Chlorophyll patches observed during summer in the main stream of the Kuroshio

Abstract Two transects through the Oyashio‐Kuroshio frontal region were made off the coast of Japan using a towed CTD‐fluorometer (Aquashuttle). These show numerous patches of elevated chlorophyll concentration adjacent to the Kuroshio front. In particular, a few patches are found in the main stream of the Kuroshio. Making use of the Temperature and Salinity (T‐S) properties of the identified patches, the origin of the patches is inferred. It is confirmed that the patches appearing in the Kuroshio are not from the adjacent coastal waters. Their T‐S properties are similar to those in the upstream portion of the Kuroshio. These facts suggest that the elevated level of chlorophyll in the patches arise because of mixing that occurs while the Kuroshio passes over the Izu Ridge. The patches found in the main stream of the Kuroshio are transported to the Kuroshio extension, which is the nursery ground for many pelagic larval fish. These patches, if they appear during the spawning season, may provide food for these larval fish. Thus mixing due to bottom topography and islands of the Izu Ridge may play an important role for the survival of larval fish downstream, in the region of the Kuroshio extension.

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