JONSIS Line

FIC is the Fair Isle Current water, defined as the mean temperature and salinity at all standard depths averaged over the first two stations at the western (Scottish) end of the JONSIS standard section. This criteria captures the characteristics of water entering the North Sea through the Fair Isle Channel. This water originates west of Scotland, and is a mixture of coastal and Atlantic water that has come onto the shelf from the slope current.

CAW is Cooled Atlantic Water, and is defined as the mean temperature and salinity at all standard depths below pressure of 50 dbar (approximately 40 meters) from the first six stations at the eastern (Norwegian) end of the line. This criteria is designed to examine the characteristics of the cool, dense lens of Atlantic water which forms in the centre of the North Sea during the summer months. During periods of vertical stratification the northern North Sea, this water mass retains the characteristics of the mixed North Sea during the previous winter. When the dense lower layer is eroded through autumnal wind mixing, it again takes on the properties of the northern North Sea as a whole. Thus it generally represents water of Atlantic origin, modified by mixing with North sea coastal waters to a varying extent.