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

• Published in: Geochemistry, geophysics, geosystems : G3 geophysics, geosystems : G3, 2006-07, Vol.7 (7), p.np-n/a
• Main Authors: Regenberg, Marcus, Nürnberg, Dirk, Steph, Silke, Groeneveld, Jeroen, Garbe-Schönberg, Dieter, Tiedemann, Ralf, Dullo, Wolf-Christian
• Format: Article
• Language: English
• Subjects: Calcification; carbonate ion concentration; Central America/Caribbean; Coverings; Dissolution; dissolution effect; Magnesium; Mathematical analysis; Mg/Ca paleothermometry; planktonic foraminifera; Tops; Water depth
• ISSN: 1525-2027; 1525-2027
• DOI: 10.1029/2005GC001019

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 Δ[CO32−] levels of ∼18–26 μmol/kg by ∼0.04–0.11 mmol/mol per 1 μmol/kg Δ[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