Climate change impacts on the waters around the UK and Ireland: Salinity
Stephen R. Dye, N. Penny Holliday, Sarah L. Hughes, Mark Inall, Kevin Kennington, Tim Smyth, Jonathan Tinker, Olga Andres and Agnieszka Beszczynska-Möller
Dye, S.R., Holliday, N.P., Hughes, S.L., Inall, M., Kennington, K., Smyth, T., Tinker, J., Andres, O. and Beszczynska-Möller, A. (2013) Climate change impacts on the waters around the UK and Ireland: Salinity. MCCIP Science Review 2013, 60-66, doi:10.14465/2013.arc07.060-066
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The salinity of the upper ocean (0-800 m) to the west and north of the UK (Region 8) has been generally increasing since a fresh period in the 1970s. A minimum occurred in the mid 1990s, and present day conditions are relatively saline. The decadal-scale pattern of change around the UK reflects the conditions of the North Atlantic.
West of the UK the water of the deep ocean (>1000 m) comes from the Labrador Sea and has freshened since 1975. North of the UK, the deep water (800 m) flows from the Nordic Seas; they have freshened since 1950 but salinity has been steady for the last decade.
In the northern North Sea (Region 1) the salinity is heavily influenced by inflowing North Atlantic water and has become more saline since the 1970s, though the trend is not clear. The salinity of the southern North Sea (Region 2) is dominated by river run-off balanced with flow through the Dover Strait and there is no clear trend since the 1970s.
The western English Channel (Region 4) is influenced by North Atlantic Water, tidal currents and local weather conditions. There is no discernible long-term trend in over a century of observations, but in recent years salinity has been higher than average
Since the mid-1960s the salinity of the Irish Sea (Region 5) shows no significant long-term trend. The decadal pattern is different to the deep offshore water; maxima occurred in the late 1970s and late 1990s; present conditions are close to the long-term mean.
There is no clear trend in the shelf waters off the west coast of Scotland (Region 6); observed changes in salinity are due to an east-west migration of salinity gradients, with warm periods being associated with higher inshore salinities.
There is considerable uncertainty regarding future salinity. The projections currently available weakly suggest that the shelf seas and adjacent ocean may be slightly fresher (less saline) in the future than at present. On the shelf the oceanic influence will dominate the mean long-term salinity.
There remains uncertainty in quantifying large-scale, long-term changes in salinity as there are considerable uncertainties on the effects of climate-driven changes in precipitation, evaporation, ocean circulation and ice-melt.