한국해양학회지:바다 (The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY)

  • 제28권1호
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  • Pages.1-18
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  • 2023
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  • 1226-2978(pISSN)
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  • 2671-8820(eISSN)
한국해양학회 (The Korean Society of Oceanography)
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기후변화에 따른 동해 심층 해수의 물리적 특성 및 순환 변화 연구 : 현황과 전망

Studies on Changes in the Hydrography and Circulation of the Deep East Sea (Japan Sea) in a Changing Climate: Status and Prospectus

  • 이호준 (해군사관학교 해양학과 ) ;
  • 남성현 (서울대학교 자연과학대학 지구환경과학부 )
  • HOJUN LEE (Department of Oceanography, Republic of Korea Naval Academy) ;
  • SUNGHYUN NAM (School of Earth and Environmental Sciences, Seoul National University)
  • 투고 : 2022.10.04
  • 심사 : 2023.01.17
  • 발행 : 2023.02.28
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초록

동해는 전 세계적으로 가장 빠른 수준의 온난화를 경험하는 해역 중 하나로서, 기후변화에 민감하게 반응할 뿐 아니라 대양에 비해 월등히 짧은 순환 주기를 가지고 있기 때문에 미래의 대양 환경 변화에도 중요한 시사점을 주는 것으로 알려져 있다. 그러나 동해 심층 해수의 특성과 순환의 변화 과정에 대한 연구는 동해 전역의 심층을 정밀하게 조사하기 위한 국제협력 프로그램이 자리잡고, 측정 장비의 분해능을 포함하는 관측기술과 수치모델 모의 능력이 크게 향상된 최근(1990년대 이후)에서야 본격화되고 있다. 여기서는 동해 심층 해수의 물리적 특성과 순환의 변화 과정에 대한 그간의 연구 결과를 요약하고, 향후 남은 과제를 제시하고자 한다. 동해는 내부에서 자체적으로 심층 해수가 생성되며 대양과 분리된 독특한 심층 순환 구조를 가진다. 동해의 수백 m 수심 아래에는 수온이 낮고(<1℃) 염분이 거의 일정(34.0-34.1)한 해수가 분포하기 때문에 오랜 기간 이 해수를 일본해고유수(동해고유수)로 명명된 단일 해수로 여겨 왔다. 그러나 1990년대 이후 정밀한 관측이 이루어지며, 동해 심층을 채우고 있는 해수가 적어도 3개의 서로 다른 물리적 특성을 가진 해수(중앙수, 심층수, 저층수)로 구성됨이 밝혀졌다. 이들 3개 해수의 물리적 특성과 해수 사이의 경계 수심은 항상 일정한 것이 아니라, 지난 수십 년 동안 유의한 수준의 변화를 겪어왔다. 동해 북부 해역의 대마난류 재순환, 해양-대기 열과 담수의 교환량, 해빙 형성에 영향을 받는 대류(심층사면대류 및 심층외양대류) 과정에 따라 심층 해수 생성에 뚜렷한 차이가 발생했기 때문이다. 생성된 심층 해수는 수심이 얕은 곳을 오른쪽에 두고 일본 분지에서부터 반시계 방향으로 울릉 분지, 야마토 분지를 차례로 거쳐 다시 일본 분지로 수송되며, 이 수평적인 심층 순환도 변화를 겪어 왔다. 수평적인 심층 순환은 동시에 남북 및 연직 방향의 순환(자오면 순환) 경로와 강도의 변화를 동반한다. 동해는 수천 년 규모의 순환 주기를 가지는 대양에 비해 훨씬 짧은 수백 년 혹은 그 이내의 순환 시간 규모를 가지기 때문에 동해 심층 해수의 물리적 특성과 자오면 순환의 급격한 변화를 더 뚜렷하게 볼 수 있을 것으로 기대 가능하다. 심층 및 자오면 순환 사이의 연계성, 대양과 동해의 유출입 해수 수송을 포함하는 동해 상층 순환과 심층 순환 사이의 연계성은 아직까지 잘 밝혀지지 않았다. 동해 심층 해수 수송의 경로와 강도를 지배하는 다양한 과정들에 대한 후속 연구들이 요구된다.

