The Lake Ohrid Drilling Project: initial interpretations of stable isotope data over the last 640 ka

Abstract:

Lake Ohrid (Macedonia/Albania) is an ancient European lake with a unique biodiversity and a site of global significance to study the influence of climate, geological and tectonic events on the biological evolution of taxa. Here, we present oxygen (δ18O) and carbon (δ13C) isotope data on carbonate from sediment cores spanning 640 ka recovered as part of the Scientific Collaboration on Past Speciation Conditions in Lake Ohrid (SCOPSCO) project. Previous work on cores from the lake (up to 15 m, <140 ka) indicated that the Total Inorganic Carbon (TIC) content of sediments was highly sensitive to climate change during the last glacial-interglacial cycle, comprising abundant endogenic calcite through interglacials and being almost absent in glacials, apart from discrete bands of early diagenetic authigenic siderite. Isotope measurements on calcite (δ18Oc and δ13Cc) reveal variations both between and within interglacials that suggest the lake has been subject to hydroclimate fluctuations on orbital and millennial timescales. We also measured isotopes on authigenic siderite (δ18Os and δ13Cs) and, with the δ18Oc and δ18Os, reconstruct δ18O of lakewater (δ18Olw). Glacials are observed to have lower δ18Olw when compared to interglacials, most likely due to cooler summer temperatures, a higher proportion of winter precipitation (snowfall), and a reduced inflow from neighbouring Lake Prespa. The isotope data suggest Lake Ohrid experienced a period of overall stability through Marine Isotope Stage (MIS) 15 to 13, highlighting MIS 14 as a particularly warm glacial, and MIS 9 was isotopically freshest. Following MIS 9, the variability between glacial and interglacial δ18Olw is enhanced and the lake became increasingly evaporated through to present day with MIS 5 having the highest average δ18Olw. These findings provide new evidence for long-term climate change in the northern Mediterranean region, which will form the basis to better understand the influence of major environmental events on endemic speciation within the lake.