Atmospheric CO 2 uptake by a coastal upwelling system

A biological pump for transferring atmospheric CO 2 to deep ocean regimes has been identified in the upwelling zone of the U.S. Pacific coast off Oregon using high‐resolution measurements of P CO2 and nutrient concentrations that were made in May through August 2001. Surface water over most of the shelf was a strong sink for atmospheric CO 2 , while a narrow nearshore strip was an intense source. The dominance of the low‐CO 2 waters over the shelf area makes the region a net sink during upwelling season. This is due to (1) upwelled water that carries abundant preformed nutrients, (2) complete photosynthetic uptake of these excess nutrients and a stoichiometric proportion of CO 2 , and (3) moderate warming of upwelled waters. If the remaining North Pacific's eastern boundary area is assumed to have similar conditions, this area should represent a sink of atmospheric CO 2 that is 5% of the annual North Pacific CO 2 uptake, and roughly equivalent to the North Pacific's uptake in the summer season. By mid‐August, P CO2 in subsurface waters increased 20–60%, corresponding to a 1.0–2.3% TCO 2 increase, due to respiration of settling biogenic debris. This water would be transported off the shelf to depth by winter downwelling flow, providing an important mechanism for sequestering atmospheric CO 2 into the oceans' interior.