Amino acid delta C-13 and delta N-15 patterns from sediment trap time series and deep-sea corals: Implications for biogeochemical and ecological reconstructions in paleoarchives

摘要

Recent work using compound-specific stable isotopes of amino acids (CSI-AA) in proteinaceous deep-sea corals opens a new realm of high-fidelity reconstruction for biogeochemical and ecological changes in the ocean. However, underlying these CSI-AA paleoceanographic applications are a series of fundamental assumptions, which hold first that baseline-proxy AA isotope values fixed at the base of food webs represent integrated delta C-13 and delta N-15 values of primary production, and second they are unaltered during subsequent export and incorporation from particles into corals. We explored long-term d13C and delta(15N) CSI-AA data on a sediment trap time series together with contemporaneous, geographically close deep-sea bamboo corals (Isidella sp.) in the California margin, directly testing these assumptions for the first time. Our data show that isotope values of essential (delta C-13(EAA)) and source AAs (delta N-15(Phe)) in sinking particles quantitatively track bulk delta C-13 and delta N-15 values of export production. These CSI-AA baseline proxies varied independently of carbon flux, trophic position (TPCSI-AA) and microbial alteration, suggesting that they were well preserved in the sinking particles consumed by corals. Paired comparisons between sinking particles and corals revealed minor elevations of delta C-13(EAA) (by similar to 2 parts per thousand) and delta N-15(Phe) (by similar to 1 parts per thousand) in available coral specimens. We hypothesize that the difference in delta 13C(EAA) is due to the geographic offset in delta C-13 values of primary production expected between the (more offshore) sediment trap site and (more onshore) coral specimens, whereas the delta N-15(Phe) offset is likely related to expected minor trophic fractionation. Using empirical models derived from the sediment trap time series, we demonstrate for the first time that CSI-AA in proteinaceous deep-sea corals can reconstruct known bulk delta N-15 values of export production, source nitrogen delta N-15 values, and exported TPCSI-AA values with very good fidelity. Together, these findings represent a major advance in our understanding of AA isotope behavior in modern and paleoarchives, and can be used to underpin the rapidly evolving use of CSI-AA-based tools in multiple paleoceanographic studies and archives. (C) 2020 Elsevier Ltd. All rights reserved.