NW Adriatic Sea variability in relation to chlorophyll-a dynamics in the last 20 years (1986-2005)

This paper presents a long-term time series (1986-2005) of hydrological and biogeochemical data, both published and unpublished. Data were collected in the northwestern area of the Adriatic Sea, at two stations that are considered hydrodynamically and trophically different. The time series have been statistically and graphically 5 investigated on a monthly scale in order to find not only possible chlorophyll-a trends over time, but also links between the concentrations of chlorophyll-a and the variability in the environment, as well as trophic differences between the two areas. Basically, in both cases the statistical test results show no significant trends in either the average 10 chlorophyll-a values or in dispersion of the data, in contrast with significant trends in temperature and salinity. The two areas have similar hydrological features, yet they present significant differences in the amount of nutrient inputs: these are in fact higher at the coastal site, which is characterized by a prevalence of surface blooms, while they are lower at the offshore station, which is mainly affected by intermediate blooms. 15 Nonetheless, throughout the whole water column, chlorophyll-a concentrations are only slightly different. Both areas are affected by riverine discharge, though in the first case considered chlorophyll-a concentrations are also driven strongly by the seasonal cycle. Finally, the results show that the two stations are not trophically different, although some controlling factors, such as zooplankton grazing in one case and light attenuation 20 in the other, may regulate the growth of phytoplankton.