Observations of the exchange of ocean waters between the Pacific Ocean and the Gulf of California

Abstract

Kinematics of seasonal exchanges of mass and heat between the Pacific Ocean and the Gulf of California are described. Results are based on 18 occupations between 1992 and 2013 of a hydrographic section across Pescadero Basin at the mouth of the Gulf and two and a half years (November 2003 to May 2006) of moored velocity and CTD measurements in 130 m of water on either side of the Pescadero Basin. Cyclonic conditions dominated in mid-winter and summer with inflow along Sinaloa and outflow along Baja California Sur (BCS). Advection of warm Gulf waters into the Pacific along BCS in late fall extended the warming along BCS by almost two months compared to Sinaloa; as a consequence, steric heights at BCS were higher, and resulted in near surface transport out of the Gulf of ~ 0.01 m s-1. During warming periods from May through November, coastal trapped waves transported heat into the Gulf along Sinaloa; the trapped wave motions along BCS were about a tenth of the amplitude of those at Sinaloa and contributed little to transport into the Pacific. Poleward monsoon winds were in phase with near-surface geostrophic flows into the Gulf which were about the same magnitude as out flow associated with much stronger equatorward wind. Next to BCS, higher salinity Gulf waters extended to 180 m depth (~26.2 kg m-3) and flow into the Pacific; these waters can be traced to subduction in the mid-Gulf region and, when they reach the Pacific, flow poleward in the undercurrent. If global warming intensifies the overturning Gulf circulation, lower oxygen and higher salinity waters may be advected northward along the continental shelf of North America.