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Brent A. McKee

Publications and source records attributed to Brent A. McKee.

4 recordsLinked to original sources
USGS2002

Black carbon from the Mississippi river: Quantities, sources, and potential implications for the global carbon cycle

Black carbon (BC) may be a major component of riverine carbon exported to the ocean, but its flux from large rivers is unknown. Furthermore, the global distribution of BC between natural and anthropogenic sources remains uncertain. We have determined BC concentrations in suspended sediments of the Mississippi River, the 7th largest river in the world in terms of sediment and water discharge, during high flow and low flow in 1999. The 1999 annual flux of BC from the Mississippi River was 5 × 10 - 4 petagrams (1 Pg = 10 15 g = 1 gigaton). We also applied a principal components analysis to particulate-phase high molecular weight polycyclic aromatic hydrocarbon isomer ratios in Mississippi River suspended sediments. In doing so, we determined that ∼27% of the BC discharged from the Mississippi River in 1999 originated from fossil fuel combustion (coal and smelter-derived combustion), implicating fluvial BC as an important source of anthropogenic BC contamination into the ocean. Using our value for BC flux and the annual estimate for BC burial in ocean sediments, we calculate that, in 1999, the Mississippi River discharged ∼5% of the BC buried annually in the ocean. These results have important implications, not only for the global carbon cycle but also for the fluvial discharge of particulate organic contaminants into the world's oceans.

Louisiana↗
USGS1999

210Pb and 210Po, manganese and iron cycling across the O2/H2S interface of a permanently anoxic fjord: Framvaren, Norway

Vertical profiles of dissolved and particulate 201 Po and 210 Pb were measured across the redox transition zone at Station F1 in Framvaren Fjord, Norway. In this fjord, a sharp decrease in pH above the O 2 /H 2 S interface facilitates the aerobic dissolution of MnO 2 . In contrast, Fe(II) concentrations begin to increase only at the O 2 /H 2 S interface depth. Activity profiles reveal that dissolved 210 Po and 210 Pb are sequestered efficiently by particulates in surface waters. As polonium-210 and lead-210 activities descend down into the aerobic manganese reduction (AMR) zone, they are remobilized during the reductive dissolution of the carrier phase oxyhydroxides. Both 210 Po and 210 Pb are highly enriched at the O 2 /H 2 S interface where an active community of microbes, such as anoxygenic phototrophs (e.g., Chromatium, Chlorobium sp.), thrives. The coincident peaks in 210 Po and 210 Pb and microbial biomass suggest a strong biological influence on the behavior of these radionuclides. There is a strong covariance between the vertical distribution of Mn and Pb, indicating that their redox cycling is closely coupled and is likely microbially mediated.

Framveran Fjord↗