Confluence and mixing of Atlantic, Pacific, and Siberian shelf water masses around the Mendeleyev Ridge of the Arctic Ocean

Importance of the Arctic Ocean to the global thermohaline circulation has been increasing, presumably due to global warming. However, the circulation scheme of the Arctic Ocean is still highly uncertain. One of the key areas to understand the Arctic Ocean circulation is that around the Mendeleyev Ridge because Atlantic, Pacific, and Siberian shelf water masses meet around the area and are likely to flow into the central Arctic Ocean. Using hydrographic data observed around the Mendeleyev Ridge during the 2000s, distribution, characteristics, and mixing processes of these water masses around the Mendeleyev Ridge were examined to understand the circulation scheme of the Arctic Ocean. In 2008, the front between Atlantic and Pacific water masses was clearly located at the western edge of Chukchi Rise. Some of the boundary current of Atlantic Water coming from the Eurasian side flows into the central Arctic Ocean along the Mendeleyev Ridge and the remainder goes along the Siberian shelf slope into the Canada Basin side. Siberian shelf water masses also flow into the central Arctic Ocean modified due to mixing with the Atlantic water and cold halocline water. It is interesting that no signal from Pacific-origin water masses can be found over the main stream of the Atlantic Water inflow to the central Arctic Ocean over the Mendeleyev Ridge, although the signals of summer/winter Pacific water masses were very clear over the Chukchi Plateau. Interannual variability in the distributions and characteristics of these water masses are discusses in this presentation and put into context with changes of atmospheric circulation pattern and recent sea ice reduction. In addition, we present preliminary results of R/V Mirai Arctic Ocean cruise during September-October 2009.