NITROGEN ISOTOPES OF AMINO ACIDS IN (SUB-) FOSSIL BIVALVE (ARCTICA ISLANDICA) SHELLS

Compound-specific nitrogen isotope analysis of individual amino acids (CSIA-δ¹⁵N_AA) overcomes challenges of bulk δ¹⁵N and enables precise estimates of the nitrogen isotope baseline and the trophic position (TP) from organisms of the food web. By applying this technique to the organics of bivalve mollusk shells, it allows to reconstruct the variability of the nitrogen sources in aquatic ecosystems and changes in the basal food web through time. An essential prerequisite to reconstructing these ecological variables using bivalve shells is to understand if the pristine isotope signals can be retrieved from shell organics. Intra-crystalline organic matrix (intra-OM), which is trapped within biomineral units and less likely contaminated, might be a good candidate for CSIA-δ¹⁵N_AA of (sub-) fossil shells. Here we present the δ¹⁵N_AA and AA composition data from the total organics and isolated intra-OM of radiocarbon dated sub-fossil shells, which are then compared to the results of modern shells. By analyzing the nitrogen isotope values in the source AA, phenylalanine, as well as the estimated TP of the fossil specimens, we explore potential changes in the marine basal food web in the northern North Sea during the Holocene. This study provides perspectives on the CSIA method in palaeoceanographic and palaeoecological studies.

Primary Presenter: Qian Huang, University of Mainz (qhuang01@uni-mainz.de)

Authors:

Qian Huang, University of Mainz  (qhuang01@uni-mainz.de)

Lukas Fröhlich, University of Mainz  (lufroehl@uni-mainz.de)

Bernd Schöne, University of Mainz  (schoeneb@uni-mainz.de)