarctic sea-ice at ‘mind-blowing’ low alarms experts
        
        Key Trends
        
        We can even see differences in just one year difference (2022-2023)
        
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        Purich and Doddridge (2023)
        
        3 more items...
        
        Models vs Observations
        
        Scientists have also been asking why models generally fail to reproduce the increase in Antarctic sea ice from 1979 to 2014. Suggestions include wind changes random variability in the climate system changes in stratospheric ozone (which was later shown to cause sea-ice loss), and freshwater from Antarctic ice shelves
        
        (Sun & Eisenman, 2021)
        
        Impacts of Sea Ice Change
        
        Wildlife
        
        As we know, sea ice acts as a habitat for many species living in the Arctic and Antarctic
        
        The loss of this habitat drives animals out of their habitat, isolating terrestrial populations and restricts gene flow
        
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        Northern Sea Routes
        
        This is a list of all the number of complete through tradeouts per flag state, meaning journeys are increasing
        
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      - Polar Feedbacks (Ice Shelf Melting / Sea Ice)
        
        Ocean Warming
        
        Ice shelf melting
        
        Freshwater release
        
        Sea ice expansion
        
        Reduced ocean warming
        
        Goosse et al. 2018
      - Deep Ocean / Thermohaline Circulation
        
        Warm surface waters flow north & cool
        
        North Atlantic Deep Water (NADW)
        
        Impact of freshwater flux on thermohaline
        
        Greenland is losing mass, both from surface melting & dynamic thinning
        
        ◦ What does this mean for the thermohaline circulation?
        
        ◦ Influx of fresh water would disrupt thermohaline circulation
        
        ◦ Remember salinity of the water is an important driving factor in the thermohaline circulation
- - - - Key components of mass balance are inputs from snowfall and outputs from ablation
    - - Some parts of Greenland land topography is below sea level – but this is due to cryogenic effects of uplift – causing the ground to sink due to its weight. If all of the ice was melted – the rock would begin to uplift.
    - - Disko Bay, Jakobshavn and Isbrae
      - South Greenland is a lot warmer – with strong ocean influences
    - - Helheim
      - Kangerdluqssuaq
    - - Petermann - 79˚N
      - Nioghalvfjerdsfjorden/ Zachariæ Isstrøm
    - - Positive in interior
      - Negative in coastal regions
      - This is fine as long as there is enough accumulation to maintain the ice sheet
    - - Greenland
        
        Brought warmer water
        
        Holland et al. (2008)
        
        Irminger current
      - Antarctica
        
        Amundsen Sea ice streams
        
        Pine Island Glacier (PIG)
        
        Thwaites Glacier
  - - - Key components of mass balance are inputs from snowfall and outputs from ablation and loss from water ice interface (underside melting) and iceberg calving (chunks breaking off)
    - - The point at which ice stops being on the bedrock substrate and begins to float. Ice hits a water boundary and is being constrained in West Antarctica
    - - The majority of the bed of the Antarctic Ice sheet is underwater. Although, there are areas above sea level, consisting of transatlantic mountains
    - - Annunden Sea Sector
        
        West point of Antarctica Pine Island, Thwaites and other numerous outlet glaciers
        
        Ice streams: Getz ice shelf and Abbot ice shelf
      - Weddel Sea Sector
        
        North-west Antartica – Flows into the Weddel Sea with Ronne ice shelf
        
        Ice streams: Institute, Rutford, Evans
      - Ross Sea Sector
        
        The ice streams in Antarctica are names after the oceans that they flow into
        
        . South Ice streams are called the Ross Ice Shelf or Siple Coast.
        
        Siple Coast
        
        Water moved from Ice stream C to ice stream B
        
        Function of the yield strength of the sediment (Tulaczyk et al. 2000)
        
        Function of the water content of the sediment and not the water pressure
        
        A function of water available (local/regional?) – didn’t allow for any water coming into and environment
    - - North East
        
        Jutulstaumen
        
        Shiraze
        
        Denman
      - Eastern
        
        Fisher, Mellor, Lambert – Worlds Largest Glacier
        
        Amery ice shelf
      - South East
        
        Totten
        
        Ninnis
        
        Mertz
    - - Key ice shelf – large iceberg broke off that has caused debate about whether this breakage is normal
    - - Surface mass balance is (mostly) positive across Antarctica
      - Ablation is largely from ice shelf melting and calving
      - East Antarctic Ice Sheet is experiencing some thickening due to surface mass balance increasing
    - - Low volume distributed system:
        Engelhardt & Kamb et al. (1997) – borehole experiments
      - Some dynamism:
        
        Anandakrishnan et al. (1997) – water piracy
        
        Tulacyzk et al., (2000) – water in sediments / cyclicity
    - - 'Evidence from ice shelves for channelized meltwater flow beneath the Antarctic Ice Sheet (Le Brocq et al. 2013)
        
        Causing depression on Antarctic Ice Sheet
        
        Sublglacial lakes – rapid discharge as subglacial lakes fill and then drain into a neighbouring lake. First evidence of dynamic Arctic water system. These large subglacial lakes are through to onset fast flowing ice streams.
  - - - o Slow flowing interior (~10 m yr-1)
        
        o This causes a lot of crevassing where slow flowing ice and fast flowing ice next to each other
  - - - 'Zwally effect'
        
        Increased water
        
        increased velocity
        
        Higher temperatures
        
        increased water
        
        Theory: Surface meltwater ponds drain through moulins to the base of the ice & ice velocity increases
      - Early research attention
        
        Identification of role of subglacial hydrology & sediment in controlling ice flow
        
        Research Examples
        
        Ice Stream C / Kamb ice stream shutdown
        
        Ice Stream B / Whillans ice stream slowdown
        
        e.g. Anandakrishnan & Alley (1997) , Tulacyk (2000)
      - The occurrence of melting of ice is dependent on whenever there is sufficient heat to turn ice back into water. This heat is supplied by solar radiation (supraglacial), friction generated by ice flow/deformation (englacial), friction generated by ice sliding across bed/substrate deformation (sublglacial) and geothermal heat (subglacial)
      - Sources of meltwater
        
        Supraglacial
        
        Solar radiation
        
        Seasonal variations
        
        e.g. Greenland melt season (May-Sept)
        
        Subglacial
        
        Friction generated by sliding across bed/substrate deformation and geothermal heat
        
        Geothermal heating
        
        e.g. Thwaites glacier in the West Antarctic
        
        High geothermal heat flux
        
        Subglacial volcanoes!
        
