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1.
The molecular sources, dynamics and analytical characterizations of the phosphorus (P) containing components of marine dissolved and particulate organic matter (OM) are reviewed. Using a combination of 13C and 31P nuclear magnetic resonance spectroscopy on samples collected from a depth profile (20-4000 m) at Station Aloha in the North Pacific subtropical gyre, the biomolecular associations of P functional groups in marine OM are identified. Compositional differences between ultrafiltered dissolved organic matter (UDOM; 1-100 nm size fraction) and ultrafiltered particulate organic matter (UPOM; 0.1-60 μm size fraction) as reflected by NMR and elemental analyses indicate that UDOM does not originate from simple solubilization of UPOM, and the aggregation of UDOM is not the primary source of UPOM. Regression analyses indicated a large fraction of the P in UDOM is associated with carbohydrates and amino acids, but not with lipids. Similar analyses for UPOM indicated that P is associated with carbohydrates, amino acids and lipids. The P functional groups also appear to be balanced in their distribution among molecular classes, because they remain in relatively constant proportion throughout the ocean. 相似文献
2.
A group of islands of varying size on the floodplain of the Okavango alluvial fan, were studied to establish the processes which lead to the initiation and growth of islands. It was found that islands are initiated by the mound-building activities of the termite Macrotermes michaelseni. These termites import fine grained materials to use as a mortar for the construction of epigeal mounds. Their activities create a topographic feature, raised above the level of seasonal flooding, and also change the physical properties and nutrient status of the mound soil. Shrubs and trees are able to colonize these mounds, which results in increased transpiration. As a result, precipitation of calcite and silica from the shallow ground water occurs preferentially beneath the mounds, resulting in vertical and especially lateral growth, causing island expansion. © 1998 John Wiley & Sons, Ltd. 相似文献
3.
Michael C. Grenfell Rolf Aalto Suzanne E. Grenfell William N. Ellery 《地球表面变化过程与地形》2019,44(1):354-366
This paper resolves the origin of clay hummock micro-topography in seasonal wetlands of the Drakensberg Foothills, providing a review and appraisal of previously-suggested mechanisms of hummock formation in the context of new field and laboratory data. Field surveys revealed neo-formation of clay hummocks in a river channel that had been abandoned in c.1984. Fresh earthworm castings were located atop hummocks protruding from inundated abandoned channel margins. Earthworm castings, and sediment cores taken in hummocks and adjacent hollows, were analysed for soil-adsorbed carbon and nitrogen using an HCN analyser, and for 210Pb activity using alpha-geochronology. 210Pb activity profiles suggest relative enrichment of the isotope in hummocks, and relative depletion in adjacent hollows. Earthworm castings are characterised by very high 210Pb activity, as well as high C and N contents. Hummocks have significantly higher C and N contents than adjacent hollows. Results suggest that it is the foraging activity of earthworms in litter-rich seasonal wetland hollows, and repeated excretion of castings atop adjacent hummocks, that is responsible for the elemental enrichment observed. The paper presents a conceptual model of hummock formation in wetlands through interactions between hydrogeomorphology and earthworm activity, and illustrates a mechanism of biogeomorphic inheritance through which ordered patterns of preferential flow can emerge in ecosystems. Further implications of hummock formation and nodal accumulation of nutrients are considered in relation to wetland resilience and regulatory ecosystem service provision.© 2018 John Wiley & Sons, Ltd. 相似文献
4.
Ellery Frahm 《Geoarchaeology》2012,27(2):166-174
As new analytical techniques are brought to sourcing studies and researchers compile data into multi‐laboratory databases, systematic evaluation is essential. The importance of precision and accuracy is clear, but Shackley (2005) also calls for “archaeological accuracy.” Hughes (1998) offered a framework to consider precision and accuracy alongside the concepts of reliability and validity. These four concepts can serve as a foundation to evaluate archaeological sourcing data and procedures, but adoption of Hughes’ framework has been nearly nonexistent. Unfortunately, Hughes’ formulations of reliability and validity are somewhat at odds with their conventional definitions, hindering his framework. Furthermore, the concept of precision has become outdated in analytical circles, and superfluous terms (e.g., replicability) have emerged in the archaeological literature. Here I consider the basis of Hughes’ framework and how its four components, when applied consistently by the sourcing community, are best applied to evaluate analytical data and techniques for sourcing. 相似文献
5.
Alex Ellery and David Wynn-Williams propose a new UK astrobiology project, in which a micro-rover would deploy ground-penetrating moles to burrow into the Martian subsurface.
One of the linchpins of the UK's contribution to the burgeoning field of astrobiology is the Beagle 2 mission, due to fly to Mars in 2003 on the Mars Express bus. Given that NASA has declared its intention to focus on "whole planet" geological investigation in its future Mars missions, beginning with the Mars Exploration Rovers which are due to fly in 2003/2004, the UK is well placed to consider post-Beagle 2 astrobiology-focused Mars missions to ensure its leadership in the future in astrobiology. In this paper we present such a proposal – Vanguard. 相似文献
One of the linchpins of the UK's contribution to the burgeoning field of astrobiology is the Beagle 2 mission, due to fly to Mars in 2003 on the Mars Express bus. Given that NASA has declared its intention to focus on "whole planet" geological investigation in its future Mars missions, beginning with the Mars Exploration Rovers which are due to fly in 2003/2004, the UK is well placed to consider post-Beagle 2 astrobiology-focused Mars missions to ensure its leadership in the future in astrobiology. In this paper we present such a proposal – Vanguard. 相似文献
6.
