The transitional climate of the late Miocene Arctic: Winter-dominated precipitation with high seasonal variability

The late Miocene (11.6-5.3 Ma) was an important transitional period following the greenhouse conditions of the Eocene. In order to gain insight into the Arctic paleoclimate of the time, we performed high-resolution intraring delta C-13 analyses on fossil wood collected from the late Miocene Khapchansky sediments of northeastern Siberia (similar to 69 degrees N). From these data we quantified the ratio of summer to winter precipitation (P-s/P-w) and compared it to current values for the region determined from modern wood samples and instrumental records. We observed much greater frequency of winter-dominated precipitation (P-s/P-w < 1) and much greater variability in P-s/P-w during the Miocene than today. Specifically, years with P-s/P-w < 1 occurred three times more often, and years with at least three times as much precipitation in summer or winter (0.33 < P-s/P-w < 3.0) occurred approximately twice as often during the Miocene than today. We attribute the high interannual variability in precipitation to an inconsistent moisture source associated with the relatively unstable and incomplete ice cover in the Arctic Ocean during the late Miocene. Our result highlights the potential for enhanced variability in Arctic precipitation in response to Arctic sea ice decline caused by anthropogenic, CO2-induced warming.