Determination of the Mg/Mn ratio in foraminiferal coatings: An approach to correct Mg/Ca temperatures for Mn-rich contaminant phases ...

• Main Authors: Haug, Gerald, Vance, Derek, Wälle, Markus, Greaves, Mervyn, Jaccard, Samuel, Martinez-García, Alfredo, Hasenfratz, Adam P.
• Format: Text
• Language: English
• Published: Elsevier 2017
• Subjects: 550 Earth sciences & geology; Antarc*; Antarctic; Southern Ocean
• Online Access: https://dx.doi.org/10.7892/boris.90474; https://boris.unibe.ch/90474/

The occurrence of manganese-rich coatings on foraminifera can have a significant effect on their bulk Mg/Ca ratios thereby biasing seawater temperature reconstructions. The removal of this Mn phase requires a reductive cleaning step, but this has been suggested to preferentially dissolve Mg-rich biogenic carbonate, potentially introducing an analytical bias in paleotemperature estimates. In this study, the geochemical composition of foraminifera tests from Mn-rich sediments from the Antarctic Southern Ocean (ODP Site 1094) was investigated using solution-based and laser ablation ICP-MS in order to determine the amount of Mg incorporated into the coatings. The analysis of planktonic and benthic foraminifera revealed a nearly constant Mg/Mn ratio in the Mn coating of ∼0.2mol/mol. Consequently, the coating Mg/Mn ratio can be used to correct for the Mg incorporated into the Mn phase by using the down core Mn/Ca values of samples that have not been reductively cleaned. The consistency of the coating Mg/Mn ratio ...