Climate Science

It's All in the Crust

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Science  07 Jun 2002:
Vol. 296, Issue 5574, pp. 1767-1769
DOI: 10.1126/science.296.5574.1767d

The intensity of North Atlantic Deep Water (NADW) production is an important determinant of global ocean thermohaline circulation and climate. It is affected over long periods by large-scale processes such as glaciation and continental drift, but different proxies (a substitute parameter that is easily measured) can provide conflicting evidence about its strength.

To help resolve these inconsistencies and to construct a more detailed record of NADW since the mid-Miocene, Frank et al. analyzed the Nd-and Pb-isotopic compositions of ferromanganese nodule crusts from the Southern ocean. Furthermore, by combining them with analyses of other nodules from the North Atlantic basin, they reconstructed the rate of NADW production over the last 14 million years. This method has two major advantages: First, Nd and Pb are not subject to biological fractionation, as are other commonly used water-mass proxies like carbon isotopes or Cd/Ca; and second, ferromanganese nodules can be dated accurately with Be-isotopic determinations. They find that there was a continuous and strong export of NADW (or a precursor of it) into the Southern Ocean between 14 and 3 million years ago and that over the past 3 million years, since the start of Northern Hemisphere glaciation, a progressive reduction of about 25% has occurred. — HJS

Paleoceanography17, 10.1029/2000PA000606 (2002).

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