Planktonic Foraminiferal δ13Corg as a novel proxy for Carbon Cycling 

<p>It has been hypothesized that lower atmospheric CO₂ concentrations and lower temperatures during glacial times caused the enrichment of carbon isotopes of particulate organic material (&#948;¹³C_org-POM) produced in the surface ocean. Some downcore measurements of organic carbon isotopes of bulk sediments show such a trend, however, others do not. The lack of a coherent picture could be due to issues relating to the bulk sediments, including diagenetic alteration, the nature of the organic material, input of allochthonous material, and sediment redistribution.</p> <p>Recent work by Hoogakker et al. (2022) shows that planktonic foraminifera-bound organic carbon &#948;¹³C values (&#948;¹³C_FBOM) are remarkably similar to those of &#948;¹³C_org-POM. Here we present the first down-core organic carbon isotope record of planktonic foraminifera-bound organic carbon (&#948;¹³C_FBOM) from the Southern Ocean (ODP Site 1088), to test for a glacial enrichment in &#948;¹³C_org-POM. The samples (<em>Globigerina bulloides</em>, <em>Globorotalia truncatulinoides,</em> and <em>G. inflata</em>) cover the last 20,000 years.</p> <p>Our &#948;¹³C_FBOM results show a slight positive trend toward the Last Glacial Maximum (LGM), in accordance with the hypothesized &#948;¹³C_org-POM trend, but not to the extent as shown in some bulk sediments from more tropical latitudes. We discuss our results in the context of predicted past &#948;¹³C_org-POM using ice core atmospheric pCO₂ concentrations, <em>G. bulloides</em> calcification DIC (from inorganic carbon isotopes), and temperature (using Mg/Ca).&#160;</p>