HR: 16:00h
AN: PP54A-01    [Abstracts]
TI: Tracking the extent of the South Pacific Convergence Zone since 1619 AD
AU: * Linsley, B K
EM: blinsley@albany.edu
AF: University at Albany-State University of New York, Department of Earth and Atmospheric Sciences, ES 351, Albany, NY 12222 United States
AU: Kaplan, A
EM: alexeyk@ldeo.columbia.edu
AF: Lamont Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, NY 10964 United States
AU: Gouriou, Y
EM: yves.gouriou@ird.fr
AF: Centre IRD de Bretagne, Technopole Pointe du Diable, B.P. 70, Plouzane, 29280 France
AU: Salinger, J
EM: j.salinger@niwa.co.nz
AF: National Institute of Water and Atmospheric Research, 269 Khyber Pass Road, Auckland, 109 695 New Zealand
AU: deMenocal, P B
EM: peter@ldeo.columbia.edu
AF: Lamont Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, NY 10964 United States
AU: Wellington, G M
EM: wellington@uh.edu
AF: Department of Biology and Biochemistry, University of Houston, 4800 Calhoun Road, Houston, TX 77004 United States
AU: Howe, S S
EM: showe@albany.edu
AF: University at Albany-State University of New York, Department of Earth and Atmospheric Sciences, ES 351, Albany, NY 12222 United States
AB: Enhanced convection and rainfall in the oceanic sectors of the Intertropical Convergence Zone (ITCZ) is one of the predicted outcomes of increasing greenhouse gas emissions and rising average global temperatures. However due to the current limited understanding of the past extent and variability of the convergence zones prior to ~1900, it has not been possible to determine pre-anthropogenic ``baseline'' convergence zone variability in order to test these predictions. Here we examine the past extent and variability of the South Pacific Convergence Zone (SPCZ), the largest and most persistent spur of the ITCZ, using multiple cores from massive coral colonies extending back to 1619. At the southeastern edge of the SPCZ near 170°W and 15°-20°S a surface ocean salinity frontal zone exists that separates fresher Western Pacific Warm Pool water from saltier and cooler waters in the east. Previous analysis of instrumental sea surface temperature (SST), sea surface salinity (SSS), and precipitation records in the SPCZ - SSS front region beginning in 1976 indicate that the amplitudes of the interannual signals in SST and precipitation are an order of magnitude less than the amplitude of the seasonal cycle, whereas for SSS, the interannual signal of 1 to 1.5 p.s.u. is double the amplitude of the seasonal signal. This analysis confirms that in the SPCZ region, SSS is higher and SST and precipitation are lower during El Niño events. The opposite occurs during La Niña events. We have generated sub-annually resolved and replicated coral oxygen isotopic time-series from Fiji (17°S, 179°E) and Rarotonga (21.5°S, 160°W) that record this same relationship between annual SST and interannual SSS. Calibration of the trends in these oxygen isotope records against instrumental SST and coral Sr/Ca from Fiji demonstrates that at lower frequencies the decadal mean position of the salinity front, and eastern extent of the SPCZ, has shifted east-west through 10° to 20° of longitude three times over the last 380 years. The most recent and largest shift began in the mid-1800s as the salinity front progressively moved eastward and salinity decreased at both sites. Our results indicate that sea surface salinity at these sites is now at the lowest levels recorded and is evidence for an unprecedented expansion of the SPCZ since the mid-1800s. The expansion of the SPCZ implies a gradual change in the South Pacific to more La Niña-like long-term mean conditions. This observation is consistent with the ocean thermostat mechanism for the coupled ocean-atmosphere system, whereby exogenous heating of the atmosphere would result in greater warming in the western Pacific and a greater east-west surface temperature gradient.
DE: 1616 Climate variability (1635, 3305, 3309, 4215, 4513)
DE: 1635 Oceans (1616, 3305, 4215, 4513)
DE: 4870 Stable isotopes (0454, 1041)
DE: 4916 Corals (4220)
DE: 4922 El Nino (4522)
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005