Short Name:
NSF-ANT06-32282

IPY/ASEP - Collaborative International Research: Amundsen Sea Influence on West Antarctic Ice Sheet Stability and Sea Level Rise.

The Office of Polar Programs, Antarctic Science Division, Ocean Climate Systems Program has made this award to support a multidisciplinary effort to study the upwelling of relatively warm deep water onto the Amundsen Sea continental shelf and how it relates to atmospheric forcing and bottom bathymetry and how the warm waters interact with both glacial and sea ice. This study constitutes a contribution of a coordinated research effort as part of the Amundsen Sea Embayment Project or ASEP. Previous work by the PI and others has shown that the West Antarctic Ice Sheet has been melting faster, perhaps by orders of magnitude, than ice shelves elsewhere around Antarctica. Submarine channels that incise the continental shelf are thought to provide fairly direct access of relatively warm circumpolar deep water to the cavity under the floating extension of the Pine Island Glacier. The proposed investigations build on previous efforts by the PI and colleagues to use hydrographic measurements to put quantitative bounds on the rate of glacial ice melt by relatively warm seawater. The region can be quite difficult to access due to sea ice conditions, and previous hydrographic measurements have been restricted to the austral summer time frame. In this project it was proposed to obtain the first austral spring hydrographic data via CTD casts and XBT drops (September-October 2007) as part of a separately funded cruise (PI Steve Ackley) the primary focus of which is sea-ice conditions to be studied while the RV Nathanial B Palmer (RVIB NBP) drifts in the ice pack. A dedicated cruise in austral summer 2009 will follow this opportunity, and both cruises would include underway and bottle sampling for pCO2 and TCO2. The principal objectives of the dedicated field program are to deploy and recover 2 years later a set of moorings with which to characterize temporal variability in warm water intrusions onto the continental shelf and to conduct repeat hydrographic surveying and swath mapping in targeted areas, ice conditions permitting. Automatic weather stations are to be deployed in concert with the program, sea-ice observations will be undertaken from the vessel and the marine cavity beneath the Pine Island Ice Shelf may be explored pending availability of the British autonomous underwater vehicle Autosub 3. These combined ocean-sea ice-atmosphere observations are aimed at a range of model validations. A well-defined plan for making data available as well as archiving in a timely fashion should facilitate a variety of modeling efforts and so extend the value of the spatially limited observations. Broader impacts: This project is relevant to an International Polar Year research emphasis on ice sheet dynamics focusing in particular on the seaward ocean-ice shelf interactions. Such interactions must be clarified for understanding the potential for sea level rise by melt-driven thinning of ice shelves, resulting in faster flow of West Antarctic Ice Sheet glaciers into the ocean. The project entails substantive international partnerships (British Antarctic Survey and Alfred Wegener Institute) and complements other ASEP proposals covering other elements of ice sheet dynamics. The proposal includes partial support for 2 graduate students and 2 post docs. Participants from the Antarctic Artists and Writers program are to take part in the cruise and so aid in outreach. In addition, the project is to be represented in the Lamont-Doherty annual open house. Updating the paragraphs above, abstracted from our 2006 proposal: The September-October cruise (NBP07-09) was delayed by a shipboard fire, leaving insufficient time to reach the Amundsen Sea, and so worked seaward of the continental shelf in the Bellingshausen Sea. The dedicated cruise in austral summer 2009 (NBP09-01) took place from 05 January through 28 February 2009, with Autosub-3 aboard, but a new ASE Project deployed the Automatic Weather Stations. In lieu of a dedicated mooring recovery cruise, time was made available on subsequent NB Palmer, JC Ross and Polarstern cruises to reach most of the mooring sites. Additional information about cruise operations, personnel, data acquisition and dissemination, findings and impacts may be found in the final fastlane report for this project. A variety of data sets and publications resulting from the grant were obtained during NB Palmer cruises 09-01 and 07-09, and are logged at the USAP Data Center MGDS/IEDA Southern Ocean portal, and at other archival sites. The observations include: Swath-mapped sea floor bathymetry, navigation, meteorological and surface measurements along most of the ship tracks; Raw, navigationally edited and final 1-m conductivity-temperature-depth-dissolved oxygen profiles from 248 casts, most during 09-01 to within 10 m of the sea floor; Lowered Acoustic Doppler Current Profiles from 158 of 160 CTD casts during 09-01, along with underway ship-mounted (SADCP) upper ocean data archived at SIO; Salinity, dissolved oxygen, total CO2 and oxygen isotope measurements from rosette water samples; Numerous XBT profiles from both cruises; Bottom- and ice-moored pressure, temperature, salinity and current observations from 5/6 sites, one available from the ITP site at WHOI. Archived reports outline cruise operations and ocean data processing methods, the latter including standard level CTD-O information, rosette bottle data, and plots of CTD-O, north/south current velocity components, T/S diagrams and station locations. Processed CTD data have also been submitted to NODC, where they carry accession numbers 0071179 and 0120761, and for 09-01 to the BODC as a Geotraces contribution. Autosub data acquired during 09-01 in work led by our NERC-supported BAS collaborators are also being reported to the BODC. More than 20 publications by grant-supported personnel and collaborators who have made use of the acquired data are listed under References at the NBP07-09 and NBP09-01 sites, the latter including several additional papers by a Stanford biology project on that cruise. Questions and comments about the ASEP data sets may be referred to S. Jacobs, C.Giulivi, F. Nitsche, B. Huber, A. Thurnherr, B Arko or K. McLain at Lamont, S. Stammerjohn at U Colorado, A. Jenkins at BAS, or P. Dutrieux at U Washington.

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