North ATLANTIC ocean circulation during marine isotopic stages 6 and 5 inferred by lead isotopic compositions of detrital sediments
Abstract
The world deep-ocean thermohaline circulation is primarily controlled by the magnitude of the North Atlantic Deep Water production. Warm and salty subtropical water is carried to the high latitudes in the North Atlantic Ocean by the North Atlantic Current. As it moves northward, this water cools sufficiently to sink, beginning the deep-ocean conveyor system. During glacial periods, the thermohaline ocean circulation was reduced and this lead to a reorganization of the oceanic currents . Therefore it is important to understand in detail the water circulation that prevailed during interglacial and glacial periods in the North Atlantic Ocean. It has been shown that the isotopic compositions of the long-lived radiogenic systems (Sr, Nd, Pb) measured in marine sediments are an efficient tool that allow us to identify the sources of detrital materials and thus to infer past ocean currents. Lead isotopic compositions have been measured in the lithic fraction of six cores sampled in the North Atlantic Ocean (from 40°N to 60°N and from 18°W to 39°W), focusing on the glacial/interglacial transition between marine isotopic stages 6 and 5e (128,000 BP). Our results are compared with isotopic compositions of the potential sources (Iceland, Scandinavian, Canadian and Greenland terrains). They confirm that lead can be used as a tracer to decipher the origin of lithic particles in this region. Source identifications and spacial distribution of the cores corroborate with two different transport regimes between interglacial and glacial periods. Indeed, during stage 5e at a first order, sediments from six out of seven cores seem to be characterized by the same isotopic signature. This is in contrast to stage 6 where the isotopic compositions of the lithic fractions is more dispersed along the trend defined by the majors sources. The isotopic compositions from the northern cores, retrieved between 50°N and 60°N, reflect non-radiogenic Iceland particles that were eroded during interglacial stage 5e. This interpretation is in agreement with the published Sr-Nd data [Revel et al. 1996]. The last core from the western part of North Atlantic Ocean is mainly influenced by input of non-radiogenic particles transported in the Baffin Bay, both in glacial and interglacial stage with a slight variation toward more radiogenic values during glacial regime. Revel M., Sinko J.A., Grousset F. E., Paleoceanography, 11-1, pp. 95-113, 1996.
- Publication:
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EGS - AGU - EUG Joint Assembly
- Pub Date:
- April 2003
- Bibcode:
- 2003EAEJA....11404T