ICEBERG SEVERITY OFF EASTERN NORTH-AMERICA - ITS RELATIONSHIP TO SEA-ICE VARIABILITY AND CLIMATE-CHANGE

Iceberg trajectory, deterioration (mass loss), and sea ice data are re viewed to identify the sources of observed interannual and seasonal va riations in the numbers of icebergs passing south of 48-degrees-N off eastern North America. The results show the dominant role of sea ice i n the observed variations. Important mechanisms involved include both seasonal modulation of the southerly iceberg flow by ice cover control of probabilities for entrapment and decay in shallow water, and the s uppression of iceberg melt/deterioration rates by high concentrations of sea ice. The Labrador spring ice extent. shown to be the critical p arameter in interannual iceberg number variability, was found to be ei ther determined by or closely correlated with midwinter Davis Strait i ce extents. Agreement obtained between observed year-to-year and seaso nal number variations with computations based upon a simple iceberg di ssipation model suggests that downstream iceberg numbers are relativel y insensitive to iceberg production rates and to fluctuations in south erly iceberg fluxes in areas north of Baffin Island. Past variations i n the Davis Strait ice index and annual ice extents are studied to ide ntify trends and relationships between regional and larger-scale globa l climate parameters. It was found that, on decadal timescales in the post- 1960 period of reasonable data quality, regional climate paramet ers have varied, roughly, out of phase with corresponding global and h emispheric changes. These observations are compared with expectations in terms of model results to evaluate current GCM-based capabilities f or simulating recent regional behavior.