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Special Session 4: Biogeochemical cycling of trace elements in the ocean: GEOTRACES and beyond |
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Coherent seawater neodymium isotopic evolution in the Southeast Atlantic and Southwest Pacific during glacial-interglacial cycles
Monday 9th @ 1055-1115
Room 4
Rong Hu* , University of Cambridge
Alexander M. Piotrowski, University of Cambridge
Presenter Email: rh530@cam.ac.uk
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| Knowledge of the geometry and strength of the deep overturning circulation is central to the understanding of past climate variability on glacial-interglacial (G-I) timescales. In this study, neodymium (Nd) isotopic ratios on planktonic foraminifera are used to reconstruct the water mass source and mixing history of intermediate and deep water in the Southeast (SE) Atlantic and Southwest (SW) Pacific over the past 200 kyr. A coherent Nd isotope change was observed in the SE Atlantic and SW Pacific intermediate and deep water with major excursion to more radiogenic ŠĆNd values during Marine Isotope Stage (MIS) 2, 4 and 6. This suggests the flux of NACW to the Southern Ocean was reduced during cold marine stages, possibly accompanied by changes in the water mass geometry. The constant 2 ŠĆNd-unit offset between intermediate water in the SE Atlantic and SW Pacific suggests the persistent propagation of less radiogenic NACW to the upper Pacific Ocean over the last glacial cycle. Moreover, the larger glacial vertical ŠĆNd gradients between the intermediate and deep waters in both the SE Atlantic and SW Pacific indicate a decreased proportion of NACW entrainment into the deep oceans, consistent with studies proposing reduced mixing between the upper and lower meridional overturning cells. |
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