        Ice Temperature
        
        Ice flow velocity is a function of temperature
        
        Warm ice deforms more readily than cold ice
        
        Surface air temp. controls ice temp. at the surface
        
        Geothermal heat flux controls temp. at the base
        
        Temp. in between is a function of ice flow and advection of cold ice from upstream
        
        Ice temperature varies with depth
        
        Englacial
        
        Friction generated by ice flow/deformation
        
        Subglacial Hydrology
        
        Subglacial Water
        
        Bindschadler, R., Harrison, W., Raymond, C., & Crosson, R. (1977). Geometry and Dynamics of a Surge-type Glacier. Journal of Glaciology, 18(79), 181-194. doi:10.3189/S0022143000021298
        
        Iken, A. (1978). Variations of surface velocities of some alpine glaciers measured at intervals of a few hours. Comparison with arctic glaciers. Z. Gletscherkd. Glazialgeol. , 13, 23-35
        
        Suggests that meltwater plays an important role in controlling ice velocity.
        
        Seasonal variations in velocity observed, e.g:
        
        Hard bed theory
        
        Water ‘drowns’ roughness (Weertman, 1964)
        
        Water depth is important
        
        Decouples the ice from the bed (Lliboutry, 1968)
        
        Water pressure is important
        
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        Groundwater
        
        Precipitation
    - - Ice Shelf Buttressing
        
        The mechanical effect of a floating ice shelf in restraining the flow of ice from the ice sheet, particularly at the grounding line where the ice sheet meets the ocean
        
        . Can also be held up by ice rises where the rising bedrock is not smooth and can be extremely raised at some points
        
        This restraint helps stabilize the ice sheet and can influence the speed and direction of ice flow, potentially affecting sea level rise.
        
        This is a map of buttressing levels in Antarctica
      - Ocean driven ice sheet change & ice tongues/shelves
        
        Greenland
        
        SW Greenland - Jaokbshavn Isbrae
        
        General surface lowering trend
        
        Pockets of overall surface increase
        
        Product of the ice flow velocity in the area
        
        We detect large variability of the velocity over time, including a slowing down from 6 700 m yr-1 in 1985 to 5 700 m yr-1 in 1992, and a subsequent speeding up to 9 400 m yr-1 by 2000 and 12 600 m yr-1 in 2003.
        
        Something has happened between 1992 and 2000 where the ice velocity speed was doubled. This was already the fastest move glacier. But why did this happen?
        
        Ocean influence
        
        This is most likely caused by the Irminger current, bringing warmer water to Greenland from the Americas
        
        1 more item...
        
        SE Greenland - Helheim Glacier
        
        Clear retreat in front position of Helheim Glacier
        
        1 more item...
        
        Complex processes in action.
        
        Warmer water is pushed into the fjord due to Irminger Current even though the its effects should like just outside of the glacier.
        
        North Greenland - Petermann Glacier
        
        2010 Calving Event – NO impact on ice velocities of the ice flowing into it.
        
        2012 Calving event – 10% speed up in ice velocity
        
        Large part of ice breaks off from the front of the glacier.
        
        This is due to the fact that that part of the ice sheet was probably already floating, and when there was no longer buttressing – it had no effect on the glacier when it broke off.
        
        This is a function of lateral confinement and ice rise
        
        North Greenland - Zachariæ Isstrøm
        
        Decay of ice shelf
        
        Led to acceleration in 2012
        
        Zachariæ Isstrøm:
        
        Reverse slope
        
        Nioghalvfjerdsfjorden
        
        Forward slope
        
        Again this is probably already a floating ice shelf – so could have little effects with further calving.
        
        Antarctica
        
        Amundsen Sea Sector (SW)
        
        Weak underbelly’ (Hughes, 1981)
        
        Marine ice sheet
        
        Reverse slopes
        
        No large ice shelf
        
        => Marine Ice Sheet Instability Hypothesis (MISIH)
        
        Amundsen Sea Ice Streams
        
        Pine Island Glacier (PIG)
        
        Observations:
        
        Rapid thinning
        
        (e.g. Shepherd et al., 2001, 2002, Pritchard et al., 2009)
        
        Velocity increase post 1994
        
        (Pine Island Glacier, Joughin et al., 2003)
        
        Grounding line retreat
        
        (Pine Island Glacier, Rignot 1998)
        
        Thwaites Glacier - shifting focus
        
        Unavoidable retreat: “This study does not undermine the importance of mitigation in limiting the impacts of climate change. Mass loss from the WAIS is just one component of sea-level rise, and other regions of Antarctica are unlikely to lose substantial mass if current emissions targets are met.
        
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        Thwaites is the widest glacier on Earth, at ~120 km (~80 miles) wide. Its fastest flowing grounded ice is centred between 50 and 100 km
        
        Thinning linked to ocean temperatures, Amundsen Sea low changes and drives CDW onto continental shelf
        
        Joughin et al. (2021)
        
        Weddell Sea Sector
        
        Presently not showing signs of change
        
        Although, model produced changing weather patterns in the future
        
        Draws CDW on to continental shelf and under the ice shelves
        
        Steep reverse bed slope at grounding line of the Weddell Sea Sector in West Antarctica (Ross et al., 2012)
        
        East Antarctic Ice Sheet
        
        Some thickening
        
        link to outlook.office365.com
        
        Surface mass balance increasing
        
        Some thinning
        
        Focus on marine areas
        
        e.g. Aurora Basin & Totten Glacier
      - Antarctic Peninsula
        
        Fastest warming place on Earth
        
        3 degrees in 50 years
        
        Limit of ice shelf ‘viability’ (Tmean= -9°C) moving South
        
        Ongoing retreat
        
        1995: Larsen A, B
        
        1996: Wordie
        
        2002: Larsen B
        
        2008: Wilkins
        
        Iceberg A-68
        
        Hard to predict whether this was a natural part of the ice glacial life cycle or whether this was caused by the increase in temperature and velocities due to ocean conditions and currents
      - Marine Ice Cliff Instability
        
        Marine ice cliff instability (MICI) refers to a process where large ice cliffs, the exposed edges of glaciers or ice sheets meeting the ocean, become unstable and collapse, potentially leading to rapid and extensive ice retreat.
        
        This instability is triggered by a combination of factors, including ice thickness, cliff height, basal ice movement, and the presence of pre-existing damage. Once an initial failure occurs, it can trigger a runaway process
        
        Pollard Model
        
        Pollard et al. (2015) & DeConto & Pollard (2016)
        Pattyn et al. (2018) & Edwards et al. (2019) for further info
      - SLR Projections
        
        2100:
        
        RCP 2.6: 0.43 m (0.29-0.59 m, likely range)
        
        RCP 8.5: 0.84 m (0.51-0.92 m, likely range)
        
        Uncertainties
        
        Antarctica
        
        How much – how fast?
        
