Lecture 15 - Eastern Boundary Current Systems Flashcards
(11 cards)
What are Eastern Boundary Currents (EBCs)?
Ocean currents flowing equatorward along the eastern side of ocean basins, often associated with coastal upwelling and high productivity.
Why are EBC regions important for fisheries?
They provide upwelled nutrients, supporting ~20% of global marine fish catches despite covering only 1% of ocean area.
What causes coastal upwelling in EBCs?
Equatorward alongshore winds drive offshore Ekman transport, which pulls nutrient-rich water up from depth.
What is curl-driven upwelling?
Upwelling caused by increasing wind stress offshore, leading to divergence of Ekman transport over a broader region.
What direction is the geostrophic flow in an EBC?
Equatorward, flowing along the coast due to a pressure gradient force (PGF) balanced by the Coriolis force.
Why does sea level lower near the coast in EBCs?
Offshore Ekman transport removes surface water, causing a sea surface slope toward the coast.
What determines the strength of the pressure gradient in EBCs?
Both sea surface slope and isopycnal slope (due to upwelled dense water) affect the pressure gradient and geostrophic velocity.
How does geostrophic velocity vary with depth in EBCs?
It decreases with depth and often vanishes by ~200 m due to compensating effects of sea surface height and density structure.
How is the rate of upwelling calculated in EBCs?
By multiplying Ekman transport velocity by the depth and width of the upwelling zone (volume flux = velocity × area).
What is the role of baroclinic conditions in EBCs?
Density differences across the slope reduce the pressure gradient at depth, slowing the current with depth.
What is curl driven downwelling?
Along-shore wind stress decreases with distance offshore
Ekman transport offshore is convergent
Waters offshore are downwelling
