북동적도태평양에서 엘니뇨, 라니냐 및 평년에 나타난 중형동물플랑크톤 분포의 위도별차이

Abstract

To investigate the effects of physical structures induced by climate change on the mosozooplankton distribution, we measured water temperature, salinity, concentrations of nitrate and chlorophyll-a (chl-a), and abundance of the mesozooplankton above 200m depth along the meridian line (5°N-12°N, 131.5°W) in the summer of 1998, 1999, and 2003. Diverse opposite directions of currents related up- and downwelling in association with the climate change affected the spatio-temporal variation of mesozooplankton latitudinal distribution by changing the concentration of nitrate and chl-a as well as physical conditions. Abundance of mesozooplankton in 1999 (La niña) was higher than that in 1998 (El niño) and 2003 (normal), and it increased as going to the north, whereas decreased in 1998 and 2003. At the study area, the locations of convergence and divergence zones and the magnitude of upwelling and downwelling differed in 1998, 1999 and 2003. A strong upwelling in the divergence zone (from 10.5°N to 11°N) might increase in the chl-a concentration and in turn the abundances of the calanoid-, cyclopoid copepods, chaetognaths, ostracods and radiolarians. However, any upwelling was not clearly detected at the study area in 1998, which might be responsible for low concentrations of nitrate, chl-a, and in turn mesozooplankton. An upwelling, observed in 2003, was located at lower latitude (9°N) than that in 1999. And the strength of the upwelling was weaker than that in 1999, which might be responsible for lower concentrations of nitrate, chl-a, and mesozooplankton than those in 1999, but higher than those in 1998. These evidences suggested that the intra- and interannual heterogeneity of mesozooplankton latitudinal distribution was related to the shift of divergence and convergence zones, which might be affected by the scales and positions of South Equatorial Current (SEC), North Equatorial Current (NEC) and North Equatorial Countercurrent (NECC) in relation