ALBERT

Description: The progress of science is tied to the standardization of measurements, instruments, and data. This is especially true in the Big Data age, where analyzing large data volumes critically hinges on the data being standardized. Accordingly, the lack of community‐sanctioned data standards in paleoclimatology has largely precluded the benefits of Big Data advances in the field. Building upon recent efforts to standardize the format and terminology of paleoclimate data, this article describes the Paleoclimate Community reporTing Standard (PaCTS), a crowdsourced reporting standard for such data. PaCTS captures which information should be included when reporting paleoclimate data, with the goal of maximizing the reuse value of paleoclimate data sets, particularly for synthesis work and comparison to climate model simulations. Initiated by the LinkedEarth project, the process to elicit a reporting standard involved an international workshop in 2016, various forms of digital community engagement over the next few years, and grassroots working groups. Participants in this process identified important properties across paleoclimate archives, in addition to the reporting of uncertainties and chronologies; they also identified archive‐specific properties and distinguished reporting standards for new versus legacy data sets. This work shows that at least 135 respondents overwhelmingly support a drastic increase in the amount of metadata accompanying paleoclimate data sets. Since such goals are at odds with present practices, we discuss a transparent path toward implementing or revising these recommendations in the near future, using both bottom‐up and top‐down approaches.

Description: The boron isotopic ratio of 11B/10B (δ11BSRM951) and trace element composition of marine carbonates are key proxies for understanding carbon cycling (pH) and palaeoceanographic change. However, method validation and comparability of results between laboratories requires carbonate reference materials. Here, we report results of an inter‐laboratory comparison study to both assign δ11BSRM951 and trace element compositions to new synthetic marine carbonate reference materials (RMs), NIST RM 8301 (Coral) and NIST RM 8301 (Foram) and to assess the variance of data among laboratories. Non‐certified reference values and expanded 95% uncertainties for δ11BSRM951 in NIST RM 8301 (Coral) (+24.17‰ ± 0.18‰) and NIST RM 8301 (Foram) (+14.51‰ ± 0.17‰) solutions were assigned by consensus approach using inter‐laboratory data. Differences reported among laboratories were considerably smaller than some previous inter‐laboratory comparisons, yet discrepancies could still lead to large differences in calculated seawater pH. Similarly, variability in reported trace element information among laboratories (e.g., Mg/Ca ± 5% RSD) was often greater than within a single laboratory (e.g., Mg/Ca 〈 2%). Such differences potentially alter proxy‐reconstructed seawater temperature by more than 2 °C. These now well‐characterised solutions are useful reference materials to help the palaeoceanographic community build a comprehensive view of past ocean changes.

Description: The ratio of sodium to calcium (Na/Ca) in foraminiferal calcite has been proposed as a proxy for salinity, yet relatively little is known about the incorporation of sodium into the shells of foraminifera. Ongoing debates include the location of Na in the calcite crystal lattice, the possibility that at least some Na might be complexed with organics, and the influence of spines/spine bases. We present new Na/Ca measurements, determined using both solution and laser ablation ICP-MS, of the planktonic foraminifera Globigerinoides ruber (white) from plankton tows and sediment traps spanning a wide salinity range (32.5–40.7 salinity units), laboratory cultures under varying carbonate chemistry, and globally-distributed core-top samples. Our results show that Na/Ca in recently living foraminifera measured by laser ablation ICP-MS is elevated by up to 5 mmol/mol (∼85%) relative to the same samples measured by solution ICP-MS (the same comparison for Mg/Ca shows excellent agreement between the techniques). Na/Ca in recently living foraminifera measured by laser ablation ICP-MS displays a significant relationship with salinity above ∼36 salinity units with a slope of ∼0.7 mmol/mol/salinity unit; however, only a weak relationship is observed between salinity and Na/Ca measured by solution ICP-MS. We propose that Na is incorporated in at least two discrete phases; a primary phase within the CaCO3 mineral, and a (or likely multiple) secondary phase(s). Possibilities for these secondary phases include residual metastable CaCO3, fluid inclusions, high Na/Ca spine bases, and organics. These secondary phases contribute to spatially-resolved analyses (i.e. laser ablation ICP-MS) of recently living foraminifera but are removed by crushing/oxidative cleaning for solution ICP-MS, and during early diagenesis, as evidenced by the agreement between laser analysis of coretop samples and Na/Ca measured by solution. The amount of one of these secondary phases, or the amount of Na within this phase, appears to vary as a function of salinity, and is likely the principal driver of the previously observed steep Na/Ca-salinity relationship in recently living foraminifera analysed by laser ablation. Overall, we find salinity, temperature, carbonate chemistry, and bottom water saturation state (Ωcalcite) all have a significant but relatively weak effect on Na/Ca in the primary calcite phase. As such, Na/Ca in planktonic foraminifera recovered from sediment cores is unlikely to find widespread utility as a salinity proxy.

Description: Seawater chemistry exerts an important control on the incorporation of trace elements into the shells of marine calcifying organisms. Variability in the major ion chemistry of seawater is a tracer of past geological processes, and the influence of seawater chemistry on trace element incorporation in calcium carbonate can be harnessed to determine changes in the composition of seawater through time. Here, we investigate whether key oceanographic parameters (temperature, salinity, and the carbonate system) affect the incorporation of potassium (K) into foraminiferal calcite, and explore the utility of K/Ca ratios in foraminifera as an indicator of past variability in the seawater Ca2+ concentration. We analysed both low-Mg and high-Mg modern foraminifera, including planktonic (Globigerinoides ruber) and shallow-dwelling larger benthic (Operculina ammonoides) species, using laser-ablation sector-field inductively-coupled plasma mass spectrometry (LA-SF-ICPMS). Both species show no resolvable influence of temperature, salinity, pH, or [CO32−] on K incorporation across the range that these vary at our samples sites. In order to determine the effect of the seawater Ca concentration ([Ca2+]sw) on K incorporation, we analysed laboratory-cultured O. ammonoides, the close living relative of the abundant Eocene Nummulites, grown at four different [Ca2+]sw. We find a significant relationship between seawater and shell K/Ca, albeit with a shallower slope compared to most other trace elements which we suggest is driven by a crystal growth rate effect on K incorporation, constrained using culture experiments of O. ammonoides grown at different pH. If the K+ concentration has remained relatively constant throughout the Phanerozoic Eon, our data may pave the way forward for the use of K/Ca as a direct proxy for past [Ca2+]sw variability. Alternatively, coupling K/Ca with the similar Na/Ca proxy would allow more accurate reconstruction of [Ca2+]sw or verification of whether [K+]sw and [Na+]sw have indeed remained within narrow bounds.

Description: Paleotemperature proxy data form the cornerstone of paleoclimate research and are integral to understanding the evolution of the Earth system across the Phanerozoic Eon. Here, we present PhanSST, a database containing over 150,000 data points from five proxy systems that can be used to estimate past sea surface temperature. The geochemical data have a near-global spatial distribution and temporally span most of the Phanerozoic. Each proxy value is associated with consistent and queryable metadata fields, including information about the location, age, and taxonomy of the organism from which the data derive. To promote transparency and reproducibility, we include all available published data, regardless of interpreted preservation state or vital effects. However, we also provide expert-assigned diagenetic assessments, ecological and environmental flags, and other proxy-specific fields, which facilitate informed and responsible reuse of the database. The data are quality control checked and the foraminiferal taxonomy has been updated. PhanSST will serve as a valuable resource to the paleoclimate community and has myriad applications, including evolutionary geochemical, diagenetic, and proxy calibration studies.