Spatial patterns in the oxygen isotope composition of daily rainfall in the British Isles     

Jonathan J. Tyler  Matthew Jones  Carol Arrowsmith  Tim Allott  Melanie J. Leng 《Climate Dynamics》2016,47(5-6):1971-1987

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Deep pore water profiles reflect enhanced microbial activity towards tidal flat margins     

Melanie Beck  Jürgen Köster  Bert Engelen  Jan M. Holstein  Antje Gittel  Martin Könneke  Thomas Riedel  Kai Wirtz  Heribert Cypionka  Jürgen Rullkötter  Hans-Jürgen Brumsack 《Ocean Dynamics》2009,59(2):371-383

Microbial activity in permeable tidal flat margin sediments is enhanced by two main processes. First, organic matter is supplied by rapid sedimentation at prograding tidal flat margins. Second, surface and deep pore water advection lead to a replenishment of the dissolved organic matter and sulfate pools. Increasing microbial activity towards the low water line is reflected in sulfate and methane profiles as well as in total cell numbers, sulfate reduction rates, and remineralization products. The impact of high sedimentation rates on pore water biogeochemistry is confirmed by inverse modeling reproducing the depth profiles obtained by measurements. In central parts of the tidal flats, low sedimentation rates and pore water flow velocities limit microbial activity despite the high availability of electron acceptors for microbial respiration such as sulfate. Therefore, tidal flat margins with high microbial activity are of special importance for budgeting biogeochemical cycling in tidal flat areas.  相似文献   

Trace metal dynamics in the water column and pore waters in a temperate tidal system: response to the fate of algae-derived organic matter     

Nicole Kowalski  Olaf Dellwig  Melanie Beck  Maik Grunwald  Sibylle Fischer  Maike Piepho  Thomas Riedel  Holger Freund  Hans-Jürgen Brumsack  Michael E. Böttcher 《Ocean Dynamics》2009,59(2):333-350

Tidal and seasonal behaviour of the redox-sensitive trace metals Mn, Fe, Mo, U, and V have been investigated in the open-water column and shallow pore waters of the backbarrier tidal flats of the island of Spiekeroog (Southern North Sea) in 2002 and 2007. The purpose was to study the response of trace metal cycles on algae blooms, which are assumed to cause significant changes in the redox state of the entire ecosystem. Trace metal data were complemented by measurements of nutrients and enumeration of algae cells in 2007. Generally, Mn and V show a tidal cyclicity in the water column with maximum values during low tide which is most pronounced in summer due to elevated microbial activity in the sediments. Mo and U behave almost conservatively throughout the year with slightly increasing levels towards high tide. Exceptions are observed for both metals after summer algae blooms. Thus, the seasonal behaviour of the trace metals appear to be significantly influenced by productivity in the water column as the occurrence of algae blooms is associated with an intense release of organic matter (e.g. transparent exopolymer particles, TEP) thereby forming larger organic-rich aggregates. Along with elevated temperatures in summer, the deposition of such aggregates favours microbial activity within the surface sediments and release of DOC, nutrients and trace metals (Mn, Mo and V) during the degradation of the aggregates. Additionally, pronounced reducing conditions lead to the reduction of Mn(IV)-oxides and Fe(III)-(oxihydr)oxides, thereby releasing formerly scavenged compounds as V and phosphate. Therefore, pore-water profiles show significant enrichments in trace metals especially from July to September. Finally, the trace metals are released to the open water column via draining pore waters (esp. Mo, Mn, and V) and/or fixed in the sediment as sulphides (Fe, Mo) and bound to organic matter (U). Non-conservative behaviour of Mo in oxygenated seawater, first observed in the investigation area by Dellwig et al. (Geochim Cosmochim Acta 71:2745–2761, 2007a), was shown to be a recurrent phenomenon which is closely coupled to bacterial activity after the breakdown of algae blooms. In addition to the postulated fixation of Mo in oxygen-depleted micro-zones of the aggregates or by freshly formed organic matter, a direct removal of Mo from the water column by reduced sediment surfaces may also play an important role.  相似文献   

Distributions and characteristics of dissolved organic matter in temperate coastal waters (Southern North Sea)     

