Modern sediment dispersal and accumulation on the outer Poverty continental margin

The Poverty margin was sampled in 2005 and 2006 as part of an international initiative to examine the terrestrial and marine sedimentary response to natural and human impacts on dispersal systems at mud-dominated coasts: the NSF MARGINS Source-to-Sink Initiative. 210Pb accumulation rates generally decrease from ~ 1 g/cm2 y in the mid-shelf depocenter on the outer shelf to ~ 0.1 g/cm2 y on the mid-slope plateau (range 0.04–2.53 g/cm2 y). Higher accumulation rates are observed all along the outer Poverty shelf, extending over the shelf break onto the upper Poverty slope in canyons and gullies. Rates are fast in gullies that incise into the shelf edge (0.75–1 g/cm2 y), particularly in the area between Waipaoa Canyon and Poverty Canyon, and in the axis of Poverty Canyon (1.29–1.89 g/cm2 y). Below ~ 1200 m water depth, rates in the axis of Poverty Canyon are no more rapid than those found at open slope cores in similar water depths (0.12–0.15 g/cm2 y). Excess 210Pb profiles generally exhibit steady state characteristics, except in the axis of Poverty Canyon, where non-steady-state 210Pb profiles are observed. 137Cs was not found above minimum detection limits or above statistical background levels in any cores from the Poverty margin. 7Be was found distributed widely along and across the margin during both summer and winter periods, observed to depths of up to 4 cm. Widespread presence of 7Be on the margin in both winter and summer suggests that terrestrially derived sediment is reaching the outer shelf and upper slope throughout the year. A sediment budget based on 210Pb accumulation rate data shows that approximately 13–18% of the Waipaoa annual discharge is accumulating on the outer Poverty margin as a whole, and approximately 11–15% of the annual discharge is accumulating on the continental slope alone. Notably, approximately 28% of the sediment annually accumulating in the outer margin is being sequestered in slope gullies and canyons, although they represent only 6% of the area of the outer margin.