U.S. Dept. of Commerce / NOAA / OAR / PMEL
/ Publications
Under-ice observations of water column temperature, salinity and spring phytoplankton dynamics: Eastern Bering Sea shelf
P. J. Stabeno,1 J. D. Schumacher,1
R. F. Davis2 and J. M. Napp3
1NOAA, Pacific Marine Environmental Laboratory, 7600 Sand Point Way NE, Seattle, Washington 98115
2Department of Oceanography, Dalhousie University, Nova Scotia, Canada
3NOAA, Alaska Fisheries Science Center, 7600 Sand Point Way NE, Seattle 98115
Journal of Marine Research, 56, 239–255, 1998.
This paper is not subject to U.S. copyright. Published in 1998 by the Journal of Marine Research
2. Background
The eastern Bering Sea covers a broad (>500 km), shallow continental shelf. The
shelf is divided into three depth domains, coastal (0-50 m), middle (50-100 m),
and outer (100-180 m), with distinctive hydrographic, circulation, and planktonic
community characteristics (Cooney
and Coyle, 1982; Coachman,
1986; Walsh
and McRoy, 1986; Schumacher
and Stabeno, 1998). During spring-summer, the hydrographic domains exhibit
distinct vertical structure: well-mixed or weakly stratified in the coastal domain;
strongly two-layered over the middle shelf; and upper and lower mixed layers separated
by a region with fine structure on the outer shelf. Mooring 2 was deployed in
the middle domain to measure biophysical variables during the evolution of the
two-layer system during spring and summer; mooring 3 was positioned to measure
changes in the more oceanic character of the outer shelf. Mooring 1 was deployed
near the Alaskan Peninsula, in a region influenced by water from Alaska Coastal
Current advected through Unimak Pass and slope water advected up Bering Canyon.
The eastern Bering Sea shelf is a marginal ice zone where polar and subarctic
systems interact. During the summer and fall the shelf is usually ice free.
In winter the juxtaposition of the Aleutian Low and Siberian High results in
strong, frigid winter winds from the northeast. These winds cause extensive
ice formation along leeward coasts, which is then advected southwestward. The
leading edge of the ice is continuously melting, introducing cold freshwater
to the water column. Maximum ice extent is typically in late March (Wyllie-Echeverria,
1995). The location of the southernmost position of the ice varies over
hundreds of kilometers. In extreme years (e.g., 1976), ice covers the entire
southeastern shelf (Fig. 1). The extent of the
ice influences the temperature and horizontal extent of a cold pool that occurs
in the lower layer of the middle shelf. The cold pool, which is 40-50 m thick,
persists through the summer, warming only slightly (often <2°C).
The eastern Bering Sea shelf is one of the most productive regions of the world's
oceans (Walsh
and McRoy, 1986). Ice-edge phytoplankton blooms are common features in marginal
ice zones during the spring (Smith,
1987; Niebauer,
1991) and produce a large fraction of the annual primary production over
the shelf. This occurs as the ice melts back in the spring and a surface mixed
layer is formed as a result of the increase in freshwater (Niebauer
et al., 1995). The rapid increase in chlorophyll can be assisted
by the seeding of the water column with ice algae (Schandelmeier
and Alexander, 1981).
Return to previous section or go to next section
PMEL Outstanding Papers
PMEL Publications Search
PMEL Homepage
