A current system consisting of surface clockwise circulation is the most remarkable feature observed in Funka Bay during early summer. The present study investigates its formation process using a numerical model driven by the following three factors during the typically strati fied season, i.e., (1) freshening of coastal water because of river discharge, (2) density inflow of Tsugaru Gyre water, and (3) surface heat flux. It was found that the “topographic heat accu mulation effect” resulting from surface heating is essential for the genesis of the surface clock wise circulation. Because of the surface offshore flow generated by the thermal contrast be tween the shallow coastal and deep central regions, a weak anti-clockwise geostrophic flow is initially formed. Nevertheless, with continuous thermal forcing, after a few months, this offshore flow gradually reinforces the upslope transport of cold dense water. When the cooling resulting from the dense water upslope dominates in comparison to the downward heating resulting from vertical diffusivity around the coastal sea bottom, the coastal water is relatively colder than the offshore surface water. Therefore, shallowing of the interface toward the coast drives the geos trophic flow proceeding along the coast to the left-handed side. In response to this change, an isolated clockwise circulation begins to establish from the surface layer of the northern bay head, while an initially formed anti-clockwise flow migrates to the deeper region.

Submesoscale phenomena are ubiquitous in global oceans and are associated with oceanic fronts and mesoscale eddies. Because they most probably play important roles in energy transport and material circulation, they have become active targets for idealized numerical experiments and simulations in recent years. While numerical studies have deepened our understand ing of their dynamical and biogeochemical importance, relatively few observations of submesoscale phenomena have been carried out. This is because they are too small and too short-lived to be captured by typical ship-based surveys. Submesoscale currents are generated and evolve by several different dynamical processes. In this paper, submesoscale phenomena are classified as one of three main phenomena and their characteristics are described. Subsequently, possible approach through in situ observation is discussed on the basis of the classification and previous observations.

The discovery of unfathomably high animal biomass inhabiting deep seafloors with geofluid input, such as hydrothermal vents, is widely recognized as one of the most extraordinary scientific achievements in recent history. Four decades since its discovery, how animals migrate between these stepping stone-like habitats remains a fascinating research topic. The concept of larval dispersal where animals migrate during their early life stages (as eggs or larvae), is generally accepted as the only viable process for this to occur. Here, we review existing studies concerning this process in three stages (emigration, migration, and colonization) and consider two different viewpoints (biological factors and seawater dynamics). Furthermore, we disentangle the obstacles and limitations related to the study of animal dispersal in hydrothermal vents, discuss new developments in the field, and provide an outlook on research in the coming decades.