HR: 1330h
AN: B12C-0795    [PDF]
TI: The Coral and the Moon: A Biological Effect Possibly Affecting the Precision of the Sr/Ca Paleotemperature Proxy
AU: * Meibom, A
EM: meibom@pangea.stanford.edu
AF: Geological and Environmetal Sciences, 320 Lomita Mall Stanford University, Palo Alto, CA 94305 United States
AU: Stage, M
EM: MGS@Geoteknisk.dk
AF: Danish Geotechnical Institute, Maglebjergvej 1, Lyngby, DK-2800 Denmark
AU: Wooden, J L
EM: jwooden@usgs.gov
AF: USGS, 345 Middlefield Road, Menlo Park, CA 94025 United States
AU: Constantz, B R
EM: brentc@stanford.edu
AF: Biomechanical Engineering Division, Stanford University, Palo Alto, CA 94305 United States
AU: Dunbar, R B
EM: dunbar@pangea.stanford.edu
AF: Geological and Environmetal Sciences, 320 Lomita Mall Stanford University, Palo Alto, CA 94305 United States
AU: Owen, A
EM: owen@stat.Stanford.EDU
AF: Department of Statistics, Stanford University, Palo Alto, CA 94305 United States
AU: Grumet, N
EM: ngrumet@stanford.edu
AF: Geological and Environmetal Sciences, 320 Lomita Mall Stanford University, Palo Alto, CA 94305 United States
AU: Bacon, C R
EM: cbacon@usgs.gov
AF: USGS, 345 Middlefield Road, Menlo Park, CA 94025 United States
AU: Chamberlain, C P
EM: chamb@pangea.stanford.edu
AF: Geological and Environmetal Sciences, 320 Lomita Mall Stanford University, Palo Alto, CA 94305 United States
AB: In thermodynamic equilibrium with sea water the Sr/Ca ratio of aragonite varies predictably with temperature and the Sr/Ca ratio in coral have thus become a frequently used proxy for past Sea Surface Temperature (SST). However, biological effects can offset the Sr/Ca ratio from its equilibrium value. We present high spatial resolution ion microprobe analyses of Sr/Ca variation in well defined skeletal elements in the reef-building coral Porites lutea from Watamu, Kenya. Our data reveal distinct monthly oscillations in the Sr/Ca ratio, with an amplitude in excess of ten percent of the average Sr/Ca ratio. Such large variations, which we speculate can be the result of metabolic changes synchronous with the lunar cycle, will introduce variability in Sr/Ca measurements based on conventional sampling techniques (e.g. dentist drill) well beyond the analytical precision. Monte Carlo simulations show that under such conditions the precision of the Sr/Ca paleo-thermometer can be limited to about two degrees. Aragonite precipitated during periods of reduced growth rate have smaller biological effects than aragonite precipitated during periods of accelerated growth. Thus, Sr/Ca-based temperature reconstructions from massive scleractinian corals, such as Porites, would potentially become more precise if the corals are preferentially sampled in low growth-rate regions of the skeleton. We therefore recommend a re-analysis of existing Sr/Ca records based on knowledge of temperature impacts on growth rates. If the biological effects observed in the Porites coral studied by us are also observed in other Porites specimens from which long SST records have been derived on the basis of the Sr/Ca paleothermometer using conventional sampling techniques, it may invalidate conclusions based on inferred SST variations of less than about two degrees. Our results also may help explain the notorious difficulties involved in obtaining an accurate and consistent calibration of the Sr/Ca vs. SST relationship. In general, our results point to a strong biological control on the Sr/Ca ratio in coralline aragonite and emphasize the importance of investigating and understanding the Sr/Ca micro-distribution.
DE: 3620 Crystal chemistry
DE: 4215 Climate and interannual variability (3309)
DE: 4227 Diurnal, seasonal, and annual cycles
DE: 4267 Paleoceanography
DE: 4294 Instruments and techniques
SC: Biogeosciences [B]
MN: 2003 Fall Meeting