Robert C. Aller
School of Marine and Atmospheric Sciences
Stony Brook University

Title: “Sedimentary dynamics and the cycling of C, Fe, and S in tropical deltaic systems”

Abstract: Tropical deltas process ~ 60 % of the global input of terrestrial sediment and carbon to the oceans. The topset and inner shelf regions of these highly productive systems, as exemplified by the Amazon – Guianas mudbelt of S. America and the Gulf of Papua clinoform on the south coast of Papua New Guinea in Oceania, often act as unsteady, suboxic batch reactors with biogeochemical properties decoupled from net accumulation rates of deposits. Frequent disturbance of the bottom inhibits macrofauna, and benthic communities are typically dominated by microbial biomass. Unsteady conditions and Fe-rich debris from the tropical drainage basins promote suboxic diagenesis, the efficient incineration of sedimentary C, and formation of authigenic Fe carbonate and clays. Despite high biogeochemical reactivity, these inner shelf regions are generally ignored in models of CO2 exchange with the atmosphere. Multiple elemental cycles and properties of the sedimentary record are coupled to seabed dynamics. The suite of authigenic minerals that results from this diagenetic regime, including small quantities of isotopically heavy residual S, could readily mislead environmental reconstruction.