Ice-sheets are dynamic systems that form an integral part of the global climate system. Glaciers and ice-sheets advance substantially during climate cooling and retreat during warming, on time-scales ranging from years to thousands of years. All of this activity leaves behind a geological imprint that provides critical proxy data on global climatic events. This week (July 09th 2008) the R.V. Celtic Explorer will set sail from Killybegs on an eight-day coring cruise to acquire a series of sediment cores on the north Irish continental margin investigating the extent and dynamics of the last Irish Ice Sheet.
Planned cruise transects and core locations on the continental shelf, slope rise of the NW Irish continental margin. The location of these transects correspond to areas of the shelf where glacial landforms are known to be located and areas further downslope where the glacial sedimentary record is likely to be best preserved. Transects and core locations have been prioritised to allow flexibility in case of equipment or weather downtime.
We are all familiar with glaciers and ice-sheets in the Artic and Antarctic, but a lesser-known ice-sheet closer to home was the last British-Irish Ice Sheet (BIIS) on the western Irish continental shelf and slope. Glacial landforms such as drumlins, ribbed moraines and end moraines provide a record of the nature, scale and timing of ice-sheet movements.
Summary map of glacial bedforms for Ireland
Although these landforms have been investigated around Ireland and the UK over the past century (see above), there is still great uncertainty concerning the dimensions, dynamics and history of the former BIIS. This is mainly because it extended offshore onto the continental shelf around Ireland and Britain (below) so it was hidden inaccessibly below sea level.
Published reconstructions of the extent of the British-Irish Ice Sheet at the Last Glacial Maximum (ca 21 thousand years ago).
Accessing this site is a major challenge for the scientific community but will provide critical information on both the extent of glaciation in this region and on the deglacial history of the BIIS and, more broadly, will help to constrain predictive modelling investigations of ice sheet-ocean-climate interactions in the North Atlantic region.
As part of the Irish National Seabed Survey (INSS) 2002 to 2005, the seabed between the shelf edge at c.180m and northern Donegal was mapped.
The INSS multibeam coverage on the northwestern Irish continental margin. The survey achieved intensive multibeam bathymetric and seabed textural mapping with gravity, magnetic and sub bottom profiling.
Interpretation of these data resulted in the identification of a series of glacial features, including submerged drumlins, ribbed moraines and several large moraine systems related to the presence of the British-Irish Ice Sheet on the Irish continental shelf at least during the last glaciation (75,000 to 12,000 years ago – below).
Example of glacial feature on the NW Irish continental shelf: the main moraine system in Donegal Bay, about 18 km long, 1 to 2 km wide and 12 m high, at a water depth around 60-70m.
Additionally, evidence of submarine failures and large sediment depocentres possibly due to an increased sediment and meltwater supply from the ice margin were revealed off the northern Irish shelf, onto the continental slope and rise, by sidescan sonar data and by the INSS deep-water multibeam data. These interpretations of marine remote sensing data lead to the speculation that glaciomarine processes had a very strong influence of the development of the northwest Irish continental margin, yet they do not provide any information on the type of processes involved nor on their timing and magnitude.
In order to fill this gap in our understanding of the dynamics of the BIIS, the July cruise will be acquiring a series of sediment cores by piston- and vibro-coring on the northern Irish continental margin. The cruise is funded by the SSTI ship time programme 2008, supported by the INFOMAR Added Value Programme that will provide technical support and equipment, including the use of the Geological Survey of Ireland’s vibrocorer Geo-corer 3000+6000.
There are three major target areas on this cruise:
- The continental shelf - Coring of all the major glacial/deglacial landforms identified from the INSS data on the continental shelf will be carried out in order to obtain a record of past ice sheet advance and retreat across the shelf and in particular to determine the timing and rate of ice retreat during deglaciation.
- The continental slope will be sampled to determine the nature of slope sedimentation during both glacial- and non-glacial periods. The multibeam data shown in figure 3 indicate the presence of major submarine channels and canyons along this part of the Irish continental margin. Such channels could have acted as pathways for sediment transfer from the shelf to the deep sea during times of glacial maxima, and sediments associated with them may provide a high-resolution record of past ice sheet activity. Thus these slope sediments form a major target of the coring proposed here.
- A series of sediment cores will be collected from sediment depocentres identified from the bathymetric data in the adjoining continental rise in order to elucidate the nature of ‘distal’ glaciomarine and non-glacial sedimentary processes. Such sediments from deep water can provide a high-resolution record of ice sheet variability and paleoceanographic change through time.
The main output of this project will be a palaeogeographic reconstruction of the glacial history of the Northwest Irish Shelf during the Late Quaternary. This will include information on:
- Timing and rate of deglaciation
- The nature of glacially-influenced and non-glacial marine sedimentation
- Temporal and spatial changes in oceanographic circulation.
Our data will provide important constraints for predictive modelling studies of ice-ocean-climate change in the North Atlantic through the identification and documentation of sedimentation styles associated with glacial retreat (grounded ice margin, decoupled ice facies, debris flows, turbidity currents and meltwater depositional events). Results from our research will help resolve long-standing scientific problems related to our ability of interpreting how existing ice sheets might change in future and how ice sheets of the last glaciation behaved in the past.
The scientific value of the dataset that will be acquired by coring the northern Irish continental margin extends well beyond reconstructing the western margin of the ice sheet (which in itself would be a significant achievement). As most sedimentological analyses performed on sediment cores require small amount of material at each selected core depth, the same cores can be used for other studies. Palaeoenvironmental reconstructions of sea level variations and climate change, geotechnical studies on the stability of the margin (relevant to the use of marine resources and hazards), identification of potential aggregate resources are just a few examples of the types of information that the cores may provide. We envisage that the cores collected on this research cruise would become accessible to the wider scientific community upon completion of our research project. Additionally, the metadata of the cruise, and at a later stage also the data interpretation, will be made freely available online through the INFOMAR’s Interactive Web Data Delivery System.
Although this project is primarily a geological survey, the cruise has a strong collaborative approach and, in addition to Marine Institute and Geological Survey of Ireland personnel, the scientific staff includes geologists from UK and Canadian universities, oceanographers from National University of Galway (NUIG) carrying out CO2 flux measurements and a Marine Mammal Observer. Several undergraduate students from NUIG, University College Dublin (UCD) and University of Ulster (UU) will also take part, either through the ‘Training Through Research’ programme or to carry out their final year or MRes projects. We will also be acquiring CTD profiles at each of the core locations for the Marine Institute Oceanographic Services to be used for modelling oceanographic circulation in Irish waters.