HR: 14:55h
AN: B13E-06    [Abstracts]
TI: Skeletal Structure and Chemistry of a Bermudan Gorgonian Plexaurella dichotoma
AU: * Bond, Z A
EM: zab@soc.soton.ac.uk
AF: Southampton Oceanography Centre, European Way, Southampton, SO14 3ZH United Kingdom
AU: Cohen, A L
EM: acohen@whoi.edu
AF: Woods Hole Oceanographic Institution, Quisset Campus, Woods Hole, MA 02543 United States
AU: Smith, S R
EM: robbie@bbsr.edu
AF: Bermuda Biological Station for Research, Ferry Reach, St Georges, GE01 Bermuda
AU: Jenkins, W J
EM: wjenkins@whoi.edu
AF: Woods Hole Oceanographic Institution, Quisset Campus, Woods Hole, MA 02543 United States
AB: Long-lived Gorgonian corals are distributed across the world's oceans from the surface to great depths. They accrete annually banded skeletons of both organic gorgonin and mineralised components and thus provide the opportunity to access previously unavailable records of climate change. We used SIMS ion microprobe to analyse Mg/Ca and Sr/Ca ratios of high-Mg calcite loculi within the skeleton of a Bermudan gorgonian, Plexaurella dichotoma collected from an inner lagoon reef site in October 2001. Loculi are 10 - 140 microns in diameter and 3-5 mm in length and are composed of radiating bundles of needle crystals. Both loculi and gorgonin are arranged in concentric rings about the axial core; loculi density decreases towards the outermost bands. Discrete sample spots, 20 microns diameter, were sputtered from individual loculi from the axial core to the outermost band, a distance of 4.75 mm. 38 annual bands were counted along the sample path, indicating an age of 38 years (1963 -2001). Both Mg/Ca and Sr/Ca ratios track the actual interannual sea surface temperature variability recorded at Hydrostation S for the corresponding time period. Mg/Ca ratios of the calcite loculi are positively correlated with temperature whereas the Sr/Ca ratios are inversely correlated with temperature, in agreement with observations for other calcite skeletons and laboratory-grown inorganic calcites. At our site, the strongest correlation amongst Mg/Ca and Sr/Ca, and temperature occurs in the autumn (October-December) indicating that maximum growth of the loculi occurs within this period, after the reproductive season has ended. The sensitivity of Mg/Ca to temperature is higher in Plexaurella dichotoma than is observed for inorganic calcite. Mg/Ca and Sr/Ca ratios within individual loculi exhibited little variability, further supporting our hypothesis that growth of these structures may be restricted to a short period of the year. These hypotheses are currently being tested with field-staining techniques. Our study demonstrates the enormous potential of gorgonian corals as archives of past ocean conditions, from the surface to the deep sea, from the equator to the subpolar regions.
DE: 3670 Minor and trace element composition
DE: 4267 Paleoceanography
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting