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Abundance and Copepod Community Size deviation to the long term average, for the Southern Ocean

The Southern Ocean region is divided into 9 areas, shown in the map above. The Abundance and Copepod Community Size time series found after sampling those areas are shown in the graph at the bottom of this page.

Since the 1930s there has been a systematic and substantial warming of the Southern Ocean with much of this concentrated in the Antarctic Circumpolar Current (Aoki et al. 2003, Böning et al. 2008, Gille 2002, 2008). There has also been a freshening of the upper surface waters of the Southern Ocean (Boyer et al. 2005, Böning et al., 2008, Rintoul et al. 2012), which will lead to increased stratification and potentially a reduction in the input of nutrients into the euphotic zone (Rintoul et al. 2012).
Global warming will affect the extent and volume of sea-ice, which in turn will affect the sea-ice organisms such as Antarctic krill. There has been an approximate 25% loss of sea-ice between the 1950s and 1970s (de la Mare 1997, 2009). The warming of the Southern Ocean, and the effects in terms of loss of sea ice, is not uniform across the region. Ducklow et al. (2007) described the western Antarctic Peninsula as "experiencing the most rapid warming of any marine ecosystem on the planet".

The Continuous Plankton Recorder sampling of some parts of the Southern Ocean extends over several decades. The Total Mesozooplankton Abundance variable shows a steady in increase in abundance over time in all four zones of the East Antarctic region. All increases were statistically significant, although the specific causes of these increases still need to be identified. By contrast the Ross Sea region showed no trend in any of the four zones over the shorter period of Continuous Plankton Recorder tows in that region. However, the total abundances of zooplankton in the Ross Sea region were generally higher than the abundances in the East Antarctic region.

The Average Copepod Community Size variable also increased significantly over time in all four zones of the East Antarctic region. The increase in Average Copepod Community Size values indicates a shift in the abundance and dominance of copepod species to larger species which is contrary to the hypothesis that warming waters, as is occurring in the region, would favour smaller warm water copepods. Other factors are thus driving the shift in species dominance and need to be determined. The Continuous Plankton Recorder operations in the Ross Sea region have not been operating long enough yet to identify any trend within the Average Copepod Community Size.