Andrea Lübben  Olaf Dellwig  Sandra Koch  Melanie Beck  Thomas H. Badewien  Sibylle Fischer  Rainer Reuter 《Ocean Dynamics》2009,59(2):263-275

The spatial and temporal distributions of chromophoric dissolved organic matter (CDOM) and dissolved organic carbon (DOC) was studied in the East-Frisian Wadden Sea (Southern North Sea) during several cruises between 2002 and 2005. The spatial distribution of CDOM in the German Bight shows a strong gradient towards the coast. Tidal and seasonal variations of dissolved organic matter (DOM) identify freshwater discharge via flood-gates at the coastline and pore water efflux from tidal flat sediments as the most important CDOM sources within the backbarrier area of the Island of Spiekeroog. However, the amount and pattern of CDOM and DOC is strongly affected by various parameters, e.g. changes in the amount of terrestrial run-off, precipitation, evaporation, biological activity and photooxidation. A decoupling of CDOM and DOC, especially during periods of pronounced biological activity (algae blooms and microbial activity), is observed in spring and especially in summer. Mixing of the endmembers freshwater, pore water, and open sea water results in the formation of a coastal transition zone. Whilst an almost conservative behaviour during mixing is observed in winter, summer data point towards non-conservative mixing.  相似文献   

Bathymetric patterns of megafaunal assemblages from the arctic deep-sea observatory HAUSGARTEN     

Thomas Soltwedel  Nina Jaeckisch  Nikolaus Ritter  Christiane Hasemann  Melanie Bergmann  Michael Klages 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(10):1856-1872

Five photographic transects, covering some 830 m² of seafloor in total, were analyzed to characterize the megabenthic community along a bathymetric gradient covering water depths from 1200 to 5500 m in the eastern Fram Strait. Megafaunal densities ranged between 11 and 38 ind. m⁻². The highest densities were found at 1650 m and the lowest densities occurred at 3000 m depth. The number of taxa and morphotypes ranged between 4 at 5500 m and 27 at 1650 m water depth. Ophiocten gracilis, a small white unidentified amphipod, Kolga hyalina, and Bathycrinus carpenteri were the dominant and characteristic species on the slope and continental rise. Elpidia heckeri dominated in the Molloy Hole, the deepest depression known in the Arctic Ocean. Megafaunal zonation patterns appeared to be mainly controlled by food availability, as indicated by phytodetrital matter measured at the seafloor, and by benthic biomass in the sediments, as indicated by sediment-bound particulate proteins and phospholipids. By contrast, physical factors, including water depth and seabed properties such as sediment porosity and hard substrata (e.g., dropstones), appear to play a secondary role in determining megabenthic zonation patterns along the bathymetric HAUSGARTEN gradient.  相似文献   

Enhancing community empowerment through participatory fisheries research     

Melanie Wiber  Anthony Charles  John Kearney  Fikret Berkes 《Marine Policy》2009

This paper reports on the outcomes of a project that engaged researchers and fishers together in adapting participatory social science approaches to the purposes and the constraints of community-based fisher organizations. The work was carried out in the Scotia-Fundy Region of Atlantic Canada (the Bay of Fundy and Scotian Shelf) between 1999 and 2003. After a period of reflection on what was collectively learned from our experiences in this project, the academics went back to the community partners in a recent workshop for further discussion and refinement of the lessons. We conclude that true participatory fishery research, utilized in support of community-based management, can be a particularly powerful tool. However, it has few effective shortcuts, it must deal early in the research process with power imbalances, and it should involve significant political engagement and empowerment through co-learning. This assessment of participatory research in coastal fisheries also has significant implications for how we think of social capital and on how we may develop community-based resource management for a sustainable future.  相似文献   

Genetic connectivity among populations of two congeneric direct-developing whelks varies across spatial scales     

Angela M. Fleming  Melanie M. Dohner  Peter A. Ritchie 《新西兰海洋与淡水研究杂志》2018,52(1):100-117

