Timing of the anthropogenic carbon invasion in the Southern California Current

Abstract. The role of Eastern Boundary Upwelling Systems (EBUS), such as the southern California Current System, is a well-known high productivity region driven by alongshore winds, although their role as atmospheric carbon sources and sinks is poorly understood in the global carbon cycle. In the southern CCS, off Baja California, wind-driven vertical mixing upwells nutrient and carbon-rich waters from late winter to early summer, while weaker winds during the rest of the year allow the intrusion of nutrients and carbon-depleted subtropical surface waters. Here, we interpret the isotopic composition of organic carbon and calcitic records spanning 150 years from high-resolution sediment cores collected off Baja California in the context of seasonal variability observed between 1990 and 2011. The results show a clear trend toward lighter carbon isotopic compositions of the organic and inorganic carbon for the past seven decades. These trends are similar to the atmospheric records associated with the Suess effect, suggesting an atmospheric carbon invasion into the surface waters of the California Current. Nevertheless, the slope of the atmospheric carbon isotopic records is steeper than our marine record, most likely related to the upward mixing of subsurface waters with a relatively heavier carbon isotopic signature and advection processes inherent to the strong seasonality of the CCS southern boundary. These results will allow a better characterization of the relative role of the EBUS regions in the global carbon cycle.