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

The Korean Society of Oceanography (한국해양학회)
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Distribution and Origin of the Mid-depth Cold Water Pools Observed in the Jeju Strait in the Summer of 2019

2019년 여름철 제주해협에서 관측된 중층 저온수의 분포와 기원

  • DOHYEOP YOO (Department of Oceanography, Chonnam National University) ;
  • JONG-KYU KIM (Research Institute for Basic Science, Chonnam National University) ;
  • BYOUNG-JU CHOI (Department of Oceanography, Chonnam National University)
  • 유도협 (전남대학교 해양학과) ;
  • 김종규 (전남대학교 기초과학연구소) ;
  • 최병주 (전남대학교 해양학과)
  • Received : 2023.01.09
  • Accepted : 2023.02.21
  • Published : 2023.02.28
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Abstract

To investigate the role of water masses in the Jeju Strait in summer on the shallow coastal region and the characteristics of water properties in the strait, temperature and salinity were observed across the Jeju Strait in June, July, and August 2019. The cold water pool, whose temperature is lower than 15℃, was observed in the mid-depths of the central Jeju Strait and on the northern bottom slope of the strait. The cold water pools have the lowest temperature in the strait. To identify water masses comprising the cold water pool in the Jeju Strait, mixing ratios of water masses were calculated. The mid-depth cold water pool of the Jeju Strait consists of 54% of the Kuroshio Subsurface Water (KSSW) and 33% of the Yellow Sea Bottom Cold Water (YSBCW). Although the cold water pool is dominantly affected by the KSSW, the YSBCW plays a major role to make the cold water pool maintain the lowest temperature in the Jeju Strait. To find origin of the cold water pool, temperature and salinity data from the Yellow Sea, East China Sea, and Korea Strait in the summer of 2019 were analyzed. The cold water pool was generated along the thermohaline frontal zone between the KSSW and YSBCW in the East China Sea where intrusion and mixing of water masses are active below the seasonal thermocline. The cold water in the thermohaline frontal zone had similar mixing ratio to the cold water pool in the Jeju Strait and it advected toward the Korea Strait and shallow coastal region off the south coast of Korea. Intrusion of the mid-depth cold water pool made temperature inversion in the Jeju Strait and affected sea surface temperature variations at the coastal region off the south coast of Korea.

여름철 제주해협 물성 분포의 특성과 제주해협 수괴가 연안에 미치는 영향을 확인하기 위하여 2019년 6월, 7월, 8월에 완도와 제주도 사이에서 수온과 염분을 관측하였다. 여름철 계절 수온약층 아래에서 15℃의 저온수가 관측되었으며, 이 저온수는 관측시기에 따라 다르지만 수심이 깊은 제주해협 남쪽 골보다는 주로 제주해협 중앙의 중층과 북쪽 사면에 분포하였다. 이 저온수를 구성하는 근원 수괴를 알아보기 위하여 제주해협에서 관측된 해수를 구성하는 주변 근원 수괴들의 혼합비(mixing ratio)를 계산하였다. 여름철 제주해협 중앙 중층과 북쪽 사면에 나타나는 저온수는 평균적으로 쿠로시오 아표층수가 54% 그리고 황해저층냉수가 33% 비율로 혼합된 해수였다. 이 중층 저온수는 제주해협 전 수층에서 가장 낮은 수온을 갖는 해수임에도 상대적으로 고온고염인 쿠로시오아표층수가 큰 구성비율을 갖고 있다. 중층 저온수가 제주해협에서 가장 낮은 수온의 분포를 갖게 된 이유는 다른 제주해협 해수에 비해 황해저층냉수의 기여도가 높기 때문이다. 제주해협 중층 저온수의 기원을 살펴보기 위하여 황해, 동중국해, 대한해협에서 2019년 여름철에 관측한 광역 수온과 염분 자료를 분석하였다. 제주도 남서쪽 동중국해 계절 수온약층 아래에서 쿠로시오 기원의 해수와 황해저층냉수가 열염전선을 형성하였고, 이 열염전선을 가로지르는 수괴의 관입에 의해 해수의 혼합이 발생하였다. 동중국해에서 형성된 이 혼합수는 제주해협에서 관측된 중층 저온수와 거의 같은 혼합비율을 가졌다. 이런 결과들을 종합하였을 때 제주해협에서 여름철에 관측된 중층 저온수는 동중국해에서 쿠로시오 아표층수와 황해저층냉수의 혼합으로 만들어진 저온수가 해류를 따라 이동한 것이다. 제주해협 중앙과 북쪽 사면으로 이동한 중층 저온수는 제주해협 중앙의 중층에서 수온역전을 만들고, 한국 남해안 연안의 표층 수온 변동에도 큰 영향을 미친다.

Keywords

Acknowledgement

황해, 동중국해, 대한해협에서 장기간 정기적으로 수온과 염분을 관측하여 연구에 사용할 수 있도록 자료를 제공해주신 국립수산과학원과 국립해양조사원 관계자분들께 감사드립니다. 이 논문은 전남대학교 학술연구비(과제번호: 2018-3521) 지원에 의하여 연구되었습니다. 또한 이 연구는 한국연구재단의 지원을 받아 수행된 기초연구사업(NRF-2016R1A6A1A03012647)의 일부입니다.

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