MID-HOLOCENE CLIMATE RECONSTRUCTION IN THE SOLEDAD BASIN USING PLANKTIC FORAM ASSEMBLAGES

The instrumental climate record for the subtropical Pacific is useful for reconstructing interannual climate variability, though it is limited by its short-term duration. Climate proxies from high-resolution sites can be used to extending this record to geologic time scales, but only if the proxies are properly calibrated. The Soledad Basin (SB) off the coast of Baja, California (25o12’ N, 112o 43’ W) is a viable locale for constructing such proxies due to its high sedimentation rate, providing a temporal resolution of ~10 yr/cm. Here we present a pilot study of modern analog temperature estimates based on planktic foraminiferal faunal assemblages from SB gravity (MV99-GC-41) and piston (MV99-PC-14) cores. The goal of this study is to explore whether productivity in the SB during the mid-Holocene, a period of strong summer insulation, was higher or lower than modern values. These faunal temperature estimates are calibrated against a 1083 sample data set (Ortiz et al., 1997) and 1995-1998 Santa Barbara Basin (34o14’N, 120o02’W) sediment trap faunas from Black et al. (2001). Comparing NCEP instrument SSTA anomalies for the equatorial Pacific NINO3 region, Santa Barbara Basin (SBB), and SB across the 1995-1998 interval (including the prominent 1997-98 El Nino event) indicates similar thermal structure at all three locations, but the SB data exhibits greater ENSO influence than the SBB. Modern analog temperature estimates using our method on the SBB sediment traps faunas indicates values that range from 9-21oC in agreement with instrumental measurements. When the modern analog method is applied to coretop samples from GC-41 and mid-Holocene samples from PC-14 we estimate mid-Holocene temperature of 9-12oC, somewhat cooler than the modern coretop value of ~14oC. Black et al. (2001) suggests that increases in the percent abundance of G. bulloides and G. quinquloba indicate enhanced La Nina like conditions, while increases in the percent abundance of G. ruber and G. rubescence indicate El Nino like conditions. A comparison of these four foram species between GC-41, PC-14, and the SBB sediment trap calibration data suggests at least part of mid-Holocene in the SB was characterized by more La Nina like conditions, a trend which is consistent with benthic foram abundances in the same samples.