The East Sea, one of the regions where the most rapid warming is occurring, is known to have important implications for the response of the ocean to future climate changes because it not only reacts sensitively to climate change but also has a much shorter turnover time (hundreds of years) than the ocean (thousands of years). However, the processes underlying changes in seawater characteristics at the sea's deep and abyssal layers, and meridional overturning circulation have recently been examined only after international cooperative observation programs for the entire sea allowed in-situ data in a necessary resolution and accuracy along with recent improvement in numerical modeling. In this review, previous studies on the physical characteristics of seawater at deeper parts of the East Sea, and meridional overturning circulation are summarized to identify any remaining issues. The seawater below a depth of several hundreds of meters in the East Sea has been identified as the Japan Sea Proper Water (East Sea Proper Water) due to its homogeneous physical properties of a water temperature below 1℃ and practical salinity values ranging from 34.0 to 34.1. However, vertically high-resolution salinity and dissolved oxygen observations since the 1990s enabled us to separate the water into at least three different water masses (central water, CW; deep water, DW; bottom water, BW). Recent studies have shown that the physical characteristics and boundaries between the three water masses are not constant over time, but have significantly varied over the last few decades in association with time-varying water formation processes, such as convection processes (deep slope convection and open-ocean deep convection) that are linked to the re-circulation of the Tsushima Warm Current, ocean-atmosphere heat and freshwater exchanges, and sea-ice formation in the northern part of the East Sea. The CW, DW, and BW were found to be transported horizontally from the Japan Basin to the Ulleung Basin, from the Ulleung Basin to the Yamato Basin, and from the Yamato Basin to the Japan Basin, respectively, rotating counterclockwise with a shallow depth on the right of its path (consistent with the bottom topographic control of fluid in a rotating Earth). This horizontal deep circulation is a part of the sea's meridional overturning circulation that has undergone changes in the path and intensity. Yet, the linkages between upper and deeper circulation and between the horizontal and meridional overturning circulation are not well understood. Through this review, the remaining issues to be addressed in the future were identified. These issues included a connection between the changing properties of CW, DW, and BW, and their horizontal and overturning circulations; the linkage of deep and abyssal circulations to the upper circulation, including upper water transport from and into the Western Pacific Ocean; and processes underlying the temporal variability in the path and intensity of CW, DW, and BW.

키워드

과제정보

이 논문은 2022년 해양수산부 재원으로 해양수산과학기술진흥원의 지원을 받아 수행된 연구임(동해 심층해수 및 물질 순환 기작 규명) (20160040).

참고문헌

  1. Belkin, I.M., 2009. Rapid warming of large marine ecosystems. Prog. Oceanogr., 81(1-4): 207-213. https://doi.org/10.1016/j.pocean.2009.04.011
  2. Bryden, H.L., H.R. Longworth and S.A. Cunningham, 2005. Slowing of the Atlantic meridional overturning circulation at 25°N. Nature, 438(7068): 655-657. https://doi.org/10.1038/nature04385
  3. Chang, K.I., K. Kim, Y.B. Kim, W.J. Teague, J.C. Lee and J.H. Lee, 2009. Deep flow and transport through the Ulleung Interplain Gap in the southwestern East/Japan Sea. Deep Sea Res. Part I Oceanogr. Res. Pap., 56(1): 61-72. https://doi.org/10.1016/j.dsr.2008.07.015
  4. Chang, K.I., N.G. Hogg, M.S. Suk, S.K. Byun, Y.G. Kim and K. Kim, 2002. Mean flow and variability in the southwestern East Sea. Deep Sea Res. Part I Oceanogr. Res. Pap., 49(12): 2261-2279. https://doi.org/10.1016/S0967-0637(02)00120-6
  5. Chang, K.I., W.J. Teague, S.J. Lyu, H.T. Perkins, D.K. Lee, D.R. Watts, Y.B. Kim, D.A. Mitchell, C.M. Lee and K. Kim, 2004. Circulation and currents in the southwestern East/Japan Sea: Overview and review. Prog. Oceanogr., 61(2-4): 105-156. https://doi.org/10.1016/j.pocean.2004.06.005
  6. Chen, C.T.A., A.S. Bychkov, S.L. Wang and G.Y. Pavlova, 1999. An anoxic Sea of Japan by the year 2200?. Mar. Chem., 67(3-4): 249-265. https://doi.org/10.1016/S0304-4203(99)00074-2
  7. Choi, Y.J. and J.H. Yoon, 2010. Structure and seasonal variability of the deep mean circulation of the East Sea (Sea of Japan). J. Oceanogr., 66(3): 349-361. https://doi.org/10.1007/s10872-010-0031-y
  8. Clayson, C.A. and M. Luneva, 2004. Deep convection in the Japan (East) Sea: A modeling perspective. Geophys. Res. Lett., 31(17).
