Beschreibung: Four species of planktic foraminifera from core-tops spanning a depth transect on the Ontong Java Plateau were prepared for Mg/Ca analysis both with (Cd-cleaning) and without (Mg-cleaning) a reductive cleaning step. Reductive cleaning caused etching of foraminiferal calcite, focused on Mg-rich inner calcite, even on tests which had already been partially dissolved at the seafloor. Despite corrosion, there was no difference in Mg/Ca of Pulleniatina obliquiloculata between cleaning methods. Reductive cleaning decreased Mg/Ca by an average (all depths) of ~ 4% for Globigerinoides ruber white and ~ 10% for Neogloboquadrina dutertrei. Mg/Ca of Globigerinoides sacculifer (above the calcite saturation horizon only) was 5% lower after reductive cleaning. The decrease in Mg/Ca due to reductive cleaning appeared insensitive to preservation state for G. ruber, N. dutertrei and P. obliquiloculata. Mg/Ca of Cd-cleaned G. sacculifer appeared less sensitive to dissolution than that of Mg-cleaned. Mg-cleaning is adequate, but SEM and contaminants (Al/Ca, Fe/Ca and Mn/Ca) show that Cd-cleaning is more effective for porous species. A second aspect of the study addressed sample loss during cleaning. Lower yield after Cd-cleaning for G. ruber, G. sacculifer and N. dutertrei confirmed this to be the more aggressive method. Strongest correlations between yield and Delta[CO3^2-] in core-top samples were for Cd-cleaned G. ruber (r = 0.88, p = 0.020) and Cd-cleaned P. obliquiloculata (r = 0.68, p = 0.030). In a down-core record (WIND28K) correlation, r, between yield values 〉 30% and dissolution index, XDX, was -0.61 (p = 0.002). Where cleaning yield 〈 30% most Mg-cleaned Mg/Ca values were biased by dissolution.

Beschreibung: A record of deep-sea calcite saturation (D[CO3**-2]), derived from X-ray computed tomography-based foraminifer dissolution index, XDX, was constructed for the past 150 ka for a core from the deep (4157 m) tropical western Indian Ocean. G. sacculifer and N. dutertrei recorded a similar dissolution history, consistent with the process of calcite compensation. Peaks in calcite saturation (~15 µmol/kg higher than the present-day value) occurred during deglaciations and early in MIS 3. Dissolution maxima coincided with transitions to colder stages. The mass record of G. sacculifer better indicated preservation than did that of N. dutertrei or G. ruber. Dissolution-corrected Mg/Ca-derived SST records, like other SST records from marginal Indian Ocean sites, showed coolest temperatures of the last 150 ka in early MIS 3, when mixed layer temperatures were ~4°C lower than present SST. Temperatures recorded by N. dutertrei showed the thermocline to be ~4°C colder in MIS 3 compared to the Holocene (8 ka B.P.).