BAT GUANO-DERIVED δ13C AND δ15N PROXY OF WINTER AND SUMMER PRECIPITATION: NW ROMANIA

δ¹³C and δ¹⁵N analysis was completed on a 285 cm guano deposit found in Măgurici Cave (NW Romania). A hiatus was found in the ~1.2 ka core between AD 1240 to AD 1651 that appears to correspond with the beginning of the Little Ice Age. δ¹³C values indicate that vegetation was exclusively C₃ plants in the region since AD 800, therefore δ¹³C values of guano are interpreted to reflect variation within the C3 pathway related to past water availability. The δ¹⁵N values of guano are correlated with δ¹³C values of the same core, suggesting that both nitrogen and carbon isotopic data result from coupled processes representing variations in wet/dry conditions. The 4‰ increase in δ¹³C values (1‰ decrease in δ¹⁵N values) between AD 850 and 1300 indicates that the climate was trending towards drier conditions leading up to the Little Ice Age. Variation of 1-2‰ in both δ¹⁵N and δ¹³C between AD 1650 and 1900 corresponds well with winter (nitrogen) and summer (carbon) precipitation values. It was found that the North Atlantic Oscillation has an influence on winter precipitation in the region, and therefore also on the nitrogen isotopic composition of the guano. Lower δ¹⁵N values occur during positive phases of the NAO, when colder and drier winters are expected in southern Europe. Alternatively, δ¹³C values appear to represent the influence of precipitation amount on plant water use efficiency during the growing season (spring/summer). These findings indicate that the δ¹⁵N and δ¹³C values from guano can be used to consider and reconstruct the seasonality of past rainfall.