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  1. Element-calcium ratios in the skeleton of cold-water coral Desmophyllum dianthus represent potential archives for paleo-reconstruction of several ocean properties including temperature and nutrient concentrations. However, relatively large uncertainties in these proxy calibrations and heterogeneity in the skeletal composition have limited its application to date. We address these issues by analyzing corals cultured under systematically varied seawater conditions (phosphate, barium, temperature, pH, feeding frequency) over a two-year period, and refine the calibration of P/Ca, Ba/Ca, U/Ca, and Li/Mg proxies for seawater phosphate, barium, carbonate ion concentration, and temperature, respectively. Composition of the corals is determined using laser-ablation ICPMS, with robust plasmamore »conditions established using the Normalized Argon Index [1], and proxy element incorporation is evaluated for influences of temperature, pH, and feeding frequency. The aragonite precipitated during the stages of the culturing experiment is identified using fluorescent and geochemical labelling of the skeleton through calcein and lead isotopes, respectively. This approach allows us to resolve monthly and annual increments in these slow growing (1-2mm/year) organisms, and also to evaluate the influence of calcification rate on the composition. We address the issue of heterogeneity by adapting methods for LA-ICPMS imaging to create macroscale images to reveal the full pattern of skeletogenesis and related compositional variability of D. dianthus. Preliminary images suggest that heterogeneity stems from the asymmetric precipitation of aragonite, and from centers of calcification (also known as early mineralization zones) that complicate the interpretation of elemental signals throughout the skeleton, but also help to identify new skeletal regions suitable for proxy measurement. Finally, we also discuss the role of endolithic organisms in some of these specimens. [1] Fietzke, J. & Frische, M. (2016), J. Anal. At. Spectrom. 31, 234–244.« less
  2. 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 FPImore »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.« less
  3. 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 FPImore »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.« less
  4. Abstract EP43E-2415
  5. Abstract PP23C-1667
  6. Abstract Neogloboquadrina pachyderma is the dominant species of planktonic foraminifera found in polar waters and is therefore invaluable for paleoceanographic studies of the high latitudes. However, the geochemistry of this species is complicated due to the development of a thick calcite crust in its final growth stage and at greater depths within the water column. We analyzed the in situ Mg/Ca and δ18O in discrete calcite zones using laser ablation‐inductively coupled plasma‐mass spectrometry, electron probe microanalysis, and secondary ion mass spectrometry within modern N. pachyderma shells from the highly dynamic Fram Strait and the seasonally isothermal/isohaline Irminger Sea. Here wemore »compare shell geochemistry to the measured temperature, salinity, and δ18Osw in which the shells calcified to better understand the controls on N. pachyderma geochemical heterogeneity. We present a relationship between Mg/Ca and temperature in N. pachyderma lamellar calcite that is significantly different than published equations for shells that contained both crust and lamellar calcite. We also document highly variable secondary ion mass spectrometry δ18O results (up to a 3.3‰ range in single shells) on plankton tow samples which we hypothesize is due to the granular texture of shell walls. Finally, we document that the δ18O of the crust and lamellar calcite of N. pachyderma from an isothermal/isohaline environment are indistinguishable from each other, indicating that shifts in N. pachyderma δ18O are primarily controlled by changes in environmental temperature and/or salinity rather than differences in the sensitivities of the two calcite types to environmental conditions.« less
  7. 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 themore »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/« less
  8. 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 millionmore »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.« less