Diatom response to the Last Glacial–Interglacial Transition in the Ioannina basin, northwest Greece: implications for Mediterranean palaeoclimate reconstruction

Uncertainty as to the pattern of Lateglacial and early Holocene climate change in the western Balkans and Greece has persisted despite extensive investigation of the Ioannina I-284 lake–sediment sequence, northwest Greece. Here we present a new diatom record from I-284 for this time period. After dominance by eurytopic small Fragilariales, the Lateglacial Interstadial (ca 14.9–12.7 cal kyr BP) is marked clearly by a relative increase in planktonic Cyclotella ocellata. A return to small Fragilariales from ca 12.7 to 11.6 cal kyr BP approximately coincides with the Younger Dryas chronozone. It is followed by a major transition to dominance by Cyclotella spp. at the Pleistocene–Holocene boundary. We interpret these shifts as a response to both lake level and productivity change induced by shifts in effective moisture and temperature, demonstrating that the diatom record provides the first strong evidence for a Younger Dryas event in northwest Greece, and for both warming and wetting during the Lateglacial interstadial and early Holocene. We also present clear evidence for an abrupt phase of catchment instability during the early Holocene. In this case we must await the results of further research to test whether it was driven by climatic or tectonic forcing.