Proxy-based reconstructions of climate variability over the last millennium provide important insights for understanding current climate change within a long-term context. Past hydrological changes are particularly difficult to reconstruct, yet rainfall patterns and variability are among the most critical environmental variables. Ombrotrophic bogs, entirely dependent on water from precipitation and sensitive to changes in the balance between precipitation and evapotranspiration, are highly suitable for such hydro-climate reconstructions. We present a multi-proxy analysis (testate amoebae, plant macrofossils, stable carbon isotopes in Sphagnum, pollen, spores and macroscopic charcoal) from an ombrotrophic peat profile from the Rodna Mountains (northern Romania) to establish a quantitative record of hydro-climatic changes. We identify five main stages: wet surface mire conditions between AD 800 and 1150 and AD 1800 and 1950, and drying of the mire surface between AD 1300 and 1450, AD 1550 and 1750 and AD 1950 and 2012. Our multi-proxy reconstructions suggest that conditions during the Medieval Climate Anomaly (MCA) period (AD 900–1150) were considerably wetter than today, while during most of the ‘Little Ice Age’ (LIA; AD 1500–1850), they were dry. Mire surface conditions in the Rodna Mountains have dried markedly over the last 40 years mainly as a result of anthropogenic climate change approaching the driest conditions seen over the last 1000 years. There is a marked difference between current hydro-climatic conditions (dry mire) and those of the MCA (wet mire). This implies that for the study region, the MCA cannot provide analogous climatic conditions to the contemporary situation. Our reconstructions are in partial agreement with water table estimates elsewhere in central and eastern Europe but generally contrast with those from NW Europe, especially during LIA. We suggest that these distinctive regional differences result from fluctuations in large-scale atmospheric circulation, which determine the relative influences of continental and oceanic air masses.

As natural and anthropogenic ecosystems are dependent on the local water availability, understanding past changes in hydroclimate represents a priority in research concerning past climate variability. Here, we used testate amoebae (TA) and chironomid analysis on a radiocarbon dated complex of small pond and peat bog sediment profiles from an ombrotrophic bog (Tăul Muced, northern Carpathians, Romania) to quantitatively determine major hydrological changes and July air temperature over the last 7500 years.Wet mire surface conditions with a pH between 2.3 and 4.5 were inferred for the periods 4500-2700 and 1300-400 cal yr BP by the occurrence of Archerella flavum, Amphitrema wrightianum and Hyalosphenia papilio. Dry phases in mire surface conditions and a pH between 3 2.5 and 5 were inferred for 7550-4500, 2750-1300 and 0 cal yr BP-present by the dominance of Nebela militaris, Difflugia pulex and Phryganella acropodia. The quantitative reconstruction of mean July temperature based on the chironomid communities suggests low summer temperatures for the periods 6550-5600, 4500-3150 and 1550-600 cal yr BP, while periods of slightly higher summer temperatures were observed for 5600-4500, 3150-1550 and 100 cal yr BP-present.There is a general good agreement between drier phases of the peat surface conditions with higher July temperature, suggesting that temperature may have been a controlling factor for water table fluctuation.Our quantitative reconstructions, among the first for central eastern Europe, show a relatively good agreement with other palaeohydrological studies from central eastern Europe, but contrast with others estimates from north-west Europe. Another important aspect of our study is that it provides valuable information on changes in local hydrology and the potential effect of the mean summer temperature over these changes.

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