Calibration of speleothem δ¹⁸O with instrumental climate records from Turkey

Stalagmite records of oxygen (δ¹⁸O) isotopes, sampled at sub-annual resolution by micro-mill techniques are correlated with climate parameters over the instrumental period (1961 to 2005 AD). The strongest correlations were found between δ¹⁸O and total amount of late autumn-winter precipitation (October to January) smoothed by 6 yr, with marginally weaker correlations between the total amount of late autumn-spring precipitation (ONDJF and ONDJFMA) smoothed over the same time period. Two smoothing options were chosen to account for variability in mixing and residence times of stored water in the karst aquifer prior to entering the cave: (1) An average of the last 6 yr of precipitation which yielded a product correlation of - 0.71 for the months ONDJ; and (2) a mixing model of 10% short term/event water (< 1 yr) and 90% water of a longer residence time in the karst aquifer (2 to 6 yr) which gave a product correlation of - 0.72 for the months ONDJ. Precipitation is calibrated over the instrumental period (1961 to 2004 AD) based on linear regression of δ¹⁸O with observed precipitation for the months ONDJ, ONDJF and ONDJFMA using both smoothing methods. An uncertainty of ± 31 mm (2 standard errors on the linear regression) is applied to the calibrations. This is the first speleothem calibration of its kind in Turkey.