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  • 1
    Book
    Book
    Mesoscale physics, biogeochemistry and ecology of the Antarctic Polar front, Atlantic sector (2002)
    Oxford [u.a.] : Pergamon
    Details Availability
    Keywords: Aufsatzsammlung
    Type of Medium: Book
    Pages: IV S., S.3707-3950 , graph. Darst., Kt
    Series Statement: Deep-sea research 49,18
    Language: English
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  • 2
    Electronic Resource
    Electronic Resource
    A comparative study of iron and manganese diagenesis in continental slope and deep sea basin sediments off Uruguay (SW Atlantic) (2000)
    Springer
    International journal of earth sciences 88 (2000), S. 619-629 
    Details
    ISSN: 1437-3262
    Keywords: Key words Iron ; Manganese ; Early diagenesis ; Redox cycling ; Surface sediment ; Argentine Basin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Pore water and solid phase from surface sediments of the continental slope off Uruguay and from the Argentine Basin (southwestern Atlantic) were investigated geochemically to ascribe characteristic early diagenetic reactions of iron and manganese. Solid-phase iron speciation was determined by extractions as well as by Mössbauer spectroscopy. Both methods showed good agreement ( 〈6% deviation) for total-Fe speciation. The proportion of easy reducible iron oxyhydroxide relative to total-Fe oxides decreased from the continental slope to the deep sea which is attributed to an increase in crystallinity during transport as well as to a general decrease of iron mobilization. The product of iron reoxidation is Fe oxyhydroxide which made up less than 5% of total Fe. In addition to this fraction, a proportion of smectite bound iron was found to be redox reactive. This fraction made up to 10% of total Fe in sediments of the Argentine Basin and was quantitatively extracted by 1 N HCl. The redox reactive Fe(+II) fraction of smectite was almost completely reoxidized within 24 h under air atmosphere and may therefore considerably contribute to iron redox cycling if bioturbation occurs. In the case of the slope sediments we found concurrent iron and manganese release to pore water. It is not clear whether this is caused by dissimilatory iron and manganese reduction at the same depth or dissimilatory iron reduction alone inducing Mn(+IV) reduction by (abiotic) reaction with released Fe2+. The Argentine Basin sediment showed a significant manganese solid-phase enrichment above the denitrification depth despite the absence of a distinct pore-water gradient of Mn. This implies a recent termination of manganese mobilization and thus a non-steady-state situation with respect to sedimentation or to organic carbon burial rate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s005310050292
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    Paper (German National Licenses)
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  • 3
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    230Th-normalization: an essential tool for interpreting sedimentary fluxes during the late Quaternary (2004)
    AGU (American Geophysical Union)
    In:  Paleoceanography, 19 (PA1018).
    Details
    Publication Date: 2017-01-23
    Description: There is increasing evidence indicating that syndepositional redistribution of sediment on the seafloor by bottom currents is common and can significantly affect sediment mass accumulation rates. Notwithstanding its common incidence, this process (generally referred to as sediment focusing) is often difficult to recognize. If redistribution is near synchronous to deposition, the stratigraphy of the sediment is not disturbed and sediment focusing can easily be overlooked. Ignoring it, however, can lead to serious misinterpretations of sedimentary fluxes, particularly when past changes in export flux from the overlying water are inferred. In many instances, this problem can be resolved, at least for sediments deposited during the late Quaternary, by normalizing to the flux of 230Th scavenged from seawater, which is nearly constant and equivalent to the known rate of production of 230Th from the decay of dissolved 234U. We review the principle, advantages and limitations of this method. Notwithstanding its limitations, it is clear that 230Th normalization does provide a means of achieving more accurate interpretations of sedimentary fluxes and eliminates the risk of serious misinterpretations of sediment mass accumulation rates.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2003PA000939
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    Quasi-conservative behaviour of 10Be in deep waters of the Weddell sea and the Atlantic sector of the Antarctic Circumpolar Current (2002)
    Elsevier
    In:  Earth and Planetary Science Letters, 201 . pp. 171-186.
