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  • Other Sources  (371)
  • Wiley  (369)
  • American Chemical Society (ACS)
  • 2010-2014  (371)
  • 1
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    An analysis of bivalve larval shell pigments using micro-Raman spectroscopy (2014)
    Wiley
    In:  Journal of Raman Spectroscopy, 45 (5). pp. 349-358.
    Details
    Publication Date: 2016-12-13
    Description: Micro-Raman spectroscopy has been used on adult bivalve shells to investigate organic and inorganic shell components but has not yet been applied to bivalve larvae. It is known that the organic matrix of larval shells contains pigments, but less is known about the presence or source of these molecules in larvae. We investigated Raman spectra of seven species of bivalve larvae to assess the types of pigments present in shells of each species and how the ratio of inorganic : organic material changes in a dorso-ventral direction. In laboratory experiments, we reared larvae of three clam species in waters containing different organic signatures to determine if larvae incorporated compounds from source waters into their shells. We found differences in spectra and pigments between most species but found less intraspecific differences. A neural network classifier for Raman spectra classified five out of seven species with greater than 85% accuracy. There were slight differences between the amount and type of pigment present along the shell, with the prodissoconch I and shell margin areas being the most variable. Raman spectra of 1-day-old larvae were found to be differentiable when larvae were reared in waters with different organic signatures. With micro-Raman spectroscopy, it may be possible to identify some unknown species in the wild and trace their natal origins, which could enhance identification accuracy of bivalve larvae and ultimately aid management and restoration efforts.
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  • 2
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    Qualitative and Spatial Metabolite Profiling of Lichens by a LC-MS Approach Combined With Optimised Extraction (2014)
    Wiley
    In:  Phytochemical Analysis, 26 (1). pp. 23-33.
    Details
    Publication Date: 2018-03-15
    Description: INTRODUCTION: Lichens are self-sustaining partnerships comprising fungi as shape-forming partners for their enclosed symbiotic algae. They produce a tremendous diversity of metabolites (1050 metabolites described so far). OBJECTIVES: A comparison of metabolic profiles in nine lichen species belonging to three genera (Lichina, Collema and Roccella) by using an optimised extraction protocol, determination of the fragmentation pathway and the in situ localisation for major compounds in Roccella species. METHODS: Chemical analysis was performed using a complementary study combining a Taguchi experimental design with qualitative analysis by high-performance liquid chromatography coupled with mass spectrometry techniques. RESULTS: Optimal conditions to obtain the best total extraction yield were determined as follows: mortar grinding to a fine powder, two successive extractions, solid:liquid ratio (2:60) and 700 rpm stirring. Qualitative analysis of the metabolite profiling of these nine species extracted with the optimised method was corroborated using MS and MS/MS approaches. Nine main compounds were identified: 1 β-orcinol, 2 orsellinic acid, 3 putative choline sulphate, 4 roccellic acid, 5 montagnetol, 6 lecanoric acid, 7 erythrin, 8 lepraric acid and 9 acetylportentol, and several other compounds were reported. Identification was performed using the m/z ratio, fragmentation pathway and/or after isolation by NMR analysis. The variation of the metabolite profile in differently organised parts of two Roccella species suggests a specific role of major compounds in developmental stages of this symbiotic association. CONCLUSION: Metabolic profiles represent specific chemical species and depend on the extraction conditions, the kind of the photobiont partner and the in situ localisation of major compounds.
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  • 3
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    Individual glass shard trace element analyses confirm that all known Toba tephra reported from India is from thec. 75-ka Youngest Toba eruption (2014)
    Wiley
    In:  Journal of Quaternary Science, 29 (8). pp. 729-734.
    Details
    Publication Date: 2020-07-20
    Description: Uncertainty over the identity and age of Toba tephras across peninsular India persists, with radiometric age dates contradicting earlier compositional data, which have been used to identify this important Stratigraphie marker as the Youngest Toba Tuff (YTT). To address this issue, new single glass shard analyses have been performed for samples from Morgaon and Bori (north-western India), which have recently been dated at c. 800 ka. These, and indeed all Toba tephra samples thus far analysed from India, show the presence of four populations of glass shards (defined by their Ba/Y ratio), which uniquely identifies them as products of the c. 75-ka Youngest Toba eruption. Confirmation that the YTT fingerprint is characteristic comes from new analyses of Oldest Toba Tuff (OTT) glass shards from five sites in the Indian Ocean. These are compositionally identical to Layer D from the ODP site 758 Sediment core (c. 800 ka), and belong to a single, low-Ba population, clearly different from YTT. These analyses show that there is essentially no reworked OTT material in the YTT eruption, and indicate unequivocally that all known Toba tephra occurrences in India belong to the c. 75-ka Youngest Toba eruption.
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  • 4
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    High Pressure Rheology of Hydrate Slurries Formed from Water-in-Mineral Oil Emulsions (2014)
    American Chemical Society (ACS)
    In:  Industrial & Engineering Chemistry Research, 53 (17). pp. 6998-7007.
    Details
    Publication Date: 2018-01-03
    Description: Structure I methane hydrates are formed in situ from water-in-mineral oil emulsions in a high pressure rheometer cell. Viscosity is measured as hydrates form, grow, change under flow, and dissociate. Experiments are performed at varying water volume fraction in the original emulsion (0–0.40), temperature (0–6 °C), and initial pressure of methane (750–1500 psig). Hydrate slurries exhibit a sharp increase in viscosity upon hydrate formation, followed by complex behavior dictated by factors including continued hydrate formation, shear alignment, methane depletion/dissolution, aggregate formation, and capillary bridging. Hydrate slurries possess a yield stress and are shear-thinning fluids, which are described by the Cross model. Hydrate slurry viscosity and yield stress increased with increasing water volume fraction. As driving force for hydrate formation decreases (increasing temperature, decreasing pressure), hydrate slurry viscosity increases, suggesting that slower hydrate formation leads to larger and more porous aggregates. In total, addition of water to a methane saturated oil can cause more than a fifty-fold increase in viscosity if hydrates form.
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  • 5
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    Forazoline A: marine-derived polyketide with antifungal in vivo efficacy (2014)
    Wiley
    In:  Angewandte Chemie International Edition, 53 (43). pp. 11583-11586.
    Details
    Publication Date: 2017-01-24
    Description: Forazoline A, a novel antifungal polyketide with in vivo efficacy against Candida albicans, was discovered using LCMS-based metabolomics to investigate marine-invertebrate-associated bacteria. Forazoline A had a highly unusual and unprecedented skeleton. Acquisition of 13C–13C gCOSY and 13C–15N HMQC NMR data provided the direct carbon–carbon and carbon–nitrogen connectivity, respectively. This approach represents the first example of determining direct 13C–15N connectivity for a natural product. Using yeast chemical genomics, we propose that forazoline A operated through a new mechanism of action with a phenotypic outcome of disrupting membrane integrity.
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  • 6
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    Macroalgal blooms alter community structure and primary productivity in marine ecosystems (2014)
    Wiley
    In:  Global Change Biology, 20 (9). pp. 2712-2724.
    Details
    Publication Date: 2017-12-21
    Description: Eutrophication, coupled with loss of herbivory due to habitat degradation and overharvesting, has increased the frequency and severity of macroalgal blooms worldwide. Macroalgal blooms interfere with human activities in coastal areas, and sometimes necessitate costly algal removal programmes. They also have many detrimental effects on marine and estuarine ecosystems, including induction of hypoxia, release of toxic hydrogen sulphide into the sediments and atmosphere, and the loss of ecologically and economically important species. However, macroalgal blooms can also increase habitat complexity, provide organisms with food and shelter, and reduce other problems associated with eutrophication. These contrasting effects make their overall ecological impacts unclear. We conducted a systematic review and meta-analysis to estimate the overall effects of macroalgal blooms on several key measures of ecosystem structure and functioning in marine ecosystems. We also evaluated some of the ecological and methodological factors that might explain the highly variable effects observed in different studies. Averaged across all studies, macroalgal blooms had negative effects on the abundance and species richness of marine organisms, but blooms by different algal taxa had different consequences, ranging from strong negative to strong positive effects. Blooms' effects on species richness also depended on the habitat where they occurred, with the strongest negative effects seen in sandy or muddy subtidal habitats and in the rocky intertidal. Invertebrate communities also appeared to be particularly sensitive to blooms, suffering reductions in their abundance, species richness, and diversity. The total net primary productivity, gross primary productivity, and respiration of benthic ecosystems were higher during macroalgal blooms, but blooms had negative effects on the productivity and respiration of other organisms. These results suggest that, in addition to their direct social and economic costs, macroalgal blooms have ecological effects that may alter their capacity to deliver important ecosystem services.
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  • 7
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    Explaining Success and Failure in Crisis Coordination (2014)
    Wiley
    In:  Geografiska Annaler: Series A, Physical Geography, 97 (1). pp. 123-135.
    Details
    Publication Date: 2017-07-25
    Description: In virtually every assessment of responses to large-scale crises and disasters, coordination is identified as a critical failure factor. After the crisis, official committees and political opponents often characterize the early phases of the response as a ‘failure to coordinate.’ Not surprisingly, improved coordination quickly emerges as the prescribed solution. Coordination, then, is apparently both the problem and the solution. But the proposed solutions rarely solve the problem: coordination continues to mar most crises and disasters. In the absence of a shared body of knowledge on coordination, it is hard to formulate a normative framework that allows for systematic assessment of coordination in times of crisis. As coordination is widely perceived as an important function of crisis and disaster management, this absence undermines a fair and balanced assessment of crisis management performance. This paper seeks to address that void. We aim to develop a framework that explains both the failure and success of crisis coordination. We do this by exploring the relevant literature, reformulating what coordination is and distilling from research the factors that cause failure and success.
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  • 8
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    The effects of caffeine on wound healing (2014)
    Wiley
    In:  International Wound Journal, 13 (5). pp. 605-613.
    Details
    Publication Date: 2017-09-20
    Description: The purine alkaloid caffeine is a major component of many beverages such as coffee and tea. Caffeine and its metabolites theobromine and xanthine have been shown to have antioxidant properties. Caffeine can also act as adenosine-receptor antagonist. Although it has been shown that adenosine and antioxidants promote wound healing, the effect of caffeine on wound healing is currently unknown. To investigate the effects of caffeine on processes involved in epithelialisation, we used primary human keratinocytes, HaCaT cell line and ex vivo model of human skin. First, we tested the effects of caffeine on cell proliferation, differentiation, adhesion and migration, processes essential for normal wound epithelialisation and closure. We used 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) proliferation assay to test the effects of seven different caffeine doses ranging from 0·1 to 5 mM. We found that caffeine restricted cell proliferation of keratinocytes in a dose-dependent manner. Furthermore, scratch wound assays performed on keratinocyte monolayers indicated dose-dependent delays in cell migration. Interestingly, adhesion and differentiation remained unaffected in monolayer cultures treated with various doses of caffeine. Using a human ex vivo wound healing model, we tested topical application of caffeine and found that it impedes epithelialisation, confirming in vitro data. We conclude that caffeine, which is known to have antioxidant properties, impedes keratinocyte proliferation and migration, suggesting that it may have an inhibitory effect on wound healing and epithelialisation. Therefore, our findings are more in support of a role for caffeine as adenosine-receptor antagonist that would negate the effect of adenosine in promoting wound healing.
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  • 9
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    First High-resolution GPR and Magnetic Archaeological Prospection at the Viking Age Settlement of Birka in Sweden (2014)
    American Medical Associa | Wiley
    In:  Archaeological Prospection, 21 (3). pp. 185-199.
    Details
    Publication Date: 2020-06-12
    Description: In May 2006 high-resolution measurements using ground-penetrating radar (GPR) and magnetic gradiometer systems conducted over selected areas at the site of the Viking Age settlement and trading place Birka in central Sweden demonstrated the suitability of these methods for archaeological prospection of Scandinavian proto-urban settlements. The non-invasive geophysical surveys revealed numerous structural details of the settlement: houses, property boundaries, track-ways, buried remains of the town ramparts dating from different building periods, including a gate, were mapped with a manually operated single-channel GPR system and a four-channel magnetometer array. The combination of these two prospection methods, state-of-the-art data processing and visualization and archaeological interpretation within a geographical information system resulted in valuable new information about the UNESCOWorld Cultural Heritage Site Birka-Hovgården.We present methodology and results of this first archaeological prospection case study conducted in 2006.
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  • 10
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    The Eastern Mediterranean Transient (2014)
    AGU (American Geophysical Union) | Wiley
    In:  In: The Mediterranean Sea. , ed. by Borzelli, G. L. E., Gačić, M., Lionello, P. and Malanotte‐Rizzoli, P. Geophysical Monograph Series, 202 . AGU (American Geophysical Union), Wiley, Washington, pp. 75-83.
    Details
    Publication Date: 2020-08-03
    Description: The eastern Mediterranean transient (EMT) was caused by a combination of high‐salinity waters intruding into the Aegean Sea and the two particularly strong winters of 1991–1992 and 1992–1993. The approach in this chapter is to search for specific signatures in the historic hydrographic observations, which date back to 1910. To deal with the problem that up into the 1950s the data not only are of limited precision but also have gaps of about 20 years, it is advantageous to consider the fact that the evolution of the actual EMT is rather well documented over a similar time span. The chapter begins by outlining the characteristics of the current EMT. Thereafter, a selection of suitable hydrographic observations among the available historic data is provided to compare these with signatures expected from the evolution of the actual EMT.
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  • 11
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    The oceanic anthropogenic CO2sink: Storage, air-sea fluxes, and transports over the industrial era (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Global Biogeochemical Cycles, 28 (7). pp. 631-647.