  9. Cui, Y. and T. Senjyu, 2010. Interdecadal oscillations in the Japan Sea proper water related to the arctic oscillation. J. Oceanogr., 66(3): 337-348. https://doi.org/10.1007/s10872-010-0030-z
  10. Cui, Y. and T. Senjyu, 2012. Has the upper portion of the Japan Sea Proper Water formation really been enhancing?. J. Oceanogr., 68(4): 593-598. https://doi.org/10.1007/s10872-012-0115-y
  11. Dickson, B., I. Yashayaev, J. Meincke, B. Turrell, S. Dye and J. Holfort, 2002. Rapid freshening of the deep North Atlantic Ocean over the past four decades. Nature, 416(6883): 832-837. https://doi.org/10.1038/416832a
  12. Gamo, T. and Y. Horibe, 1983. Abyssal circulation in the Japan Sea. J. Oceanogr. Soc. Jpn., 39(5): 220-230. https://doi.org/10.1007/BF02070392
  13. Gamo, T., 1999. Global warming may have slowed down the deep conveyor belt of a marginal sea of the northwestern Pacific: Japan Sea. Geophys. Res. Lett., 26(20): 3137-3140. https://doi.org/10.1029/1999GL002341
  14. Gamo, T., 2011. Dissolved oxygen in the bottom water of the Sea of Japan as a sensitive alarm for global climate change. Trends Analyt Chem, 30(8): 1308-1319. https://doi.org/10.1016/j.trac.2011.06.005
  15. Gamo, T., N. Momoshima and S. Tolmachyov, 2001. Recent upward shift of the deep convection system in the Japan Sea, as inferred from the geochemical tracers tritium, oxygen, and nutrients. Geophys. Res. Lett., 28(21): 4143-4146. https://doi.org/10.1029/2001GL013367
  16. Gamo, T., N. Nakayama, N. Takahata, Y. Sano, J. Zhang, E. Yamazaki, S. Taniyasu and N. Yamashita, 2014. The Sea of Japan and its unique chemistry revealed by time-series observations over the last 30 years. Monogr Environ Earth Planets, 2(1): 1-22. https://doi.org/10.5047/meep.2014.00201.0001
  17. Gamo, T., Y. Nozaki, H. Sakai, T. Nakai and T. Tsubota, 1986. Spacial and temporal variations of water characteristics in the Japan Sea bottom water. J. Mar. Res., 44(4): 781-793. https://doi.org/10.1357/002224086788401620
  18. Han, M., Y.K. Cho, H.W. Kang and S. Nam, 2020. Decadal changes in meridional overturning circulation in the East Sea (Sea of Japan). J. Phys. Oceanogr., 50(6): 1773-1791. https://doi.org/10.1175/JPO-D-19-0248.1
  19. Han, M., Y.S. Chang, H.W. Kang, D.J. Kang and Y.S. Kim, 2021. Turnover time of the East Sea (Sea of Japan) meridional overturning circulation. Front. Mar. Sci., 8.
  20. Jamet, Q., W.K. Dewar, N. Wienders, B. Deremble, S. Close and T. Penduff, 2020. Locally and remotely forced subtropical AMOC variability: a matter of time scales. J. Clim., 33(12): 5155-5172. https://doi.org/10.1175/jcli-d-19-0844.1
  21. Jeong, Y., S. Nam, J.I. Kwon, U. Uppara and Y.H. Jo, 2022. Surface Warming Slowdown with Continued Subsurface Warming in the East Sea (Japan Sea) over Recent Decades (2000-2014). Front. Mar. Sci., 173.
