Autosub Under Ice (AUI) was established to investigate the marine environment of floating ice shelves with a view to advancing our understanding of their role in the climate system. The work focused on
- water masses
- ice formation beneath ice shelves and in adjacent continental shelf waters
- seasonal and perennial sea-ice cover
- air-ice-ocean interaction in sea ice regions
- ice-ocean interaction beneath ice shelves
- the structure of the seabed and nature of the sedimentary record left by past and present configurations of the ice sheet and sea ice
Fieldwork was conducted during 2003, 2004 and 2005 near Greenland and Antarctica in the respective summer seasons for each hemisphere. During the fieldwork, Autosub (an Autonomous Underwater Vehicle) was deployed. Autosub had been upgraded to achieve 1000 km range and 2500 m water depth, which provided unprecedented access to ice covered regions. An ice-capable research vessel provided the launch and retrieval platform for the Autosub, and also acted as a platform for additional measurements in the support of the science programme.
The areas for research were ice shelves and proximate continental shelf areas
- near the 79N Glacier at the east margin of the Greenland Ice Sheet
- in the eastern Pacific sector of Antarctica, in the vicinity of Pine Island Glacier, and Wilkins and George VI ice shelves
- in the Weddell Sea sector of Antarctica, under and north of the Filchner-Ronne Ice Shelf.
Autosub measurements included
Sub-bottom acoustic profiling was available to reveal structures of glacial origin in the sea floor sediments. A water sampler collected samples for geochemical and biological analyses. Side scan sonar gave measurements of ice shelf, sea ice and ocean bottom relief at high resolution.
Principal questions which motivated the programme are
- How do ice shelves and icebergs affect the ocean, by contributing to water mass transformation, both near surface and at depth?
- How do the seasonal inputs of brine and of fresh ice melt water influence the circulation and stratification on and near the continental shelves?
- How can we parameterise sea ice and dense water production rates in climate models which do not represent the ice shelves and the adjacent polynyas?
- Which climatic factors affect the rate of net basal melting from Antarctic and Greenland ice shelves?
- What are the processes of sea ice formation beneath and near ice shelves?
- What controls the distribution, deformation and thickness of sea ice, and what is the role of sea ice in forming dense shelf waters?
Marine Geology and Geophysics
- How do we interpret the sedimentary record left by ice shelves in past climates?
- What are the sediment discharge rates at ice shelf grounding lines?
- What is the bathymetry beneath perennially ice covered regions?
- How does the ice cover affect the ecosystem of the continental shelf waters, and what impact does this have on the sedimentary record?
The questions were tackled by a range of methods in addition to Autosub missions. For example, support was available for
- ice shelf and sea ice modelling
- surface ice observations
- satellite observations
- ship borne oceanographic, atmospheric and biological measurements
- ship borne bathymetric surveys
where these were relevant to the interpretation or extension of data collected by Autosub.
The AUI programme sought to build up an active and collaborating community, bringing together people with Autosub experience (but not necessarily polar experience) with those with polar experience who may not have used Autosub before.