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- Brunnegård, Jenny, 1973, et al.
(author)
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Nitrogen cycling in deep-sea sediments of the Porcupine Abyssal Plain, NE Atlantic
- 2004
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In: Progress in Oceanography. - : Elsevier BV. - 0079-6611. ; 63:4, s. 159-181
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Journal article (peer-reviewed)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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| 2. |
- Omstedt, Anders, 1949, et al.
(author)
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Knowledge of the Baltic Sea physics gained during the BALTEX and related programmes
- 2004
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In: Progress in Oceanography. - : Elsevier BV. - 0079-6611. ; 63:1-2, s. 1-28
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Journal article (peer-reviewed)abstract
- Review is given about the main results of the oceanographic component of the BALTEX research programme (one of the six continental scale experiments within GEWEX-WCRP to study water and energy cycles in the regional climate system) and related programmes/projects over the last 10 years. Working closely together with two other components regional meteorology and hydrology of the Baltic Sea drainage basin - oceanographic research has considerably improved the understanding of and ability to model the Baltic Sea marine system. In the Baltic Sea physics seven different broad topics are identified where knowledge has significantly improved. These are reviewed together with a discussion of gaps in knowledge. The focus is on the water and energy cycles of the Baltic Sea, but various aspects of forcing and validation data and modelling are also discussed. The major advances achieved through BALTEX and related programmes are: Meteorological, hydrological, ocean and ice data are now available for the research community. Progress in understanding of the strong impact of large-scale atmospheric circulation on Baltic Sea circulation, water mass exchange, sea ice evolution, and changes in the ocean conditions of the Baltic Sea. Progress in understanding of the importance of strait flows in the exchange of water into and within the Baltic Sea. Progress in understanding of intra-basin processes. Ocean models introduced into Baltic Sea water and energy studies. Development of turbulence models and 3D ocean circulation models for application to the Baltic Sea. Improved Baltic Sea ice modelling and increased understanding of the need for coupled atmosphere-ice-ocean-land models. (C) 2004 Elsevier Ltd. All rights reserved.
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| 3. |
- Tengberg, Anders, 1962, et al.
(author)
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Intercalibration of benthic flux chambers I. Accuracy of flux measurements and influence of chamber hydrodynamics
- 2004
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In: Progress in Oceanography. - : Elsevier BV. - 0079-6611. ; 60:1, s. 1-28
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Journal article (peer-reviewed)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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