Modern organic carbon burial fluxes, recent sedimentation rates, and particle mixing rates from the upper continental slope near Cape Hatteras, North Carolina (USA)

The prominent band of organic-rich surface sediment (2-3% organic carbon) that straddles the upper continental slope near Cape Hatteras suggests that this region may be an important depocenter for phytodetritus exported from the highly productive shelf waters of the Mid-Atlantic Bight (MAB). To understand better the role of modern (post-1955) carbon burial in continental slope sediments, we quantified rates of recent (defined as < 10(2)-yr timescale) sediment accumulation, particle mixing, and organic carbon burial for 12 cores from 10 upper slope stations (212-1004 m) in the proximity of Cape Hatteras. Recent sedimentation and mixing rates were evaluated using diagenetic models calibrated by coupling two modern particle tracers with distinct input functions: excess (210)Pb and fallout Pu. These two radionuclides provide independent information that can be used to deconvolve the effects of sediment accumulation and mixing. Recent sedimentation rates range from 10 to 425 cm. kyr(-1) (mean = 106 cm kyr(-1)) and biodiffusion coefficients for the deep mixing layer (9-21 cm) range from 0.3 to 5.2 cm(2) yr(-1) (mean = 1.3cm(2) yr(-1)). Total carbon burial for this region based on recent sedimentation rates (1.1 mol C m(-2) yr(-1)) is considerably higher than that reported for the more northern sections of the MAR Although the narrowing shelf and convergence of southward flowing shelf waters and the north-flowing Gulf Stream promote carbon export and deposition off Cape Hatteras, we estimate that modern carbon burial in upper slope sediments in this region accounts for much less than 1% of the shelf production. (C) 2002 Elsevier Science Ltd. All rights reserved.