Ocean Circulation Tyburn Marine Biology - Spring 2019
Ocean currents have a big effect on the weather! The Scilly Isles – only 30 miles off the coast of Cornwall, England (lat 50o!) but in the warm Gulf Stream! Ocean currents have a big effect on the weather! Iceland Weather…
The Mediterranean Sea, seen from the Space Shuttle, looking toward the east
GYRE – The flow around the periphery of an ocean basin (from gyros = a circle)
Surface Winds drive the initial surface gyres…
But it’s more complicated! Four Forces – surface winds, the Sun’s heat, Coriolis Force, and Gravity – determine the exact patterns for ocean currents
North Atlantic Gyre Coriolis Force effects
Coriolis Forces play an even more important role for ocean currents than for atmospheric winds – because these small but persistent forces have more time to act on slower-moving ocean currents! Video1! Video2!
The Ekman “spiral”
Overall water column movement is about 45o to RIGHT of winds (N. Hem)
Wind North Atlantic Water!
“center” of hill!
The Result…
Global Ocean SURFACE Currents
Western Boundary Currents – the fastest on Earth! A Sverdrup (sv) = 1 million m3 per second!
The Gulf Stream
The Gulf Stream
Gulf Stream “eddies”
A photo mosaic of several day’s IR data
An eddy off the coast of Japan!
Transverse Currents – provide the links for the northward and southward flowing currents
Today will be hazy, hot, and humid in Annapolis … Today will be hazy, hot, and humid in Annapolis ….summertime weather is affected by ocean and atmosphere currents
Equatorial Upwelling
Coastal Upwelling (or subsidence Coastal Upwelling (or subsidence!) is caused by the Coriolis transport of water near the surface (where the angle is nearly 90 degrees)
Growth of phytoplankton in the nutrient-rich waters where upwelling is taking place off the California coast.
caused by winds that blow steadily across a wide ocean area Langmuir Circulation caused by winds that blow steadily across a wide ocean area
A “non-El Nino” year!
El Nino year has unusually warm eastern Pacific waters!
A quick return to cooler conditions Peak El Nino
Thermohaline Circulation a VERTICAL, density-driven ocean circulation! Mixing of equal-density water from points a and b would produce MORE dense water at point c – it would SINK!
Basin-driven vertical circulations – the Strait of Gibralter between Spain and Morocco
“Classic” Thermohaline circulation
Atlantic Ocean Water Layers and Sources
Convergence and Divergence of Surface Waters
Measuring Ocean Currents
1992 “Rubber Ducky” accident SOFAR float (11,500 ft!)
Current Measuring Devices A “Woodhead” seabed drifter
Ekman Flow meter
A Slocum Glider – uses energy from gravity, buoyance, heat and batteries to “swim” for months and report info about currents from it’s GPS