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abstracts
Surface and thermocline records of Mg/Ca derived temperatures in the Holocene subpolar North Atlantic
Elizabeth Farmer, Mark Chapman, Julian Andrews
Mg/Ca ratios from planktonic and benthic foraminifera are now routinely used as an independent proxy for past ocean temperature. Analysing d18O from the same sample potentially allows the separation of the foraminiferal d18O signal into its salinity/seawater d18O and temperature components. Mg/Ca derived temperature estimates are dependent on the choice of species-specific Mg/Ca-temperature calibrations. The analysis of multiple species of planktonic species may provide insight into changes occurring throughout the upper water column. Other factors, such as changes in depth habitat or a shift in seasonal production patterns, should also be considered when interpreting Mg/Ca records.
Here we present a high resolution record of Mg/Ca ratios measured on two planktonic foraminifers, Globigerina bulloides and Globorotalia inflata, from the subpolar North Atlantic core MD99-2251 (57º 26’N, 27º 54’W; 2620 m water depth), extending throughout the Holocene at ~ 20-70 year resolution. Core site oceanography is dominated by the convection of the warm saline waters of the North Atlantic Current. Shell chemistry reflects spring to summer conditions at the near surface (G. bulloides) and thermocline (G. inflata). Our records indicate variability throughout the Holocene, with ratios ranging from 1.6 to 2.6 mmol/mol for G. bulloides and 1.0 to 1.7 mmol/mol for G. inflata. Mg/Ca derived temperatures at the surface are typically in the range of ~7-13 ºC, with both species exhibiting Holocene variability of 3-4 ºC. A long term warming trend at both the surface and the thermocline is also revealed, particularly over the last 5 ka.
Elizabeth Farmer, School of Environmental Sciences, University of East Anglia,Earlham Road, Norwich, Norfolk, NR4 7TJ, United Kingdom, e.farmer@uea.ac.uk
Mark Chapman, University of East Anglia, School of Environmental Sciences, Norwich, Norfolk, NR4 7TJ, United Kingdom
Julian Andrews, University of East Anglia, School of Environmental Sciences, Norwich, Norfolk, NR4 7TJ, United Kingdom
Session: F2: Regional Climate Dynamics
Download Talk:
> YSM09_OralB_Farmer.pdf
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