[1] Univ Cambridge, Dept Geog, Cambridge CB2 3EN, England
[2] Columbia Univ, Lamont Doherty Earth Observ, Palisades, NY 10964 USA
[3] NORCE Norwegian Res Ctr, N-5007 Bergen, Norway
[4] Bjerknes Ctr Climate Res, N-5007 Bergen, Norway
[5] Oregon State Univ, Coll Earth Ocean & Atmospher Sci, Corvallis, OR 97331 USA
[6] Univ Sheffield, Sch Math & Stat, Sheffield S3 7RH, S Yorkshire, England
[7] Coll William & Mary, Dept Geol, Williamsburg, VA 23187 USA
[8] Purdue Univ, Dept Phys & Astron, W Lafayette, IN 47907 USA
[9] Purdue Univ, Dept Earth Atmospher & Planetary Sci, W Lafayette, IN 47907 USA
[10] Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA
[11] Univ Cambridge, Godwin Lab Palaeoclimate Res, Dept Earth Sci, Cambridge CB2 3EQ, England