Surface Currents

wind currents

wind blowing over the sea moves water by pulling orbitals

convection cells

areas with contained density differences; caused by earth’s tilt and uneven solar heating

coriolis effect

deflection of air/water from its path as a result of earth rotation

which direction is air/water deflected in the northern hemisphere?

clockwise

which direction is air/water deflected in the southern hemisphere?

counterclockwise

what creates surface currents?

global wind patterns, earth’s rotation, shape of ocean basins

trade winds

0-30° N/S

westerlies

30-60° N/S

polar easterlies

60-90° N/S

ekman transport

water moves at 20-40° to the right of the wind in northern hemisphere; essential for upwelling and downwelling

how does ekman transport work?

wind pulls surface water molecules > water molecules pull water molecules in below layer by energy transfer > friction between layers forms a spiral to move water

net movement of water

90° to wind

how many convection cells exist?

3 in each hemisphere

doldrums

windless waters near the equator where trade winds converge and rise; intertropical convergence zone

gyres

big system of rotating ocean currents, e.g., great pacific garbage patch

5 major gyres

N pacific subtropical, S pacific subtropical, N atlantic subtropical, S atlantic subtropical, indian ocean subtropical

are most gyres convergent or divergent?

convergent (spiral towards middle)

geostrophic flow

balance between gravity and coriolis force that dictates when currents are deflected

how is the great ocean conveyer belt formed?

interconnecting surface and deep water currents

north atlantic gulf stream

regulates W europe’s climate and involves north atlantic oscillation (NAO)

atlantic meridional overtunring (AMO)

stream transporting water around the atlantic driven by wind and arctic freezing which creates cold oxygenated water for the deep ocean

deep water masses created by AMO

upper north atlantic deep water and lower north atlantic deep water

what intensifies the antarctic circumpolar circuit (ACC)?

high co2 levels pushing the westerlies south and increasing upwelling and warming the water

importance of wind in slowing climate change

increased wind offsets ice melt by driving atlanic meridional overturning circulation (AMOC)

great salinity anomaly

very freshwatery part of NE atlantic due to melting of greenland ice sheets 

what causes the AMOC to weaken?

freshwater accumulation in N atlantic due to melting ice

increased surface current warming causes…

heating of the gulf stream, increased stratification, decrease in nutrients and o2 at surface

north atlantic oscillation (NAO)

european ENSO, oscillating pressure difference which either warms or cools europe dependant on subtropical and subpolar pressure systems

NAO negative mode

pressure difference < average, jet stream curves up and down; cold dry weather

NAO positive mode

pressure difference > average, jet stream goes straight across ocean; warm wet weather

areas of permanent coastal upwelling

canaries, humboldt, benguela current

areas of seasonal coastal upwelling

california (spring and summer)

where does coastal upwelling occur?

on west coasts with short continental shelves

el nino

warm surface current displaces cold upwelling current and prevents upwelling, causing westerlies to weaken; BAD

la nina

cooling of warm water currents and increased upwelling caused by strong westerlies

example of ENSO impact on biodiversity

1982-1984 californian kelp forests are killed b/c no nutrients and warm water > loss of food source (drifting kelp) for sea urchin spp. > sea urchins eat live kelp > shore becomes more exposed > intertidal organisms dry out and die