    Details
    Publication Date: 2016-02-25
    Description: This study presents a new estimate of the oceanic anthropogenic CO2(Cant) sink over the industrial era (1780 to present), from assimilation of potential temperature, salinity, radiocarbon, and CFC-11 observations in a global steady state ocean circulation inverse model (OCIM). This study differs from previous data-based estimates of the oceanic Cant sink in that dynamical constraints on ocean circulation are accounted for, and the ocean circulation is explicitly modeled, allowing the calculation of oceanic Cant storage, air-sea fluxes, and transports in a consistent manner. The resulting uncertainty of the OCIM-estimated Cant uptake, transport, and storage is significantly smaller than the comparable uncertainty from purely data-based or model-based estimates. The OCIM-estimated oceanic Cant storage is 160–166 PgC in 2012, and the oceanic Cant uptake rate averaged over the period 2000–2010 is 2.6 PgC yr−1 or about 30% of current anthropogenic CO2 emissions. This result implies a residual (primarily terrestrial) Cant sink of about 1.6 PgC yr−1 for the same period. The Southern Ocean is the primary conduit for Cant entering the ocean, taking up about 1.1 PgC yr−1 in 2012, which represents about 40% of the contemporary oceanic Cant uptake. It is suggested that the most significant source of remaining uncertainty in the oceanic Cant sink is due to potential variability in the ocean circulation over the industrial era.
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  • 12
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    From regionally predictable to locally complex population structure in a freshwater top predator: river systems are not always the unit of connectivity in Northern PikeEsox lucius (2014)
    Wiley
    In:  Ecology of Freshwater Fish, 24 (2). pp. 305-316.
    Details
    Publication Date: 2016-03-18
    Description: Contemporary genetic diversity is the product of both historical and contemporary forces, such as climatic and geological processes affecting range distribution and continuously moulded by evolutionary forces selection, gene flow and genetic drift. Predatory freshwater fishes, such as Northern Pike Esox lucius, commonly exhibit small population sizes, and several local populations are considered endangered. Pike inhabit diverse habitat types, including lakes, rivers and brackish marine waters, thus spanning from small isolated patches to large open marine systems. However, pike population structure from local to regional scales is relatively poorly described, in spite of its significance to developing conservation measures. We analysed microsatellite variation in a total of 1185 North European pike from 46 samples collected across both local and regional scales, as well as over time, to address two overarching questions: Is pike population structure associated with local and/or regional connectivity patterns, and which factors likely have the main influence on the contemporary distribution of genetic diversity? To answer this, we combined estimators of population diversity and structure to assess evidence of whether populations within (i) habitats, (ii) drainage systems and (iii) geographical regions are closer related than among these ranges, and whether patterns are temporally stable. Contrasting previous predictions that genetic drift obscures signals of postglacial colonisation history, we identified clear regional differences in population genetic signatures, suggesting a major effect of drainage divides on colonisation history and connectivity. However, several populations deviated from the general pattern, showing that local processes may be complex and need to be examined case-by-case.
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  • 13
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    Where is mineral ballast important for surface export of particulate organic carbon in the ocean? (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Geophysical Research Letters, 41 (23). pp. 8460-8468.
    Details
    Publication Date: 2019-07-08
    Description: Correlations between particulate organic carbon (POC) and mineral fluxes in the deep ocean have inspired the inclusion of “ballast effect” parameterizations in carbon cycle models. A recent study demonstrated regional variability in the effect of ballast minerals on the flux of POC in the deep ocean. We have undertaken a similar analysis of shallow export data from the Arctic, Atlantic, and Southern Oceans. Mineral ballasting is of greatest importance in the high-latitude North Atlantic, where 60% of the POC flux is associated with ballast minerals. This fraction drops to around 40% in the Southern Ocean. The remainder of the export flux is not associated with minerals, and this unballasted fraction thus often dominates the export flux. The proportion of mineral-associated POC flux often scales with regional variation in export efficiency (the proportion of primary production that is exported). However, local discrepancies suggest that regional differences in ecology also impact the magnitude of surface export. We propose that POC export will not respond equally across all high-latitude regions to possible future changes in ballast availability.
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  • 14
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    Genomic atolls of differentiation in coral reef fishes (Hypoplectrusspp.,Serranidae) (2014)
    Wiley
    In:  Molecular Ecology, 23 (21). pp. 5291-5303.
    Details
    Publication Date: 2019-09-23
    Description: Because the vast majority of species are well diverged, relatively little is known about the genomic architecture of speciation during the early stages of divergence. Species within recent evolutionary radiations are often minimally diverged from a genomic perspective, and therefore provide rare opportunities to address this question. Here, we leverage the hamlet radiation (Hypoplectrus spp., brightly coloured reef fishes from the tropical western Atlantic) to characterize genomic divergence during the early stages of speciation. Transect surveys and spawning observations in Belize, Honduras and Panama confirm that sympatric barred (H. puella), black (H. nigricans) and butter (H. unicolor) hamlets are phenotypically distinct and reproductively isolated, although hybrid spawnings and individuals with intermediate phenotypes are seen on rare occasions. A survey of approximately 100 000 restriction site-associated SNPs in 126 samples from the three species across the three replicate populations reveals extremely slight genomewide divergence among species (FST = 0.0038), indicating that ecomorphological differences and functional reproductive isolation are maintained in sympatry in a backdrop of extraordinary genomic similarity. Nonetheless, a very small proportion of SNPs (0.05% on average) are identified as FST outliers among sympatric species. Remarkably, a single SNP is identified as an outlier in repeated populations for the same species pair. A minicontig assembled de novo around this SNP falls into the genomic region containing the HoxCa10 and HoxCa11 genes in 10 teleost species, suggesting an important role for Hox gene evolution in this radiation. This finding, if confirmed, would provide a better understanding of the links between micro- and macroevolutionary processes.
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  • 15
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    The significance of the episodic nature of atmospheric deposition to Low Nutrient Low Chlorophyll region (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Global Biogeochemical Cycles, 28 (11). pp. 1179-1198.
    Details
    Publication Date: 2021-04-23
    Description: In the vast Low Nutrient Low-Chlorophyll (LNLC) Ocean, the vertical nutrient supply from the subsurface to the sunlit surface waters is low, and atmospheric contribution of nutrients may be one order of magnitude greater over short timescales. The short turnover time of atmospheric Fe and N supply (〈1 month for nitrate) further supports deposition being an important source of nutrients in LNLC regions. Yet, the extent to which atmospheric inputs are impacting biological activity and modifying the carbon balance in oligotrophic environments has not been constrained. Here, we quantify and compare the biogeochemical impacts of atmospheric deposition in LNLC regions using both a compilation of experimental data and model outputs. A metadata-analysis of recently conducted field and laboratory bioassay experiments reveals complex responses, and the overall impact is not a simple “fertilization effect of increasing phytoplankton biomass” as observed in HNLC regions. Although phytoplankton growth may be enhanced, increases in bacterial activity and respiration result in weakening of biological carbon sequestration. The application of models using climatological or time-averaged non-synoptic deposition rates produced responses that were generally much lower than observed in the bioassay experiments. We demonstrate that experimental data and model outputs show better agreement on short timescale (days to weeks) when strong synoptic pulse of aerosols deposition, similar in magnitude to those observed in the field and introduced in bioassay experiments, is superimposed over the mean atmospheric deposition fields. These results suggest that atmospheric impacts in LNLC regions have been underestimated by models, at least at daily to weekly timescales, as they typically overlook large synoptic variations in atmospheric deposition and associated nutrient and particle inputs. Inclusion of the large synoptic variability of atmospheric input, and improved representation and parameterization of key processes that respond to atmospheric deposition, is required to better constrain impacts in ocean biogeochemical models. This is critical for understanding and prediction of current and future functioning of LNLC regions and their contribution to the global carbon cycle.
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  • 16
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    Impact of dissolved inorganic carbon concentrations and pH on growth of the chemolithoautotrophic epsilonproteobacterium Sulfurimonas gotlandica GD1T (2014)
    Wiley
    In:  MicrobiologyOpen, 3 (1). pp. 80-88.
    Details
    Publication Date: 2016-10-26
    Description: Epsilonproteobacteria have been found globally distributed in marine anoxic/sulfidic areas mediating relevant transformations within the sulfur and nitrogen cycles. In the Baltic Sea redox zones, chemoautotrophic epsilonproteobacteria mainly belong to the Sulfurimonas gotlandica GD17 cluster for which recently a representative strain, S. gotlandica GD1T, could be established as a model organism. In this study, the potential effects of changes in dissolved inorganic carbon (DIC) and pH on S. gotlandica GD1T were examined. Bacterial cell abundance within a broad range of DIC concentrations and pH values were monitored and substrate utilization was determined. The results showed that the DIC saturation concentration for achieving maximal cell numbers was already reached at 800 μmol L−1, which is well below in situ DIC levels. The pH optimum was between 6.6 and 8.0. Within a pH range of 6.6–7.1 there was no significant difference in substrate utilization; however, at lower pH values maximum cell abundance decreased sharply and cell-specific substrate consumption increased.
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  • 17
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    Climate change and regulation of hepatotoxin production in Cyanobacteria (2014)
    Wiley
    In:  FEMS Microbiology Ecology, 88 (1). pp. 1-25.
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    Publication Date: 2015-05-27
    Description: Harmful, bloom-forming cyanobacteria (CyanoHABs) are occurring with increasing regularity in freshwater and marine ecosystems. The most commonly occurring cyanobacterial toxins are the hepatotoxic microcystin and nodularin. These cyclic hepta- and pentapeptides are synthesised nonribosomally by the gene products of the toxin gene clusters mcy and nda, respectively. Understanding of the regulation of hepatotoxin production is incomplete, although there is strong evidence supporting the roles of iron, light, higher nitrate availability and inorganic carbon in modulating microcystin levels. The majority of these studies have focused on the unicellular freshwater, microcystin-producing strain of Microcystis aeruginosa, with little attention being paid to terrestrial or marine toxin producers. This review intends to investigate the regulation of microcystin and nodularin production in unicellular and filamentous diazotrophic cyanobacteria against the background of changing climate conditions. Special focus is given to diazotrophic filamentous cyanobacteria, for example Nodularia spumigena, capable of regulating their nitrogen levels by actively fixing dinitrogen. By combining data from significant studies, an overall scheme of the regulation of toxin production is presented, focussing specifically on nodularin production in diazotrophs against the background of increasing carbon dioxide concentrations and temperatures envisaged under current climate change models. Furthermore, the risk of sustaining and spreading CyanoHABs in the future ocean is evaluated.
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  • 18
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    glUV: a global UV-B radiation data set for macroecological studies (2014)
    Wiley
    In:  Methods in Ecology and Evolution, 5 (4). pp. 372-383.
    Details
    Publication Date: 2020-07-01
    Description: 1. Macroecology has prospered in recent years due in part to the wide array of climatic data, such as those provided by theWorldClim and CliMond data sets, which has become available for research. However, important environmental variables have still been missing, including spatial data sets on UV-B radiation, an increasingly recognized driver of ecological processes. 2. We developed a set of globalUV-B surfaces (glUV) suitable to match common spatial scales in macroecology. Our data set is based on remotely sensed records fromNASA’sOzone Monitoring Instrument (Aura-OMI). Following a similar approach as for theWorldClim and CliMond data sets, we processed daily UV-B measurements acquired over a period of eight years into monthly mean UV-B data and six ecologically meaningful UV-B variables with a 15-arc minute resolution. These bioclimatic variables represent Annual Mean UV-B, UV-B Seasonality, Mean UV-B of Highest Month, Mean UV-B of Lowest Month, Sum of Monthly Mean UV-B during Highest Quarter and Sum of Monthly Mean UV-B during Lowest Quarter. We correlated our data sets with selected variables of existing bioclimatic surfaces for land and with Terra–MODIS Sea Surface Temperature for ocean regions to test for relations to known gradients and patterns. 3. UV-B surfaces showed a distinct seasonal variance at a global scale, while the intensity of UV-B radiation decreased towards higher latitudes and was modified by topographic and climatic heterogeneity. UV-B surfaces were correlated with global mean temperature and annual mean radiation data, but exhibited variable spatial associations across the globe.UV-B surfaces were otherwise widely independent of existing bioclimatic surfaces. 4. Our data set provides new climatological information relevant for macroecological analyses. As UV-B is a known driver of numerous biological patterns and processes, our data set offers the potential to generate a better understanding of these dynamics inmacroecology, biogeography, global change research and beyond. The glUV data set containing monthly mean UV-B data and six derived UV-B surfaces is freely available for download at: http://www.ufz.de/gluv.
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  • 19
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    Omaezallene from Red AlgaLaurenciasp.: Structure Elucidation, Total Synthesis, and Antifouling Activity (2014)
    Wiley
    In:  Angewandte Chemie-International Edition, 53 (15). pp. 3909-3912.
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    Publication Date: 2015-06-18
    Description: Natural antifouling products have been the subject of considerable attention. We screened marine algae for antifouling activity and discovered omaezallenes, the new bromoallene-containing natural products isolated from the red alga Laurencia sp. Described is the isolation, structure elucidation, and total syntheses of omaezallenes. The relative and absolute configurations of natural omaezallenes were unambiguously established through total synthesis. The antifouling activities and ecotoxicity of omaezallenes were also evaluated.
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    Magnetite formation from ferrihydrite by hyperthermophilic archaea from Endeavour Segment, Juan de Fuca Ridge hydrothermal vent chimneys (2014)
    Wiley
    In:  Geobiology, 12 (3). pp. 200-211.
