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Millennial-scale cold reversals in the high latitudes of both hemispheres interrupted the last transition from full glacial to interglacial climate conditions. The presence of the Younger Dryas stadial (∼12.9 to ∼11.7 kyr ago) is established throughout much of the Northern Hemisphere, but the global timing, nature and extent of the event are not well established. Evidence in mid to low latitudes of the Southern Hemisphere, in particular, has remained perplexing. The debate has in part focused on the behaviour of mountain glaciers in New Zealand, where previous research has found equivocal evidence for the precise timing of increased or reduced ice extent. The interhemispheric behaviour of the climate system during the Younger Dryas thus remains an open question, fundamentally limiting our ability to formulate realistic models of global climate dynamics for this time period. Here we show that New Zealand’s glaciers retreated after ∼13 kyr bp, at the onset of the Younger Dryas, and in general over the subsequent ∼1.5-kyr period. Our evidence is based on detailed landform mapping, a high-precision 10Be chronology and reconstruction of former ice extents and snow lines from well-preserved cirque moraines. Our late-glacial glacier chronology matches climatic trends in Antarctica, Southern Ocean behaviour and variations in atmospheric CO2. The evidence points to a distinct warming of the southern mid-latitude atmosphere during the Younger Dryas and a close coupling between New Zealand’s cryosphere and southern high-latitude climate. These findings support the hypothesis that extensive winter sea ice and curtailed meridional ocean overturning in the North Atlantic led to a strong interhemispheric thermal gradient during late-glacial times, in turn leading to increased upwelling and CO2 release from the Southern Ocean, thereby triggering Southern Hemisphere warming during the northern Younger Dryas. [ABSTRACT FROM AUTHOR]

Ice cores extracted from the Antarctic ice sheet suggest that glacial conditions, and the relationship between isotopically derived temperatures and atmospheric have been constant over the last 800,000 years of the Late Pleistocene epoch. But independent lines of evidence, such as the extent of Northern Hemisphere ice sheets, sea level and other temperature records, point towards a fluctuating severity of glacial periods, particularly during the more extreme glacial stadials centred around 340,000 and 420,000 years ago (marine isotope stages 10 and 12). Previously unidentified mechanisms therefore appear to have mediated the relationship between insolation, CO2 and climate. Here we test whether northward migration of the subtropical front (STF) off the southeastern coast of South Africa acts as a gatekeeper for the Agulhas current, which controls the transport of heat and salt from the Indo-Pacific Ocean to the Atlantic Ocean. Using a new 800,000-year record of sea surface temperature and ocean productivity from ocean sediment core MD962077, we demonstrate that during cold stadials (particularly marine isotope stages 10 and 12), productivity peaked and sea surface temperature was up to 6 °C cooler than modern temperatures. This suggests that during these cooler stadials, the STF moved northward by up to 7° latitude, nearly shutting off the Agulhas current. Our results, combined with faunal assemblages from the south Atlantic show that variable northwards migration of the Southern Hemisphere STF can modulate the severity of each glacial period by altering the strength of the Agulhas current carrying heat and salt to the Atlantic meridional overturning circulation. We show hence that the degree of northwards migration of the STF can partially decouple global climate from atmospheric partial pressure of carbon dioxide, , and help to resolve the long-standing puzzle of differing glacial amplitudes within a consistent range of atmospheric . [ABSTRACT FROM AUTHOR]

Factors controlling the position and strength of the surface winds during the Last Glacial Maximum (LGM) are examined using a global, multilevel, moist, atmospheric model. The idealized aquaplanet model is bounded below by a prescribed axisymmetric temperature distribution that corresponds to an ocean-covered surface. Various forms of this distribution are used to examine the influence of changes in the surface cooling and baroclinicity rates. The model omits seasonal variations. Increasing the cooling lowers the tropopause and greatly reduces the moist convection in the Tropics, thereby causing a weakening and equatorward contraction of the Hadley cell. Such a cooling also weakens the surface westerlies and shifts the peak westerly stress equatorward. An extra surface baroclinicity in midlatitudes—implicitly associated with an increase in the polar sea ice—also shifts the peak westerly stress equatorward, but strengthens the surface westerlies. Thus, calculations with combined surface cooling and baroclinicity increases, representative of the Last Glacial Maximum, reveal an absence of change in the amplitude of the peak westerly stress but exhibit a substantial equatorward shift in its position, 7° for a 3-K cooling and 11° for a 6-K cooling. The easterlies, however, always increase in strength when the surface westerlies move equatorward. The application of these results to the LGM must take into account the model’s assumption of symmetry between the two hemispheres. Any changes in the climate’s hemispheric asymmetry could also cause comparable latitudinal shifts in the westerlies, probably of opposite sign in the two hemispheres. Published coupled-model simulations for the LGM give an equatorward shift for the peak westerlies in the Northern Hemisphere but give contradictory results for the Southern Hemisphere. [ABSTRACT FROM AUTHOR]

Reports on research that attempts to explain how temperate species survived difficult climatic conditions. How identification of locations of glacial survival could prove important in understanding patterns of species distribution; Glacial history of the coniferous tree Fitzroya cupressoides in South America; Conclusion that the biotic impact of the glacial cycles was greater in the Northern Hemisphere.

The article provides information on a study conducted by Robert P. Ackert Jr. and colleagues in order to determine whether or not southern Patagonia's glacial advance that created it occurred during the chronozone of the Younger Dryas. It mentions that the Ackert and colleagues measured the cosmic-ray exposure ages of the southern Patagonia's glacial moraine. Soon after the end of the Younger Dryas, moraine was deposited followed by the growth of the glacier in response to more precipitation. This suggests that Southern Hemisphere's temperature did not drop like those in the Northern Hemisphere during the Younger Dryas.