Model evaluation of the coherence of a common source water oxygen isotopic signal recorded by tree-ring cellulose and speleothem calcite

Abstract

Oxygen isotopic compositions (δ18O) of tree rings and speleothems inherit δ18O of precipitation (δ18Oppt) and are used to reconstruct past variations in the amount of precipitation or temperature. Integration of δ18O records of both the proxies for a multiproxy climate reconstruction necessitates understanding of the extent to which the initial δ18Oppt is modified in both the proxies before getting preserved in them. A forward modeling approach, assuming both the proxies have access to a common source water δ18O signal, is employed to assess the expected maximum correlation between the δ18O records of the two proxies on interannual time scale and the factors influencing the correlation. Variations in the leaf temperature, relative humidity, δ18O of atmospheric water vapor introduce variations in δ18O of tree-ring cellulose, while the variations in the cave temperature and oxygen isotopic equilibrium/disequilibrium conditions between calcite and drip water influence δ18O of speleothem calcite. Variation introduced by these factors in δ18O of individual proxies as compared to the variation in δ18Oppt is crucial in deciding the correlation between δ18O records of the two proxies. When the former is higher than or comparable with the latter, finding one to one correspondence between the δ18O records of the two proxies could be challenging. Modeling exercise revealed a favorable climatic condition at Jagdalpur (19.08°N, 82.03°E), a potential tropical location for tree ring and speleothem-based climate reconstruction, for inheriting a common source water δ18O signal in both the proxies. δ18O records of tree ring and annually resolved speleothem from Jagdalpur could be integrated for the multiproxy climate reconstruction.