THE SEASONAL CYCLES OF TEMPERATURE, SALINITY, NUTRIENTS AND SUSPENDEDSEDIMENT IN THE SOUTHERN NORTH-SEA IN 1988 AND 1989

Simple statistical analyses are used to summarize the large data set a vailable from the 15 consecutive monthly surveys of the U.K. North Sea Project (NSP). The seasonal cycles of temperature, salinity, phosphat e, nitrate, nitrite, silicate, ammonium and suspended particulate matt er (SPM) are approximated by a mean value plus a year-long cosine wave . The mean concentrations, with standard deviation(c) given in parenth eses, for each of these water quality parameters covering the whole ar ea throughout the 15-month period are: salinity 34.26 (+/-0.74), ammon ia 1.3 (+/-1.0) mu M, nitrate 4.9 (+/-6.0) mu M, nitrite 0.4 (+/-0.5) mu M, phosphate 0.5 (0.3) mu M, silicate 2.5 (+/-2.5) mu M and suspend ed sediment 2.6 (+/-3.5) mg l(-1). This approximate seasonal cycle acc ounts for most of the variance in temperature and nutrients. The spati ally-averaged seasonal amplitudes for both nitrate and silicate are ap proximately equal to their mean values-this is consistent with these b eing limiting nutrients. Salinity shows little seasonality. Spatial di stributions are shown of the mean values, the seasonal amplitudes and the percentage variances accounted for by a combination of these mean values and seasonal amplitudes. Correlations between the determinands are calculated; these confirm the similarity in the spatial distributi ons for the nutrients, especially between nitrate, phosphate and silic ate. Maximum concentrations are confined to the coastal regions, excep t for ammonium and nitrite for which they occur offshore. Spatial dist ributions of the anomalous (non-seasonal) components can be interprete d to indicate the effect of specific riverine and oceanic exchanges. C orrelations between nitrate, nitrite and ammonium correspond to the in terconversion of these compounds. The oceanic/riverine inflow rates of phosphate, nitrate and silicate are shown to be insufficient to suppo rt their seasonal variability, suggesting that internal recycling is r equired to maintain the seasonal cycle. (C) 1997 Academic Press Limite d.