Observations of flow and ice-ocean interaction beneath the McMurdo Ice Shelf, Antarctica

The first oceanographic data from beneath the McMurdo Ice Shelf, Antarctica, are presented here with synchronous observations from southern McMurdo Sound. Multilevel current profiles at three sites over spring tide revealed primarily K1 diurnal tides with net transport from McMurdo Sound into the basin beneath the McMurdo Ice Shelf. The time series in southern McMurdo Sound captured the 14 day tidal phase shift and showed that transport into the subice shelf cavity was even greater over neap tide, with average transport similar to 1.8 Sv. McMurdo Sound sea ice cover during this period was the heaviest in 25 years of satellite record and was associated with the proximity of two massive icebergs, B-15a and C-19. The warmest waters observed beneath the ice shelf were set at the surface freezing temperature, probably through recent interaction with this extensive sea ice cover. Observed ranges of temperature and salinity were narrowed to the extent that neither Antarctic Surface Water nor High Salinity Shelf Water were observed beneath the ice shelf. We anticipate that in years with more typical summer sea ice cover surface waters swept beneath the ice shelf will be significantly warmer, having even greater potential for basal melt near the ice shelf front. Our observations also exhibit some of the interactions particular to the subice shelf ocean environment. These include occurrence of platelet ice in ice shelf meltwater, boundary layer friction effects from the ice cover on the ocean, and tidal currents driving enhanced melting near the ice shelf front.