Assessing the effect of dissolution on planktonic foraminiferal Mg/Ca ratios: Evidence from Caribbean core tops

Abstract

In order to assess the dissolution effect on foraminiferal Mg/Ca ratios, we analyzed Mg/Ca of seven planktonic foraminiferal species and four of their varieties from Caribbean core tops from ∼900-4700 m water depth. Depending on the foraminiferal species and variety, Mg/Ca start to decline linearly below A[CO32-] levels of ∼18-26 μmol/kg by ∼0.04-0.11 mmol/mol per 1 μmol/kg A[CO32-], similar to decreases of ∼0.5-0.8 mmol/mol per kilometer below ∼2500-3000 m water depth. Above these species-specific critical levels, Mg/Ca remains stable with higher intraspecific Mg/Ca variability than below. We developed routines to correct Mg/Ca from below these critical thresholds for dissolution effects, which reduce the overall intraspecific variability by ∼24-64%, and provide dissolution-corrected Mg/Ca appropriate to calculate Holocene paleotemperatures. When taking into account only dissolution-unaffected Mg/Ca from <2000 m, the systematic succession of foraminiferal species according to their Mg/Ca reflects expected calcification depths. Copyright 2006 by the American Geophysical Union.