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1. The Mg/Ca proxy for temperature: A Uvigerina core-top study in the Southwest Pacific

   https://doi.org/https://doi.org/10.1016/j.gca.2021.06.015  

   Cassandre R. Stirpe, Katherine A. (June 2021, Geochimica et cosmochimica acta)

   The Mg/Ca ratio of the infaunal benthic foraminifer Uvigerina peregrina is a commonly used proxy for reconstructing bottom water paleotemperatures because it is hypothesized to be insensitive to changes in bottom water carbonate chemistry. This study presents core-top U. peregrina samples from the southwest Pacific from 0.6 to 4.4 km water depth, corresponding to water temperatures of 1–9
   C. Samples from New Zealand’s Bay of Plenty and Chatham Rise were compared to previous calibrations to assess Mg/Ca temperature sensitivity. Published core-top temperature sensitivies can explain U. peregrina Mg/Ca at a majority of our study sites, with the exception of sites at intermediate depths of ~2.4–3.3 km, where the Mg/Ca ratios are substantially higher than expected from these calibrations, possibly reflecting diagenetic or non-thermal effects. Stable isotope measurements (d18O and d13C), laser ablation analyses, and scanning electron microscope imagery complement trace element measurements to assess variables potentially affecting U. peregrina Mg/Ca at these sites. Morphotype variability, contamination, dissolution, and recrystallization all failed to provide satisfactory explanations for anomalously high Mg/Ca observations. We infer that a non-temperature control, perhaps related to carbonate chemistry, may be affecting the Mg incorporation in some U. peregrina specimens, though no factor has yet been clearly identified. It is unclear whether the factor affecting these sites is constant through time or could vary. For this reason, we recommend that Mg/Ca of recent specimens at each core site should be checked against established calibration curves prior to pursuing down-core paleotemperature reconstructions using U. peregrina. Where possible, paleotemperature estimates should also be validated using other independent proxies. Existing core-top calibrations effectively predict U. peregrina Mg/Ca at the majority of our study sites, but our findings underscore the need for a more thorough understanding of non-temperature factors that can influence Mg/Ca in U. peregrina. 

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2. Thermal and Non‐Thermal Controls on Benthic Foraminiferal Mg/Ca, Sr/Ca, B/Ca, and Mg/Li: Global Core‐Top Compilation, Revised Calibrations, and Application to the Geologic Record

   https://doi.org/10.1029/2025PA005176  

   Nauter‐Alves, Andressa; Evans, David; Katz, Miriam E; Gray, William R; Rae, James_W B; Borrelli, Chiara (December 2025, Paleoceanography and Paleoclimatology)

   Abstract Benthic foraminiferal Mg/Ca, Sr/Ca, B/Ca, and Mg/Li data are used to reconstruct deep‐sea temperature and seawater carbonate chemistry. However, the concurrent influence of various environmental parameters on these proxies is not fully understood. Here, we compile published and unpublished element/Ca core‐top data fromCibicidoides mundulus,C. pachyderma, Lobatula wuellerstorfi,Oridorsalis umbonatus,Nuttallides umbonifera, andUvigerinaspp. to determine the sensitivity of these species' Mg/Ca, Sr/Ca, B/Ca, and Mg/Li to temperature, calcite saturation state (Ω_calcite), dissolved inorganic carbon (DIC), and salinity. By applying multivariate linear regression analysis, we disentangle the effects of these environmental parameters on these species element/Ca. Based on this, we provide multivariate element/Ca calibrations with temperature and Ω_calcitesensitivities for all species‐elemental system combinations. Overall, our analysis reveals that: (a) the Mg/Ca‐sensitivity to temperature is substantially lower compared to most previous approaches when accounting for the effect of Ω_calcite; (b) Sr/Ca is driven dominantly by Ω_calcite; (c) B/Ca can be linearly related to Ω_calcite; and (d) Mg/Li‐temperature calibrations have substantially lower degrees of unexplained variance compared to Mg/Ca. Our calibrations offer a statistically robust approach that also allows us to quantify the uncertainties in the reconstruction of temperature and carbonate chemistry when these element/Ca proxies are used. Finally, we present user‐friendly data processing software (“ElCaRBenthic”) that can simultaneously solve up to two benthic foraminiferal element/Ca data sets for temperature and Ω_calcite(e.g., Mg/Ca and Sr/Ca), while providing the ability to correct for long‐term changes in seawater elemental chemistry and propagating all sources of uncertainty. 

