Constraining ocean circulation modes and balancing the 14C-cycle of the last 40 ka based on dating of ultra-small carbonate samples from ODP Site 1063.
Final Report Abstract
The Atlantic Ocean holds a key role in the climatic system of our planet by controlling the global transport of heat and CO2. In our project we investigated the radiocarbon content of the water masses in the western north Atlantic within the period between 35 and 14 ka before present. For this project, only very small amounts of carbonate material were available due to the huge water depths of the ODP site 1063 sediment core. Therefore, we used cutting edge technology to obtain reliable radiocarbon results. With a gas ion source, developed at ETH Zurich, it was possible to determine the radiocarbon content of marine carbonate samples as small as 10µg carbon. While the radiocarbon reservoir of the bottom water barely varied between 35 and 14ka, we found large differences in the radiocarbon reservoir at the surface. Especially surprising are the large differences between two prominent Northern Hemisphere cold events (H1 and H2). The measurements within H2 reveal surface radiocarbon content similar to that of the atmosphere, while during H1 the surface water has much less 14C than the atmosphere. This is especially interesting, since all other ocean ventilation parameters, obtained in this and previous studies (radiocarbon in bottom water, sortable silt, Neodymium isotopes and Pa/Th ratios) are similar in both cold events. The surface radiocarbon results from the H2 event indicate a good ventilation and equilibration of surface waters with the atmosphere. This implies a relatively low CO2 concentration and a strong stratification of surface water. With the latter preventing old, carbon rich bottom waters from upwelling. In contrast to H2, H1 surface waters seem not to have experienced such stratification. Radiocarbon depleted bottom waters, which were most probably rich in carbon due to their southern origin, as derived from high εNd values, must have upwelled in this region to maintain the low radiocarbon content of the surface waters for the whole period.
Publications
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(2012) Constraining changes in ocean circulation modes and 14C reservoir ages in the NW Atlantic between 35 and 15 ka BP, Goldschmidt Abstract
J. Fohlmeister, J. Lippold, M. Kucera, L. Wacker, M. Bayer
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2012, A statistical approach to construct composite climate records of dated archives. Quaternary Geochronology, 14, 48-56
Fohlmeister, J.
