Saturday, 5 September 2015

Sample, Log, Repeat: the quest for dating the retreat of the British Irish Ice Sheet

The BGS vibrocorer on the RRS James Cook
On 3 July 2015 EPC's Sally Morgan departed on a month-long research cruise (JC123) as part of the BRITICE-CHRONO project.

The JC123 cruise, led by Professor Colm O’Cofaigh of Durham University, is the second of 2 marine-based coring programmes that are central to the 5-year BRITICE-CHRONO NERC Consortium Grant which aims to collect and date material to constrain the timing and rates of change of the collapsing British-Irish Ice Sheet (BIIS).  This year’s project was staffed by scientists from a number of institutions across the UK, including the universities of Bangor, Durham, Leicester, Liverpool, Sheffield, Stirling, and Ulster, as well as the British Geological Survey.
Similar to the first BRITICE-CHRONO cruise (JC106) that took place in 2014, JC123 was on board the Royal Research Ship James Cook and set sail from Southampton. The cruise surveyed and sampled material along 3 main transects in The Minch, Shetland and the North Sea areas.  Coring targets in these transects were identified using the surveying data collected on board, notably multibeam echo sounder and sub-bottom profiler data.  Most of the cores were acquired utilising the British Geological Survey’s vibrocorer system (up to 6 m penetration), with a few cores sampled using the National Oceanographic Centre’s piston corer (up to 10 m penetration).  Over 170 individual cores were collected, totalling in excess of half a kilometre of core material. 
Once recovered to the ship, the cores were cut into metre-long sections and curated, after which they were measured on Leicester’s containerised Geotek multi-sensor core logger system, operated by Sally.  This system allows for the acquisition of the physical properties of the cores, including the bulk density, acoustic velocity, magnetic susceptibility and electrical resistivity.  Once the cores were measured they were returned to the core description team who split the cores in half lengthways, sampled and described the cores, and then packed them up ready for shipment to different institutions at the end of the cruise for further analyses (including C14-dating and optically stimulated luminescence dating) and archiving.  Used in combination with the descriptions and geochronological data derived from the cores, the physical properties data will be used to help better understand the timing of the BIIS recession at the end of the last glaciation.   
Work on these cores, the cores acquired during JC106, and material collected from the equivalent land-based studies, will continue through 2017, after which it is hoped that predictive ice sheet modelling will be significantly improved, with the BIIS forming an important benchmark.
Further information about the project is available via the BRITICE-CHRONO webpage and you can also follow the project’s progress on Twitter:  @BRITICECHRONO

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