Indian margin methane hydrate dissociation recorded in the carbon isotopes of benthic (Miliolida) foraminifera

Abstract

Methane hydrates in ocean sediments have been investigated across various timescales using a broad array of indicators to better understand hydrate dynamics and climate linkages. Here we report individual benthic and planktonic foraminiferal isotopic analyses at three sites from distinct oceanic environments in the northern Indian Ocean. The multi-species, multi-site analyses identify a unique δ13C response in Miliolida benthic foraminifera Pyrgo spp., Quinqueloculina spp., and Spiroloculina spp. suggesting that some species within these genera record the location and timing of past methane hydrate dissociation in the stable carbon isotopic composition of their skeletal (test) material. Our results document that dissociation occurred in the Mahanadi offshore basin, northwest Bay of Bengal, during glacial, transitional, and interglacial intervals of the past 1.5 million years. More negative test δ13C coupled with more positive δ18O supports the inference of interglacial-age dissociation, likely driven by increased intermediate water temperatures.