Recent sediments, sediment accumulation and carbon burial at Goban Spur, N.W. European Continental Margin (47–50°N)

Abstract

To quantify recent sediment accumulation, carbon fluxes and cycling, three N.W. European Continental Margin transects on Goban Spur and Meriadzek Terrace were extensively studied by repeated box- and multicore sampling of bottom sediments. The recent sediment distribution and characteristics appear directly related to the near-bed hydrodynamic regime on the margin, which at the upper slope break on the Goban Spur results in along-slope and periodic off-slope directed transport of particles, possibly by entrainment of particles in a detached bottom or intermediate nepheloid layer. From the shelf to the abyssal plain the surface sediments on the Goban Spur change from terrigenous sandy shelf sediments into clayey silts. 210Pb activity decreases exponentially down core, reaching a stable background value at 10 cm (shallower stations) to 5 cm (deeper stations) sediment depth. 210Pb profiles of repeatedly sampled stations indicate negligible annual variability of mixing and flux. The 210Pb xs flux to the sediment shows a decreasing trend with increasing water depth. Below about 2000 m the average 210Pb xs flux is about 0.3 dpm cm −2 y −1, a third of the fluxes measured on the shelf and upper slope stations. Sediment mixing rates (D b) correlate with macro- and meiofaunal density changes and are within the normal oceanic ranges. Lower mixing rates on the lower slope likely reflect lower organic carbon fluxes there. Mass accumulation rates on Meriadzek Terrace are at maximum 80 g m −2 y −1, almost twice as high as at Goban Spur stations of comparable depth. A minimum accumulation rate of 16.6 g m −2 y −1 is found at the Goban Spur upper slope break. Organic carbon burial rates are low compared to other margins and range from a lowest value of 0.05 g m −2 y −1 at the upper slope break to 0.11 g m −2 y −1 downslope. A maximum organic carbon burial rate of 0.41 g m −2 y −1 is found on Meriadzek Terrace. Carbonate burial rates increase along the northern transect from the shelf (13 g m −2 y −1) via a low (9.3 g m −2 y −1) on the upper slope break to the deep sea (30.7 g m −2 y −1). Carbonate burial is highest on Meriadzek Terrace (44.5 g m −2 y −1). The N.W. European Margin at Goban Spur and Meriadzek Terrace cannot be considered a major carbon depocenter.