California margin Bamboo corals: Spatial variability in stable carbon and nitrogen isotope composition

Deep-sea bamboo corals (order Gorgonacea, family Isididae) found on seamounts on the California margin (37° - 32°N; 800 to 2100m depth) have the potential to record annual to subannual changes in water mass chemistry over long periods of time (75-350 years). These corals are composed of a two-part skeleton of calcite internodes segmented by gorgonin organic nodes. Radiocarbon analyses of the organic nodes show the presence of the anthropogenic bomb spike, indicating a surface-derived food source for the corals (pre-bomb values of -81.3‰ to -116.9‰; post-bomb values of 61.8‰ to 81.3‰). Carbon and nitrogen isotope analyses of the organic nodes (average δ13C = -15.9‰ to -18.2‰; average δ15N = 13.8‰ to 18.3‰) suggest selective feeding on surface-derived organic matter as well as a denitrification signal due to high surface productivity and suboxic subsurface zones at the sample sites. This study examines the spatial variability of bamboo coral organic node carbon and nitrogen stable isotopic composition of specimens sampled along the California Margin in 2004 and 2007. Strong relationships between coral δ15N and sample depth show that these corals have the potential to serve as indicators of water column denitrification. Organic node carbon isotopes suggest differences in food source between localities and/or terrestrial carbon influence.