    Details
    Publication Date: 2016-11-15
    Description: We present the first transect of dissolved 10Be depth profiles across the Antarctic Circumpolar Current (ACC) in the Atlantic sector. North of the Polar Front the 10Be concentrations increase continuously from very low values at the surface to values of up to 1600 atoms/g at depth. Deep water 10Be concentrations of particular water masses are consistent with earlier results obtained further north. South of the Polar Front and in the Weddell Sea the distribution of 10Be is also characterised by low surface concentrations but below 1000 m depth the concentrations are relatively constant and significantly higher (up to 2000 atoms/g) than further north, probably as a result of mixing and advection of water masses of Pacific origin. Overall the deep water 10Be distribution is obviously not significantly affected by scavenging processes or ice melt and comparison with the density distribution suggests that 10Be can be viewed as a quasi-conservative tracer. This provides a tool for an improved understanding of the behaviour of other more particle reactive trace metals in the Southern Ocean such as 230Th: in deep waters north of the ACC/Weddell Gyre boundary (AWB) 10Be/230Th has a relatively constant value (1.7±0.3×109 atoms/dpm) over a wide density range whereas south of the AWB the ratio is significantly lower (1.1±0.2×109 atoms/dpm). This normalisation to 10Be corroborates that 230Th is enriched by 50% due to accumulation south of the AWB as a consequence of minimal particulate fluxes. The quasi-conservative behaviour deduced from our results also implies that 10Be can only be used as a tracer for Southern Ocean particle fluxes in the past if ocean circulation patterns and water mass residence times did not change significantly.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/S0012-821X(02)00688-X
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    Trapping efficiencies of sediment traps from the deep Eastern North Atlantic: the 230Th calibration (2001)
    Pergamon Press
    In:  Deep Sea Research Part II: Topical Studies in Oceanography, 48 . pp. 2383-2408.
    Details
    Publication Date: 2020-08-05
    Description: Bottom-tethered sediment traps deployed in the deep eastern North Atlantic between 54°N 20°W and 33°N 20°W (L1, L2, L3), at the European continental margin at 49°N (OMEX) and off the Canary Islands (ESTOC) were investigated for the determination of 230Th trapping efficiencies. The ratios of 230Th flux measured in the traps (Fa) to the expected 230Th flux from the production rate of 230Th in the overlying water column (Fp) ranged between 0.09 and 1.26. For the traps with deployment periods 〉300 days the interannual variation of Fa/Fp ratios (different years but same location and water depth) were up to 10%, suggesting that the average 230Th flux to the sediment traps did not vary significantly. The influence of lateral advection on the 230Th flux was taken into account either by applying a mass balance of 230Th and 231Pa or by assuming a constant removal rate of 230Th from the water column, an assumption based on similar 230Th concentration-depth profiles observed at most locations investigated. 230Th trapping efficiencies were between 9 and 143%, showing a trend of increasing efficiencies with increasing water depth. No relation was found between current velocities and 230Th trapping efficiencies. Our investigations suggest that the observation of constant or even increasing particle flux rates with increasing water depths in several sediment trap arrays investigated may be a result of sediment trap biases. The correction for the trapping biases is important for the understanding of the regional differences in the particle flux in the eastern North Atlantic.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/S0967-0645(00)00176-4
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    Similar glacial and interglacial export bioproductivity in the Atlantic sector of the Southern Ocean: Multiproxy evidence and implications for atmospheric CO2 (2000)
    AGU (American Geophysical Union)
    In:  Paleoceanography, 15 . pp. 642-658.
    Details
    Publication Date: 2019-07-02
    Description: We present time series of export productivity proxy data including 230Thex-normalized deposition rates (rain rates) of 10Be, dissolution-corrected biogenic Ba, and biogenic opal as well as authigenic U concentrations which are complemented by rain rates of total (detrital) Fe and sea ice indicating diatom abundances from five sediment cores across the Atlantic sector of the Southern Ocean covering the past 150,000 years. The results suggest that 10Be rain rates and authigenic U concentration cannot serve as quantitative paleoproductivity proxies because they have also been influenced by detrital particle fluxes in the case of 10Be and bulk sedimentation rates (sediment focussing) and deep water oxygenation in the case of U. The combined results of the remaining productivity proxies of this study (rain rates of biogenic opal and biogenic Ba in those sections without authigenic U) and other previously published proxy data from the Southern Ocean (231Pa/230Th and nitrogen isotopes) suggest that a combination of sea ice cover, shallow remineralization depth, and stratification of the glacial water column south of the present position of the Antarctic Polar Front and possibly Fe fertilization north of it have been the main controlling factors of export paleoproductivity in the Southern Ocean over the last 150,000 years. An overall glacial increase of export paleoproductivity is not supported by the data, implying that bioproductivity variations in the Southern Ocean are unlikely to have contributed to the major glacial atmospheric CO2 drawdown observed in ice cores.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2000PA000497
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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