Compound specific amino acid delta Carbon-13 patterns in a deep-sea proteinaceous coral: Implications for reconstructing detailed delta Carbon-13 records of exported primary production.

摘要

Deep-sea proteinaceous corals represent high-resolution Holocene paleoarchives, potentially extending biogeochemical time series far beyond recent instrumental data. Recent studies have applied compound specific amino acid delta15N (delta15N-AA) measurements of organic skeletal layers to investigate the Holocene N cycle, but potential applications of amino acid delta13C (delta13C-AA) in proteinaceous corals have never previously been examined. Here we assess delta13C-AA patterns in an ~80 year old bamboo coral specimen (Isidella sp.) from the Monterey Canyon, and compare AA isotopic data with the bulk delta13C record. Preserved essential AA delta13C (delta13C-EAA) patterns corresponded closely with those expected from living organisms, and hydrolyzable AA delta13C values were able to reproduce bulk skeletal delta13C values within error. The delta13C-EAA patterns closely matched those expected from phytoplankton, supporting the hypothesis that these represent unaltered delta13C signatures of primary production sources. The bulk delta13C record showed cyclic 0.5 / variations over the last century, with an excursion in the early 1960s. Variations in delta13C-EAA values closely followed bulk delta13C signatures, although both the range in values and the magnitude of change in the bulk delta13C record was highly attenuated vs. delta13C-EAA. We propose delta13C-EAA in proteinaceous corals as a new, direct proxy for delta13C variation in primary production. We used existing plankton delta13C-AA data to derive a correction for the offset between bulk delta13C and delta13C-EAA. Applied to our Isidella data, our reconstructed record of phytoplankton delta13C values that corresponded to expectations for regional phytoplankton values; by contrast, bulk delta13C values of coral skeletal material were strongly elevated. These results suggest that delta13C-EAA in deep-sea proteinaceous corals can represent a powerful new tool for investigating oceanographic delta13C variations during the late Holocene.