A Triple Threat: Stable Isotopes of Fluid Inclusions, Clumped Isotopes and Conventional Oxygen Isotopes from Modern and Ancient Caves in the Bahamas

Abstract:

The δ¹³C and δ¹⁸O of speleothems are widely used as environmental proxies in spite of the fact that it is acknowledged that they are significant non-equilibrium problems associated with their formation. Although some attempts have been made to test for kinetic effects by lateral sampling such kinetic effects still remain are emphasized by the large departure of the temperatures calculated using the Δ₄₇proxy in speleothems.

Here we present data from conventional δ¹⁸O isotopes in modern and ancient samples from the same cave and compare these with δ¹⁸O w analyses from drip water and from fluid inclusions. Finally these data are compared with Δ₄₇ measurements. These data show that it is possible to reconcile all the data using the approach of Wainer et al. (Quaternary Science Reviews, 30, 130-146, 2011) which compares the offset of the Δ₄₇ from the correct value and the difference between the δ¹⁸O data and the Kim and O'Neil ( Geochimica et Cosmochimica Acta, v. 61, 3461-3475, 1997) relationship in the modern samples. Using this slope the kinetic fractionation can be accounted for and a temperature estimated. The relationship can then be applied to ancient stalagmites from the Bahamas to distinguish between temperature and δ¹⁸Ow influences during important climatic events such as the Heinrich stadials. These data can then be verified by using the alternate approach of distinguishing temperature and δ¹⁸Ow, using the δ¹⁸O of water extracted from fluid inclusions to correct the δ¹⁸O of the calcite. Such suggested minimal changes in the δ¹⁸Ow and larger changes in temperatures during Heinrich events in the sub-tropics.