Oxygen and carbon isotopes were measured for several planktonic foraminifera species (Globigerina bulloides, Neogloboquadrina pachyderma sinistral (sin.), Globoconella spp.) and the benthic foraminifera genus Cibicidoides spp. in samples from Ocean Drilling Program (ODP) Site 1088B. Typically, 10-15 planktonic specimen and five benthic specimen larger than 150μm were picked per sample. Foraminifera were crushed, rinsed twice with deionized water and once with MeOH and dried overnight at 50°C. Samples were analyzed at ETH Zurich on a GAS BENCH II system coupled to a Delta V Plus irMS (Thermo Scientific) following procedures described by Breitenbach and Bernasconi (2011). Analytical precision after system calibration by two in-house standards and international standards NBS-19 and NBS-18 was 0.07‰ for both stable isotopes. Values are reported relative to the VPDB standard.
Different alkenone ratios (U_37^k' and C37.2/C38.2) were directly estimated with a Thermo Scientific Trace 1310 Gas Chromatograph (GC) equipped with a flame ionization detector (FID). Lab-sample replicates and in-house alkenone standard were injected every sequence to determine instrument drift and to guarantee long-term validation giving a precision of 0.025 U_37^k' units. Alkenone-derived SST was calculated from U_37^k' using the global calibration from Müller et al. (1998).
Carbon isotopic compositions of C37.2 alkenones were measured on a Thermo Scientific Delta V mass spectrometer interfaced with a Thermo Scientific Trace 1310 Gas Chromatograph (GC-irMS) at ETH Zurich. Replicates, in-house alkenone standard, and known isotopic mixtures A5 and B4 (supplied by Arndt Schimmelmann, Univ. of Indiana) were injected at every sequence to determine the analytical accuracy of the measurement and an uncertainty of 0.4‰ is reported. Carbon isotopes are reported relative to the Vienna PeeDee Belemnite (VPDB) standard.
The isotopic fractionation (εp) during photosynthetic fixation of carbon between [CO2]aq and algal biomass is calculated using the equation originally described by Freeman and Hayes (1992). The carbon isotopic composition of C37.2 alkenones represents the organic part whereas carbon isotopes from the planktonic formaninifera species N. pachyderma sin. are used as an assumption of dissolved inorganic carbon. To carefully include and propagate the uncertainties of each parameter introduced, a full Monte Carlo simulation (n = 10'000) was conducted and the respective 1 sigma confidence intervals are reported in this table.
A quantitative estimation of the mean size of the alkenone producing coccolithophorid Reticulofenestra pseudoumbilicus was carried out using polarized light microscopy and the C-Calcita software (Fuertes et al., 2014).
