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KQ1: What are the main characteristics of oceans? - Coggle Diagram
KQ1: What are the main characteristics of oceans?
Ocean ecosystems
Interactions in marine ecosystems:
all life needs energy provided by carbohydrates by autotrophic organisms (photosynthesis or chemosynthesis)
consumers get energy from feeding on autotrophs, heterotrophs
food chain of primary, secondary, tertiary or quaternary consumers
food chains or food webs (webs show all inter-relationships in one ecosystems)
Factors limiting photosynthesis:
1) temperature
2) concentration of CO2
3) nutrients
4) amount of light
5) amount of water
Carbon pumps:
inorganic carbon pump = carbonate pump, marine organisms at ocean surface produce PIC in the form of calcium carbonate, CaCO3 is what forms hard parts like shells
biological carbon pump = respiration 'remineralise' the organic carbon, turning it back to CO2 and water, when they die their remains sink as detritus & decompose releasing CO2 & nutrients
The ocean as a carbon sink:
absorbs and stores atmospheric carbon with physical or biological mechanisms
oceans carbon sink depends on how much carbon can be dissolved based on...
1) solubility of CO2, greater in cold temp
2) the thermohaline circulation
more carbon stored in deep waters, temp lower
Carbon flux in oceans:
sinks between Russia & N.America
sources between S.America & Australia
equilibrium between Africa & Australia
Marine biodiversity in oceans:
concentrated in major coastlines, N & S Atlantic, high in Indian Ocean & West Pacific coast, low in Pacific, near zones of upwelling
Feeding relationships:
primary producers, basis of chain, photosynthesis or chemosynthesis
phytoplankton, contain chlorophyll & require sunlight, 2 main classes: dinoflagellates & diatoms
Algal bloom:
likely in October in New Zealand
summer in S.Hemisphere, light levels increase
phytoplankton grow explosively
can cover hundred of km2, visible in satellite images
can last several weeks, life span of individual phytoplankton only a few days
Ocean nutrients:
agricultural runoff, sewage, industrial discharges
rivers, products of chemical weathering
atmosphere, gas exchange
Marine snow:
dead animals, plants, faecal matter, sand, soot, inorganic dust
some flakes fall for weeks before reaching ocean floor
important food source for deep ocean creatures
small % not consumed becomes muddy "ooze" blanketing the sea floor, 75% of deep ocean covered in this, collects as much as 6 meters every million years
Whale fall:
carcass of a whale fallen onto ocean floor at a depth greater than 1,000, in the abyssal zones
food source for many animals
Hydrothermal vents:
black smoker emits jets of particle-laden fluids, mainly very fine grained sulphide minerals formed when hot hydrothermal fluids mix near-freezing water
minerals solidify, forming chimneys
organisms feast on this
Cold seeps:
occurs where highly saline & hydrocarbon-rich fluids, like methane and sulphides, escape from seafloor at close to ambient temps
bacterial mats are indicative of methane seepage (e.g. canyon off Pea Island, North Carolina)
Eutrophication:
occurs when environment enriched with nutrients, increasing plant & algae growth
algae increase, plants die, bacteria eat, CO2 release, animals die
Coastal nutrients:
Julu 2021, Southern Water fined £90m for deliberately dumping billions of litres of raw sewage into the sea; company admitted to almost 7000 illegal spills
less than 2 weeks later pipe burst at Bulverhythe causing more than 540 liters/ second of foul water & sewage to be released into sea
Upwelling & people:
water rises due to upwelling, colder & rich in nutrients
nutrients "fertilise" surface waters, high biological productivity, good fishing founds here
Alexander Von Humboldt, current named after, driven by strong winds, displace warm & nutrient poor allowing cold Antarctic to rise creating upwelling
Humboldt current produces best fisheries, 20% global fish stock from here
Patterns of currents
Ocean surface currents:
the Coriolis effect
large scale ocean currents due to global wind systems fuelled by energy from the sun
prevailing winds that blow across the water surface create the major ocean surface currents, only top 100-200m of water
deep thermohaline circulation is around 90% of oceans water
