Continental input and its relationship with biological sedimentary constituents over the MIS 6 to MIS 1 in the SW Gulf of Mexico

To unveil the relationship between reconstructed paleoclimatic and paleoceanographic changes based on geochemical proxies, we analyzed the marine sediment Core RC10-265PC retrieved from the Gulf of Mexico (GoM). The core spans the interval from Marine Isotope Stage (MIS)-6 to MIS-1 at a glacial to interglacial scale resolution. We studied the relationship between changes in biogenic constituents as proxies of primary productivity and those in continental terrigenous contributions as a source of micronutrients. The core constituents were identified and described by determining carbon content, the elemental concentration by X-ray fluorescence (XRF), and the mineral phases by X-ray diffraction (XRD). The biological constituents include total organic carbon (TOC) and calcium carbonate (CaCO₃), whereas terrigenous constituents mainly include the major elements Si, Fe, K, Al, and Ti. In the core, we observed four ash deposits with high Si, K, and Zr concentrations but low in Al, Fe and Ca. Although they were a few cm thick, they did not contribute to increasing primary production. The XRD analysis in the bulk sediments shows that the most abundant mineral phases are calcite, phyllosilicates, quartz, feldspar, and pyroxene. Overall, increases in terrigenous components occurred during the early MIS-6, from MIS-5e to MIS-2, and during MIS-1. In parallel, a decrease in CaCO₃ occurred, sometimes coincident with TOC increases. The former suggests a dilution of calcareous by terrigenous components that possibly arrived at the basin by riverine inputs. Such an input increase is not in tune with the latitudinal displacement of the Intertropical Convergence Zone nor with orbital periodicities. However, neighbouring evidence suggests moisture and runoff increase at the regional level, revealing that the oligotrophic oceanographic conditions in the GoM have remained for approximately 180 ka. Such findings expose several ecological implications if eutrophic conditions emerge under modern climate change.