Evidence of long-term NAO influence on East-Central Europe winter precipitation from a guano-derived δ15N record

Currently there is a scarcity of paleo-records related to the North Atlantic Oscillation (NAO), particularly in East-Central Europe (ECE). Here we report delta N-15 analysis of guano from a cave in NW Romania with the intent of reconstructing past variation in ECE hydroclimate and examine NAO impacts on winter precipitation. We argue that the delta N-15 values of guano indicate that the nitrogen cycle is hydrologically controlled and the delta N-15 values likely reflect winter precipitation related to nitrogen mineralization prior to the growing season. Drier conditions indicated by delta N-15 values at AD 1848-1852 and AD 1880-1930 correspond to the positive phase of the NAO. The increased frequency of negative phases of the NAO between AD 1940-1975 is contemporaneous with higher delta N-15 values (wetter conditions). A 4% decrease in delta N-15 values at the end of the 1970's corresponds to a strong reduction in precipitation associated with a shift from negative to positive phase of the NAO. Using the relationship between NAO index and delta N-15 values in guano for the instrumental period, we reconstructed NAO-like phases back to AD 1650. Our results advocate that delta N-15 values of guano offer a proxy of the NAO conditions in the more distant past, helping assess its predictability.