North Atlantic Gyre:
Coriolis deflects the current 45 degrees to the right, in Northern Hemisphere
western boundary currents, currents run along the western side of the ocean basin, come from the equator
eastern boundary currents, high latitude areas deliver cold water to low latitudes
together these currents create gyres
there are 5 major gyres
Upwelling and downwelling currents:
N.Hemisphere, wind blowing from the north is deflected to the right away from the coastline, where surface water moves offshore deep water upwells to replace the water flowed away
in the N.Hemisphere, wind blowing from the south is deflected to right towards the coastline, where surface water moves towards the shore it downfalls to make room for more water
Ekman transport
= deeper waters are not affected by surface winds & move at 90 degrees to the right (NH) / left (SH) of the trade winds due to Coriolis
Ocean currents:
surface currents driven by wind & global circulation pattern, up to 400m deep
deep ocean currents driven by density differences (salt water denser), salt water sinks it is replaced with less salty surface water - thermohaline circulation
at the poles ice fractionates fresh water, leaving behind salt which becomes more concentrated, hence water saltier at poles
Gyres:
gyres are looping currents, large system of rotating ocean currents
due to Coriolis effect, gyres travel clockwise in the N.Hemisphere and anticlockwise in S.Hemisphere
Why is upwelling and downwelling important:
cold deep ocean water is nutrient rich, locations with regular upwelling have a high biological productivity
downwelling supplies deeper ocean with dissolved gases such as C02, stays as carbon sink
abudance of fish in areas, making human population along with coasts vulnerable to changes
Patterns of circulations
El Nino and La Nina:
on El Nino is declared when sea temperatures in the tropical eastern Pacific rise 0.5 degrees above the long-term average
this causes a reversal in ocean currents where warm water is transported westwards in the Pacific towards South America
La Nina is the opposite
average period of time between a major El Nino event is around 15-17 years
3 phases, positive feedback loops:
neutral, warm moist air driven towards Western Pacific, humble current causes upwelling, thermocline deepens, heavy rain due to convection
El Nino, trade winds drop, wam water is nutrient poor and driven eastwards, a convergence zone from leading to convection and heavy rain in S.America
La Nina, strong trade winds, walker circulation intensified, convection causes heavy rain in Pacific, cold air moves and sinks, sea surface temps in Western Pacific warmer than normal, upwelling leads to low sea temps
The global conveyor belt:
thermohaline circualtion of deep ocean currents & winds driven surface currents combine to form a winding lisp known as the global conveyor belt
redistributes heat
brings cold water to tropics, takes warm water to the poles, regulates climate
What causes oscillation in ENSO:
ocean atmospheric interactions, causing positive feedback
1) ocean component, average water temps are 0.5 degrees higher than normal, high energy store in oceans
2) atmospheric component, sea surface temps cause air pressure changes
most important driver is change in position of the thermocline
Sargasso Sea:
region of the Atlantic Ocean bounded by 4 currents forming an ocean gyre
no land boundaries unlike all others, characteristic brown Sargussum Seaweed
delimited by Gulf Stream in the NW, the N.Atlantic current in the West, Canary current in the south and N.equatorial current to the east
Horizontal and vertical variations
Horizontal variations:
salinity, around 3.5% at equator, reaches 3.7% around latitudes 20N/S, decreases towards high latitudes (polar areas, 3.5%)
temp, 24 degrees at equator, higher in Caribbean (28), falling to 1-2 degrees at poles, Antarctica has cooled surface temps (around 0) than Artic (2-4)
Vertical variations:
salinity, beneath 1,000m little variation, around 3.5% salinity all latitudes, above the halocline there is more variation described above
temp, large variations at surface depending on latitude, fall beneath 1000m he water is around 2 degrees all latitudes
Ocean salinity:
average seawater salinity = 3.5%
main constituents of ocean salinity (chloride 55%, sodium 30.6%...)
