255 ISSN 0001-4370, Oceanology, 2008, Vol. 48, No. 2, pp. 255–267. © Pleiades Publishing, Inc., 2008. Original Russian Text © Yu.S. Dolotov, N.N. Filatov, V.P. Shevchenko, M.P. Petrov, A.V. Tolstikov, R.E. Zdorovennov, A.V. Platonov, A.S. Filippov, K.L. Bushuev, I.P. Kutcheva, N.V. Denisenko, R. Stein, C. Saukel, 2008, published in Okeanologiya, 2008, Vol. 48, No. 2, pp. 276–289. INTRODUCTION Onega Bay is the largest (12300 km 2 ) [1] and shal- lowest bay of the White Sea. On average, it is shallower than 20 m, being shallower than 3 m in the end part and approximately 50–60 m deep in its open part. The east- ern (Onezhskii) coast of the bay is relatively gentle, while the western one (Pomorskii) is steep. The tidal processes in the region under consider- ation were discussed earlier [8] in connection with the transport patterns of pollutants. Some aspects of the distribution of suspended particulate matter, zooplank- ton, and zoobenthos were studied in previous years [1, 9, 11, 14, 18, 22, 23, 32]. The bottom of Onega Bay is characterized by a rel- atively complex topography: flattened surfaces largely composed of fine-grained sediments alternate with pos- itive morphological structures connected with exposed (or near-surface) bedrocks [15]. The bottom is usually covered by well-sorted fine-grained sands with spots of clayey silts. In the open part of the bay, the sediments are largely represented by sands with an admixture of gravel and pebbles. The bottom in the central part of the bay is occupied by well-sorted sands, while its end part is covered by muddy sand and mud. The study area represents a typical marginal filter [12]. The purpose of our studies was to establish the role of tidal currents in the physical, chemical, geolog- ical, and biological processes [6] in the zone influenced by the large Onega River with an annual runoff of 15.9 km 3 [2]. They continue the studies conducted in the frame- works of the program for the research of the Karelian coast of the White Sea and “The White Sea System” project [4–7, 13, 14, 34]. MATERIALS AND METHODS Field works in Onega Bay and the Onega River estu- ary were conducted in the first half of August 2004 on board R/V Ekolog belonging to the Institute of Water Problems of the North (Karelian Scientific Center, RAS). The multidisciplinary studies included the fol- lowing procedures: (1) in-situ measurements of the temperature, salinity, velocity, and direction of currents during different tidal phases; (2) water sampling for chemical analyses; (3) determination of the contents of particulate matter in the water column; (4) monitoring of the plankton distribution; (5) sampling of the bottom sediments for the grain-size and other analyses, the content of benthos included; and (6) an echo sounding survey. Simultaneously, measurements were carried out at an autonomous buoy-based station (water depth of 6 m) to determine variations in the sea level, salinity, and temperature in the water column and the velocities and direction of currents. Most of the measurements were performed along five profiles (Fig. 1): the profile across the main and subsidiary branches of the Onega River (up to the coastal sea waters), three offshore pro- files at different distances from the river mouth (at differ- ent depths), and the median profile across Onega Bay. The temperature and salinity were measured using a Quanta probe; an IST-1 device was used to measure the velocities and directions of the currents. In more detail, MARINE GEOLOGY Multidisciplinary Studies in Onega Bay of the White Sea and the Estuary of the Onega River during the Summer Period Yu. S. Dolotov a , N. N. Filatov b , V. P. Shevchenko c , M. P. Petrov b , A. V. Tolstikov b , R. E. Zdorovennov b , A. V. Platonov b , A. S. Filippov c , K. L. Bushuev c , I. P. Kutcheva d , N. V. Denisenko d , R. Stein e , and C. Saukel e a Water Problems Institute, Russian Academy of Sciences, Moscow, Russia b Institute of Water Problems of the North, Karelian Scientific Center, Russian Academy of Sciences, Petrozavodsk, Russia c Shirshov Institute of Oceanology, Russian Academy of Sciences, Moscow, Russia d Zoological Institute, Russian Academy of Sciences, St. Petersburg, Russia e Alfred Wegener Institute of Polar and Marine Research, Bremerhaven, Germany e-mail: vshevch@ocean.ru Received October 17, 2006 Abstract—The distribution of the temperature and salinity, current velocities, suspended particulate matter, bottom sediments, bottom morphology, and planktonic and benthic organisms during the summer period are studied in the estuary of the large Onega River and the coastal areas of Onega Bay (White Sea) influenced by interacting marine and riverine factors. DOI: 10.1134/S0001437008020136