Carbonate ion concentration in glacial‐age deep waters of the Caribbean Sea

Abstract

On the basis of the whole foraminifera shell weights for G. sacculifer and N. dutertrei from Caribbean cores, it appears that the carbonate ion concentration of water at 1800 m depth in the open Atlantic (i.e., the depth of the Caribbean sill) was ∼14 μmol/kg greater during glacial time than during the Holocene. The sense of this difference is consistent with the observation that the 13 C/ 12 C ratio for benthic foraminifera from glacial‐age Atlantic upper deep water was higher than that for their Holocene equivalents. It is also consistent with fragment to whole foraminifera results. However, as several questions regarding the assumptions involved in converting shell weights to paleocarbonate ion concentrations remain unanswered, this reconstruction must be considered tentative. Critical in this regard are the assumptions that shell‐wall thicknesses were the same as today's at any given site during glacial time and that the 0.3 μg per μmol/kg relationship between shell weight and carbonate ion concentration is applicable over the entire deep water column. The records reported here reveal no evidence for an early Holocene preservation event. However, that for core V28‐122 documents a dissolution event close to the MIS 5‐4 boundary.