We examined the phylogeographic structure of two congeneric, direct-developing, intertidal whelks endemic to New Zealand, Cominella virgata and C. maculosa. A total of 855 specimens were collected from 23 rocky shore locations and we used them to determine the level of DNA sequence variation at the mitochondrial DNA (mtDNA) cytochrome c oxidase subunit I gene. Cominella virgata and C. maculosa have relatively high levels of haplotype diversity but low levels of nucleotide diversity. Sample sites formed regional groups that were composed of genetically differentiated populations, a finding consistent with their limited dispersal abilities. Cominella virgata showed higher levels of regional differentiation than C. maculosa, and there were also species-specific differences in genetic patterns within some regions. Both species exhibited genetic homogenisation among proximate sites within groups, suggesting some dispersal does occur between areas that are not connected by contiguous rocky shore habitat.  相似文献   

Magnetism and mineralogy of Almahata Sitta polymict ureilite (= asteroid 2008 TC3): Implications for the ureilite parent body magnetic field     

Viktor H. HOFFMANN  Rupert HOCHLEITNER  Masayuki TORII  Minoru FUNAKI  Takashi MIKOUCHI  Melanie KALIWODA  Peter JENNISKENS  Muawia H. SHADDAD 《Meteoritics & planetary science》2011,46(10):1551-1564

Abstract– The Almahata Sitta meteorite is the first case of recovered extraterrestrial material originating from an asteroid that was detected in near Earth space shortly before entering and exploding in the high atmosphere. The aims of our project within the 2008 TC₃ consortium were investigating Almahata Sitta’s (AS) magnetic signature, phase composition and mineralogy, focussing on the opaque minerals, and gaining new insights into the magnetism of the ureilite parent body (UPB). We report on the general magnetic properties and behavior of Almahata Sitta and try to place the results in context with the existing data set on ureilites and ureilite parent body models. The magnetic signature of AS is dominated by a set of low‐Ni kamacites with large grain sizes. Additional contributions come from micron‐sized kamacites, suessite, (Cr) troilite, and daubreelite, mainly found in the olivine grains adjacent to carbon‐rich veins. Our results show that the paleomagnetic signal is of extraterrestrial origin as can be seen by comparing with laboratory produced magnetic records (IRM). Four types of kamacite (I–IV) have been recognized in the sample. The elemental composition of the ureilite vein metal Kamacite I (particularly Co) clearly differs from the other kamacites (II‐IV), which are considered to be indigenous. Element ratios of kamacite I indicate that it was introduced into the UPB by an impactor, supporting the conclusions of Gabriel and Pack (2009) .  相似文献   

Intercomparison of PIXE and ICP‐AES Analyses of Aeolian Dust from Owens (Dry) Lake,California     

Lila Rojo  Melanie A. Barnes  Thomas E. Gill 《Geostandards and Geoanalytical Research》2012,36(1):83-102

Particle‐induced X‐ray emission (PIXE) and ICP‐AES can be combined to obtain a wider range of detected elements, augment previous data and/or to verify measured concentrations of heavy and trace metals in geological samples. Intercomparison of data sets generated by multiple techniques is challenging due to the differing processes and methods of each technique. Here, we compare elemental data obtained by both techniques for aeolian dust from Owens (Dry) Lake, California. Nineteen elements were detected by PIXE, sixteen by ICP‐AES and ten elements were detected by both techniques. Statistical analyses of data set groupings illustrated which parameters differed significantly between PIXE and ICP‐AES. Relative variation (%) showed that PIXE gave higher concentrations than ICP‐AES for Al, As, Cu, Fe, K, Mn, Ni, Sr, Ti and Zn in all samples. For As, Cu, Sr and Zn, relative variation was variable between the techniques. PIXE detection limits exceeded ICP‐AES concentrations for Ba, Cd, Co, Cr, Pb and Mo. Low ICP‐AES percentage recoveries of Al, Fe, K, Mn and Ti for NIST SRM 2710 indicated incomplete dissolution during digestion (EPA Method 3050B), since elements were bound in silicate structures. Variability between the two data sets is explained by differences between analytical techniques, sample preparation methods and/or variability in sample matrices.  相似文献   

Settling and compaction of olivine in basaltic magmas: an experimental study on the time scales of cumulate formation     

Max W. Schmidt  Melanie Forien  Giulio Solferino  Nickolai Bagdassarov 《Contributions to Mineralogy and Petrology》2012,164(6):959-976

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