| 1. |
- 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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| 2. |
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| 3. |
- 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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| 4. |
- Dahllöf, Ingela, 1963, et al.
(författare)
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The Effect of TBT on the Structure of a Marine Sediment Community - a Boxcosm Study
- 2001
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Ingår i: Marine Pollution Bulletin. - 0025-326X .- 1879-3363. ; 42:8, s. 689-695
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Tidskriftsartikel (refereegranskat)abstract
- The effect of tri-n-butyl tin (TBT) on an intact marine sediment community after five months exposure was investigated. Changes in the structure of macro- and meiofauna communities were determined, as well as the functional diversity of the microbial community using BIOLOG microplates for Gram negative bacteria. Development of tolerance in the microbial community was investigated using Pollution Induced Community Tolerance (PICT) experiments with fluxes of nutrients as effect indicators. TBT affected the structure and recruitment of the macro- and meiofauna at nominal additions of 30137 mol TBT/m2 sediment. Number of species, diversity, biomass and community similarity was reduced at these concentrations compared to control. Species that molt seemed to be the most tolerant since they were predominant in boxes that had received the highest TBT addition and echinoderms were the most sensitive species. Renewed addition of TBT in PICT experiments with sediment from each boxcosm showed that TBT had an effect on individual nutrient fluxes from all sediments. Analyses of the flux patterns revealed a memory of previous TBT exposure, either due to induced tolerance or other community conditioning.
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| 5. |
- Gustafsson, Mikael, 1965, et al.
(författare)
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Benthic foraminiferal tolerance to tri-n-butyltin (TBT)
- 2000
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Ingår i: Marine Pollution Bulletin. ; 40, s. 1072-1075
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Tidskriftsartikel (refereegranskat)abstract
- Tri-n-butyltin (TBT) has been used in the marine environment as a toxic agent in antifouling paints, but unfortunately it also has negative effects on non-target organisms in the environment. In this study, intact coastal sediment was exposed for seven months to three levels of TBT corresponding to nominal additions of 0.00, 0.02 and 2.00 nmol TBT per g dry sediment. This paper presents the first attempt to find out how living benthic foraminifera respond to TBT, Increased foraminiferal abundance in the 0.02 nmol mesocosm could be an effect of decreased predation (competition), since other representatives of meiofauna and macrofauna tended to be less tolerant to TBT, Increasing toxicity in the most contaminated mesocosm group (2.00 nmol) resulted in a less abundant foraminiferal population suggesting that TBT affects the foraminiferal community.
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| 6. |
- Naumburg, Estelle, et al.
(författare)
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Intrauterine exposure to diagnostic X rays and risk of childhood leukemia subtypes
- 2001
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Ingår i: Radiation Research. - 0033-7587 .- 1938-5404. ; 156, s. 718-
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Tidskriftsartikel (refereegranskat)abstract
- The relationship between childhood leukemia and prenatal exposure to low-dose ionizing radiation remains debatable. This population-based case-control study investigated the association between prenatal exposure to diagnostic X-ray examinations (for different types of examinations and at different stages of pregnancy) and the risk of childhood lymphatic and myeloid leukemia. All children born and diagnosed with leukemia between 1973-1989 in Sweden (578 lymphatic and 74 myeloid) were selected as cases, and each was matched (by sex and year of birth) to a healthy control child (excluding Down's syndrome). Exposure data were abstracted blindly from all available medical records. Odds ratios (OR) and 95% confidence intervals (CI) were calculated by conditional logistic regression. It was found that prenatal X-ray examinations resulting in direct fetal exposure were not associated with a significant overall increased risk for childhood leukemia (OR = 1.11, 95% CI 0.83-1.47), for lymphatic leukemia (OR = 1.04, 95% CI 0.77-1.40), or for myeloid leukemia (OR = 1.49, 95% CI 0.48-4.72). There was little evidence of a dose response or variation in risk by trimester of exposure or age at diagnosis. Thus X-ray examinations performed during pregnancy in the 1970s and 1980s in Sweden did not affect the risk of childhood leukemia discernibly.
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| 7. |
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| 8. |
- 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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| 9. |
- Ståhl, H., et al.
