Ocean Currents: 4 causes 1. Wind: Friction with the wind drags the ocean surface to produce a current, down to about 300m. 2. Thermohaline circulation: Density variations in water arise from differences in temperature (warmer=> less dense) and salinity (more salty=>more dense). More dense water tends to sink relative to less dense water, giving rise to vertical circulations. Coriolis Effect: The earth is spinning. Points at the equator move faster than those at the poles. Airplanes, and ocean water, not attached to the earth, curve to the right (clockwise) in the northern hemisphere. In the southern hemisphere, they curve to the left (counterclockwise). Interactions with Land: seafloor, islands, and continents.

Ocean Currents: 4 causes 3. Coriolis Effect: The earth is spinning. Points at the equator move faster than those at the poles. Airplanes, and ocean water, not attached to the earth, curve to the right (clockwise) in the northern hemisphere. In the southern hemisphere, they curve to the left (counterclockwise). 4. Interactions with Land: seafloor, islands, and continents.

Ocean Currents: FUNCTIONS Move HEAT…to the poles Huuuuuuuge weather impacts Cold seawater holds more CO2 THINK GLOBAL WARMING 2. Move Nutrients and Pollution Leads to biological migrations…trash accumulations 3. Shipping – speed = $$

Basic Ocean Circulations

Thermohaline Circulation

Thermohaline Circulation Wind and the rotation of the Earth are important in determining the flow of surface currents and local areas of upwelling and downwelling, but the true driving force of deep water movement is thermohaline circulation.  Sometimes called the ocean conveyer belt, this mechanism is responsible for bringing the oxygen that sustains life to the deepest reaches of the sea, and in moving warmer waters from the tropics towards the poles. Movement of this conveyer belt depends on sinking of cold water in certain polar regions, thereby triggering the global thermohaline circulation. 

Follow the conveyor Belt … 1. Water heats up at Equator. 2. Currents move warm water to poles, where it cools. 3. As it freezes (ice), it kicks out the salt. 4. Salty, cold water sinks because it’s more dense. 5. Cold water moves along the sea floor, back to Equator. ‘round and ‘round

VARIATIONS ON NORMAL CURRENT CIRCULATION … EL NINO

El Nino OLD DEFINITION: Annual warming of water off Coast of Peru around Christmas. “El Nino” = Christ child. NOW… Any warm water occurring off Peruvian Coast Deeply affects marine life…fish and corals Occurs every 2-5 years

El Nino El Nino Sea Surface Temperature Anomaly

Consequences of Global Warming to Thermohaline Circulation Ice cap melts creating an excess of floating fresh water in the Arctic Ocean Permafrost and glaciers, particularly in Siberia, melt, causing huge flux of warm fresh water into Arctic Ocean via northward draining rivers. Low density water inhibits subduction and supply of deep water to the cold conveyor belt Gulf Stream slows, and turns east at much lower latitude because it is no longer being driven northward Cessation of northward heat transport causes Europe, and northeast North America to become colder

How do ocean currents affect weather and climate? Oceans store and transport heat. The high heat capacity of water makes it an excellent mechanism to store the sun’s energy and transport it from one place to another Oceans store liquid water and pump vapor into the air as a key link in the global water and energy cycle. Ocean storage and release of heat is a key forcing mechanism for weather Oceans absorb (release) atmospheric gasses, such as oxygen and CO2. Absorption of CO2 by oceans is the most important sink of CO2 from the atmosphere Amount of CO2 that the oceans can hold is inversely proportional to temperature, i.e. colder water holds more CO2 and warmer water (think global warming here) holds less. Oceans are a major source of oxygen for the atmosphere due to photosynthesis of microscopic plants in the ocean.

Global Warming and Thermohaline circulation Gulf Stream transports warm water from tropics to North Atlantic This keeps Europe warm for its latitude: London at same latitude as Hudson Bay Sweden at same latitude as Greenland Gulf Stream driven by: Wind stress from the North Atlantic Gyre Thermohaline circulation…subduction (sinking of high density water under lower density water) of cold salty water from Arctic, draws up Gulf Stream to replace the water mass lost. Subduction driven by: Very cold water produced by long winter nights Increased water density due to increased salinity of water in contact with the forming Arctic ice. Freezing of ice cap, forces salt out of the ice thereby increasing salinity (saltiness) of water in contact with the developing ice