  22. Kang, D.J., J.Y. Kim, T. Lee and K.R. Kim, 2004. Will the East/Japan Sea become an anoxic sea in the next century?. Mar. Chem., 91(1-4): 77-84. https://doi.org/10.1016/j.marchem.2004.03.020
  23. Kang, D.J., S. Park, Y.G. Kim, K. Kim and K.R. Kim, 2003. A moving-boundary box model (MBBM) for oceans in change: An application to the East/Japan Sea. Geophys. Res. Lett., 30(6).
  24. Kim, B.-G., Y.-K. Cho and Y. Noh, 2022a. Deep convection along the continental slope in the East/Japan Sea: A large-eddy simulation study. Front. Mar. Sci., 9:824256.
  25. Kim, H., N. Hirose and K. Takayama, 2022b. Physical and Biological Factors Underlying Long-Term Decline of Dissolved Oxygen Concentration in the East/Japan Sea. Front. Mar. Sci., 9: 851598.
  26. Kim, K., K.R. Kim, D.H. Min, Y. Volkov, J.H. Yoon and M. Takematsu, 2001. Warming and structural changes in the East (Japan) Sea: a clue to future changes in global oceans?. Geophys. Res. Lett., 28(17): 3293-3296. https://doi.org/10.1029/2001GL013078
  27. Kim, K., K.R. Kim, Y.G. Kim, Y.K. Cho, D.J. Kang, M. Takematsu and Y. Volkov, 2004. Water masses and decadal variability in the East Sea (Sea of Japan). Prog. Oceanogr., 61(2-4): 157-174. https://doi.org/10.1016/j.pocean.2004.06.003
  28. Kim, K., K.R. Kim, Y.G. Kim, Y.K. Cho, J.Y. Chung, B.H. Choi, S.K. Byun, G.H. Hong, M. Takematsu, J.H. Yoon, Y. Volkov and M. Danchenkov, 1996. New findings from CREAMS observations: Water masses and eddies in the East Sea. J. Korean Soc. Oceanogr., 31(4): 155-163.
  29. Kim, K.R. and K. Kim, 1996. What is happening in the East Sea (Japan Sea)?: Recent chemical observations during CREAMS 93-96. J. Korean Soc. Oceanogr., 31(4): 164-172.
  30. Kim, K.R., G. Kim, K. Kim, V. Lobanov, V. Ponomarev and A. Salyuk, 2002. A sudden bottom-water formation during the severe winter 2000-2001: The case of the East/Japan Sea. Geophys. Res. Lett., 29(8): 75-1-75-4. https://doi.org/10.1029/2001GL014498
  31. Kim, Y.-B. and G.-T. Yi, 2017. Historical background and its scientific meaning of the Japanese hydrographic survey of the East Sea in 1932. J. Fis. Mar. Sci. Edu., 29(5): 1373-1383. https://doi.org/10.13000/JFMSE.2017.29.5.1373
  32. Kosugi, N., N. Hirose, T. Toyoda and M. Ishii, 2021. Rapid freshening of Japan Sea Intermediate Water in the 2010s. J Oceanogr., 77(2): 269-281. https://doi.org/10.1007/s10872-020-00570-6
  33. Kumamoto, Y.I., M. Yoneda, Y. Shibata, H. Kume, A. Tanaka, T. Uehiro and K. Shitashima, 1998. Direct observation of the rapid turnover of the Japan Sea bottom water by means of AMS radiocarbon measurement. Geophys. Res. Lett., 25(5):651-654. https://doi.org/10.1029/98GL00359
  34. Kwon, Y.O., K. Kim, Y.G. Kim and K.R. Kim, 2004. Diagnosing long-term trends of the water mass properties in the East Sea (Sea of Japan). Geophys. Res. Lett., 31(20).
  35. Lee, E.Y. and K.A. Park, 2019. Change in the recent warming trend of sea surface temperature in the East Sea (Sea of Japan) over decades (1982-2018). Remote Sens., 11(22): 2613.
