The movement of the surface layer of the ocean is driven mostly by wind currents. As the surface water sinks into the deep ocean, it forces the deep water to move horizontally until it can find a region on the globe where it can rise back to the surface and complete its circulation loop.
This usually occurs in equatorial regions of oceans, typically in the Pacific and Indian Oceans. The surface ocean current brings new water into the northern regions from the South Atlantic by way of the Gulf Stream and the water returns to the South Atlantic using the North Atlantic Deep Water current.
The constant influx of warm water into the North Atlantic polar ocean keeps the regions around Iceland and southern Greenland mostly free of sea ice year round. The thermohaline circulation loop is quite complex Figure 1. The Bering Straight inhibits deep currents from flowing out of the Arctic Ocean and into the Pacific Ocean because of its shallow ocean floor. Like the Bering Straight passage, a shallow portion of the ocean floor blocks the flow of water from moving into the Pacific Ocean.
This causes the thermohaline circulation to move east where it splits in two directions. When sea ice moves south through the Fram Strait into the North Atlantic, it melts and creates a layer of fresh water at the surface of the ocean. This fresh water is less dense than saline water and tends to stay at the top of the ocean.
The actual flows in this model are based on current theories of the thermohaline circulation rather than actual data. The thermohaline circulation is a very slow moving current that can be difficult to distinguish from general ocean circulation. Therefore, it is difficult to measure or simulate. Skip to main content. Informal , Formal , 9 - 12 , 6 - 8. These two regions don't mix except in certain special areas, which creates a large slow current called the thermohaline circulation.
Download Video. Video Description:. Cold winds blowing over the oceans chill the waters beneath them. These winds also increase evaporation rates, further removing heat from the water. These chilled waters have increased densities, and thus tend to sink. Formation of sea ice also helps to increase the density of water near Earth's poles. As seawater freezes, salt is forced out of the ice in a process called "brine exclusion". The ice is essentially not salty.
The excluded salt increases the salinity of the cold water immediately below the ice, making it denser still. The salty, cold water near the poles sinks toward the ocean floor. Just as rivers on land flow downhill towards the sea, deep density-driven currents in the oceans move along submarine valleys towards the deepest parts of the ocean.
The cold, salty waters that drive the thermohaline circulation form in the Arctic Ocean, the North Atlantic, and the Southern Ocean. The shallow ocean floor along the Bering Straight prevents deep currents from flowing out of the Arctic Ocean into the Pacific.
Dense water on the floor of the North Atlantic moves southward, eventually joining the sinking waters of Southern Ocean in the far South Atlantic. Once again, a shallow section of the ocean floor blocks the flow from moving into the Pacific.
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