Oceanography in Japan

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Interannual variations in spring primary production in the upstream part of the Kuroshio Extension(KE) are known to affect many types of fish. A recent study demonstrated that the layered structure causedby the subduction of Oyashio water below Kuroshio water gives rise to favorable conditions for photosynthesis conditions, causing high productivity. Here, we hypothesize that the areal extent of the Kuroshio-Oyashio layered structure varies from year to year and that this interannual variability affects primary production in the KE. To investigate this link, we conducted a correlation analysis using high-resolution reanalysis temperature and salinity data and satellite chlorophyll-a data. The results show that there is a significant positive correlation between the interannual variability in the area of the Kuroshio-Oyashio layered structure and the chlorophyll-a concentration. Specifically, the spring chlorophyll-a concentration tends to be high during years in which the Kuroshio-Oyashio layered structure has a large areal extent in the KE.

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