    Details
    Publication Date: 2017-09-26
    Description: Hyperthermophilic iron reducers are common in hydrothermal chimneys found along the Endeavour Segment in the northeastern Pacific Ocean based on culture-dependent estimates. However, information on the availability of Fe(III) (oxyhydr) oxides within these chimneys, the types of Fe(III) (oxyhydr) oxides utilized by the organisms, rates and environmental constraints of hyperthermophilic iron reduction, and mineral end products is needed to determine their biogeochemical significance and are addressed in this study. Thin-section petrography on the interior of a hydrothermal chimney from the Dante edifice at Endeavour showed a thin coat of Fe(III) (oxyhydr) oxide associated with amorphous silica on the exposed outer surfaces of pyrrhotite, sphalerite, and chalcopyrite in pore spaces, along with anhydrite precipitation in the pores that is indicative of seawater ingress. The iron sulfide minerals were likely oxidized to Fe(III) (oxyhydr) oxide with increasing pH and Eh due to cooling and seawater exposure, providing reactants for bioreduction. Culture-dependent estimates of hyperthermophilic iron reducer abundances in this sample were 1740 and 10 cells per gram (dry weight) of material from the outer surface and the marcasite-sphalerite-rich interior, respectively. Two hyperthermophilic iron reducers, Hyperthermus sp. Ro04 and Pyrodictium sp. Su06, were isolated from other active hydrothermal chimneys on the Endeavour Segment. Strain Ro04 is a neutrophilic (pHopt 7–8) heterotroph, while strain Su06 is a mildly acidophilic (pHopt 5), hydrogenotrophic autotroph, both with optimal growth temperatures of 90–92 °C. Mössbauer spectroscopy of the iron oxides before and after growth demonstrated that both organisms form nanophase (〈12 nm) magnetite [Fe3O4] from laboratory-synthesized ferrihydrite [Fe10O14(OH)2] with no detectable mineral intermediates. They produced up to 40 mm Fe2+ in a growth-dependent manner, while all abiotic and biotic controls produced 〈3 mm Fe2+. Hyperthermophilic iron reducers may have a growth advantage over other hyperthermophiles in hydrothermal systems that are mildly acidic where mineral weathering at increased temperatures occurs.
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    Specificity and transcriptional activity of microbiota associated with low and high microbial abundance sponges from the Red Sea (2014)
    Wiley
    In:  Molecular Ecology, 23 (6). pp. 1348-1363.
    Details
    Publication Date: 2019-01-10
    Description: Marine sponges are generally classified as high microbial abundance (HMA) and low microbial abundance (LMA) species. Here, 16S rRNA amplicon sequencing was applied to investigate the diversity, specificity and transcriptional activity of microbes associated with an LMA sponge (Stylissa carteri), an HMA sponge (Xestospongia testudinaria) and sea water collected from the central Saudi Arabia coast of the Red Sea. Altogether, 887 068 denoised sequences were obtained, of which 806 661 sequences remained after quality control. This resulted in 1477 operational taxonomic units (OTUs) that were assigned to 27 microbial phyla. The microbial composition of S. carteri was more similar to that of sea water than to that of X. testudinaria, which is consistent with the observation that the sequence data set of S. carteri contained many more possibly sea water sequences (~24%) than the X. testudinaria data set (~6%). The most abundant OTUs were shared between all three sources (S. carteri, X. testudinaria, sea water), while rare OTUs were unique to any given source. Despite this high degree of overlap, each sponge species contained its own specific microbiota. The X. testudinaria-specific bacterial taxa were similar to those already described for this species. A set of S. carteri-specific bacterial taxa related to Proteobacteria and Nitrospira was identified, which are likely permanently associated with S. carteri. The transcriptional activity of sponge-associated microorganisms correlated well with their abundance. Quantitative PCR revealed the presence of Poribacteria, representing typical sponge symbionts, in both sponge species and in sea water; however, low transcriptional activity in sea water suggested that Poribacteria are not active outside the host context.
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    The Eastern Mediterranean Transient: evidence for similar events previously? (2014)
    AGU (American Geophysical Union) | Wiley
    In:  In: The Mediterranean Sea: Temporal variability and spatial patterns. Geophysical Monograph Series, 202 . AGU (American Geophysical Union), Wiley, Washington, USA, pp. 75-83.
    Details
    Publication Date: 2015-09-28
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    Role of gas hydrates in slope failure on frontal ridge of northern Cascadia margin (2014)
    Wiley
    In:  Geophysical Journal International, 199 (1). pp. 441-458.
    Details
    Publication Date: 2015-10-13
    Description: Several slope failures are observed near the deformation front on the frontal ridges of the northern Cascadia accretionary margin off Vancouver Island. The cause for these events is not clear, although several lines of evidence indicate a possible connection between the occurrence of gas hydrate and submarine landslide features. The presence of gas hydrate is indicated by a prominent bottom-simulating reflector (BSR), at a depth of ∼265–275 m beneath the seafloor (mbsf), as interpreted from vertical-incidence and wide-angle seismic data beneath the ridge crests of the frontal ridges. For one slide, informally called Slipstream Slide, the velocity structure inferred from tomography analyses shows anomalous high velocities values of about 2.0 km s−1 at shallow depths of 100 mbsf. The estimated depth of the glide plane (100 ± 10 m) closely matches the depth of these shallow high velocities. In contrast, at a frontal ridge slide just to the northwest (informally called Orca Slide), the glide plane occurs at the same depth as the current BSR. Our new results indicate that the glide plane of the Slipstream slope failure is associated with the contrast between sediments strengthened by gas hydrate and overlying sediments where little or no hydrate is present. In contrast, the glide plane of Orca Slide is between sediment strengthened by hydrate underlain by sediments beneath the gas hydrate stability zone, possibly containing free gas. Additionally, a set of margin perpendicular normal faults are imaged from seafloor down to BSR depth at both frontal ridges. As inferred from the multibeam bathymetry, the estimated volume of the material lost during the slope failure at Slipstream Slide is about 0.33 km3, and ∼0.24 km3 of this volume is present as debris material on the ocean basin floor. The 20 per cent difference is likely due to more widely distributed fine sediments not easily detectable as bathymetric anomalies. These volume estimates on the Cascadia margin are approaching the mass failure volume for other slides that have generated large tsunamis—for example 1–3 km3 for a 1998 Papua New Guinea slide.
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    Revealing microbial functional activities in the Red Sea sponge Stylissa carteriby metatranscriptomics (2014)
    Wiley
    In:  Environmental Microbiology, 16 (12). pp. 3683-3698.
    Details
    Publication Date: 2017-03-30
    Description: Sponges are important components of marine benthic environments and are associated with microbial symbionts that carry out ecologically relevant functions. Stylissa carteri is an abundant, low-microbial abundance species in the Red Sea. We aimed to achieve the functional and taxonomic characterization of the most actively expressed prokaryotic genes in S. carteri. Prokaryotic mRNA was enriched from sponge total RNA, sequenced using Illumina HiSeq technology and annotated using the metagenomics Rapid Annotation using Subsystem Technology (MG-RAST) pipeline. We detected high expression of archaeal ammonia oxidation and photosynthetic carbon fixation by members of the genus Synechococcus. Functions related to stress response and membrane transporters were among the most highly expressed by S. carteri symbionts. Unexpectedly, gene functions related to methylotrophy were highly expressed by gammaproteobacterial symbionts. The presence of seawater-derived microbes is indicated by the phylogenetic proximity of organic carbon transporters to orthologues of members from the SAR11 clade. In summary, we revealed the most expressed functions of the S. carteri-associated microbial community and linked them to the dominant taxonomic members of the microbiome. This work demonstrates the applicability of metatranscriptomics to explore poorly characterized symbiotic consortia and expands our knowledge of the ecologically relevant functions carried out by coral reef sponge symbionts.
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    Climate, land use, and conflict in Northern Africa: MPI-M/CliSAP Workshop on Climate, Land Use, and Conflict in Northern Africa,Lübeck, Germany, 22–25 September 2014 (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Eos, Transactions American Geophysical Union, 95 .
    Details
    Publication Date: 2016-10-05
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    Visualization and Analysis Tools for Ultrascale Climate Data (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Eos, Transactions American Geophysical Union, 95 (42). pp. 377-378.
    Details
    Publication Date: 2016-05-30
    Description: Increasingly large climate model simulations are enhancing our understanding of the processes and causes of anthropogenic climate change, thanks to very large public investments in high-performance computing at national and international institutions. Various climate models implement mathematical approximations of nature in different ways, which are often based on differing computational grids. These complex, parallelized coupled system codes combine numerous complex submodels (ocean, atmosphere, land, biosphere, sea ice, land ice, etc.) that represent components of the larger complex climate system.
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    Strength by Joining Methods: Combining Synthesis with NMR, IR, and Vibrational Circular Dichroism Spectroscopy for the Determination of the Relative Configuration in Hemicalide (2014)
    Chemistry Europe | Wiley
    In:  Chemistry - A European Journal, 20 (52). pp. 17385-17394.
    Details
    Publication Date: 2020-07-27
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    Impact of warming on phyto-bacterioplankton coupling and bacterial community composition in experimental mesocosms (2014)
    Wiley
    In:  Environmental Microbiology, 16 (3). pp. 718-733.
    Details
    Publication Date: 2019-09-23
    Description: Global warming is assumed to alter the trophic interactions and carbon flow patterns of aquatic food webs. The impact of temperature on phyto-bacterioplankton coupling and bacterial community composition (BCC) was the focus of the present study, in which an indoor mesocosm experiment with natural plankton communities from the western Baltic Sea was conducted. A 6°C increase in water temperature resulted, as predicted, in tighter coupling between the diatom-dominated phytoplankton and heterotrophic bacteria, accompanied by a strong increase in carbon flow into bacterioplankton during the phytoplankton bloom phase. Suppressed bacterial development at cold in situ temperatures probably reflected lowered bacterial production and grazing by protists, as the latter were less affected by low temperatures. BCC was strongly influenced by the phytoplankton bloom stage and to a lesser extent by temperature. Under both temperature regimes, Gammaproteobacteria clearly dominated during the phytoplankton peak, with Glaciecola sp. as the single most abundant taxon. However, warming induced the appearance of additional bacterial taxa belonging to Betaproteobacteria and Bacteroidetes. Our results show that warming during an early phytoplankton bloom causes a shift towards a more heterotrophic system, with the appearance of new bacterial taxa suggesting a potential for utilization of a broader substrate spectrum.
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    A high-resolution Lateglacial and Holocene palaeoceanographic record from the Greenland Sea (2014)
    Wiley
    In:  Boreas, 43 (2). pp. 273-285.
    Details
    Publication Date: 2014-06-04
    Description: We present an unprecedented multicentennial sediment record from the foot of Vesterisbanken Seamount, central Greenland Sea, covering the past 22.3 thousand years (ka). Based on planktic foraminiferal total abundances, species assemblages, and stable oxygen and carbon isotopes, the palaeoenvironments in this region of modern deepwater renewal were reconstructed. Results show that during the Last Glacial Maximum the area was affected by harsh polar conditions with only episodic improvements during warm summer seasons. Since 18 ka extreme freshwater discharges from nearby sources occurred, influencing the surface water environment. The last major freshwater event took place during the Younger Dryas. The onset of the Holocene was characterized by an improvement of environmental conditions suggesting warming and increasing ventilation of the upper water layers. The early Holocene saw a stronger Atlantic waters advection to the area, which began around 10.5 and ended quite rapidly at 5.5 ka, followed by the onset of Neoglacial cooling. Surface water ventilation reached a maximum in the middle Holocene. Around 3 ka the surface water stratification increased leading to subsequent amplification of the warming induced the North Atlantic Oscillation at 2 ka.
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    Climate change in the oceans: evolutionary versus phenotypically plastic responses of marine animals and plants (2014)
    Wiley
    In:  Evolutionary Applications, 7 (1). pp. 104-122.
    Details
    Publication Date: 2014-04-24
    Description: I summarize marine studies on plastic versus adaptive responses to global change. Due to the lack of time series, this review focuses largely on the potential for adaptive evolution in marine animals and plants. The approaches were mainly synchronic comparisons of phenotypically divergent populations, substituting spatial contrasts in temperature or CO2 environments for temporal changes, or in assessments of adaptive genetic diversity within populations for traits important under global change. The available literature is biased towards gastropods, crustaceans, cnidarians and macroalgae. Focal traits were mostly environmental tolerances, which correspond to phenotypic buffering, a plasticity type that maintains a functional phenotype despite external disturbance. Almost all studies address coastal species that are already today exposed to fluctuations in temperature, pH and oxygen levels. Recommendations for future research include (i) initiation and analyses of observational and experimental temporal studies encompassing diverse phenotypic traits (including diapausing cues, dispersal traits, reproductive timing, morphology) (ii) quantification of nongenetic trans-generational effects along with components of additive genetic variance (iii) adaptive changes in microbe–host associations under the holobiont model in response to global change (iv) evolution of plasticity patterns under increasingly fluctuating environments and extreme conditions and (v) joint consideration of demography and evolutionary adaptation in evolutionary rescue approaches.
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    Habitat traits and food availability determine the response of marine invertebrates to ocean acidification (2014)
    Wiley
    In:  Global Change Biology, 20 (3). pp. 765-777.
    Details
    Publication Date: 2019-09-23
    Description: Energy availability and local adaptation are major components in mediating the effects of ocean acidification (OA) on marine species. In a long-term study, we investigated the effects of food availability and elevated pCO2 (~ 400, 1000 and 3000 μatm) on growth of newly settled Amphibalanus (Balanus) improvisus to reproduction, and on their offspring. We also compared two different populations, which were presumed to differ in their sensitivity to pCO2 due to differing habitat conditions: Kiel Fjord, Germany (Western Baltic Sea) with naturally strong pCO2 fluctuations, and the Tjärnö Archipelago, Sweden (Skagerrak) with far lower fluctuations. Over 20 weeks, survival, growth, reproduction and shell strength of Kiel barnacles were all unaffected by elevated pCO2, regardless of food availability. Moulting frequency and shell corrosion increased with increasing pCO2 in adults. Larval development and juvenile growth of the F1 generation were tolerant to increased pCO2, irrespective of parental treatment. In contrast, elevated pCO2 had a strong negative impact on survival of Tjärnö barnacles. Specimens from this population were able to withstand moderate levels of elevated pCO2 over 5 weeks when food was plentiful but showed reduced growth under food limitation. Severe levels of elevated pCO2 negatively impacted growth of Tjärnö barnacles in both food treatments. We demonstrate a conspicuously higher tolerance to elevated pCO2 in Kiel barnacles than in Tjärnö barnacles. This tolerance was carried-over from adults to their offspring. Our findings indicate that populations from fluctuating pCO2 environments are more tolerant to elevated pCO2 than populations from more stable pCO2 habitats. We furthermore provide evidence that energy availability can mediate the ability of barnacles to withstand moderate CO2 stress. Considering the high tolerance of Kiel specimens and the possibility to adapt over many generations, near future OA alone does not seem to present a major threat for A. improvisus
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    Large-scale impact of Saharan dust on the North Atlantic Ocean circulation (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research - Oceans, 119 (2). pp. 704-730.
