Intra-annual variability of extremely rapid sedimentation onto Gardar Drift in the northern North Atlantic

Abstract: North Atlantic sediment drifts are valuable archives for paleoceanographic reconstructions spanning various timescales. However, the short-term dynamics of such systems are poorly known, and this impinges on our ability to quantitatively reconstruct past change. Here we describe a high-resolution 319-day time-series of hydrodynamics and near-bottom (4m) particulate matter flux variability at a 2600m deep site with an extremely high sediment accumulation rate on the southern Gardar Drift in the North Atlantic. We compare our findings with the actual deposits at the site. The total annual particle flux amounted to ∼360gm−2 yr−1, varied from ∼0.15 to >5.0gm−2 day−1 and displayed strong seasonal compositional changes, with the highest proportion of fresh biogenic matter arriving after the spring bloom in June and July. Flux variability also depended on the changing input of lithogenic matter that had been (re)suspended for a longer time (decades). Active focussing of material from both sources is required to account for the composition and the magnitude of the total flux, which exceed observations elsewhere by an order of magnitude. The enhanced focussing or increased delivery appeared to be positively related to current velocity. The intercepted annual particle flux accounted for only 60% of the sediment accumulation rate of 600±20gm−2 yr−1 (0.20±0.07cmyr−1), indicating higher intra- and inter-annual variability of both the biogenic and lithogenic fluxes and/or advection of additional sediment closer to the seafloor (i.e. <4m). This temporal variability in the composition and amount of material deposited highlights intra-annual changes in the flux of lithogenic material, but also underscores the importance of (reworked) sediment focussing and seasonality of the biogenic flux. All should be taken into account in the interpretation of the paleorecord from such depositional settings. [Copyright &y& Elsevier]