ULTRA-HIGH-RESOLUTION PROXY RECORD OF LAST MILLENNIUM NORTH ATLANTIC TEMPERATURE ANOMALIES ('ULTRA')

The shells of many marine bivalve molluscs, in particular Arctica islandica, contain annual growth bands. The fact that the bands in Arctica are annual has been demonstrated by stable oxygen isotope profiles across the growth increments, which show seasonal cycles of seawater temperature, and by marking live individuals and examining the incremental growth after repeated recaptures. Counting the increments demonstrates that this species has extraordinary longevity: one live specimen from Icelandic waters collected by the Bangor group in 2006, and which will form a central plank in the research proposed here, has at least 500 annual increments. This is considered the longest-lived non-colonial animal known to science. Furthermore, we have been able to cross-match the growth series from such live individuals with dead shells dredged from the seabed to construct long absolute chronologies. Cross-matching demonstrates that individuals within a region respond to the same environmental, possibly climatic, stimuli. North of Iceland we have established that there is a significant statistical relationship between the width of the growth increments and seawater temperature, with wider increments being laid down in warmer years. We have now constructed a cross-matched record covering the last 1000 years from this region and it is this already assembled archive that we propose to use in this project. We will analyse the stable oxygen isotopes contained within the annual growth increments. By carefully comparing the isotope measurements with local instrumental records of seawater temperature and other variables collected over the last 50 years, we will be able to convert reliably the isotope data into temperature reconstructions. This will help test how robust the reconstructions based on increment width alone are. We have preliminary data which suggest that there were major hydrographic changes north of Iceland during the last 1000 years, notably the migration of the North Atlantic Polar Front (NAPF) separating the warm Irminger Current from the cold East Icelandic Current. These changes are directly linked to the wider circulation of the North Atlantic. It is this circulation system - the North Atlantic meridional overturning circulation (AMOC) - that currently provides the heat that controls the climate of NW Europe. By reconstructing, in great detail, the variability in the position of the NAPF north of Iceland over the last 1000 years from the oxygen isotopes in the Arctica record, we will enhance our understanding of how frequent the flips in the system are and how quickly these transitions take. Direct measurement of the AMOC have only been available for a few years. Longer records - which are crucial for identifying the sensitivity of the AMOC to perturbations, notably increases in freshwater flux to the ocean - rely on proxy records. The importance of generating records such as this was highlighted in the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC, 2007). IPCC stated that the compilation of various instrumental and proxy climate records over the last 1300 years provides critical evidence of the variations in average large-scale surface temperatures, and clearly emphasize the prominence of the recent warming, especially in the last two to three decades. However, IPCC also recognise that there is an urgent need to reduce the uncertainty in such compilations, via the update of existing records, many of which were assembled up to 20 years ago, and the generation of additional, especially early, palaeoclimate series with much wider geographic coverage. This proposal seeks to contribute to this goal through the generation of a unique 1000-year palaeotemperature record based on oxygen isotopic analysis of annual increments of Arctica islandica in order to identify the natural variability of temperature anomalies linked to the meridional migration of the NAPF on the north Icelandic shelf.