Korean Journal of Environmental Biology (환경생물)

Korean Society of Environmental Biology (한국환경생물학회)
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Influences of Coastal Upwelling and Time Lag on Primary Production in Offshore Waters of Ulleungdo-Dokdo during Spring 2016

2016년 춘계 울릉도-독도주변해역에서 동해 연안 용승과 시간차에 의한 일차생산력 영향

  • 백승호 (한국해양과학기술원 위해성분석연구센터) ;
  • 김윤배 (한국해양과학기술원 울릉도.독도해양연구기지)
  • Received : 2018.04.30
  • Accepted : 2018.05.21
  • Published : 2018.06.30
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Abstract

In order to investigate the upwelling and island effects following the wind storm events in the East Sea (i.e., Uljin-Ulleungdo-Dokdo line) during spring, we assessed the vertical and horizontal profiles of abiotic and biotic factors, including phytoplankton communities. The assessment was based on the Geostationary Ocean Color Imager (GOCI) and field survey data. A strong south wind occurred on May 3, when the lowest sea level pressure (987.3 hPa) in 2016 was observed. Interestingly, after this event, huge blooms of phytoplankton were observed on May 12 along the East Korean Warm Current (EKWC), including the in the offshore waters of Ulleungdo and Dokdo. Although the diatoms dominated the EKWC area between the Uljin coastal waters and Ulleungdo, the population density of raphidophytes Heterosigma akashiwo was high in the offshore waters of Ulleungdo-Dokdo. Based on the vertical profiles of Chlorophyll-a (Chl. a), the sub-surface Chl. a maximum appeared at 20 m depths between Uljin and Ulluengdo, whereas relatively high Chl. a was distributed equally across the entire water column around the waters of Ulleungdo and Dokdo islands. This implies that the water mixing (i.e., upwelling) at the two islands, that occurred after the strong wind event, may have brought the rapid proliferation of autotrophic algae, with nutrient input, to the euphotic layer. Therefore, we have demonstrated that a strong south wind caused the upwelling event around the south-eastern Korean peninsula, which is one of the most important role in occurring the spring phytoplankton blooms along the EKWC. In addition, the phytoplankton blooms may have potentially influenced the oligotrophic waters with discrete time lags in the vicinity of Ulleungdo and Dokdo. This indicates that the phytoplankton community structure in the offshore waters of Ulleungdo-Dokdo is dependent upon the complicated water masses moving related to meandering of the EKWC.

본 연구에서는 강풍에 의한 연안 용승 및 섬효과를 구체적으로 파악하기 위해서 춘계 강한 저기압 통과 전후를 대상으로 위성자료, 해양환경 및 물리적인 수직 구조와 함께 식물플랑크톤의 군집구조를 파악하였다. 5월 3일 강한 저기압이 통과하면서 남풍계열의 바람이 우점하였고, 10일 정도의 시간차를 둔 5월 12일에는 동한난류가 이동한 경로주변해역에서 높은 엽록소값이 관찰되었다. 식물플랑크톤 수평적 군집조성은 동한난류의 영향을 강하게 받은 울진 연안과 울릉도 사이의 정점에서는 규조류가 극히 높은 밀도로 우점하였고, 상대적으로 외양인 울릉도와 독도 섬주변에서는 섬효과에 의하여 침편조류 H. akashiwo가 높은 개체수를 유지하였다. 엽록소의 수직적 분포는 울진에서 울릉도로 이어지는 정점에서 엽록소 아표층극대 (Sub-surface Chl-a Maximum)가 20 m 층에서 관찰되었고, 울릉도와 독도 섬주변의 대부분 정점에서는 30~40 m 층까지 전 수층에 걸쳐 균일하게 높은 엽록소 형광값이 관찰되었다. 이는 섬효과에 의하여, 강한 수층혼합이 일어난 것을 의미하고, 그 결과 유광층 상부에 공급된 영양염류에 의하여 식물플랑톤이 대발생하였다. 결과적으로 춘계 한반도 남동해역(울진-울릉도-독도)에서는 남풍계열의 바람이 우점하면, 연안 용승이 발생할 수 있고, 이는 식물플랑크톤의 대발생에 중요한 역할을 하는 것으로 관찰되었다. 아울러, 동해 연안해역에서 기인된 식물플랑크톤은 동해 중앙 및 남서해역으로 공간이동하면서 울릉도-독도의 섬효과와 함께 동한난류의 사행, 소용돌이의 발달 등에 따라서 종조성이 다르게 나타날 가능성을 시사하였다.

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