Assessing N₂ fixation flux and its controlling factors in the (sub)tropical western North Pacific through high‐resolution observations

AbstractThe (sub)tropical western North Pacific is potentially an area of intense nitrogen (N2) fixation in the global ocean, despite limited understanding of the flux and controlling factors. We conducted high‐resolution observations from 2016 to 2021 in this region and used machine learning algorithms to simulate N2 fixation flux. Models estimated an N2 fixation flux from 5.72 to 6.45 Tg N yr−1, with strong seasonal variation and peak rates in summer. The western North Pacific Subtropical Gyre and the Kuroshio Current contributed more to N2 fixation flux than did the adjacent areas. Models suggested that sea surface temperature, photosynthetically available radiation, and nutrient supply were most strongly correlated with seasonal and spatial variations in N2 fixation. This study provides an improved estimation of N2 fixation in the western North Pacific and advances our understanding of its role in ocean productivity.