Glacial activity and catchment dynamics in northwest Greece: Long-term river behaviour and the slackwater sediment record for the last glacial to interglacial transition

Abstract

Pleistocene glacial activity transformed the runoff regimes and sediment loads of many river systems in the Mediterranean region. New data from northwest Greece show marked contrasts in ice volume and extent between cold stages of the Middle and Late Pleistocene. These altered the long-term meltwater routes and sediment supply conditions in glaciated river catchments. The Voidomatis River basin (384 km 2) of northwest Greece now contains one of the best dated records of Middle and Late Pleistocene glacial and fluvial activity that is constrained by over 40 radiometric dates. This paper evaluates the glacial and fluvial geomorphological records to establish a series of correlations and to produce a fuller picture of Middle and Late Pleistocene landscape dynamics in a glaciated Mediterranean catchment. We propose a model of long-term river response to headwater glaciation for the Voidomatis River basin that may have some broader significance for mountain catchments in the Mediterranean and elsewhere. The transfer and storage of coarse-grained river sediment during the Late Pleistocene was strongly conditioned by the major Middle Pleistocene glaciations of MIS 12 and MIS 6. Glaciers were much smaller during the last cold stage (MIS 5d to 2), but meltwater floods still dominated suspended sediment fluxes throughout this period. Uniquely, the Voidomatis River basin contains fine-grained slackwater sediments that record the transition from glacial to interglacial conditions in the Mediterranean region at the end of the last cold stage. Sediment source data from the slackwater deposits record a relatively rapid reorganisation of the hydrology and sediment supply conditions in the catchment between about 20 and 17 ka. These deposits have allowed us to explore flood history and the dynamics of suspended sediment sources during this period for the first time. The use of quantitative sediment fingerprinting in palaeoflood studies has yielded a new understanding of long-term catchment dynamics that has not hitherto been attainable using conventional techniques.