        Ice dynamics:
        
        How fast will unstable retreat mechanisms act?
        
        Role of Marine Ice Cliff instability?
        
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        Mass Balance:
        
        How long will the surface mass balance increase be able to offset retreat?
        
        Greenland
        
        How much – how fast?
        
        Ice dynamics:
        
        Response to ocean forcing?
        
        Role of surface meltwater in regulating flow?
        
        1 more item...
        
        Mass Balance:
        
        How much will change in albedo affect surface melting?
        
        “In summary, new modelling since AR5 is consistent with previous studies suggesting future Greenland ice loss over the 21st century will be dominated by surface processes, rather than dynamic ice discharge to the ocean, regardless of which emissions scenario is followed (high confidence).”
  - - - Whole ice sheet: ~58 m
      - West Antarctic Ice Sheet (WAIS): ~ 5 m
      - Marine parts of WAIS: ~3.3 m
      - Marine parts of EAIS: ~17 m
    - - Whole ice sheet: ~7 m
      - Will be strongly effected by surface melting – so surface mass balance is very important to monitor in Greenland
        
        Findings of increased flow speed on a large East Antarctic outlet glacier caused by glacial floods (Stearns et al., 2009)
  - - - Radar altimetry
        
        GRACE – two satellites travelling parallel – study separation of paths due to satellites being pulled down differently due to gravitational pull of the area. This measures different densities.
      - Laser altimetry
    - - Mass budget method
        
        Mass Budget Method – we know how fast the ice is flowing and how thick the ice is – we can calculate the fluxgate (comparing how much ice is lost compared to amount of accumulation)
      - Gravimetry
    - - Surface Elevation Change
        
        This can be compared to the gravity change – which is a low resolution way of showing change in gravity in Greenland which reflects the surface lowering – which matches with the surface elvation lowering
        
        Over Greenland, we can see that lots of areas are experiencing surface lowering.
      - Causes of change
        
        ◦ Increased surface melting
        
        ◦ Hydrology (lecture 7)
        
        ◦ Ocean driven change & ice tongues / shelves (lecture 8)
        
        Surface Mass Balance
        
        We can see a decrease in SMB anomaly, showing that Greenland is experiencing increasing ablation
    - - Surface Elevation Change
        
        In North and East Antarctica – due to the climate, there is an increases in accumulation due to warm air trapping snowfall
        
        . In South and West Antarctica – there is a showing of surface elevation lowering which is the beginning of the Marine Ice sheet instability.
        
        . This accumulation and ablation might cancel each other out (equilibrium). These surface elevation values also match that seen in the gravity change models.
      - Causes of change
        
        ◦ Increased accumulation (East Antarctica)
        
        ◦ Internal variability (lecture 7)
        
        ◦ Ocean driven change & ice shelves (lecture 8)
    - - By 2100
        
        RCP 2.6: 0.43 m (0.29-0.59 m, likely range)
        
        RCP 8.5: 0.84 m (0.51-0.92 m, likely range)
  - - - Direct ice mass loss
    - - Increased / decreased velocity
        
        Dynamic thinning / thickening
      - These are deep uncertainties (IPCC AR6)
    - - Grounding line retreat / advance
        
        Velocity increase / decrease
        
        Dynamic thinning / thickening
- - - - About 915 million people live in mountainous regions
        
        < 150 million people live above 2,500 m above sea level
        
        < 30 million people live above 3,000 m above sea level
  - - - This does not include large ice sheets but does include some of the largest ice caps.
    - - The largest mountain glaciers in the Southern Hemisphere is the Andes and in New Zealand
        
        New Zealand glaciers have a high mass balance meaning that the ice is very low in elevations in a very mild climate with high snowfall.
      - The largest glaciers in the Northern Hemisphere are located in Greenland
        
        We can determine the type of glacier and whether it is land terminating or marine terminating (green and blue on the graph).
  - - - High relief leads to high spatial variability (micro-climates)
      - Relatively few observational records / weather stations / not easily accessible
      - Steep terrain also causes highly variable climate
    - - Influences the surface energy balance ie determines ablation
    - - Sometimes counteracts warming
    - - e.g proglacial lake, type of bedrock sediment, supraglacial debris etc
    - - But these are the easiest measurements to make
    - - Servere glacial change in Greenland and Scandinavia
      - Large glacial change in Southern Andes, Caucasus and Middle East and Central Europe
    - - The ‘third pole’ is the planet’s largest reservoir of ice and snow after the Arctic and Antarctic
        
        Hosts the world’s 14 highest mountains
        
        Around 100,000 square kilometres of glaciers (an area the size of Iceland).
      - Encompasses the Himalaya–Hindu Kush mountain ranges and the Tibetan Plateau.
        
        Started forming about 50 million years ago which is geologically young
        
        Rivers draining these mountains influence the lives of about 40 % of the world’s population
      - Observed changes (HKH)
        
        Few long term observations!
        
        High spatial variability
        
        Temperature has increased over the last century by ~1.5C
        
        Distinct warming in 1990s
        
        Tmin (night) increased faster than Tmax (day)
        
        Diurnal range decreased
        
        Krishnan et al (2019)
        
        Precipitation and Snow
        
        Complex picture of change with no strong trends
        
        Precipitation increased slightly since 1950
        
        But some indications that Indian monsoon in weakening
        
        Snow cover is highly variable and poorly known
        
        Slight decrease indicated
        
        Observed trends in snow cover are generally weak
        
        Karakoram Anomaly
        
        On average, glacier areas in the Karakoram have not changed significantly
        
        Individual glaciers have shown large area increases or decreases due to surge behaviour – non-surge-type glaciers were stable over the last decade. Transition from bare ice glacier – to ablation zone. Ice underneath is accommodating this behaviour.
        
        Looping of moraines with frontal glacier combining with tributary glacier. Can infer past conditions form interpreting moraines around the ice flow dynamics
        
        This surging is not to do with external flows, but perhaps driven by water within the glacier lubricating the glacier and causing them to flow along the bedrock.
        
        Surging Glaciers
        
        Surging glaciers exhibit recurrent periods of elevated flow velocity (or surges) at rates of one to two orders of magnitude greater than during their periods of inactivity (or quiescence).
        