  36. Levin, L.A. and N. Le Bris, 2015. The deep ocean under climate change. Science, 350(6262): 766-768. https://doi.org/10.1126/science.aad0126
  37. Lindsey, R. and L. Dahlman, 2020. Climate Change: Ocean Heat Content. Climate.gov, August, 17.
  38. Marshall, J. and F. Schott, 1999. Open-ocean convection: Observations, theory, and models. Rev. Geophys, 37(1): 1-64. https://doi.org/10.1029/98rg02739
  39. Min, D.H. and M.J. Warner, 2005. Basin-wide circulation and ventilation study in the East Sea (Sea of Japan) using chlorofluorocarbon tracers. Deep Sea Res. Part II Top. Stud. Oceanogr., 52(11-13): 1580-1616. https://doi.org/10.1016/j.dsr2.2003.11.003
  40. Minami, H., Y. Kano and K. Ogawa, 1999. Long-term variations of potential temperature and dissolved oxygen of the Japan Sea Proper Water. J Oceanogr., 55(2): 197-205. https://doi.org/10.1023/A:1007889929187
  41. Mooers, C.N., H. Kang, I. Bang and D.P. Snowden, 2006. JES CIRCULATION. Oceanography., 19(3): 86.
  42. Na, T., J. Hwang, S.Y. Kim, S. Jeong, T. Rho and T. Lee, 2022. Large increase in dissolved organic carbon in the East Sea (Japan Sea) from 1999 to 2019. Front. Mar. Sci., 108. ADD Page number.
  43. Nitani, H., 1972. On the deep and bottom waters in the Japan Sea, in Research in Hydrography and Oceanography, edited by D. Shoji, pp. 151-201, Hydrogr. Dep. of Jpn. Mar. Safety Agency, Tokyo.
  44. Noh, Y., C.J. Jang and J.W. Kim, 1999. Large eddy simulation of open ocean deep convection with application to the deep water formation in the East Sea (Japan Sea). J. Oceanogr., 55(2): 347-367. https://doi.org/10.1023/A:1007889229058
  45. Pai, S.C., G.C. Gong and K.K. Liu, 1993. Determination of dissolved oxygen in seawater by direct spectrophotometry of total iodine. Mar. Chem., 41(4): 343-351. https://doi.org/10.1016/0304-4203(93)90266-Q
  46. Park, K.A., K. Kim, P.C. Cornillon and J.Y. Chung, 2006. Relationship between satellite-observed cold water along the Primorye coast and sea ice in the East Sea (the Sea of Japan). Geophys. Res. Lett., 33(10).
  47. Park, Y.G., 2007. The effects of Tsushima Warm Current on the interdecadal variability of the East/Japan Sea thermohaline circulation. Geophys. Res. Lett., 34(6).
  48. Postlethwaite, C.F., E.J. Rohling, W.J. Jenkins and C.F. Walker, 2005. A tracer study of ventilation in the Japan/East Sea. Deep Sea Res. Part II Top. Stud. Oceanogr., 52(11-13): 1684-1704. https://doi.org/10.1016/j.dsr2.2004.07.032
  49. Send, U., M. Lankhorst and T. Kanzow, 2011. Observation of decadal change in the Atlantic meridional overturning circulation using 10 years of continuous transport data. Geophys. Res. Lett., 38(24).
  50. Senjyu, T. and H. Sudo, 1993. Water characteristics and circulation of the upper portion of the Japan Sea Proper Water. J. Mar. Syst., 4(4): 349-362. https://doi.org/10.1016/0924-7963(93)90029-L
  51. Senjyu, T. and H. Sudo, 1994. The upper portion of the Japan Sea Proper Water; its source and circulation as deduced from isopycnal analysis. J. Oceanogr., 50(6): 663-690. https://doi.org/10.1007/BF02270499
  52. Senjyu, T., 2022. Changes in Mid-Depth Water Mass Ventilation in the Japan Sea Deduced From Long-Term Spatiotemporal Variations of Warming Trends. Front. Mar. Sci.
  53. Senjyu, T., H.R. Shin, J.H. Yoon, Z. Nagano, H.S. An, S.K. Byun and C.K. Lee, 2005. Deep flow field in the Japan/East Sea as deduced from direct current measurements. Deep Sea Res. Part II Top. Stud. Oceanogr., 52(11-13): 1726-1741. https://doi.org/10.1016/j.dsr2.2003.10.013
  54. Senjyu, T., T. Aramaki, S. Otosaka, O. Togawa, M. Danchenkov, E. Karasev and Y. Volkov, 2002. Renewal of the bottom water after the winter 2000-2001 may spin-up the thermohaline circulation in the Japan Sea. Geophys. Res. Lett., 29(7): 53-1-53-3. https://doi.org/10.1029/2001GL014093
  55. Shin, J., S. Noh and S. Nam, 2020. Intraseasonal abyssal current variability of bottom-trapped topographic Rossby waves in the Southwestern East Sea (Japan Sea). Front. Mar. Sci., 7: 579680.
