NOAA/WDS Paleoclimatology - Cross Seamount, North Pacific Geochemistry and Amino Acid d15N and d13C Data over the last 12,000 Years

Paleoproxy records in proteinaceous deep-sea coral skeletons can reconstruct past ocean conditions on centennial to millennial time scales. Commonly recovered subfossil specimens could potentially extend these archives through the Holocene. However, protein matrix stability and integrity of isotopic and chemical proxies over multi-millennial timescales in such specimens have never been examined. Here we compared isotopic data and skeletal composition of live-collected and subfossil (~9.6-11.6 kyrs BP) Kulumanamana haumeaae specimens from the central Pacific to understand the effects of long-duration benthic oxic exposure on skeletal protein composition and isotope values. The subfossil coral had large, coupled shifts in bulk d15N (~7‰) and d13C (~2‰) in the outermost portion (<10 mm), coincident with extensive alteration of the protein matrix. Physical changes coincided with increased C/N ratio (+0.8) and isotope-based amino acid degradation parameters (e.g. SV =3), indicating extensive degradation of seawater exposed gorgonin. However, interior gorgonin (>10 mm) remained preserved at both molecular and isotopic level. Little change occurred in AA molar composition with the exception of glycine loss, and d15N and d13C compound-specific patterns of amino acids (CSI-AA) were generally unaltered in the inner subfossil coral. These results indicate that while bulk isotope data may be compromised, CSI-AA data can reconstruct paleo-oceanographic biogeochemical and ecosystem information in subfossil corals beyond a clear “burn in” horizon which is strongly impacted by biotic and abiotic diagenesis. We propose that C/N ratios together with the SV degradation proxy can identify zones where isotopic and paleoproxy information remains viable.