Seasonal Influence of the Front Area on Sediment Deposition in the Northwestern Adriatic Sea
425
show some interesting features. Organic nitrogen
displays the same pattern but with increasing
values in winter and the lowest values during
summer 1997. Organic carbon shows a shift of
the highest value toward deeper waters during
the same period. The C/N ratio shows a decrease
in the last season suggesting an increased importance of marine organic matter. The recognized
trend of 137CS and nutrients seems to point out a
general decrease of the influence of riverborne
material as seen in the northern area, and an
increased input of marine particulate matter
deposition onto the sea floor. The general lower
values of nutrients, and in particular of nitrogen,
during summer 1997, account for a low productive summer, with a possible depletion of nitrogen in the sediment due to the benthic activity or
to a deposition of particulate matter already
nitrogen -depleted.
Conclusions
The frontal system seems to exert a strong influence on the very short time-scale deposition of
particulate matter in the northern area, as pointed out by the 2*rh behaviour. The influence is
enhanced by the large spatial shift of the frontal
system over this shallow area. 234Th and 137CS can
help to characterise the particulate matter produced by marine processes from that introduced
by riverborne discharges, which are characterised by relatively higher contents of radiocaesium. In the southern area, the shifts of the
frontal system are less wide, influencing in a similar way the deposition during the whole year.
Nevertheless, the land-sea slope gradient and the
presence of seasonal currents parallel to the
coast at different water depths influence the
deposition and resuspension of the fresh sedimentary material with a net offshore transport.
Both areas show a decreasing input of riverborne material to the sea floor during the study
period, suggested by decreasing 137 Cs surficial
activities and C/N values. The lowering of river
input of particulate matter seems to affect the
activity of organisms at the frontal system with a
consequent decrease of fresh sedimentary material reaching the sea floor. In fact, it seems that
summer 1997 was less productive than 1996, as
suggested by the low excess thorium activities
and inventory at site B and the low nutrient concentrations in the bottom sediment of the southern area.
Acknowledgements. Funds were provided by the National
Italian Project "Prisma 2". We wish to thank Captains E.
Gentile and V. Lubrano, their officers and crew for the assistance during the four cruises Prisma 2 subproject 2 onhoard
the RJV Urania, E. Manini. E. Via, R. Danovaro and the
research group of Ancona University for the fundamental collaboration in the fieldwork, T. Bernardi, A. Filippi, R.
Lorenzelli and L. Tositti for some 234Th analyses, G. Marozzi
for core photos and X-ray scans, A. Magagnoli and M. Mengoli
for their assistance and technical support with sedimentological analyses, G. Rovatti for the CHN analyses, G. Zini for the
drawings.
This is paper N. 1219 from the Istituto di Geologia Marina.
CNR. Bologna.
References
Albertazzi S,Alboni M, Frignani M, Langone L, Ravaioli M. Tesini
E (1992) Chernobyl derived radiocesium in marine sediments near the Po River Delta. Rapp Comm Int Mer
Mediterr 33: 337
Albertazzi S, Bopp RF, Frignani M, Hieke Merlin 0, Menegazw
Vitturi L et al (1984) Cs-137 as a tracer for processes of
m3l'ine sedimentation in the vicinity of the Po River Delta
(Northern Adriatic Sea). Mem Soc Gool Ital27: 447-459
Artegiani A, Bregant D, Paschlni E, Pinardi N, Raidch F, Russo A
(1997a) The Adriatic Sea general circulation. I. Air-sea interactions and water mass structure. J Pbys Ocean 27: 14921514
Artegiani A, Bregant D, Paschini E, Pinardi N, Raidch F, Russo A
(1997b) The Adriatic Sea general circulation. II. BarocHnic
circulation structure. J Pbys Ocean 27: 1515-1532
Berner RA (1971). Principles of chemical sedimentology.
McGraw-Hill, New York
Franco P, Jeftic L, Malanotte Rizzoti P, Michelato A, Orlic M (1982)
Descriptive model of the Northern Adriatic. Oceanol Acta 5:
379-389
Frascari F, Frignani M, Guerzoni S, Ravaioli M (1988) Sediments
and pollution in the Northern Adriatic Sea. In: Living in a
chemical world. Ann New Acad Sci Spec Publ534: 1000-1020
Frignani M. Langone L (1991) Accumulation rates and 131CS distribution in sediments off the Po River delta and the EmiliaRomagna coast (northwestern Adriatic Sea. Italy). Cont Shelf
Res 11: 525-542
Frignani M, Langone L. Ravaioli M. Sticchl A (1991) CroDologia di
sedimenti Marini - analisi di radionuclidi naturali ed artifidali mediante spettrometria gamma. Tech Rep 24, CNRIGM, Bologna, Italy
Malanotte Rizzoli P, Bergamasco A (1983) The dynamics of the
coastal region of the Northern Adriatic Sea. f Phys Ocean 13:
1105-1130
Orlic M. Gadc M, La Violette PE (1992) The currents and circulation of the Adriatic Sea. Oceanol Acta 15: 109-124
Tomasino MG (1996) Is it feasible to predict "slime blooms" or
"mucilage" in the northern Adriatic Seaf Ecol Model 84:
189-198
425
show some interesting features. Organic nitrogen
displays the same pattern but with increasing
values in winter and the lowest values during
summer 1997. Organic carbon shows a shift of
the highest value toward deeper waters during
the same period. The C/N ratio shows a decrease
in the last season suggesting an increased importance of marine organic matter. The recognized
trend of 137CS and nutrients seems to point out a
general decrease of the influence of riverborne
material as seen in the northern area, and an
increased input of marine particulate matter
deposition onto the sea floor. The general lower
values of nutrients, and in particular of nitrogen,
during summer 1997, account for a low productive summer, with a possible depletion of nitrogen in the sediment due to the benthic activity or
to a deposition of particulate matter already
nitrogen -depleted.
