OCN 5401

Chapter 7

Major Ocean Currents

Instructor: Dr. George A. Maul

gmaul@fit.edu / 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: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 1893BLUE: Fram's drift in the ice from the New Siberian Islands, north and west to Spitsbergen, September 1893 – August 1896GREEN: 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 1896PURPLE: Nansen and Johansen's return to Vardø from Cape Flora, August 1896YELLOW: 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

𝑑𝑣𝑑𝑡

=−𝛼𝛻𝑝−2Ω𝑥𝑣+𝑔+𝛼𝛻⋅𝜏

Equatorially trapped currents

ζ+f= constant

El Niño SSTs

La Niña SSTs

ENSO Animation

ENSO – El Niño Southern

Oscillation

Enso String Quartet

ENSO Teleconnections

http://www.ospo.noaa.gov/Products/ocean/sst/anomaly/

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?

It flows to the south?

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