Amino acid δ13C records from deep-sea corals of the NW Atlantic: Reconstructing plankton community composition in a rapidly changing ocean

Owen Sherwood1, Chelsea Renée Fougère1, Blake S Tibert2 and Kelton McMahon3, (1)Dalhousie University, Department of Earth and Environmental Sciences, Halifax, NS, Canada, (2)Dalhousie University, NS, Canada, (3)University of Rhode Island, Graduate School of Oceanography, Narragansett, RI, United States
Deep-sea corals of the species Primnoa resedaeformis secrete annually-banded, two-part skeletons of calcite and a diagenetically-resistant, fibrillar protein. The protein component is derived from sinking particles and thus records the geochemistry of export productivity over the century scale lifespans of individual colonies. Previous work on bulk and amino acid-specific δ15N records from Primnoa colonies from the Northeast Channel, offshore Nova Scotia, documented an anomalous 20th century decrease in δ15N that was attributed to increasing northward advection of Gulf Stream-associated waters along the continental slope (Sherwood O.A., et al., Proc. Nat. Acad. Sci. 108(3), 1011-1015, 2011). Here we examine δ13C records spanning from the year 1935 to present from the same original suite of Primnoa colonies and additional colonies collected more recently. Records of bulk δ13C from different colonies show remarkable reproducibility over interannual timescales, with an amplitude of 2 ‰ after correcting for the Suess effect. The δ13C of essential amino acids (δ13CEAA) was more variable than that of bulk δ13C, up 5‰ for phenylalanine. Isotope mixing models [McMahon K.W., et al., Science 350(6267), 1530-1533, 2015) reveal interannual variability in δ13CEAA signatures that suggest changes in plankton community composition through time, but also highlight the need for improved characterization of plankton end-member δ13CEAA signatures in the NW Atlantic. Overall, these results further demonstrate the use of δ13CEAA signatures in marine bio-archives as a proxy for primary producer functional diversity through time.