Observations of oceanic fronts and water-mass properties in the central Japan Sea: Repeated surveys from an underwater glider

Abstract Repeated glider surveys were conducted in the Japan Sea during April–June 2016. Observations revealed mesoscale hydrographic structures of the subpolar front, the Tsushima Warm Current, and eddies formed around flows in the central Japan Sea off Sado Island, in addition to fine-scale water properties associated with mesoscale variation. Data collected from satellite altimeters and thermometers, profiling floats, and ship conductivity–temperature–depth profiles were also analyzed to elucidate spatiotemporal characteristics in multiscale phenomena: mesoscale to fine scale. We present new quantitative estimates of the geostrophic volume transports of the Tsushima Warm Current and the subpolar front current in the central Japan Sea, based on hydrographic data from the glider's transects: they are, respectively, 2.5–2.7 Sv and 1.1–1.4 Sv. The mesoscale frontal/eddy structures varied greatly on a timescale of less than one month. We classified water masses, which revealed that the upper-layer, the low-salinity water within an anticyclonic eddy, was characterized in terms of salinity 100 m in this region, for which there are few hydrographic measurement data.

[1]  I. Han,et al.  Seasonal volume transport variation in the Tsushima Warm Current through the Tsushima Straits from 10 years of ADCP observations , 2010 .

[2]  Bartolomé Garau,et al.  A toolbox for glider data processing and management , 2015 .

[3]  Yongjun Tian,et al.  Response of yellowtail, Seriola quinqueradiata, a key large predatory fish in the Japan Sea, to sea water temperature over the last century and potential effects of global warming , 2012 .

[4]  Kay I. Ohshima,et al.  The flow system in the Japan Sea caused by a sea level difference through shallow straits , 1994 .

[5]  Y. Sakurai,et al.  Effect of water temperature on gonadal development and emaciation of Japanese common squid Todarodes pacificus (Ommastrephidae) , 2008, Fisheries Science.

[6]  W. Koterayama,et al.  The Current Structure of the Tsushima Warm Current along the Japanese Coast , 1999 .

[7]  B. Qiu,et al.  The Annual Cycle of the Japan Sea Throughflow , 2016 .

[8]  Jing Zhang,et al.  Water Mass Analysis and End‐Member Mixing Contribution Using Coupled Radiogenic Nd Isotopes and Nd Concentrations: Interaction Between Marginal Seas and the Northwestern Pacific , 2018 .

[9]  Tatsuro Watanabe,et al.  Structure of the Tsushima warm current in the northeastern Japan Sea , 2006 .

[10]  T. Senjyu,et al.  Interannual salinity variations in the Tsushima Strait and its relation to the Changjiang discharge , 2006 .

[11]  Bartolomé Garau,et al.  Vertical motion in the upper ocean from glider and altimetry data , 2009 .

[12]  J. Edmond,et al.  Chemical dynamics of the Changjiang estuary , 1985 .

[13]  Masahisa Kubota,et al.  An introduction to J-OFURO3, a third-generation Japanese ocean flux data set using remote-sensing observations , 2018, Journal of Oceanography.

[14]  B. Hoskins,et al.  A new look at the ?-equation , 1978 .

[15]  Tatsuro Watanabe,et al.  High‐salinity intermediate water of the Japan Sea in the eastern Japan Basin , 2001 .

[16]  A. Yankovsky,et al.  Transition of the Tsushima Warm Current Path Observed over Toyama Trough, Japan , 2017 .

[17]  Jong Hwan Yoon,et al.  The Tsushima Warm Current through Tsushima Straits Estimated from Ferryboat ADCP Data , 2005 .

[18]  H. Hasumi,et al.  Modeling low salinity waters along the coast around Japan using a high-resolution river discharge dataset , 2015, Journal of Oceanography.

[19]  T. Senjyu,et al.  Water characteristics and circulation of the upper portion of the Japan sea proper water , 1993 .

[20]  D. Smeed,et al.  Current measurements from autonomous underwater gliders , 2008, 2008 IEEE/OES 9th Working Conference on Current Measurement Technology.

[21]  J. Fukuoka.  On the Tsushima Current , 1957 .

[22]  Ananda Pascual,et al.  Glider and satellite high resolution monitoring of a mesoscale eddy in the algerian basin: Effects on the mixed layer depth and biochemistry , 2016 .

[23]  W. Teague,et al.  Currents in Korea‐Tsushima Strait during summer 1999 , 2000 .

[24]  Y. Sakurai,et al.  Impact of a climate regime shift on the migration of Japanese common squid (Todarodes pacificus) in the Sea of Japan , 2010 .

[25]  Bartolomé Garau,et al.  Thermal Lag Correction on Slocum CTD Glider Data , 2011 .

[26]  M. Kawabe.  Branching of the Tsushima current in the Japan Sea , 1982 .

[27]  R. Reynolds,et al.  The NCEP/NCAR 40-Year Reanalysis Project , 1996, Renewable Energy.

[28]  T. Ichiye.  Some Problems of Circulation and Hydrography of the Japan Sea and the Tsushima Current , 1984 .