Lecture 16 - Wind-driven Gyres Flashcards
(11 cards)
What is a subtropical ocean gyre?
A large-scale, wind-driven circulation in ocean basins with equatorward interior flow and poleward western boundary currents.
What wind patterns drive subtropical gyres?
Mid-latitude westerlies and trade winds, which generate Ekman convergence and downwelling in the gyre center.
What is Ekman downwelling?
The sinking of water in the ocean interior due to convergence of Ekman transport, often in the center of gyres.
What is vorticity in oceanography?
A measure of a fluid parcel’s tendency to spin, with two components: relative vorticity (from flow shear) and planetary vorticity (from Earth’s rotation).
What is potential vorticity (PV)?
The ratio of absolute vorticity (ξ + f) to fluid column height (H), conserved as water moves: PV = (ξ + f) / H.
How does a squashed fluid column respond to conserve PV?
It moves equatorward to reduce planetary vorticity (f), since PV must remain constant.
What happens For flow in the ocean’s interior, in terms of the PV equation?
For flow in the ocean’s interior, away from the ocean’s boundaries (i.e. western boundary current), relative vorticity is negligible
So the equation becomes PV = f/H
What is Sverdrup transport?
The equatorward flow in the ocean interior driven by downwelling and conservation of potential vorticity.
What are western boundary currents?
Narrow, fast, poleward flows that return Sverdrup transport volume, breaking the Sverdrup balance due to high shear.
Why are western boundary currents warming?
Stronger mid-latitude winds and poleward shifts have increased heat transport into boundary current extensions.
what ecosystem impact has been linked to subtropical gyre spin-up?
Warming from the East Australian Current has harmed giant kelp forests in Tasmania by allowing invasive sea urchins to thrive.
