GEOCHEMICAL CYCLICITY IN COLONIAL DEEPWATER CORALS FROM THE CHARLESTON BUMP, BLAKE PLATEAU

Living colonial ahermatypic corals were collected from a depth of approximately 600m at the Charleston Bump (Western Atlantic, Blake Plateau, ~150 km southeast of Charleston, South Carolina, USA) in August 2003 using a submersible. Ontogenetic microsampling of the skeletal aragonite revealed stable carbon and oxygen isotope and Sr:Ca profiles that often oscillate in tandem with visible growth bands apparent in cross section. Otherwise sinusoidal geochemical profiles are interrupted by zones of more abrupt variation, suggesting periods of growth diminishment or cessation. This observed elemental and isotopic cyclicity may enable coral growth rate analysis and therefore facilitate future development of these corals as paleoclimate proxies.

Abundant fossil corals are also present in this location and many have been recovered adjacent to the living analogue specimens described here. The isotopic and elemental data contained in these fossils may represent a valuable paleoclimate archive. The Charleston Bump is an area of significant relief (~300 m rise from the Blake Plateau), consisting principally of limestone and extensive manganese-phosphorite pavement. It is situated so as to deflect the Gulf Stream, causing large-scale eddies and upwelling, such as the biologically productive Charleston Gyre. Therefore, unlike many other deepwater coral habitats, the Charleston Bump is comparatively dynamic with respect to temperature, current flow, and other climate-related variables. As such, coral climate proxies from this region may be sensitive indicators of past Gulf Stream variation.