Climate variability during the Holocene and last interglacial: High resolution stable isotope and biogenic silica evidence from the Santa Barbara Basin

Through the use of high resolution sampling and analysis of marine sediments, detailed climatic histories of the current and last interglacial (the Holocene and Marine Isotope Stage 5, respectively) have been constructed for the Santa Barbara Basin, offshore southern California. The data sets presented herein are among the most highly resolved marine records available for these two warm intervals, and they document that large climate changes have occurred on decadal time scales in the recent geologic past. The data also demonstrate that during the middle Holocene when climate was warmer than today, El Niño warm events were much more frequent and intense than they have been over the past century. When compared to pollen and benthic foraminiferal data from the last interglacial, the biogenic silica records and stable oxygen isotopes from two species of planktonic foraminifera suggest warming of the surface ocean and the adjacent continent several thousand years before melting of the ice sheets. This lag is possibly the result of the difference in response time between the surface marine and terrestrial reservoirs and the cryosphere. The silica and isotope data also indicate dramatic differences between the evolution of the two most recent interglacial periods. Using six years of modern sediment trap data from the Santa Barbara Basin as a basis for interpreting the past, it appears that the seasonal changes in hydrography and productivity seen in the modern basin have been a feature of the climate record throughout the Holocene. On the other hand, a seasonal cycle similar to today's was not apparent in the basin until several thousand years after the beginning of the last interglacial. According to models of solar insolation, maximum Northern Hemisphere summer sunlight peaked near the beginning of the Holocene but well after the beginning of the last interglacial. Perhaps the differing patterns of solar radiation during these two warm intervals is one of the drivers of the differences observed in the paleoclimatic data.