Water masses and decadal variability in the East Sea (Sea of Japan) (original) (raw)
Related papers
Review of recent findings on the water masses and circulation in the East Sea (Sea of Japan
Journal of Oceanography, 2008
Recent findings on water masses, biogeochemical tracers, deep currents and basin-scale circulation in the East/Japan Sea, and numerical modeling of its circulation are reviewed. Warming continues up to 2007 despite an episode of bottom water formation in the winter of 2000–2001. Water masses have definitely changed since the 1970s and further changes are expected due to the continuation of warming. Accumulation of current data in deep waters of the East/Japan Sea reveals that the circulation in the East/Japan Sea is primarily cyclonic with sub-basin scale cyclonic and anticyclonic cells in the Ulleung Basin (Tsushima Basin). Our understanding of the circulation of intermediate water masses has been deepened through high-resolution numerical studies, and the implementation of data assimilation has had initial success. However, the East/Japan Sea is unique in terms of the fine vertical structures of physical and biogeochemical properties of cold water mass measured at the highest precision and their rapid change with the global warming, so that full understanding of the structures and their change requires in-depth process studies with continuous monitoring programs.
Re-initiation of bottom water formation in the East Sea (Japan Sea) in a warming world
Scientific reports, 2018
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 ...
Izvestiya, Atmospheric and Oceanic Physics, 2008
In this study, the hydrological characteristics of water in the Japan Sea are considered on the basis of the GDEM data of climatic distribution of temperature and salinity . Using a regional-scale numerical model, we investigate the dynamics of these waters and perform a detailed analysis of the formation and propagation of intermediate waters in the Japan Sea. On the basis of numerical modeling, we reveal that the process of the formation and propagation of intermediate waters can be separated into three stages. The first stage is related to the accumulation of a significant water reserve with properties close to the type of intermediate waters in the vicinity of the Peter the Great Bay. The second stage involves the penetration of these waters into intermediate layers as a result of deep convection in the presence of a winter monsoon. The third stage occurs for a reduced subpolar front and leads to the propagation of intermediate waters southward to the Ulung and Yamato basins as well as to their partial recirculation within the northern gyre.
Oceanography of the East Sea (Japan Sea)
2016
The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, express or implied, with respect to the material contained herein or for any errors or omissions that may have been made. Cover Image: The image shows a distribution of chlorophyll a concentration over the East Sea derived from Geostationary Ocean Color Imager (GOCI) observations taken in September, 2011. It reveals various ocean surface features such as fronts, plumes, filaments and eddies. Natural color composite is shown on the land. GOCI, the first ocean color instrument operated on geostationary orbit, is collecting ocean color radiometry data since July, 2010. GOCI has an unprecedented capability to provide eight images a day with a 500 m resolution for the North East Asian seas around Korean peninsula.
The Upper-Layer Circulation of the Japan Sea: Historical Data Analysis
2014
The circulation of the Japan/East Sea is characterized by significant temporal and spatial variability due to several factors, including seasonal fluctuations in the warm inflow through Tsushima Strait, branching of the Tsushima Warm Current downstream of the strait, and the formation of mesoscale eddies along these branches. The long-range objective of the Japan/East Sea study is to understand the dynamical processes that govern this variability. Methods: We used the very large AXBT data set from NAVOCEANO to investigate a) the structure and distribution of intra-thermocline eddies and b) the seasonal variability in the three-dimensional, synoptic temperature structure and circulation in the East China, southern Yellow and southeastern Japan/East Seas in the upper 400 m. The study region is shown in Figure 1. Previously, we converted the vast store of XBT data to dynamic height following the methods of Lagerloef [1994] to address our original objective of describing the spatio-temp...
