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.