ESTIMATES OF THE NUTRIENTS FLUXES IN PARTICULAR WATER MASSES ALONG THE SECTION GARGANO-SPLIT

Transcription

1 II WORKSHOP ANNUALE VECTOR (Roma, febbraio 2009) ESTIMATES OF THE NUTRIENTS FLUXES IN PARTICULAR WATER MASSES ALONG THE SECTION GARGANO-SPLIT F. Grilli 1, M. Marini 1, A. Campanelli, E. Paschini 1, A. Russo 2, A. Coluccelli 2 1 Istituto of Marine Sciences, CNR-ISMAR, Ancona, Italy 2 Department of Marine Sciences, Polytechnic University of Marche, Ancona, Italy

2 VulnErabilità delle Coste e degli ecosistemi marini italiani ai cambiamenti climatici e loro ruolo nei cicli del carbonio mediterraneo VECTOR Linea 6: Il ruolo della piattaforma continentale dell'adriatico Settentrionale nei cicli del carbonio mediterraneo (CARADRI) Responsabile scientifico: Mariangela Ravaioli Attività 2: Misure in continuo e campionamenti periodici nei siti (boe) e transetti fissi (Golfo TS e VE, Delta Po, sezione Vieste-Spalato) Responsabile attività: Mariangela Ravaioli Sub-attività 2.6: Transetto Vieste-Spalato idrografia bi-mensile (T, S, O2, DIC, DOC, PIC, POC) e misure di corrente con ADCP posizionati in prossimità del fondo nell ambito di una cooperazione scientifica con il Naval Research Laboratory, USA Responsabile sub-attività: Mauro Marini

3 outline some preliminary results from the measurements of physical and chemical parameters of the four cruises and identification of the water masses properties computation of estimates of the fluxes of water and dissolved inorganic nutrients from the northern shelf area, where large nutrient inputs comes from rivers, towards the deep sea due to both the surface and deep circulation. estimates of the water and nutrient fluxes in WAC, NAdDW, MAdDW and MLIW

4 The Gargano-Split transect, which approximately marks the borderline between the middle and southern Adriatic, is exposed to the influences both from the northern and southern Adriatic and its dynamics is controlled also by the topographic effect induced by the Pelagruža Sill. This Sill is an area with a strong temporal variability of thermoaline structure 46 N caused by seasonally dependent circulation Venezia Trieste in the surface and intermediary layer. 45 N 44 N 43 N 42 N Po Delta Cattolica Ancona Pescara Rovigno 50 Giulianova Fosse di Pomo Pola Vasto Soglia di Pelagosa 100 Vieste Isola Incoronata Sibenik Split Lissa Curzola Dubrovnik The mean surface circulation of the Adriatic consists of a basin-wide cyclonic gyre with a northward flow along the eastern side (Albanian and Croatian coasts) and a southward return flow along the Italian coast on the western side Eastern Adriatic Current (EAC) Western Adriatic Curret (WAC) 41 N Bari 800 probably mesoscale cyclonic gyre centred near the Pelagusa Sill 40 N Otranto 39 N MAR IONIO 12 E 13 E 14 E 15 E 16 E 17 E 18 E 19 E

5 The North Adriatic Dense Water (NAdDW) produced in the autumn and winter in the North Adtriatic flows southwards along isobaths near the bottom of the Italian shelf. The flow partially sinks into the Jabuka pit, although the major portion moves further southwards to reach the shelf off Bari in the following spring and summer. The Middle Adriatic Dense Water (MAdDW) forms in the Middle Adriatic and resides throughout the year in the bottom layer of the Jabuka pits. In the Jabuka depression the NAdDW can partially mix with the MAdDW and continue along western coast at depths between 75 and 200 m. When large quantities of MAdDW are produced, this water can overeach the Jabuka pits joining with the NAdDW and flowing towards the Gargano (Vilibic and Supic, 2005) The transect is also under the influence at intermediate depth of advection of saltier water (the Modified Levantine Intermediate Water, MLIW) from southern Adriatic which reflects the Mediterranean influence evident as a maximum in the salinity field

