Description: Here we performed pulse-chase experiments with 13C-enriched dissolved inorganic carbon, followed by TEM and quantitative NanoSIMS isotopic imaging to visualize photosynthetic C assimilation by individual symbiotic dinoflagellates and subsequent translocation to their Orbulina universa host. NanoSIMS image processing was carried out as described in LeKieffre et al. (2017) and Nomaki et al. (2018). Briefly, TEM images were aligned with corresponding NanoSIMS 12C14N- images (Online Resource 1) using the software Look@NanoSIMS (Polerecky et al. 2012), which allows a user to hand-draw regions of interest (ROIs) corresponding to different organelles (e.g., dinoflagellate starch grains, foraminiferal lipid droplets, and fibrillar bodies). For each type of organelle and each time point, the average 13C-enrichment and its standard deviation were calculated based on 3 replicate foraminifera (except for the 6 h and 30 h time points, where only 2 replicates were available). The ROIs drawn on TEM images were also used to assess the relative abundance (in %) of lipid droplets in the foraminiferal endoplasm and starch grains in the dinoflagellate cytoplasm, respectively. Lipid droplet abundance was determined as the number of pixels occupied by lipid droplets divided by the total number of pixels of foraminiferal endoplasm. Starch grain abundance was determined as the number of pixels of occupied by starch grains divided by the total number of pixels covering dinoflagellate cytoplasm.

Description: Dataset contains seawater and foraminiferal chemical composition from the paper referenced above. Paper abstract: Ba/Ca ratios in many non-spinose planktic foraminifera are markedly higher than those observed in spinose planktic species, but the cause for these high Ba/Ca ratios is not understood. A better understanding of this geochemical anomaly could provide insights into the habitat and/or controls over Ba incorporation in these species and expand their utility in paleoclimate research. In spinose species, shell Ba/Ca depends only on the Ba/Ca ratio of seawater. Proposed explanations for high non-spinose Ba/Ca include (1) the empirical partition coefficient, DBa, differs from the spinose species, (2) shell Ba varies with seawater temperature and pH, or (3) non-spinose foraminifers have a preference for prey that has elevated Ba. We performed laboratory culture experiments to determine DBa for the thermocline-dwelling non-spinose planktic foraminifer Neogloboquadrina dutertrei. We find that the Ba/Ca ratio of foraminiferal calcite secreted in the laboratory varies linearly with the Ba/Ca ratio of the seawater. The DBa for this species, 0.11 ± 0.008 (2SE; 95% CL), is similar to the DBa for spinose species (0.13 ± 0.004, 2SE; 95% CL). As in spinose species, the Ba/Ca ratio of cultured specimens of N. dutertrei is not influenced by culture temperature (12-22 °C) or seawater pHNBS (range 7.8-8.3). However, the Ba/Ca ratio of individual plankton-tow N. dutertrei specimens that completed their lifecycle in the ocean exceeds the Ba/Ca ratio of cultured specimens by up to three orders of magnitude. It is unlikely this difference between cultured specimens and ocean-grown specimens is due to seawater [Ba] variability, since seawater Ba/Ca ratios calculated using our DBa are much higher than exist in the ocean. Rather, we suggest that elevated shell Ba/Ca in plankton tow and fossil N. dutertrei is due to calcification in the microenvironment of marine organic aggregates such as marine snow, where [Ba] is elevated as a result of Ba release from biogenic particulates.

Description: Estimates of the change in surface seawater d18O (d18Osw) between the Last Glacial Maximum (LGM) and Late Holocene (LH) are derived from homogenous data sets with rigorous age control, namely MARGO sea surface temperature (SST) estimates and oxygen isotopic ratios (d18O) of planktonic foraminifers. Propagation of uncertainties associated with each proxy allows the identification of robust patterns of change in d18Osw. Examination of these patterns on a regional scale highlights which changes in surface currents and hydrological cycle are consistent with both planktonic isotopic data and reconstructed SST.

Description: Mg/Ca ratio paleothermometry in foraminifera is an important tool for the reconstruction and interpretation of past environments. However, existing Mg/Ca:temperature relationships for planktic species inhabiting mid- and high- latitude environments are limited by a lack of information about the development and impact of low-Mg/Ca ratio “crusts” and the influence of the carbonate system on Mg/Ca ratios in these groups. To address this, we cultured individual specimens of Neogloboquadrina incompta and Neogloboquadrina pachyderma in seawater across a range of temperature (6 °- 12 °C) and pH (7.4 – 8.2). We found by laser ablation inductively couple mass spectrometry analyses of shells that culture-grown crust calcite in N. incompta had a lower Mg/Ca ratio than ontogenetic calcite formed at the same temperature, suggesting that temperature is not responsible for the low Mg/Ca ratio of neogloboquadrinid crusts. The Mg/Ca:temperature relationship for ontogenetic calcite in N. incompta was consistent with the previously published culture-based relationship and no significant relationship was found between Mg/Ca ratios and pH in this species. However, the Mg/Ca ratio in laboratory cultured N. pachyderma was much higher than that reported in previous core-top and sediment trap samples, due to lack of crust formation in culture. Application of our ontogenetic calcite-specific Mg/Ca:temperature relationships to fossil N. pachyderma and N. incompta from five intervals in cores from the Santa Barbara Basin and the Bering Sea show that excluding crust calcite in fossil specimens may improve Mg/Ca-based temperature estimates.

Description: The calcite shells, or tests, of foraminifera provide a window into Earth history because they are archived in most marine sediments and contain useful geochemical proxies for paleoceanography. Previous observations of diurnal heterogeneity in proxies like Mg/Ca demonstrate a complex relationship between environmental conditions and test composition. The causes for this diurnal banding and the potential impact for proxy interpretation in systems other than Mg/Ca have yet to be determined. Recently, Mg and Na in shells of the planktic foraminifer species Orbulina universa have been observed to be high at the location of the primary organic sheet (POS), i.e. the organic template upon which the calcite test is formed. Here we use time-of-flight secondary ion mass spectrometry (ToF-SIMS), a chemical and isotope mapping technique with a spatial resolution of 300 nm, to show that Na banding is a consistent feature in the tests of 45 individual cultured O. universa. This banding occurs in two distinct forms: (1) sharp Na bands associated with organic sheets that are embedded in the calcite test after chamber formation; and (2) regular, thicker, but lower-amplitude Na bands that are found throughout the test. We use the pattern of the first type of banding to indicate the extent and sequence of calcite growth during chamber formation. Specifically, we show that new chamber formation involves growth over the previous chamber in Orbulina bilobata, a morphotype of O. universa that develops a second partial spherical chamber attached to the primary sphere. This is consistent with a bilamellar model of foraminiferal growth. However, a SIMS mapping survey of the morphologically more complex Globigerina bulloides and Neogloboquadrina dutertrei suggests that the pattern of growth during chamber formation and the prevalence of different types of Na bands may be species-specific. The wide, repeating Na bands that occur throughout the test of O. universa generally occur in an inverse pattern with respect to Mg banding for the first few days of the foraminifer's life, but this pattern changes as the organism ages. We use the magnitude, timing, and coherency between Na and Mg bands to put constraints on various proposed mechanisms for banding, including antiport Mg2+-2Na+ exchange and kinetic growth rate effects.