Compound specific amino acid δ13C patterns in a deep-sea proteinaceous coral: Implications for reconstructing detailed δ13C records of exported primary production

Deep-sea proteinaceous corals represent high-resolution paleoarchives, extending biogeochemical time series far beyond recent instrumental data. While recent studies have applied compound specific amino acid delta N-15 (delta N-15-AA) measurements of their organic skeletal layers to investigate Holocene nitrogen cycling, potential applications of amino acid delta C-13 (delta C-13-AA) in proteinaceous corals have not yet been examined. Here we developed delta C-13-AA analysis in deep-sea bamboo coral (Isidella sp.) from the Monterey Canyon to reconstruct exported primary production over an similar to 80 year record. Preserved deep-sea coral essential amino acid delta C-13-AA patterns (delta C-13-EAA) closely matched those expected from natural and cultured phytoplankton, supporting the hypothesis that deep-sea coral delta C-13-EAA values represent unaltered signatures of exported primary production sources. The coral bulk delta C-13 record showed cyclic 0.5% variations over the last century, with a shift to lower delta C-13 values in the early 1960s. Variations in coral delta C-13-EAA values closely followed bulk delta C-13 signatures, although both the range and the magnitude of change in the bulk delta C-13 record were highly attenuated compared to the delta C-13-EAA record. Our results indicate that delta C-13-EAA in proteinaceous corals represent a new, direct proxy for delta C-13 in primary production that is more sensitive and accurate than bulk PC. To test this idea, we used existing phytoplankton PC-AA data to calculate an offset between bulk delta C-13 and delta C-13-EAA. When applied to our data, a reconstructed record of delta C-13 values for exported organic matter was consistent with regional phytoplankton dynamics and expected trophic transfer effects, suggesting significant AA resynthesis only in the non-essential AA pool. Together, these results indicate that delta C-13-EAA in deep-sea proteinaceous corals provide a powerful new long-term, high resolution tool for investigating variations in exported primary production and biogeochemistry. (C) 2014 Published by Elsevier B.V.