Ice with everything - Antarctica: Global Science from a Frozen Continent - page 75

Figure 3.8 Schematic of the global ocean overturning circulation. Red indicates upper

ocean flow, blue and purple are deep flows, and yellows and greens represent transitions
between depths. (Credit: Sabrina Speich)

is crucial for an improved modelling of sea ice in global climate models. What is
particularly challenging is the interplay between the small-scale features of the sea
ice structure, its deformation, brine channels, which offer a major seasonal habitat
for a wide range of organisms, and the large scale of its impacts on the Southern
Ocean biology and climate.
The formation of sea ice in coastal polynyas has a dramatic effect on ocean
circulation. Three processes are at play: first, the surface ocean water cooling enhances

its density which is dependent on temperature. Second, as sea ice crystallises salt is
squeezed out into the surrounding ocean, increasing its salinity and density. Finally,
the freezing of ocean water removes heat from the ocean, due to the heat energy
required for freezing. Together, these processes produce 10million km 3 of the coldest,
saltiest and densest ocean water in the world. This extremely dense water sinks towards
the depth of the Southern Ocean and fills the deepest parts of the global ocean

system, during a journey lasting thousands of years. These deep ocean masses play
an important role in the global carbon cycle. The solubility of carbon dioxide in
water increases when temperature decreases. As a result, the formation of deep-
watermassesnearAntarcticatransferscarbon dioxide from the atmosphere into the
depths of ocean basins. Antarctica is not only the cold point of our climate machine,
but also the factory for dense bottom ocean waters and plays a key role in carbon
sinks. Therefore, what happens in Antarctica has direct relevance for our global
climate.