Norwegian Sea intermediate water in the Faroe-Shetland Channel

Abstract

During the 1980s the presence of a salinity minimum was noted in the water column of the Faroe-Shetland Channel at temperatures close to 0°C between Arctic intermediate (AI) water, formed along the Faroe-Iceland Ridge, and the Norwegian Sea deep (NSD) water occupying the lowest levels of the channel. The minimum was most marked in the north-east entrance to the channel, indicating a Norwegian Sea origin. Analysis of the long series of Nolsø-Flugga hydrographic sections shows a relatively large salinity variability which coincides with the depth of this minimum, suggesting that this water could have been present but undetected over many years. Similar water has been recently noted throughout the southern Norwegian Sea by Blindheim (1990 Deep-Sea Research, 37, 1474–1489), although his name for it, Arctic intermediate water, conflicts with the established use of this term for the warmer AI water found at lesser depths between northern Iceland and the Faroe-Shetland Channel. Hence the term Norwegian Sea intermediate (NSI) water is used here. Although modern CTD profiles greatly aid identification of this water, careful scrutiny of past water bottle sampling reveals evidence of its presence over the past three decades, the period for which high-quality salinity determinations have been available, showing that its presence is not solely a phenomenon of the 1980s. An additional indicator appears to be a dissolved silica minimum, which suggests a relatively recent connection with the upper waters. The minimum salinity of water between 0 and 1°C was therefore compared with the mean salinity of the upper north Atlantic (NA) water of the Faroe–Shetland Channel. A peak correlation at the 0.1 probability level was found to occur with a time-lag of 7 years between the salinity fluctuations of NA water passing into the Norwegian Sea and those appearing in the NSI water in the depths of the same channel.