Magnesium in subaqueous speleothems as a potential palaeotemperature proxy.

Few palaeoclimate archives beyond the polar regions preserve continuous and datablepalaeotemperature proxy time series over multiple glacial-interglacial cycles. This hampersefforts to develop a more coherent picture of global patterns of past temperatures. Here weshow that Mg concentrations in a subaqueous speleothem from an Italian cave track regionalsea-surface temperatures over the last 350,000 years. The Mg shows higher values duringwarm climate intervals and converse patterns during cold climate stages. In contrast toprevious studies, this implicates temperature, not rainfall, as the principal driver of Mgvariability. The depositional setting of the speleothem gives rise to Mg partition coefficientsthat are more temperature dependent than other calcites, enabling the effect of temperaturechange on Mg partitioning to greatly exceed the effects of changes in source-water Mg/Ca.Subaqueous speleothems from similar deep-cave environments should be capable of providingpalaeotemperature information over multiple glacial-interglacial cycles.