SEA SURFACE TEMPERATURE RECORD IMPLICATIONS FOR THE WESTERN EQUATORIAL PACIFIC WARM POOL

Planktic foraminifer assemblages and alkenone unsaturation ratios have been analyzed for ODP Site 1115, located in the western equatorial Pacific (WEP) off the coast of New Guinea. Cold and warm season sea surface temperature (SST) estimates were determined for the mid-Piacenzian (3.3 to 2.9 Ma) using the modern analog technique. ODP core 1115B, located just south of the transition between the planktic foraminifer tropical and subtropical faunal provinces, approximates the southern boundary of the WEP warm pool. Comparison of the faunal and alkenone SST estimates with an existing nannofossil climate proxy shows similar trends. Based on increased seasonal variability during the 3.22 to 3.10 Ma interval, we conclude that the boundary between the subtropical and tropical faunal provinces may have migrated north of Site 1115B during cool events, possibly resulting from an influx of cooler water carried by the South Equatorial Current. In addition, the data indicate that the WEP warm pool may have contracted relative to today during the interval of high seasonality, as SST did not remain above 29°C year round. Based on this quantitative faunal analysis, the WEP warm pool, at least at times within the mid-Piacenzian, did not extend to the Solomon Sea region of the Southern Pacific. Models of mid-Piacenzian climate conditions suggest modest warming of the warm pool region, but these proxy data do not indicate this is the case at Site 1115.