    Details
    Publication Date: 2014-09-01
    Description: The potential for a dynamical impact of Saharan mineral dust on the North Atlantic Ocean large-scale circulation is investigated. To this end, an ocean general circulation model forced by atmospheric fluxes is perturbed by an idealized, seasonally varying, net shortwave flux anomaly, as it results from remote sensing observations of aerosol optical thickness representing Saharan dust load in the atmosphere. The dust dynamical impact on the circulation is assessed through a comparison between perturbed and an unperturbed run. Results suggest that, following the dust-induced shortwave irradiance anomaly, a buoyancy anomaly is created in the Atlantic offshore the African coast, which over the course of the time propagates westward into the interior Atlantic while progressively subducting. Changes in the large-scale barotropic and overturning circulations are significant after 3 years, which coincides with the elapsed time required by the bulk of the buoyancy perturbation to reach the western boundary of the North Atlantic. Although small in amplitude, the changes in the meridional overturning are of the same order as interannual-to-decadal variability. Variations in the amplitude of the forcing lead to changes in the amplitude of the response, which is almost linear during the first 3 years. In addition, a fast, but dynamically insignificant, response can be observed to propagate poleward along the eastern boundary of the North Atlantic, which contributes to a nonlinear response in the subpolar region north of 40°N.
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    Linking elements to biochemicals: effects of nutrient supply ratios and growth rates on fatty acid composition of phytoplankton species (2014)
    Wiley
    In:  Journal of Phycology, 50 (1). pp. 117-130.
    Details
    Publication Date: 2018-05-30
    Description: Three species of marine phytoplankton, Rhodomonas sp., Isochrysis galbana Parke, and Phaeodactylum tricornutum Bohlin, were cultivated in semicontinuous cultures to test biochemical responses (fatty acids; FAs) to five nitrogen (N):phosphorus (P) supply ratios and four growth rates (dilution rates). The characteristic FA profile was observed for each algal species (representing particular algal class), which remained relatively stable across the entire ranges of N:P supply ratios and growth rates. For all species, significant direct effects of N:P supply ratios on FAs were found at lower growth rates. The highest saturated and monounsaturated fatty acid (SFA and MUFA) contents were observed under N deficiency at the lowest growth rate in all three species, while responses of polyunsaturated fatty acids (PUFAs) revealed no consistent pattern. Total FAs (and SFAs and MUFAs) in all species showed significant negative correlations with N cell quota (QN) under N deficiency, but PUFAs had species-specific correlations with QN. The results show that characteristic FA profiles of algal genus or species (representing particular algal classes) underlie fluctuations according to culture conditions. The significant correlation between FAs and QN under N deficiency suggests that elemental and biochemical limitation of phytoplankton should be considered mutually as determinants of food quality for zooplankton in marine ecosystems.
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    Marine-based multiproxy reconstruction of Atlantic multidecadal variability (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Geophysical Research Letters, 41 (4). pp. 1295-1300.
    Details
    Publication Date: 2017-04-10
    Description: Atlantic multidecadal variability (AMV) is known to impact climate globally, and knowledge about the persistence of AMV is important for understanding past and future climate variability, as well as modeling and assessing climate impacts. The short observational data do not significantly resolve multidecadal variability, but recent paleoproxy reconstructions show multidecadal variability in North Atlantic temperature prior to the instrumental record. However, most of these reconstructions are land-based, not necessarily representing sea surface temperature. Proxy records are also subject to dating errors and microenvironmental effects. We extend the record of AMV 90 years past the instrumental record using principle component analysis of five marine-based proxy records to identify the leading mode of variability. The first principal component is consistent with the observed AMV, and multidecadal variability seems to persist prior to the instrumental record. Thus, we demonstrate that reconstructions of past Atlantic low-frequency variability can be improved by combining marine-based proxies.
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    Effects of sea surface warming on marine plankton (2014)
    Wiley
    In:  Ecology Letters, 17 (5). pp. 614-623.
    Details
    Publication Date: 2019-09-23
    Description: Ocean warming has been implicated in the observed decline of oceanic phytoplankton biomass. Some studies suggest a physical pathway of warming via stratification and nutrient flux, and others a biological effect on plankton metabolic rates; yet the relative strength and possible interaction of these mechanisms remains unknown. Here, we implement projections from a global circulation model in a mesocosm experiment to examine both mechanisms in a multi-trophic plankton community. Warming treatments had positive direct effects on phytoplankton biomass, but these were overcompensated by the negative effects of decreased nutrient flux. Zooplankton switched from phytoplankton to grazing on ciliates. These results contrast with previous experiments under nutrient-replete conditions, where warming indirectly reduced phytoplankton biomass via increased zooplankton grazing. We conclude that the effect of ocean warming on marine plankton depends on the nutrient regime, and provide a mechanistic basis for understanding global change in marine ecosystems.
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    Tropical influence independent of ENSO on the austral summer Southern Annular Mode (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Geophysical Research Letters, 41 (10). pp. 3643-3648.
    Details
    Publication Date: 2017-04-10
    Description: A link between atmospheric variability in the Tropics independent of ENSO and the Southern Annular Mode (SAM) is found based on seasonal mean data for austral summer. Variations associated with El Niño Southern Oscillation (ENSO) are removed usinga linear method and a Tropics Index (TI) is defined as the zonal average of the ENSO-removed 500 hPa geopotential height between 10°S and 10°N. Since the detrended TI shows no link to SST variability in the Tropics, it appears to be related to internal atmospheric variability. We find that the TI can explain about 40% variance of the SAM interannual variability and about 75% of the SAM long term trend between 1957/58 and 2001/02, where here the SAM includes the ENSO signal. Positive/negative values of the TI are associated with the positive/negative SAM. A possible link between the TI and global warming is noted.
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    Male mate choice relies on major histocompatibility complex class I in a sex-role-reversed pipefish (2014)
    Wiley
    In:  Journal of Evolutionary Biology, 27 (5). pp. 929-938.
    Details
    Publication Date: 2019-07-09
    Description: Mate choice for compatible genes is often based on genes of the major histocompatibility complex (MHC). Although MHC-based mate choice is commonly observed in female choice, male mate choice remains elusive. In particular, if males have intense paternal care and are thus the choosing sex, male choice for females with dissimilar MHC can be expected. Here, we investigated whether male mate choice relies on MHC class I genes in the sex-role reversed pipefish Syngnathus typhle. In a mate choice experiment, we determined the relative importance of visual and olfactory cues by manipulating visibility and olfaction. We found that pipefish males chose females that maximize sequence-based amino acid distance between MHC class I genotypes in the offspring when olfactory cues were present. Under visual cues, large females were chosen, but in the absence of visual cues, the choice pattern was reversed. The use of sex-role reversed species thus revealed that sexual selection can lead to the evolution of male mate choice for MHC class I genes.
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    Pacific-to-Indian Ocean connectivity: Tasman leakage, Indonesian Throughflow, and the role of ENSO (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research: Oceans, 119 (2). pp. 1365-1382.
    Details
    Publication Date: 2019-09-23
    Description: The upper ocean circulation of the Pacific and Indian Oceans is connected through both the Indonesian Throughflow north of Australia and the Tasman leakage around its south. The relative importance of these two pathways is examined using virtual Lagrangian particles in a high-resolution nested ocean model. The unprecedented combination of a long integration time within an eddy-permitting ocean model simulation allows the first assessment of the interannual variability of these pathways in a realistic setting. The mean Indonesian Throughflow, as diagnosed by the particles, is 14.3 Sv, considerably higher than the diagnosed average Tasman leakage of 4.2 Sv. The time series of Indonesian Throughflow agrees well with the Eulerian transport through the major Indonesian Passages, validating the Lagrangian approach using transport-tagged particles. While the Indonesian Throughflow is mainly associated with upper ocean pathways, the Tasman leakage is concentrated in the 400–900 m depth range at subtropical latitudes. Over the effective period considered (1968–1994), no apparent relationship is found between the Tasman leakage and Indonesian Throughflow. However, the Indonesian Throughflow transport correlates with ENSO. During strong La Niñas, more water of Southern Hemisphere origin flows through Makassar, Moluccas, Ombai, and Timor Straits, but less through Moluccas Strait. In general, each strait responds differently to ENSO, highlighting the complex nature of the ENSO-ITF interaction.
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    The viscosity effect on marine particle flux: A climate relevant feedback mechanism (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Global Biogeochemical Cycles, 28 (4). pp. 415-422.
    Details
    Publication Date: 2018-03-19
    Description: Oceanic uptake and long-term storage of atmospheric carbon dioxide (CO2) are strongly driven by the marine “biological pump,” i.e., sinking of biotically fixed inorganic carbon and nutrients from the surface into the deep ocean (Sarmiento and Bender, 1994; Volk and Hoffert, 1985). Sinking velocity of marine particles depends on seawater viscosity, which is strongly controlled by temperature (Sharqawy et al., 2010). Consequently, marine particle flux is accelerated as ocean temperatures increase under global warming (Bach et al., 2012). Here we show that this previously overlooked “viscosity effect” could have profound impacts on marine biogeochemical cycling and carbon uptake over the next centuries to millennia. In our global warming simulation, the viscosity effect accelerates particle sinking by up to 25%, thereby effectively reducing the portion of organic matter that is respired in the surface ocean. Accordingly, the biological carbon pump's efficiency increases, enhancing the sequestration of atmospheric CO2 into the ocean. This effect becomes particularly important on longer time scales when warming reaches the ocean interior. At the end of our simulation (4000 A.D.), oceanic carbon uptake is 17% higher, atmospheric CO2 concentration is 180 ppm lower, and the increase in global average surface temperature is 8% weaker when considering the viscosity effect. Consequently, the viscosity effect could act as a long-term negative feedback mechanism in the global climate system.
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    Abyssal ocean warming around Antarctica strengthens the Atlantic overturning circulation (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Geophysical Research Letters, 41 (11). pp. 3972-3978.
    Details
    Publication Date: 2019-09-23
    Description: The abyssal warming around Antarctica is one of the most prominent multidecadal signals of change in the global ocean. Here we investigate its dynamical impacts on the Atlantic Meridional Overturning Circulation (AMOC) by performing a set of experiments with the ocean-sea ice model NEMO-LIM2 at 1/2 degrees horizontal resolution. The simulations suggest that the ongoing warming of Antarctic Bottom Water (AABW), already affecting much of the Southern Hemisphere with a rate of up to 0.05 degrees C decade(-1), has important implications for the large-scale meridional overturning circulation in the Atlantic Ocean. While the abyssal northward flow of AABW is weakening, we find the upper AMOC cell to progressively strengthen by 5-10% in response to deep density changes in the South Atlantic. The simulations suggest that the AABW-induced strengthening of the AMOC is already extending into the subtropical North Atlantic, implying that the process may counteract the projected decrease of the AMOC in the next decades.
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  • 41
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    Extensive hydrogen supersaturations in the western South Atlantic Ocean suggest substantial underestimation of nitrogen fixation (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research: Oceans, 119 (7). pp. 4340-4350.
    Details
    Publication Date: 2019-09-23
    Description: The nitrogen cycle is fundamental to Earth's biogeochemistry. Yet major uncertainties of quantification remain, particularly regarding the global oceanic nitrogen fixation rate. Hydrogen is produced during nitrogen fixation and will become supersaturated in surface waters if there is net release from diazotrophs. Ocean surveys of hydrogen supersaturation thus have the potential to illustrate the spatial and temporal distribution of nitrogen fixation, and to guide the far more onerous but quantitative methods for measuring it. Here we present the first transect of high resolution measurements of hydrogen supersaturations in surface waters along a meridional 10,000 km cruise track through the Atlantic. We compare measured saturations with published measurements of nitrogen fixation rates and also with model-derived values. If the primary source of excess hydrogen is nitrogen fixation and has a hydrogen release ratio similar to Trichodesmium, our hydrogen measurements would point to similar rates of fixation in the North and South Atlantic, roughly consistent with modelled fixation rates but not with measured rates, which are lower in the south. Possible explanations would include any substantial nitrogen fixation by newly discovered diazotrophs, particularly any having a hydrogen release ratio similar to or exceeding that of Trichodesmium; under-sampling of nitrogen fixation south of the equator related to excessive focus on Trichodesmium; and methodological shortcomings of nitrogen fixation techniques that cause a bias towards colonial diazotrophs relative to unicellular forms. Alternatively our data are affected by an unknown hydrogen source that is greater in the southern half of the cruise track than the northern.
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  • 42
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    Large volume submarine ignimbrites in the Shikoku Basin: An example for explosive volcanism in the Western Pacific during the Late Miocene (2014)
    Wiley
    In:  Geochemistry, Geophysics, Geosystems, 15 (5). pp. 1837-1851.
    Details
    Publication Date: 2018-02-27
    Description: During IODP Expedition 322, an interval of Late Miocene (7.6 to ∼9.1 Ma) tuffaceous and volcaniclastic sandstones was discovered in the Shikoku Basin (Site C0011B), Nankai region. This interval consists of bioturbated silty claystone including four 1–7 m thick interbeds of tuffaceous sandstones (TST) containing 57–82% (by volume) pyroclasts. We use major and trace element glass compositions, as well as radiogenic isotope compositions, to show that the tuffaceous sandstones beds derived from single eruptive events, and that the majority (TST 1, 2, 3a) came from different eruptions from a similar source region, which we have identified to be the Japanese mainland, 350 km away. In particular, diagnostic trace element ratios (e.g., Th/La, Sm/La, Rb/Hf, Th/Nb, and U/Th) and isotopic data indicate a marked contribution from a mantle source beneath continental crust, which is most consistent with a Japanese mainland source and likely excludes the Izu-Bonin island arc and back arc as a source region for the younger TST beds. Nevertheless, some of the chemical data measured on the oldest sandstone bed (TST 3b, Unit IIb) show affinity to or can clearly be attributed to an Izu-Bonin composition. While we cannot completely exclude the possibility that all TST beds derived from unknown and exotic Izu-Bonin source(s), the collected lines of evidence are most consistent with an origin from the paleo-Honshu arc for TST 1 through 3a. We therefore suggest the former collision zone between the Izu-Bonin arc and Honshu paleo-arc as the most likely region where the eruptive products entered the ocean, also concurrent with nearby (∼200 km) possible Miocene source areas for the tuffaceous sandstones at the paleo-NE-Honshu arc. Estimating the distribution area of the tuffaceous sandstones in the Miocene between this source region and the ∼350 km distant Expedition 322, using bathymetric constraints, we calculate that the sandstone beds represent minimum erupted magma volumes between ∼1 and 17 km3 (Dense Rock Equivalent (DRE)). We conclude that several large volume eruptions occurred during the Late Miocene time next to the collision zone of paleo-Honshu and Izu-Bonin arc and covered the entire Philippine Sea plate with meter thick, sheet-like pyroclastic deposits that are now subducted in the Nankai subduction zone.