        Surging glaciers are especially common in the Karakoram (Paul 2015; Sevestre and Benn 2015)
        
        These surges can make it more difficult to discern glacier response to climate change
        
        Also common in other regions e.g. Svalbard
        
        There is not universal law that causes all surging behaviour, it is likely there are various external and internal reasons.
        
        It is not understood why this region of the Himalyas has so mant surging glaciers but here is another cluster similar to this in Svalbard and they probably have similar causes.
        
        Krishnan et al., 2019; Maurer et al., 2019
        
        Since the 1950s, only reductions in glacier area have been observed .
        
        Similar mass loss rates across subregions and a doubling of the average rate of loss during 2000–2016 relative to the 1975–2000 interval.
        
        Variability in the acceleration of mass loss driven my local factors
        
        Possibly due to trends in monsoon
        
        Smaller glaciers are shrinking faster on average than larger ones
        
        Some regions receive much more attention than others
        
        No observations for some Tibetan plateau glaciers
    - - Pass through 7 countries and is the Earths longest mountain chain (8900 km long, ~330 km wide), the one that makes up the Antarctic Peninsular.
      - Subduction zone of the EP plate subducted under the continental south America. This is unlike the Himalayas at a collision zone so geologically very different.
      - Demographics of the Andes Mountains
        
        Using demographics like this, we can look at which countries are mostly at risk of glacier retreat and change in the Andes.
        
        The places with the highest GDP are more likely to be able to adapt – although the highest GDP like Chile, there is a lot of conflict between mining companies and the government who are in aid of copper and lithium companies who do not see the important of the glaciers and have even removed glaciers in the past to access mineral ores in the mountains and the locals and scientists who can see the environmental impact of this loss of ice mass in these South American countries.
        
        Copper and Lithium are very important minerals for the future of Earths sustainability – with most renewable technologies requiring copper for the wiring and electric vehicles requiring lithium.
        
        There has been significant net mass loss from the Andes, increasingly so in the present – with a steeply declining mass balance over time which can be seen in most areas except Martal Este (although this is a much smaller area)
        
        Cumulative Net Mass Balance in the Andes
        
        Climate and mountain glaciers
        
        Understanding the links between climate and glacier mass balance is important for:
        
        a) Managing water resources
        
        b) Mitigating/adapting to hazards such as GLOFs
        
        Challenges:
        
        Uncertainty of past weather/climate in mountains
        
        Glacier response times (mass balance gradients)
        
        Local topography (wind-blown snow, avalanches)
        
        Supraglacial debris (increase or decrease melting?)
        
        Internal glacier/water dynamics (Surging?)
        
        Lack of access/dangerous
        
        Debris
        
        High-relief glacial valleys supply a large amount of supraglacial rock debris
        
        0 - 25% of the total glacierized area in HKH is debris-covered
        
        Ablation leads to build-up of thick layer of debris in the lower part of the glacier.
        
        Impact on melting uncertain:
        
        Small amounts thought to enhance ablation due to lower albedo
        
        Large amounts thought to protect the ice beneath
        
        Leads to ice cliffs / supraglacial ponds
        
        Makes it difficult to accurately determine ice extent/thickness
        
        The Andes
        
        Glacier runoff in the Andes is just as important as it is in the Hindu Kush Himalaya.
        
        Because of the way the catchment is oritented – the rivers tend the flow short distances from the source to the West Coast.
        
        To the East side, rivers are likely to pass through more than one country. There is a much higher rate of precipitation in the East side (amazon rainforest) while the West Coast is very aris and at risk of water scarcity.
        
        Bolivia have a high proportion of glacier meltwater for domestic use and irrigation – followed by Peru and Chile. Populations in Peru (Rio Santa) and are generally more at risk even though Bolivia use more, Peru is more vulnerable. This also means that Peru, Bolivia and Chile are at risk of water conflict.
  - - - Extrapolated to the rest of the glacier
      - Provide detailed information but are laborious and can therefore only be obtained for relatively few glaciers.
    - - Large regions can be investigated simultaneously
      - But constrained by the availability of suitable data
      - With that we can observe not only length changes but also mass changes and we can calculate mass budgets
    - - Southern Andes, Asia and Low Latitudes can all be seen with a negative mass budget
        
        This is a map of global mass budget in Gt yr compared to area size. The larger the red dot the more minus digits there are, more negative mass balance
    - - Total number and coverage of glaciers remains uncertain
        
        The current best estimate (IPCC 5AR) is around 170,000 covering a total area of about 730,000 km2
      - Global ice mass is more uncertain because thickness measurements are sparse
        
        Estimated by applying scaling relation (e.g. Radic and Hock, 2010)
        
        Global glacier mass that is likely between 114,000 and 192,000 Gt (314 to 529 mm SLE)
  - - - Glacier changes
      - Permafrost thaw – destabilises large parts of the mountain slopes
      - These are made up of ice, snow, rock, soil – very dense material
      - Very dangerous, dense, fast – high potential for destruction
      - Ice Avalanches
        
        Ice avalanches occur when part of a steep glacier breaks away, falls down a steep slope and runs out into a valley where it is likely to have the greatest impact.
        
        Complex is causes by melting permafrost that destabilises the soil. But they both have a similar effect and sometimes it is unclear which one has occurred after the event.
        
        Ice falling directly onto settlements can be a huge hazard
        
        Indirect effects
        
        Blocking of river valleys
        
        Temporarily damming rivers
        
        Collapsing into moraine-dammed lakes
        
        Very damaging flood event (GLOFs)
        
        GLOF Mitigation
        
        Mitigation measures to reduce GLOF risk are primarily to reduce the volume of water in the lake
        
        Different ways to achieve this, either alone or in combination:
        
        Controlled breaching of the moraine dam – allow water to escape in a control way and allow people to evacuate
        
        Construction of an outlet control structure – not just emptying it as a one off – but implanting technology to allow it to be drained consistently.
        
        Pumping or siphoning the water from the lake
        
        Tunnelling through the moraine barrier or under an ice dam
        
        Simple avalanches tend to have restricted direct impact as run-out distances are generally short and mass input lower due to lower density material
        
        Complex Ice Avalanches
        
        Complex avalanches occur in combination with rock falls and can have much more serious consequences e.g.
        
        Combined break-off of rock and glacier
        
        Transformation of ice avalanches into mud or debris flows
        
        Have been known to trigger Lake outburst floods
        
        Glacier Lakes
        
        Glacial lakes are lakes that are fed by glacier meltwater. This can include:
        
        lakes on top of glaciers (supra-glacial),
        
        lakes in front of glaciers (pro-glacial),
        
        and glacier-fed lakes that are disconnected from glaciers but close to glacier termini.
        
