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1. QUANTIFYING DIAGENESIS, CONTRIBUTING FACTORS, AND RESULTING ISOTOPIC BIAS IN BENTHIC FORAMINIFERA USING THE FORAMINIFERAL PRESERVATION INDEX: MAJOR IMPLICATIONS FOR GEOCHEMICAL PROXY RECORDS

   Poirier, R.K. ; Gaetano, M.Q. ; Acevedo, K. ; Schaller, M.F. ; Raymo, M.E. ; Kozdon, R. ( July 2020 , GSA Annual Meeting)

   Geochemical records generated from the calcite shells (tests) of benthic foraminifera, especially those of the genera Cibicidoides and Uvigerina, provide the basis of the majority of long-term climate records in a variety of proxy reconstructions. However, the extent to which benthic foraminifera are affected by post-depositional alteration is poorly constrained in the literature. Furthermore, how diagenesis may alter the geochemical composition of benthic foraminiferal tests, and thereby biasing a variety of proxy-based climate records, is also poorly constrained. We present the Foraminiferal Preservation Index (FPI) as a new metric to quantify preservation quality based on objective, well-defined criteria. The FPI is used to identify and quantify trends in diagenesis temporally, from modern coretop samples to the Mid-Pliocene Warm Period (0.0-3.3 million year ago), and spacially in the deep ocean. The FPI identifies the chemical composition of deep ocean water masses to be the primary driver of diagenesis through time, while also serving as a supplementary method of identifying periods of changing water mass influence at a given site through time. Additionally, we present stable isotope data (d18O, d13C) generated from individual Cibicidoides tests of various preservation quality that demonstrate the likelihood of significant biasing in a variety of geochemical proxy records, especially those used to reconstruct past changes in ice volume and sea level. These single-test data also demonstrate the robustness of paleorecords generated from carefully selected specimens of only the highest quality of preservation. 

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2. Changes in benthic foraminifera assemblage preservation associated with onset of deep AMOC during the last deglaciation

   Poirier, R. K. ; Gaetano, M. Q. ; Acevedo, K. ; Kozdon, R. ; Raymo, M. E. ( October 2018 , AGU Fall Meeting)

   Benthic foraminifera are used to generate the majority of paleo-proxy records reconstructing past ocean changes including variations in the strength of AMOC. To assess the reliability of geochemical proxy records generated using benthic foraminifera, a Foraminifera Preservation Index (FPI) was developed to quantify assemblage-wide changes in visual preservation quality. The qualitative criteria for preservation included in the FPI are supported by stable isotope and trace element datasets. Early application of the FPI on Cibicidoidesassemblages from the deep Pacific Ocean (IODP Sites 846, 1143, 1208) reveal quantifiably better preservation during glacial periods relative to interglacial periods for the last ~1 million years. Here, we present results from two summer REU projects tracking such preservation changes in the deep North and South Atlantic Ocean prior to and throughout the last deglaciation (~0-35 ka). Changes in Cibicidoides FPI from IODP Site 1089 in the deep South Atlantic (~4600m water depth: primarily bathed by Antarctic Bottom Water - AABW) mirror those in the Pacific with better preservation during the glacial maximum of Marine Isotope Stage (MIS 2) than the Holocene interglacial (MIS 1). Alternatively, Cibicidoides FPI from IODP Site 1059 (~3000m water depth: bathed by North Atlantic Deep Water [NADW] during interglacials; and by AABW during glacials) reveal better preservation during the Holocene relative to MIS 2. Despite these opposing trends, changes in FPI occur at both sites at ~15 ka corresponding to major changes to AMOC documented throughout the deep Atlantic basin. These findings imply that the same processes involved in water mass CO2-carbonate chemistry on glacial-interglacial timescales affect preservation of benthic foraminifera. Furthermore, our results suggest that the FPI can track major changes in deglacial AMOC, potentially providing an inexpensive method to produce preliminary data prior to or in unison with more expensive geochemical analyses. 

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3. Assessing potential for diagenetic overprinting of climatic signals in benthic foraminifera: Preliminary results.

   Poirier, R.K. ; Kozdon, R. ; Raymo, M.E. ; Schaller, M.F. ( July 2018 , FORAM2018)

