STABLE CARBON ISOTOPE ANALYSIS FROM BENTHIC FORAMINIFERA IN THE NORTHERN GULF OF MEXICO

The Deep Water Horizon (DWH) oil spill occurred in the Northern Gulf of Mexico (NGoM) in 2010. Over 700 million liters of oil spilled into the NGoM in the 87 days the wellhead was actively leaking. Samples were taken from sites annually to semi-annually from 2010-2023 to provide a spatial and temporal benthic assessment for the NGoM. Reference conditions provide an ecological snapshot of the marine environment and allow for quantitative assessment of impact and response in the case of future oil spills. Benthic foraminifera, which are single-celled, testate organisms that inhabit the seafloor have proven to be excellent indicators and records of ecological change. Stable carbon isotopes in benthic foraminifera shells (tests) have also proven to be effective indicators of petroleum carbon incorporation into the benthic system. Seafloor sediment cores were most recently collected in 2023, at specific time series sites in the NGoM, as a part of the Scientist-At-Sea program. The sediment cores were subsampled at 2 mm increments. Calcareous foraminifera species, Cibicidoides pachyderma and C. wuellerstorfi, were isolated for stable isotope (oxygen and carbon) analysis using a stable isotope ratio mass spectrometer (SIRMS). Stable isotopes from benthic foraminifera from two of the time-series sites have been measured continually from 2010 to 2017. This study will provide a comparison of the latest benthic foraminifera stable carbon isotopes profiles with previous collections to determine long-term recovery of the system, gain insight into natural variability, and establish long-term preservation of the DWH signal in fossil (downcore) benthic foraminifera tests. These records will continue to aid in the understanding of natural seafloor carbon cycling, and also in the event of future pollution events such as oil spills.