16 ROGER FLOWER ET AL A GEOPASS-NERC PROJECT ON DIATOM DEPOSITION AND SEDIMENT ACCUMULATION IN LAKE BAIKAL, SIBERIA ROGER J. FLOWER 1 , RICHARD W. BATTARBEE 1 , JOAN LEES 2 , OLGA V. LEVINA 3 , DAVID H. JEWSON 4 , ANSON W. MACK AY 1 , DAVID RYVES 1 , MICHAEL STURM5 AND ELENA G. VOLOGINA 3 ('Environmental Change Research Centre, University College London, 26 Bedford Way, London WC1H OAP, UK. 2 School of Natural and Environmental Sciences, University of Coventry, Priory Street, Coventry CV1 5FB, UK. 3 Limnological Institute, Irkutsk, Siberia, Russia. 4 Freshwater Laboratory, University of Ulster, Traad Point, Ballyronan, Northern Ireland BT45 6LR, UK. 5 EAWAG, CH-8600 Duebendorf Switzerland.) Introduction Siberian Lake Baikal is arguably the world's most interesting freshwater lake. Its main features of great age and depth and a high incidence of endemism are well known (e.g. Koshov 1963). The lake has attracted much international attention during the 1990s and joint British research on Baikal was summarized previously in Freshwater Forum (Flower 1994). However, there is now increasing interest in the palaeoenvironmental records stored in the ca. 7 km of sediments that lie beneath modern Lake Baikal (BDP-93 1997). These deposits offer major opportunities for reconstructing environmental change over a variety of time-scales ranging from decades (Flower et al. 1995; Mackay et al. 1998) to millennia (Grachev et al. 1997; Williams et al. 1997). Sediment records of climate change over the past 5 million years are the focus of an international deep-drilling programme, the Baikal Drilling Project (BDP; see BPD-93 1997). The lake is also a key site in the Pole-Equator-Pole (PEP II) programme that aims to produce a coherent quantitative record of global palaeoclimates during the Quaternary Period (PAGES 1995). Reconstructing palaeoclimates for the Holocene/Pleistocene periods is a primary goal of much Quaternary research in Lake Baikal (e.g. Peck et al. 1994; Colman et al. 1995, 1996). Sedimentary planktonic diatoms are important palaeoclimate indicators (Bradbury & Dieterich-Rurup 1993) and in Baikal sediment they are abundant, generally well preserved, and exhibit marked abundance changes during glacial and inter-glacial periods (Grachev et al. 1997; Julius et al. 1997). These Baikal microfossils potentially offer a powerful proxy method of reconstructing climate change. However, before confident quantitative palaeolimnological reconstructions can be undertaken, we need a better understanding of the factors that control the abundance of modern planktonic diatoms and those that influence the composition of