Oceanography 11 – Ocean currents

question

Oceanic circulation is determined by…
answer

wind and density/gravity (sun) Shallow = wind, Deep = Thermohaline circulation
question

Surface Currents
answer

top 10% (400m) of oceans = wind driven 3% of wind speed. Easterlies at equator + Westerlies
question

Gyres
answer

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.
question

Ekman spirals
answer

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)
question

Ekman transport
answer

causes water to gather at center of the gyres. Balance between ekman spiral and gravity (try to flat it out).
question

Geostrophic Currents
answer

Currents of gyros.
question

western boundary currents
answer

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
question

Kelvin-Helmholtz instabilities
answer

formed from turbulence generated by shear at an interface between two moving fluids (western boundary currents)
question

Eastern boundary currents
answer

broad (<1000 km), • shallow • slow • cold • flow toward the equator.
question

Transverse currents
answer

flow eastward or westward, linking boundary currents together in the gyres.
question

Why are western boundary currents concentrated and fast and eastern boundary currents diffuse and slow?
answer

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
question

Western/Eastern boundary currents also transports different temp water…
answer

warm water western boundary currents to north. Cold water eastern boundary currents to south.
question

Upwelling…
answer

Upwelling has effect on climate and organic productivity. Upwelling occur at equator and some Coastal.
question

Downwelling…
answer

usually at poles
question

Equatorial upwelling
answer

made possible by ekman transport/surface wind. Water moves out to enable new space.
question

Coastal upwelling
answer

west side of continents
question

Langmuir circulation
answer

Caused by slow, steady winds that form windrows (sea foam)
question

El Nino
answer

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).
question

La Nina
answer

years are essentially strong normal years
question

Three ways the atmosphere (and ultimately the Sun) forces the ocean patterns:
answer

Winds, Heating/Cooling, Evaporation/Precipitation
question

Thermohaline circulation
answer

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.
question

brinicles
answer

Formed when the very cold and salty sea water downwells and freezes near-by water.
question

caballing (aka cabbeling)
answer

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.
question

Antarctic Bottom Water (AABW)
answer

extremely dense (the densest water in ocean) due to its extreme cold and salty nature. Formed from southern Hemisphere sea ice formation.
question

North Atlantic Deep Water (NADW).
North Atlantic Deep Water (NADW).
answer

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.
question

Antarctic Intermediate Water, North Atlantic Intermediate Water
answer

generated by caballing
question

Mediterranean Deep Water
answer

generated by very salty (3.8%), very warm water emanating from the Mediterranean Sea. Below atlantic ocean.
question

The downwelling at poles are countered by upwelling from…
answer

(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
question

Water mass
answer

Body of water in the ocean with distinct physical and chemical properties (temp, salinity, nutrients, gases, etc) obtained at the sea surface.

Get instant access to
all materials

Become a Member