HR: 10:20h
AN: PP32A-01    [Abstracts]
TI: Decadal and Lower Frequency South Pacific Climate Variability Since 1619 AD from Replicated Coral Records
AU: * Linsley, B K
EM: blinsley@albany.edu
AF: University at Albany-State University of New York, Earth and Atmospheric Sciences, Albany, NY 12222 United States
AU: Wellington, G M
EM: wellington@uh.edu
AF: University of Houston, Department of Biology, Houston, TX 77004 United States
AU: Kaplan, A
EM: alexeyk@ldeo.columbia.edu
AF: Lamont Doherty Earth Observatory of Columbia University, 61 Route 9W, Palidades, NY 10964 United States
AU: deMenocal, P B
EM: peter@ldeo.columbia.edu
AF: Lamont Doherty Earth Observatory of Columbia University, 61 Route 9W, Palidades, NY 10964 United States
AB: A notable aspect of multi-century oxygen isotope (\delta$^{18}$O) time-series generated from modern Pacific Porites corals in the convergence zone is the presence of a trend component of progressively lower \delta$^{18}$O in the top (younger) sections of most published \delta$^{18}$O series. The climatic significance of this trend has remained controversial in part due to the paucity of multi-century long coral records. Here we present sub-annually resolved and replicated Porites \delta$^{18}$O records from Fiji (17S, 179E) (1619-2001AD, replicated from 1780) and Rarotonga (21.5S, 160W) (1726-1997AD; replicated from 1874) in the southwestern Pacific to evaluate the significance of the \delta$^{18}$O trend in this region. As part of this study we also analyzed bulk skeletal Sr/Ca from each of the 5 coral cores (2 subannual, 3 annually averaged). The coral \delta$^{18}$O series from Fiji and Rarotonga document site reproducible trends (similar timing within each site, and total magnitudes of 0.30 to 0.35 per mil since 1850AD) towards progressively lower and unprecedented \delta$^{18}$O in the late 20th century. However, the Sr/Ca records from the same cores do not replicate completely before 1950AD, indicating that at these sites, and in some corals, Porites bulk skeletal Sr/Ca is not strictly a function of SST or external-to-the-coral environmental variability. For skeletal \delta$^{18}$O, the overall reproducibility of the \delta$^{18}$O trend in different age corals at each site, supports a locally consistent, primarily environmental origin for this mode of \delta$^{18}$O variability. Comparison of the \delta$^{18}$O trend modes at Fiji and Rarotonga to each other and to instrumental SST and precipitation data suggests that the coral \delta$^{18}$O trend at each site is due to regionally variable but progressive warming and salinity reduction. If this interpretation is correct, the second half of the 20th century was the warmest and least saline at both sites since the early 1600s. Since Fiji and Rarotonga are both influenced to varying degrees by the South Pacific Convergence Zone (SPCZ) one explanation for the \delta$^{18}$O trend is that the SPCZ has been intensifying over the last 200 years with increasing cloud cover and rainfall as the surface ocean warmed. On decadal-interdecadal time-scales, comparison of the Fiji and Rarotonga coral \delta$^{18}$O series to other coral \delta$^{18}$O records from New Caledonia and the Great Barrier Reef indicates that some interdecadal climate shifts apparently were related to changes in the SPCZ and others apparently were unrelated to the SPCZ. This observation suggests the possibility that decadal-interdecadal climate variability in the South Pacific has multiple sources, and may at times be related to higher latitude South Pacific processes.
DE: 3344 Paleoclimatology
DE: 4267 Paleoceanography
DE: 1600 GLOBAL CHANGE (New category)
DE: 1620 Climate dynamics (3309)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting