The environmental and evolutionary history of Lake Ohrid (FYROM/Albania): interim results from the SCOPSCO deep drilling project

摘要

This study reviews and synthesises existing information\udgenerated within the SCOPSCO (Scientific Collaboration\udon Past Speciation Conditions in Lake Ohrid)\uddeep drilling project. The four main aims of the project are\udto infer (i) the age and origin of Lake Ohrid (Former Yugoslav\udRepublic of Macedonia/Republic of Albania), (ii) its\udregional seismotectonic history, (iii) volcanic activity and climate\udchange in the central northern Mediterranean region,\udand (iv) the influence of major geological events on the evolution\udof its endemic species. The Ohrid basin formed by\udtranstension during the Miocene, opened during the Pliocene\udand Pleistocene, and the lake established de novo in the\udstill relatively narrow valley between 1.9 and 1.3 Ma. The\udlake history is recorded in a 584m long sediment sequence,\udwhich was recovered within the framework of the International\udContinental Scientific Drilling Program (ICDP) from\udthe central part (DEEP site) of the lake in spring 2013. To\uddate, 54 tephra and cryptotephra horizons have been found\udin the upper 460m of this sequence. Tephrochronology and\udtuning biogeochemical proxy data to orbital parameters revealed\udthat the upper 247.8m represent the last 637 kyr. The\udmulti-proxy data set covering these 637 kyr indicates longterm\udvariability. Some proxies show a change from generally\udcooler and wetter to drier and warmer glacial and interglacial\udperiods around 300 ka. Short-term environmental\udchange caused, for example, by tephra deposition or the climatic\udimpact of millennial-scale Dansgaard–Oeschger and\udHeinrich events are superimposed on the long-term trends.\udEvolutionary studies on the extant fauna indicate that Lake\udOhrid was not a refugial area for regional freshwater animals.\udThis differs from the surrounding catchment, where the\udmountainous setting with relatively high water availability\udprovided a refuge for temperate and montane trees during the\udrelatively cold and dry glacial periods. Although Lake Ohrid\udexperienced significant environmental change over the last\ud637 kyr, preliminary molecular data from extant microgastropod\udspecies do not indicate significant changes in diversification\udrate during this period. The reasons for this constant\udrate remain largely unknown, but a possible lack of environmentally\udinduced extinction events in Lake Ohrid and/or the\udhigh resilience of the ecosystems may have played a role.