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Chapter 1: Ocean as a habitat (Ocean in motion (Ocean tides (Long period…
Chapter 1: Ocean as a habitat
Changing Marine environment
The beginning
Ocean basins have undergone a lot of change over time. Material from the mantle has extended continents, making them bigger and higher, while oceans get deeper.
Earths early life forms represented by bacterial fossils about 3.5 billion years old.
Molecular oxygen began being produced increasingly by microscopic photosynthetic prokaryotes.
O2 levels have greatly increased since the 'beginning'.
Organisms taking advantage of aerobic respiration became dominant
Explosion of marine species (Worms, sponges, corals, animals and plants)
Increasingly abundant O2 some became ozone (O3)
The O2 concentration on land became its current level in the Mesozoic era
Atmospheric pollutants are gradually damaging the ozone layer
Different view of the Ocean floor
Continental drift is what causes the supercontinent Pangaea to break up
Seafloor spreading and plate tectonics
Spreading crust folds into mountain ranges or slips down into mantle and melts
New crust material is formed either side the axes of oceanic ridges and rises, these move away in opposite directions carrying sediments and attached continental masses
Created ocean basins
Other processes alter the ocean basins
Ice age freezing and remelting
Flooding alters coral reefs eastuaries and other shallow habitats
Warmer summers in Antarctica cause more melting
The Ocean world
Visualizing the world Ocean
Average depth of about 3800 km
Large portion of deep ocean basins are called abyssal plains
Sediment blanket often covers crustal elevations called abyssal hills
Marine earth is a single large interconnected ocean system
4 major ocianic basins (with smaller projecting seas) separated by continental barriers - Atlantic, Pacific, Arctic and Indian
Most of the southern hemisphere is water, most of the north is land
Equator is a physical boundry
The continental shelf is the extension of shoreline and is part of landmass
Outer edge of shelf is called the shelf break
Shelf break leads to continental slope
Ridge and rise systems are rugged linear features forming underwater mountain chain that encircles the earth
Trenches are where the crust sinks down and under another plate and extend deeper then 6000m
Islands, Seamounts and Abyssal hills are formed by volcanic activity. Islands are volcanic mountains that have broken the surface, Seamounts remain submerged.
Seeing in the dark
Seawater is more transparent to sound then light
Electronic sonar used to 'see' sea floor etc.
Properties of Sea water
Pure water
Water molecules form a 4-cornered tetrahedron with a 105 degree angle between the 2 hydrogen
Asymmetric molecule that forms weak h-bonds bonds with other water molecules. These bonds are easily broken and reformed
Water must be heated to a much higher temperature to boil because of H-bonds
Water on earth remains liquid, allow life
Atoms held together with covenant bonds. Oxygen end slightly negative, Hydrogen end slightly positive.
VISCOSITY AND WATER TENSION
H-bonding creates stickiness between molecules = Viscosity
Reduces sinking by increasing friction
Mutually attracted water molecules crates 'skin' on surface = Surface tension
DENSITY-TEMP RELATIONSHIP
Over most temp ranges, behaves normally - density decreases as temp rises
But unusually, density also decreases ad temp decreases as molecules form a crystal lattice (Ice)
Ice floats not sinks, which stops lakes and seas freezing from the bottom up
HEAT CAPACITY
Heat is energy - most provide by sum
Transferred by
convection
(mixing) and
conduction
(Exchange between molecules)
Water and absorb and release heat while remaing at a reasonably stable temperature
Heat energy is absorbed when air is warmer and given up when air cooler, providing crucial global scale temperature moderation mechanisms
High heat=high energy required for evaporation, so large bodies of water can resist temperature fluctuations
SOLVENT ACTION
Can interact and dissolve most natural substances, especially salt
Not a solvent for waxes, oils and small molecules the hold little electrical charge
Seawater
Accumulation of billions of years of condensed rain water and eroding rock/soil.
