HR: 09:45h
AN: PP41C-08    [Abstracts]
TI: Tropical Indian Ocean Temperatures from Sr/Ca Ratios of Modern Porites Corals: Assessing the Impact of 20th Century Warming on Tropical Rainfall
AU: * Pfeiffer, M
EM: mpfeiffer@ifm-geomar.de
AF: IFM-GEOMAR, Wischhofstrasse 1-3, Kiel, 24148 Germany
AU: Timm, O
EM: timm@hawaii.edu
AF: IPRC/SOEST, University of Hawaii, POST Bldg. 413 1680 East West Road, Honolulu, 96822 United States
AU: Dullo, W
EM: cdullo@ifm-geomar.de
AF: IFM-GEOMAR, Wischhofstrasse 1-3, Kiel, 24148 Germany
AB: The progressive warming of the tropical oceans over the second half of the 20th century is thought to contribute to the trend of the North Atlantic Oscillation. In this context, the warming of the equatorial Indian Ocean and associated changes in boreal winter precipitation/atmospheric circulation may be of primary importance. However, instrumental records of SST in this region are unreliable prior to the 1950s. Here, we present a 119-year record of monthly coral Sr/Ca ratios measured at a coral from the Chagos Archipelago (central Indian Ocean). A calibration with instrumental data confirms that coral Sr/Ca is a reliable recorder of SST on interannual and decadal/interdecadal time scales. Furthermore, the reproducibility of the coral proxy (and the warming trend during the second half of the 20th century) is corroborated by two additional coral Sr/Ca records that extend from 1950-1995. Previous work on the oxygen isotopic composition of the Chagos corals, which record variations in boreal winter rainfall, provides evidence of a major shift in the ENSO-teleconnection. A strong ENSO signal only emerges after the mid-1970s. We have proposed that this shift results from an increase in mean SSTs in the tropical Indian Ocean: after the 1970s, mean SSTs at the Chagos are close to a critical threshold (28.5°C), which is required to trigger deep convection in the atmosphere, and hence strong rainfall events. At this critical level, small ENSO related SST anomalies in the tropical Indian Ocean (0.5 to 1°C) may exert a strong control on atmospheric convection and hence rainfall variability. Coral Sr/Ca confirms the importance of the Indian Ocean warming during the 20th century: the Sr/Ca ratios show a stable relationship with local SST before and after the 1970s. The relationship between local SST and the oxygen isotopes (recording rainfall variations), measured at the same coral core, changes and becomes much stronger after 1970s. Thus, it is clear that the warming of the Indian Ocean has the potential to alter atmospheric convection and precipitation patterns. Our new proxy dataset may help to evaluate the role of the Indian Ocean in long-term climate change.
DE: 1854 Precipitation (3354)
DE: 4220 Coral reef systems (4916)
DE: 4504 Air/sea interactions (0312, 3339)
DE: 4900 PALEOCEANOGRAPHY (0473, 3344)
DE: 4922 El Nino (4522)
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005