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Figure 2. Summary of Arctic sea-ice extent from August 2011 to December 2011.
4 Dramatic Changes in the Hudson Bay Complex
While climate change research has focused primarily on the dramatic changes that are taking place in the
high arctic many of the publications documenting and interpreting these changes are very relevant to
what is happening in the Hudson Bay region. Satellite monitoring since 1971, and especially after 1979,
has enabled scientists to monitor parameters such as the extent and volume of sea-ice and sea-surface
temperatures in the Arctic Ocean as well as in subarctic seas such as Hudson Bay. There have also been a
number of books and special issues of science journals that focus primarily on the conditions in the Hudson
Bay region.
As in the high Arctic, much of the focus is on the ice regime, and satellite surveillance has provided a
powerful means of real-time monitoring of the status and trends in ice cover. There are important
differences in the ice regimes. The Arctic Ocean has a perennial ice cap that partially melts each melt
season. An important signal of climate warming is the minimal extent of ice cover at the end of the melt
season, which ordinarily occurs in September of each year. In contrast, the Hudson Bay Complex is
typically ice free in the late summer and early fall, so the focus for documenting the pace of change has
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been primarily on ice break-up and freeze-up dates with a warming climate resulting in earlier break-up
and later freeze-up.
While results are variable depending on the time frames and regions chosen for study, most have
documented significantly advancing break-up dates and delayed freeze-up dates for most areas over most
time periods. In recent years, especially since about 1995, the indicators of a warming climate have
become more general and more pronounced throughout the region.
The Hudson Bay System is featured in a number of recent major compilations. The December 2011 issue
of the
Journal of Marine Systems (Macdonald & Kruzyk, eds.) has a preface aptly entitled: “The Hudson
Bay system: A northern inland sea in transition.” The 12 papers in this special issue constitute a major
contribution to our understanding of the Hudson Bay marine system, with a special focus on the changes
occurring in the system. They also provide a glimpse of what to expect in the future. In addition, a 2010
book entitled A Little Less Arctic: Top Predators in the World’s Largest Northern Inland Sea (Ferguson,
Loseto, & Mallory, eds.) provides an up-to-date assessment of the status and trends in major mammal
and waterfowl populations in this system. Most importantly, many of the authors emphasize the many
direct and indirect links between these ice-adapted top predators, including humans and climate change.
Finally, Stewart and Lockhart (2005) put together a major compendium entitled “An overview of the
Hudson Bay marine ecosystem.”
The seasonal ice cover of the Hudson Bay Complex has a profound and overarching influence on the
ecology of the marine system and on the plants and animals that are adapted to living in this system. The
ice cover also has a major impact on regional climate and terrestrial ecosystems. The sea-ice platform is
also of great importance to the inhabitants of the region who, for thousands of years, have relied on a
safe and predictable ice cover to enable them to hunt and harvest marine mammals, waterfowl, fish and
invertebrates from the sea. Until recently the aboriginal peoples living along the coastline were almost
entirely dependent on the harvesting of animals from the sea for their livelihood and survival. These
bounties from the sea continue to provide “country food” and to be culturally and economically important
to Inuit communities around the Hudson Bay Complex.
Many of the investigators have, for obvious reasons, focused on the linkages between surface air
temperatures and the timing of freeze-up and sea-ice melt. The seasonal sea-ice cover is a defining feature
of the system and has a profound impact on its physical, chemical and biological characteristics. The ice
cover directly influences sea-ice-atmosphere connections and the ice regime is both an indicator of
climate change and a significant driver of regional climate. Figure 3 is a simple schematic that illustrates
how the snow and ice cover reflect the sun’s energy back into space.
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Figure 3. A schematic illustration of the albedo effect of the snow and ice cover that reflect solar energy back into
space. In the absence of ice cover, much more of the solar energy is absorbed. This absorbed energy adds heat and
contributes to the further melting of the ice cover. Ice algae and their associated food webs are currently very
important to ice-associated species such as ringed seal.
Ice and snow cover has a dramatic effect on the fate of solar energy reaching the Earth’s surface. Typically
about 80 per cent of the incoming radiation that strikes a snow covered ice surface is reflected back into
space, whereas an ice-free sea surface absorbs some 90–95 per cent of incoming radiation into the water
body. This absorbed energy is then available to accelerate the melting of the remaining ice cover and
delays the formation of ice in the fall and winter. When, as is now the case, atmospheric forcing (warming)
is advancing the dates of ice melt, the positive feedback from the increased absorbance of energy further
advances the melt dates while delaying freeze-up dates. All of this leads to a longer ice-free season.
The Hudson Bay Complex is profoundly influenced by its freshwater budget and also annually receives
approximately 940 km³ of freshwater from rivers entering the Hudson Bay Complex, a quantity
comparable to the combined discharges of the St Lawrence and Mackenzie rivers. The melting of sea ice
adds an even large volume (~1,500 km³) of freshwater to the surface of the complex. The river runoff is
ICE COVER
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