Multi-century time-series of 15N and 14C in bamboo corals from deep Tasmanian seamounts: evidence for stable oceanographic conditions

Abstract

Bamboo corals (Family Isididae) are an important component of seamount benthos south of Tasmania. Besides having lifespans of up to 400 yr, little is known about their basic ecology, nor how to decode potential climate signals encoded in their skeletons. We explored the stable nitrogen isotope and radiocarbon compositions of the skeletal organic fraction of the genera Isidella, Keratoisis and Lepidisis collected from 3 Tasmanian seamounts. Analyses were performed on tissues and organic node growth rings sampled at a temporal resolution of 1 to 4 yr. Radiocarbon chronologies exhibited nuclear bomb signals characteristic of surface waters and constrained radial growth rates to ~35 ± 10 µm yr -1 for 3 specimens of the genus Lepidisis and 113 ± 17 µm yr -1 for 1 specimen of Isidella. δ 15 N values of the living tissue and underlying gorgonin were similar and averaged 9 to 12 ‰. Records of δ 15 N from 8 different specimens showed subtle, quasi-decadal patterns over the last 100 yr, although the amplitude of these features (~1 ‰) was similar to the average intra-and intercolony reproducibility. These results demonstrate the utility of deep-sea corals to track seamount biogeochemical processes over long time scales, and suggest that the extent of nutrient depletion of surface waters and associated trophic dynamics have remained relatively constant in this region over centuries. This provides an important baseline for the evaluation of the impacts of anthropogenic climate change.

Environmental and compositional correlates of growth rate in deep-water bamboo corals (Gorgonacea; Isididae)

“…The cause of this difference is not clear, but one possibility is that it reflects differences in food availability. Surface productivity tends to be high in the NE Pacific relative to most other parts of the world's oceans (Koblentz-Mishke et al 1970), and isotopic evidence indicates that bamboo corals feed on suspended matter derived from surface production (Roark et al 2005, Sherwood et al 2009, in this Theme Section). However, surface productivity also tends to be high in the NW Atlantic, for which colony growth rates are close to or even slightly lower than predicted.…”

Effects of chronic low carbonate saturation levels on the distribution, growth and skeletal chemistry of deep-sea corals and other seamount megabenthos

“…Although saturation levels in those studies are considerably higher than those experienced by the deep-sea taxa we observed, the principle that elevated food availability could compensate for the higher costs of calcification in heterotrophic deepsea species appears plausible. Radiocarbon and 15 N studies show that to depths of at least 1000 m, bamboo corals consume sinking particulate organic carbon (Sherwood et al 2009). A similar food source has been speculated for other deep-water corals (Roberts et al 2009).…”

Impact of skeletal heterogeneity and treatment method on interpretation of environmental variability from the proteinaceous skeletons of deep-sea gorgonian octocorals

“…These results are consistent with previous studies that used the HCl pretreatment to remove calcite in the Primnoa sp. skeleton (e.g., Sherwood et al, 2009, Williams et al, 2007b. While the standard 5% acidification pretreatment did significantly alter octocoral skeleton bulk δ 13 C values, it did not significantly impact the δ 13 C values of the individual AAs that make up that bulk material (Table 2).…”