Temperature, salinity, nutrients and chlorophyll a in coastal waters of the Southern California Bight

Abstract

The seasonal variability of dissolved inorganic nutrients (phosphates, PO^–3₄; nitrates, NO^–₃; nitrites, NO^–₂) and chlorophyll a was studied during five surveys in nearshore waters of the southern region of the Southern California Bight (SCB). The seasonal changes in the physical properties of the area are derived mainly from the regional processes of the adjacent Pacific Ocean. The water present in the coastal zone seems to be related to the dynamics of the California Current System and its seasonal variability. Highsalinity (33.7) and low-temperature (11ºC) water sampled in March and June is derived from upwelled subsurface water, and is associated with an increase in nutrient concentrations (nitrates, 127 µmol m^–2; phosphates, 22 µmol m^–2) and chlorophyll a (74 mg m^–2) in the water column. The cool and relatively high-salinity water is the result of the mixing of modified Subarctic Water with Equatorial Pacific Water, which flows into SCB during coastal upwellings. The increase in temperature (~18°C) and decrease in salinity (~33.4) during September and October can be explained by the decrease in coastal upwelling due to reduced wind stress. During these months, there is an increase in the flow of warmer and surface water that is poor in nutrients, derived from the cyclonic eddy off the coast of SCB. The seasonal variability of temperature and salinity measured in the coastal zone follows the general pattern of the southern region of the SCB.