High resolution paleoceanography of the southern Gulf of California: A 400 year record.

摘要

The goal of this dissertation was to evaluate long-term changes in oceanographic and climatic conditions in the southern Gulf of California, using the stable isotopic composition (delta18O and delta13C) of planktonic (Globigerina bulloides and Pulleniatina obliquiloculata) and benthic (Bolivina subadvena) foraminifera in sediment cores. The cores, which were collected from the Alfonso (western margin) and Pescadero (eastern margin slope) Basins, were composed of laminated sediments, and were sampled at 2 mm intervals. delta 18O and delta13C values were used to reconstruct sea surface temperature (SST), water column structure, and primary productivity during the past four centuries.; Two distinct periods were recognized in the oceanographic history of the Gulf. The first period (1650-1850) was characterized by relatively constant delta 18O values. The second period (1850-2000) was characterized by decreasing delta 18O values, interpreted as increasing SSTs, by highly variable delta 13C values, and by decreasing abundance of G. bulloides. These trends indicated decreasing upwelling during this period, attributable to increased solar irradiance after the end of the Little Ice Age, and the northward displacement of the Inter-Tropical Convergence Zone (ITCZ).; Wavelet analyses of delta18O and delta13C values for G. bulloides and delta13C values for B. subadvena, indicated that maximum oceanographic variability occurred during the warmest period examined, i.e. the 20th Century. The proposed northward migration of the ITCZ corresponded to the high than average temperatures recorded in the Northern Hemisphere during this time. Overall, results of the present research support the hypothesis that increased thermal energy input to the climate-ocean system enhances variability in SST, upwelling, and primary productivity.