HR: 17:00h
AN: PP54A-05    [Abstracts]
TI: Controls on the relationship between salinity and the oxygen isotopic composition of seawater: Implications for past estimates of salinity
AU: * Swart, P
EM: pswart@rsmas.miami.edu
AF: RSMAS, University of Miami, 4600 Rickenbacker Causeway, Miami, Fl 33149 United States
AU: Rosenheim, B
EM: brosenheim@whoi.edu
AF: WHOI, National Ocean Sciences Accelerator Mass Spectrometer Department of Geology and Geophysics Woods Hole Oceanographic Institution, Woodshole, MA 02543 United States
AU: Spero, H
EM: spero@geology.ucdavis.edu
AF: University of California, Davis, One Shields Ave., Davis, CA 95616 United States
AB: Past estimates of salinity are normally made by removing the temperature effect from the oxygen isotope signal in calcareous organisms through the use of a proxy such as the Sr/Ca or Mg/Ca ratio in the skeleton. The residual oxygen isotopic composition is then directly related to salinity. However the slope of such a relationship varies appreciably, dependent upon whether salinity variations result from mixing of riverine water with ocean water or whether changes result from evaporation. Relationships between δ¹⁸O and salinity arising from mixing of large rivers such as the Amazon and the Mississippi with typical isotopic composition of between -8 and -6 %produce slopes between salinity and δ¹⁸O of 0.17 to 0.22. With the addition of local precipitation in the sub-tropics which has an isotopic composition of 0 to -3% typically salinity vs. δ¹⁸O relationship in the Caribbean and equatorial regions are approximately 0.12 to 0.14. In large regions of the oceans salinity vs. δ¹⁸O relationships are >> 0.14 not as a result of dilution by freshwater, but as a result of evaporation. Typically evaporation of seawater in the range 35 -37 produces slopes of 0.4 -0.6 with higher values occurring under conditions of higher relative humidity (> 90 %). A change in the temperature of evaporation has little influence upon the relationship. Failure to recognize the changing role of evaporation on the salinity vs. δ¹⁸O relationship can lead to the calculation of unrealistic changes in paleo-salinity from proxy data obtained from organisms such as corals, sclerosponges and foraminifera.
DE: 1050 Marine geochemistry (4835, 4845, 4850)
DE: 1615 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 4805, 4912)
DE: 1655 Water cycles (1836)
DE: 1724 Ocean sciences
DE: 4924 Geochemical tracers
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005