Carbon Cycling in the Coastal Ocean off California

Wind driven coastal upwelling events along the California coast result in advection of high nutrient and pCO2 to the euphotic zone. Relaxation of the upwelling favorable winds results in rapid uptake of nutrients by the phytoplankton, with accompanying drawdown of pCO2 levels below on a time scale of several days. However, this normal sequence of nutrient uptake and pCO2 drawdown may be disrupted by anthropogenic inputs from coastal cities. The Gulf of the Farallones receives water from San Francisco estuary through the Golden Gate that contains anthropogenic ammonium. Along the Marin coast, from the Golden Gate to Point Reyes, both intensive upwelling with pCO2 up to 1000 ppm, and high ammonium concentrations sufficient to suppress phytoplankton nitrate uptake occur. The ammonium from the San Francisco Bay outflow can be traced along the Marin coast up to the Bodega Bay upwelling center where it influences the pattern of nitrate uptake, driving phytoplankton productivity offshore and delaying the new production process. These results suggest that human activities and the huge increases in nitrogen input to coastal waters may have influenced and may be influencing the way in which coastal regions contribute to the ocean-atmosphere carbon cycle.