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Freshening of deep Antarctic water could prove catasterophic

Posted by feww on April 18, 2008

Scientists have detected changes in salinity of the antarctic water that could drmatically change the ocean currents and the world’s climate.

They found that salty, dense water that sinks near the edge of Antarctica to the bottom of the ocean about 5 km (3 miles) down is becoming fresher and more buoyant.

The Antarctic “bottom water” is responsible for the great ocean conveyor belt, a system of currents that move throughout the Southern, Pacific, Indian and Atlantic Oceans distributing warm water around the globe.

The edge of the remaining part of an ice shelf in the Weddell Sea in Antarctica photo taken on March 4, 2008. REUTERS/Mariano Caravaca/Handout

“The main reason we’re paying attention to this is because it is one of the switches in the climate system and we need to know if we are about to flip that switch or not,” said Rintoul of Australia’s research arm the CSIRO.

“If that freshening trend continues for long enough, eventually the water near Antarctica would be too light, too buoyant to sink and that limb of the global-scale circulation would shut down,” he said earlier today.

the great ocean conveyor belt delivers warm water into the north Atlantic, making Europe warmer than it would otherwise be. The slowing down or stopping of these currents could result in catastrophic changes in the world’s climate.

“We don’t see any evidence yet that the amount of bottom water that’s sinking has declined. But by becoming fresher and less dense it’s moving in the direction of an ultimate shutdown.” Report


The Thermohaline Circulation (THC)

The thermohaline circulation (THC) is the global density-driven circulation of the oceans. Derivation is from thermo- for heat and -haline for salt, which together determine the density of sea water. Wind-driven surface currents (such as the , ) head polewards from the equatorial Atlantic Ocean, cooling all the while and eventually sinking at high latitudes (forming North Atlantic Deep Water). This dense water then flows into the ocean basins. While the bulk of it upwells in the Southern Ocean, the oldest waters (with a transit time of around 1600 years) upwell in the North Pacific (Primeau, 2005). Extensive mixing therefore takes place between the ocean basins, reducing differences between them and making the Earth’s ocean a global system. On their journey, the water masses transport both energy (in the form of heat) and matter (solids, dissolved substances and gases) around the globe. As such, the state of the circulation has a large impact on the climate of the Earth.

The thermohaline circulation is sometimes called the ocean conveyor belt, the great ocean conveyer, the global conveyor belt, or, most commonly, the meridional overturning circulation (often abbreviated as MOC). (Source: wikipedia)

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