We thank Andrew McMinn, Lloyd Burckle, and David Harwood for constructive reviews of the manuscript and John Barron for helpful discussion on aspects of Southern Ocean diatom taxonomy and biostratigraphy. We also thank Hans Schrader for his detailed critique of an early version of the manuscript. S. Bohaty thanks David Harwood for use of laboratory and microscopy facilities at the University of Nebraska-Lincoln. S. Wise, R. Duncan, and P. Wallace received support from the U.S. Science Support Program for the Ocean Drilling Program. The Ocean Drilling Program (ODP) provided samples upon request for the shore-based diatom study. ODP is sponsored by the U.S. National Science Foundation (NSF) and participating countries under management of Joint Oceanographic Institutions (JOI), Inc.