Compound Specific δ13C of Amino Acids in a Deep-Sea Coral (Isidella) from the Monterey Canyon

Deep-sea proteinaceous corals have proven to be highly effective biological archives for the reconstruction of δ13C and δ15N late Holocene oceanic environments. These corals can have lifespans of hundreds to thousands of years depending on the species, and their annual band growth allows for high resolution records that extend biogeochemical time series beyond instrumental data. Compound-specific isotope analysis of amino acids (CSI-AA) can be readily applied to expand stable isotopic information beyond what is possible from bulk δ13C and δ15N isotope analyses. However, while recent studies have shown that δ15N CSI-AA in deep sea corals can be a robust paleoceanographic tool, to our knowledge the potential of δ13C CSI-AA for these archives has not yet been examined. Here we present results of the δ13C of amino acids in one ~100-year old bamboo coral (Isidella) from the Monterey Canyon, and compare the CSI-AA results with the bulk δ13C record from the same specimen. We explore the potential of the essential amino acid group to reconstruct a direct and highly detailed record of exported primary production δ13C, decoupled from the confounding effects of food webs and trophic transfer. Our preliminary results show cyclic variations in δ13C values of ~1‰, along with a general decline in bulk δ13C consistent with the Suess effect over the last century. This suggests the occurrence of regular excursions of primary production δ13C values along the California coastal region over the last hundred years. We have calibrated our CSI-AA results with existing plankton δ13C CSI-AA data to create corrected δ13C values which we propose as a foundation for deducing a direct record of the δ13C of exported primary production in the Montery Bay for the 20th century. Our results suggest that δ13C CSI-AA, coupled with deep sea proteinaceous coral archives, will represent a powerful new tool for highly detailed isotopic records of the late Holocene carbon cycle.