IVANOV G.I., SHEVCHENKOV.P., KALENiCHA.P., IVANOV A.G.

'SEVMORGEO, Russia Р.Р. Shirshov Institute ofOceanology RAS, Moscow, Russia Saint-Petersburg State University, Russia

Mixing zones of riverine freshwater and marine saline water have been attracting attention of geologists for a long time, being an important physico-chemical barrier for pollutants entering marine ecosystems.

Lately they have been attached a great deal of importance. This issue is taking on special significance for the West-Arctic shelf having such an important feeding province as the Novaya Zemlya Archipelago with its large rivers.

From the theoretical point of view, ecogeochemical barrier zone as a system of marginal filter (SMF) was the most extensively described by Lisitzin (1994,1999). SMF appears in mixing zones of freshwater and marine waters in estuaries. Its sizes range from hundreds of meters to hundreds of kilometers for large rivers. SMF is characterized by physico-geographical conditions and climatic zonality.

Studies carried out on the Novaya Zemlya shelf in 1992-2005 revealed a range of original features of SMF (Ivanov et al. 2004b, 2005, Ivanov et al., 2004a). The most comprehensive studies were conducted in the Bezimyannaya Bight receiving waters from the river of the same name.
The most important peculiarity of the Novaya Zemlya shelf is tidal currents changing the sea level in a range of 70 to 100 cm. Besides, intensive neotectonic movements promoted formation of a considerable number of bays and shallow lagoons cut long into the land.

Detailed hydrochemical investigations and field observations showed that the structure of the marginal filter has not only frontal but also horizontal frontier. The rates of physico-chemical processes at these frontiers are characterized by different directions and values. Thus, during the rising tide, "heavy" dense saline waters move towards the bight propping up the inflowing freshwater of the Bezimyannaya River. Freshwater, lighter and less dense, spreads out over the marine water forming a lateral zone of water mixing over the whole area of the bight. At the same time it is significant that movement of heterogeneous water masses differs both in rate and direction.

During the ebb we observe quite a different picture. Both freshwater and saline water move in one and the same direction but with different velocity depending on their physical and chemical features. At that very time, a lengthwise vertical mobile zone of water mixing appears at the river mouth where saline water flowing out of the lagoon and freshwater of the river meet with saline water coming back from the bay.

An important factor forming the structure of the SMF is geomorphologic characteristics of the bay, i.e. the existence of rapids, shallow gutters and canyons.

Because of high dynamics of processes characterized by change of intensity and direction, there is no accumulation of matter in bottom sediments. It is carried away out of the marginal filter and then transported further by powerful (up to 110 cm per second) alongshore currents.

Contrast of zonality depends to a great extent on the season, hydrometeorologic conditions, strength and direction of storms. Detailed organic geochemical studies showed that organic carbon has a terrigenous genesis, great fractional conversion and low levels (1% on average).

The studies were funded by the Russian Fund of Fundamental Investigations (grant # 02-05-65080).

References
Lisitzin A. P., (1994): Marginal filter of oceans. Oceanologia, 34 (5), 735-747 (In Russian)
Lisitzin A. P., (1999): The continental-ocean boundary as a marginal filter in the World Ocean. In Gray J. S., W. Ambrose Jr., Szaniawska (eds.): Biogeochemical Cycling and Sediment Ecology. Dordrecht: Kluwer Academic Publishers. P. 69-109.
Ivanov, G. L, A. P. Kalenich, A.G. Ivanov, (2004a): Migration heavy metals in ore deposit-river-sea system (Novaya Zemlya Archipelago). Inter, conf. on Arctic Geology, Energy Resources and Environmental Challenges, Tromse, NPI, p. 34-36
Ivanov G. I., V. P. Shevchenko, A. G. Ivanov, (2004b): Features of the structure of the marginal filter of the Novaya Zemlya shelf. In: Evolution of marine and land ecosystems in periglacial zones. Southern Science Center, Rostov-on-Don. P. 47-49
Ivanov G. I., (2005): Marginal filter of the Novaya Zemlya shelf. In: Theory and practice of complex marine investigations in the interests if economy and safety if the Russian North. Apatity, Kola Science Center of the Russian Academy of Sciences. P. 53-55

OIL AND GAS OF ARCTIC SHELF 2006 (PROCEEDINGS OF INTERNATIONAL CONFERENCE)