Reevaluation of the CaCO3 size index paleocarbonate ion proxy

Measurements of the CaCO3 size index [Broecker and Clark, 1999] and of whole foraminifera shell weights [Lohmann, 1995] on glacial age sediment from a series of water depths on the Ceara Rise in the west equatorial Atlantic clearly demonstrate that the relationship between size index and pressure-normalized carbonate ion concentration established for Holocene equatorial sediments does not apply to glacial sediments. Rather, it appears that the ratio of fine to coarse CaCO3 raining to the seafloor was greater during glacial time than during the Holocene. This finding squelches our previous enthusiasm regarding the application of the size index as a paleocarbonate ion proxy.