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  • 1
    ISSN: 1365-2389
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: As a consequence of heterogeneous transport in soils, only a small part of the soil might be responsible for sorbing incoming elements. After staining preferential flow paths in forested Dystric Cambisol with a colour dye, we sampled soil material from the flow paths and from the soil matrix. We measured chemical properties and sorption isotherms of these two flow regions and estimated the significance of preferential flow paths for the transport of solutes leached from wood ash applied at the surface. In the A horizon (0–9 cm depth), the cation exchange capacity of the flow paths was 83.8 mmolc kg−1, while that of the soil matrix was only 74.6 mmolc kg−1. The base saturation was 42% and soil organic matter content was 41% larger in flow paths than in the soil matrix. The sorption capacity for Cu was also larger than in the matrix, whereas the sorption capacity for Sr was similar in both flow regions. The impact of the addition of 8 t wood ash ha−1 on soil chemical properties was restricted mainly to the flow paths in the uppermost 20 cm of the soil; it was negligible in the matrix and at greater depths. Concentrations of exchangeable Ca in the flow paths increased nearly 10-fold during the 6 months following the addition of the wood ash, and those of organically bound Pb by 50%. The opposite effect was found for exchangeable Al. Our results show that only part of the whole soil volume, approximately 50% of 0–20 cm in our study, is involved in transporting and sorbing the elements applied with the wood ash or as tracers. Such differences must be considered when calculating the maximal impact of any addition of fertilizer, wood ash, or liming agent.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    ISSN: 1365-2389
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Cryptopodzolic Soils are characterized by a thick blackish-brown mineral horizon rich in organic matter, the dark colour of which masks the morphological characteristics of podzolization. Little is known about the specific site factors that lead to the formation of these soils. Four representative soil profiles from a typical toposequence between 1700 and 500 m above sea level in southern Switzerland, embracing Haplic Podzols, Humic Cambisols and Cryptopodzolic Soils, are described morphologically, chemically and physically. The Cryptopodzolic Soils in this region are characterized by weak to moderate A1 and Fe translocation, and by a uniform incorporation of organic matter deep into the soil. The most prominent feature is the exceptional stability of the soil organic matter with a maximum in the spodic horizon. All these characteristics can be explained by the unique combined effect of a mild, wet climate, an Fe- and Al-rich acid bedrock and a litter layer providing dissolved organic matter rich in polyphenolic substances with strong metal-binding properties.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1365-2389
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: The relative contributions of sources of carbon in soils, such as throughfall, litter, roots, microbial decay products and stable organic fractions, to dissolved organic C are controversial. To identify the origin of dissolved organic C, we made use of a 4-year experiment where spruce and beech, growing on an acidic loam and on a calcareous sand, were exposed to increased CO2 that was depleted in 13C. We traced the new C inputs from trees into dissolved organic C, into water-extractable organic C, and into several particle-size fractions. In addition, we incubated the labelled soils for 1 year and measured the production of dissolved organic C and CO2 from new and old soil C. In the soil solutions of the topsoil, the dissolved organic C contained only 5–10% new C from the trees. The δ13C values of dissolved organic C resembled those of C pools smaller than 50 µm, which strongly suggests that the major source of dissolved organic C was humified old C. Apparently, throughfall, fresh litter and roots made only minor contributions to dissolved organic C. Water-extractable organic C contained significantly larger fractions of new C than did the natural dissolved organic C (25–30%). The δ13C values of the water-extractable organic C were closely correlated with those of sand fractions, which consisted of little decomposed organic carbon. The different origin of dissolved and water-extractable organic C was also reflected in a significantly larger molar UV absorptivity and a smaller natural 13C abundance of dissolved organic C. This implies that the sampling method strongly influences the characteristics and sources of dissolved organic C. Incubation of soils showed that new soil C was preferentially respired as CO2 and only a small fraction of new C was leached as dissolved organic C. Our results suggest that dissolved organic C is produced during incomplete decomposition of recalcitrant native C in the soils, whereas easily degradable new components are rapidly consumed by microbes and thus make only a minor contribution to the dissolved C fraction.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1365-2389
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Soil contains the major part of carbon in terrestrial ecosystems, but the response of this carbon to enriching the atmosphere in CO2 and to increased N deposition is not completely understood. We studied the effects of CO2 concentrations at 370 and 570 μmol CO2 mol−1 air and increased N deposition (7 against 0.7 g N m−2 year−1) on the dynamics of soil organic C in two types of forest soil in model ecosystems with spruce and beech established in large open-top chambers containing an acidic loam and a calcareous sand. The added CO2 was depleted in 13C and thus the net input of new C into soil organic carbon and the mineralization of native C could be quantified.Soil type was the greatest determining factor in carbon dynamics. After 4 years, the net input of new C in the acidic loam (670 ± 30 g C m−2) exceeded that in the calcareous sand (340 ± 40 g C m−2) although the soil produced less biomass. The mineralization of native organic C accounted for 700 ± 90 g C m−2 in the acidic loam and for 2800 ± 170 g C m−2 in the calcareous sand. Unfavourable conditions for mineralization and a greater physico-chemical protection of C by clay and oxides in the acidic loam are probably the main reasons for these differences. The organic C content of the acidic loam was 230 g C m−2 more under the large than under the small N treatment. As suggested by a negligible impact of N inputs on the fraction of new C in the acidic loam, this increase resulted mainly from a suppressed mineralization of native C. In the calcareous sand, N deposition did not influence C concentrations. The impacts of CO2 enrichment on C concentrations were small. In the uppermost 10 cm of the acidic loam, larger CO2 concentrations increased C contents by 50–170 g C m−2. Below 10 cm depth in the acidic loam and at all soil depths in the calcareous sand, CO2 concentrations had no significant impact on soil C concentrations. Up to 40% of the ‘new’ carbon of the acidic loam was found in the coarse sand fraction, which accounted for only 7% of the total soil volume. This suggests that a large part of the CO2-derived ‘new’ C was incorporated into the labile and easily mineralizable pool in the soil.