Conclusions
The frontal system seems to exert a strong influence on the very short time-scale deposition of
particulate matter in the northern area, as pointed out by the 2*rh behaviour. The influence is
enhanced by the large spatial shift of the frontal
system over this shallow area. 234Th and 137CS can
help to characterise the particulate matter produced by marine processes from that introduced
by riverborne discharges, which are characterised by relatively higher contents of radiocaesium. In the southern area, the shifts of the
frontal system are less wide, influencing in a similar way the deposition during the whole year.
Nevertheless, the land-sea slope gradient and the
presence of seasonal currents parallel to the
coast at different water depths influence the
deposition and resuspension of the fresh sedimentary material with a net offshore transport.
Both areas show a decreasing input of riverborne material to the sea floor during the study
period, suggested by decreasing 137 Cs surficial
activities and C/N values. The lowering of river
input of particulate matter seems to affect the
activity of organisms at the frontal system with a
consequent decrease of fresh sedimentary material reaching the sea floor. In fact, it seems that
summer 1997 was less productive than 1996, as
suggested by the low excess thorium activities
and inventory at site B and the low nutrient concentrations in the bottom sediment of the southern area.
Acknowledgements. Funds were provided by the National
Italian Project "Prisma 2". We wish to thank Captains E.
Gentile and V. Lubrano, their officers and crew for the assistance during the four cruises Prisma 2 subproject 2 onhoard
the RJV Urania, E. Manini. E. Via, R. Danovaro and the
research group of Ancona University for the fundamental collaboration in the fieldwork, T. Bernardi, A. Filippi, R.
Lorenzelli and L. Tositti for some 234Th analyses, G. Marozzi
for core photos and X-ray scans, A. Magagnoli and M. Mengoli
for their assistance and technical support with sedimentological analyses, G. Rovatti for the CHN analyses, G. Zini for the
drawings.
This is paper N. 1219 from the Istituto di Geologia Marina.
CNR. Bologna.
References
Albertazzi S,Alboni M, Frignani M, Langone L, Ravaioli M. Tesini
E (1992) Chernobyl derived radiocesium in marine sediments near the Po River Delta. Rapp Comm Int Mer
Mediterr 33: 337
Albertazzi S, Bopp RF, Frignani M, Hieke Merlin 0, Menegazw
Vitturi L et al (1984) Cs-137 as a tracer for processes of
m3l'ine sedimentation in the vicinity of the Po River Delta
(Northern Adriatic Sea). Mem Soc Gool Ital27: 447-459
Artegiani A, Bregant D, Paschlni E, Pinardi N, Raidch F, Russo A
(1997a) The Adriatic Sea general circulation. I. Air-sea interactions and water mass structure. J Pbys Ocean 27: 14921514
Artegiani A, Bregant D, Paschini E, Pinardi N, Raidch F, Russo A
(1997b) The Adriatic Sea general circulation. II. BarocHnic
circulation structure. J Pbys Ocean 27: 1515-1532
Berner RA (1971). Principles of chemical sedimentology.
McGraw-Hill, New York
Franco P, Jeftic L, Malanotte Rizzoti P, Michelato A, Orlic M (1982)
Descriptive model of the Northern Adriatic. Oceanol Acta 5:
379-389
Frascari F, Frignani M, Guerzoni S, Ravaioli M (1988) Sediments
and pollution in the Northern Adriatic Sea. In: Living in a
chemical world. Ann New Acad Sci Spec Publ534: 1000-1020
Frignani M. Langone L (1991) Accumulation rates and 131CS distribution in sediments off the Po River delta and the EmiliaRomagna coast (northwestern Adriatic Sea. Italy). Cont Shelf
Res 11: 525-542
Frignani M, Langone L. Ravaioli M. Sticchl A (1991) CroDologia di
sedimenti Marini - analisi di radionuclidi naturali ed artifidali mediante spettrometria gamma. Tech Rep 24, CNRIGM, Bologna, Italy
Malanotte Rizzoli P, Bergamasco A (1983) The dynamics of the
coastal region of the Northern Adriatic Sea. f Phys Ocean 13:
1105-1130
Orlic M. Gadc M, La Violette PE (1992) The currents and circulation of the Adriatic Sea. Oceanol Acta 15: 109-124
Tomasino MG (1996) Is it feasible to predict "slime blooms" or
"mucilage" in the northern Adriatic Seaf Ecol Model 84:
189-198