Seminar: WTK/CPS Seminar
date: 2017 January 24(Tue)15:00-
room: CPS Seminar room
speaker: Kay I. Ohshima (Professor, Institute of Low Temperature Science, Hokkaido University)
organizer: Takahiro Iwayama
title: Global view of sea-ice production and its linkage with dense/deep water formation
abstract: Global overturning circulation is driven by density differences: water sinks in dense water formation areas and then gradually upwells in other areas. Saline water rejected during sea-ice formation is the main source of dense water, and thus sea-ice production is a key factor in the overturning circulation. Recently, methods to estimate sea-ice production in large scales have been developed from satellite microwave radiometer data with heat flux calculation. Global mapping of sea-ice production demonstrates that the production rate is overall high in the Antarctic coastal polynyas, in contrast to the Arctic ones. This is consistent with the formation of Antarctic Bottom Water (AABW), the densest water mass which occupies the abyssal layer of the global ocean. The Cape Darnley polynya (65°−69°E) is found to be the second highest ice production area in the Southern Hemisphere. Recent Japanese IPY observations revealed that this is the missing (fourth) source of AABW. In the region off the Mertz Glacier Tongue (MGT), the third source of AABW, sea-ice production decreased by as much as 40%, due to the MGT calving in early 2010, resulting in a significant decrease of AABW production. The Okhotsk Northwestern polynya exhibits the highest ice production in the Northern Hemisphere, and the resultant dense water formation leads to the overturning in the North Pacific extending to the intermediate layer. These demonstrate the strong linkage between sea-ice production and bottom/intermediate water formation.

Regarding the ice production and subsequent dense/deep water formation, following issues are now under investigation.
1) High ice production process in a polynya
2) Investigation of less-known areas (Japan Sea and Bering Sea)
3) Relationship with the ice-shelf/glacier change
4) Impact on material cycle and biological productivity
5) Improvement of the ice production algorithm
6) Creation of data set for heat/salt flux associated with ice production/melt
keywords: Thermohaline circulation, sea-ice production, Antarctic Bottom Water, Coastal polynya