A. Karageorgis á Ch. Anagnostou á D. Georgopoulos M. Albuisson Distribution of suspended particulate matter determined by in-situ observations and satellite images in the NW Aegean Sea Greece) Received: 3 August 1999 / Revision accepted: 15 March 2000 Abstract Suspended particulate matter SPM) patterns in the surface waters of the NW Aegean Sea were studied by 1) determining SPM concentration by water ®ltration, 2) measuring light transmission, and 3) evaluating satellite images. The SPM signals of the three major rivers discharging into the study area were recorded by all three methods, thereby providing infor- mation about the sources, transport pathways, and regional dispersion patterns of the SPM. The ®ltration of water samples and light transmission measurements were found to be good indicators of SPM concentrations in surface waters. Most of the SPM is composed of terrigenous minerals, thus explaining the correlation between the beam attenuation coecient and the SPM concentration. A Landsat image obtained for the study period was found to adequately reveal regions with high SPM concentrations. Low concentrations, on the other hand, remain obscured. Introduction The study of suspended particulate matter SPM) pro- vides information about material transfer between sources and sinks. The main pathways of SPM into the sea are rivers, the atmosphere, coastal erosion and, in some cases, resuspension processes. Light attenuation and turbidity variations in the seawater are strongly dependent on SPM concentrations. Over the past 20 years numerous studies have focused on these processes, both in the open ocean e.g., Baker and Hickey 1986; Hickey et al. 1986; Richardson 1987; Gardner 1989a; Gardner et al. 1990, 1995) and in continental shelf waters e.g., Moody et al. 1987; Hue et al. 1990; Palanques and Biscaye 1992; Puig and Palanques 1998). The purpose of this paper is to provide some infor- mation about the mechanisms of material transfer and the associated dynamics in a coastal environment of the Aegean Sea which is characterized by a substantial riverine sediment input. SPM concentrations were determined by water ®ltration, light transmission mea- surements, and the evaluation of concurrent satellite images. A critical assessment of the three methodologi- cal approaches has revealed the bene®ts and drawbacks of each method. Geographic and oceanographic settings The area under investigation is located in the NW Ae- gean Sea Greece), comprising the Thermaikos Gulf and the Sporades Basin delimited by the geographic coor- dinates 39°00¢N±22°30¢E, 40°40¢N±24°30¢E Fig. 1). The embayment receives the waters and sediment loads of the perennial rivers Axios, Aliakmon both in the north) and Pinios in the west). In addition, smaller rivers and many ephemeral streams discharge during the winter and spring seasons. The Axios River supplies more than 50% of the total fresh water of the Thermaikos Gulf Table 1). Over the past decades, the extensive use of fresh water for irrigation purposes and also for the construction of hydroelectric dams has resulted in a signi®cant reduction in river water and solid discharge Poulos and Chronis 1997). During the Holocene, ¯uvial deposits have constructed the Thermaikos plateau which today forms a wide continental shelf bordering the Sporades Basin in the south Fig. 1). The basin has a maximum depth of 1400 m. The sur®cial sediments on the shelf mainly comprise terrigenous muds, the outer shelf being composed of relict sands. By contrast, the deep Sporades Basin is characterized by ®ne clayey sediments Chronis 1986; Lykousis and Chronis 1989). Geo-Marine Letters 2000) 20: 93±100 Ó Springer-Verlag 2000 A. Karageorgis &) á Ch. Anagnostou á D. Georgopoulos National Centre for Marine Research, Agios Kosmas, 166 04 Elliniko, Athens, Greece e-mail: ak@¯.ncmr.gr M. Albuisson Ecole des Mines de Paris, BP 207, 06904 Sophia Antipolis cedex, France