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  • 43
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    Nutrient availability determines dimethyl sulfide and isoprene distribution in the eastern Atlantic Ocean (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Geophysical Research Letters, 41 (9). pp. 3181-3188.
    Details
    Publication Date: 2019-09-24
    Description: Continuous high-resolution underway measurements of dimethyl sulfide (DMS) and isoprene in the ocean surface were conducted from Germany to South Africa in November 2008. DMS, total dimethylsulfoniopropionate (DMSPt), isoprene and 19'-hexanoyloxyfucoxanthin (19'-hex) correlated in nitrogen-depleted regions when they were clustered by nitrogen to phosphorous ratio (N:P). The 19'-hex-containing algae groups might be a common source of DMS, DMSPt, and isoprene in the low N: P regions. Additionally, DMS and isoprene correlated in nitrate-depleted regions when they were clustered against nitrate concentrations. Correlations between DMS and isoprene were also found within nitrate-depleted eddies encountered along the cruise track. Eddies with N: P of similar to 2.8 showed the highest positive correlations between DMS and isoprene. We conclude that the DMS/isoprene relationships in the eastern Atlantic Ocean were influenced by nutrient availability, with implications for using nutrients to predict the DMS and isoprene concentrations over a range of oceanographic areas depleted in nitrogen
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  • 44
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    Assessment of observed and model-derived soil moisture-evaporative fraction relationships over the United States Southern Great Plains (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research: Atmospheres, 119 (11). pp. 6279-6291.
    Details
    Publication Date: 2018-02-06
    Description: The relationship between soil moisture (SM) and evaporative fraction (EF) is an important component of land-atmosphere interactions. Frequently, land-atmosphere studies are based on land-surface models and not on observations. This study examines SM-EF interactions over the United States Southern Great Plains using both in situ observations and simulations from the Variable Infiltration Capacity hydrologic model. Specifically, we evaluate how the relationship between SM and EF varies by season, we determine why these variations occur, and we compare model-derived and observed SM-energy flux relationships. Data from four sites (2004-2008) that are part of the United States Department of Energy's Atmospheric Radiation MeasurementSouthern Great Plains network are used in this study. Results show that SM-EF interactions in both the model and observations are in general agreement with the evaporative regime theory described in past studies. That is, EF is a linear function of SM when SM is between the wilting point and the critical value, and when SM is above the critical value, EF is not dependent on SM. However, SM-EF relationships vary substantially from year to year. EF is a linear function of SM only when daily net radiation is above normal. Our results suggest that the strength of SM-EF interactions is not solely controlled by soil wetness but is also strongly influenced by daily net radiation and meteorological conditions.
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  • 45
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    Synthesis and Cytotoxic Activity of a Small Naphthoquinone Library: First Synthesis of Juglonbutin (2014)
    Wiley
    In:  European Journal of Organic Chemistry, 2014 (24). pp. 5318-5330.
    Details
    Publication Date: 2018-06-20
    Description: A synthetic protocol has been designed to synthesize grecoketidone (2k), 5-hydroxylapachol (2g), and the recently discovered natural products juglonbutin (2o) and its derivatives, leading to a small library of different 1,4-naphthoquinones with the intention of finding new active compounds. Within our collection, 2-O-alkylated naphthoquinones with an ester functionality in the side-chain and a free OH group at C-5 showed the best activities. Compounds 2f, 2m, and 2n showed GI50 values against 12 tumor cell lines in the lower micromolar range and juglonbutin (2o) showed remarkably efficient inhibition of the glycogen synthase kinase 3β with an IC50 value of 2.03 μM. Furthermore, studies on the mode of action of the most active cytotoxic compounds have been carried out. To the best of our knowledge, this is the first report on the synthesis of juglonbutin (2o) and its biological activity.
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  • 46
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    Constraining mid to late Holocene relative sea level change in the southern equatorial Pacific Ocean relative to the Society Islands, French Polynesia (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Geochemistry, Geophysics, Geosystems, 15 (6). pp. 2601-2615.
    Details
    Publication Date: 2018-02-28
    Description: Precisely quantifying the current climate-related sea level change requires accurate knowledge of long-term geological processes known as Glacial Isostatic Adjustments (GIA). Although the major postglacial melting phase is likely to have ended ∼6–4 ka BP (before present), GIA is still significantly affecting the present-day vertical position of the mean sea surface and the sea bottom. Here we present empirical rsl (relative sea level) data based on U/Th dated fossil corals from reef platforms of the Society Islands, French Polynesia, together with the corresponding GIA-modeling. Fossil coral data constrain the timing and amplitude of rsl variations after the Holocene sea level maximum (HSLM). Upon correction for isostatic island subsidence, we find that local rsl was at least ∼1.5 ± 0.4 m higher than present at ∼5.4 ka. Later, minor amplitude variations occurred until ∼2 ka, when the rsl started dropping to its present position with a rate of ∼0.4 mm/yr. The data match with predicted rsl curves based on global ice-sheet chronologies confirming the role of GIA-induced ocean siphoning effect throughout the mid to late Holocene. A long lasting Late Holocene highstand superimposed with second-order amplitudinal fluctuations as seen from our data suggest that the theoretical predicted timing of rsl change can still be refined pending future calibration.
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  • 47
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    Experimental parasite infection reveals costs and benefits of paternal effects (2014)
    Wiley
    In:  Ecology Letters, 17 (11). pp. 1409-1417.
    Details
    Publication Date: 2017-02-23
    Description: Forces shaping an individual's phenotype are complex and include transgenerational effects. Despite low investment into reproduction, a father's environment and phenotype can shape its offspring's phenotype. Whether and when such paternal effects are adaptive, however, remains elusive. Using three-spined sticklebacks in controlled infection experiments, we show that sperm deficiencies in exposed males compared to their unexposed brothers functionally translated into reduced reproductive success in sperm competition trials. In non-competitive fertilisations, offspring of exposed males suffered significant costs of reduced hatching success and survival but they reached a higher body condition than their counterparts from unexposed fathers after experimental infection. Interestingly, those benefits of paternal infection did not result from increased resistance but from increased tolerance to the parasite. Altogether, these results demonstrate that parasite resistance and tolerance are shaped by processes involving both genetic and non-genetic inheritance and suggest a context-dependent adaptive value of paternal effects
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  • 48
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    Helium Isotope Variations and mantle plume-spreading ridge interactions along the Galápagos Spreading Center (2014)
    Wiley
    In:  In: The Galápagos: A natural laboratory for Earth Sciences. , ed. by Harpp, K., Mittelstaedt, E., d'Ozouville, N. and Graham, D. W. AGU Geophysical Monograph, 204 . Wiley, Hoboken, NJ, pp. 393-414. ISBN 978-1-118-85241-5
    Details
    Publication Date: 2014-09-22
    Description: Along the Galápagos Spreading Center (GSC), 3He/4He varies from 8.5–5.9 RA. High 3He/4He ratios, resembling those in the western and southern Galápagos islands, are absent. This lack of high 3He/4He contrasts markedly with other localities of plume–ridge interaction, such as Iceland, Easter, and Amsterdam/St. Paul. The most striking feature is a 3He/4He gradient, decreasing westward from 8.4–7.0 RA between 89 and 93°W, where the GSC is shallowest and shows “axial high” morphology. The intra-segment 3He/4He variability within this region indicates that magma crosses the mantle/crust boundary at multiple points beneath individual ridge segments, and lateral mixing within the crust and upper mantle is limited. Some of the 3He/4He variability may also reflect transfer of discrete heterogeneity from beneath the northern sector of the Galápagos plateau. One possible explanation for the absence of high 3He/4He along the GSC is that helium is a relatively ineffective downstream tracer of mantle material from the core of the Galápagos plume, due to its preferential extraction beneath the archipelago compared to other incompatible, lithophile tracers. A second explanation is that the heterogeneous Galápagos plume is sheared in the upper mantle by motion of the Nazca Plate relative to the migrating GSC. In this case, plume core material having high 3He/4He (from beneath Fernandina and Isabela) would be dispersed mostly away from the ridge, while plume edge material having low 3He/4He plus enriched Sr and Pb isotope signatures (from beneath the northern periphery of the archipelago) is smeared into the sub-ridge mantle.
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  • 49
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    A ventilation-based framework to explain the regeneration - scavenging balance of iron in the Ocean (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Geophysical Research Letters, 41 (20). pp. 7227-7236.
    Details
    Publication Date: 2021-04-23
    Description: Our understanding of the processes driving the patterns of dissolved iron (DFe) in the ocean interior, either in observations or models, is complicated by the combined influences of subduction from the surface mixed layer, notable subsurface sources, regeneration, and scavenging loss. We describe a ventilation-based framework to quantify these processes in a global ocean biogeochemical model including diagnostics along potential density surfaces. There is a prevailing control of subsurface DFe by the subduction of surface DFe as preformed DFe augmented by benthic sources of DFe from hydrothermal activity and sediments. Unlike phosphate, there is often a first-order balance with a near cancelation between regeneration and scavenging with the remaining “net regeneration” controlled by the ventilation of surface excesses in Fe-binding ligands. This DFe framework provides a more stringent test of how the total DFe distribution is mechanistically controlled within a model and may be subsequently used to interpret observed DFe distributions.
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  • 50
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    Low-frequency ocean bottom pressure variations in the North Pacific in response to time-variable surface winds (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research: Oceans, 119 (8). pp. 5190-5202.
    Details
    Publication Date: 2018-02-27
    Description: One decade of time-variable gravity field observations from the GRACE satellite mission reveals low-frequency ocean bottom pressure (OBP) variability of up to 2.5 hPa centered at the northern flank of the subtropical gyre in the North Pacific. From a 145 year-long simulation with a coupled chemistry climate model, OBP variability is found to be related to the prevailing atmospheric sea-level pressure and surface wind conditions in the larger North Pacific area. The dominating atmospheric pressure patterns obtained from the climate model run allow in combination with ERA-Interim sea-level pressure and surface winds a reconstruction of the OBP variability in the North Pacific from atmospheric model data only, which correlates favorably (r=0.7) with GRACE ocean bottom pressure observations. The regression results indicate that GRACE-based OBP observations are indeed sensitive to changes in the prevailing sea-level pressure and thus surface wind conditions in the North Pacific, thereby opening opportunities to constrain atmospheric models from satellite gravity observations over the oceans.
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  • 51
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    Ontogeny of long distance migration (2014)
    Wiley
    In:  Ecology, 95 (10). pp. 2840-2850.
    Details
    Publication Date: 2017-02-21
    Description: The movements of some long-distance migrants are driven by innate compass headings that they follow on their first migrations (e.g., some birds and insects), while the movements of other first-time migrants are learned by following more experienced conspecifics (e.g., baleen whales). However, the overall roles of innate, learned, and social behaviors in driving migration goals in many taxa are poorly understood. To look for evidence of whether migration routes are innate or learned for sea turtles, here for 42 sites around the world we compare the migration routes of 〉400 satellite-tracked adults of multiple species of sea turtle with ∼45 000 Lagrangian hatchling turtle drift scenarios. In so doing, we show that the migration routes of adult turtles are strongly related to hatchling drift patterns, implying that adult migration goals are learned through their past experiences dispersing with ocean currents. The diverse migration destinations of adults consistently reflected the diversity in sites they would have encountered as drifting hatchlings. Our findings reveal how a simple mechanism, juvenile passive drift, can explain the ontogeny of some of the longest migrations in the animal kingdom and ensure that adults find suitable foraging sites. Read More: http://www.esajournals.org/doi/abs/10.1890/13-2164.1
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  • 52
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    PCR and DNA Sequencing (2014)
    Wiley
    In:  In: Biofouling Methods. , ed. by Dobretsov, S., Williams, D. N. and Thomason, J. Wiley, New York, USA, pp. 93-113. ISBN 978-0-470-65985-4
    Details
    Publication Date: 2014-11-06
    Type: Book chapter , NonPeerReviewed
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    Evolutionary conservation-evaluating the adaptive potential of species (2014)
    Wiley
    In:  Evolutionary Applications, 7 (9). pp. 963-967.
    Details
    Publication Date: 2019-09-23
    Description: Despite intense efforts, biodiversity around the globe continues to decrease. To cease this phenomenon, we urgently need a better knowledge not only of the true extent of biodiversity, but also of the evolutionary potential of species to respond to environmental change. These aims are the heart of the developing field of Evolutionary conservation. Here, after describing problems associated with implementing evolutionary perspectives into management, we outline how evolutionary principles can contribute to efficient conservation programmes. We then introduce articles from this special issue on Evolutionary conservation, outlining how each study or review provides tools and concepts to contribute to efficient management of species or populations. Ultimately, we highlight what we believe can be future research avenues for evolutionary conservation.
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  • 54
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    ENSO-driven interhemispheric Pacific mass transports (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research: Oceans, 119 (9). pp. 6221-6237.
