Storminess along the Black Sea coast records a shift in atmospheric circulation patterns 5000 years ago

Climatic conditions in SE Europe result from a complex interplay between Atlantic, continental and Mediterranean influences. Competing and/or mutually reinforcing large-scale modes of climate variability led to complex climatic conditions, whose dynamics in the past remain poorly understood. The regional climate is strongly seasonal, with hot and dry summers associated with the northward expansion of mid-latitude anticyclonic cells and cold and wet winters, resulting from the complex interplay of southward outbursts of Siberian cold air and the northward intrusion of moisture carried by Mediterranean cyclones. While climate reconstructions offer information on past air temperature and precipitation variability in the region, changes in the strength, direction and spatio-temporal variability of winds and storms, linked to large-scale atmospheric circulation pattern variability are virtually unknown. To address this gap in our knowledge of these parameters of past climatic conditions, we present here the first reconstruction of mid-to-late Holocene storminess along the western shore of the Black Sea, based on geochemical and sedimentological proxies from a radiocarbon-dated core located in a coastal marsh (Mangalia Herghelie, SE Romania). Our data shows two climatically distinct periods, with an interval of strong NE winds and marine storminess before ca. 5000 cal BP, followed by a period, between 5000 and 2000 cal BP of intense SW winds. Our data, combined with seasonally-distinct climate reconstructions, suggest a major reorganization of large-scale atmospheric circulation patterns around 5000 cal BP, with more frequent northward expansion of Mediterranean cyclones and a reduction in the southward advection of cold air, likely the result of the weakening of the Siberian High.