normal open ocean is 3.3-3.8%, tap water 0.08%
Salinity variations reasons:
horizontal: polar low salinity due to melting ice in summer, ITCZ low salinity due to high levels of rainfall diluting water, mid-latitudes high salinity due to high evaporation low precipitation
vertical, all difference in salinity due to surface processes (decreasing = precipitation, runoff, icebergs melting, sea ice melting) (increasing = sea ice forming, evaporation), salinity in deeper water relatively uniform as It is unaffected by these processes
Temperature variations reasons:
horizontal: polar water receive little solar warmth, more solar energy available at tropics so warmer
vertical, polar regions not much of a thermocline as surface waters similar temp to deep waters, in other areas solar energy is reflected or absorbed at the surface resulting in less warming in deep waters
Atmosphere and ocean interactions
Differential heating:
longer vs shorter distance effecting earth's heating from sun's radiation, occurs due to earth's curvature, greater depth of atmosphere and tilt of the earth
The Coriolis Effect & Winds:
pattern of deflection taken by objects not connected to the ground
spin of the Earth to the right in the N.Hemisphere, to the left in the S.Hemisphere
earths surface rotates faster at equator than the poles
as air flows to the equator, it is deflected west in both hemispheres, trade winds
trade winds are air currents closer to the Earth's surface & blow from east to west near equator, dominant wind patterns
Ocean stratification:
layers within it
1) thermocline, rapid change in temp
2) halo cline, rapid change in salinity
3) pycnocline rapid change in density
ocean is stratified by density, a function of temp & salinity
in tears of pressure, there Is 3 layers: mixed layer, pycnocline, deep layer
pycnocline, zone in which density increases rapidly with increasing depth
Global circulation:
earth rotates comprised of land & water masses (contrasting thermal properties), a 3 cell atmospheric circulation pattern
ascending air masses lead to low pressure (higher levels of rainfall)
low pressure at tropics & equator, higher pressure at poles due to low ocean temp there causing sinking air
Ocean basin relief
Main features:
continental shelf
continental slope
continental rise
abyssal plain
seamounts & guyots
mid ocean ridges & rifts
Continental shelf:
area of sea floor at the edge of continental landmass, below sea level but part of the continent, gently slops at a depth of 150-200m giving way to continental slope, formed of continental crust, few earthquakes
extends to shelf break, where shelf depends to slope
Continental slope:
steeper 4 degrees slope, about 200m deep merges to abyssal plain at 1500-3500m deep, deep submarine canyons cut across slope in places, sediments transported down slope by submarine avalanches called turbidity currents
Submarine canyons:
a cut ravine into the continental slope
form where rivers enter the sea and cut a cavine into the continental slope
transports sediment in mass flows (turbidity currents)
Turbidity currents:
down slope and deposit sediment in fans
rapid, downhill flow of water caused by increased density due to high amounts of sediment
sediments may cascade continually down the canyons but earthquakes can shake loose huge masses of boulders and sand that rush down the edge of the shelf, scouring the canyon as they go deeper
Continental rise:
gentle incline from abyssal plain to continental slope
Abyssal plain:
deep ocean basin 3-5km deep, flat with mafic rocks of oceanic crust covered by thin beds of fine grained, slowly deposited pelagic sediment with wind-blown dust, volcanic ash, skeletons of microscopic plankton organisms, thicker deposits of coarser sediment carried in turbidity currents
aseismic, no earthquakes
Seamounts & Guyots:
seamount = submarine basalt volcano rising at least 1000m above ocean floor without reaching sea level, may be singly or in groups or chains
some topped by coral atoll
a seamount with an eroded top is a guyot
Oceanic ridges:
connected & represent longest & most continuous mountain chain in the world
over 60,000km & crisscrossed by transform faults
the center of a MOR is either convex or occupied by a Rift Valley created by extreme faulting
a MOR is caused by frequent shallow earthquakes & eruptions
seafloor spreading, causes a rift, hot buoyant crust expand & elevates causing a ridge, as the crust moves away from the ridge it cools, contracts and increases in density, sinking to form abyssal plains
spreading very slow, max 10cm/year
Mid ocean ridges and rifts:
mid oceanic ridge = elongated submarine ridge in the middle of the ocean rising 2 or 3km above abyssal plain and up to 1000km wide made of basalt extruded at divergent plate boundary where 2 oceanic plates move apart by sea floor spreading, an axial Rift Valley (deep valley with steep mountainous sides), spit summit of ridge, frequent shallow earthquakes due to rising magma & movement along transform faults
Why are ridges different?
the Mid Atlantic Ridge has a slow spreading ridges so has a steeper profile with a Rift Valley at the centre, newly formed crust cools slowly & starts to sink into the mantle near its point of origin at the MOR (South Atlantic 4cm/year, North Atlantic 2cm/year); rift zone along the axis, mountain ranges
the East Pacific Ridge is fast spreading ridge, gently elevation as newly formed crust moves away more quickly, doesnt sink into the mantle near its points of origin
ridge push is more significant force at slow spreading ridge (up to 16cm/year between Nazcar and Pacific Plates); axial rift, faults and grabbers
Ridge push mechanism:
the buoyant upwelling mantle causes the ridge to form & rise 2-3km about the abyssal plain
magma melts & hot magma rises & convection currents cause plates to diverge
gravity acts on the elevated ridge producing a pushing force down the plate
as rocks cool & contract, increases in density adds to the force
gravitational sliding off the elevated MOR
Hydrothermal vents and black smokers:
1977, discovery of hydrothermal vents, areas of known volcanic activity, discovered by Dr Bob Ballard in Alvin submersible
Chemicals of silica, manganese, hydrogen, sulphur and methane, for chemosynthesis
organisms like tube worms surround these
Water seeps into the earth’s crust through cracks and fissures, becoming heated by hot magma in the earth’s layers, as it boils up to be released, the water picks up dissolved metals and minerals, it comes up the crust causing vent structures