        Lake area expected to increase in a warming climate and we now have strong evidence of this and depending on how these lakes are impounded
        
        Pro-glacial lakes pose a serious risk when the moraine (or glacier) dam fails and the water drains catastrophically as a glacial lake outburst flood
        
        Such events can have significant and long-lasting human and physical impacts (Richardson and Reynolds 2000).
        
        Glacial Lake Outburst Floods (GLOFs)
        
        Potentially dangerous lakes typically require a trigger
        
        Moraine collapse due to seepage,
        
        Melt of ice-cored moraine
        
        Causes more moraine collapse
        
        Causes more flooding
        
        Displacement waves from ice avalanches,
        
        Degrading high-mountain permafrost increasing probability of rock ice/avalanches from steep slopes reaching glacial lakes and triggering GLOF events.
        
        1941 Palcacocha GLOF, Peru
        
        The deadliest historical GLOF occurred in 1941 at Lake Palcacocha, Peru
        
        6 more items...
        
        Will GLOF risks increase due to climate change?
        
        1 more item...
    - - Snow changes
    - - Lake changes
      - Melt/rainfall changes
    - - Changing water quality
    - - Every year there are on average 76 hazard events in the HKH, with the highest number noted in China (25) and India (18)
      - Active tectonics in HKH make hazards more severe than in other mountain regions.
        
        More vulnerable to earthquakes, landslides, and erosion.
        
        Potential trigger for GLOFs
      - Most recently, the 2015 Gorkha earthquake in Nepal (Mw = 7.8) all led to huge losses of life and property
        
        and increased soil erosion
        
        triggered landslides, rockfalls
      - Water Quality
        
        Due to its multifaceted nature, water quality itself is a complex environmental issue, encapsulating water quality indicators such as pH, clarity, smell and chemical composition.
        
        . Another characteristic of the complexity of water quality is that a number of determinants are “hidden” from the naked eye (e.g. heavy metal content, temperature and oxygen levels (Flotemersch & Aho, 2021)) and require measurement and analysis in a laboratory or in-situ (e.g. pharmaceutical pollution (Wilkinson et al., 2022)).
        
        Comprehensive in-situ assessments of water quality determinants are challenging in many regions due to low accessibility and associated costs, in addition to the demands of sampling/monitoring programmes required to assess temporal and spatial dynamics
        
        Water quality is fundamental to ecosystem health and functioning and human development and well-being. “The physical, chemical, biological and organoleptic properties of water” (WMO 2012)
        
        Water quality indicators include water temperature, dissolved oxygen, pH, turbidity, electrical conductivity, colour, taste, odour, dissolved solids, trace & heavy metals, bacteria, algae etc.
        
        Acid Rock Drainage (ARD)
        
        Ice retreat exposes metal-rich rocks to the atmosphere, causing the entrainment of metals in water bodies, negatively impacting access to safe water for human consumption, agriculture and livestock.
        
        ARD can be caused by glacial retreat over metal-rich geologies, but also by mining activities (Guittard et al., 2017).
        
        Tributary to the Rio Santa suffers from “natural” ARD – water pH as low as 3
    - - Changes in Himalayan Glaciers
        
        Temperatures risen 1.5 °C since ~1900
        
        2x the global average
        
        Faster at higher altitudes
        
        Slight ride in rainfall
        
        Slight decline in snowfall
        
        Short Lived Climate Pollutants (SLCPs, or black carbon)
        
        Produced by electricity generation, biomass burning, and brick factories
        
        SLCPs affect snow and ice melt rates
        
        Decreased albedo
        
        Local warming of surface and near-surface air
        
        Net effect of SLCPs may be up to an order of magnitude greater than that observed from CO2 alone Ramanathan and Carmichael 2008; Jacobi et al. 2015).
      - Water from Glaciers
        
        Glacier meltwater provides a regular and reliable source of streamflow in glacierized river basins.
        
        In the post-monsoon (HMA) or dry season (Andes)
        
        Especially vital for regions with lower summer precipitation.
        
        But how will this be effected in the future?
        
        This figure shows us clear spatial varitaiton in where a large amount of contribution of water comes from glacial melt water. This can be useful for local communities to undetstand what may occur when these glaciers begin the reduce/retreat.
        
        Nearly 100% of all water availability in the upper North regions (A) is provided from glacial melt. And we can see that in C the majority of water availability comes from rainfall. So these graphs are basically the inverse of each other
        
        The southern catchments flowing from Nepal into India has the least reliance on glacial melt and the most on rainfall – but this is the most populated area on this map, so population must be taken into account because this can also be a risk factor for water scarcity.
        
        In the North Andes, we believe that peak water has already been reached in the 1970s/80s – with the dark colours representing external factors and recent peak water reached. In the more central and southern Andes, we believe that most of these glaciers are expected to reach peak water in the near future.
        
        This can be extremely useful for local communities to take these models and confer and confirm these estimates – against what communities are experiencing. This allows modellers to go back and assess what their models are not taking into account. This requires an inter-disciplinary approach on multiple scales of power.
        
        Longer Term Changes
        
        Glacier decline will eventually limit total meltwater production. Most basins in the extended HKH are expected to have reduced glacier melt contributions before 2100 (Shea and Immerzeel 2016).
        
        More precipitation at high elevation implies more snowfall and more glacier accumulation.
        
        Longer period before ice volumes become so small that the contribution to river runoff diminishes.
        
        Overall: Reduced ‘buffering capacity’ of a catchment with higher susceptibility to both extreme runoff and prolonged low flows (more droughts).
        
        This is due to excess snowfall with a higher emissions scenario causing a rapid decline of sea ice -> more evaporation -> more snowfall. But this is likely to only happen for glaciers that are located near oceans that will be susceptible to higher snowfall.
        
        IPCC SROCC 2019
        
        This figure shows the order in which different regions with reach peak water under different emissions scenarios (2.6 and 8.5 – best and worse case by 2100.)
      - Changing Hazards
        
        Evidence Cryospheric hazards in mountain areas are changing
        
        E.g. short-term increases in runoff and lake levels
        
         To assess the level of risk to local and downstream populations, we also need to consider levels of:
        
        Vulnerability – what is at risk? People? Utilities? Culture? Heritage Sites? (Think broad)
        
        Exposure – what is the likelihood of this happening
        
        SROCC (2019)
        
        Nature of hazard depends on whether glacier is advancing (+ mass balance), retreating (- mass balance) or stationary (0 mass balance).
        
