Antarctic Science 17: 171-182 (2005)
Decadal-scale changes in the climate and biota of the Pacific sector of the Southern Ocean, 1950s to the 1990s.
Ainley D, Clarke E, Arrigo K, Fraser W, Kato A, Barton K, Wilson P
Simultaneous, but contrary, decadal-scale changes in population trajectories of two penguin
species in the western Pacific and Ross Sea sectors of the Southern Ocean, during the early/mid-1970s and
again during 1988-89, correspond to changes in weather and sea ice patterns. These in turn are related to
shifts in the semi-annual and Antarctic oscillations. Populations of the two ecologically dissimilar penguin
species - Adelie Pygoscelis adeliae and emperor Aptenodytes forsteri - have been tallied annually since the
1950s making these the longest biological datasets for the Antarctic. Both species are obligates of sea ice
and, therefore, allowing for the demographic lags inherent in the response of long-lived species to habitat or
environmental variation, the proximate mechanisms responsible for the shifts involved changes in coastal
wind strength and air and sea temperatures, which in turn affected the seasonal formation and decay of sea
ice and polynyas. The latter probably affected such rates as the proportion of adults breeding and ultimately
the reproductive output of populations in ways consistent with the two speciesf opposing sea ice needs.
Corresponding patterns for the mid-1970s shift were reflected also in ice-obligate Weddell seal
Leptonychotes weddelli populations and the structure of shallow-water sponge communities in the Ross Sea.
The 1988-89 shift, by which time many more datasets had become available, was reflected among several
ice-frequenting vertebrate species from all Southern Ocean sectors. Therefore, the patterns most clearly
identified in the Pacific Sector were apparently spread throughout the high latitudes of the Southern Ocean.
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