Coastal fresh water discharge in the northeast Pacific


  • Thomas C. Royer


Very high annual rates of precipitation in the coastal mountains that border the northeast Pacific Ocean produce large fresh water discharges (23000 m3 s−1). This discharge has been ignored previously since it does not enter the ocean in the form of large rivers, but, instead, the water enters by way of numerous small rivers and streams. Thus, it acts as a line source instead of a point source. This coastal discharge contributes at least 40% of the fresh water that enters the northeast Pacific from the atmosphere. The discharge is comparable to the mean annual discharge of the Mississippi River system. The fresh water creates a cross-shelf density gradient that drives an alongshore baroclinic jet. The width of this jet is less than 25 km with speeds in excess of 100 cm s−1. It extends along the coast from southeast Alaska to at least Kodiak Island. Apparently, the flow is maintained as a narrow current adjacent to the coast by wind stress that causes downwelling conditions here throughout most of the year.