145 since 1961 BALTICA Volume 29 Number 2 December 2016: 145–155 http://dx.doi.org/10.5200/baltica.2016.29.13 Grain size variability as an indicator of sediment transport alongshore the Curonian Spit (south-eastern Baltic Sea) Olga Kovaleva, Boris Chubarenko, Donatas Pupienis Kovaleva, A., Chubarenko, B., Pupienis, D., 2016. Grain size variability as an indicator of sediment transport alongshore the Curonian Spit (south-eastern Baltic Sea). Baltica, 29 (2), 145–155. Vilnius. ISSN 0067-3064. Manuscript submitted on 20 October 2016 / Accepted 30 November 2016 / Published online 10 December 2016 © Baltica 2016 Abstract Sediment samples have been collected along the sea coast of the Curonian Spit in summer season of 2011, 2014 and 2015-years. According to grain size analysis the shoreline and the berm consist of well and very well-sorted sand, medium-sized on the southern (Russian) part of the spit, medium and fne on the northern (Lithuanian) part. ‘McLaren’ method was applied to determine the long-shore sediment transport di- rections. Mismatch of results with those obtained by methods based on simulation of resulted wave action did not prove the hypothesis that ‘McLaren’ method was able to reveal long-term resulted sediment transport. The hypothesis that ‘McLaren’ method indicates the directions of alongshore sediment transport during the stormy conditions preceding the sampling period was not proved also. It was concluded that application of ‘McLaren’ method in respect of the Curonian Spit shore, which is a transit one without permanent sources or sinks of sedi- ments, is not effcient. ‘McLaren’ method was applied to describe the cross-shore sediment movement. It was found that deposits from the trough (located between the bar and shoreline) are transported to the shoreline that is in a line with the known fact about cross-shore transport of bottom material during the calm weather. Keywords • sediment transport • grain size analysis • grain-size distribution statistics •‘McLaren’ method Olga Kovaleva [olya_pavlikova@mail.ru], Immanuel Kant Baltic Federal University, Al. Nevskogo srt., 14, 236041, Kaliningrad, Russia; Boris Chubarenko [chuboris@mail.ru], P.P. Shirshov Institute of Oceanology of Russian Academy of Sciences, Atlantic Branch, Prospect Mira, 1, 236022, Kaliningrad, Russia; Donatas Pupienis [donatas.pupienis@ gf.vu.lt], Vilnius University, Universiteto g. 3,Vilnius, 01513, Lithuania INTRODUCTION The Curonian Spit (Tonisson et al. 2013) is an elongated sand peninsula, 98 km long and 0.35–0.8 km wide, located in the south-eastern part of the Baltic Sea (Fig.1). The spit is extended in north-north-eastern direction and separates the Curonian Lagoon from the Baltic Sea. The Russian-Lithuanian border divides the spit in two almost equal parts: Russian in the south, Lithuanian in the north. The Curonian Spit is a nature protected area and it is included in World Heritage List of UNESCO [http://whc.unesco.org/en/list]. There are two main hypotheses about the long- shore sediment transport along the Curonian Spit. The idea about mono-directed Eastern-Baltic north- wards sediment fow from the Cape Taran along the Curonian Spit till the Cape Kolka was formulated by Knaps (Knaps 1952) and supported by scientists dur- ing decades. An opposite conception about existence of the counter fow was proposed in 1968 (Kirlys 1968). Starting from that time both hypotheses have been under discussions and the subject of studies (Žaromskis, Gulbinskas 2010; Viška, Soomere 2013; Krek et al. 2016; Pupienis et al. 2016). Analysis of beach sediment grain-size distribution along the shore of the South-eastern Baltic (Agapov, Zhindarev 1990) pointed out the fragmentation of long-shore sediment fows within the limits of iso- lated morpholithodynamic cells. The studies based on application of an up-to-date numerical model pro-