DISSOLVING SALTS =
SALINITY
Ranges from near 0 at river entrances to 40% in arid areas (average is 35%)
Salt addition and removal are evaporation, river run off, precipitation and sea ice freezing/thawing
Dissolving salts release + and - charged ions
SALT & WATER BALANCE
Homeostasis of marine organisms maintained by selectively-permeable membranes
Diffusing through concentration gradients
LIGHT & TEMP AT SEA
Light drives photosynthesis so most organisms stay in the upper portions of the ocean (Photic zone) where light penetrates
Dust, clouds and gasses and scatter or absorb some of the incoming radiation
Sun absorption causes water molecules to move more
Piokilotherms
= not mechanisms for body regulation. Many also considered
Ectotherms
as body temp regulated by outside water temp.
Some Piokilothermes are endothermic by using muscle movement, but body temp still fluctuated with outside temp (Large tuna, sharks)
Birds and mammals are
endothermic
and produce their own heat so are less restricted by environmental temps
SALINITY-TEMP-DENSITY RELATIONSHIP
Denser water sink so deep water is denser
Processes creating dense water happen at surface ( Evaporation, freezing and cooling
Only mechanism for vertical ocean circulation
Thermocline
= subsurface zone of rapid cooling with depth
Pycnocline
= Zone of density increase with depth
2 layered system: thin well-mixed surface layer above the thermocline, and a heavy cold, thick and more stable zone beneath
Winter means the surface cools to similar temp as lower layers so the thermocline disappears and mixing occurs
Stable earth temp relies of the release of heat back into space while some remains in atmosphere with a natural green house effect - this stops the earth freezing
Burning fossil fuels and reducing vegetation means more CO2 in atmosphere trapping too much excess heat
DISSOLVED GASES & ACID BASE BUFFERING
Gas solubility influenced by temperature
Nitrogen, carbon dioxide and oxygen most abundant dissolved in seawater
CO2 easily absorbed as i does not remain a gas when dissolved, combines with water to form weak acid
The carbonic acid-bicarbonate-carbonate system, functions as buffer to limit pH changes in sea water
Water not a good solvent of Oxygen
Animal respiration and bacterial decomposition use O2 as fast as it is created so produces a oxygen minimum zone
DISSOLVED NUTIENTS
Nitrate and phosphate dissolved are crucial sea fertilizers
Waste material sinks, the distribution and concentration down is opposite to oxygen
Warm, low density, oxygen rich, nutrient poor surface layer
Thicker, colder, high density, oxygen poor, nutrient rich bottom layer
Ocean in motion
Wind waves
Earths curvature causes differently warmed atmospheres, driving mind patterns
Size and energy of wave depends on wind velocity and fetch (distance of contact)
Once created, travels away changing shape. Water particles don't actually move forward but they move in a vertical net circle
In shallow areas bottom friction causes the base of the wave to lag and the crest then collapses. This released energy has a major effect of the shaping of the coastline.
Surface currents
Caused by a long enough constant wind blowing in one direction. Surface current do not represent horizontal movement, unlike waves
3 Major wind belts - Trade winds, westerlies and the polar-easterlies.
water movement not parallel to the wind, goes right in the north and left in the south =
CORIOLIS EFFECT
. Produced a spiral pattern going down the depths called
EKMAN SPIRAL
Except for the north of Antarctica, currents are obstructed and ocean piles up. This build-up will either flow back (counter-current) of flows along the edge of the shore (continental boundary current)
Gyres
= large circular patters produced by merging currents.
Ocean tides
Long period waves only noticeable oat shoreline (High and low tides) (Neap and spring tides)
Vertical difference between the two tides is called the tidal range
Caused by moons gravity and movement, combined with earths rotation
Semidiurnal
= 2 tide pairs daily
Diurnal
= 1 tide pair daily
Mixed semidiurnal
= 2 pairs of tides daily, but at different heights
Vertical water movement
Up-welling and sinking that tend to break down the pycnocline and providing deep-water nutrients
Thermohaline circulation
= vertical circulation
Sinking highly oxygenated water provides oxygen to deep areas. Located in colder latitudes