The Kuroshio flowing over seamounts and associated submesoscale flows drive 100-km-wide 100-1000-fold enhancement of turbulence

Although previous studies reported that currents over topographic features, such as seamounts and ridges, cause strong turbulence in close proximity, it has been elusive how far intense turbulence spreads toward the downstream. Here, we conducted a series of intensive in-situ turbulence observations using a state-of-the-art tow-yo microstructure profiler in the Kuroshio flowing over the seamounts of the Tokara Strait, south of Kyusyu Japan, in November 2017, June 2018, and November 2019, and employed a high-resolution numerical model to elucidate the turbulence generation mechanisms. We find that the Kuroshio flowing over seamounts generates streaks of negative potential vorticity and near-inertial waves. With these long-persisting mechanisms in addition to other near-field mixing processes, intense mixing hotspots are formed over a 100-km scale with the elevated energy dissipation by 100- to 1000-fold. The observed turbulence could supply nutrients to sunlit layers, promoting phytoplankton primary production and CO2 uptake.

Phylogeographic patterns of intertidal arthropods (Acari, Oribatida) from southern Japanese islands reflect paleoclimatic events

The Japanese islands represent one of the world’s biodiversity hotspots. Their geological history and present geography resulted in a high number of endemic species in nearly all major metazoan clades. We investigated the phylogeography of three different intertidal mite species from the Ryukyu islands and southern mainland by means of morphometry and molecular genetics. None of the species represents an endemic, nearly all show distributions ranging over at least the southern and central Ryukyus. Two species, Fortuynia shibai and F. churaumi sp. n. clearly represent sister species that are derived from a common Eastern ancestor. Molecular genetic results indicate that these species separated approx. 3 Ma before the opening of the Okinawa trough, whereas F. shibai most likely showed an ancestral distribution stretching from the central Ryukyus across the Tokara strait to Japanese mainland, whereas F. churaumi probably evolved somewhere south of the Tokara strait. Phylogenetic data further indicates that long periods of isolation resulted in heterogeneous genetic structure but subsequent low sea level stands during Pleistocene allowed recent expansion and gene flow between island populations. Comparing these patterns with those of other animals, these tiny wingless mites apparently show better dispersal abilities than partially volant terrestrial organism groups.