1. Department of Geosciences, University of Massachusetts, Amherst, MA 01003, USA.
2. Climatic Research Unit, University of East Anglia, Norwich NR4 7TJ, UK.
3. Department of Oceanography, Texas A&M University, College Station, TX 77843, USA.
4. Laboratory of Tree-Ring Research, University of Arizona, Tucson, AZ 85721, USA.
5. Department of Environmental Sciences, University of Virginia, Charlottesville, VA 22903, USA