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| 2. |
- Brunnegård, Jenny, 1973, et al.
(författare)
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Nitrogen cycling in deep-sea sediments of the Porcupine Abyssal Plain, NE Atlantic
- 2004
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Ingår i: Progress in Oceanography. - : Elsevier BV. - 0079-6611. ; 63:4, s. 159-181
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Tidskriftsartikel (refereegranskat)abstract
- Rates of transformation, recycling and burial of nitrogen and their temporal and spatial variability were investigated in deep-sea sediments of the Porcupine Abyssal Plain (PAP), NE Atlantic during eight cruises from 1996 to 2000. Benthic fluxes of ammonium (NH4) and nitrate (NO3) were measured in situ using a benthic lander. Fluxes of dissolved organic nitrogen (DON) and denitrification rates were calculated from pore water profiles of DON and NO3, respectively. Burial of nitrogen was calculated from down core profiles of nitrogen in the solid phase together with C-14-based sediment accumulation rates and dry bulk density. Average NH4 and NO3-effluxes were 7.4 +/- 19 mumol m(-2) d(-1) (n = 7) and 52 +/- 30 mumol m(-2) d(-1) (n = 14), respectively, during the period 1996-2000. During the same period, the DON-flux was 11 +/- 5.6 mumol m(-2) d(-1) (n = 5) and the denitrification rate was 5.1 +/- 3.0 mumol m(-2) d(-1) (n = 22). Temporal and spatial variations were only found in the benthic NO3 fluxes. The average burial rate was 4.6 +/- 0.9 mumol m(-2) d(-1). On average over the sampling period, the recycling efficiency of the PON input to the sediment was similar to94% and the burial efficiency hence similar to6%. The DON flux constituted similar to14% of the nitrogen recycled, and it was of similar magnitude as the sum of burial and denitrification. By assuming the PAP is representative of all deep-sea areas, rates of denitrification, burial and DON efflux were extrapolated to the total area of the deep-sea floor (>2000 m) and integrated values of denitrification and burial of 8 +/- 5 and 7 +/- 1 Tg N year(-1), respectively, were obtained. This value of total deep-sea sediment denitrification corresponds to 3-12% of the global ocean benthic denitrification. Burial in deep-sea sediments makes up at least 25% of the global ocean nitrogen burial. The integrated DON flux from the deep-sea floor is comparable in magnitude to a reported global riverine input of DON suggesting that deep-sea sediments constitute an important source of DON to the world ocean. (C) 2004 Elsevier Ltd. All rights reserved.
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| 3. |
- Hall, Per, 1954, et al.
(författare)
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Dissolved organic matter in abyssal sediments: Core recovery artifacts
- 2007
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Ingår i: Limnology and Oceanography. - 0024-3590. ; 52:1, s. 19-31
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Tidskriftsartikel (refereegranskat)abstract
- We report measurements of pore-water dissolved organic carbon (DOC), dissolved organic nitrogen, total dissolved carbohydrates, dissolved free monosaccharides, and ammonium in recovered deep-sea sediments from the Porcupine Abyssal Plain (PAP), Northeast Atlantic. There were distinct maxima close to the sediment–water interface of these constituents at all times of the year. The very high diffusive effluxes calculated from these porewater distributions were not compatible with simultaneous sediment trap measurements of particulate organic carbon, nitrogen, and carbohydrate fluxes toward the seafloor. Effluxes calculated from pore-water DOC distributions in recovered cores from another Atlantic deep-sea site, showing almost identical maxima as those at PAP, were more than an order of magnitude greater than simultaneous in situ chamber DOC flux measurements. We suggest that the dissolved organic matter maxima are predominantly artifacts induced by lysis of, or leakage from, mainly bacterial biomass resulting from decompression and/or warming during recovery of the sediment cores from the abyssal seafloor. Temperature elevation during core recovery from the abyss gives a N2 saturation of about 150%, and the combined effect of warming and decompression results in a CO2 saturation of about 135%, which together plausibly are associated with bubble formation creating cell bursting. Previous estimates of microbial biomass in abyssal sediments may be underestimates because of the difficulty of counting lysed bacterial cells. Since exoenzymes are inducible, previous measurements of their activities in recovered abyssal sediments may be overestimates.
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| 4. |
- Ståhl, H., et al.
(författare)
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Factors influencing organic carbon recycling and burial in Skagerrak sediments
- 2004
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Ingår i: Journal of Marine Research. - : Journal of Marine Research/Yale. - 0022-2402 .- 1543-9542. ; 62:6, s. 867-907
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Tidskriftsartikel (refereegranskat)abstract
- Different factors influencing recycling and burial rates of organic carbon (OC) were investigated in the continental margin sediments of the Skagerrak (NE North Sea). Two different areas, one in the southern and one in the northeastern part of the Skagerrak were visited shortly after a spring bloom (March 1999) and in late summer (August 2000). Results suggested that: (1) Organic carbon oxidation rates (C-ox) (2.2-18 mmol Cm-2 d(-1)) were generally larger than the O-2 uptake rates (1.9-25 mmol m(-2) d(-1)). Both rates were measured in situ using a benthic lander. A mean apparent respiration ratio (C-ox:O-2corr) of 1.3 +/- 0.5 was found, indicating some long-term burial of reduced inorganic substances in these sediments. Measured O-2, fluxes increased linearly with increasing C-ox rates during the late summer cruise but not on the, early spring cruise, indicating a temporal uncoupling of anaerobic mineralization and reoxidation of reduced substances. (2) Dissolved organic carbon (DOC) fluxes (0.2-1.0 mmol Cm-2 d(-1)) constituted 3-10% of the C-ox rates and were positively correlated with the latter, implying that net DOC production rates were proportional to the overall sediment OC remineralization rates. (3) Chlorophyll a (Chl-a) concentrations in the sediment were significantly higher in early spring compared to late summer. The measured C-ox rates, but not O-2 fluxes, showed a strong positive correlation with the Chl-a inventories in the top 3 cm of the sediment. (4) Although no relationship was found between the benthic fluxes and the macrofaunal biomass in the chambers, total in situ measured dissolved inorganic carbon (C-T) fluxes were 1-5.4 times higher than diffusive mediated C-T fluxes, indicating that macrofauna have a significant impact on benthic exchange rates of OC remineralization products in Skagerrak sediments. (5) OC burial fluxes were generally higher in northeastern Skagerrak than in the southern part. The same pattern was observed for burial efficiencies, with annual means of similar to62% and similar to43% for the two areas respectively. (6) On a basin-wide scale, there was a significant positive linear correlation between the burial efficiencies and sediment accumulation rates. (7) The calculated particulate organic carbon (POC) deposition, from benthic flux and burial measurements, was only 24-78% of the sediment trap measured POC deposition, indicating a strong near-bottom lateral transport and resuspension of POC. (8) A larger fraction of the laterally advected material of lower quality seemed to settle in the northeastern Skagerrak rather than in the southern Skagerrak. (9) Skagerrak sediments, especially in the northeastern part, act as an efficient net sink for organic carbon, even in a global continental margin context.
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| 5. |
- Ståhl, H., et al.
(författare)
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Recycling and burial of organic carbon in sediments of the Porcupine Abyssal Plain, NE Atlantic
- 2004
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Ingår i: Deep-Sea Research Part I-Oceanographic Research Papers. ; 51:6, s. 777-791
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Tidskriftsartikel (refereegranskat)abstract
- 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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