When the dissolved metals and minerals reach the cold ocean water, they solidify in layers, causing massive structures called chimneys
Some chimneys are up to 18 stories tall
Black smokers:
rich in sulphur bearing minerals
White smokers:
characterised by the barium, calcium and silicone minerals
Cold seeps:
In the last decade, cold seeps have been discovered
low-temperature flows of water found in shallower water than hydrothermal vents
dependent on chemical rather than solar energy
Hydrocarbons such as methane or hydrogen sulphide supply the energy
Other:
Some vent fluids are not characterised by a specific colour, but due to the shine they emit due to different water temperatures
Some simply emit streams of bubbles due to carbon dioxide
Seamounts & Guyots formation:
when volcanoes form on the seafloor, they build up overtime as they erupt volcanic lava that cools to become basalt (hotspots)
if a volcano does not reach the surface of the ocean, it is called a seamount
if it grows in height & volume, enough to reach the surface, it becomes a volcanic island (e.g. Hawaii)
waves and other sub-ariel processes will cause erosion of the volcano
overtime, these processes will erode flanks at the top of the seamount / island, eventually forming a flat shelf to form a guyot
in addition, the cooling oceanic crust becomes more dense and sinks back down
volcanoes get progressively older away from the mantle plume due to the movement of the pacific plate
seamount -> volcanic island -> mantle erosion -> guyot (not all seamounts will become this)
Seamounts provide:
a hard substrate for marine organisms to attach
a habitat for marine invertebrates
nurseries for deep sea fish e.g. squat lobsters
influence the flow of deeper waters which results in the upwelling of nutrient-rich waters towards the sea surface
Atolls:
a ring of coral that originally grew completely around the shoreline of an island, which continues to grow upwards on top of itself as the island subsides or eroded away
as reef building corals thrive only in warm waters, atolls are only found in tropics & subtropics
Formation:
corals begin to settle and grow around an oceanic island forming a fringing reef (can take 10,000 years)
over the next 100,000 years, if conditions favourable, the reef will continue to expand
as it expands, the interior island usually begins to subside and fringing reef turns into a barrier reef
when the island completely subsides beneath the water, leaving a ring of growing coral with an open lagoon in its centre, it is called an atoll (process of atoll formation can take as long as 30,000,000 years)
1) island and ocean floor subsides, coral growth builds a fringing reef, often including a shallow lagoon beneath the land and the main reef
2) as the subsidence continues, the fringing reef becomes a larger barrier reef, further from the shore with bigger & deeper lagoon inside
3) the island sinks below the sea due to subsidence of the volcanic island, and the barrier reef becomes an atoll enclosing the open lagoon
Trenches and Island Arcs:
largely destructive plate boundaries, subduction zones
Ocean trenches:
also called deep sea trenches
long, narrow, steep-sided depressions in the ocean bottom in which occur at the maximum oceanic depths (approx 7,300 - more than 10,000 meters)
deepest known is Mariana Trench, in the Western North Pacific Ocean, reaches 10,929m at deepest point (Challenger Deep)
1960, Don Walsh & Jacques Piccard, first 2 to reach Challenger Deep
Formation:
ocean crust forms at MOR, crust cools becomes dense and sinks, dense crust subducts below warmer (younger) plate forming a depression, the plate pulls downwards depressing the crust forming a trench
MOR -> Abyssal plain -> Trench -> Island Arc
Abyssal plains and hills:
sediment comes from rivers & turbidity currents
sediment deposits are not as thick closer to the ridge because as the crust moves away from the ridge, more sediment accumulates over time (sediment thicker & older further from the ridge)
The world's oceans
Locating:
Arctic, smallest, 4.3% area, 1.4% volume, 1.205m depth
Pacific, largest, 46.6% area, 50.1% volume, 3,970m depth
Atlantic, 23.5%, 23.3%, 3646m
Indian, 19.5%, 19.8%, 3,741m
Southern, 6.1%, 5.4%, 3,270m
seas are found on the margins of oceans and are partially enclosed by land
Influence:
the ocean is large, average temp 3.9 degrees, covers average 331 million km2, volume of 1.3 billion km3
on a planetary scale is insignificant, 0.02% of the earths mass
significant influence on the planet
Bathymetry:
marine geologists can provide a clear image of the ocean's bathymetry (variation in depth) based on solar & satellite measurements
ocean contains broad bathymetric provinces, distinguished by their water depth
oceans exist as oceanic and continental lithosphere differ markedly from one another
Mapping:
mapping of oceans
New Antarctic Mapping:
scientists made most precise map yet of the mountains, oceans & plains that make up the floor of Antartica's encircling Southern Ocean
map covers 48 million sq km, found deepest point (7,432m, Factorian Deep)
knowledge of earths oceans important for safe navigation, marine conservation and understanding of Earths history
new map made possible by financing from Japan's Nippon Foundation & support from SeaBed2030, intentional effect to properly chat Earth's ocean floor by end of decade
5 Deeps expedition
deepest point in Southern ocean found, Factorian Deep
key locations where seafloor bottoms out was mapped in this expedition
Deepest = challenger deep, 10,924, in Pacific Ocean, Mariana Trench
RS Sir David Attenborough
UK's new ship, equipped to map millions of km's across the oceans bottoms
Earth topography:
70.5% of earths surface is located beneath sea level
largest % is between 4-5km and then between 0-1km
Isostacy:
land composed of lighter, more buoyant continental crust (granitic) 2.7g/cm3
ocean crust is heavier, more dense (basaltic) 2.8-3g/cm3
compensation depth = line of equal pressure
causes high continents & low ocean floor
How old are oceans:
ocean crust is younger at mid ocean ridges & oldest furthest away & near continents
youngest crust is in Red Sea and oldest in Mediterranean
oceans from at mid-oceanic ridges, destroyed at subduction zones
oldest 'intact' slice of oceanic crust is 340ma in the Mediterranean
oldest known relics of the oceans is 3.8 billion years old in Greenland
Why do we have an ocean?
