Collaborative Research: Does Calcification By Paleoceanographically Relevant Benthic Foraminifera Provide A Record Of Localized Methane Seepage?

Woods Hole Oceanographic Institution, Woods Hole MA

Investigators

Abstract

Methane occurs in great quantities on continental margins as solid gas hydrates in seafloor sediments. It is also a powerful greenhouse gas that has the potential, when released from sediment-hosted gas hydrates, to dramatically increase global warming. Unfortunately, methane gas hydrates are ephemeral minerals that leave no direct evidence in the rock record. A long-lived indicator of past methane-rich marine environments would be a useful tool for assessing the impact of methane release from marine sediments in the past, which could help us estimate how our presently warming oceans, which can destabilize seafloor methane hydrate deposits and cause them to release their gases, may induce methane gas releases in the future. This research is focused on exploring the use of the carbon isotopic composition of calcareous tests of tiny sediment-living single-celled organisms called foraminifera (i.e., forams) to realize such a proxy for the occurrence of past seafloor methane seep environments. This research will study whether foram tests record the seepage of methane by examining whether the calcium carbonate that makes up their tests records the isotopic signature of carbon in methane, which is significantly different from that precipitated from seawater. Broader impacts of the work include the development of teaching units on foraminifera for visually impaired K-12 students at a school in Watertown MA. The curriculum will consist of a multisensory presentation (cold, sound, smell, touch, and heat). It will include 3D models generated by a 3Dprinter from micro-CT scans of foraminifera with known ecology and cell biology. This module will also be included in the curriculum of a local high school in Woods Hole MA and at the Florida Museum of Natural History. Goals of the research will be to see if forams calcify their tests in active seep environments and if the signature of the carbon in the seeping methane is recorded in the calcium carbonate the organism deposits. Approximately 40 to 50 forams taken from a 1200 meter deep methane seep site on the Vestnesa Ridge west of Svalbard, Norway will be studied. Multiple cutting-edge analytical techniques will be employed. Individual foram tests will undergo a three-step investigation that consists of (1) micro-computed tomography analysis to determine presence of authigenic carbonate overgrowths, (2) stable isotope mass spectrometry to determine stable carbon isotope values of the calcite, and (3) transmission electron microscopy of the decalcified cell body to establish the organism's viability and adaptation to methane seep habitats via symbionts. Coexisting pore waters from the same sediment cores from which the forams were extracted will be analyzed for inorganic carbon isotopic composition and other geochemical environmental species. Broader impacts of the work include the development of teaching units on foraminifera for visually impaired K-12 students at a school in Watertown MA. The curriculum will consist of a multisensory presentation (cold, sound, smell, touch, and heat). It will include 3D models generated by a 3Dprinter from micro-CT scans of foraminifera with known ecology and cell biology.