Ryan McCabe explains his work on water physics and chemistry. Photo credit: Ed Farley
We are interested in understanding how changes in the physical and chemical environment of the Chukchi Sea, such as the water column heat content, stratification, and nutrients, ultimately impact the regional ecosystem. To help achieve these goals we use a multi-platform approach to examine the physics and chemistry and work with other project scientists to relate these parameters to various ecosystem components, including phytoplankton, zooplankton, and fish.
Early in the cruise, a suite of moored instruments were deployed at select locations to record environmental conditions such as ocean currents, temperature, salinity, dissolved oxygen, and chlorophyll-a fluorescence. Most of these instruments will remain in the water over winter, and once recovered, the data will illustrate how conditions at those sites evolved over time in response to changes in atmospheric conditions and sea ice coverage.
We have also been taking profiles of water properties throughout the water column using a CTD (conductivity-temperature-depth) package aboard the R/V Ocean Starr. Our shipboard survey will provide a quasi-synoptic map of how water properties such as heat and nutrients are distributed spatially along and across the shelf. A series of four high-resolution coastal transects were occupied from Point Hope all the way up to the continental slope near Barrow on the first leg of the survey. More recently we have been making headway on sampling grid stations in conjunction with other sampling such as the plankton tows and bottom trawls.
Map of sampling stations completed as of early September. Shades of blue indicate water depth in meters.
So far, our coastal transects have documented the relatively warm, low-salinity water of the Alaska Coastal Current near shore as far north as Icy Cape, as well as a pool of cold, salty water at depth over the Chukchi shelf. Off the northern continental slope we found the signature of recently melted ice in a shallow layer at the surface, and the relatively warm layer of Atlantic Water at depth that can get upwelled onto the shelf. We have encountered both surface and subsurface peaks in chlorophyll fluorescence and we have noticed how small arctic cod tend to congregate in relatively warmer subsurface layers of water. We are looking forward to recovering our moored instrumentation to help place this season’s cruise sampling within a longer-term context.