Foraminiferal amino acid stratigraphy of the Nordic Seas: geological data and pyrolysis experiments

Abstract

Based on pyrolysis experiments and dated geological samples, kinetic parameters for the isoleucine epimerization in the foraminiferal species Neogloboquadrina pachyderma (sin) and Cibicides wuellerstorfi have been calculated. From these parameters and the down core change in the degree of isoleucine epimerization in two cores from the Norwegian Sea, it is concluded that the Norwegian Sea bottom water temperature was 2-4°C higher in oxygen isotope stages 2 and 3 than during stage 5 to 4 and stage i. Compared with epimerization data from the North Atlantic, the Norwegian Sea data suggest a smaller gradient in bottom water temperatures between the oceans during the glacial stages than during the interglacial stages. Geological data suggest a reduction in rate constant for the isoleucine epimerization in N. pachyderma at an alle/Ile ratio close to 0.28, whereas the pyrolysis experiments indicate a higher level for this inflection point. Such a temperature dependency for when the change in reaction rate occurs, could be related to different activation energies for the epimerization and hydrolysis reactions.