Hydrographic observations and mixing processes

A series of 15 hydrographic cruises in the New York Bight over 1975-1977 is described and analyzed. The cruises cover all seasons but focus primarily on spring and summer. Tem-perature and salinity data show wide seasonal and interannual variability. Each of the three regions- inner bight, midshelf, and outer shelf slope-has distinctive properties and dynam-ics. The inner bight properties are affected primarily by river flow and wind-driven flows up the shelf valley which often splits the freshwater surface layer into two plumes, one east and one west of the valley head. The “cold pool ” temperature structure on the midshelf is dif-ferent each year. The water with the lowest recorded temperature (2.58%) was on the bottom after the thermocline formation in May 1977. Mixing models of the inner bight confirmed previous estimates of residence time as 6.8 days and yielded K, = 5 x 106 cm2 es- ’ with an advective transport component of 1 cm. s-r to the southwest. A model of the mixing of the lower layer cold pool on the midshelf with onshore, offshore, and upper layer waters yields K, = 7 x 106 and & = 0.1 cm2. s- ’ as the on-offshore horizontal and vertical diffusion coefficients. The New York Bight is the section of continental shelf between Cape May, at the mouth of Delaware Bay, and Mon-tauk Point, at the eastern tip of Long Is-land (Fig. 1). An investigation of the area has been underway since mid-1973 un-der the direction of the National Oceanic and Atmospheric Administration/Marine Ecosystem Analysis Program. This study included a series of cruises in which per-tinent hydrographic and chemical mea-surements were made over a grid of sta-tions with a lo-20-km spacing and with vertical resolution <l m. The statio