Denitrification in continental shelf sediments has been estimated to be a significant sink of oceanic fixed nitrogen (N).
The significance and mechanisms of denitrification in organic-poor sands, which comprise 70% of continental shelf sediments,
are not well known. Core incubations and isotope tracer techniques were employed to determine processes and rates of denitrification
in the coarse-grained, sandy sediments of the Georgia continental shelf. In these sediments, heterotrophic denitrification
was the dominant process for fixed N removal. Processes such as coupled nitrification-denitrification, anammox (anaerobic
ammonium oxidation), and oxygen-limited autotrophic nitrification-denitrification were not evident over the 24 and 48 h time
scale of the incubation experiments. Heterotrophic denitrification processes produce 22.8–34.1 μmole N m-2 d-1 of N2 in these coarse-grained sediments. These denitrification rates are approximately two orders of magnitude lower than rates
determined in fine-grained shelf sediments. These lower rates may help reconcile unbalanced marine N budgets which calculate
global N losses exceeding N inputs. 相似文献
7.
The geomorphology and dynamics of the Mfolozi River floodplain and estuary, located in the subtropical region of northern KwaZulu-Natal, South Africa, were considered with respect to existing models of avulsion and alluvial stratigraphy. The Mfolozi River floodplain may be divided into regions based on longitudinal slope and dominant geomorphic processes. Confinement of the Mfolozi River above the floodplain has led to the development of an alluvial fan at the floodplain head, characterized by a relatively high sedimentation rate and avulsion frequency, at a gradient of 0.10%. The lower floodplain is controlled by sea level, with an average gradient of 0.05%. Between the two lies an extremely flat region with an average gradient of 0.02%, which may be controlled by faulting of the underlying bedrock.Avulsion occurrences on the Mfolozi floodplain are linked to the two main zones of aggradation, the alluvial fan at the floodplain head, and toward the river mouth in the lower floodplain. On the alluvial fan, normal flow conditions result in scour from local steepening. During infrequent, large flood events, the channel becomes overwhelmed with sediment and stream flow, and avulses. The resulting avulsion is regional, and affects the location of the channel from the floodplain head to the river mouth. Deposits resulting from such avulsions contribute significantly to the total volume of sediment stored in the floodplain, and tend to persist for long periods after the avulsion. Contrastingly, on the lower floodplain, reaching of the avulsion threshold is not necessarily linked to large flood events, but rather to long-term aggradation on the channel that decreases the existing channels gradient while increasing its elevation above the surrounding floodplain. Resultant avulsions tend to be local and do not contribute significantly to the overall volume of floodplain alluvium. 相似文献
8.
There has traditionally been a dichotomy in the space community regarding the efficacy of human versus robotic exploration
of space. I argue that no such dichotomy is necessary, and that there is a natural and synergistic division of labour between
man and machine, and that this division of labour will evolve in symbiotic fashion. The present state-of-the-art robotics
technology is insufficient to replace the human in space, but is sufficient to act as a useful, even necessary, tool in aiding
the astronaut in the conduct of useful work. I further argue that as robotics technology advances, the human will be further
relieved to perform tasks best suited to human decision-making and flexibility that is unlikely in the near-term to be matched
by autonomous or teleoperated machines.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
9.
The Mkuze Wetland System, forming part of the iSimangaliso World Heritage Site, is South Africa’s largest freshwater wetland area and is known to act as a sink for naturally occurring solutes within the landscape. The chemistry of groundwater and porewater samples, collected from two transects on the Mkuze River floodplain, was investigated to identify processes involved in the control of solute concentrations. Results show that solutes in the groundwater become increasingly concentrated under the influence of evapotranspiration, resulting in the saturation, precipitation, and accumulation of less soluble compounds. Trends in porewater chemistry and calculated saturation indices support previously documented mineralogical and sediment geochemical investigations, with CaCO3 and silica precipitation, and Fe-rich smectite neoformation identified as the major controls on solute concentration. The association of these mineral phases with zones of high salinity suggests that mineral precipitation is an active process on the floodplain which results in the progressive development of salinity, particularly in areas dominated by deep-rooted trees. Similarities between geochemical processes documented in the Okavango Delta (Botswana) and those identified in this study suggest that evapotranspiration-induced chemical sedimentation is an important process in southern African wetlands, which has the potential to influence vegetation distribution, hydrological flows, and local topography. 相似文献
10.
Alex Ellery and the SPRN team report on the inaugural meeting of a cross-disciplinary initiative to bring together and enhance UK expertise in robotics and space engineering. 相似文献