NSF OPP93-42954
Geological Record of Late Wisconsin/Holocene Ice Sheet Advance and Retreat from the Ross Sea
(project still under progress)
Over the past three years we have made considerable progress in our understanding of the timing and nature of ice sheet recession from the Ross Sea continental shelf. With the acquisition of new core material (NB Palmer cruise 94-1 and 95-1) we have expanded our chronologic control for the retreat of the West Antarctic Ice Sheet and have gained in our understanding of the facies changes preserved in the Ross Sea.
First, our total organic carbon work and application of new core techniques (kasten cores) has revealed that a significant transitional facies exists between the contact of till and open marine siliceous mud. Organic carbon contents are uniform and low for the till and are moderate and variable for the transitional facies. As one moves upward through the diamicton unit the TOC contents increase indicating an increase in marine influence during glacial marine deposition. Magnetic susceptibility records also demonstrate the transitional facies. At present we are in the process of correlating this transitional facies between sites. The significance of the transitional unit is that it implies a period of time between ice sheet retreat (lift off from the bed and ice shelf conditions) and open marine conditions. Our 14C chronology is interpreted with this in mind and several papers are in press or in preparation.
At present we have obtained 100 new radiocarbon ages (Arizona AMS Lab) for the sedimentary sequence in the Ross Sea, we are awaiting an additional 20 dates. The preliminary results indicate that the ice sheet receded from the western Ross Sea sometime around 12,000 years B.P., perhaps earlier. The transition to open marine conditions took place sometime after this, at around 10,000 years B. P. At present we are evaluating these dates with respect to the organic carbon (productivity) and ice rafted record.
NSF DPP89-15977, RUI,
Depositional Processes and Stratigraphy of Antarctic Fjords and Ice Shelf Environments
This project was a multidisciplinary investigation which has as its field area the western side of the Antarctic Peninsula from Lallemand Fjord to the South Shetland Islands. We investigated the depositional processes operating within fjords by a combination of CTDT profiles, underwater photography, and sediment trap deployments. The CTDT profiles were useful in delineating the dynamics of cold tongues adjacent to the Cayley Glacier (Knowlton et al., 1992). It now appears that surface melting can not be implicated in the operation of the cold tongues, rather basal melting and tidal processes are the most likely mechanisms which control the dynamics of the cold tongue features. Underwater photography has also delineated the exact mechanism of particle transport within the cold tongue features (Foss, 1991; and Domack et al., in review).
Sediment trap deployments in Andvord Bay were useful in illustrating the role of secondary resuspension to the transport of sediment into the fjord basins. The total sediment flux for this Antarctic fjord was shown to be much greater than any other site previously studied in the Antarctic (Mammone, 1992). Total carbon flux was also very high attesting to the relatively high productivity of the fjord environment. Together these results support the contention that Antarctic fjords contain a very high resolution record of depositional events over, at least, the past several thousand years (Mashiotta, 1992; and Stein, 1992).
Stratigraphic studies were aided by the use of Kasten and Piston cores, magnetic susceptibility, Huntec deep towed siesmic reflection and 3.5 kHz bottom profiles. Sediment core studies of a small ice shelf setting in Lallemand fjord documented the recent formation of the Muller Ice shelf and its historic recessional history (Frederick, et al., 1991; Stein, 1992; Denny et al., 1992). Deep towed (Huntec) seismic reflection profiles revealed thick sediment accumulations in several basins (Figure 1). A comparison of reflection character to sediment composition allowed us to recognize those sections which are dominated by pelagic, hemipelagic, and ice rafted sediment from those dominated by fine grained turbidity current deposition (Kirby, 1993; and Domack et al., 1993a). Using the reflection character alone one can now recognize which sites would be ideal for core collection allowing us to avoid turbidity current deposits.
Detailed examination of magnetic susceptibility records has allowed us to establish a definite stratigraphy for the last several thousand years. This has allowed us to correlate our core records for the first time between the fjords and bays of the Gerlache Strait and the Bellingshausen Sea continental shelf. We believe the change in the magnetic susceptibility is a reflection of the onset of the Neoglaciation as it controlled the coverage and extent of sea ice across the study area (Kirby, 1993; and Domack et al., 1993a). Superimposed upon this long term change are higher frequency cycles of organic matter preservation on the time scale of 300 years (Mashiotta, 1992; and Domack et al, 1993b).
This project was part of the Research in Undergraduate Institution program of NSF and as such involved significant participation of undergraduate research assistants. Thirteen undergraduate students actually participated in field work in Antarctica aboard the RV Polar Duke. Of these thirteen students, eleven have gone on to continue their studies at graduate schools across the country. Three of these students have continued in polar marine research. Hence the past record of this program in preparing and motivating undergraduates for graduate school has been remarkable.
Created by:
Jonathan Marcel
Last Modified: 12/5/96