Productivity Along the California Margin During the Pliocene

The early Pliocene (3-5 Ma) is the most recent time in Earth history when CO₂ levels were similar to today, yet average global temperatures were 3-4°C warmer than today. Given the similar climate boundary conditions in the early Pliocene compared to today (CO₂, continental positions, ocean circulation) the early Pliocene is the best analogue for future climate in the paleo-record. In today's ocean primary productivity in coastal upwelling regions is an important component of the global carbon cycle. Our understanding of how productivity in these upwelling areas responded to early Pliocene warmth is very limited. In the modern California margin, cold nutrient rich water is upwelled from below the thermocline, supporting a diverse ecosystem. California margin Pliocene sea surface temperatures (SST) were 3-9°C warmer than today. If the thermocline and nutricline were coupled during the Pliocene as they are today, warmer SST would imply lower nutrient concentrations and lower productivity. However, previous paleo-records do not show a clear relationship between SST and productivity, indicating that the nutricline and thermocline were decoupled during the Pliocene. We will present a series of Pliocene aged particle size analysis and smear slide analysis for three ODP sites along the California margin. The combination of smear slide and particle size analysis allows us to characterize the dominant biological organisms in the sediment. Diatoms tend to flourish under high nutrient upwelling conditions while coccolithophorids are more abundant in stratified ocean conditions, therefore any changes in the relative abundance of these phytoplankton indicate changes in upwelling conditions and nutrient supply. This project utilizes three California margin ODP sites forming a latitudinal transect: ODP site 1014 (32.5°N, 120.0°W), is located in Tanner Basin ~150 km off the coast, ODP site 1016 (34.0°N, 122.0°W) is located off Point Conception and is within an important transitional zone for modern flora and fauna, and ODP site 1022 (40.0°N, 125.5°W) is the most northerly site and is located on the continental slope ~90 km off the northern California coast. Data from this project, in combination with previously published data, will provide a more complete picture of nutrient availability and primary productivity along the California upwelling margin during the early Pliocene.