    Type of Medium: Electronic Resource
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  • 5
    Publication Date: 2018-11-27
    Description: The neodymium isotope proxy has become a valuable tool for the reconstruction of past ocean water mass provenance and mixing. For its accurate application, knowledge about the origin and preservation of Nd in sedimentary archives is crucial. Recently, concerns have emerged regarding the applicability of neodymium isotopes as a conservative palaeo water mass tracer, given potential Nd fluxes from sediments into bottom waters (Abbott et al., 2015a) and inferred relabelling of ocean waters by settling detrital material (Roberts and Piotrowski, 2015). Consequently, a decoupling of water mass provenance and proxy variations may arise. We investigate the mobility of Nd around extreme detrital sedimentation events such as glacial ice rafting pulses and turbidite deposition in the Northeast Atlantic. The constructed records from sediment leachates span extreme Nd isotope variations including volcanic (εNd ∼ 0) and Laurentian (εNd ∼ −27) sources. We find that Nd was released into pore waters from reactive detritus inside some detrital layers during early diagenesis, thereby overprinting any archived bottom water Nd signature and precluding the reconstruction of past water mass provenance during the affected time intervals. However, we do not observe any definite indication of diffusive vertical migration of Nd into adjacent layers. Furthermore, bottom water Nd isotope signatures were not modified to a measurable degree by any potential benthic flux of Nd during the deposition of these detrital sediment layers. Consequently, the Nd isotope composition of the pelagic glacial Northeast Atlantic water masses were resilient to such episodic large detrital fluxes. Apart from extreme local sedimentation events, we confirm the presence of detritally overprinted deep waters north of 47°N during the peak glacial from comparison of Northeast Atlantic depth transects. We furthermore suggest that the sensitivity of deep waters to this overprinting effect increased during periods of reduced Atlantic Meridional Overturning Circulation and elevated ice rafting. Overall, our study demonstrates that a thorough evaluation of the proportion of Nd originating from physical water mass advection versus in situ chemical inputs is crucial for the reliable application of Nd isotopes as a water mass tracer.
    Type: Article , PeerReviewed
    Format: text
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  • 6
    ISSN: 1435-0661
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: 3 and imogolite, (HO)3Al2O3SiOH, reached a constant value after reaction times of 16 d. For pH 〉4.1, the compilation of all data revealed pAl + 0.5 pSi = 3.05 pH − 7.04 (r 2 = 0.99) and pAl = 2.87 pH − 8.07 (r 2 = 0.99). These data could be shown to be consistent with either Al solubility control by imogolite-type material (ITM) with a log *K0 s = 6.53 ± 0.09, which dissolves incongruently, or a simultaneous equilibrium with ITM and hydroxy-Al interlayers of clay minerals. For pH 〈4.1, data indicated solubility control by a 1:1 aluminosilicate, e.g., poorly crystalline kaolinite.
    Type of Medium: Electronic Resource
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  • 7
    Publication Date: 2018-06-04
    Description: Oceans and climate are a tightly coupled system interacting with each other in various ways such as storage of carbon dioxide in the deep ocean. Within the global conveyor belt the Atlantic Meridional Overturning Circulation (AMOC) holds a key function, transporting warm salty surface waters from the tropical to the northern Atlantic where deep water formation takes place. Following the continental rise of North America this newly formed deep water propagates southward as Western Boundary Undercurrent (WBUC) ventilating the deep Atlantic. In the past (e.g. the last glacial cycle) strength and geometry of the AMOC have changed significantly. This study aims to provide a better understanding of the temporal and spatial (also depth depended) evolution of the AMOC in the western Atlantic sector since the last glacial (∼30 ka). We have investigated four sediment cores of the Blake Outer Ridge (30°N, 74°W; ODP 1059 to 1062) in a depth transect from 3000 to 4700 m water depth in the main flow path of the WBUC. We measured four down-core profiles of neodymium (εNd) and 231Pa/230Th isotopes for the reconstruction of water mass provenance and circulation strength of the last ∼30 ka. In contrast to published Nd isotope and 231Pa/230Th records from the Blake Ridge area our records are of unprecedented resolution, resolving climate key features of the North Atlantic region: Heinrich Stadials (HS) 1 and 2, the Last Glacial Maximum (LGM), the Bølling-Allerød and Younger Dryas (YD). Radiogenic Nd isotope signatures during the LGM reveal AABW to be the prevalent water mass in the deep western North Atlantic. The trend to more unradiogenic signatures during the deglaciation point to an increased formation of NADW which was again replaced by AABW during YD. The Holocene shows the most unradiogenic signatures and therefore established NADW. The circulation strength-proxy 231Pa/230Th indicates reduced LGM deep circulation, a pronounced slowdown during HS1 and a strong and deep circulation during the Holocene. Compared to isotopic records from the Bermuda Rise (ODP 1063) we found depth depended geometry changes of the WBUC which have occurred through the last glacial. Here, we focus on how deep northern sourced water has reached during phases of reduced circulation (indicated by increased 231Pa/230Th ratios) and the timing of this southward progradation of lower NADW.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
    Format: application/pdf
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  • 8
    ISSN: 1420-9039
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Physics
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1420-9039
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Physics
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    ISSN: 1420-9039
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Physics
    Type of Medium: Electronic Resource
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