A biological pump for transferring atmospheric CO2 to deep ocean regimes has been identified in the upwelling zone of the U.S. Pacific coast off Oregon using high-resolution measurements of PCO2 and nutrient concentrations that were made in May through August 2001. Surface water over most of the shelf was a strong sink for atmospheric CO2, while a narrow nearshore strip was an intense source. The dominance of the low-CO2 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 CO2, 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 CO2 that is 5% of the annual North Pacific CO2 uptake, and roughly equivalent to the North Pacific's uptake in the summer season. By mid-August, PCO2 in subsurface waters increased 20--60%, corresponding to a 1.0--2.3% TCO2 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 CO2 into the oceans' interior.