SHELF-BASN EXCHANGE PROCESSES IN THE BEAUFORT SEA AND CANADIAN ARCTIC ARCHIPELAGO
Eddy C. Carmack
Istitute of Ocean Sciences, Sidney, British Columbia, Canada
1. ITRODUCTION
Researches on continental shelf and deep-sea oceanography have traditionally followed separate paths (as witnessed by two journals published by Pergamon Press). To link these two regimes is the challenge of this workshop. Since the early 1980s much attention has been paid to shelf waters spreading into the Arctic interior, especially viz halocline formation and ventilation issues. But only recently has the complexity of this shelf-basin interaction become evident. Here, attention is paid to a number of other key questions: What is the disposition of Mackenzie River water on the broad Mackenzie Shelf? What are the scales of temporal and spatial variability in flows near the shelf-break? What is the influence of Mackenzie Canyon on cross-shelf flow, upwelling, and eddy generation? What are the joint effects of baroclinic and barotropic tidal motions? What behavior is exhibited by water masses exiting the Canada Basin through the passages of the western Canadian Arctic Archipelago?
I cautiously approach this formidable subject by briefly reviewing observations related to shelf-basin exchange processes which have been obtained in the Beaufort Sea and Canadian Arctic Archipelago during the past decade. The overview is aimed, not towards answering the above questions, but rather towards providing a framework for the planning of future investigations elucidating shelf-basin interaction (see Figure 1 for schematic drawing of processes). I acknowledge major intellectual input from my colleagues; especially Robie Macdonald, Fiona McLaughlin, Knut Aagaard, and Eugene Kulikov.
2. OBSERVATIONS
Shelf-basin interaction begins with the inflow of river water, and its is here that the Mackenzie River provides an excellent case study of both summer (ice-free) and winter (ice-covered) conditions. During summer fresh water and sediment particles move cross-shelf through inner, middle and outer shelf domains, each of which require separate consideration. Winter conditions involving the under-ice spreading of new river water have been examined by Robie Macdonald and co-workers (cf. Macdonald and Carmack, 1991 ; Macdonald et al., 1995, 1998), while modeling of the seasonal salinity cycle is discussed in Omstedt et al. (1994).
Processes at the shelf break of the Beaufort Sea remain poorly understood, specially with regards to the mean flow and baroclinic structure adjacent to the shelf break. Questions include: What drives the Beaufort Undercurrent and is topostrophic forcing important (cf. Eby and Holloway, 1994)? What is the partitioning of kinetic energy (cf. Kulikov et al., 1998)? What is the coupling between the Beaufort Gyre and the Beaufort Undercurrent (cf. Aagaard, 1986)? How important are tide-related processes (Kulikov et al., in preparation)? What is the relative importance of brine-driven density flows in material transport off shelf (cf. Aagaard et al., 1981; Melling and Lewis, 1982)? How important are recurrent polynyas such as those off the Mackenzie, Banks Island shelves and in Amundsen Gulf on salt budgets and convection?
Cross-shelf submarine canyons are likely key conduits in shelf-basin exchange. In the present talk current meter data is presented to give examples of motions within and downstream of the Mackenzie Canyon where apparent upwelling excursions reach amplitudes of 400m or more, and along-shelf eddy-like motions are generated (Carmack and Kulikov, 1998).
Eddy C. Carmack, Institute of Ocean Sciences, 9860 West Saanich Road, Sidney, British Columbia, Canada V8L 4B2
email: carmacke@dfo-mpo.gc.ca