Monographs on Environment, Earth and Planets, 2014
Chemical tracers in seawater, as well as physical parameters such as temperature and salinity, have been measured to better characterize the dynamics of water convection and its spatiotemporal changes in the Sea of Japan (also called the Japan Sea), a semi-closed, hyperoxic marginal sea (maximum depth: ∼3,800 m) in the northwestern corner of the Pacific Ocean. Repeated conductivity, temperature, and depth (CTD) observations and measurements of dissolved oxygen, for more than 30 years, have confirmed that the bottom layer of the Japan Sea, with a thickness of ∼1 km below the boundary at a depth of ∼2,500 m, is characterized by vertical homogeneity with fluctuations of potential temperature and dissolved oxygen of <0.001 • C and <0.5 µmol kg −1 , respectively. The timescale of the abyssal circulation in the Japan Sea has been estimated to be 100-300 years, using 14 C and other chemical tracers. Stable isotope analyses for dissolved He, O 2 and CH 4 have given us information on their unique geochemical cycles in the Japan Sea. Profiles of the short-lived radioisotope 222 Rn just above the sea bottom have brought new insights into the short-term lateral water movement with a timescale of several days in the Japan Sea bottom water. It is of special concern that the gradual deoxygenation and warming of the bottom water over the last 30 years have resulted in an ∼10% decrease in dissolved oxygen and ∼0.04 • C increase in potential temperature, suggesting a change of the deep convection system in the Japan Sea. The temporal changes in the vertical profiles of tritium from 1984 to 1998 have suggested a shift of the abyssal circulation pattern from a "total (overall) convection mode" to a "shallow (partial) convection mode". It is likely that the global warming since the last century has hindered the formation of dense surface seawater and its ability to sink down to the bottom, isolating the bottom layer from the deep convection loop that is indispensable as the source of cold and oxygen-rich water. However, the decreasing trend of bottom dissolved oxygen between 1977 and 2010 was not monotonous; rather, it was interrupted by an occasional break in the winter of 2000-2001, when severely cold weather may have resulted in especially dense surface water to sink down to the bottom layer for its ventilation.
A new perspective on origin of the East Sea Intermediate Water: Observations of Argo floats
Progress in Oceanography, 2018
The East Sea Intermediate Water (ESIW), defined as the salinity minimum in the East Sea (hereafter ES) (Sea of Japan), is examined with respect to its overall characteristics and its low salinity origin using historical Argo float data from 1999 to 2015. Our findings suggest that the ESIW is formed in the western Japan Basin (40-42°N, 130-133°E), especially west of the North Korean front in North Korean waters, where strong negative surface wind stress curl resides in wintertime. The core ESIW near the formation site has temperatures of 3-4°C and less than 33.98 psu salinity, warmer and fresher than that in the southern part of the ES. In order to trace the origin of the warmer and fresher water at the sea surface in winter, we analyzed the data in three different ways: (1) spatial distribution of surface water properties using monthly climatology from the Argo float data, (2) seasonal variation of heat and salt contents at the formation site, and (3) backtracking of surface drifter trajectories. Based on these analyses, it is likely that the warmer and fresher surface water properties found in the ESIW formation site are attributed to the low-salinity surface water advected from the southern part of the ES in autumn.