    Details
    Publication Date: 2019-09-23
    Description: Previous studies have shown that ENSO's anomalous equatorial winds, including the observed southward shift of zonal winds that occurs around the event peak, can be reconstructed with the first two Empirical Orthogonal Functions (EOFs) of equatorial region wind stresses. Using a high-resolution ocean general circulation model, we investigate the effect of these two EOFs on changes in warm water volume (WWV), interhemispheric mass transports, and Indonesian Throughflow (ITF). Wind stress anomalies associated with the first EOF produce changes in WWV that are dynamically consistent with the conceptual recharge oscillator paradigm. The ITF is found to heavily damp these WWV changes, reducing their variance by half. Wind stress anomalies associated with the second EOF, which depicts the southward wind shift, are responsible for WWV changes that are of comparable magnitude to those driven by the first mode. The southward wind shift is also responsible for the majority of the observed interhemispheric upper ocean mass exchanges. These winds transfer mass between the Northern and the Southern Hemisphere during El Niño events. Whilst water is transferred in the opposite direction during La Niña events, the magnitude of this exchange is roughly half of that seen during El Niño events. Thus, the discharging of WWV during El Niño events is meridionally asymmetric, while the WWV recharging during a La Niña event is largely symmetric. The inclusion of the southward wind shift is also shown to allow ENSO to exchange mass with much higher latitudes than that allowed by the first EOF alone.
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  • 55
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    Pigments accumulation via light and oxygen in Rhodobacter capsulatus strain XJ-1 isolated from saline soil (2014)
    Wiley
    In:  Journal of Basic Microbiology, 54 (8). pp. 828-834.
    Details
    Publication Date: 2017-07-03
    Description: A Rhodobacter capsulatus strain, designated XJ-1, isolated from saline soil, accumulated almost only one kind of bacteriochlorophyll a anaerobically in the light, aerobically in the light and dark, and the relative contents of the bacteriochlorophyll a were 44.61, 74.89, and 77.53% of the total pigments, respectively. A new purple pigment appeared only in aerobic-light grown cells, exhibited absorption maxima at 355, 389, 520, 621, and 755 nm, especially distinctly unusual peak at 621 nm, whereas vanished in anaerobic-light and in aerobic-dark culture. Spheroidene and OH–spheroidene predominated in anaerobic phototrophic cultures. Spheroidenone was the sole carotenoid when exposed to both light and oxygen. The second keto-carotenoids, OH–spheroidenone, presented only in aerobic-dark culture in addition to spheroidenone. Strain XJ-1 would be a good model organism for the further illustration of the regulation of bacteriochlorophyll biosynthesis gene expression in response to unique habitat.
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  • 56
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    Unique mitochondrial DNA lineages in Irish sticklebackpopulations: cryptic refugium or rapid recolonization? (2014)
    Wiley
    In:  Ecology and Evolution, 4 (12). pp. 2488-2504.
    Details
    Publication Date: 2014-08-11
    Description: Repeated recolonization of freshwater environments following Pleistocene glaciations has played a major role in the evolution and adaptation of anadromous taxa. Located at the western fringe of Europe, Ireland and Britain were likely recolonized rapidly by anadromous fishes from the North Atlantic following the last glacial maximum (LGM). While the presence of unique mitochondrial haplotypes in Ireland suggests that a cryptic northern refugium may have played a role in recolonization, no explicit test of this hypothesis has been conducted. The three-spined stickleback is native and ubiquitous to aquatic ecosystems throughout Ireland, making it an excellent model species with which to examine the biogeographical history of anadromous fishes in the region. We used mitochondrial and microsatellite markers to examine the presence of divergent evolutionary lineages and to assess broad-scale patterns of geographical clustering among postglacially isolated populations. Our results confirm that Ireland is a region of secondary contact for divergent mitochondrial lineages and that endemic haplotypes occur in populations in Central and Southern Ireland. To test whether a putative Irish lineage arose from a cryptic Irish refugium, we used approximate Bayesian computation (ABC). However, we found no support for this hypothesis. Instead, the Irish lineage likely diverged from the European lineage as a result of postglacial isolation of freshwater populations by rising sea levels. These findings emphasize the need to rigorously test biogeographical hypothesis and contribute further evidence that postglacial processes may have shaped genetic diversity in temperate fauna.
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  • 57
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    Submarine gas seepage in a mixed contractional and shear deformation regime: Cases from the Hikurangi oblique-subduction margin (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Geochemistry, Geophysics, Geosystems, 15 (2). pp. 416-433.
    Details
    Publication Date: 2018-02-27
    Description: Gas seepage from marine sediments has implications for understanding feedbacks between the global carbon reservoir, seabed ecology and climate change. Although the relationship between hydrates, gas chimneys and seafloor seepage is well established, the nature of fluid sources and plumbing mechanisms controlling fluid escape into the hydrate zone and up to the seafloor remain one of the least understood components of fluid migration systems. In this study we present the analysis of new three-dimensional high-resolution seismic data acquired to investigate fluid migration systems sustaining active seafloor seepage at Omakere Ridge, on the Hikurangi subduction margin, New Zealand. The analysis reveals at high resolution, complex overprinting fault structures (i.e. protothrusts, normal faults from flexural extension, and shallow (〈1 km) arrays of oblique shear structures) implicated in fluid migration within the gas hydrate stability zone in an area of 2x7 km. In addition to fluid migration systems sustaining seafloor seepage on both sides of a central thrust fault, the data show seismic evidence for sub-seafloor gas-rich fluid accumulation associated with proto-thrusts and extensional faults. In these latter systems fluid pressure dissipation through time has been favored, hindering the development of gas chimneys. We discuss the elements of the distinct fluid migration systems and the influence that a complex partitioning of stress may have on the evolution of fluid flow systems in active subduction margins.
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  • 58
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    Monitoring of gas and seismic energy release by multiparametric benthic observatory along the North Anatolian Fault in the Sea of Marmara (NW Turkey) (2014)
    Wiley
    In:  Geophysical Journal International, 196 (2). pp. 850-866.
    Details
    Publication Date: 2015-07-24
    Description: Episodic gas seepage occurs at the seafloor in the Gulf of Izmit (Sea of Marmara, NW Turkey) along the submerged segment of the North Anatolian Fault (NAF), which ruptured during the 1999 Mw7.4 Izmit earthquake, and caused tectonic loading of the fault segment in front of the Istanbul metropolitan area. In order to study gas seepage and seismic energy release along the NAF, a multiparametric benthic observatory (SN-4) was deployed in the gulf at the western end of the 1999 Izmit earthquake rupture, and operated for about 1 yr at 166 m water depth. The SN-4 payload included a three-component broad-band seismometer, as well as gas and oceanographic sensors. We analysed data collected continuously for 161 d in the first part of the experiment, from 2009 October to 2010 March. The main objective of our work was to verify whether tectonic deformation along the NAF could trigger methane seepage. For this reason, we considered only local seismicity, that is, within 100 km from the station. No significant (ML ≥ 3.6) local earthquakes occurred during this period; on the other hand, the seismometer recorded high-frequency SDEs (short duration events), which are not related to seismicity but to abrupt increases of dissolved methane concentration in the sea water that we called MPEs (methane peak events). Acquisition of current velocity, dissolved oxygen, turbidity, temperature and salinity, allowed us to analyse the local oceanographic setting during each event, and correlate SDEs to episodic gas discharges from the seabed. We noted that MPEs are the result of such gas releases, but are detected only under favourable oceanographic conditions. This stresses the importance of collecting long-term multiparametric time-series to address complex phenomena such as gas and seismic energy release at the seafloor. Results from the SN-4 experiment in the Sea of Marmara suggest that neither low-magnitude local seismicity, nor regional events affect intensity and frequency of gas flows from the seafloor.
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    Eddies and an extreme water mass anomaly observed in the eastern south Pacific at the Stratus mooring (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research: Oceans, 119 (2). pp. 1068-1083.
    Details
    Publication Date: 2019-09-23
    Description: In the tropical eastern South Pacific the Stratus Ocean Reference Station (ORS) (∼20°S, 85.5°W) is located in the transition zone between the oxygen minimum zone (OMZ) and the well-oxygenated subtropical gyre. In February/March 2012, extremely anomalous water mass properties were observed in the thermocline at the Stratus ORS. The available eddy oxygen anomaly was −10.5 × 1016 µmol. This anomalous water was contained in an anticyclonic mode-water eddy crossing the mooring site. This eddy was absorbed at that time by an anticyclonic feature located south of the Stratus mooring. This was the largest water property anomaly observed at the mooring during the 13.5 month deployment period. The sea surface height anomaly (SSHA) of the strong mode-water eddy in February/March 2012 was weak, and while the lowest and highest SSHA were related to weak eddies, SSHA is found not to be sufficient to specify the eddy strength for subsurface-intensified eddies. Still, the anticyclonic eddy, and its related water mass characteristics, could be tracked backward in time in SSHA satellite data to a formation region in April 2011 off the Chilean coast. The resulting mean westward propagation velocity was 5.5 cm s−1. This extremely long-lived eddy carried the water characteristics from the near-coastal Chilean water to the open ocean. The water mass stayed isolated during the 11 month travel time due to high rotational speed of about 20 cm s−1 leading to almost zero oxygen in the subsurface layer of the anticyclonic mode-water eddy with indications of high primary production just below the mixed layer.
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    Modifying the PEG model for Mediterranean lakes - no biological winter and strong fish predation (2014)
    Wiley
    In:  Freshwater Biology, 59 (6). pp. 1136-1144.
    Details
    Publication Date: 2018-06-08
    Description: The widely cited Plankton Ecology Group (PEG) model of plankton seasonal succession is often used as a template to explain the seasonal changes in plankton communities outside the cold temperate zone, where it was developed, but this may be inappropriate for lower-latitude lakes. Lower-latitude lakes have high light availability in winter and less pronounced seasonal variations in fish predation on zooplankton. We might therefore expect higher phytoplankton crops in winter and much more predation on zooplankton by fish than in colder lakes. This might lead to less grazing in summer and relatively higher phytoplankton crops. We compared data on phytoplankton biovolume, zooplankton biomass and body size from 18 German and 6 Greek lakes to test these hypotheses.
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    Quantitative estimate of the paleo-Agulhas leakage (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Geophysical Research Letters, 41 (4). pp. 1238-1246.
    Details
    Publication Date: 2017-04-10
    Description: The Indian-Atlantic water exchange south of Africa (Agulhas leakage) is a key component of the global ocean circulation. No quantitative estimation of the paleo-Agulhas leakage exists. We quantify the variability in interocean exchange over the past 640,000 years, using planktic foraminiferal assemblage data from two marine sediment records to define an Agulhas leakage efficiency index. We confirm the validity of our new approach with a numerical ocean model that realistically simulates the modern Agulhas leakage changes. Our results suggest that, during the past several glacial-interglacial cycles, the Agulhas leakage varied by ~10 sverdrup and more during major climatic transitions. This lends strong credence to the hypothesis that modifications in the leakage played a key role in changing the overturning circulation to full strength mode. Our results are instrumental for validating and quantifying the contribution of the Indian-Atlantic water leakage to the global climate changes.
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    Glyoxal observations in the global marine boundary layer (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research - Atmospheres, 119 (10). pp. 6160-6169.
    Details
    Publication Date: 2015-12-01
    Description: Glyoxal is an important intermediate species formed by the oxidation of common biogenic and anthropogenic volatile organic compounds such as isoprene, toluene and acetylene. Although glyoxal has been shown to play an important role in urban and forested environments, its role in the open ocean environment is still not well understood, with only a few observations showing evidence for its presence in the open ocean marine boundary layer (MBL). In this study, we report observations of glyoxal from ten field campaigns in different parts of the world's oceans. These observations together represent the largest database of glyoxal in the MBL. The measurements are made with similar instruments that have been used in the past, although the open ocean values reported here, average of about 25 pptv with an upper limit of 40 pptv, are much lower than previously reported observations that were consistently higher than 40 pptv and had an upper limit of 140 pptv, highlighting the uncertainties in the Differential Optical Absorption Spectroscopy (DOAS) method for the retrieval of glyoxal. Despite retrieval uncertainties, the results reported in this work support previous suggestions that the currently known sources of glyoxal are insufficient to explain the average MBL concentrations. This suggests that there is an additional missing source, more than a magnitude larger than currently known sources, which is necessary to account for the observed atmospheric levels of glyoxal. Therefore it could play a more important role in the MBL than previously considered.
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    Seismic and gravity constraints on the nature of the basement in the Africa-Eurasia plate boundary: New insights for the geodynamic evolution of the SW Iberian margin (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research - Solid Earth, 119 (1). pp. 127-149.
    Details
    Publication Date: 2015-07-24
    Description: We present a new classification of geological domains at the Africa-Eurasia plate boundary off SW Iberia, together with a regional geodynamic reconstruction spanning from the Mesozoic extension to the Neogene-to-present-day convergence. It is based on seismic velocity and density models along a new transect running from the Horseshoe to the Seine abyssal plains, which is combined with previously available geophysical models from the region. The basement velocity structure at the Seine Abyssal Plain indicates the presence of a highly heterogeneous, thin oceanic crust with local high-velocity anomalies possibly representing zones related to the presence of ultramafic rocks. The integration of this model with previous ones reveals the presence of three oceanic domains offshore SW Iberia: (1) the Seine Abyssal Plain domain, generated during the first stages of slow seafloor spreading in the NE Central Atlantic (Early Jurassic); (2) the Gulf of Cadiz domain, made of oceanic crust generated in the Alpine-Tethys spreading system between Iberia and Africa, which was coeval with the formation of the Seine Abyssal Plain domain and lasted up to the North Atlantic continental breakup (Late Jurassic); and (3) the Gorringe Bank domain, made of exhumed mantle rocks, which formed during the first stages of North Atlantic opening. Our models suggest that the Seine Abyssal Plain and Gulf of Cadiz domains are separated by the Lineament South strike-slip fault, whereas the Gulf of Cadiz and Gorringe Bank domains appear to be limited by a deep thrust fault located at the center of the Horseshoe Abyssal Plain.
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    Strong responses of Southern Ocean phytoplankton communities to volcanic ash (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Geophysical Research Letters, 41 (8). pp. 2851-2857.
