Key points are not available for this paper at this time.
Author Posting. © Oceanography Society, 2011. This article is posted here by permission of Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 24 no. 3 (2011): 126–135, doi:10.5670/oceanog.2011.64.
Toole et al. (2011) studied this question.