Zooplankton and micronekton respond to climate fluctuations in the Amundsen Sea polynya, Antarctica

Hyoung Sul La1, Keyhong Park2, Anna Wahlin3, Kevin R Arrigo4, Dongseon Kim5, Eun Jin Yang6, Angus Atkinson7, Sophie Fielding8, Jungho Im9, Tae-Wan Kim10, Hyeong Chul Shin11, SangHoon Lee2 and Ho Kyung Ha12, (1)Korea Polar Research Institute, Incheon, South Korea, (2)KOPRI Korea Polar Research Institute, Incheon, Korea, Republic of (South), (3)University of Gothenburg, Gothenburg, Sweden, (4)Stanford University, Earth System Science, Stanford, CA, United States, (5)Korea Ocean Research & Develop, Ansan, Korea, Republic of (South), (6)Korea Polar Research Institute, Division of Ocean Sciences, Incheon, South Korea, (7)Plymouth Marine Lab, Plymouth, United Kingdom, (8)British Antarctic Survey, Cambridge, United Kingdom, (9)Ulsan National Institute of Science and Technology, Department of Civil, Urban, Earth, and Environmental Engineering, Ulsan, South Korea, (10)KOPRI Korea Polar Research Institute, Incheon, South Korea, (11)KOPRI, South Korea, (12)Inha University, Ocean Sciences, Incheon, South Korea
The vertical migration of zooplankton and micronekton (hereafter ‘zooplankton’) has ramifications throughout the food web. Here, we present the first evidence that climate fluctuations affect the vertical migration of zooplankton in the Southern Ocean, based on multi-year acoustic backscatter data from one of the deep troughs in the Amundsen Sea, Antarctica. High net primary productivity (NPP) and the annual variation in seasonal ice cover make the Amundsen Sea coastal polynya an ideal site in which to examine how zooplankton behavior responds to climate fluctuations. Our observations show that the timing of the seasonal vertical migration and abundance of zooplankton in the seasonally varying sea ice is correlated with the Southern Annular Mode (SAM) and El Niño Southern Oscillation (ENSO). Zooplankton in this region migrate seasonally and overwinter at depth, returning to the surface in spring. During +SAM/La Niña periods, the at-depth overwintering period is shorter compared to SAM/El Niño periods, and return to the surface layers starts earlier in the year. These differences may result from the higher sea ice cover and decreased NPP during +SAM/La Niña periods. This observation points to a new link between global climate fluctuations and the polar marine food web.