The flushing of two deep-sea basins, southern California borderland

A time series of water temperature, salinity, and nutrient measurements has been made in San Pedro and San Nicolas Basins of the southern California borderland between 1977 and 1988. These basins exhibit temporally coincident changes in temperature and nutrient content defining a period of basin flushing (1982–1984) and a period of stagnation (1984–1987). During the flushing period, cooler, oxygen- and NO3‒-rich water replaces warmer, oxygen- and NO3‒-depleted bottom water. Flushing produces a decrease of 0.2°C in the average temperature of San Pedro Basin bottom water (790–900 m) and an increase in the average oxygen content by 12 µM. These values are 0.1 and 3 for San Nicolas Basin (1,400–1,800 m). The residence time of water in San Pedro Basin during the flushing period is 12±6 months and 9±2 months in San Nicolas Basin. A box model approach, constrained by the time-series data for the stagnation period, was used to determine values of the effective vertical eddy diffusivities for the 790-m horizon in San Pedro Basin and 1,400-m horizon in San Nicolas Basin (1.3±0.4 and 9.9±3.4 cm2 s‒1 respectively).