| Abstract |
The deep ocean general circulation (deep circulation: thermohaline circulation) is created when heavy water sinks in the polar oceans and gradually rises as it spreads across the entire ocean depths. The heavy water is primarily derived from the large amounts of cold, high-salinity water (brine) discharged from the coastal polynya, an area of very high sea ice production. Sea ice production is therefore an important factor in the thermal salt cycle. We have developed an algorithm to estimate sea ice production using satellite data and heat balance calculations, and have been the first in the world to conduct global mapping of sea ice production. The results show that the Southern Ocean has very high sea ice production in the coastal polynya, which explains why the Antarctic Bottom Water, which extends into the deepest layers of the entire ocean, is formed here. The Southern Ocean, which is not surrounded by land, is a divergence zone for sea ice in the coastal areas, which facilitates the emergence of polynyas, in contrast to the Arctic Ocean, which is surrounded by land. Sea ice production mapping reveals that the Cape Dunley polynya, 1,200 km east of Showa Station, Antarctica, is the second most productive high sea ice production area in the Southern Ocean, suggesting that it is an unknown (fourth) Antarctic bottom water production area. Furthermore, Japanese IPY observations have succeeded in confirming this. On the other hand, in the offshore area of Mertz Glacier, the third Antarctic bottom water production area, the glacier collapse in 2010 caused a 40% decrease in sea ice production, which was accompanied by a sharp decrease in the production of Antarctic bottom water. In the North Pacific, the heaviest water is produced by high sea ice production in the Sea of Okhotsk polinia, creating a thermohaline circulation that extends into the middle North Pacific. As described above, it has become clear that sea ice production is strongly linked to the formation of mesopelagic water and even its fluctuation. Currently, we are focusing our research on the following points regarding sea ice formation and mesopelagic water formation.
1) The process of efficient sea ice formation in coastal polynyas
2) Unknown deep-water formation areas due to sea ice formation (northern Sea of Japan? Anadyr Bay in the Bering Sea?)
3) Relationship with ice shelf and glacier fluctuations
4) Impacts on material cycles and biological production
5) Improvement of satellite sea ice production algorithm
6) Heat and salt flux data from sea ice production and melting |
