1. 1Earth Observatory of Singapore, Nanyang Technological University, 50 Nanyang Avenue, Block N2-01a-15, Singapore 639798
2. 2Asian School of the Environment, Nanyang Technological University, 50 Nanyang Avenue, Block N2-01C-63, Singapore 639798
3. 3Department of Earth and Environmental Sciences, Columbia University, 557 Schermerhorn Extension, 1200 Amsterdam Avenue, New York, New York 10027, USA
4. 4Lamont-Doherty Earth Observatory, 61 Route 9W, Palisades, New York 10964, USA
5. 5Department of Geological Sciences and Engineering, University of Nevada, Reno, 1664 North Virginia Street, Reno, Nevada 89557, USA
6. 6Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, California 94550, USA
7. 7Anthropology, Geography, and Environmental Studies, California State University, East Bay, 25800 Carlos Bee Boulevard, Robinson Hall (Room) 211, Hayward, California 94542, USA