   Assessing potential for diagenetic overprinting of climatic signals in benthic foraminifera: Preliminary results. Robert K. Poirier, Reinhard Kozdon, Maureen Raymo, Morgan Schaller Benthic foraminiferal stable isotope records (δ18O, δ13C) are the most common paleoclimate records produced to date, which capture changes in temperature, ice volume, and the global carbon system on orbital to sub-millennial timescales. General relationships between deep sea δ18O and sea level have long been established, and more recent paired δ18O and Mg/Ca records seek to disentangle the temperature and ice volume components of corresponding sea level records. However, the extent to which diagenesis may potentially alter the original isotopic signature recorded in tests of benthic foraminifera remains relatively undefined. We present preliminary results of a project focused on constraining the extent to which such diagenetic overprinting might alter sea level estimates based on records produced from modern to mid-Pliocene Cibicidoides and Uvigerina specimens. These include advanced imaging techniques (SEM, CL-spectroscopy), single shell stable isotope analyses (δ18O, δ13C), and chamber wall trace metal profiles (LA-ICPMS) paired with in situ δ18O analyses (SIMS). In addition, we present strict specimen screening criteria developed based on a new quantitative assessment of visual preservation in both individual foraminiferal tests and whole assemblages. http://forams2018.wp.st-andrews.ac.uk Session II: Advances in Foraminiferal Geochemistry Conveners: Jelle Bijma, Howard Spero Session Overview: http://forams2018.wp.st-andrews.ac.uk/program/ 

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4. ABUNDANCES, DIVERSITY, AND ECOLOGY OF BENTHIC FORAMINIFERA FROM THE SOUTHERN CALIFORNIA BIGHT

   Ononame, O. ; Burkett, A. ; Rathburn, A. ( March 2023 , Geological Society of America South Central Section)

   none. (Ed.)

   Foraminifera are single celled organisms that have tests that are composed of calcium carbonate or detrital materials. The assemblages of foraminifera have been influenced by their immediate environment which depict the influence and results of man’s activities and other natural processes that occur in the environment. These environmental changes include salinity, pH, hydrocarbon pollution and organic matter. With these factors, paleoenvironmental interpretations are made by identifying the different patterns in the foraminifera communities. Variations in oxygen concentrations at the sediment-water interface have a significant impact on benthic foraminiferal assemblages and morphologic properties. This is seen in the vertical distribution of foraminifera in response to factors such as food, pore water, and oxygen. This study documents foraminiferal ecology and abundances across an oxygen transect off the coast of San Diego. Available oxygen ranges from >1.0ml/l are considered oxic; O2 values from 0.1 - 1.0ml/l will be considered dysoxic and O2 values <0.10ml/l will be considered anoxic. Previous work in this region has suggested that sediment grain size, rather than oxygen availability, may have as much of an impact on foraminiferal assemblages. These observations were made based on the fact that Cibicidoides wuellerstorfi, an epibenthic foraminifera preferring elevated substrates in well-oxygenated environments, were found in greater abundances at areas with coarser grained materials despite low available oxygen. C. wuellerstorfi has also been found to have I/Ca and test porosity (size and abundance of pores on the surface of the test) which correlate to the available oxygen in bottom waters at the time of test formation. Not only will this study document foraminiferal assemblages and abundances across an oxygen transect, but C. wuellerstorfi from key oxygen environments will be examined under SEM and used in porosity and I/Ca analyses which will contribute to the development of a quantitative oxygen proxy. The development of this quantitative oxygen proxy is essential because despite oxygen being one of the primary variables influencing major geochemical and faunal responses within the world’s ocean, no clear proxy currently exists in paleoceanographic reconstructions. 

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5. Reassessment of the latitudinal temperature gradient across the Pacific during the EECO using a novel combination of instrumentation

   Zill, Michelle E. ; Kozdon, Reinhard ( October 2022 , AGU Fall Meeting 2022, held in Chicago, IL, 12-16 December 2022, id. PP32C-0959.)

   The early Eocene Climatic Optimum (EECO; ~ 53.3 to 49.1 Ma) was a period of the warmest sustained temperatures of the Cenozoic caused by perturbations to the global carbon cycle. Deep sea sediment cores and the microfossils preserved within them are the primary sources of information for these changes in climate and global carbon cycling but are subject to diagenetic alteration after deposition. One of the great challenges in paleoclimate research is determining how to accurately interpreting the proxy record by identifying the amount of chemical alteration of the isotopic and elemental compositions locked within microfossils such as foraminifera. The planktic foraminifera record has been biased by digenesis, provoking questions about the strength of the latitudinal temperature gradient throughout the EECO, specifically with respect to mismatches between proxy data and climate model simulations that remain unresolved. To investigate this question, we selected three deep sea sites that span across the Pacific Ocean, ODP Sites 865, 1209 and DSDP Site 207. From these sediments we extracted carefully screened planktic foraminifera and conducted analysis by two independent approaches on splits of the same individual foraminiferal shells. We measured the δ18O composition by conventional analysis (gas source mass spectrometry), and Mg/Ca ratios on fragments of the same shells by LA-ICP-MS that allows for a careful diagenetic screening. We then independently estimate sea surface temperatures and compare records to quantify the extent of bias in the planktonic foraminifera record. This approach helps to reassess the latitudinal temperature gradients across the EECO. 

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