ALBERT

Description: Recent culture studies of living coccolithophores have established a biogeochemical framework for the use of the geochemical compositions of their calcite biominerals as proxies in palaeoceanography. Yet, questions remain regarding the transferability of such experimental data to fossil coccoliths. Here we analysed the carbon and oxygen isotopic composition of Miocene coccoliths to assess the suitability of such data for reconstructing the past environment. We found that the oxygen isotopic compositions of the relatively small Noelaerhabdaceae coccoliths gathered in the 3-5 μm fractions appear to be a suitable material to derive temperatures after a correction for a constant vital offset of 0.8‰. The interpretation of the isotopic signal of the relatively large Coccolithales coccoliths (5-8 μm fractions) is more complex, but supports results from cultures. The expression of the carbon and oxygen vital effect in coccoliths appears to be limited during the so-called Miocene Climate Optimum (MCO), a period of relatively elevated atmospheric pCO~2~. Subsequently, during the Miocene Climatic Transition (MCT; 14 Ma), which saw a decline in pCO~2, large carbon and oxygen vital effects were expressed in coccolith calcite. This phenomenon predates the postulated “Late Miocene Threshold” by approximately 4 Ma, and cannot be reconciled as a temporally-synchronous nor localised feature. Furthermore, we observed a statistically significant correlation between the oxygen and carbon offsets of the small relative to large coccoliths (hence, the vital effect per se) that is likely linked to variations in atmospheric CO~2~. This biogeochemical correlation further supports a forcing of the environment on the cellular physiology (growth rate and utilisation of intracellular carbon) and ultimately the magnitude of isotopic vital effects in fossil coccoliths.

Description: This data product contains dissolved silicon concentrations and isotopic composition, major ion concentrations and discharge for streams in Potter Peninsula, King George Island and Commonwealth Stream, McMurdo Dry Valleys, Antarctica.

Description: Yellowstone Plateau Volcanic Field, USA: Ge concentrations measured by inductively coupled plasma mass spectrometry (ICP-MS), Si concentrations measured by inductively coupled plasma optical emission spectrometry (ICP-OES), Ge/Si ratio, Si isotope compositions (d30Si and standard deviation SD) measured by Multicollector ICP-MS, concentrations in Ca, Na, Mg, K measured by ICP-OES, and concentrations in SO4 and Cl measured by ion chromatography in thermal waters, major rivers draining the Yellowstone Plateau Volcanic Field, and creeks flowing into Yellowstone Lake.