Collaborative Research: The Norrona Project: An International Collaboration for Sustained Studies of the Meridional Overturning Circulation between Denmark, the Faroes and Iceland.

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The presence of and flow of warm salty water across the northern North Atlantic plays a key role in shaping the mild climate of central and northern Europe. This flow is in large measure controlled by enormous heat losses in the Nordic Seas that transform this water into very dense water that eventually spill back out into the deep North Atlantic. Since 2008, the flow of North Atlantic Water into the Nordic Seas has been measured where it passes through natural choke points: the Faroe-Shetland Channel (FSC) and the Iceland-Faroe Ridge (IFR). The measurements come from a shipboard acoustic Doppler current profiler (ADCP) that scans currents at high horizontal resolution along the track of the high-seas ferry M/F Norröna. While this has been a tremendous success, during rough weather in the winter bubbles are swept down and interfere with the instrument. To mitigate this problem, the instrument was recently moved further aft to the skeg, where fewer bubbles are expected. This project will allow the researchers to assess the improvement in data quality, and participate in the operation of the instrument and scientific analyses for another two years over which the operation will be handed over to scientists at the Institute of Marine Research (IMR) in Bergen, Norway and at Faroes Marine Research Institute. The Iceland-Faroe-Scotland ridge separates two large and distinctly different water mass systems (the North Atlantic and the Arctic Mediterranean) that communicate through warm, salty inflow and dense water outflow through the deep gaps in the ridge. The inflow is quantified with these ADCP current profiles, coupled with temperature profiles from XBTs deployed automatically at selected sites from the Automated eXpendable Instrument System (AXIS) on the same vessel. On shorter time scales exchange is likely wind-driven, while on longer time scales (seasonal and longer) buoyancy loss must be of paramount importance. With sustained and improved Norröna monitoring of the inflows and moored ADCPs monitoring the outflow through the deep gaps (a Faroes-Norway program), one can examine in considerable detail the space-time response of these fluxes to time-varying atmospheric forcing including the well-known North-Atlantic Oscillation.