1. Climate and Environmental Physics, Physics Institute, University of Bern, 3012 Bern, Switzerland.
2. Oeschger Center for Climate Change Research, University of Bern, 3012 Bern, Switzerland.
3. Institute of Geological Sciences, University of Bern, 3012 Bern, Switzerland.
4. Department of Archaeology and Center for Past Climate Change, School of Archaeology, Geography and Environmental Science, University of Reading, Reading, UK.
5. Department of Earth Sciences, University of Minnesota, Minneapolis, MN 55455, USA.
6. Institute of Global Environmental Change, Xi’an Jiatong University, Xi’an 710049, China.