Elemental Fluxes to the Seafloor: Pleistocene Climate and Submarine Hydrothermal Activity

Abstract

Marine sedimentary records of major and trace element deposition provide a means to examine the temporal variability and interactions between a wide variety of Earth processes, including fluctuations in atmospheric and oceanographic circulation as well as variations in the hydrothermal fluid output of mid-ocean ridges. The extensive advance and retreat of continental ice sheets during Pleistocene glacial-interglacial cycles drives variations in sea level on the order of a hundred meters that may provide a sufficient forcing pressure to modulate the degree of submarine hydrothermal circulation. This work presents new records of hydrothermal flux variability from the Mid-Atlantic Ridge and the Juan de Fuca Ridge that span the past 50,000 years and 600,000 years, respectively, to provide observational constraints with which to examine the potential relationship between glacially-driven sea level changes and submarine hydrothermal activity. Hydrothermal iron fluxes recorded in sediments from both the Mid-Atlantic Ridge and the Juan de Fuca Ridge suggest two to eight-fold variability in the elemental output of hydrothermal systems on timescales ranging from thousands to hundreds of thousands of years. If representative of a global trend, as the limited suite of exiting studies suggest, variations in dissolved hydrothermal iron flux from mid-ocean ridges to the deep ocean over glacial timescales may introduce significant levels of variability into the global biogeochemical cycling of iron. The generation of long-term hydrothermal flux records from marine sediment cores provides an opportunity to investigate additional sources of variability in elemental fluxes to the seafloor and examine the climatic signal deposited in such records. Accordingly, this work presents new records of wind-blown dust deposition to the Mid-Atlantic spanning the past 70,000 years. The Mid-Atlantic dust flux data suggest that millennial-scale changes in wind-strength and continental aridity generate higher levels of North African dust emissions than are observed during orbital-scale climate extremes, such as the Last Glacial Maximum or Marine Isotope Stage 4. The hydrothermal records examined in this work suggest that the potential relationship between sea level changes and submarine hydrothermal activity are likely to be complex. Nonetheless, significant correlations are observed between hydrothermal iron fluxes and sea level over multiple glacial cycles on the Juan de Fuca Ridge. The results of this work encourage continued investigation into the proposed relationship between Pleistocene sea level variability and submarine hydrothermal circulation.