Flux of nutrients between the middle and southern Adriatic Sea (Gargano-Split section)

Abstract

The transect Gargano-Split at the borderline between the middle and southern Adriatic on the Palagruža Sill is exposed to the influences both from the northern and southern Adriatic and is a main transition point for the Adriatic. Thus, water and dissolved inorganic nutrients fluxes between the northern shelf area and the southern deep sea can be estimated at this point. During the Dynamic of the Adriatic in Real Time (DART) project, 12 bottom-mounted Acoustic Doppler Current Profilers (ADCPs) were deployed from November 2005 to September 2006 along the Gargano-Split section. During the same period four different oceanographic cruises were carried out (in November 2005, March, April and July 2006). Hydrographic stations were sampled with the CTD/Rosette to measure physical (temperature, salinity and density) and chemical (oxygen, orthosilicate, orthophosphate and nitrite+nitrate) parameters. Measurements of current velocities allowed estimation of water fluxes and the net nutrient transports were estimated from these and nutrient concentrations. The orthosilicate flux across the transect for inflow and for outflow was higher (except for March) than the nitrite+nitrate and the orthophosphate fluxes. The outflowing nutrient fluxes in the Western Adriatic Current (WAC) were much lower than the total nutrient flux outflow as a large portion of the nutrient flux towards the southern Adriatic was carried by other outflowing waters including North Adriatic Dense Water (NAdDW) flowing along the Italian bottom slope and Middle Adriatic Dense Water (MAdDW) flowing through the deepest passage in the center of the Sill. The July survey provided the first opportunity for direct measurements of total nutrient fluxes across a full basin transect of the central Adriatic. The measurements suggest that the nutrient import and nutrient export were roughly in balance. Modified Levantine Intermediate Water (MLIW) significantly contributed to a total nutrient influx across the transect that was strong enough to counter-balance the nutrient export by the WAC, NAdDW, MAdDW, and other sources.