Restrictions in Mg/Ca-Paleotemperature Estimations in High-Latitude Bottom Waters: Evidence from the Fram Strait and the Nordic Seas

Thursday, 18 December 2014
Kirstin Werner1, Thomas M Marchitto Jr2, Christelle Not3, Robert F Spielhagen3 and Katrine Husum4, (1)Byrd Polar Research Center, Columbus, OH, United States, (2)Institute for Arctic and Alpine Research and Univ Colorado, Boulder CO, USA, Boulder, CO, United States, (3)GEOMAR Helmholtz Centre for Ocean Research, Kiel, Germany and Academy of Sciences, Humanities, and Literature, Mainz, Germany, Kiel, Germany, (4)Norwegian Polar Institute, Tromsø, Norway
Mg to Ca ratios of the benthic foraminifer species Cibicidoides wuellerstorfi provide a great potential for reconstructing bottom water temperatures, especially from the lower end of the temperature range between 0 and 6°C (Tisserand et al., 2013). A set of core top samples from the Fram Strait and the Norwegian margin have been studied for Mg/Ca ratios in C. wuellerstorfi in order to establish a calibration relationship to the environmental conditions. In this part of the northern North Atlantic the bottom water temperature range between -0.5 and -1°C. For the calibration to modern water mass conditions, modern oceanographic data from both existing conductivity-temperature-depth (CTD) casts and the World Ocean Data Base 2013 (Boyer et al., 2013) have been used. Benthic Mg/Ca ratios are relatively high suggesting a preference of C. wuellerstorfi to incorporate Mg below 0°C. Although no correlation has been found to existing temperature calibrations, the data are in line with earlier Mg/Ca data from C. wuellerstorfi in the area (Martin et al., 2002; Elderfield et al., 2006). The carbonate ion effect is most likely a main cause for the relatively high Mg/Ca ratios found in core top samples from the Fram Strait and the Nordic Seas, however, other factors may influence the values as well. Holocene records of benthic trace metal/Ca ratios from the eastern Fram Strait display trends similar to those found in other proxy indicators, despite the difficulties to constrain a temperature calibration for this low temperature range. In particular, the benthic B/Ca and Li/Ca records resemble trends in Holocene planktic foraminifer assemblages, suggesting to be influenced by environmental factors such as the carbonate ion effect consistent for the entire water column.