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Thermohaline circulation crisis and impacts during the mid-Pleistocene transition

Science  18 Jul 2014:
Vol. 345, Issue 6194, pp. 318-322
DOI: 10.1126/science.1249770

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Circulating between different cycles

Around a million years ago, large-scale ocean circulation changed dramatically during the switch from ∼41,000- to ∼100,000-year long glacial cycles. Pena and Goldstein analyzed the isotopic composition of neodymium in marine sediments from the South Atlantic. The results suggest how the contributions of deep water from northern and southern sources varied across the transition. The boundary between the two glacial states appears to have been marked by a dramatic weakening, perhaps even a shutdown, of deep-water currents.

Science, this issue p. 318

Abstract

The mid-Pleistocene transition (MPT) marked a fundamental change in glacial-interglacial periodicity, when it increased from ~41-thousand-year to 100-thousand-year cycles and developed higher-amplitude climate variability without substantial changes in the Milankovitch forcing. Here, we document, by using Nd isotopes, a major disruption of the ocean thermohaline circulation (THC) system during the MPT between marine isotope stages (MISs) 25 and 21 at ~950 to 860 thousand years ago, which effectively marks the first 100-thousand-year cycle, including an exceptional weakening through a critical interglacial (MIS 23) at ~900 thousand years ago. Its recovery into the post-MPT 100-thousand-year world is characterized by continued weak glacial THC. The MPT ocean circulation crisis facilitated the coeval drawdown of atmospheric CO2 and high-latitude ice sheet growth, generating the conditions that stabilized 100-thousand-year cycles.

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