Reference
Solari, M.A., Herve, F., Le Roux, J.P., Airo, A. and Sial, A.N. 2010. Paleoclimatic significance of lacustrine microbialites: A stable isotope case study of two lakes at Torres del Paine, southern Chile. Palaeogeography, Palaeoclimatology, Palaeoecology 297: 70-82.
Description
Working along the shore of Lago Sarmiento (51°03'00"S, 72°45'01"W) in southern Chile, where massive dead carbonate microbialites are exposed, Solari et al. obtained a δ18O record stretching back in time about 1200 years, to which they applied a "well-established, temperature-dependent oxygen isotope equilibrium fractionation equation between calcite and water" that yielded values of surface water temperature at a number of different dates, the two oldest of which (AD 800 and 1100) bracketed the MWP at that location. The warmest of these values was 9.5°C, which is 1.26°C greater than the mean surface water temperature of 8.24°C that they calculated from actual temperature measurements made every 20 minutes from April 1, 2003 to March 15, 2004. However, a δ18O-based surface water temperature of 8.9°C is indicated fairly close to the present. Thus, to be conservative, we calculate the peak temperature of the MWP to have been only 0.6°C greater than the peak temperature of the CWP.