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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]

The modern Indian summer monsoon (ISM) is characterized by exceptionally strong interhemispheric transport, indicating the importance of both Northern and Southern Hemisphere processes driving monsoon variability. Here, we present a high-resolution continental record from southwestern China that demonstrates the importance of interhemispheric forcing in driving ISM variability at the glacial-interglacial time scale as well. Interglacial ISM maxima are dominated by an enhanced Indian tow associated with global ice volume minima. In contrast, the glacial ISM reaches a minimum, and actually begins to increase, before global ice volume reaches a maximum. We attribute this early strengthening to an increased cross-equatorial pressure gradient derived from Southern Hemisphere high-latitude cooling. This mechanism explains much of the nonorbital scale variance in the Pleistocene ISM record. [ABSTRACT FROM AUTHOR]

The dominant period of Pleistocene glacial cycles changed during the mid-Pleistocene from 40,000 years to 100,000 years, for as yet unknown reasons. Here we present a 2.1-million-year record of sea surface partial pressure of CO2 (Pco2), based on boron isotopes in planktic foraminifer shells, which suggests that the atmospheric partial pressure of CO2 (pco2) was relatively stable before the mid-Pleistocene climate transition. Glacial Pco2 was ∼31 microatmospheres higher before the transition (more than 1 million years ago), but interglacial Pco2 was similar to that of late Pleistocene interglacial cycles (<450,000 years ago). These estimates are consistent with a close linkage between atmospheric CO2 concentration and global climate, but the lack of a gradual decrease in interglacial Pco2 does not support the suggestion that a long-term drawdown of atmospheric CO2 was the main cause of the climate transition. [ABSTRACT FROM AUTHOR]

The article discusses research by Z. An et al. which used analysis of the organic carbon content of ancient lake sediments in the Heqing Basin in southwestern China to study the Indian summer monsoon (ISM) annual climate cycle during the Pleistocene period. Previous research indicated that the expansion of glaciers in the Northern Hemisphere (NH) led to a weaker ISM, but the data gathered by An et al. suggests that ISM development during glacial periods was driven by cooling in the Southern Hemisphere (SH).

The article explores whether spruce grew in southern Greenland during the Pleistocene period and thus provided evidence that the ice sheet was sufficiently reduced to allow for regional development of boreal forests. It says that there is independent evidence to prove that spruce lived in Greenland in the mid-Pleistocene. Meanwhile, it cites pollen data suggesting that the Greenland ice sheet was much smaller during previous warm periods. It predicts that the Arctic region will likely become warmer than it was during the Pleistocene period and will remain warmer for thousands of years if greenhouse gas concentrations continue to increase over the next century.