40-year long monthly-resolved Sr/Ca record from 2.35 ka Bonaire coral, sample BON-6-A

We present a 40-year long monthly resolved Sr/Ca record from a fossil Diploria strigosa coral from Bonaire (Southern Caribbean Sea) dated with U/Th at 2.35 ka before present (BP). Secondary modifiers of this sea surface temperature (SST) proxy in annually-banded corals such as diagenetic alteration of the skeleton and skeletal growth-rate are investigated. Extensive diagenetic investigations reveal that this fossil coral skeleton is pristine which is further supported by clear annual cycles in the coral Sr/Ca record. No significant correlation between annual growth rate and Sr/Ca is observed, suggesting that the Sr/Ca record is not affected by coral growth. Therefore, we conclude that the observed interannual Sr/Ca variability was influenced by ambient SST variability. Spectral analysis of the annual mean Sr/Ca record reveals a dominant frequency centred at 6-7 years that is not associated with changes of the annual growth rate. The first monthly resolved coral Sr/Ca record from the Southern Caribbean Sea for preindustrial time suggests that fossil corals from Bonaire are suitable tools for reconstructing past SST variability. Coastal deposits on Bonaire provide abundant fossil D. strigosa colonies of Holocene age that can be accurately dated and used to reconstruct climate variability. Comparisons of long monthly resolved Sr/Ca records from multiple fossil corals will provide a mean to estimate seasonality and interannual to interdecadal SST variability of the Southern Caribbean Sea during the Holocene.

Geochemistry of planktonic foraminifera of sediment core MD97-2121

In situ measurements of Mg/Ca, Zn/Ca, Mn/Ca, and Ba/Ca in Globigerinoides bulloides and Globigerina ruber from southwest Pacific core top sites and plankton tow are reported and their potential as paleoproxies is explored. The modern samples cover 20° of latitude from 34°S to 54°S, 7-19°C water temperature, and variable influence of subantarctic (SAW) and subtropical (STW) surface waters. Trace element signatures recorded in core top and plankton tow planktic foraminifera are examined in the context of the chemistry and nutrient profiles of their modern water masses. Our observations suggest that Zn/Ca and Mn/Ca may have the potential to trace SAW and STW. Intraspecies and interspecies offsets identified by in situ measurements of Mg/Ca and Zn/Ca indicate that these ratios may also record changes in thermal and nutrient stratification in the upper ocean. We apply these potential proxies to fossilized foraminifera from the high-resolution core MD97 2121. At the Last Glacial Maximum, surface water Mg/Ca temperature estimates indicate that temperatures were approximately 6-7°C lower than those of the present, accompanied by low levels of Mn/Ca and Zn/Ca and minimal thermal and nutrient stratification. This is consistent with regional dominance of SAW and reduced STW inflow associated with a reduced South Pacific Gyre (SPG). Upper ocean thermal and nutrient stratification collapsed during the Antarctic Cold Reversal, before poleward migration of the zonal winds and ocean fronts invigorated the SPG and increased STW inflow in the early Holocene. Together with reduced winds, this favored a stratified upper ocean from circa 10 ka to the present.