Evidence for benthic–pelagic food web coupling and carbon export from California margin bamboo coral archives

[摘要] Deep-sea bamboo corals (order Gorgonacea, family Isididae) are known torecord changes in water mass chemistry over decades to centuries. Thesecorals are composed of a two-part skeleton of calcite internodes segmentedby gorgonin organic nodes. We examine the spatial variability of bamboocoral organic node ¹³C/¹²C and ¹⁵N/¹⁴N from 13bamboo coral specimens sampled along the California margin (37–32° N,792–2136 m depth). Radiocarbon analyses of the organicnodes show the presence of the anthropogenic bomb spike, indicating thecorals utilize a surface-derived food source (pre-bomb D¹⁴C values of∼−100‰, post-bomb values up to82‰). Carbon and nitrogen isotope data from the organicnodes (δ¹³C = −15.9‰ to−19.2‰;δ¹⁵N = 13.8‰ to 19.4‰) suggest selective feeding on surface-derivedorganic matter or zooplankton. A strong relationship between coral δ¹⁵N and habitat depth indicates a potential archive of changing carbonexport, with decreased δ¹⁵N values reflecting reduced microbialdegradation (increased carbon flux) at shallower depths. Using fourmulti-centennial-length coral records, we interpret long-term δ¹⁵N stability in the California Current. Organic node δ¹⁵C values record differences in carbon isotope fractionation dictatedby nearshore vs. offshore primary production. These findings imply strongcoupling between primary production, pelagic food webs, and deep-sea benthiccommunities.

[学科分类] 地球化学与岩石