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Physical Versus Anthropogenic Control of Nutrient Concentrations in the Irish Sea

The modeling study described in the paper has investigated the physical influences on salinity and nutrient concentrations in the Irish Sea, including the role of climate variability. Previous observational work had noted an inverse relationship between salinity and nitrate concentrations in the Irish Sea, and highlighted the effect of moving water mass boundaries on observations at a fixed sampling site. The process studies described here have demonstrated how high frequency pulses of lower salinity, high nutrient concentration waters could be observed at a fixed sampling site near the Isle of Man (the Cypris station), mainly through the effects of direct wind forcing. Far field forcing for the two arbitrary years used in the study acted to retain material in the western Irish Sea, thus providing a weak background concentration of nutrients to the sampling site. Although daily variability in river flows did not appear to have a significant influence on the high frequency variability at the Cypris station , an arbitrary doubling of river inflows caused a shift t the southwest of the water mass containing higher tracer concentrations. Thus longer term changes in freshwater inflows, for example through increases in precipitation in positive NAO years, could have a significant effect on the decadal scale salinity variability observed at the Cypris station by causing a westwards movement of the boundary between fresh and saltwater masses. To further investigate influences on the long term variability of salinity at the Cypris station, a 40 year hindcast simulation was completed for the period 1960-1999. A comparison of modeled temperatures with observed values from 5566 CTD profiles throughout the 40 years, demonstrated the ability to reproduce the observed seasonal and longer term cycles, with mean and RMS errors of 0.002 degrees Celsius and 0.773 degrees Celsius. The long term temperature variability at the Cypris station was also reproduced. These results suggest that observations taken at fixed sampling sites in active environments such as the Irish Sea should be treated with a degree of caution. Although anthropogenic loading undoubtedly has some influence on nutrient concentrations, much of the observed variability may be due to climate variability, in particular the combined effects of freshwater inflows (dependent on precipitation) and far field forcing of saltwater masses on the geographical position of the water mass boundary.

Language

  • English

Media Info

  • Media Type: Print
  • Features: Figures; References;
  • Pagination: pp 256-272
  • Monograph Title: Estuarine and Coastal Modeling

Subject/Index Terms

Filing Info

  • Accession Number: 01005945
  • Record Type: Publication
  • ISBN: 0784407347
  • Files: TRIS
  • Created Date: Oct 21 2005 7:59AM