Marine geological processes and sediments beneath floating ice shelves in Greenland and Antarctica: investigations using the Autosub AUV

Overview

The aim of this project was to investigate the marine geological processes and sediments beneath ice shelves and tidewater glacier margins in Greenland and Antarctica using a variety of geophysical equipment deployed from the Autosub Autonomous Underwater Vehicle (AUV) and the RRS James Clark Ross.

Sediments transported by ice sheets and glaciers are released to the surrounding seas at the ice-ocean interface represented by ice shelves and tidewater glacier margins. Very few direct observations of marine geological processes and sediments beneath floating ice masses and adjacent to tidewater glacier margins have been made as these areas are largely inaccessible to conventional ship-based surveying and sampling methods. The Autosub AUV, and the instrument packages it carries, is used to investigate such areas. In addition, the project also involves marine geophysical and geological investigations of the glacier-influenced fjords, continental shelf, slope and deep ocean environments of Greenland and Antarctica using ship-based systems in order to provide a broader, longer-term context to the modern ice proximal work. The project is, therefore, also involved in reconstructing the glacial history and dynamics of the West Antarctic Ice Sheet (in Pine Island Bay, Amundsen Sea) and the Greenland Ice Sheet (in East and NE Greenland).

(1) Investigations using the AutoSub AUV

The Autosub AUV was equipped with an EM2000 swath bathymetry system and sub-bottom profiler as part of this project. Data were acquired using Autosub from Courtauld Fjord, adjacent to the margin of Courtauld Glacier (feeding into the Kangerdlugssuaq Fjord system), that provide high resolution imagery of ice-proximal sedimentary features.

Figure 1. Location map of Kangerdlugssuaq Fjord system at 68ºN, East Greenland

	Figure 2. Landsat ETM+ image of the Kangerdlussuaq Fjord region of East Greenland showing Courtauld Glacier draining into Courtauld Fjord.
	Figure 3. AutoSub AUV being deployed in the ice proximal environment.

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Figure 4. (A) High resolution EM2000 swath bathymetry record (grid cell sizes ~2m x 2m) of sea floor about 75 m from Courtauld Glacier. The record shows a very smooth sea floor and a streamlined subglacial bedform produced by the glacier when it last advanced over this area of the fjord, probably during the Little Ice Age. (B) High resolution Edgetech sub-bottom profiler record acquired proximal to Courtauld Glacier. Image shows an acoustically distinct but prolonged sea-floor reflector indicative of a coarse-grained sedimentary substrate. This was probably deposited by a combination of ice-rafted debris and meltwater plumes derived from the glacier margin.

(2) Investigations in the fjords, continental shelf, slope and deep sea off Antarctic and Greenland.

Glacier-influenced sea floor morphology and sediments were investigated during cruises of the RRS James Clark Ross in 2003 and 2004 in several areas of the Antarctic and Arctic seas: (a) Gerlache Strait and the continental shelf west of the Antarctic Peninsula, (b) in Pine Island Bay and the Amundsen Sea in West Antarctica, and (c) in the Kangerdlugssuaq Fjord system and the continental shelf and slope of East and NE Greenland:

Figure 5. Location map of Greenland and Antarctic study areas in this project.

2.1 East and NE Greenland fjords and continental shelf and slope

Figure 6. EM120 swath bathymetry records from the Kangerdlugssuaq Fjord system and adjacent East Greenland continental shelf showing: (A) Subglacial lineations and crudely streamlined drumlins within inner Courtauld Fjord produced when Courtauld Glacier advanced down-fjord from its present position during the Little Ice Age, and submarine channels or gullies in the outer fjord incised by subaqueous mass wasting from the steep sides of the fjord; and (B) Glacial lineations and mega-scale glacial lineations within Kangerdlugssuaq Trough on the inner-middle East Greenland shelf, produced beneath a palaeo-ice stream draining the Greenland Ice Sheet across the shelf during the last glaciation.

Figure 7. EM120 swath bathymetric record from a prominent bathymetric trough on the NE Greenland continental shelf (~80ºN). Well-defined mega-scale glacial lineations are present within the trough, produced by a palaeo-ice stream draining the Greenland Ice Sheet across the continental shelf. The distribution of subglacial bedforms indicates that the Greenland Ice Sheet extended much further across the NE Greenland shelf during the last glaciation than has been previously thought.

2.2 Antarctic Peninsula and West Antarctic margin

Subglacial bedforms preserved on the sea floor provide direct evidence for the expansion of the Antarctic Peninsula and West Antarctic Ice Sheets across the Pacific continental margin during the last glaciation. The distribution of megascale glacial lineations in Pine Island Bay demonstrates for the first time that the West Antarctic Ice Sheet reached the shelf edge during the last glaciation, and was drained by a palaeo-ice stream through a prominent cross-shelf bathymetric trough that opened directly at the upper continental slope. Sediments delivered directly to the shelf edge by the ice sheet were remobilised down the continental slope by turbidity currents and debris flows, producing a dense network of gullies and channels that extend down into the deepest regions of the Amundsen Sea.

Figure 8. Swath bathymetric record from the Gerlache Strait, west of the Antarctic Peninsula, showing subglacial drumlins, crudely streamlined bedforms and irregular scalloped bedforms formed in bedrock by the Antarctic Peninsula Ice Sheet during the last glaciation.

Figure 9. EM120 swath bathymetric records from Pine Island Bay and the Amundsen Sea, West Antarctica, showing: (A) Mega-scale glacial lineations within a prominent cross-shelf bathymetric trough that connects directly with the Pine Island Bay continental slope. These features were produced beneath a palaeo-ice stream draining the WAIS to the shelf edge during the last glaciation. A well-developed network of submarine gullies and channels on the continental slope, produced by subaqueous sediment gravity flows delivered by an ice sheet margin at the shelf edge during full glacials, is also shown; (B) Mega-scale glacial lineations within a cross-shelf bathymetric trough extending through Pine Island Bay, produced by a palaeo-ice stream draining the WAIS; and (C) Large-scale channels on the Pine Island Bay continental slope produced by down-slope sediment gravity flows derived from glacial sediment and delivered to the shelf edge by the WAIS.

Papers relating to this project

• Evans, J., Dowdeswell, J.A., Ó Cofaigh, C., 2004. Late Quaternary submarine bedforms and ice-sheet flow in Gerlache Strait and on the adjacent continental shelf, Antarctic Peninsula. Journal of Quaternary Science, 19, 397-407.
• Dowdeswell, J.A., Evans, J., Ó Cofaigh, C., Anderson, J.B., in press. Morphology and processes on the continental slope off Pine Island Bay, Amundsen Sea, West Antarctica. Bulletin of the Geological Society of America.
• Evans, J., Dowdeswell, J.A., Ó Cofaigh, C., Benham, T.J., and Anderson, J.B., Submitted. Extent and dynamics of the West Antarctic Ice Sheet on the outer continental shelf of Pine Island Bay, Amundsen Sea, during the last glaciation. Marine Geology.

Funding sources

Natural Environment Research Council Grant NER/T/S/2000/00986 as part of the 'Autosub under Ice' Thematic Programme.