A Seaglider's View of Hawai‘i

Abstract

Variation in the waters off the south shore of Oahu and near Station ALOHA have been observed. Both high salinity anomalies ( 35.2) and water properties from varying source regions are investigated using Seaglider data. Observed salinity anomalies that can exceed the average profile by up to 0.3 occur approximately once a month and exist in the upper 50 m of the water column. Anomalies coincide with the presence of a cyclonic eddy both north and south of the main Hawaiian Islands. The eddy south of the islands outcrops the 100− 120 m isotherms lifting high salinity water (subsurface salinity maxima) to the surface. Eddy interaction and eddy-island interaction cause deformation of the cyclonic eddies resulting in advection of the high salinity water away from the eddy, along equipotential surfaces, into the study site. For two sites (PacIOOS and ALOHA), the mean regional profiles calculated by Lumpkin [1998] were compared to observed T-S relationships. A RMS calculation was used to identify regions with the most similar water properties. While the entire profile is used in the comparison, most of the variation is in the upper waters (especially at ALOHA) with a secondary STD maximum at PacIOOS at the salinity minimum. Surprisingly, variation indictive of multiple source regions was found at both sites. Of particular interest, most of the observed water properties at PacIOOS (60%) match those found north of the islands. HYCOM 1/12 degree model velocities were used to assess flow in the region and possible advective pathways for the observed T-S curves.