Earth Science

Sedimentary History

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Science  22 Aug 2003:
Vol. 301, Issue 5636, pp. 1019
DOI: 10.1126/science.301.5636.1019d

Understanding changes in the delivery of eroded material to the oceans is of fundamental importance for determining the relation between climate and continental weathering. Typically, the record of terrigenous input is reconstructed by analyzing the isotopic composition of seawater on the basis of proxies such as the calcium carbonate skeletons of foraminifera or the ferromanganese crusts of deep-sea nodules. There hasn't been as much work carried out directly on material transferred from land to ocean.

Using marine sediments recovered from the tropical Atlantic Ocean, Abouchami and Zabel have measured the isotopic composition of continental sedimentary Pb for the past 200,000 years in order to determine its provenance and whether Pb isotopes respond to variations in Earth's orbit. They find a clear signal of climate in the isotopic compositions of these sediments, regardless of whether they were transported by wind or rivers, and they also find systematic glacial-interglacial variations in the relative contributions of their sources. The probable cause of these covariations, they suggest, is changes in large-scale atmospheric circulation patterns in general, and in the position of the intertropical convergence zone in particular. — HJS

Earth Planet. Sci. Lett. 10.1016/S0012-821X(03)00304-2 (2003).

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