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Articles by V Kitidis
Total Records ( 2 ) for V Kitidis
  T. J Smyth , J. R Fishwick , L AL Moosawi , D. G Cummings , C Harris , V Kitidis , A Rees , V Martinez Vicente and E. M. S. Woodward

The marine laboratories in Plymouth have sampled at two principle sites in the Western English Channel for over a century in open-shelf (station E1; 50° 02'N, 4° 22'W) and coastal (station L4; 50° 15'N, 4° 13'W) waters. These stations are seasonally stratified from late-April until September, and the variable biological response is regulated by subtle variations in temperature, light, nutrients and meteorology. Station L4 is characterized by summer nutrient depletion, although intense summer precipitation, increasing riverine input to the system, results in pulses of increased nitrate concentration and surface freshening. The winter nutrient concentrations at E1 are consistent with an open-shelf site. Both stations have a spring and autumn phytoplankton bloom; at station E1, the autumn bloom tends to dominate in terms of chlorophyll concentration. The last two decades have seen a warming of around 0.6°C per decade, and this is superimposed on several periods of warming and cooling over the past century. In general, over the Western English Channel domain, the end of the 20th century was around 0.5°C warmer than the first half of the century. The warming magnitude and trend is consistent with other stations across the north-west European Shelf and occurred during a period of reduced wind stress and increased levels of insolation (+20%); these are both correlated with the larger scale climatic forcing of the North Atlantic Oscillation.

  N. J Wyatt , V Kitidis , E. M. S Woodward , A. P Rees , S Widdicombe and M. Lohan

In this study, we investigated the impact of CO2 induced seawater acidification on the concentration of inorganic nutrients, nitrate, nitrite, ammonium, soluble reactive phosphorous (SRP) and silicate at a coastal site in the Western English Channel (WEC). Samples were collected and filtered weekly during the spring to summer transition between 17th March and 21st July 2008. Ambient pH varied by 0.2 units over the study period, while purging with CO2 (380, 500, 760 and 1000 ppmv) resulted in a maximum pH decrease of 0.4 units. Surface nitrate was depleted during the spring phytoplankton bloom and nitrogen limitation was prevalent thereafter. Acidification did not change the concentrations of nitrate, nitrite, SRP or silicate. An average increase in total ammonium of 0.17 µmol L–1 (20%) was observed in acidified seawater during the pre-bloom period. We suggest that this increase was not a biological interaction but due to the influx of gaseous ammonia from the atmosphere; CO2 induced acidification shifted the seawater dissolved ammonium–ammonia equilibrium towards the former and thereby decreased the sea-air concentration gradient of ammonia. Using the results from this study, a simple zero-dimensional model for the WEC was constructed which shows that this region will become a net sink for 300 µmol m–2 a–1 for NH3 if atmospheric CO2 concentrations increase to 717 ppm. The increase in the total ammonium inventory of the WEC surface waters may increase phytoplankton biomass in the future.

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