        Glacial hazards attract attention because of the risk of loss of life and the serious threat to infrastructure such as hydropower installations, roads etc.
        
        Human activity is extending more and more into mountainous regions so the threat of glacier hazards is increasing
        
        Applied Risk Assessment
        
        More avalanches (ice) and could be either more or less snow avalanches due to reduced snowfall and increase melting.
        
        Predicted to have more flooding creating more and larger glacial lakes
        
        More unstable slopes and landslides – with smaller glaciers less stable and thawing permafrost causing mountains to saturate and become unstable.
        
        Calls for an approach with a mixture of modelling and computer lab analysis and working with locals and observation of data and active hazards and their real effects on people
        
        Are hazards increasing?
        
        Warming reduces snow cover, melts glaciers, and degrades permafrost. Also enlarges and increases number of glacial lakes (Shugar et al., 2020)
        
        Warmer temperatures increases ground instability in permafrost regions, and increased likelihood of rock/complex avalanches (Pathak & Mool, 2010). Risk assessment studies (Zhang et al. 2024) have identified specific possible GLOF triggers from:
        
        Ice avalanches from advanced glacier tongues
        
        Ablation of dead ice beneath moraine ridges
        
        Glacier Lake Changes
        
        If Glacial Lakes will be larger, surely the hazard of their GLOF will be more extreme?
        
        The red on this figure shows an intense volume increase of water in glacial lakes
        
        Very high glacial lake increase in the Andes (Chile) and much more muted/less in the Himalayas
        
        This figure plots the glacial lake area change against arial population growth (with the size of the circle reflecting the amount of the population exposed to GLOFs) – which can be used to prioritise where mitigation attempts should be focused (Nepal, Chile, Georgia)
        
        Need to assess risk using hazard, vulnerability and exposure
  - - - Meltwater from glaciers provides much of the water for populations in temperature and sub-tropical latitudes. This is particularly the case for the west side of the Andes where rainfall is less common.
    - - Identified mountains containing glaciers as proportion of meltwater of total runoff. This helps us to understand where the regions are where people heavily depend on glacier meltwater (red lines on graph).
        
        MMP = Maximum monthly glacier melt as % of total water
        PIX = (Population Impact index) = MMP x population in each altitude band
      - In Rio Santa, 80% of their water supply is glacier meltwater – but it is very sparsely population, although when the glaciers do melt, these small communities will be at risk.
      - This is measured long the PIX (Population Impact Index). These can be sen on another scale with the Danube in which a smaller percent of their water supply is glacial meltwater – but there is a large population living with in the basin, so a lot more people will be affected.
    - - This is just within the Aral Sea, Indus and Ganges region
    - - Glacier-fed rivers provide water for agriculture, sanitation, drinking, and power generation (+ aquaculture, industry, transport…)
      - IPCC estimates suggest that warming of 1°C could lead to 43% loss in glacial cover, leaving some of these countries unglaciated, with significant water resource implications
      - Although, there are large uncertainties around this, where we don’t even know the total amount of ice on Earth – so it is hard to take these numbers exactly – although this is still a large problem
      - Glacier water for energy
        
        Scientists and engineers in several countries have worked together to generate electricity from glacier runoff
        
        Norway, Iceland, Switzerland etc
        
        Reservoirs are needed – also can be a good store of water which can be used to reduce the flashiness (peakiness) of the hydrology
        
        Water reservoirs important to mitigate floods and droughts while generating clean and affordable energy
        
        How ‘renewable’ in the longer-term? – Expensive to run, not infinite
        
        There will not be glaciers forever, they will have melted
        
        Hydropower Systems
        
        Meltwater directed through tunnels into turbines to generate power
        
        Outlet into fjords/rivers minimises environmental impact
        
        Best suited for local power uses
        
        Avoids infrastructure costs and transmission losses
        
        Hydropower meets almost all of Norway’s energy needs.
        
        Close to 50 percent of the reservoir capacity in Europe is located in Norway.
        
        Very suited for Hydropower (High Terrain, High Rainfall and Potential for Reservoirs)
        
        We can study the potential for hydropower – with China having the largest potential for reservoir capacity, although it is small for its population/land area
        
        Compared to its size, Nepal has high potential for hydropower.
        
        Capacity for hydropower can only be reached if there is enough money/investment into it
        
        Countries with a lower GDP cannot afford to take advantage of this
        
        Population Factors
        
        Water stress increases with reduction in supply and/or increase in demand
        
        Climate change in the future as warming increasing causes more ablation and melting of glaciers
        
        Social changes in the region have at least as much of an effect on water stress
        
        Future population growth is uncertain, but increasing urbanization puts rural poor people at risk because they are less likely to adapt to environmental risks.
    - - Glaciated mountains are ‘water towers’ for many large areas and human habitats
      - Glacial meltwater feeds rivers during the warm/dry season
      - Glaciers ‘buffer’ water to reduce the seasonality of water availability
        
        Short term: water all year round
        
        Long term: no water in the warm/dry season
      - Meltwater from glacierized regions is also intensively used for hydropower generation (provides nearly 100% of available in some areas)
        
        Short term: more water available
        
        Long term: no water available for hydropower generation, leading to wider societal issues
      - Hydropower and Renewables
        
        Dams have been constructed to receive meltwater in summer for use in power generation in winter
        
        Decreasing river flow, warmer water temperatures, critical conditions for fish and other aquatic forms of life, lower groundwater levels, less soil humidity, drier vegetation, more frequent forest fires, stronger needs for irrigation water, and rising demands for energy (such as air conditioning) coupled with reduced hydropower generation and less river cooling for nuclear power plants.
        
        Perhaps the most critical regions will be those where large populations depend on water from glaciers during the dry season, such as in China and other parts of Asia, including India.
        
