Current state, scales of variability, and trends of biogeochemical properties in the northern Adriatic Sea

Abstract

This paper illustrates the main results of a statistical analysis performed on a data set obtained by integrating experimental observations collected during many oceanographic research projects on the northern Adriatic Sea (NAS). The observations cover the last 20 years and provide a robust base for the assessment of the current state and scales of variability for temperature, salinity, nutrients, dissolved oxygen, and chlorophyll. The results confirmed a clear seasonal cycle and marked spatial gradients for most parameters in all seasons. The largest proportion of the river Po input flows south along the coast, but significant eastward freshwater fluxes are also present in all seasons, more markedly in winter. The coastal belt south of the Lagoon of Venice is the most eutrophic area, mainly because of river inputs, while an oligotrophic condition prevails along the eastern part of the basin. Small-scale structures, including eddies and jets, are permanent features of the system. In order to test the existence of significant trends of variation in the physical and biogeochemical parameters, the data set has been enlarged by including observations from 1976. Analyses of trends over 30 years show an increase in salinity, which might be a consequence of both reduced outflows from rivers and a more sustained inflow of water along eastern coast, and a clear reduction in concentrations of phosphate and ammonia in coastal areas, probably due to new regulations regarding the control of nutrient loads and possibly suggesting the occurrence of cultural oligotrophication. No decrease is instead observed for concentration of nitrate

Development of BFMCOUPLER (v1.0), the coupling scheme that links the MITgcm and BFM models for ocean biogeochemistry simulations

“…As an example, Fig. 9 shows that the nitrate patterns display a longitudinal gradient along the Adriatic and northern Ionian seas, and these results are consistent with the current climatologies (Cossarini et al, 2012;Solidoro et al, 2009;Zavatarelli et al, 1998). In the open-sea area of the Ionian Sea, the surface circulation is dominated by large mesoscale structures and a basin-scale anticyclone in the middle, and the downwelling area is characterized by minimal nitrate and chlorophyll concentrations (Fig.…”

“…8), was chosen because it is characterized by a wide range of interconnected ecosystems that span coastal areas, which are influenced by river discharges, and offshore regions, which are characterized by open-sea dynamics. Indeed, the northern part of the Adriatic is a continental shelf area influenced by terrestrial input (Solidoro et al, 2009;Cossarini et al, 2015a). This area is a site of dense water formation (Gačić et al, 2001;Querin et al, 2013) and represents one of the most productive areas of the Mediterranean Sea (Mangoni et al, 2008).…”

Changes in the Adriatic oceanographic properties induced by the Eastern Mediterranean Transient

“…Aside for that, the Adriatic Sea upper layer circulation is driven by the freshwater input, particularly of the northern Adriatic rivers that result in a cyclonic surface circulation, with the outflowing West Adriatic Current (WAC) along the western coastline and the inflowing LIW and the surface Ionian waters along the eastern coastline. Although the nutrient load by the northern Adriatic rivers is significant, this impact is mainly restricted to the northern Adriatic and the WAC (Grilli et al, 2005;Polimene et al, 2006;Solidoro et al, 2009), as the nutrients are normally consumed very fast during their transport towards the southeast and the open Adriatic (Campanelli et al, 2011). The same, i.e.…”

Linking 1D coastal ocean modelling to environmental management: an ensemble approach

“…The pressure determined by the nutrient land-based input can be considered as directly acting on the coastal ocean environmental dynamics. The exclusive focus on the reduction of the land-based nutrient load conveyed to the coastal ocean, is motivated by the successful application of the EU regulations (648/2004 and 259/2012) concerning the abatement of phosphate (the limiting nutrient in the Mediterranean, including the northern Adriatic Sea: Marty et al 2002, Krom et al 2004, Solidoro et al 2009) and phosphorus compounds in detergents. The implementation of such abatement policy contributed to a marked reduction of the phosphate riverload affecting the Mediterranean Sea (Ludwig et al 2009(Ludwig et al , 2010 and resulting, for the northern Adriatic Sea, in a rearrangement of its trophic state towards more oligotrophic conditions (Solidoro et al 2009;Djakovac et al 2012).…”