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, 9 (1), 10087

Zooplankton and Micronekton Respond to Climate Fluctuations in the Amundsen Sea Polynya, Antarctica


Zooplankton and Micronekton Respond to Climate Fluctuations in the Amundsen Sea Polynya, Antarctica

Hyoung Sul La et al. Sci Rep.


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.

Conflict of interest statement

The authors declare no competing interests.


Figure 1
Figure 1
Multi-year ocean mooring data and related time series. (a) Net primary production (NPP), sea ice concentration (SIC), and surface solar radiation (SSR). (b) POC flux measured at the sediment trap of the K1 mooring. (c) Seasonal changes in the total number of intact post-larval zooplankton in the sediment trap from January 2011 to March 2013. (d) Mean volume backscatter strength (MVBS) measured at the S1 mooring. Black dots indicate the daily mean depth of the maximum MVBS (DMVBS). (e) Monthly means of acoustic intensity (grey bar) and DMVBS (red line).
Figure 2
Figure 2
Temporal variability of the Southern Annular Mode (SAM) and El Niño Southern Oscillation (ENSO). (a) Mean Oceanic Niño Index (ONI). (b) SAM. (c) SIC during the summer (from January to March) in the period 1990 to 2014. (d) The relationship between the ONI and SAM in the period 1990 to 2014. (e) The relationship between the SIC and ONI (or SAM) during in-phase periods (+SAM/La Niña and −SAM/El Niño). The shaded areas in (a–c) indicate the mooring campaign periods.
Figure 3
Figure 3
Effects of climate forcing on biological processes in the Amundsen Sea coastal polynya under two distinct climate regimes. The schematic illustration explains how climate fluctuations affect the phytoplankton bloom and SIC that control the seasonal vertical migration of zooplankton. Zooplankton remain longer near the bottom beginning to ascend in October when the summer SIC is low with high PP under −SAM/El Niño; in August, they begin to ascend to the surface when the summer SIC is high with low PP under +SAM/La Niña. The overwintering depth is shallower during the high summer SIC and low PP under +SAM/La Niña.

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