Deep Sea Research Part II: Topical Studies in Oceanography, 2010
The East/Japan Sea (EJS) has unique water-mass characteristics in the western Pacific marginal seas due to limited exchange with open North Pacific. The major inflow of source water mass is North Pacific Subtropical Water (NPSW) carried by the Kuroshio branching and Tsushima Current. The locally formed cold/fresh waters from the Tatar Strait and Russia coast by winter convection mix with NPSW contributing to water mass transformation, especially during winter when upper isopycnal surfaces outcrop and thermocline is ventilated. The geographic limit of the Korea/Tsushima Strait (KTS) with a sill depth of about 120-140 dbar confines the inflow of lower NPSW, and so the EJS thermocline layer is somewhat truncated with a rather thin layer for about 100 dbar. This study uses high resolution conductivity-temperature-depth (CTD) and Argo data with a third decimal or higher accuracy for temperature and salinity obtained mainly by Research Institute of Oceanography, Seoul National University through domestic and international collaboration with several Korean ocean research institutes and Russia and USA partners since early 1990s. The basin covered data were divided into summer and winter half year representing seasonal difference since most CTD surveys were conducted purposely in summer and winter. Analysis is made for the upper layer, about 50-70 dbar, from the surface to the upper main thermocline and the thermocline layer down to about 150-180 dbar south of the subpolar front (SPF). The lower thermocline is defined slightly below the sill depth of the KTS, considering the deepening of NPSW after passing through the KTS. The thermocline layer is encompassed by three selected neutral density surfaces N =25.8, 26.4 and 27.0 with a distance of about 40 dbar between two neighboring surfaces. The core of thermocline is followed by the N =25.8 surface characterized by a salinity maximum and a minimum of potential vorticity. Winter convection is discussed and compared with three other major convection sites of the world's oceans, the Gulf of Lions, Labrador Sea and Greenland Sea, showing some common and distinctive features, especially the extremely low salinity of the EJS. Water-mass properties on neutral density surfaces are analyzed with the water-mass Turner angle (WTu) and circulation and transport are deducted from geostrophic calculations. From the 15 year mean hydrography, a basin-wide net annual mean transport of about 2.10±0.29 Sv (1 Sv=10 6 m 3 s -1 ) is estimated with summer and winter transports of 2.56±0.36 and 1.63±0.23 Sv, respectively. This transport is slightly less than the annual mean transport of the Tsushima Current at the KTS, 2.4 Sv from 3 cable and 2.3 Sv from other direct current meter and geostrophic methods but matches the ±14% error bar of ±0.29 Sv adjusted by ±150 dbar from the reference level of 800 dbar. This error bar is close to the error of ±0.34 Sv determined from water-mass conservation residual in a separated study. Three mechanisms are discovered to explain the seasonal difference in the Tsushima Current transports: the stronger winter Ekman pumping, outcropping and southward crossing flow. During winter, the Tsushima Current branches are imposed under strong wind stress curl in the Ulleung Basin and Yamato Basin, showing a doubling Ekman downwelling transport, partly weakening the Tsushima Current flow in the eastern boundary. Meanwhile the thermocline isopycnal surfaces outcrop in winter, reducing volume transport due to reduced space and thickness. The southward currents in the southern Ulleung Basin and Yamato Basin are perpendicular to the Tsushima Current branches west of Japan, which weakens the eastern boundary current in winter. Here NPSW is defined as the shallow component of North Pacific Central Water (NPCW). Since isopycnal surfaces in NPSW outcrop southeast of Japan where salinity and temperature maximum is found in the subtropical gyre center, NPSW is characterized by a distinct temperature and salinity maximum. NPSW is formed by Kuroshio recirculation in the first meander of the Kuroshio Extension. In contrast, the lower component of NPCW is formed east of Honshu, south of the subarctic-tropical frontal zone (SATFZ) with a slightly low salinity. Therefore, the latitudes of NPCW formation region are generally referred to about 35-40ºN (Tomczak and Godfrey, 2003), about 5º farther north of the NPSW formation region. The North Pacific Subtropical Mode Water (NPSTW) (Masuzawa, 1969) is a special case of NPSW, i.e., a freshly formed and well mixed component of NPSW characterized by a thermostad and pycnostad.
A sudden bottom-water formation during the severe winter 2000-2001: The case of the East/Japan Sea
Geophysical Research Letters, 2002
We observed a sudden initiation of bottom-water formation in the East/Japan Sea associated with a severely cold winter in 2000-2001. An increase in dissolved oxygen concentration as well as decreases in temperature and nutrient concentrations for the bottom waters provides unequivocal evidence that cold, oxygen-rich and nutrient-poor surface waters were injected directly to the bottom. Since the conveyor-belt in the East Sea has been undergoing dramatic change with a complete halt to bottom-water formation since the mid-1980s, this sudden episode of bottom-water formation could easily be detected. Though the amount of bottom water formed was rather small, being only about 0.03% of the volume in the past time, the observation clearly demonstrates that the conveyor-belt is directly connected to the weather system.