ADCP measurements on the Western Antarctic Peninsula Shelf

 

Susan L. Howard, Laurie Padman, Robin D. Muench, and John Gunn

 

Earth & Space Research, 1910 Fairview Ave. East, Suite 102, Seattle, WA 98102-3620

 

 

Data from vessel-mounted acoustic Doppler current profilers (ADCPs) were collected on each of the five Southern Ocean GLOBEC cruises between March and September 2001. The 150 kHz ADCPs recorded data in 5-minute ensemble averages and 8-m depth bins. Water velocity was typically measured down to ~350 m, although ADCP performance was significantly reduced while underway during storms. The spatial coverage was fairly complete. Data from multiple cruises were obtained in the northern part of the survey region and Marguerite Bay. The southern portion of the grid is covered primarily by the NBP0103 data. Ice interfered with underway ADCP measurements from the GLOBEC II (winter) cruises; however, on station data for these cruises exist and will be analyzed. At this time, not all post-cruise calibrations have been carried out. Single-ping data were also collected and are being archived.

 

We will describe the distribution of good data, and present preliminary velocity maps for various levels. The strongest currents occur in the surface layer, and throughout the measured water column near the coast and the shelf break. We find a strong (~15-25 cm/s) coastal current flowing southward along Adelaide Island and into Marguerite Bay, then continuing southward along Alexander and Charcot Islands. Currents at the continental shelf break can approach 40 cm/s. However, their magnitude and direction vary significantly, possibly in response to incursions of the Antarctic Circumpolar Current or diurnal tidal topographic vorticity waves that are predicted in this region. The ADCP data, combined with hydrographic data from CTD stations, is used to investigate the small-scale processes that drive the flux of heat from intrusions of upper circumpolar deep water into the surface mixed layer and to the sea surface or base of the sea ice. Strong velocity shears occur at the top of the permanent pycnocline in several locations. This shear often results in low gradient Richardson numbers, signifying that turbulent mixing is likely. We examine the spatial extent of the mixing and identify some of the probable sources.