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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. [ABSTRACT FROM AUTHOR]

Presents research which concluded that during the Earth's last glacial period, the climate underwent frequent and abrupt changes due to the ability of the ocean's thermohaline circulation to assume more than one mode of operation. Record in ancient sedimentary rocks; Possible trigger mechanism for such reorganizations; Impact of another such reorganization due to an increase in atmospheric carbon dioxide levels.

The article discusses research by Pena and Goldstein in the same issue that used the composition of neodymium in marine sediments to study the change in ocean circulation between glacial cycles.

One of the most commonly accepted views of the relation between climate and ocean circulation is known popularly as the "global conveyer," meaning that deep water forms in the North Atlantic Ocean in large amounts during interglacial periods and in smaller volumes during glacial intervals, producing significant changes in the rate of large-scale ocean circulation. Much of the evidence for this belief is based on studies of the carbon isotopic composition of benthic foraminifera, i.e., those that lived on the sea floor over the last glacial/interglacial cycle. Researchers examine this proposition in more detail by comparing and contrasting carbon isotopic profiles from seven sites in the North Atlantic covering the last 27 glacial cycles, a time span of nearly 2 million years.