Relationships Among Decadal Changes in Nitrate and Salinity in the Eastern and Western North Pacific Ocean After 2000

Abstract Decadal changes in nitrate and preformed nitrate, as detected by the most accurate observations possible, were small in the subsurface layer around the subarctic front in the North Pacific Ocean. However, the patterns of differences in vertical sections were similar to those in repeat observations along survey Line P and were caused mainly by decadal rather than year‐to‐year changes. The changes in nitrate and preformed nitrate along Line P after 1996 were correlated with those based on high‐accuracy observational data along 165°E (with lags of a few years). Whereas similar relationships at bidecadal timescales were reported previously based on more long‐term historical data, the high‐accuracy methods in this study allowed us to detect smaller decade‐scale differences and compare the amplitudes of the changes. Furthermore, the patterns of changes were correlated with those for salinity, which a previous study considered to be formed mainly by eastward propagation of the decadal changes observed in the western part of the northern North Pacific. The time lags between the time series for nitrate and preformed nitrate were similar to the time required for the salinity anomalies to reach the Alaska Gyre from the western part of the subarctic front, which suggests that changes in the western part of the northern North Pacific Ocean affect those in the eastern part.