(författare)
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Respiration and sequestering of organic carbon in shelf sediments of the oligotrophic northern Aegean Sea
- 2004
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Ingår i: Marine Ecology-Progress Series. ; 269, s. 33-48
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Tidskriftsartikel (refereegranskat)abstract
- Respiration and sequestering of organic carbon was investigated in northern Aegean Sea sediments (NE Mediterranean). Benthic total carbonate (C-T, also called SigmaCO(2) or dissolved inorganic carbon, DIC) fluxes and O-2 uptake rates were measured in situ using a benthic lander. Dissolved organic carbon (DOC) fluxes were calculated from pore water gradients, taking into account the influence of biodiffusion/bioirrigation. Macrofaunal biomass was determined in the sediment collected by the chambers of the benthic lander. Chl a distributions were used as a tracer of high-quality sedimentary organic carbon. The measured benthic C-T fluxes were positively correlated with the O-2 uptake rates. The obtained average apparent respiration ratio (C-T flux:O-2 flux) of 0.90 +/- 0.36 suggests a clear dominance of aerobic respiration in these organic carbon-poor shelf sediments. The C-T efflux, the 02 uptake rate, and the DOC flux were significantly higher in spring than in fall at 2 of the stations. The Black Sea water, which enters the Aegean Sea in the study area, did not influence benthic respiration rates or organic carbon sequestering rates. A strong positive correlation between both the C-T and O-2 fluxes and the mean chl a concentration in surficial sediment suggests that benthic respiration, to a large extent, was controlled by the availability of labile phytodetrital organic matter. There was no influence of macrofaunal biomass (dry weight) on C-T fluxes or oxygen uptake rates. The calculated benthic DOC fluxes made up 7.2 to 27 % (average 14 +/- 8.1 %) of the C-T fluxes, indicating that their contribution to the overall recycling of organic carbon in these sediments was important. The organic carbon burial efficiency ranged from 0.1 to 5.3 %, but at Stn KA1 it was considerably higher (average 4%) than at the other stations (average 0.3%). Except for this station, the obtained burial efficiencies were very low compared to other sediments with similar accumulation rates. The average burial flux of organic carbon corresponded to less than 1 % of the annual mean primary production (PP) for the Aegean Sea at Stn KA1, and to less than 0.1 % of PP at the other stations.
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| 10. |
- Tengberg, Anders, 1962, et al.
(författare)
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Intercalibration of benthic flux chambers I. Accuracy of flux measurements and influence of chamber hydrodynamics
- 2004
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Ingår i: Progress in Oceanography. - : Elsevier BV. - 0079-6611. ; 60:1, s. 1-28
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Tidskriftsartikel (refereegranskat)abstract
- The hydrodynamic properties and the capability to measure secliment-water solute fluxes, at assumed steady state conditions, were compared for three radically different benthic chamber designs: the "Microcosm", the "Mississippi" and the "Coteborg" chambers. The hydrodynamic properties were characterized by mounting a PVC bottom in each chamber and measuring mixing time, diffusive boundary layer thickness LDBL thickness) shear velocity (W), and total pressure created by the water mixing. The Microcosm had the most even distribution of DBL thickness and u*, but the highest differential pressure at high water mixing rates. The Mississippi chamber had low differential pressures at high u*. The Goteborg chamber was in between the two others regarding these properties. DBL thickness and u* were found to correlate according to the following empirical formula: DBL = 76.18(u*)(-0.933). Multiple flux incubations with replicates of each of the chamber types were carried out on homogenized, macrofauna-frce sediments in four tanks. The degree of homogeneity was determined by calculating solute fluxes (of oxygen, silicate, phosphate and ammonium) from porewater profiles and by sampling for porosity, organic carbon and meiofauna. All these results, except meiofauna, indicated that there were no significant horizontal variations within the sediment in any of the parallel incubation experiments. The statistical evaluations also suggested that the occasional variations in meiofauna abundance did not have any influence on the measured solute fluxes. Forty-three microelectrode profiles of oxygen in the DBL and porewater were evaluated with four different procedures to calculate diffusive fluxes. The procedure presented by Berg, Risgaard-Petersen and Rysgaard, 1989 [Limnol. Oceanogr. 43, 1500] was found to be superior because of its ability to fit measured profiles accurately, and because it takes into consideration vertical zonation with different oxygen consumption rates in the sediment. During the flux incubations, the mixing in the chambers was replicated ranging from slow mixing to just noticeable sediment resuspension. In the "hydrodynamic characterizations" these mixing rates corresponded to average DBL thickness from 120 to 550 mum, to u* from 0.12 to 0.68 cm/s, and to differential pressures from 0-3 Pa. Although not directly transferable, since the incubations were done on a "real" sediment with a rougher surface while in the characterizations a PVC plate simulated the sediments surface, these data give ideas about the prevailing hydrodynamic condition in the chambers during the incubations. The variations in water mixing did not generate statistically significant differences between the chamber types for any of the measured fluxes of oxygen or nutrients. Consequently it can be concluded that, for these non-permeable sediments and so long as appropriate water mixing (within the ranges given above) is maintained, the type of stirring mechanism and chamber design used were not critical for the magnitude of the measured fluxes. The average measured oxygen flux was 11.2 +/- 2.7 (from 40 incubations), while the diffusive flux calculated (from 43 profiles using the Berg et al., 1989 [Limnol. Oceanogr. 43, 1500] procedure) was 11.1 +/- 3.0 mmol m(-2) day(-1). This strongly suggests that accurate oxygen flux measurements were obtained with the three types of benthic chambers used and that the oxygen uptake is diffusive. (C) 2004 Elsevier Ltd. All rights reserved.
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