Ice-Rafted Debris on the Antarctic Continental Margin and the Dynamics of the Antarctic Ice Sheet
The aim of this project is to reconstruct the behaviour of the Antarctic Peninsula Ice Sheet (APIS) throughout the Quaternary, with particular reference to the last glacial maximum (LGM). Considerable debate exists as to the extent of the APIS at the LGM, with reconstructions ranging from a grounded ice sheet that reached the continental shelf edge to a more restricted ice sheet that extended only to the mid-shelf. Furthermore, little is known about the subsequent retreat history of the APIS and whether this was catastrophic or slow.
This project addresses these issues using two approaches:
(1) Investigation of ice-rafted debris in deep-ocean sediments.
Piston cores from sediment drifts along the continental rise west of the Antarctic Peninsula were investigated for ice-rafted debris (IRD):
These drifts have served as depocentres for sediment delivery from the Antarctic Peninsula during Quaternary glacial and interglacial periods. If large-scale collapses of the APIS have occurred during the recent geological past, a record of these may be preserved in the sediment drifts in the form of IRD layers similar to the Heinrich layers of the North Atlantic. Our investigations indicate that although the cores contain intervals with IRD, this is the result of low sedimentation rates and current winnowing, rather than regional-scale episodes of increased iceberg rafting. This implies that the APIS has not undergone widespread catastrophic collapse along its western margin during the late Quaternary (isotope stages 1-7).
(2) Marine geological & geophysical investigations on the continental shelf & slope
Glacial landforms and sediments on the continental shelf west of the Antarctic Peninsula were investigated during cruises of the RRS James Clark Ross in 2001 and 2002:
Geophysical data from Marguerite Bay reveal a series of streamlined subglacial bedforms on the floor of a cross-shelf bathymetric trough that extends from the inner bay to the continental shelf edge:
These bedforms record flow of a grounded APIS to the shelf edge as an ice stream during the LGM. Sediment cores indicate that these bedforms are composed predominantly of till. Using these geophysical and geological data we have been able to reconstruct the dimensions of this ice stream and are currently investigating what process(es) was driving the fast flow.
Swath bathymetric data and vibrocores were also obtained from the continental slope offshore of Marguerite Trough in order to investigate the sedimentary architecture and processes that characterise this environment. The cores and geophysical data indicate that slope progradation has occurred in front of the ice-stream terminus, whereas in areas away from the terminus, well-developed gullies reflect lower sediment delivery.
Papers relating to this project
- Ó Cofaigh, C., Dowdeswell J.A. and Pudsey, C. J. (2001). Late Quaternary iceberg-rafting along the Antarctic Peninsula continental rise and in the Weddell and Scotia seas. Quaternary Research, 56, 308-321.
- Ó Cofaigh, C., Pudsey, C. J., Dowdeswell J.A. and Morris, P. (2002). Evolution of subglacial bedforms along a paleo-ice stream, Antarctic Peninsula continental shelf. Geophysical Research Letters, 29 (8), 10.1029/2001GL014488.
- Ó Cofaigh, C., Taylor, J., Dowdeswell, J.A. and Pudsey, C.J., 2003. Palaeo-ice streams, trough-mouth fans and high-latitude continental slope sedimentation. Boreas, v. 32, p. 37-55.
- Dowdeswell, J.A., Ó Cofaigh, C. and Pudsey, C.J., 2004a. Thickness and extent of the subglacial till layer beneath an Antarctic paleo-ice stream. Geology, v. 32, p. 13-16.
- Dowdeswell, J.A., Ó Cofaigh, C. and Pudsey, C.J., 2004b. Continental slope morphology and sedimentary processes at the mouth of an Antarctic palaeo-ice stream. Marine Geology, v. 204, p. 203-214.
Natural Environment Research Council, grants GR3/JIF/02 and GR3/AFI/48