The Northern Transpolar Gateways
Final Report Abstract
The quality of proxy data for sea surface temperatures (SST) in high-latitude oceans is crucial for the understanding of past changes in Atlantic Meridional Overturning Circulation (AMOC). However, most of the known temperature proxies tend to overestimate temperatures near the “cold end” and thus here hamper accurate paleo-hydrographic reconstructions. Therefore it was a major purpose in the frame of “Denmark Strait” to develop and to test d44/40Ca as a novel “paleothermometer” for the reconstruction of sea surface temperatures (SST) in cold subarctic and polar water masses. Major results are a robust d44/40Ca vs. temperature calibration of the polar planktonic foraminifera Neogloboquadrina pachyderma sin. valid for a temperature range of 3.5° to 8°C. Validity robustly extends to genetically different populations of N. pachyderma sin. in either hemispheres and probably also to extinct ancestors of this species. Below 3.5 °C the sensitivity of the new paleo-thermometer is however lost. A narrow habitat preference of N. pachyderma sin.near the pycnocline could be shown based on paired stable isotope and trace metal signatures. A two-phase biomineralisation model was developed demonstrating differential calcification strategies inherent to cold water foraminifera responsible for the differential d44/40Ca temperature dependency in polar and Atlantic water masses of the Nordic Seas. This model may be also invoked to better understand and to further refine existing geochemical approaches to quantitatively reconstruct temperatures from isotopic and trace metal signals in foraminiferal tests.
Publications
- 2005. Glacial sea-surface temperatures from assemblages of planktonic foraminifera: a framework for regional reconstructions based on multi-technique consensus. Quaternary Science Reviews, 24, 951- 998
Kucera, M., Weinelt, M., Kiefer, T., Pflaumann, U., Hayes, A., Weinelt, M., Barrows, T., Chen, M.-T., Cortijo, E., Duprat, J., and Waelbroeck, C.
- (2007). Calcium isotopic composition of high-latitude proxy carrier Neogloboquadrina pachyderma (sin.). Biogeosciences Discuss., 4, 3301–3330
Hippler, D., Kozdon, R., Darling, K.F., Eisenhauer, A., Nägler, T.F.
- 2007. delta 44/40Ca, Mg/Ca and delta 18O ratios of planktonic foraminifera. PhD thesis, University of Kiel, 2007
Kozdon, R.
- 2008. Ocean Paleotemperatures, In: V. Gornitz (ed.) Encyclopedia of Paleoclimatology, Earth Science Series, Springer
Weinelt, M.