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3. Benthic Foraminiferal Mg-Sr-B-Li/Ca: Interspecies correction factors and environmental reconstructions from the Late Cretaceous to the Paleogene along an Atlantic paleodepth transect

   Nauter-Alves, Andressa; Evans, David; Katz, Miriam E; Borrelli, Chiara (June 2026, FORAMS 2026)

   The magnesium-to-calcium ratio measured on benthic foraminiferal species (Mg/Cabf) is a commonly used proxy for reconstructing deep-ocean temperatures. However, its application over the geological record can be challenging, mostly due to non-thermal effects that influence Mg2+ incorporation into the calcite lattice. Previous work showed that the deep-sea carbonate chemistry, such as the carbonate ion saturation ([CO32-]) or the calcite saturation state (Ωcalcite), can reduce the Mg/Cabf sensitivity to temperature. In addition, interspecies element/Ca offsets complicate the use of multiple benthic foraminiferal species in the same samples. In this study, we present downcore measurements of Mg/Cabf and Sr-B-Li/Cabf to reconstruct temperature and carbonate chemistry from ~23 to ~76 Ma. We analyzed element/Ca ratios (89 samples) in multiple benthic foraminiferal species (Cibicidoides hyphalus, C. mundulus, C. praemundulus, C. proprius, C. pseudoperlucidus, C. velascoensis, Nuttallides umbonifera, N. truempyi, O. umbonatus, P. costata, P. renzi, S. beccariiformis) in samples located at different paleodepths in the Atlantic Ocean and spanning the Late Cretaceous and Paleogene. Benthic foraminiferal element/Ca data were collected using Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). Test preservation and contamination were assessed by measuring test Al-Mn-Si-Fe/Ca. Selected specimens were also analyzed using a Scanning Electron Microscope. The statistical treatment of our data shows that the correlation between Mg/Cabf and B/Cabf is very weak (Spearman’s ρ=0.01), whereas Mg/Ca and Sr/Ca show a moderate correlation (ρ=0.4). The strongest relationship is observed between Mg/Ca and Li/Ca (ρ= 0.7). Linear regression analysis demonstrates that C. hyphalus, C. praemundulus, N. truempyi, and S. beccariiformis present statistically significant correlations (p-value <0.05) with O. umbonatus, with R2 values ranging from 0.56 (S. beccariiformis) to 0.76 (C. hyphalus). The element/Ca variability among species exhibits a paleodepth gradient, with sites located at 3000-3500 m showing lower element/Ca compared to sites at 2300–2400 m and 1000–1400 m within time slices. The moderate correlation between Mg/Cabf and Sr-Li/Cabf, alongside the observed paleodepth element/Ca gradient, indicates that interspecies element/Ca variability is likely influenced by the depth-related variation in Ωcalcite. Overall, the data collected in this study will improve our ability to reconstruct deep-sea temperature and Ωcalcite in the Late Cretaceous and Paleogene. In addition, we show that the application of species-specific correction factors can result in trace element records that can be evaluated using coretop O. umbonatus calibrations, thus providing a method of reconstructing deep ocean temperature and saturation state in the absence of extant species. 

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4. Evaluating primary and secondary influences on benthic foraminiferal Mg/Ca, Mg/Li, Sr/Ca, and B/Ca: A global coretop compilation and revised species-specific calibrations

   Nauter-Alves, Andressa; Evans, David; Katz, Miriam E; Gray, William R; Rae, James; Borrelli, Chiara (June 2026, FORAMS 2026)

   Benthic foraminiferal Mg/Ca and Mg/Li are often used to reconstruct deep-sea temperatures, whereas Sr/Ca and B/Ca are proxies used to estimate past seawater carbonate chemistry. Thus, these geochemical proxies are essential to investigating past oceanic environmental conditions. However, their interpretation remains challenging because the influence of additional variables on element/Ca of the benthic foraminiferal calcite is still not fully understood. To address this gap, we compiled published and unpublished element/Ca coretop datasets for multiple benthic foraminiferal species (Cibicidoides mundulus, C. pachyderma, Lobatula wuellerstorfi, Oridorsalis umbonatus, Nuttallides umbonifera and Uvigerina spp.). We reanalyzed these datasets to determine the sensitivity of each species’ Mg/Ca, Mg/Li, Sr/Ca, and B/Ca to in situ temperature and calcite saturation state (Ωcalcite), simultaneously using a multivariate linear regression analysis. Although we also explored models including dissolved inorganic carbon (DIC) and salinity, these parameters did not improve the explained variance in the element/Ca dataset and were therefore not included in the linear regression analysis. Overall, our results indicate that, compared to previous studies, the Mg/Ca sensitivity to temperature is reduced when the Ωcalcite is included in the regression analysis, whereas Mg/Li yields more precise and accurate temperature reconstruction with no significant influence from Ωcalcite. In addition, Sr/Ca and B/Ca are primarily controlled by Ωcalcite across species, although C. pachyderma Sr/Ca also exhibits a temperature influence. We further demonstrate that, based on the coretop analysis, the accuracy and precision of temperature and carbonate chemistry reconstructions depend on the species-specific calibrations. Finally, based on our multivariate regression results, we developed a user-friendly processing software (ElCarBenthic) that can be used to reconstruct deep-sea temperatures and the carbonate chemistry by combining benthic foraminiferal Mg/Ca or Mg/Li with Sr/Ca or B/Ca measurements, while fully propagating reconstruction uncertainties. 

