Oceanography 11 – Ocean currents – Flashcards
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Oceanic circulation is determined by...
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wind and density/gravity (sun) Shallow = wind, Deep = Thermohaline circulation
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Surface Currents
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top 10% (400m) of oceans = wind driven 3% of wind speed. Easterlies at equator + Westerlies
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Gyres
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generated by tradewinds. —surface currents that flow in a circle around the periphery of an ocean basin due to Coriolis effect. Without Coriolis, water moves in same direction.
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Ekman spirals
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Water deep can flow in the opposite direction of the wind but NET transport of water to be 90 degrees from the wind direction. (Ekman transport)
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Ekman transport
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causes water to gather at center of the gyres. Balance between ekman spiral and gravity (try to flat it out).
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Geostrophic Currents
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Currents of gyros.
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western boundary currents
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The fastest, deepest and warmest geostrophic currents are found at the western boundaries of ocean basins. Gulf Stream (2 m/s, 70 km wide, 450 m deep) = largest (55 million m3/s
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Kelvin-Helmholtz instabilities
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formed from turbulence generated by shear at an interface between two moving fluids (western boundary currents)
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Eastern boundary currents
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broad (<1000 km), • shallow • slow • cold • flow toward the equator.
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Transverse currents
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flow eastward or westward, linking boundary currents together in the gyres.
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Why are western boundary currents concentrated and fast and eastern boundary currents diffuse and slow?
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western turn faster to the right cause away from equator. Eastern moves towards the equator so much slower and less Coriolis. Thus the hill of water is more western than center
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Western/Eastern boundary currents also transports different temp water...
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warm water western boundary currents to north. Cold water eastern boundary currents to south.
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Upwelling...
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Upwelling has effect on climate and organic productivity. Upwelling occur at equator and some Coastal.
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Downwelling...
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usually at poles
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Equatorial upwelling
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made possible by ekman transport/surface wind. Water moves out to enable new space.
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Coastal upwelling
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west side of continents
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Langmuir circulation
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Caused by slow, steady winds that form windrows (sea foam)
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El Nino
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trades weaken or reverse, upwelling is surpressed, and warm water spreads over most of the Pacific, including offshore of Central and South America (areas where water is typically cold).
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La Nina
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years are essentially strong normal years
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Three ways the atmosphere (and ultimately the Sun) forces the ocean patterns:
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Winds, Heating/Cooling, Evaporation/Precipitation
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Thermohaline circulation
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whole-ocean circulation driven by density imbalances related to variations in water temperature ("thermo-"), and also salt content ("-haline"). Entire ocean; it is sometimes referred to as the "global conveyor belt". Currents are slow and deep.
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brinicles
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Formed when the very cold and salty sea water downwells and freezes near-by water.
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caballing (aka cabbeling)
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the mixing of two water masses (A,B) with different temperatures and salinities, which generates a third mass that is more dense (C) and consequently sinks beneath the parent water masses.
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Antarctic Bottom Water (AABW)
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extremely dense (the densest water in ocean) due to its extreme cold and salty nature. Formed from southern Hemisphere sea ice formation.
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North Atlantic Deep Water (NADW).
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warm, salty North Atlantic Ocean cools as cold winds from Northern Canada sweep over it. It drops from 10° to 2°C in the process, and sinks to depth.
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Antarctic Intermediate Water, North Atlantic Intermediate Water
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generated by caballing
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Mediterranean Deep Water
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generated by very salty (3.8%), very warm water emanating from the Mediterranean Sea. Below atlantic ocean.
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The downwelling at poles are countered by upwelling from...
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(1) Wind driven upwelling, and (2) turbulent mixing acrossthe thermocline (mixed-layer + abyssal layer) Water remain down there for Pacific is the oldest in the ocean—about 1200 years on average. Water in the Atlantic and Arctic oceans is younger, about 200-600 years old
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Water mass
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Body of water in the ocean with distinct physical and chemical properties (temp, salinity, nutrients, gases, etc) obtained at the sea surface.
