G02_05

Dissolved inorganic radiocarbon (DI¹⁴C) constraints on the biogeochemistry of marine dissolved organic matter (DOM)

Beaupre S¹,  Walker B², Druffel E³

¹School of Marine and Atmospheric Sciences, Stony Brook University, Stony Brook, United States, ²Department of Earth and Environmental Science, University of Ottawa, Ottawa, Canada, ³Department of Earth System Science, University of California Irvine, Irvine, United States

Marine dissolved organic matter (DOM) comprises all organic substances smaller than ~1 μm in seawater, with myriad physical properties, chemical reactivities, and biogeochemical lifetimes ranging from seconds to millennia.  Yet, global DOM concentrations and Δ¹⁴C values have remarkably predictable vertical distributions.  This may be due, in part, to DOM’s shared propensity for transport predominantly as solutes in moving currents.  Dissolved inorganic carbon (DIC) is both a tracer of ocean circulation and the ultimate source of most DOM carbon atoms (DOC). In this way, DIC Δ¹⁴C can also be used as a tool to constrain the biogeochemistry of DOM.  Analyses of the concentrations and fractionation-corrected ¹⁴C atom abundances (¹⁴C*) of DOC and DIC in contemporaneous profiles show consistency with the simple two-component mixing model and yet, simultaneously, reveal readily distinguishable depths exerting unique biogeochemical controls on DOM.  Variability in DOM concentrations and Δ¹⁴C values are dominated by net imbalances of in situ production and loss processes in the upper ocean, and by transport in the deeper ocean.  In addition, profiles of Z-scores of DOC and DIC concentrations and ¹⁴C abundances are identical throughout the deeper ocean at Station M in the eastern North Pacific, demonstrating that their biogeochemical sources and sinks are tightly coupled.  Collectively, DIC and conservation of mass may be useful tools for constraining the net reactivity of DOC in the deep sea, and for predicting and interpreting the global distribution of DOC Δ¹⁴C values.