        But it will also affect mountain ranges which are densely populated and highly developed, such as the European Alps.
  - - - Map of irrigated land in the HKH
  - - - GLOF mitigation
        
        Since 1972 mitigation procedures established
        
        Excavating tunnel through moraine dam
        
        Channel excavated through top of moraine to allow water to drain into stream below
        
        When desired level is reached permanent concrete drainage pipe is constructed within moraine
        
        Permanent Drainage channel contsructed downstream
        
        Moraine is then rebuilt to original level using compacted earth covered by rocks and concrete
    - - GLOF from glacial lake Palcacocha killed an estimated 5,000 people
    - - Rock and ice avalanche from Huascarán Norte severely affected the city of Yungay. Approximately 23,000 people died.
- - - - This map projection is a ‘polar projection’ that allows us to view the arctic in a real representative way – as a standard 2D map often warps the shape and size of polar regions.
  - - - Ice - 0.3
      - Vegetation and dark soil - 0.2
      - Ocean water - 0.1
      - Fresh snow - 0.9
    - - → more incoming radiation reflected back → greater potential for temperature lowering
        
        → Glaciation
    - - less incoming radiation reflected back → greater potential for temperature rise
        
        → Deglaciation
  - - - Defined by area <50,000 km2
      - Flade Isblink, Greenland (~8,500 km2)
      - Vatnajökull, Iceland (~8,100 km2)
        
        Is excess snowfall countering higher temperatures as the mass balance is still in equilibrium at most of these Icelandic islands
      - Austfonna, Svalbard (~8,100 km2)
        
        Seeing thickening at higher elevations and thinning at lower ones, but also extreme elevation changes around ‘basin 3’
        
        The same can be seen on the Vavilov ice cap too.
      - Needs to cover the topography – not constrained by a valley or something
    - - Strong levels of glacial thinning.
      - The same can be seen on the Barnes Ice cap that is thinning by 2m a year. It 100% ablation zone with no accumulation.
      - We believe that the Barnes ice cap is the last remaining section of the Laurentide ice sheet from the LGM and sea levels were 120m lower. But they will not last forever
      - Look at Tepes et al., (2021)
  - - - Transverse ice crevasses form – due to longitudinal extension which causes icebergs to calve
      - . What controls calving processes/rate? It is a form of ablation so we need it to understand how the mass balance behaves.
    - - Benn et al. (2007) Calving processes and the dynamics of calving glaciers, Earth Science Reviews.
      - Common factor in all calving events
        
        Formation and growth of fractures (crevasses)
        
        Stress conditions can form basis of calving classification
        
        Rate of ice flowing over the grounding line
      - Steady state: Ice flux over the grounding line = calving rate
      - Calving Criteria
        
        Crevasse-depth calving models (it is assumed that these rates are equal):
        
        (a) Waterline crevasse-depth criterion;
        
        (b) Full depth crevasse criterion as suggested by C.J van der Veen. (Benn et al., 2007a)
        
        We try hard to ensure that our models can captivate and replicate the processes of calving
  - - - Very fast flow after long periods of low activity
      - Repeated
      - Regular surge intervals
      - ~ 1% of glaciers worldwide
      - Non-randomly distributed
      - These repeat over a set amount of time (each one is different)
    - - Observed velocity ≠ balance velocity (flow velocity that is needed to maintain steady ice shape)
      - When comparing ablation and accumulation, we assume that the balance velocity is equal/constant
      - Can't make a mass balance assumption on glaciers that are seen to be surging as the balance velocity is not the observed velocity
  - - - The latest surge, a few decades earlier than expected, may have come early because the glacier geometry has changed over the years of thinning and retreat.
        
        Alternatively, a warmer and wetter recent climate in Svalbard may have triggered the surge early
  - - - What is causing these large changes in dynamics?
        
        No single explanation
        
        Internal (hydrology, unlithified marine sediments)
        
        External (climate change)
        
        We are starting to re-think the response times of ice caps and ice sheets
        
        Ice caps can respond quickly to climate change...but not instantly
        
        Modelling of observed changes required to better understand the details of the mechanisms – to make projections of future changes
  - - - Perennially frozen ground
      - Underlies 26% of Earth’s land surface
      - Wherever summer heating doesn’t thaw ground at depth
      - Active permafrost is permafrost that is constantly melting over long periods of time
    - - Since LGM, a lot of the water that was in this sea ice is now melted in the ocean and risen sea levels – there is an isostatic rebound causing sea level to drop following melting of large ice sheets as viscous mantle flows in to fill in the now missing space.
      - Although sea level has changed, in some places the ground is rising – so there can be sea level rise and sea level fall at the same time in different areas.
    - - This image shows a thermokarst image of large scale permafrost in a karst region (limestone dominated). There are unfrozen pockets of land within these large permafrost features called ‘taliks’.
        
        Permafrost (perenially frozen ground) is overlain by a zone of seasonally thawed ground: the active layer
        
        The ratio of taliks to permanetently frozen ice determines how it is classified as permafrost
        
        Permafrost acts as an insulator between the geothermal heat flux of the mantle and the air – meaning that when you get low enough there is a permafrost free/unfrozen ground.
      - Types of Permafrost
        
        Continuous: Pervasive permafrost beneath the active layer (90-100% area)
        
        Discontinuous: Continuity of permafrost broken by through-going taliks (50-90% area)
        
        Sporadic/Isolated: Isolated blocks of relatively thin permafrost - most common at margins of periglacial environments (10-50% area)
        
        These are distributed with the further North you get the more continuous (higher ratio of permafrost to taliks) meaning it is frozen more. The further south you get it turns discontinuous and finally sporadic
        
        Permafrost Landscape Features
        
        a) Thermokarst lakes – 100,000s of lakes
        
        b) Lake expansion
        
        c) Coastal RTS (Retrogressive Thaw Slump) soil failure due to permafrost thawing – less volume in the soil due to slumping
        
        d) Inland RTS
        
        e) Burn scar
        
        f) Active tundra fire – increasing frequency of arctic wildfire (up to 30-40 degrees in continental areas in the Arctic over summer caused by lightning strikes which burn and accelerate thawing of ground ice
        
        Nitze et al. (2019)
        
        Thermokarst Expansion
        
        Landscape features caused by structural failure following melting of ground ice in a region underlain by permafrost
        
        Resemble karst landscapes formed by solution in limestone
        
        As the Arctic warms there is increasing evidence for thermokarst
        
        Similar to how snowmen are the last to melt as the surface to volume ratio meaning that they melt the slowest – which is seen in Pingos
        
        Batagaika Crater, Russia
        
        Lake Thermokarst experiencing rapid permafrost thaw
        
        Thermokarst Landscapes
        
        a) Thermokarst bogs - waterlogged meadows surrounded by frozen ground
        
        b) Lake thermokarst – batagaika crater
        
        c) Hillslope thermokarst – steep slope causing gravitational driving stress causing more hillslope instability
        
        Olefeldt et al., 2016
        
        Gradual or rapid thaw?
        
        Previously assumed permafrost thaw would be gradual – perhaps 300 years – modelled simply, leaving complex hillslope processes out as these process expose more ice to surface temperatures
        
        Features like Batagaika show that abrupt permafrost thaw is occurring
        
        The pan-Arctic distribution and rates of change of these ‘abrupt thaw’ features has not (yet) been mapped
        
        1/5 of thawing soils are thawing ‘rapidly’ – releasing carbon globally, reducing soil stability locally
        
        Turetsky et al. 2019
        
        Growing and Disappearing Lakes
        
        Satellite data reveal that in the continuous permafrost zone of Siberia, total lake area increased by about 12% and lake number rose by 4% during the past three decades (Smith et al., 2005).
        
