Geoscience Reference
In-Depth Information
Chapter 1
Introduction
Abstract: Earth's polar regions play a pivotal role in climate, both as an important
mediator in exchanges between the atmosphere and global ocean, and as a harbinger
of climate change. Central to this impact is a thin layer of sea ice that is predomi-
nantly seasonal, and at maximum extent (at the end of austral winter) covers roughly
8% of the world ocean area. Sea ice affects climate in several important ways. It ef-
fectively insulates the ocean from the cold polar atmosphere, reducing both outgoing
longwave radiation and convective heat exchange; it reflects a much higher propor-
tion of incoming shortwave radiation than does open water; and by rejecting salt as it
freezes, is capable of producing the cold, saline water that constitutes the end point
in mixing processes that determine the density of the abyssal ocean. This chapter
discusses the rationale behind a monograph on how sea ice affects atmosphere-
ocean exchanges and how studies of turbulent exchange in the ice-ocean boundary
layer have revealed much about how planetary boundary layers (where rotation is
important) work in general. It briefly describes pertinent ice-station exercises, and
lays out the framework for subsequent chapters.
1.1 Arctic Change
In early October 1997, I was part of a large party of polar scientists establishing
the Surface Heat Budget of the Arctic (SHEBA) ice station, which was slated to
drift for a year in multiyear pack ice over the Canadian Basin in the western Arctic
Ocean. Its purpose was to assess the various energy components responsible for
maintaining the perennial sea ice of the Arctic. Earlier, after a long week waiting in
Tuktoyaktuk, NWT, for decent flying weather, most of us had boarded the Canadian
Coast Guard icebreaker
Des Grosiellier
, which was to serve as our drifting base for
the next year, anticipating an arduous trip following our escort icebreaker (the CCS
Louis St. Laurent
) as it battered its way through thick ice toward the center of the
Beaufort Gyre. Instead, those of us who had been in that part of the Arctic before
were astonished at how easy our passage was in ice often a meter or less thick. After