earths early atmosphere condensed & rain filled the oceans
degassing of eater vapour from cooling magma
after earth's surface has cooled to temp below boiling point of water, rain filled for centuries
water drained into great hollows in earths surface, primeval ocean came into existance
forces of gravity prevented water leaving the planet
Summary:
ocean basins form 70% of earth
oceans vary in size, shape and relief
oldest known oceans are 340Ma
oceans started to form 3.8b years ago
growth & destruction of oceans is related to plate tectonics, explained by the Wilson cycle
The Wilson cycle:
model of how oceans are formed and destroyed
1) embryonic e.g. East Africa - rift zone
2) juvenile e.g. Red Sea
3) mature e.g. Atlantic Ocean - ocean
4) declining e.g. Pacific Ocean- subduction
5) terminal e.g. Mediterranean
6) suturing e.g. Himalayas- collision
Ocean biodiversity
80% of all life on Earth is found in the oceans
Net Primary Productivity:
rate of production of new biomass per unit area by autotrophs
takes place by photosynthesis or chemosynthesis
measured as grams of carbon per unit area per year
gross production - respiration = NPP
Coastal areas have higher NPP than deep oceans:
less sunlight in deep oceans
upwelling to coasts
highest NPP where dissolved nutrients are highest, rivers bring to ocean, coastal shelves keep high NPP by runoff from land & shallow water
deep oceans vast volume of water and virtually no dissolved nutrients
Biodiversity and depth:
increasing depth, decreasing light
level of water where not enough light for photosynthesis = photic zone (around 200m deep, 25% marine species live on coral reefs within this zone)
Deep ocean food chains and webs:
chemical energy from fissures
primary produces of bacteria, use chemosynthesis
Gulf of Mexico, tubeworms, mussels, crabs etc
Cold seeps:
hydrocarbon-rich water flowing from cold seep, releases methane gas bubbles
allows community of organisms in the deep ocean
Interactions at cold seeps:
large chemosynthetic bacteria, food source for bacteriovores
organisms feed on the detritus produced by clams and tubeworms
his attracts predatory organisms
many species present are only found in cold seeps (400 species)
consistent, rich food courses & habitat complexity
Inter-tidal ecosystems:
intertidal zone between high & low tide, consistent wetting and drying
Challenges organisms may face:
deep ocean: lack of sunlight, high pressure, lack of primary producers away from hydrothermal vents & cold seeps
intertidal zone: wave action, temperature change, inundation with water / drying out, lack of substrate to attach to
Adaptations:
ITCZ, mussels have shock absorbing cables (byssal threads), sand crabs live in substrate and move based on water level
Deep, vampire squid, bioluminescence to scary off predator, startles, distracts, causes confusion
Salt marshes:
part of ITZ
halophytes near ocean, salt loving plants e.g. eel grass near sea - vegetation succession
Salt marsh formation:
accumulation of silt & clay 10cm/year
vegetation traps sediment, reduces energy, fall out of silt & clay occurs, raises surface gradually
plant succession occurs, stabalises
factos influencing: low energy condition for deposition, sediment supply, periodic tidal flooding
salt marshes often form estuaries, causes a reduction in wave shock
salinity can vary from seawater, brackish & freshwater
NPP very high, availability of nutrients, variety of organisms, strong sunlight