Speleothem isotopic evidence of winter rainfall variability in northeast Turkey between 77 and 6 ka

An oxygen isotope record from a stalagmite that grew between 77 ka and 6 ka in northeast Turkey contains both a strong precessional signal, and sub-orbital oscillations similar to those in Greenland ice cores and Chinese speleothem records of monsoon intensity. Fluid inclusion evidence of a negative shift in the isotopic composition of dripwater during the Lateglacial supports interpretation of the isotope curve as an insolation-forced record of changes in rainfall seasonality. The high-amplitude millennial-scale fluctuations are caused by rapid changes in rainfall seasonality and/or switching of moisture source areas, both of which are associated with the stadial–interstadial climatic oscillations linked to the changing modes of the North Atlantic meridional overturning circulation (MOC). Winter rainfall maxima in northeast Turkey coincide with interstadial conditions in Greenland and with periods of intensified Asian monsoon activity. The isotopic shifts in the record are in antiphase with, and are generally much larger in amplitude than, published data from stalagmites in northwest Turkey, most likely because of differing moisture source areas. Carbon isotope ratios are probably kinetically enriched by partial degassing of seepage water in the epikarst, but although often difficult to decypher, particularly during Marine Isotope Stage (MIS) 2, broadly support the interpretations of the oxygen data.

► Continuous speleothem isotopic record for northeast Turkey between 77 and 6 ka.
► Record shows temporal variations in rainfall.
► Long-term variations were controlled by Earth's precessional cycle.
► Millennial variations controlled by North Atlantic overturning circulation.
► At all timescales the variations correlate with the strength of the Asian Monsoon.