Seasonal temperature dynamics of the upper ocean in the Southern California Bight

Abstract

Long‐duration temperature measurements from a variety of sources, including island thermographs, CalCOFI cruise archives, NOAA buoys, and coastal piers are analyzed to determine the seasonal dynamics of the upper ocean (0–30 m) in the Southern California Bight. Dynamics in the Bight differ significantly from those found either to the north or south, with seasonal temperatures in the Bight having greater amplitude and peaking earlier in the year. The time of the seasonal peak varies with depth within the inner Bight such that the maximum temperature at 30 m occurs six weeks after the 5‐m maximum. In contrast, the water column outside the Bight changes temperature uniformly with depth. A simple diffusion equation is employed to model this change in the inner Bight and estimate the vertical eddy‐diffusion coefficient, determined to be 10 −4 m 2 s −1 . The CalCOFI data also indicate the seasonal dynamics vary with the phase of the Pacific Decadal Oscillation; during the cold phase there is a smaller seasonal amplitude and later time for maximum temperature.