More Like this

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

   Robert, 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. 

   more » « less
2. Quantifying Diagenesis, Contributing Factors, and Resulting Isotopic Bias in Benthic Foraminifera Using the Foraminiferal Preservation Index: Implications for Geochemical Proxy Records

   https://doi.org/10.1029/2020PA004110  

   Poirier, Robert K. ; Gaetano, Madison Q. ; Acevedo, Kimberly ; Schaller, Morgan F. ; Raymo, Maureen E. ; Kozdon, Reinhard ( May 2021 , Paleoceanography and Paleoclimatology)

   Geochemical records generated from the calcite tests of benthic foraminifera, especially those of the generaCibicidoidesandUvigerina, provide the basis for proxy reconstructions of past climate. However, the extent to which benthic foraminifera are affected by postdepositional alteration is poorly constrained. 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 late Pliocene to modern coretop samples (3.3–0 Ma), as well as spatially 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. Additionally, we present stable isotope data (δ¹⁸O, δ¹³C) generated from individualCibicidoidesspecimens 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 further demonstrate that when incorporating carefully selected tests of only the highest preservation quality, robust paleorecords can be generated.

    

   more » « less
3. 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. 

   more » « less
4. 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/ 

   more » « less
5. Correlation between mass, size, and preservation of fossil Cibicidoides shells from the Atlantic and Pacific

   Betancourt, Xavier ; Poirier, Robert K ; Kozdon, Reinhard ( December 2020 , AGU Fall Meeting Abstracts)

   The isotopic and chemical compositions of benthic foraminifera have been used for decades to deduce a broad variety of paleoclimate information. However, there has been little research as to what extent quantitative physical characteristics of benthic foraminifer shells such as their size and mass are related to the quality of their preservation. We used a large data set containing detailed information about individual shell weights, shell sizes, and preservational quality of fossil benthic foraminifera of the genus Cibicidoides from the Pacific ODP Site 846 and the Atlantic ODP Sites 929 and 1089, spanning the last deglaciation (~0-25 ka). We found that during both MIS 1 (~0-8 ka) and 2 (~18-25 ka), smaller and lighter Cibicidoides shells from Pacific Site 846 were typically better-preserved than shells from larger size fractions. Poorly-preserved shells from ODP Site 846 feature a higher mass/size ratio than their better-preserved counterparts that cannot be attributed to the filling of chambers by clay or other contaminant phases. Interestingly, opposite trends were observed at both Atlantic sites, where larger and heavier shells and shells exhibiting higher mass/size ratios are among the best-preserved. These findings point towards minute differences in the ontogenetic development of Cibicidoides shells from Atlantic and Pacific waters, allowing for a better presentation of certain size-ranges, and/or different mechanisms controlling preservation and diagenesis in Atlantic and Pacific deep waters. In addition to these mass/size metrics, we also examine the progression of diagenesis through internal wall structures via SEM images of shell cross sections, as well as the impact on trace metal concentrations measured via LA-ICPMS. 

   more » « less