SALINE INTRUSIONS IN THE INTERMEDIATE WATERS NORTH OF OAHU, HAWAII

The Hawaii Ocean Time-series (HOT) hydrographic observations at statio n ALOHA (22 degrees 45'N, 158 degrees W) reveal that the region is som etimes the site of intrusive interleaving of different water types nea r the salinity minimum of the North Pacific Intermediate Waters. This interleaving is associated with saline laminae, or lenses, 5-30 km lon g (submesoscale) and 5-100 m thick (finestructure). The temporal varia bility of these intermediate waters is investigated statistically, and a background water type is defined against which to measure the stren gth of intrusions. The salinity minimum shows a relative maximum in va riability, caused mainly by the episodic appearance of the saline, fin estructure intrusions, which are correlated with low oxygen and silica te concentrations. The intermediate salinity minimum has its southern boundary near the latitude of the Hawaiian Islands, where salinity inc reases towards the south and oxygen gradually decreases. Thus, stirrin g processes local to the Hawaiian Ridge may explain the observations. Possible mechanisms are suggested, including fluctuations of the subtr opical gyre southern boundary and a hydrodynamically unstable flow at intermediate depths along the ridge. Either process could transport re latively saline water into the ALOHA region, and would lead to interle aving, driven by double diffusion on scales of the order of 10 m in th e vertical. Copyright (C) 1996.