NOAA/WDS Paleoclimatology - Amino Acid d13C and d15N Data from Monterey Bay, California from 1998-2004 CE

Recent implementation of compound-specific stable isotopes of amino acids (CSI-AA) to proteinaceous deep-sea corals opens a new realm of high-fidelity reconstructions of 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 d13C and d15N values of primary production, and second they stay unaltered during subsequent export and incorporation from particles into corals. Here, we explore the first long-term d13C and d15N CSI-AA data on a sediment trap time series together with contemporaneous deep-sea bamboo corals (Isidella sp.) in the California margin to for the first time directly test these assumptions. We found that the isotope values of essential (d13CEAA) and source AAs (d15NPhe) in sinking particles can quantitatively track bulk d13C and d15N values of export and primary production. These CSI-AA baseline proxies varied independently of carbon flux, trophic position (TPCSI-AA), and microbial degradation and resynthesis, suggesting good preservation in sinking particles. Paired comparisons between sinking particles and deep-sea corals revealed only small elevations of d13CEAA (~2 per mil) and d15NPhe (~1 per mil) in the coral skeletons, near the magnitude of analytical uncertainty. We hypothesize the difference in d13CEAA is due to the geographic offset in d13C values of primary production expected between the (more offshore) sediment trap site and (more onshore) coral specimens, whereas the d15NPhe offset is more likely related to a minor trophic fractionation. Using the derived empirical models, we demonstrated that CSI-AA applied to proteinaceous deep-sea corals can reconstruct bulk d15N values of export and primary production, baseline nitrogen d15N, and exported TPCSI-AA values with remarkable fidelity. Together, these findings improve our understanding of AA isotope behaviors in modern and paleoarchives and provide a strong field support for applying the rapidly evolving CSI-AA-based tools to paleoceanographic studies.