        BUT – overall lake area has decreased by more than 5%
        
        How can this happen?
        
        Because while new lakes are forming in some areas (like Siberia's continuous permafrost), in other areas—especially the discontinuous or degrading permafrost zones—lakes are draining or shrinking. This happens because:
        
        Thawed permafrost can lead to lakes draining through new subsurface pathways
        
        Climate warming can increase evaporation
        
        Vegetation can invade and dry out former lake beds
        
        Impermeable ground surface with undrainable frozen lower permafrost that does not allow drainage. Opposite seen with sporadic permafrost where lake expands into an area where ground is no longer frozen causing the lakes to disappear.
      - Permafrost Change
        
        Since 1930s
        
        Thickness of seasonally frozen ground in NH decreased by 32 cm
        
        Since 1970s
        
        In NH, southern limit of permafrost moving North
        
        Since 1980s
        
        Increasing permafrost Temp by up to 2C
        
        Active layer thickness increased by up to 90 cm
        
        Thawing Permafrost causing Coastal Erosion
        
        Thawing permafrost more prone to erosion: structurally weaker
        
        Mud-rich coasts with no beaches,
        
        Declining sea ice
        
        Increasing wave erosion – large waves due to less sea ice and large fetch (space for waves to build up)
        
        In the Beaufort Sea area, rate of coastal erosion has doubled between 1955-1985 and 1985-2005
        
        ~ 1km recession over 50 years
        
        Canada in the Beaufort sea
        
        Ground Ice Thawing in Coastal Regions
        
        The extent and thickness of sea ice are really dramatically declining.
        
        This figure shows a retrogressive thaw slump, causing the soil to become like liquid and slump into the ocean.
        
        This causes more sediment to be discharged into the ocean – which causes increase nutrient sediment driven ocean processes to increase.
        
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        Resulting in larger areas of open water creating increased fetch (increase wind creates bigger waves).
        
        This is occurring on top of the thawing of ground ice causing soil erosion – with higher wave power.
        
        Climate change will also create increase energetic storms – which has been observed at lower latitudes, and there is some evidence that this will occur at higher latitudes.
        
        These three factors will create a coastline that is very vulnerable to coastal erosion
        
        These effects of this can be determined by how vulnerable to rock is to erosion.
        
        The lithified coastline is the least vulnerable to these soil erosions (Green and Yellow).
        
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        Increasingly, as the rock becomes unlithified (sedimentary) it becomes increasingly vulnerable to soil erosion – catalysed by the positive feedback of these coastal processes (seen in the Orange-Purple lines in the figure)
        
        Thawing of Peat Bogs
        
        With thawing permafrost, we can also ask about peat bogs
        
        Peatlands that are located in the Arctic (particularly in the Russian Arctic) – could the thawing of these ‘carbon sinks’ cause a great release of carbon and greenhouse gases
        
        . These are also made vulnerable by the occurance of wildfires in Siberia.
        
        Impacts of Permafrost Thaw
        
        Impacts can either be assessed on two different scales:
        
        Global: There are impacts on global climate from thawing permafrost
        
        Soils in the northern permafrost region store a large amount of organic carbon, estimated at 1460–1600 PgC across surface soils and deeper deposits (Hugelius et al., 2014; Strauss et al., 2017; Mishra et al., 2021) - almost double the amount of Carbon in Earth’s.
        
        Carbon can be added to the atmosphere via:
        
        Bubbling of methane from thermokarst lakes
        
        Tipping points reaching a new regime of abrupt permafrost thaw and carbon and methane into the atmosphere
        
        Photosynthesis is still fixating carbon into the soils – which are more available due to permafrost melt
        
        Microbes: very resistant to low temperatures, species vary upon location globally. Arctic soil microbes are some of the most resistantly adapted to low temperatures in the World.
        
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        Worry about potentially harmful pathogens locked up into ice
        
        Microbial decomposition of carbon-rich soils
        
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        Local: There are significant localised impacts on humans and ecosystems of permafrost degradation
        
        North American settlements that are Arctic (Alaska and sub-arctic, Yukon in Canada). There are not many communities in the high Arctic, and when they are – they are mostly situated around the coast or rivers.
        
        Long history of colonisation in the European Arctic – with a lot of settlement in the High Arctic in Russia in the Soviet Era, claiming colonies and parts of the state that were located in places like Siberia. Most European arctic settlements are very large due to geopolitical strategical placements for military and power dynamics.
        
        Majority of Arctic settlements are in Russia, US and Canada (followed by Sweden, Norway, Iceland and Finland).
        
        Yakutsk is the largest settlement that is built on continuous permafrost and is located in the upper Artic in Russia.
        
        We are observing large decline in settlements in the upper Arctic in Russia near the border with Finland. People are choosing to move away for quality of life reasons
        
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        Localised Impacts
        
        Local Subsidence - Permafrost degradation is an issue responsible for damage to houses, roads, airports, pipelines, and other facilities founded on ice-rich permafrost.
        
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        Estimated damages from permafrost
        
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        Impacts on Climate
        
        We suspect there is a positive feedback mechanism that has been observed in past climate: warming soils will release more carbon and methane into the atmosphere, which will lead to further warming and represents a positive feedback
        
        This may be offset by the ‘greening’ of the Arctic. Not only does increased vegetation fixate carbon in photosynthesis – but the increased growth can cause stabilisation of the soil due to increase growth networks of roots that help to anchor soil and protect it from soil erosion.
        
        Can this offset the carbon and methane that is released from the thawing permafrost?
        
        IPCC AR6 (Ch 5): thawing terrestrial permafrost will lead to carbon release under continued warming (high confidence), but that incomplete knowledge and representation in models of driving processes represents a major limitation in our understandings of the rates, magnitudes and linearity of the permafrost climate feedback
    - - • Snow/ice –albedo feedbacks have led to amplification of warming in the Arctic
      - • more than 2 x the global average (~5oC per decade)
      - • This is has led to observed warming at monitored borehole sites
- - - - Glaciers have been receding since the end of the ‘Little Ice Age’ (~1850)
        
        Mass loss has increased significantly in recent decades as a response to late 20th Century warming
        
        Predicting glacier response is important for managing water resources and mitigation against hazards such as GLOFs