Ice shelf - ocean interaction in the cavity beneath the Amery Ice Shelf

Brief description

---- Public Summary from Project ----
Most of the snow falling on inland Antarctica drains via large ice streams and floating ice shelves to the sea where it lost by iceberg calving or as melt beneath the shelves. Ocean interaction beneath the shelves is complicated, and regions of basal refreezing as well as melt occur. These processes are important not only because they are a major component of the Antarctic mass budget, but because they also modify the characteristics of the ocean, influencing the formation of Antarctic Bottom Water which plays a major role in the global ocean circulation. The processes are sensitive to climate change, and shifts in ocean temperature or circulation near Antarctica could lead to the disappearance of all Antarctic ice shelves.

The Amery
Ice Shelf is the major embayed shelf in East Antarctica, and the subject of considerable previous ANARE investigation. Ocean interaction processes occurring beneath the shelf are only poorly understood, and this project will directly measure water characteristics and circulation in the cavity underneath the ice shelf, and the rates of melt and freezing on the bottom of the shelf. These measurements will be made through a number of access holes melted through the shelf. The project is closely linked with other projects investigating the circulation and interactions in the open ocean to the north of the shelf, and studies of the ice shelf flow and mass budget.

There will be child records for each of the following data sets:
AM01 and AM01 b boreholes
* CTD profiles through water column
* CTD annual records at selected depths
* Ocean current profiles through water column
* Temperature measurements through ice shelf and across ice-water interface
* Small ice core samples
* 0.5 m sea floor sediment core
* Video footage of borehole walls (including marine ice) and sea floor benthos
* GPS records of surface tidal motion
* Video

AM02 borehole
* CTD profiles through water column
* CTD annual records at selected depths
* Borehole diameter caliper profiles
* Temperature measurements through ice shelf and across ice-water interface
* 1.5 m sea floor sediment core
* GPS records (surface elevation, ice motion)

AM03 borehole
* Aquadopp current meter data
* Brancker thermistor data
* Caliper data
* FSI-CTD profile data
* Drilling parameters data
* Seabird MicroCAT CTD moorings at three depths in ocean cavity beneath the shelf
* Video

AM04 borehole
* Aquadopp current meter data
* Brancker thermistor data
* Caliper data
* FSI-CTD profile data
* Drilling parameters data
* Seabird MicroCAT CTD moorings at three depths in ocean cavity beneath the shelf
* Video

AM05 borehole
* Aquadopp current meter data
* Caliper data
* FSI-CTD profile data
* Drilling parameters data
* Seabird MicroCAT CTD moorings in ocean cavity beneath the shelf

AM06 borehole
* Aquadopp current meter data
* Caliper data
* FSI-CTD profile data
* Drilling parameters data
* Seabird MicroCAT CTD moorings in ocean cavity beneath the shelf


Taken from the 2008-2009 Progress Report:
Progress Against Objectives:
The work undertaken in the past 12 months has continued to relate chiefly to the first of our objectives - "quantify the characteristics and circulation of ocean water in the cavity beneath the Amery Ice Shelf". Data from the AMISOR project have provided the first record of a seasonal cycle of ice shelf-ocean interaction. After recovering the 2008 data we now have near-continuous oceanographic data from beneath the Amery at 3 different depths for 6, 6, 3, and 3 years from 4 different sites. Note that the instruments at AM01 and AM02 (6 annual cycles of data each) are no longer recording due to expiration of the onboard batteries (3-5 years expected life cycle). This allows us to investigate the "real" 3-D, seasonally varying, circulation and melt/freezing cycle beneath an ice shelf - rather than the steady state, simplified "2-D ice pump circulation" that has mostly been assumed previously.

As much as 80% of the continental ice that flows into the Amery Ice Shelf from the Lambert Glacier basin is lost as basal melt melt beneath the southern part of the shelf, but a considerable amount of ice is also frozen onto the base in the north-western part of the shelf. These processes of melt and refreezing are due to a pattern of water circulation beneath the ice shelf which is driven by sea ice formation outside the front of the shelf. Our multi-year data from 4 sites beneath the Amery ice shelf show that there is a very strong seasonal cycle in the characteristics of the ocean water beneath the shelf, and strong interseasonal variability in this. The seasonal cycle is driven mostly by the seasonal cycle of sea ice formation and decay in Prydz Bay, and interseasonal variations are due to differences in the general ocean circulation, and in particular the upwelling of Circumpolar Deep Water onto the continental shelf in Prydz Bay. The melt and freeze processes beneath the ice shelf, also themselves modify the water characteristics.

Taken from the 2009-2010 Progress Report:
The AMISOR project drilled two new 600 m deep boreholes on the Amery Ice Shelf in 2009-10: the first on the marine ice flowline to enhance understanding of the re-freezing process beneath the shelf; and the second in a region of known interest with respect to circulation patterns in the ocean cavity below the shelf. Instrument deployments at both sites should provide valuable annual cycle data over the next 4-5 years.

Lineage

Progress Code: onGoing

Statement: See Readme files in the download files of the child metadata records for details of data quality and equipment down-time.

Note - depths provided in spatial coverage are referenced back to sea level. The minimum depth asl refers to the height of the ice surface.