| Summary: | 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 (C-T) and alkalinity (A(T)) were measured in situ using benthic chambers of a free-vehicle benthic lander on four of the cruises. To obtain the OC oxidation rate (C-ox), the C-T 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 C-14 dating of foraminifera. Results obtained showed that during 1996-1999 C-ox 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 C-ox 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, similar to94% of the particulate organic carbon (POC) deposited was recycled as C-T to the overlying water and similar to6% was buried. The calculated mean POC demand during 1996-1999 of 0.49 +/- 0.37 mmol m(-2) d(-1) (the sum of corrected C-T 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. (C) 2004 Elsevier Ltd. All rights reserved.
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