6 Deep (dense) water mass properties (Vilibic and Orlic, 2002) Water mass Temperature ( C) Salinity (psu) Density (sigma-t) NAdDW ± ± 0.28 > 29.3 MAdDW ± ± 0.15 > 29.2 LIW ± ± 0.15 > 29.05

7 seawater collection The collection of seawater samples and CTD casts were made on four different cruises (08 November 2005, 26 March 2006, 24 April 2006 and 18 July 2006). Only the cruise made in July is completed, the others are up to the Croatian territorial water. Date 08 November March April 2006 Research Vassel G. Dallaporta G. Dallaporta G. Dallaporta 18 July 2006 Alliance Casts Hydrographic stations were sampled with the CTD/Rosette to measure physical (temperature, salinity,density and fluorescence) and chemical (oxygen, ammonium NH4, nitrite NO2, nitrate NO3, orthophosphate PO4 and orthosilicate SiO4) parameters. Seawater samples were collected with Niskin bottles mounted on a rosette at 2 8 oceanographic depths (surface, 10, 30, 50, 100, 130, 150 and 2 m above the bottom), depending on station sonic depths.

8 08 November 2005

9 26 March 2006

10 24 April 2006

11 18 July 2006

12 T-S diagram of CTD data MLIW MAdDW NAdDW

13 18 July 2006

14 current field and flux computation During the Dynamic of the Adriatic in Real Time (DART), the U.S. Naval Research Laboratory (NRL) together with the NATO Undersea Research Centre (NURC) deployed 12 bottom-mounted Acoustic Doppler Current Profilers (ADCPs) from November 2005 to September 2006 to measure currents throughout the water column. 200m GS12 GS11 GS10 GS9 Split GS8 GS7 GS6 GS4 GS5 GS2 GS1 GS3 Cape 100m Gargano 50m 100m 200m 500m 1000m The east current component across the section was taken as representative of the flow perpendicular to the section. The average current field was then interpolated over a regular grid and the flux of the water across the transect calculated.

15 Water transport (m 3 /s) November November March March April April July July

16 Water fluxes (10 6 m 3 /s) November 2005 March 2006 April 2006 Southward 0.59 Northward Southward Northward Southward Northward Southward July 2006 Northward Gacic et al. (1999) used current measurements along a section over the Pelagruža Sill up to the Croatian territorial water to estimate only the water and biogeochemical southward fluxes through the transect. They found a water southward fluxes of m 3 /s in summer and m 3 /s in winter.

17 Nutrients flux (moli/s) November 2005 March 2006 April 2006 July 2006 Nutrients Southward Northward Southward Northward Southward Northward Southward Northward NO 2 +NO 3 Silicate Phosphate Phosphate Nutrients flux (moli/s) (Gacic( et al., 1999) Nutrients NO 2 +NO 3 Silicate summer Southward winter Southward

18 Vertical distribution of Orthosilicate net transport (mol s 1 ) November 05 March 06 April 06 July 06

19 in the WAC (Western Adriatic Coastal Current) Water flux (10 6 m 3 /s) November 2005 March 2006 April 2006 July Nutrients flux (moli/s) November 2005 March 2006 April 2006 July 2006 NO 2 +NO 3 Silicate Phosphate

20 Nutrients flux (moli/s) in the water masses April 2006 July 2006 MAdDW NAdDW MAdDW NAdDW MLIW NO 2 +NO Silicate Phosphate

21 CONCLUSION there is very little known about the net transport of water and nutrients in this crucial area exposed to the influences both from the northern and southern Adriatic. For the first time it has been possible to have height resolution of the transect obtained from long term measurements of current velocities and seasonal samplings of chemical parameters it has also been possible to calculate the nutrient fluxes in the different water masses. The nutrients flux in NAdDW is higher in respect to the MAdDW and the orthosilicates flux is always predominant Thank you for your attention