Last glacial and Holocene stable isotope record of fossil dripwater from subtropical Brazil based on analysis of fluid inclusions in stalagmites

Publication Type:

Journal Article

Source:

Chemical Geology, Volume 468, p.84-96 (2017)

Abstract:

<p>The stable isotope composition of fossil dripwater preserved in stalagmites fluid inclusions is a promising tool to reconstruct paleopluviosity in the tropics and subtropics. Here we present delta D and delta O-18 records of fossil drip water from two stalagmites collected in Botuvera Cave (subtropical Brazil), covering the last glacial period and the Holocene. The observed millennial-scale variability of fossil dripwater delta D and delta O-18 values is of the order of 10 to 20 parts per thousand and 1 to 3.5 parts per thousand (V-SMOW), respectively. Fluid inclusion delta D and delta O-18 values are higher than the weighted mean delta D and delta O-18 values of modern precipitation, suggesting a possible intensification of extratropical cold surges during both the last glacial period and the Early Holocene, followed by a progressive Late Holocene transition towards modern pluviosity conditions. Fluid inclusions delta O-18 values vary in parallel with stalagmite delta O-18 values during the Holocene but not during the last glacial period. This suggests that the delta O-18 value of precipitation may not be the only dominant factor controlling the delta O-18 values of the analyzed stalagmites. Isotope disequilibrium effects arising from Prior Calcite Precipitation (PCP) possibly affected stalagmites 8180 values to a greater extent than previously considered, though this effect does not bias non-quantitative paleopluviosity reconstructions based on stalagmite delta O-18 values. Isotope-based paleotemperature calculated for the Late Holocene matches modern cave temperature (19 degrees C) within +/- 2.4 degrees C. This encourages further application of isotope analyses of fluid inclusion for climatic reconstructions.</p>