Environmental Sciences Research Institute

Late Glacial Sea Level Minima

Contact: Prof Andrew Cooper for further details
NERC Grant NE/H024301/1

Staff

Principal investigator:
Andrew Cooper, University of Ulster

Co-principle investigator:
Antony Long, Durham University

Co-investigators:
Derek Jackson, University of Ulster
Rory Quinn, University of Ulster

Project partners:
Joseph Kelley, University of Maine
Daniel Belknap, University of Maine
Robin Edwards, Trinity College Dublin
Glenn Milne, University of Ottawa
David Long, British Geological Survey
Xavier Monteys, Geological Survey of Ireland

Research Associate:
Ruth Plets, University of Ulster

Summary

Relative sea level (RSL) change reflects the interplay between a large number of variables operating at scales from global to local. Changes in RSL around the British Isles (BI) since the height of the last glaciation (ca. 24 000 years ago), are dominated by two key variables: (i) the rise of ocean levels caused by climate warming and the melting of land-based ice; and (ii) the vertical adjustment of the Earth’s surface due to the redistribution of this mass (unloading of formerly glaciated regions and loading of the ocean basins and margins). As a consequence, RSL histories vary considerably across the region once covered by the British-Irish Ice Sheet (BIIS). The variable RSL history means that the BI is a globally important location for studying the interactions between land, ice and the ocean during the profound and rapid changes that followed the last glacial maximum. The BI RSL record is an important yardstick for testing global models of land-ice-ocean interactions and this in turn is important for understanding future climate and sea level scenarios. At present, the observational record of RSL change in the British Isles is limited to shallow water areas because of accessibility and only the later part of the RSL curve is well studied. In Northern Britain, where the land has been rising most, RSL indicators are close to or above present sea level and the RSL record is most complete. In southern locations, where uplift has been less, sea level was below the present for long periods of time but there is very little data on RSL position. There are varying levels of agreement between models and existing field data and we cannot be certain of model projections of former low sea levels. Getting the models right is important for understanding the whole global pattern of land-ice-ocean interactions in the past and into the future. To gather the missing data and thus improve the utility of the British RSL curves for testing earth-ice-ocean models, we will employ a specialised, interdisciplinary approach that brings together a unique team of experts in a multidisciplinary team.

We have carefully selected sites where there is evidence of former sea levels definitely being preserved and we will use existing seabed geological data in British and Irish archives to plan our investigations. The first step is marine geophysical profiling of submerged seabed sediments and mapping of surface geomorphological features on the seabed. These features include the (usually) erosional surface (unconformity) produced by the rise in sea level, and surface geomorphological features that indicate former shorelines (submerged beaches, barriers and deltas). These allow us to identify the position (but not the age) of lower than present sea levels. The second step is to use this stratigraphic and geomorphological information to identify sites where we will take cores to acquire sediments and organic material from low sea-level deposits. We will analyse the sediments and fossil content of the cores to find material that can be closely related to former sea levels and radiocarbon dated. The third step in our approach is to extend the observed RSL curves using our new data and compare this to model predictions of RSL. We can then modify the parameters in the model to obtain better agreement with observations and thus better understand the earth-ice-ocean interactions.

These data are also important for understanding the palaeogeography of the British Isles. Our data will allow a first order reconstruction of former coastlines, based upon the modern bathymetry, for different time periods during the deglaciation. This is of particular importance to the presence or absence of potential landbridges that might have enabled immigration to Ireland of humans and animals. They will also allow us to identify former land surfaces on the seabed. The palaeogeography is crucial to understanding the evolving oceanographic circulation of the Irish Sea.

Objectives

The objectives are as follows:

1. to collect new geophysical and sea bed sediment cores from six field sites in the Irish Sea region in order to reconstruct the depth and timing of the Late Glacial relative sea level (RSL) lowstand along an isostatic gradient between the Last Glacial Maximum (LGM) ice limit and the former ice centre in SW Scotland. This will significantly extend the observational record of RSL in the British Isles and enhance existing RSL curves that are currently largely based on Holocene data and comparatively shallow depths. The last marine-based campaign of this type was completed in the North Sea basin under the NERC Land Ocean Interaction Project in the mid 1990s. No equivalent effort has thus far been directed to the Irish Sea basin.

2. to test and improve existing models of glacio-isostatic rebound and associated RSL change in the Irish Sea basin. Existing models predict different RSL curves that have varying levels of agreement with field observations of RSL data. The most crucial area in which data are lacking is the Late Glacial lowstand and during this interval a paucity of field data mean model differences cannot be resolved. We will compare our our newly acquired RSL data to existing model simulations and re-run the BIM-1 model to minimise discrepancies with field data. Improving these models is important since they enable us to reconstruct former ice sheet loading scenarios and help establish key parameters of earth rheology (lithospheric thickness and mantle viscosity).

3. to use our newly aquired RSL observations and seabed bathymetry to produce new palaeogeographic reconstructions of the evolution of the Irish Sea Basin from the LGM through to the mid Holocene. These maps, constructed at 1000 year intervals, will enable us to test long-standanding debates regarding the insularity of Ireland, human migration, palaeoecology and palaeo-oceanography in the region.

Progress

Compilation and review of existing data

In the first instance, extant data were compiled and processed for the following areas: Bantry Bay, Waterford, Co. Louth, Belfast Lough, Cardigan Bay and South off the Isle of Man. Datasets from the Republic of Ireland (Bantry, Waterford, Louth), consist of high resolution bathymetry and backscatter multibeam (1x1m) and seismic pinger data. These data were collected between 2004 and 2008 as part of the Infomar (the INtegrated Mapping FOr the Sustainable Development of Ireland’s MArine Resource) programme, a joint venture between the Geological Survey of Ireland and the Marine Institute of Ireland.

Multibeam bathymetry and backscatter data were collected by the Royal Navy and the Agri-Food and Biosciences Institute in 2003 and 2009 over an extensive area from the mouth of Belfast Lough to Glenarm Point (Northern Ireland). The only seismic data available for Belfast Lough consists of a number of Chirp lines acquired by the University of Ulster in 1997.

There are no multibeam data available for the areas of interest in Cardigan Bay and off the Isle of Man. The British Geological Survey (BGS) have, however, supplied us with a number of scanned seismic lines acquired in the 1960s and 1970s. A large quatity of samples (cores and boreholes) have been recovered by the BGS in these areas over the past 50 years, the logs of which will be made available to the project.

A first scan of the existing regional scale datasets for features of interest (such as channels, cliffs and unconformities) allowed us to target more specific zones during the geophysical survey in 2011.

Geophysical survey 2011

The first field season of data collection was completed between 16th and 29th of June 2011, leaving from Bantry Bay and finishing in Belfast Lough. A ship-based marine seismic reflection survey, using a towed Boomer system and hull-mounted Pinger source, was undertaken onboard RV Celtic Voyager. Furthermore, multibeam data were collected in areas where no such data exists. Study areas targeted were: (i) Bantry Bay, (ii) Waterford, (iii) Louth and Dublin (Boyne), (iv) Cardigan Bay, (v) Isle of Man, (vi) Kilkeel, (vii) Dundrum Bay and (viii) Belfast Lough. Over 2000 km of seismic data were collected.

Please read the cruise report for further details about the cruise:


Celtic Voyager


Multibeam acquisition


Boomer catamaran


Boomer acquisition set-up

Outputs

Conference presentations and posters

Cooper J.A.G et al. Late glacial sea level minima in the Western British Isles: observed and modelled. INQUA-Congress 2011, Bern Switzerland.

Papers