HR: 0800h
AN: PP31C-0542    [Abstracts]
TI: Relating Productivity Events to Holocene Bivalve Shell Growth Rates
AU: * Huntley, J W
EM: jhuntley@vt.edu
AF: Department of Geosciences, Virginia Polytechnic Institute and State University, 4044 Derring Hall, Blacksburg, VA 24061, United States
AU: Krause, R A
EM: richard.krause@MUSEUM.HU-Berlin.de
AF: Museum fuer Naturkunde Humboldt Universitaet zu Berlin, Invalidenstrasse 43, Berlin, D-10115, Germany
AU: Kowalewski, M
EM: michalk@vt.edu
AF: Department of Geosciences, Virginia Polytechnic Institute and State University, 4044 Derring Hall, Blacksburg, VA 24061, United States
AU: Romanek, C S
EM: romanek@srel.edu
AF: Savannah River Ecology Laboratory, Drawer E, Aiken, SC 29808, United States
AU: Kaufman, D S
EM: darrell.kaufman@nau.edu
AF: Department of Geology, Northern Arizona University, Rm 100 Frier Hall, Knoles Ave, Flagstaff, AZ 86011, United States
AU: Simoes, M G
EM: btsimoes@ibb.unesp.br
AF: Instituto de Biociencias, Universidade Estadual Paulista, Botucatu, SP, Sao Paulo, 18618000, Brazil
AB: The growth rate of a bivalve can be influenced by many environmental factors that can change during the life of the organism. In this contribution we present initial data from a millennium scale chronology to assess the relationship between ontogenetic growth in the bivalve Semele casali and paleoenvironmental conditions preserved in the shell using growth increment analysis, radiocarbon-calibrated amino acid racemization dating techniques, stable isotopes (C and O) and high spatial resolution (125-150 samples per cm of shell profile) trace element (Ba, Mn) analysis (LA-ICPMS). Time-averaged specimens of S. casali were dredged from two sites at 10 meters and 30 meters depth along the inner continental shelf at Ubatuba Bay in the Southeast Brazilian Bight, an area influenced by productivity pulses triggered by coastal runoff events and coastal upwelling. Seventy-five individual valves were dated using amino acid racemization (aspartic acid). Dates were calculated using an expanded version of a previously published relationship (Barbour Wood et al., 2006 Quaternary Research 323- 331) between aspartic acid ratios and AMS radiocarbon dates of twelve S. casali individuals from the same sampling locations. The resulting time series has complete coverage for the past three thousand years at centennial resolution. From this time series, a sub-sample of dated valves was selected for more detailed growth increment, stable isotope and high-resolution trace element (Ba/Ca and Mn/Ca) analyses. Oceanic productivity is expressed differentially in the trace element profiles of S. casali with elevated Ba/Ca and Mn/Ca ratios capturing nutrient input through coastal runoff events while elevated Ba/Ca and depressed Mn/Ca ratios represent input through coastal upwelling. Fluctuations in Ba/Ca and Mn/Ca are not correlated to fluctuations in relative growth throughout the ontogeny of an individual bivalve, nor are they expected to be as periods of increased productivity are transient events relative to the organism's lifespan. However, there are isolated intervals within valves where changes in the trace element proxies are coupled with growth rate, suggesting that nutrient availability can influence the growth rate of bivalves. While our results are preliminary, the analysis of additional valves will enable us to better understand the influence of productivity on S. casali growth rates and how the frequency of these upwelling and runoff associated productivity events changed during the Holocene. The addition of stable isotope data will enable us to determine if bivalve growth and productivity events were seasonal and how such seasonality may have changed in the Holocene.
DE: 4950 Paleoecology
DE: 4964 Upwelling (4279)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting