The Subarctic Frontal Zone (SAFZ) of the Pacific Ocean is an economically important fishing region, serving as a primary feeding and growing area for Pacific salmon and other commercially valuable species. In this study, we propose and test a new approach for identifying the mean long-term position of the SAFZ. The study uses monthly reanalysis data from GLORYS12v1. We divide the study area into one-degree-wide longitudinal bands. For each band, we identify temperature and salinity gradient peaks at specific depth horizons and on the isopycnal surface of 26.4 kg/m³. This isopycnal corresponds to the density of the Central Mode Water (CMW) formed within the frontal zone through winter convection, providing a physically robust basis for frontal mapping. These peaks are interpreted as the southern and northern boundaries of the SAFZ. We then compile generalized maps of the mean long-term SAFZ position and its fluctuations. Using this approach, we reveal a previously unknown moderate, negative and statistically significant correlation between the long-term dynamics of the SAFZ position and the major modes of North Pacific climate variability - the Pacific Decadal Oscillation (PDO) and the North Pacific Gyre Oscillation (NPGO). Furthermore, we demonstrate a significant northward shift over the last 30 years of the SAFZ, reaching in certain regions rates of 0.8-1° latitude per decade. These findings provide new insights into the response of a key productive oceanic front to large-scale climate variability and have important implications for the long-term forecasting of salmon feeding conditions and ecosystem-based fisheries management in the North Pacific. For example, significant northward shift of the SAFZ could narrow the natural habitat of salmon and force them to migrate further into the Arctic.

 

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