( <97%) for the layer compared to adjacent waters 

 (>100%) (fig. 103). 



A T-S analysis was attempted to determine the 

 source of the warm water mass. Because of its 

 relatively warm, saline properties, a hypothesis 

 was tested that the origin of the water mass is the 

 Bering Sea — Chukchi Sea. T-S data (surface to 

 bottom) from the Bering Strait (Husby, 1971; 

 Husby and Hufford, 1971) and the Chukchi Sea 

 (Ingham et al. 1972) were compared to the T-S 

 data from the western Beaufort Sea 

 (WEBSEC-71) (fig. 101). It is significant to note 

 that the sigma-t of the warm water mass lies in the 

 range of 23.7 to 25.7, the same as the sigma-t 

 range of the near surface waters of the Bering 

 Sea — Chukchi Sea. 



The minor temperature maximum ( — .8 to 



— 1.2°C) found at 75 meters in the northern 

 Beaufort Sea (Coachman and Barnes, 1961) does 

 not seem to be developed in the survey area of 

 WEBSEC-71 and 72. The absence of the max- 

 imum in the western Beaufort Sea is probably due 

 to mixing with surrounding waters and/or the 

 presence of the warm water mass (described 

 above) masking the feature. The western Beaufort 

 Sea is at the farthest distance from the source of 

 the temperature maximum (northern Chukchi 

 Sea) because of circulation patterns. The max- 

 imum has been shown to decrease in temperature 

 from the northern Chukchi Sea as it flows around 

 in the Beaufort Sea anticyclonic gyre (Coachman 

 and Barnes, 1961). 



A subsurface temperature minimum ( — 1.4 to 



— 1.6°C) was observed at 130-150 meters depth 

 during both WEBSEC-71 and 72 (figs. 32 and 

 33). This minimum corresponds to the minimum 

 described by Coachman and Barnes (1961) and 

 Kinney et al. (1970) and is attributed to advection 

 of Bering Sea winter water. Relatively high nutrient 

 concentrations (PO4 >1.6, NO3 >12, SiOs 



>30 ^tg-at/1) were associated with the tempera- 

 ture minimum (figs. 38-43). 



The layer from 150 m down to 250 m (upper 

 boundary of the Atlantic Water) has properties 

 (except dissolved oxygen) intermediate between 

 those of the subsurface layers and Atlantic Water 

 (figs. 32-43). These intermediate values result 

 from mixing of the subsurface and Atlantic layers. 

 Since these layers are in more or less continuous 



supply there is a quasi-steady state distribution of 

 the properties at this level. 



A dissolved oxygen minimum ( <6.0 ml/1) was 

 observed at 200 m, fifty meters below the nutrient 

 maximum (figs. 36 and 37). This feature has been 

 observed in the northern Beaufort Sea by Kinney 

 et al. (1970), and they suggest that it is partially 

 due to advection processes rather than in situ 

 oxidation alone. Source of the advection is un- 

 known. It is noted that the oxygen minimum cor- 

 responds to a sharp change in the thermocline 

 (figs. 32 and 33). 



Atlantic Water (250 To 900 m) 



The middle layer of the three layered system in 

 the Arctic Ocean consists of Atlantic Water which 

 enters through the strait lying between Spits- 

 bergen and Greenland and than occupies the 

 level between 250 and 900 meters (Cochman, 

 1963). The water mass is characterized by rela- 

 tively high temperature (>0°C) and salinities of 

 34.6 to 35.07oo. 



During WEBSEC-71 and 72, Atlantic Water 

 (0.00 to 0.48°C, 34.6 to 35.07oo) was found at 

 depths from 250-300 meters down to 900 meters 

 (figs. 32-35). The upper and lower boundaries are 

 indicated by the 0°C isotherms (figs. 56-61, 

 80-85) with the maximum temperature (0.44°C, 

 1971 ; 0.48°C, 1972) found at the core (400 to 450 

 m). The temperature gradients on the upper side 

 of the layer are much steeper than on the lower 

 side, suggesting that loss of heat from the layer is 

 not the same across the upper and lower bound- 

 aries. The most striking feature of the Atlantic 

 Water was the uniformity of temperature and sa- 

 linity in the core from station to station. Assuming 

 a uniform decrease in temperature and salinity 

 along the core it appears that the layer has re- 

 tained approximately 15% of its original charac- 

 teristics exhibited upon entrance into the Arctic 

 Ocean. This percentage fits the value found by 

 Coachman and Barnes (1962) for Atlantic Water 

 in the northern Beaufort Sea. 



The dissolved oxygen concentration of the At- 

 lantic layer is greater than 6.0 ml/1 ( >70% 

 saturation) exhibiting a slight maximum (6.8 

 ml/1) at 600 m and then decreasing slightly (6.7 

 ml/1) to 900 m (figs. 36 and 37). Nutrient con- 



11 