    Details
    Publication Date: 2021-04-23
    Description: Volcanic eruptions have been hypothesized as an iron supply mechanism for phytoplankton blooms; however, little direct evidence of stimulatory responses has been obtained in the field. Here we present the results of twenty-one 1-2day bottle enrichment experiments from cruises in the South Atlantic and Southern Ocean which conclusively demonstrated a photophysiological and biomass stimulation of phytoplankton communities following supply of basaltic or rhyolitic volcanic ash. Furthermore, experiments in the Southern Ocean demonstrated significant phytoplankton community responses to volcanic ash supply in the absence of responses to addition of dissolved iron alone. At these sites, dissolved manganese concentrations were among the lowest ever measured in seawater, and we therefore suggest that the enhanced response to ash may have been a result of the relief of manganese (co)limitation. Our results imply that volcanic ash deposition events could trigger extensive phytoplankton blooms, potentially capable of significant impacts on regional carbon cycling.
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    Surface nitrification: a major uncertainty in marine N2O emissions (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Geophysical Research Letters, 41 (12). pp. 4247-4253.
    Details
    Publication Date: 2019-09-23
    Description: The ocean is responsible for up to a third of total global nitrous oxide (N2O) emissions, but uncertainties in emission rates of this potent greenhouse gas are high (〉100%). Here we use a marine biogeochemical model to assess six major uncertainties in estimates of N2O production, thereby providing guidance in how future studies may most effectively reduce uncertainties in current and future marine N2O emissions. Potential surface N2O production from nitrification causes the largest uncertainty in N2O emissions (estimated up to ~1.6 Tg N yr-1, or 48% of modeled values), followed by the unknown oxygen concentration at which N2O production switches to N2O consumption (0.8 Tg N yr-1, or 24% of modeled values). Other uncertainties are minor, cumulatively changing regional emissions by 〈15%. If production of N2O by surface nitrification could be ruled out in future studies, uncertainties in marine N2O emissions would be halved.
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    Geochemistry of volcanic glasses from the Louisville Seamount Trail (IODP Expedition 330): Implications for eruption environments and mantle melting (2014)
    Wiley
    In:  Geochemistry, Geophysics, Geosystems, 15 (5). pp. 1718-1738.
    Details
    Publication Date: 2019-09-23
    Description: Volcanic glasses recovered from four guyots during drilling along the Louisville Seamount Trail, southwest Pacific, have been analyzed for major, trace, and volatile elements (H2O, CO2, S, and Cl), and oxygen isotopes. Compared to other oceanic island settings, they are geochemically homogeneous, providing no evidence of the tholeiitic stage that characterizes Hawaii. The degrees and depth of partial melting remained constant over 1–3 Ma represented by the drill holes, and along-chain over several million years. The only exception is Hadar Guyot with compositions that suggest small degree preferential melting of an enriched source, possibly because it erupted on the oldest and thickest lithosphere. Incompatible element enriched glass from late-stage volcaniclastics implies lower degrees of melting as the volcanoes moved off the melting anomaly. Volcaniclastic glasses from throughout the igneous basement are degassed suggesting generation during shallow submarine eruptions (〈20 mbsl) or as subaerial flows entered the sea. Drill depths may no longer reflect relative age due to postquench downslope movement. Higher volatile contents in late-stage volcaniclastics indicate submarine eruptions at 118–258 mbsl and subsidence of the edifices below sea level by the time they erupted, or generation in flank eruptions. Glass from intrusion margins suggests emplacement ∼100 m below the surface. The required uplift to achieve these paleo-quench depths and the subsequent subsidence to reach their current depths exceeds that expected for normal oceanic lithosphere, consistent with the Louisville melting anomaly being 〈100°C hotter than normal asthenosphere at 50–70 Ma when the guyots were erupted. Key Points: - Louisville glasses show remarkable temporal geochemical homogeneity - All recovered Louisville glasses are variably degassed - Louisville melting anomaly was 〈100°C hotter than normal asthenosphere
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    Ice production in Storfjorden (Svalbard) estimated from a model based on AMSR-E observations: impact on water mass properties (2014)
    Wiley
    In:  Journal of Geophysical Research - Oceans, 119 . pp. 377-393.
    Details
    Publication Date: 2017-01-01
    Description: Storfjorden, which hosts a latent heat polynya, is a well known region of dense water formation. This Brine-enriched Shelf Water (BSW) displays substantial year to year variability in its properties, which is partly linked to interannual variations in ice production. Here we have developed a model based on high-resolution AMSR-E satellite sea-ice concentration data, available between 2002 and 2011, and atmospheric forcing to estimate the ice production in the polynya and associated salt release. The average modeled ice production for the epoch 2002–2011 is 47 km3 per year, corresponding to a salt release of 1200 × 109 kg. The two most anomalous winters were 2004–2005 (salt deficit of −367 × 109 kg) and 2007–2008 (salt excess of 398 × 109 kg). Available observations of BSW properties are relatively scarce during this period and are here augmented with data collected in March 2007 from an ice-tethered mooring to the northwest of the fjord. BSW was found up to the surface, with maximum salinity and density of 35.27 and 28.4 kg m−3, respectively, at 55 m. In addition, supercooled water was found down to 10 m under relatively mild atmospheric conditions. It is shown to have formed a week before, during an intense frazil ice formation episode, exceeding 2 km3 of frazil ice according to the model. Although observations remain too few to robustly assess the relation between ice production and BSW properties, there is suggestion of a direct impact for most anomalous years. The exceptional ice production in 2007–2008 is most likely the cause of the very saline BSW in 2008 and strong plume of dense water toward Fram Strait reported by other authors. Anomalous ice production appears predominantly driven by the duration of the freezing season and anomalous opening of the polynya.
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    Variability in under-ice export fluxes of biogenic matter in the Central Arctic Ocean (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Global Biogeochemical Cycles, 28 (5). pp. 571-583.
    Details
    Publication Date: 2014-08-27
    Description: A critical question regarding the organic carbon cycle in the Arctic Ocean is whether the decline in ice extent and thickness and the associated increase in solar irradiance in the upper ocean will result in increased primary production and particulate organic carbon (POC) export. To assess spatial and temporal variability in POC export, under-ice export fluxes were measured with short-term sediment traps in the northern Laptev Sea in July-August-September 1995, north of the Fram Strait in July 1997, and in the Central Arctic in August–September 2012. Sediment traps were deployed at 2–5 m and 20–25 m under ice for periods ranging from 8.5 to 71 h. In addition to POC fluxes, total particulate matter, chlorophyll a, biogenic particulate silica, phytoplankton, and zooplankton fecal pellet fluxes were measured to evaluate the amount and composition of the material exported in the upper Arctic Ocean. Whereas elevated export fluxes observed on and near the Laptev Sea shelf were likely the combined result of high primary production, resuspension, and release of particulate matter from melting ice, low export fluxes above the central basins despite increased light availability during the record minimum ice extent of 2012 suggest that POC export was limited by nutrient supply during summer. These results suggest that the ongoing decline in ice cover affects export fluxes differently on Arctic shelves and over the deep Arctic Ocean and that POC export is likely to remain low above the central basins unless additional nutrients are supplied to surface waters.
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    Marine CDOM accumulation during a coastal Arctic mesocosm experiment: No response to elevated pCO2levels (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research: Biogeosciences, 119 (6). pp. 1216-1230.
    Details
    Publication Date: 2020-10-20
    Description: A large-scale multidisciplinary mesocosm experiment in an Arctic fjord (Kongsfjorden, Svalbard; 78°56.2′N) was used to study Arctic marine food webs and biogeochemical elements cycling at natural and elevated future carbon dioxide (CO2) levels. At the start of the experiment, marine-derived chromophoric dissolved organic matter (CDOM) dominated the CDOM pool. Thus, this experiment constituted a convenient case to study production of autochthonous CDOM, which is typically masked by high levels of CDOM of terrestrial origin in the Arctic Ocean proper. CDOM accumulated during the experiment in line with an increase in bacterial abundance; however, no response was observed to increased pCO2 levels. Changes in CDOM absorption spectral slopes indicate that bacteria were most likely responsible for the observed CDOM dynamics. Distinct absorption peaks (at ~ 330 and ~ 360 nm) were likely associated with mycosporine-like amino acids (MAAs). Due to the experimental setup, MAAs were produced in absence of ultraviolet exposure providing evidence for MAAs to be considered as multipurpose metabolites rather than simple photoprotective compounds. We showed that a small increase in CDOM during the experiment made it a major contributor to total absorption in a range of photosynthetically active radiation (PAR, 400–700 nm) and, therefore, is important for spectral light availability and may be important for photosynthesis and phytoplankton groups composition in a rapidly changing Arctic marine ecosystem.
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    Thermogenic methane injection via bubble transport into the upper Arctic Ocean from the hydrate-charged Vestnesa Ridge, Svalbard (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Geochemistry, Geophysics, Geosystems, 15 (5). pp. 1945-1959.
    Details
    Publication Date: 2017-09-15
    Description: We use new gas-hydrate geochemistry analyses, echosounder data, and three-dimensional P-Cable seismic data to study a gas-hydrate and free-gas system in 1200 m water depth at the Vestnesa Ridge offshore NW Svalbard. Geochemical measurements of gas from hydrates collected at the ridge revealed a thermogenic source. The presence of thermogenic gas and temperatures of similar to 3.3 degrees C result in a shallow top of the hydrate stability zone (THSZ) at similar to 340 m below sea level (mbsl). Therefore, hydrate-skinned gas bubbles, which inhibit gas-dissolution processes, are thermodynamically stable to this shallow water depth. This was confirmed by hydroacoustic observations of flares in 2010 and 2012 reaching water depths between 210 and 480 mbsl. At the seafloor, bubbles are released from acoustically transparent zones in the seismic data, which we interpret as regions where free gas is migrating through the hydrate stability zone (HSZ). These intrusions result in vertical variations in the base of the HSZ (BHSZ) of up to similar to 150 m, possibly making the shallow hydrate reservoir more susceptible to warming. Such Arctic gas-hydrate and free-gas systems are important because of their potential role in climate change and in fueling marine life, but remain largely understudied due to limited data coverage in seasonally ice-covered Arctic environments.
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    Contrasting conditions of rift and off-rift silicic magma origin on Iceland (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Geophysical Research Letters, 41 (16). pp. 5813-5820.
    Details
    Publication Date: 2017-04-10
    Description: Factors controlling the origin of silicic magmas on Iceland are poorly constrained. Here we present new data on H2O content, pressure, temperature, oxygen fugacity, and oxygen isotope composition of rhyolites from Askja, Öræfajökull, and Hekla volcanoes. All these parameters correlate with tectonic (rift and off-rift) setting of the volcanoes. Askja rift rhyolites originate through extensive assimilation of high-temperature hydrothermally altered crust (δ18O 〈 2‰) at shallow depths (≥1.8 km). These rhyolites are hot (935–1008°C), relatively dry (H2O 〈 2.7 wt%), and oxidized (QFM = +1.4). Cooler (874–902°C), wet (H2O = 4-6.3 wt%), and non-oxidized (~QFM to QFM-1) off-rift rhyolites (Öræfajökull, Hekla) originate through differentiation deeper in the crust (≥4 km) with almost no or little assimilation of high-T, altered crust, as reflected by slightly lower to normal δ18O values (5.2–6‰). Although off-rift rhyolites predominate during the Holocene, older silicic rocks on Iceland primarily formed in a rift setting possibly analogous to the oldest continental crust on Earth.
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    Experimental evolution of external immune defences in the red flour beetle (2014)
    Wiley
    In:  Journal of Evolutionary Biology, 27 (8). pp. 1562-1571.
    Details
    Publication Date: 2017-07-10
    Description: The red flour beetle, Tribolium castaneum, secretes quinones that control the microbial flora in the surrounding environment. These secretions act as an external immune defence that provides protection against pathogens. At high concentrations, however, these secretions are harmful to the host itself, and selection may thus have optimized the level of expression under natural conditions. Here, we show that the expression of external immunity responded to selection during experimental evolution within a few generations. At the same time, one component of internal immune defence (phenoloxidase activity) was compromised in beetles selected for either high or low external defences. Intriguingly, offspring protection against a natural pathogen was reduced in flour obtained from beetle lines selected for low amounts of secretions. Altogether, this suggests that external and internal immune defences work together efficiently under natural conditions, whereas every manipulation on the side of external immune defence comes with costs to the internal immune defence.
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    Sulfur budget and global climate impact of the AD 1835 eruption of Cosigüina volcano, Nicaragua (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Geophysical Research Letters, 41 (19). pp. 6667-6675.
    Details
    Publication Date: 2017-04-10
    Description: Large explosive volcanic eruptions can inject massive amounts of sulfuric gases into the Earth's atmosphere and, in so doing, affect global climate. The January 1835 eruption of Cosigüina volcano, Nicaragua, ranks among the Americas’ largest and most explosive historical eruptions, but whether it had effects on global climate remains ambiguous. New petrologic analyses of the Cosigüina deposits reveal that the eruption released enough sulfur to explain a prominent ca. AD 1835 sulfate anomaly in ice cores from both the Arctic and Antarctic. A compilation of temperature-sensitive tree-ring chronologies indicates appreciable cooling of the Earth's surface in response to the eruption, consistent with instrumental temperature records. We conclude that this eruption represents one of the most important sulfur-producing events of the last few centuries and had a sizable climate impact rivaling that of the 1991 eruption of Mount Pinatubo.
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    Seaglider observations of equatorial Indian Ocean Rossby waves associated with the Madden-Julian Oscillation (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research: Oceans, 119 (6). pp. 3714-3731.
    Details
    Publication Date: 2018-02-26
    Description: During the CINDY–DYNAMO field campaign of September 2011–January 2012, a Seaglider was deployed at 80°E and completed 10 north-south sections between 3 and 4°S, measuring temperature, salinity, dissolved oxygen concentration, and chlorophyll fluorescence. These high-resolution subsurface observations provide insight into equatorial ocean Rossby wave activity forced by three Madden-Julian Oscillation (MJO) events during this time period. These Rossby waves generate variability in temperature O(1°C), salinity O(0.2 g kg−1), density O(0.2 kg m−3), and oxygen concentration O(10 μmol kg−1), associated with 10 m vertical displacements of the thermocline. The variability extends down to 1000 m, the greatest depth of the Seaglider observations, highlighting the importance of surface forcing for the deep equatorial ocean. The temperature variability observed by the Seaglider is greater than that simulated in the ECCO-JPL reanalysis, especially at depth. There is also marked variability in chlorophyll fluorescence at the surface and at the depth of the chlorophyll maximum. Upwelling from Rossby waves and local wind stress curl leads to an enhanced shoaling of the chlorophyll maximum by 10–25 m in response to the increased availability of nutrients and light. This influence of the MJO on primary production via equatorial ocean Rossby waves has not previously been recognized.
