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Ocean and Climate I
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Physical Characteristics of the Ocean Surface area: 3.61·1014 m2
Mean depth: 3.7 km Ocean volume: 3.2·1017 m3 Mean density: 1.035·103 kg/m3 Ocean mass: 1.3·1021 kg
Ocean Development By Plate Tectonics Alfred Wegener (1880-1930)
The deeper layers of Earth
Underwater lava eruption along the rift can lead to local warming of deep water environment with heat transport by Eddy currents to the surface
Shape of ocean floors
Ocean Currents
Eddies, Gyres, and Geostrophic flows
Collectors of human garbage: from hundreds of shipwrecks to ten thousands of plastic ducks
More than 10,000 ocean containers are lost each year over the side in the world ocean trades -- the result of high seas perils.
Ocean impact on climate
Heat exchange with atmosphere by condensation and other processes
Meridional heat transport from tropic to polar regions
Heat capacity of ocean causes the ocean to serve as a thermal reservoir balancing rapid climate changes
Wind surface water interaction causes ocean currents
Earth rotation couples with ocean current through Coriolis force
Inertia of dense water flow continues currents even without wind
Salinity of water affects the flow pattern of ocean currents
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Atmosphere is vertically structured with high altitude events impacting climate. The role of ocean is limited to the surface layers
Atmospheric currents (winds) are largely unbounded. Oceans are laterally bounded by continents (except for southern ocean where fluid can pass around the globe)
Atmosphere is largely transparent to radiation and is heated from below by convection. Ocean absorbs radiation and surface region is heated by absorption.
Wind driven and buoyancy driven circulations of ocean current provide very fast energy transport.
Difference to Atmosphere
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The cryosphere
2% of the planetary water is frozen (ice sheets, sea ice, glaziers, permafrost), most of it is contained in ice sheets over land, Antarctica (89%), Greenland (8%), increasing the average Albedo. 7% of the ocean is covered by ice. Sea ice regulates heat exchange, moisture and salinity and insulates “warm ocean water from cold polar atmosphere.
Ice Melting
Ocean parameters Surface area: 3.61·1014 m2
Ocean volume: 3.2·1017 m3 Mean density: 1.035·103 kg/m3 Ocean mass: 1.3·1021 kg
Assume 50% of ice sheet melts, corresponding to 1% of the ocean water mass: Mmelt≈1.3∙10
19 kg.
mm
m
S
VH
mV
mkg
kgMV
melt
melt
meltmelt
351061.3
1026.1
1026.1
/10035.1
103.1
214
316
316
33
19
Challenger Expedition 1873-1875
Exploration of the Seas - Oceanography
Sir John Murray John Buchanan Sir Charles WyvilleThomson
A 68,890-nautical-mile (127,580 km) journey
At 360 stations the crew measured the bottom depth, temperature at different depths, observed weather and surface ocean conditions, and collected seafloor, water, and biota samples.
Properties of sea water
3
3
3
3 10035.110999.02 m
kg
m
kgwaterseaOH
At 273 K, variations of density are within few percent only!
PST ,, Cold water is denser than warm water Salty water is denser than fresh water Pressure increases density of water
Salinity is defined in practical salinity units psu in terms of electrical conductivity, which is close to the relative proportion of the dissolved salts in g per kg water (or ‰). Seawater has 34.5 psu.
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Chloride: 18.98‰ (g/kg) Sodium: 10.568‰ (g/kg) Sulphate: 2.65‰ (g/kg) Magnesium: 1.27‰ (g/kg) Calcium: 1.27‰ (g/kg)
Potassium: 0.38‰ (g/kg) Bicarbonate: 0.14‰ (g/kg) Others: 0.11‰ (g/kg)
Salinity: 34.48‰ ≈34.48 psu
Sea water composition
Since ocean atmosphere interactions are limited to the surface region, the pressure dependency of the water density is neglected. There is, however, sensitive temperature dependencies!
ST ,
Contour plot of seawater density deviations shown as function of salinity and temperature at the ocean surface. The conditions of relevance for oceans are shown at the right hand side.
31000
m
kgrefref
Density increases with temperature and salinity (1psu≈1g/kg=1‰), Fresh water has maximum density at 4oC (cooling forms ice) At 15oC the water at the ocean surface (S≈36 psu) has ≈26.7 kg/m3 which translates into a lower density =1026.7 kg/m3 compared to a temperature of 0oC.
Temperature and salinity patterns Steady Temperature decline towards the polar regions, visible is the impact of the cold North Pacific current branching down the US Northwest coast and the Humboldt current branching from the West Wind Drifts northwards along the South American west coast.
Regions of high salinity in middle latitude range north and south of the equator regions. Polar regions show low salinity including cold water currents such as the North Pacific current in the American Northwest and the Humboldt current.
Early exploration of salinity
Georg Wüst Meteor Expedition 1925-1927
1925
1926
1927
Horizontal salinity patterns
Longitudinal cut across the western (top) and the eastern (bottom) regions of the Atlantic Ocean showing the horizontal distribution of salinity, based on Meteor observations.
Modern Results WOCE (1990s) The Hydrographic Program of the World Ocean Circulation Experiment (WOCE) was a comprehensive global hydrographic survey of physical and chemical properties of the oceans.
WOCE Oxygen & Salinity
Mixed layer and thermocline
mixed layer
thermocline
abyssal layer
Mixed layer has constant temperature due to wind and density driven convective motion, balanced by radiative heating and radiative and/or wind cooling as well as latent heat effects by evaporation processes. The thermocline layer represents an exponential decline of temperature to nearly constant abyssal sea depth temperatures.
Typical temperature & salinity profile for mid-latitude ocean.
