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The full programme book (PDF) - Royal Geographical Society

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T5<br />

A Pb isotope tracer of ocean-ice sheet interaction:<br />

<strong>The</strong> record from the NE Atlantic during the last glacial/interglacial cycle<br />

Kirsty C. Crocket* 1a , G.L. Foster 2b , D. Vance 2c , D.A. Richards 1 , M. Tranter 3<br />

1 Bristol Isotope Group, School of <strong>Geographical</strong> Sciences, University of Bristol<br />

2 Bristol Isotope Group, School of Earth Sciences, University of Bristol<br />

3 Bristol Glaciology Centre, University of Bristol<br />

a Now at: Scottish Association for Marine Science, Oban<br />

b Now at: National Oceanography Centre Southampton<br />

c Now at: Department of Earth Sciences, ETH Zürich, Switzerland<br />

Ice sheet-ocean interactions are both a response to climate forcing and a source of<br />

climate feedback, releasing freshwater to the surface ocean and influencing climate and<br />

atmospheric CO 2 through changes in ocean circulation. Documenting the outcomes of<br />

these interactions for recent glacial cycles is important given current and future scenarios<br />

of polar ice retreat. However, this is currently hampered by lack of accurate constraints on<br />

ice sheet development and demise. Marine sedimentary Pb isotope records have potential<br />

to investigate these aspects of ice sheet feedbacks at high temporal resolution because of<br />

the sensitivity of the Pb isotope composition to continental weathering intensity and solute<br />

flux. Here we present a Pb isotope record sourced from the FeMn oxyhydroxide fraction in<br />

marine sediments from ODP Site 980 on Feni Drift (2168 mbsl, Rockall Trough, NE<br />

Atlantic), spanning the last 43 ka (Crocket et al., in press). <strong>The</strong> location of Site 980 at the<br />

northern edge of the British-Irish Ice Sheet (BIIS) makes it well-placed to monitor changes<br />

in BIIS development as it responded to migration of the Polar Front during the last<br />

glacial/interglacial cycle. <strong>The</strong> data reveal millennial-scale cyclicity in Pb isotope<br />

composition, reminiscent of Dansgaard-Oeschger cycles, from the start of the record until<br />

Heinrich event 2 (43 to 24 ka), characterised by extreme shifts to radiogenic compositions<br />

(i.e. variation in 206 Pb/ 204 Pb from ~18.9 to 20.5). <strong>The</strong> period 24 to 17.5 ka is also<br />

characterised by exceptionally radiogenic and highly variable Pb isotope compositions,<br />

associated with the rapid and repeated expansion and collapse of the BIIS. <strong>The</strong> presence<br />

of such radiogenic Pb isotope compositions during periods of maximum ice sheet activity<br />

support interpretation of the subglacial environment as an active weathering environment,<br />

contributing to biogeochemical cycles through the transport vectors of meltwater release<br />

and debris-laden ice calving.<br />

Keywords: Pb isotopes; British-Irish Ice Sheet (BIIS); Last Glacial Maximum;<br />

glacial/interglacial cycles; chemical weathering; authigenic and pre-formed FeMn<br />

oxyhydroxides<br />

Crocket, K.C., Foster, G.L., Vance, D., Richards, D.A., Tranter, M., in press. A Pb isotope tracer of<br />

ocean-ice sheet interaction: <strong>The</strong> record from the NE Atlantic during the last glacial/interglacial cycle.<br />

Quaternary Science Reviews.

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