On the seasonal and interannual migrations of the transition zone chlorophyll front

Abstract

High‐resolution satellite measurements of ocean color and surface winds, along with historical in situ data, are used to explore interannual variability in the annual migration of the transition zone chlorophyll front (TZCF) in the central North Pacific Ocean. Significant variations in frontal position and annual range were observed, including a significant southerly displacement during El Niño events. This displacement, apparently forced by enhanced surface convergence and vertical mixing in the transition zone, creates vast regions of anomalously high wintertime surface chlorophyll in the North Pacific Subtropical Gyre. A remarkably close correspondence between the positions of the TZCF and the 18°C surface isotherm over a portion of the central North Pacific allows historical temperature data to be used as a proxy for TZCF position. This surface temperature proxy has revealed decadal‐scale variability in frontal position, with greater (lesser) annual range and southerly extent following the large‐scale 1976–77 (1998–99) climate shifts. Interannual variations in TZCF position could have important implications for the distribution and survival of a number of apex predators that utilize the TZCF as a migratory and foraging habitat.