Magnesium in subaqueous speleothems as a potential palaeotemperature proxy

Russell Drysdale,Ilaria Isola,Trevor Ireland,Giovanni Zanchetta,Leonardo Piccini,Peter Holden,John Hellstrom,Ellen Corrick,Jon Woodhead,Polychronis C Tzedakis,Aline Govin,Alan Greig,Eleonora Regattieri,Henri Wong,Isabelle Couchoud

doi:10.1038/s41467-020-18083-7

Abstract

Few palaeoclimate archives beyond the polar regions preserve continuous and datable palaeotemperature proxy time series over multiple glacial-interglacial cycles. This hampers efforts to develop a more coherent picture of global patterns of past temperatures. Here we show that Mg concentrations in a subaqueous speleothem from an Italian cave track regional sea-surface temperatures over the last 350,000 years. The Mg shows higher values during warm climate intervals and converse patterns during cold climate stages. In contrast to previous studies, this implicates temperature, not rainfall, as the principal driver of Mg variability. The depositional setting of the speleothem gives rise to Mg partition coefficients that are more temperature dependent than other calcites, enabling the effect of temperature change 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 providing palaeotemperature information over multiple glacial-interglacial cycles.

Highlights

Few palaeoclimate archives beyond the polar regions preserve continuous and datable palaeotemperature proxy time series over multiple glacial-interglacial cycles
Magnesium-to-calcium ratios (Mg/Ca) in carbonates are widely used in the marine sciences to study surface- and deepocean temperatures[4,5,6,7]
There is clear correspondence between Mg and sea-surface temperatures (SSTs) at the orbital scale, but across Termination II (T-II) the structural agreement is very strong, in that Mg captures the sharp rise in SST at the end of the Heinrich Event 11 (H11) stadial

Summary

Introduction

Few palaeoclimate archives beyond the polar regions preserve continuous and datable palaeotemperature proxy time series over multiple glacial-interglacial cycles. This can cause prior calcite (or aragonite) precipitation (PCP) and/or incongruent dissolution of dolomite (IDD)[19], both of which can raise percolation-water Mg/Ca by 50% or more around mean values[20,21] These changes override the effect of temperature on the partitioning of Mg from the source water to the speleothem and produce the familiar pattern of higher (lower) speleothem Mg/Ca during periods of low (high) recharge[22,23,24,25,26,27,28]. We conclude that high-resolution Mg profiles from this and similar speleothems have excellent potential for providing rare terrestrial palaeotemperature records, and for tracking major changes in regional SSTs. Besides providing muchneeded temperature data, this may help anchor ocean-sediment records in radiometric time through Mg-SST synchronization

Methods

Results

Conclusion