Assessing the effects of calcite saturation on the benthic foraminiferal Mg/Ca-temperature relationship using a homothermal depth transect in the Norwegian Sea

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Under this award the PIs will be address the question: What is the effect of calcite saturation on the Mg/Ca - temperature relationship in benthic foraminifera?They propose an 11 day cruise in the Norwegian Sea to collect about 30 multi-cores and 15 giant gravity cores that cover a range of calcite saturation levels at constant temperature and salinity. Benthic foraminiferal Mg/Ca from lightly saturated waters display a steep decrease with increasing water depth. The current global Mg/Ca-temperature relationship can only explain a fraction of the decrease, leading to the hypothesis that the degree of calcite saturation also affects benthic foraminiferal Mg/Ca at the low temperatures typical of themajority of the deep ocean. The depth transect from the homothermal and homohaline Norwegian Sea, that was previously studied by Mackensen et al., (1985) provides an ideal opportunity not only to test the hypothesis, but also to quantify the Mg/Ca - calcite saturation relationship at low temperatures. The PI propose to reoccupy the sites that were used for the Mackensen et al. 1985 faunal study (). Based on that study, they expect a high abundance of live benthic foraminifera. To further test their hypothesis they propose studying two down-core records (one spanning the HL-LGM transition at 150 yr resolution and one record spanning 0 to 35 ka at 250 yr resolution). Because Norwegian Sea's bottom water temperature (BWT) is close to freezing, they expect little Glacial-Interglacial variation. Any significant down-core change would suggest additional control on Mg/Ca ratios in benthic foraminifera.