Precisely dated climate records challenge the Southern Hemisphere glacial aridity paradigm

Le résumé fourni par la source

While global changes in temperature during the last 1.5 Ma are well constrained, the terrestrial response to these changes is less understood, particularly in the Southern Hemisphere. Late Pleistocene ice-age climates are routinely characterised as having imposed moisture-stress on low/mid-latitude ecosystems. This idea is largely based on fossil pollen evidence for widespread, low-biomass glacial vegetation, interpreted as indicating climatic dryness. However, woody plant growth is inhibited under low atmospheric CO2, so understanding glacial environments requires the development of new palaeoclimate indicators that are independent of vegetation. Here, we present two new, well-dated speleothem records from subtropical, southern Australia, both spanning the last three glacial-interglacial cycles. We show that, contrary to expectations, over the past ~350 ka, peaks in southern Australian climatic moisture availability were largely confined to glacial periods, including the last glacial maximum, while warm interglacials were relatively dry. By measuring the timing of speleothem growth in the Southern Hemisphere subtropics, which today has a predominantly negative annual moisture balance, we developed a record of climatic moisture availability that is independent of vegetation and extends through multiple glacial-interglacial cycles. Our results demonstrate that a cool-moist response is consistent across the austral subtropics, and in part may result from reduced evaporation under cool glacial temperatures. Insofar as cold glacial environments in the Southern Hemisphere subtropics have been portrayed as uniformly arid, our findings suggest that their characterisation as evolutionary or physiological obstacles to movement and expansion of animal, plant and, potentially, human populations should be reconsidered.

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