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Smith, R.C., K.S. Baker, and S.E. Stammerjohn, 1998: Exploring sea ice indexes for polar ecosystem studies. Bioscience, 48, 83-93.
Nothing more dramatically illustrates the extreme seasonality of the Southern Ocean physical environment than the annual waxing and waning of sea ice over 20 million km[sup2] of ocean. In winter, sea ice can almost double the surface area of the Antarctic continent, whereas in summer, sea ice covers approximately one-sixth of the area it covers in winter and is confined to just a few basins. These differences are as extreme as the perpetual night and day associated with those two seasons, except that seasonal changes in both the timing and magnitude of sea ice coverage are far more variable than seasonal changes in solar radiation. In this tempestuous environment, local atmospheric and oceanic forces shape the vast sea ice landscape of the Southern Ocean, creating not only high seasonal variability but also high spatial variability and, consequently, different regional sea ice environments.
In the context of this high regional variability, marine ecologists seek to understand how interannual fluctuations and the extreme seasonality of sea ice coverage are linked to variability in the marine ecosystem. External physical forcing plays a more dominant role in causing variability in marine ecosystems than internal biological mechanisms, which may be more dominant in causing variability in terrestrial ecoystems. To compare how sea ice coverage influences biological and ecological phenomena, a quantitative reference system is needed. However, no accepted standard exists to describe sea ice variability. Therefore, we propose a set of sea ice indexes that provide quantitative definitions of the timing and magnitude of sea ice coverage on temporal and spatial scales that are relevant to testing ice—ecosystem linkages. A sea ice index is a number (or, at most, a few numbers) that derives from a set of sea ice observations during a year and that may be used as a simplified ecological indicator of annual sea ice variability.
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