ASSESSING THE IMPACT OF DIAGENETIC BIAS ON MARINE ISOTOPE STAGE 3 SEA-LEVEL RECONSTRUCTIONS BASED ON DEEP-SEA BENTHIC FORAMINIFERAL STABLE ISOTOPE RECORDS

One of the emerging debates regarding past sea-level variability and how it pertains to future changes is focused on the discrepancies between reconstructions based on deep-sea proxies and those based on modeling simulations and geologic data from land-based deposits during Marine Isotope Stage (MIS) 3 (~60-35 ka). For example, sea-level estimates derived from deep-sea benthic foraminiferal stable isotope records indicate a range of sea level between approximately 60m and 90m below present during MIS 3. Alternatively, glacio-isostatic modeling and ice sheet reconstructions based on land-based geochronology range from approximately 30m to 50m below present. We focus on the extent to which diagenetic alteration may have biased deep-sea benthic foraminiferal stable isotope records. Building on work by Poirier et al. (2021), we generated new single-test stable isotope records on specimens of the genus Cibicidoides from Ocean Drilling Program Sites 846 (deep equatorial Pacific) and 929 (deep equatorial North Atlantic) spanning MIS 3. Data were generated on ideally-preserved specimens (i.e., glassy), in addition to those being moderately- (i.e., pseudo-glassy) and poorly-preserved (i.e., frosty) to determine the extent to which inclusion of moderately and poorly preserved specimens in pooled-test records may affect sea-level estimates. Using the results from only ideally-preserved specimens, we can use an ocean basin water mass mass-balance to calculate new MIS 3 sea-level estimates and compare them to land-based records.

Reference Cited:

Poirier, R.K., Gaetano, M.Q., Acevedo, K., Schaller, M.F., Raymo, M.E., and R. Kozdon (2021). Quantifying Diagenesis, Contributing Factors, and Resulting Isotopic Bias in Benthic Foraminifera using the Foraminiferal Preservation Index: Implications for Geochemical Proxy Records. Paleoceanography and Paleoclimatology, 36(5), e2020PA004110. https://doi.org/10.1029/2020PA004110.