Mass flux, major components and the Lead 210 concentration of sediment collected using a Bottom Boundary (BOBO) lander at the Gardar Drift in the North Atlantic

To monitor particle fluxes and near bottom hydrographic variability a modified version of the benthic Bottom Boundary (BOBO) lander was deployed at 57 29.09 N, 27 54.53 W on the Gardar Drift at a water depth of 2630 m. The lander was fitted with three extended Technicap PPS 4/3 sediment traps, each with a baffled collecting area of 0.05 m2 positioned at 4 metres above the seafloor. Trap bottles were filled with ambient seawater and poisoned with a pH-buffered HgCl2 solution and rotated every 11 days. To test the performance of each sediment trap, two traps were programmed to collect material synchronously for three intervals during the deployment. Fluxes were intercepted successfully from 2007-09-19 through 2008-08-03. Full details about the deployment can be found in Jonkers et al., 2010 (doi:10.1016/j.dsr.2010.05.005). Pitch and roll of the lander were recorded and displayed very little variation (1.8370.031 and 0.3370.041, respectively); trapping efficiency was thus uncompromised by the movement of the lander. Upon recovery the pH of the supernatant was measured and found to range from 8.5 to 8.8, indicating minimum sample degradation. The samples were stored at 4 degC. Before sample processing in the laboratory the supernatant was sampled for dissolved Si analysis to correct for the dissolution of the particulate biogenic silica (doi:10.1016/j.margeo.2005.11.001; doi:10.1016/S0967-0645(97)00018-0). Swimmers larger than 1 mm were removed prior to splitting of the samples for further analysis. Carbon and nitrogen were separately analysed on weighed aliquots of the bulk material before and after removal of the carbonate-carbon (doi:10.1016/S0967-0637(02)00030-4) using a Carlo Erba Instruments Flash 1112 elemental analyzer. Biogenic silica (BSi) was determined by continuous alkaline leaching that accounts for contributions by co-leaching of Al-silicates (doi:10.1023/A:1020318610178). The lithogenic content was calculated according to doi:10.1016/S0924-7963(02)00189-6. Samples were analysed for 210Pb activity using the granddaughter 210Po by means of spectrometry. About 10 mg of trap material was spiked with 209Po and leached with concentrated HCl. Polonium isotopes were collected onto silver disks and counted for at least two days with Canberra alpha detectors.