Recycling and burial of organic carbon in sediments of the Porcupine Abyssal Plain, NE Atlantic

Rates of degradation, recycling and burial of organic carbon (OC) and their temporal and spatial variability were investigated in deep-sea sediments of the Porcupine Abyssal Plain (PAP) in the Northeast Atlantic Ocean (depth 4800–4850 m) during six cruises in August 1996—April 1999. Benthic fluxes of total dissolved inorganic carbon (CT) and alkalinity (AT) were measured in situ using benthic chambers of a free-vehicle benthic lander on four of the cruises. To obtain the OC oxidation rate (Cox), the CT flux in each chamber was corrected for CaCO3 dissolution. Burial of OC was determined by using downcore profiles of OC (n=20) in the solid phase of the sediment and sediment accumulation rates estimated from a model age based on 14C dating of foraminifera. Results obtained showed that during 1996–1999 Cox rates in PAP sediments varied between deployments from 0.21±0.04 to 0.86±0.23 mmol m−2 d−1 with a total mean of 0.46 mmol m−2 d−1 (SD±0.37, n=31). No statistically significant spatial (between stations) or temporal (seasonal as well as interannual) variation in the Cox rates could be detected during the sampling period. The mean burial rate was determined to be 0.03±0.01 mmol m−2 d−1. On average over the sampling period, ∼94% of the particulate organic carbon (POC) deposited was recycled as CT to the overlying water and ∼6% was buried. The calculated mean POC demand during 1996–1999 of 0.49±0.37 mmol m−2 d−1 (the sum of corrected CT and burial fluxes) was not significantly different from the annual integrated mean POC supply (1997–1999) of 0.24±0.06 mmol m−2 d−1 estimated from calibrated sediment traps 1800 mab at the same locality.