|Understanding stable isotopic disequilibrium in benthic foraminifera from hydrocarbon seeps
Anthony E. Rathburn (Indiana State University), Jon Martin (University of Florida)
This project eeks answers to the question: What controls the carbon isotopic composition of benthic foraminiferal tests (shells)? Answers to this question will be crucial for paleoenvironmental reconstructions in both hydrocarbon seep and non-seep environments. In order to address this question, in July 2007 we will use the ROV Jason to examine environments with "extreme" chemical gradients that accentuate chemical differences between biogenic carbonate and ambient conditions as well as those of "normal" deep-sea conditions. Extreme isotopic gradients present at cold methane seeps provide an ideal habitat to examine the effects of carbon isotopic disequilibrium (up to 40 ?), between foraminiferal calcite and dissolved inorganic carbon (DIC) of ambient water. Recent work suggests that biological factors ("vital effects") and/or ambient isotopic compositions influence carbon isotopic signatures of foraminiferal calcite.
The project integrates microbiological techniques and ecological methods with geochemical analyses (pore-water and foraminiferal chemistry) using novel approaches, such as the Fluorescently-Labeled Embedded Core (FLEC) method and epifluorescence microscopic methods to identify live foraminifers. This integrated and detailed approach, specifically examining benthic foraminiferal cytoplasmic ultrastructure for symbiont presence and food composition, along with foraminiferal sub-millimeter distribution and isotope geochemistry, has never been attempted in any natural environment. These techniques will provide new and basic information about the effects of environment, distribution, diet, and symbiont presence/absence on stable isotope signals in foraminiferal tests.