The Holocene (12 000 years ago until now?) was a period where temperature was relatively constant and the volume of ice at the caps was relatively stable. How much this climate varied naturally is a key issue in understanding the human influence on today’s climate.
There were several climatic events during the Holocene (e.g. 9 200 and 500 years ago), but the largest temperature irregularity, discovered from δ18O in Greenland ice cores, was at about 8200 years ago. At this time, there was a catastrophic release of fresh water from glacial lakes Agassiz and Ojibway in Canada, which is thought to have resulted in a 1.5 to 2°C cooling of the North Atlantic. This slowed the Meridional Overturning Circulation (MOC) in the North Atlantic by about 40%, cooling the land at high latitudes for a geologically short interval of time (100–200 years).
This event (also known as 'the 8.2 event'), and a similar one at 9200 years ago ('the 9.2 event'), is believed to be a useful comparison for future changes to the North Atlantic system, given the prediction that, as the ice sheets melt in the coming decades, large quantities of freshwater are expected to be released into the North Atlantic. A better understanding of the events in the Holocene is therefore needed to help predict potential consequences to the North Atlantic system.
The BGS Climate Change Team is studying core from the central Irish Sea to see how the environment was influenced by climatic changes in the Holocene.
BGS borehole 89/15 (pictured right) is from a site in the central Irish Sea. The site thought to be well situated to monitor changes to British and Irish climate during the climatic events 9200 and 8200 years ago (and possibly the 'Little Ice Age' as well).
The core is 38 metres long and was drilled through Holocene deposits. This is believed to be one of the most expanded marine Holocene sections in Europe (other cores from this time are less than 38 metres thick providing a more compressed view of this period; this core is such that information about the Holocene climate can be extracted at about ten-year resolution).
To understand changes in temperature, acidity and source of the water mass, the following analyses will be carried out:
Other analyses include bulk sediment UK37' analysis for sea surface temperature and micropalaeontological assemblage (pictured below) study for changes in ecology, water masses, and stratification (layering of salinity, oxygenation, density and temperature within sea water).
Through this study, and by comparison with other UK boreholes, we hope to measure oceanic change during the Holocene and, in turn, the potential effect of North Atlantic MOC disturbances and cooling to the Irish Sea and UK continental shelf.
Dickson, C, & Whatley, R. 1996. The biostratigraphy of a Holocene borehole from the Irish Sea. 145-148. In: Keen, MC (Ed.) Proceedings of the 2nd European Ostracodologists’ Meeting, University of Glasgow, 23rd-27th July 1993.
Marshall, J. D., Lang, B. Crowley, D. F., Weedon, G. P., van Calsteren, P., Fisher, E. H., Holme, R., Holmes, J. A., Jones, R. T., Bedford, A., Brooks., S. J., Bloemendal, J. Kiriakoulakia, K. and Ball, J. D. (2007), Terrestrial impact of abrupt changes in the North Atlantic thermohaline circulation: Early Holocene, UK, Geology, 35, 639– 642.
Scourse, J.D., Austin, W.E.N., Long, B.T., Assinder, D.J. and Huws, D. 2002. Holocene evolution of seasonal stratification in the Celtic Sea: refined age model, mixing depths and foraminiferal stratigraphy. Marine Geology, 191, 119-145.