HR: 16:45h
AN: PP34A-04 INVITED    [Abstracts]
TI: Working at the margins with sessile proxy archives: Different considerations for anthropogenic-scale reconstructions
AU: * Rosenheim, B E
EM: brosenheim@whoi.edu
AF: Woods Hole Oceanographic Institution, Department of Geology and Geophysics MS #8, Woods Hole, MA 02543, United States
AU: Swart, P K
EM: pswart@rsmas.miami.edu
AF: Rosenstiel School of Marine and Atmospheric Sciences, University of Miami MGG, Miami, FL 33149, United States
AU: Lini, A
EM: alini@uvm.edu
AF: University of Vermont, Department of Geology Delehanty Hall, Burlington, VT 05405, United States
AU: Mehrtens, C
EM: cmehrtens@uvm.edu
AF: University of Vermont, Department of Geology Delehanty Hall, Burlington, VT 05405, United States
AB: On the time scale most applicable to questions of anthropogenic climate change (centuries to millennia), considerations regarding reconstructions of temperature and salinity differ from those necessary on glacial/deglacial time scales. These different considerations involve the assumptions that 1. significant changes in the salinity/oxygen isotope relationship may have occurred during the record, 2. recorded changes are indicative of open ocean conditions, and 3. global scale change is best measured in well defined climatic zones. The first assumption is required in glacial/interglacial work due to the large volume of meltwater and resultant change in the isotopic value of the fresh water end-member. On the anthropogenic time scale, one can assume a constant relationship between oxygen isotopes and salinity in most locations, eliminating one source of propagated error. The second assumption is often made in glacial/deglacial studies, as well as other studies using proxy records archived in sediments, because sediment constituents live in the water column of the open oceans. Anthropogenic-scale salinity and temperature reconstructions often rely on massive accretionary skeletons of organisms such as corals and sclerosponges which grow in proximity to land masses that support sessile organisms. The effects of landmasses cannot be underestimated - data from the island of Roatan, Honduras, show the affects of local land use patterns on oxygen isotope ratios, one of the key proxies for temperature and salinity reconstructions. Additionally, sclerosponge salinity reconstructions from the Bahamas corroborate coral reconstructions across the Atlantic basin at the decadal scale, however local effects preclude reproducibility on high-frequency time scales. Care must be taken to apply these data to open ocean interpretations. Finally, subtle changes in ocean circulation at the anthropogenic time scale are best observed in proxy records from the margins of water masses rather than the cores of well-defined water masses or climatic zones. Here, large changes resulting in heave or lateral movement of a water mass can be mistaken for unbelievable trends in a single water mass. Cycles observed in the cores of single water masses may yield to "trends" near the margins of the same water masses due to long- period changes in local and regional circulation patterns. Ultimately, anthropogenic-scale temperature and salinity reconstructions are more precise at the first order, but prescription of either regional or marginal reconstructions to global, open ocean changes involves different assumptions than reconstructions at the glacial/deglacial time scale.
DE: 4220 Coral reef systems (4916)
DE: 4283 Water masses
DE: 4825 Geochemistry
DE: 4870 Stable isotopes (0454, 1041)
DE: 4954 Sea surface temperature
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting