These measurements by sonar are consistent with observed hydrochemical signatures of ice production based on oxygen isotope analysis (Melling and Riedel 1996).

Flaw leads are ice factories, where freezing occurs under very dynamic conditions. The strong winds which drive the ice frown these areas also have a strong effects on ocean circulation. The effects of freezing, wind and shelf currents are strongly coupled and should not be considered separately. The production of ice in flaw leads is episodic: the time interval between the opening and closing is usually short (3-5 days); that of open water is much shorter (0.5 day).

6. LONG-TERM TRENDS

　

A regional survey of oceanic temperature and salinity has been completed in the southern Canada Basin during most winters between 1979 and 1996. These observations reveal an interesting warming trend in the temperature of the upper halocline in this area (Figure 5). The temperature has increased by about 0.15℃ and 0.10℃ at 33.5 and 33.1 salinity, respectively. Since the temperature of the upper halocline is the result of the counteracting influences of upward heat diffusion from Atlantic waters and lateral intrusions of cold shelf waters, Figure 5 suggests that the supply of cold waters to the upper halocline from the shelves in this area has been decreasing over the last two decades. Since atmospheric circulation is a strong determinant of ventilation, decadal changes in sea-level pressure fields reported by Walsh et al. (1995) are implicated here.

　

7. SUMMARY

　

Halocline ventilation has been observed off windward shores in two areas of the North American Arctic.

Winds in autumn exert a strong influence on the subsequent occurrence of ventilation in winter by: dispersing fresh river and melt water, driving entrainment of salt into the surface layer, and at times forcing an upwelling of saline water to the freezing interface.

Winds in winter are responsible for the episodic opening and closing of coastal polynyas. During opening, winds maintain enhanced rates freezing and salt input to shelf waters. During closing, winds generate the heavy ridging which separates coastal and offshore oceanic regimes, and which 'makes space' for new ice-free areas following wind chnage.

Ice production is enhanced in flaw polynyas, but not astoundingly so. Thus, freezing is necessary to the ventilation of the upper Arctic halocline, but not sufficient.

Important variations occur in upper halocline ventilation in the Arctic occur on inter-annual and decadal time scales.

　

REFERENCES

　

Aagaard K., L.K. Coachman & E.C. Carmack, 1981. DeeP-Sea Res. 28A, 529-545.

Aagaard K., J. Swift & E.C. Carmack, 1985. J. Geophys. Res. 90, 4833-4846.

Garrison G.R, & P. Becker, 1976. J, Geophys. Res. 81,4445-4453.

Macdonald R.W. & E.C. Carmack, 1991. Atmos.Oc.29, 37-53.

Melling H. & R.M. Moore, 1995. Cont. Shelf Res. 15(1), 81-113.

Melling H. 1993. Cont. Shelf Res. 13, 1123-1147.

Melling H. & E.L. Lewis, 1982. DeeP-Sea Res. 29A, 967-985.

Melling H. & R.M. Moore, 1995. Cont. Shelf Res. 15, 89-113.

Melling H. & D.R. Riedel, 1996. J. Geophys. Res. 101, 11975-11991.

Mountain D. & K. Aagaard, 1976. J. Geophys. Res.

Weingartner T. et al., 1998. J. Geophys. Res. (in press)

Walsh et al., 1995. Mon. Wea. Rev.

　

International Workshop on Exchange Processes between the Arctic Shelves and Basins

Yokohama, Japan, 17-19 February 1998

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