A description of water types on the Mackenzie Shelf of the Beaufort Sea during winter

Abstract

For a number of years during the 1980s, observations of the physical and chemical properties of seawater in the southeastern Beaufort Sea have been acquired in late winter. The most complete data set, from 1987, has been used in a comparison of winter and summer (Macdonald et al., 1989) water properties in the area. Most obvious is an increase in the salinity of surface waters in winter. The magnitude of this increase varies dramatically from year to year. Part of the increase is a consequence of brine rejection during the growth of sea ice, and part is associated with an intrusion over the shelf of a water mass of high nutrient and low oxygen concentrations which is a feature of the entire western Arctic Ocean. Principal component analysis was used to allow all five chemical tracers to be combined and viewed simultaneously. The properties of the upper 120 m are found to lie, to a close approximation, on a plane. This leads us to simple interpretation based on a three-component mixing model involving river runoff, water from the nutrient maximum, and an offshore near-surface component. It is shown that the best fit plane occupied by arctic surface waters in the Beaufort Sea closely matches that defined by the influences of river inflow, of the freeze-melt cycle, and of photosynthesis and respiration. However, the effects of freezing/melting and of river inflow cannot be clearly distinguished using the chosen suite of tracers. It has been determined that if the waters of the upper 250 m are to be represented in the same manner, a fourth end member is required.