Chemical weathering and organic carbon fluxes from the Fly River, Papua New Guinea

Chemical weathering of silicate bedrock and sediment in soil consumes atmospheric CO2 and produces clay minerals that control organic carbon burial in river-dominated ocean margins. The high standing islands of Oceania, Papua New Guinea (PNG) in particular, are globally important sources of weathering and organic carbon fluxes. The Fly River is the largest river in PNG, and an important system to study in order to understand the global significance of this critical region.;We measured the chemistry of bedrock, soils, sediment and solutes in the Fly River basin to understand weathering sources and fluxes from this system. Although weathering of carbonate rocks dominates the river's solute flux, weathering of silicates consumes 36-46 x 109 mol/y of atmospheric CO2 in our study area. This amounts to the 6th highest area-normalized CO2 consumption rate of the world's 60 largest rivers. The majority of the Fly River's solute flux is generated in the highlands, but sediments deposited in the floodplains of the system continue to mature chemically, consuming at least 1.8 x 109 mol/y of atmospheric CO2 in the basin of the Middle Fly River, ∼5% of the river's total silicate CO2 consumption.;Along with silicate weathering, burial of organic matter is second major sink for atmospheric CO2 on geologic time scales. Soil organic matter appears to be the largest source of particulate organic material (POM) delivered to the Gulf of Papua from the Fly River, while freshwater algae is a secondary source of POM. A 2.7‰ enrichment in the d13C of organic matter in the Fly River delta/clinoform compared to POM in the river itself is attributed to diagenetic remineralization of organic carbon in surface sediments of the delta/clinoform.;The final chapter of this thesis focuses on the ancient carbon cycle, specifically during the Paleocene-Eocene Thermal Maximum. We see no peak in the concentration of sedimentary graphitic black carbon (GBC, a paleo-wildfire tracer). Furthermore, a shift in d13C of GBC indicates a recent, rather than fossil, organic matter source for this GBC. Our data appear to refute, but cannot rule out, biomass burning as the cause of the PETM.