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5. Core top compilation of published and unpublished benthic foraminiferal Mg/Ca, Sr/Ca, B/Ca, and Li/Ca data

   https://doi.org/10.1594/pangaea.986730  

   Nauter-Alves, Andressa; Evans, David; Katz, Miriam E; Gray, William Robert; Rae, James_W B; Borrelli, Chiara (January 2025, PANGAEA)

   Here we present a compilation of published and unpublished globally-distributed core top Mg/Ca, Sr/Ca, B/Ca, and Li/Ca data for Cibicidoides mundulus, C. pachyderma, Lobatula wuellerstorfi, Nuttallides umbonifera, Oridorsalis umbonatus, and Uvigerina spp. Species-specific data are accompanied by information on water depth, geographic coordinates, and core identifiers. Bottom water properties (temperature, salinity, pH, delta-carbonate saturation) were compiled from published sources. Hydrographic parameters were recalculated here using the World Ocean Atlas of Temperature (WOAT, Locamini et al., 2018), and World Ocean Atlas of Salinity (WOAS, Zweng et al., 2019). Carbonate chemistry parameters were calculated using CO2SYS (Lewis et al., 1998) using Total Alkalinity (GLODAP), pre-industrial DIC (Lauvset et al., 2016), WOAT, and WOAS estimates. File descriptions: Column Descriptions:Event - Unique identifier for core sitesBasin - Ocean basin (e.g., Atlantic, Pacific)Latitude [°N] - Site latitude in decimal degreesLongitude [°E] - Site longitude in decimal degreesWater Depth [m] - Depth of the seafloor at the siteBWT (source) [°C] - Bottom water temperature reported in the original publicationpH (source) - In-situ pH from original publicationSalinity (source) [psu] - Salinity reported in the original publicationΔ[CO₃²⁻] (source) [µmol/kg] - delta-carbonate saturation reported in the original publicationBWT (WOA) [°C] - Interpolated bottom water temperature from World Ocean Atlas (Locamini et al., 2018)Salinity (WOAS) [psu] - Salinity from World Ocean Atlas (Zweng et al., 2019)pH (WOA) - pH calculated using CO2SYS (Lewis et al., 1998)Ω Calcite - calculated using CO2SYS (Lewis et al., 1998)1 / (Ω²) - Inverse square of saturation stateDIC [µmol/kg] - Dissolved Inorganic Carbon from pre-industrial values (Lauvset et al., 2016)Alkalinity [µmol/kg] - Total Alkalinity derived from Global Ocean Data Analysis Project (GLODAP)CO₃²⁻ [µmol/kg] - Carbonate ion concentration, calculated using CO2SYS (Lewis et al., 1998)Species - Benthic foraminiferal species considered in the compilationMorphotype - Morphological variant, if relevantMg/Ca [mmol/mol] - Mg/Ca ratio data in mmol/molMg/Ca: flagged - Quality flag for Mg/Ca value (e.g., analytical outlier), as reported in the original publicationMg/Ca: contamination - Contamination indicator when specified in the original publicationTemperature flag - Indicates of BWT temperature estimate that that is offset from the original publicationB/Ca [µmol/mol] - B/Ca ratio data in µmol/molB/Ca: flagged - Quality flag for B/Ca value (e.g., analytical outlier), as reported in the original publicationB/Ca: contamination - contamination - Contamination indicator when specified in the original publicationLi/Ca [µmol/mol] - B/Ca ratio data in µmol/molLi/Ca: flagged - Quality flag for Li/Ca value (e.g., analytical outlier), as reported in the original publicationLi/Ca: contamination - contamination - Contamination indicator when specified in the original publicationSr/Ca [mmol/mol] - B/Ca ratio data in mmol/molSr/Ca: flagged - Quality flag for Sr/Ca value (e.g., analytical outlier), as reported in the original publicationCleaning - Indicates the cleaning protocol used during analysis according to the original publication (e.g.,oxidative)Method - Analytical technique used (e.g., ICP-OES)Reference - Reference for published dataURL source - URL from original publicationComments - Notes on individual data points 

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