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We present a global atlas of downcore foraminiferal oxygen and carbon isotope ratios available at 10.1594/PANGAEA.936747 (Mulitza et al., 2021a). The database contains 2106 published and previously unpublished stable isotope downcore records with 361 949 stable isotope values of various planktic and benthic species of Foraminifera from 1265 sediment cores. Age constraints are provided by 6153 uncalibrated radiocarbon ages from 598 (47 %) of the cores. Each stable isotope and radiocarbon series is provided in a separate netCDF file containing fundamental metadata as attributes. The data set can be managed and explored with the free software tool PaleoDataView. The atlas will provide important data for paleoceanographic analyses and compilations, site surveys, or for teaching marine stratigraphy. The database can be updated with new records as they are generated, providing a live ongoing resource into the future. [ABSTRACT FROM AUTHOR]

We present a global atlas of downcore foraminiferal oxygen and carbon isotope ratios available at https://doi.pangaea.de/10.1594/PANGAEA.936747 (Mulitza et al., 2021). The database contains 2,108 published and previously unpublished stable isotope downcore records with 362,067 stable isotope values of various planktonic and benthic species of foraminifera from 1,265 sediment cores. Age constraints are provided by 6,153 uncalibrated radiocarbon ages from 598 (47 %) of the cores. Each stable isotope and radiocarbon series is provided in a separate netCDF file containing fundamental meta data as attributes. The data set can be managed and explored with the free software tool PaleoDataView. The atlas will provide important data for paleoceanographic analyses and compilations, site surveys, or for teaching marine stratigraphy. The database can be updated with new records as they are generated, providing a live ongoing resource into the future. [ABSTRACT FROM AUTHOR]

Abstract: The middle Miocene climate approximately 14 Ma ago was characterized by the glaciation of Antarctica, deep-ocean cooling and variations in the global carbon cycle. Although the Southern Ocean underwent significant oceanographic changes, there is limited information on their spatial extent and timing. However, such knowledge is crucial for understanding the role of the Southern Ocean and the Antarctic Circumpolar Current (ACC) for Antarctic glaciation and the coupling between the ocean and continental climate. We have reconstructed surface temperatures and seawater oxygen isotopes at Ocean Drilling Program (ODP) Site 1092 in the Polar Frontal Zone of the Atlantic sector of the Southern Ocean from foraminiferal oxygen isotopes (δ 18O) and magnesium to calcium ratios (Mg/Ca). Sea surface cooling by ~4 °C and freshening indicated by the ~1‰ reduction of seawater δ 18O (δ 18Osw) at 14.2 Ma precede the major step in Antarctic ice sheet growth at 13.8–13.9 Ma. This pattern qualitatively mirrors previous findings from the Pacific sector, and we interpret the surface hydrographic changes to reflect the circum-Antarctic northward shift of the Southern Ocean fronts and specifically at Site 1092 the passage of the Subantarctic Front. The magnitude of change in reconstructed δ 18Osw requires a δ 18Osw: salinity gradient significantly higher than the modern value (~0.52‰) and it possibly exceeded 1.1‰. This implies the Polar Frontal Zone was influenced by freshwater derived from Antarctica, which in turn confirms higher than modern continental precipitation. The latter has previously been suggested to have contributed to Antarctic glaciation. [Copyright &y& Elsevier]

Abstract: We sampled the upper water column for living planktic foraminifera along the SW-African continental margin. The species Globorotalia inflata strongly dominates the foraminiferal assemblages with an overall relative abundance of 70–90%. The shell δ 18O and δ 13C values of G. inflata were measured and compared to the predicted oxygen isotope equilibrium values (δ 18Oeq) and to the carbon isotope composition of the total dissolved inorganic carbon (δ 13CDIC) of seawater. The δ 18O of G. inflata reflects the general gradient observed in the predicted δ 18Oeq profile, while the δ 13C of G. inflata shows almost no variation with depth and the reflection of the δ 13CDIC in the foraminiferal shell seems to be covered by other effects. We found that offsets between δ 18Oshell and predicted δ 18Oeq in the surface mixed layer do not correlate to changes in seawater [CO3 2−]. To calculate an isotopic mass balance of depth integrated growth, we used the oxygen isotope composition of G. inflata to estimate the fraction of the total shell mass that is grown within each plankton tow depth interval of the upper 500 m of the water column. This approach allows us to calculate the Δδ 13Cinterval added-DIC; i.e. the isotopic composition of calcite that was grown within a given depth interval. Our results consistently show that the Δδ 13CIA-DIC correlates negatively with in situ measured [CO3 2−] of the ambient water. Using this approach, we found Δδ 13CIA-DIC/[CO3 2−] slopes for G. inflata in the large size fraction (250–355 μm) of −0.013‰ to 0.015‰ (μmol kg− 1)− 1 and of −0.013‰ to 0.017‰ (μmol kg− 1)− 1 for the smaller specimens (150–250 μm). These slopes are in the range of those found for other non-symbiotic species, such as Globigerina bulloides, from laboratory culture experiments. Since the Δδ 13CIA-DIC/[CO3 2−] slopes from our field data are nearly identical to the slopes established from laboratory culture experiments we assume that the influence of other effects, such as temperature, are negligibly small. If we correct the δ 13C values of G. inflata for a carbonate ion effect, the δ 13Cshell and δ 13CDIC are correlated with an average offset of 2.11. [Copyright &y& Elsevier]