  56. Srokosz, M., M. Baringer, H. Bryden, S. Cunningham, T. Delworth, S. Lozier, J. Marotzke and R. Sutton, 2012. Past, present, and future changes in the Atlantic meridional overturning circulation. Bull Am Meteorol Soc, 93(11): 1663-1676. https://doi.org/10.1175/BAMS-D-11-00151.1
  57. Stouffer, R.J., J. Yin, J.M. Gregory, K.W. Dixon, M.J. Spelman, W. Hurlin, A.J. Weaver, M. Eby, G.M. Flato, H. Hasumi, A. Hu, J.H. Jungclaus, I.V. Kamenkovich, A. Levermann, M. Montoya, S. Murakami, S. Nawrath, A. Oka, W.R. Peltier, D.Y. Robitaille, A. Sokolov, G. Vettoretti and S.L. Weber, 2006. Investigating the causes of the response of the thermohaline circulation to past and future climate changes. J. Clim., 19(8): 1365-1387. https://doi.org/10.1175/JCLI3689.1
  58. Sudo, H., 1986. A note on the Japan Sea proper water. Prog. Oceanogr., 17(3-4): 313-336. https://doi.org/10.1016/0079-6611(86)90052-2
  59. Talley, L., D.H. Min, V. Lobanov, V. Luchin, V. Ponomarev, A. Salyuk, A. Shcherbina, P. Tishchenko and I. Zhabin, 2006. Japan/East Sea water masses and their relation to the sea's circulation. Oceanography., 19(3): 32-49. https://doi.org/10.5670/oceanog.2006.42
  60. Talley, L.D., V. Lobanov, V. Ponomarev, A. Salyuk, P. Tishchenko, I. Zhabin and S. Riser, 2003. Deep convection and brine rejection in the Japan Sea. Geophys. Res. Lett., 30(4).
  61. Tanaka, K., 2014. Formation of bottom water and its variability in the northwestern part of the Sea of Japan. J. Geophys. Res. Oceans, 119(3): 2081-2094. https://doi.org/10.1002/2013JC009456
  62. Teague, W.J., K.L. Tracey, D.R. Watts, J.W. Book, K.I. Chang, P.J. Hogan, D.A. Mitchell, M.S. Suk, M. Wimbush and J.H. Yoon, 2005. Observed deep circulation in the Ulleung Basin. Deep Sea Res. Part II Top. Stud. Oceanogr., 52(11-13): 1802-1826. https://doi.org/10.1016/j.dsr2.2003.10.014
  63. Tsunogai, S., Y.W. Watanabe, K. Harada, S. Watanabe, S. Saito and M. Nakajima, 1993. Dynamics of the Japan Sea deep water studied with chemical and radiochemical tracers. In Elsevier oceanography series, Vol. 59, Elsevier, pp. 105-119.
  64. Uda, M., 1934. The results of simultaneous oceanographic investigations in the Japan Sea and its adjacent waters in May and June, 1932. J. Imp. Fish. Exp. Stn., 5: 57-190.
  65. Worthington, E.L., B.I. Moat, D.A. Smeed, J.V. Mecking, R. Marsh and G.D. McCarthy, 2021. A 30-year reconstruction of the Atlantic meridional overturning circulation shows no decline. Ocean Sci., 17(1): 285-299. https://doi.org/10.5194/os-17-285-2021
  66. Yoon, S.T., K.I. Chang, S. Nam, T. Rho, D.J. Kang, T. Lee, K.A. Park, V. Lobanov, D. Kaplunenko, P. Tishchenko and K.R. Kim, 2018. Re-initiation of bottom water formation in the East Sea (Japan Sea) in a warming world. Sci. Rep., 8(1): 1-10. https://doi.org/10.1038/s41598-018-19952-4
  67. Yoshikawa, Y., T. Awaji and K. Akitomo, 1999. Formation and circulation processes of intermediate water in the Japan Sea. J. Phys. Oceanogr., 29(8): 1701-1722. https://doi.org/10.1175/1520-0485(1999)029<1701:FACPOI>2.0.CO;2