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    Western Pacific atmospheric nutrient deposition fluxes, their impact on surface ocean productivity (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Global Biogeochemical Cycles, 28 (7). pp. 712-728.
    Details
    Publication Date: 2018-02-27
    Description: The atmospheric deposition of both macronutrients and micronutrients plays an important role in driving primary productivity, particularly in the low-latitude ocean. We report aerosol major ion measurements for five ship-based sampling campaigns in the western Pacific from similar to 25 degrees N to 20 degrees S and compare the results with those from Atlantic meridional transects (similar to 50 degrees N to 50 degrees S) with aerosols collected and analyzed in the same laboratory, allowing full incomparability. We discuss sources of the main nutrient species (nitrogen (N), phosphorus (P), and iron (Fe)) in the aerosols and their stoichiometry. Striking north-south gradients are evident over both basins with the Northern Hemisphere more impacted by terrestrial dust sources and anthropogenic emissions and the North Atlantic apparently more impacted than the North Pacific. We estimate the atmospheric supply rates of these nutrients and the potential impact of the atmospheric deposition on the tropical western Pacific. Our results suggest that the atmospheric deposition is P deficient relative to the needs of the resident phytoplankton. These findings suggest that atmospheric supply of N, Fe, and P increases primary productivity utilizing some of the residual excess phosphorus (P*) in the surface waters to compensate for aerosol P deficiency. Regional primary productivity is further enhanced via the stimulation of nitrogen fixation fuelled by the residual atmospheric iron and P*. Our stoichiometric calculations reveal that a P* of 0.1 mu mol L-1 can offset the P deficiency in atmospheric supply for many months. This study suggests that atmospheric deposition may sustain similar to 10% of primary production in both the western tropical Pacific.
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    Stable isotopic evidence for Middle Pleistocene environmental change from a loess-paleosol sequence: Kärlich, Germany (2014)
    Wiley
    In:  Boreas, 43 (4). pp. 818-833.
    Details
    Publication Date: 2018-06-08
    Description: Loess-paleosol sequences are important terrestrial archives of palaeoenvironmental change. Such sequences are rich in pedogenic carbonate, the oxygen and carbon isotopic values of which can provide important palaeoenvironmental information. Although some studies have pioneered the use of O and C isotopes in loess-paleosol sequences, they are not routinely used as palaeoclimate proxies. In this study we analysed the sedimentology, micromorphology, geochronology and isotopic geochemistry of a Middle Pleistocene loess-paleosol section, located at Kärlich, Germany. The section studied correlates with the Elsterian glacial (MIS 12) and Holsteinian interglacial (MIS 11). Embedded tephra layers yielded 40Ar/39Ar ages of 466±3 ka, 447±1 ka and 361±3 ka. The sedimentology and micromorphology of the sequence record a shift from accretionary loess accumulation (MIS 12) to prolonged pedogenesis at a stable land surface (MIS 11). Soil carbonate δ18O values record an enrichment of ∼3‰ during the accumulation of the loess, reaching peak values comparable with those found in the MIS 11 soil. The δ18O signal is interpreted as reflecting temperature, highlighting the potential of δ18O analysis of European loess soil carbonates as a means of reconstructing palaeotemperature history.
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    Anthropogenic hybridization between endangered migratory and commercially harvested stationary whitefish taxa (Coregonus spp.) (2014)
    Wiley
    In:  Evolutionary Applications, 7 (9). pp. 1068-1083.
    Details
    Publication Date: 2020-10-26
    Description: Natural hybridization plays a key role in the process of speciation. However, anthropogenic (human induced) hybridization of historically isolated taxa raises conservation issues. Due to weak barriers to gene flow and the presence of endangered taxa, the whitefish species complex is an excellent study system to investigate the consequences of hybridization in conservation. We focused on three naturally reproductively isolated whitefish taxa in Germany: the endangered, anadromous North Sea houting (NSH) and Baltic houting (BH), which were reintroduced after local extinction, and the commercially stocked European whitefish (EW). To evaluate the genetic integrity of each taxon, source and reintroduced populations of NSH and BH, and EW populations were characterized based on two mitochondrial and 17 microsatellite loci. Additionally, we investigated gill raker counts as an adaptive phenotypic trait. Even though clear genetic and phenotypic differentiation confirmed the houtings as separate evolutionarily significant units, admixture analyses revealed an extensive hybrid zone. Hybridizations were introgressive, positively correlated with genetic diversity, and were reflected in the gill raker counts. The BH distribution range showed higher heterogeneity and stronger admixture than the NSH range. Erroneous stocking with non-native genotypes best explained these patterns, which pose challenges for the conservation of the endangered NSH and BH.
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  • 78
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    Regional-scale input of dispersed and discrete volcanic ash to the Izu-Bonin and Mariana subduction zones (2014)
    Wiley
    In:  Geochemistry, Geophysics, Geosystems, 15 (11). pp. 4369-4379.
    Details
    Publication Date: 2018-02-27
    Description: We have geochemically and statistically characterized bulk marine sediment and ash layers at Ocean Drilling Program Site 1149 (Izu-Bonin Arc) and Deep Sea Drilling Project Site 52 (Mariana Arc), and have quantified that multiple dispersed ash sources collectively comprise ~30-35% of the hemipelagic sediment mass entering the Izu-Bonin-Mariana subduction system. Multivariate statistical analyses indicate that the bulk sediment at Site 1149 is a mixture of Chinese Loess, a second compositionally distinct eolian source, a dispersed mafic ash, and a dispersed felsic ash. We interpret the source of these ashes as respectively being basalt from the Izu-Bonin Front Arc (IBFA) and rhyolite from the Honshu Arc. Sr-, Nd-, and Pb isotopic analyses of the bulk sediment are consistent with the chemical/statistical-based interpretations. Comparison of the mass accumulation rate of the dispersed ash component to discrete ash layer parameters (thickness, sedimentation rate, and number of layers) suggests that eruption frequency, rather than eruption size, drives the dispersed ash record. At Site 52, the geochemistry and statistical modeling indicates that Chinese Loess, IBFA, dispersed BNN (boninite from Izu-Bonin), and a dispersed felsic ash of unknown origin are the sources. At Site 1149 the ash layers and the dispersed ash are compositionally coupled, whereas at Site 52 they are decoupled in that there are no boninite layers, yet boninite is dispersed within the sediment. Changes in the volcanic and eolian inputs through time indicate strong arc- and climate-related controls.
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  • 79
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    Effects of ocean acidification on the biogenic composition of the sea-surface microlayer: Results from a mesocosm study (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research: Oceans, 119 (11). pp. 7911-7924.
    Details
    Publication Date: 2019-09-23
    Description: The sea-surface microlayer (SML) is the ocean's uppermost boundary to the atmosphere and in control of climate relevant processes like gas exchange and emission of marine primary organic aerosols (POA). The SML represents a complex surface film including organic components like polysaccharides, proteins, and marine gel particles, and harbors diverse microbial communities. Despite the potential relevance of the SML in ocean-atmosphere interactions, still little is known about its structural characteristics and sensitivity to a changing environment such as increased oceanic uptake of anthropogenic CO2. Here we report results of a large-scale mesocosm study, indicating that ocean acidification can affect the abundance and activity of microorganisms during phytoplankton blooms, resulting in changes in composition and dynamics of organic matter in the SML. Our results reveal a potential coupling between anthropogenic CO2 emissions and the biogenic properties of the SML, pointing to a hitherto disregarded feedback process between ocean and atmosphere under climate change.
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  • 80
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    A Bayesian approach for estimating length-weight relationships in fishes (2014)
    Wiley
    In:  Journal of Applied Ichthyology, 30 (1). pp. 78-85.
    Details
    Publication Date: 2019-09-23
    Description: A Bayesian hierarchical approach is presented for the estimation of length-weight relationships (LWR) in fishes. In particular, estimates are provided for the LWR parameters a and b in general as well as by body shape. These priors and existing LWR studies were used to derive species-specific LWR parameters. In the cases of data-poor species, the analysis includes LWR studies of closely related species with the same body shape. This approach yielded LWR parameter estimates with measures of uncertainty for practically all known 32 000 species of fishes. Provided is a 3 large LWR data set extracted from www.fishbase.org, the source code of the respective analyses, and ready-to-use tools for practitioners. This is presented as an example of a self-learning online database where the addition of new studies improves the species-specific parameter estimates, and where these parameter estimates inform the analysis of new data.
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  • 81
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    Escapement success of silver eels from a German river system is low compared to management-based estimates (2014)
    Wiley
    In:  Freshwater Biology, 59 (1). pp. 64-72.
    Details
    Publication Date: 2019-09-23
    Description: The European eel (Anguilla anguilla) stock experienced a sharp decline during the last decades and is suffering from massive anthropogenic impacts on inland waters. To evaluate the benefit of management measures and to better understand the contribution of single drainage systems to spawner production, knowledge of the respective silver eel escapement is required. Furthermore, a better understanding of environmental conditions that potentially trigger the onset of spawning migration is needed to reduce anthropogenic mortalities during riverine eel migration. Investigations are also necessary to clarify whether fish protecting devices and bypasses at barriers are functional and truly increase eel survival and escapement rates. In this study, total female silver eel escapement from a northern German drainage system (Schwentine River) was assessed over a period of three consecutive years, and downstream migration patterns were compared to potential environmental triggers. Furthermore, the benefit of two fish bypasses (surface and deep) and a trash rack at the hydropower station for the survival of migrating eels was examined, and the spawner quality of escaping silver eels was determined by analysing lipid content and infection intensities with the swimbladder parasite Anguillicoloides crassus. The results indicate that silver eel escapement from the Schwentine drainage system is far below the estimated values underlying the respective eel management plan, highlighting the necessity of direct migration assessments to validate indirect estimations that include multiple assumptions and uncertainties. Major downstream migration events took place during short time periods in autumn and appear to be influenced by river discharge and water temperatures, suggesting that a precise prediction of escapement events is possible. Regarding spawner quality, fat reserves appear sufficient for escaping silver eels to migrate and spawn. However, high A. crassus prevalence and infection intensities are assumed to further reduce the number of potential spawners. Another matter of concern is the high trash rack mortality at the hydropower station that illustrates the need of fish protecting devices that fulfil eel-specific requirements.
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  • 82
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    Community composition has greater impact on the functioning of marine phytoplankton communities than ocean acidification (2014)
    Wiley
    In:  Global Change Biology, 20 (3). pp. 713-723.
    Details
    Publication Date: 2018-05-17
    Description: Ecosystem functioning is simultaneously affected by changes in community composition and environmental change such as increasing atmospheric carbon dioxide (CO2) and subsequent ocean acidification. However, it largely remains uncertain how the effects of these factors compare to each other. Addressing this question, we experimentally tested the hypothesis that initial community composition and elevated CO2 are equally important to the regulation of phytoplankton biomass. We full-factorially exposed three compositionally different marine phytoplankton communities to two different CO2 levels and examined the effects and relative importance (ω2) of the two factors and their interaction on phytoplankton biomass at bloom peak. The results showed that initial community composition had a significantly greater impact than elevated CO2 on phytoplankton biomass, which varied largely among communities. We suggest that the different initial ratios between cyanobacteria, diatoms, and dinoflagellates might be the key for the varying competitive and thus functional outcome among communities. Furthermore, the results showed that depending on initial community composition elevated CO2 selected for larger sized diatoms, which led to increased total phytoplankton biomass. Our study highlights the relevance of initial community composition, which strongly drives the functional outcome, when assessing impacts of climate change on ecosystem functioning. In particular, the increase in phytoplankton biomass driven by the gain of larger sized diatoms in response to elevated CO2 potentially has strong implications for nutrient cycling and carbon export in future oceans.
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  • 83
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    On the spatial and temporal distribution of near-inertial energy in the Southern Ocean (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research: Oceans, 119 (1). pp. 359-376.
    Details
    Publication Date: 2019-09-23
    Description: We use an eddying realistic primitive equation model of the Southern Ocean to examine the spatial and temporal distribution of near-inertial wind-power input (WPI) and near-inertial energy (NIE) in the Southern Ocean. We find that the modelled near-inertial WPI is almost proportional to inertial wind-stress variance (IWSV), while the modelled NIE is modulated by the inverse of the mixed-layer depth. We go on to assess recent decadal trends of near-inertial WPI from trends of IWSV based on reanalysis wind-stress. Averaged over the Southern Ocean, annual-mean IWSV is found to have increased by 16 percent over the years 1979 through 2011. Part of the increase of IWSV is found to be related to the positive trend of the Southern Annular Mode over the same period. Finally, we show that there are horizontal local maxima of NIE at depth that are almost exclusively associated with anticyclonic eddies.
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  • 84
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    Crustal thinning in the northern Tyrrhenian Rift: Insights from multichannel and wide-angle seismic data across the basin (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research: Solid Earth, 119 . pp. 1655-1677.
    Details
    Publication Date: 2018-02-27
    Description: Extension of the continental lithosphere leads to the formation of rift basins or rifted continental margins if breakup occurs. Seismic investigations have repeatedly shown that conjugate margins have asymmetric tectonic structures and different amount of extension and crustal thinning. Here we compare two coincident wide-angle and multichannel seismic profiles across the northern Tyrrhenian rift system sampling crust that underwent different stages of extension from north to south and from the flanks to the basin center. Tomographic inversion reveals that the crust has thinned homogeneously from ~24 km to ~17 km between the Corsica Margin and the Latium Margin implying a β factor of ~1.3–1.5. On the transect 80 km to the south, the crust thinned from ~24 km beneath Sardinia to a maximum of ~11 km in the eastern region near the Campania Margin (β factor of ~2.2). The increased crustal thinning is accompanied by a zone of reduced velocities in the upper crust that expands progressively toward the southeast. We interpret that the velocity reduction is related to rock fracturing caused by a higher degree of brittle faulting, as observed on multichannel seismic images. