Temporal variability of the overturning circulation in the Arctic Ocean and the associated heat and freshwater transports during 2004-2010

This study quantifies the overturning circulation in the Arctic Ocean, and associated heat transport (HT) and freshwater transport (FWT) from October 2004 to May 2010 based on hydrographic and current observations. Our main data source consists of 1,165 moored instrument records in the four Arctic main gateways: Davis Strait, Fram Strait, Bering Strait and the Barents Sea Opening. We employ a box inverse model to obtain mass and salt balanced velocity fields, which are then used to quantify the overturning circulation as well as HT and FWT. Atlantic Water is transformed into two different water masses in the Arctic Ocean at a rate of 3.9 Sv. Combined with 0.6 Sv Bering Strait inflow and 0.1 Sv surface freshwater flux, 1.8 Sv flows back to the south through Davis Strait and western Fram Strait as the upper limb of the overturning circulation, while 2.8 Sv returns southward through Fram Strait as the lower limb of the overturning. The Arctic Ocean imports heat of 180±57 TW (long-term mean ± standard deviation of monthly means) with a methodological uncertainty of 20 TW and exports FW of 156±91 mSv with an uncertainty of 61 mSv over the six years with a potential offset of ~30 mSv. The HT and FWT have large seasonalities ranging between 110-260 TW (maximum in winter) and 40-260 mSv (maximum in winter), respectively. The obtained overturning circulation and associated HT and FWT presented here are vital information to better understand the northern extent of the Atlantic Meridional Overturning Circulation.