OCN 5401 Chapter 7 Major Ocean Currents Instructor: Dr. George A. Maul / X 7453

Ocean Circulation has two components Wind driven (surface) Thermohaline (deep)

The Wind-Driven Circulation Benjamin Franklin’s Map Computer Model Map Warm currents in red; Cold currents in blue.

Global Winds

Arctic Ocean Currents RV Fram Fridtjof Nansen

Map of the Arctic Ocean showing the routes taken during the 1893–96 Nansen's Fram expedition:Nansen's Fram expedition RED: Fram's route eastward from Vardø to the Siberian coast, turning north at the New Siberian Islands to enter the pack ice, July – September 1893 BLUE: Fram's drift in the ice from the New Siberian Islands, north and west to Spitsbergen, September 1893 – August 1896 GREEN: Nansen and Johansen's march to Farthest North, 86°20'N, and their subsequent retreat to Cape Flora in Franz Josef Land. February 1895 – June 1896 PURPLE: Nansen and Johansen's return to Vardø from Cape Flora, August 1896 YELLOW: Fram's voyage from Spitsbergen to Tromsø, August 1896 RV Fram Expedition

Western Boundary Currents SSH variability

Eastern Boundary Currents coastal deserts Benguela Current California Current Kon Tiki

Indian Ocean Currents sea surface temperature SSH Modeled SSH, March

Ocean Currents of South Africa

Southern Ocean Currents dissolved silica

Equatorial Currents Equatorially trapped currents ζ+f= constant

El Niño SSTs La Niña SSTs

ENSO Animation

ENSO – El Niño Southern Oscillation Enso String Quartet

ENSO Teleconnections

Thermohaline Circulation

Transect along western Atlantic Ocean showing water masses and general circulation processes. Water Mass Formation

North Atlantic Deep Water (NADW) when warm salty surface water from south cools and sinks to form a deep western boundary current (DWBC). Stommel, 1958

Deep Western Boundary Current You’re kidding, right?

The major thermohaline circulation cells that make up the global conveyer belt are driven by exchange of heat and moisture between the atmosphere and the ocean. Conventional Wisdom

The Conveyor Belt - but is it correct? “For the past several decades, oceanographers have embraced the dominant paradigm that the ocean’s meridional overturning circulation operates like a conveyor belt, transporting cold waters equatorward at depth and warm waters poleward at the surface. Within this paradigm, the conveyor, driven by changes in deepwater production at high latitudes, moves deep waters and their attendant properties continuously along western boundary currents and returns surface waters unimpeded to deepwater formation sites. A number of studies conducted over the past few years have challenged this paradigm by revealing the vital role of the ocean’s eddy and wind fields in establishing the structure and variability of the ocean’s overturning. Here, we review those studies and discuss how they have collectively changed our view of the simple conveyor-belt model.” M.S. Lozier, Science, 2010.

OCN 5401 Questions? Chapter 7