Key points are not available for this paper at this time.
Author Posting. © American Geophysical Union, 2014. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography 29 (2014): 190-209, doi:10.1002/2013PA002557.
Geoffrey Gebbie (Thu,) studied this question.