Abstract
The East Sea (Japan Sea), a small marginal sea in the northwestern Pacific, is ventilated deeply down to the bottom and sensitive to changing surface conditions. Addressing the response of this marginal sea to the hydrological cycle and atmospheric forcing would be helpful for better understanding present and future environmental changes in oceans at the global and regional scales. Here, we present an analysis of observations revealing a slowdown of the long-term deepening in water boundaries associated with changes of water formation rate. Our results indicate that bottom (central) water formation has been enhanced (reduced) with more (less) oxygen supply to the bottom (central) layer since the 2000s. This paper presents a new projection that allows a three-layered deep structure, which retains bottom water, at least until 2040, contrasting previous results. This projection considers recent increase of slope convections mainly due to the salt supply via air-sea freshwater exchange and sea ice formation and decrease of open-ocean convections evidenced by reduced mixed layer depth in the northern East Sea, resulting in more bottom water and less central water formations. Such vigorous changes in water formation and ventilation provide certain implications on future climate changes.
Highlights
The East Sea (ES) is a small marginal sea in the northwestern Pacific enclosed by countries such as Korea, Russia, and Japan (Fig. 1a)
Deep structural changes are clearly observed at a group of stations, located in the central Japan Basin (JB), which is the deepest part of the ES (Fig. 1a)
We analysed previous observations of a slowdown of long-term deepening in water boundaries associated with changes of water formation rates in the ES
Summary
The East Sea (ES) is a small marginal sea in the northwestern Pacific enclosed by countries such as Korea, Russia, and Japan (Fig. 1a). Its total area and average water depth are approximately 106 km[2] and 1,700 m, respectively This deep marginal sea, connected to the Pacific through narrow and relatively shallow straits, has the highest deep-water dissolved oxygen (DO) in the Pacific because it is well ventilated through diverse processes such as brine rejection, convection, and subduction[1,2,3,4,5]. Results of the moving boundary five-box model applied to the ES suggested a shift in ventilation from the bottom to central/deep layers, resembling the weakening of deep ventilation in the global ocean[2,7] Such shifts provide a clue to future changes in the global ocean[1,12,13]. Future ventilation is newly projected based on a 1-D advection-diffusion model
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