AON: Monitoring the Western Arctic Boundary Current in a Warming Climate
As Earth's climate has warmed over the past few decades, our planet has experienced a multitude of profound changes. Nowhere have the changes been more pronounced, nor happened as quickly, as in the Arctic Ocean. Pack-ice is melting, water is warming, storms are becoming stronger and more frequent, and basic circulation patterns are being altered. Our project focuses on the fate of the Pacific water that enters the Arctic Ocean through the Bering Strait. Pacific water plays a critical role in the western Arctic ecosystem. In wintertime the cold inflowing water provides nutrients that spur the growth of phytoplankton at the base of the food chain. In summertime, the warm water melts pack ice and provides freshwater to the Arctic Ocean. After the water crosses the Chukchi Sea, north of Bering Strait, some of it forms a narrow current at the edge of the shelf and flows eastward. As part of our project we will continue to maintain a mooring positioned in the center of the current to measure its physical and biological properties. The mooring has been deployed (with a few gaps) since 2002, and during this time it has measured striking changes that need to be placed in the context of the evolving Arctic system. In addition, we will carry out shipboard surveys of the current and adjacent waters when we service the mooring, to provide a larger-scale view of the fate of the Pacific water. The monitoring mooring is situated at 152oW near the Beaufort Sea shelf break, roughly 150 km downstream of Pt. Barrow. It will be deployed for two years from fall 2016 to fall 2018. This will extend the time series at this location to 13 years. The mooring records the velocity of the water column and pack ice using two ADCPs, and measures temperature, salinity, and pressure using a series of MicroCats spaced along the wire. Chlorophyll fluorescence and nitrate will be measured at 35 m (at the top float of the mooring), and a passive acoustic recorder situated near the base of the mooring will record marine mammal calls. Zooplankton concentration will be estimated using the ADCP backscatter data. Among other things, this will allow us to determine how much water, heat, nutrients, chlorophyll, and freshwater are transported by the current, and, importantly, assess how much exchange occurs between the interior of the Arctic Ocean and the boundary waters. Upwelling occurs during all seasons along the Beaufort slope, and it appears to be increasing as the climate warms. The mooring is ideally suited to quantify the upwelling, as well any downwelling that occurs. The shipboard sampling will include sampling of some of the Distributed Biological Observatory transects, which will contribute to those ongoing time series.