Studying Past Atmospheric CO2 Concentrations Using Mass Spectrometer Analysis of Foraminifera-Bound Organic Matter

Abstract

Although research has been done to analyze the δ\(^{13}\)C of bulk sediment matter and phytoplankton biomarkers for pCO\(_{2}\) reconstruction, little is known about the reliability of using foraminifera microfossils for this purpose, since the quantity of organic matter bound within these microfossils is extremely small and no operative combustion system has had the capability of analyzing such limited samples of foraminifera-bound organic matter (Maslin et al. 1996; Al-Roussan et al. 2004). The Sigman Lab has adopted the online Dumas combustion system based approach of Polissar et al. 2009 to build a system capable of measuring nanomolar quantities of organic carbon from core material found in ~0.1 mg of picked foraminifera. The goal of the research presented in this thesis is to determine the carbon isotope compositions of the organic matter bound within the Globigerinoides ruber foraminifera microfossil species from two cores, VM23-110A and ODP999A, in the tropical North Atlantic in order to investigate foraminifera-bound organic matter (FBOM) as a possible proxy for reconstructing atmospheric CO\(_{2}\) concentrations in the geologic past. In VM23-110A, the δ\(^{13}\)C of FBOM is elevated by ~2‰ during the last glacial maximum, which is consistent with the δ\(^{13}\)C of FBOM responding to the lower atmospheric CO\(_{2}\) concentration of the ice age. However, at ODP Site 999A, the δ\(^{13}\)C of FBOM is ~1‰ lower during the last ice age, which may be due to previously undocumented environmental conditions at this Caribbean site, such as stronger equatorial upwelling. Alternatively, it may indicate a significant sensitivity of G. ruber FBOM δ\(^{13}\)C to some factor other than surface water CO\(_{2}\) concentration.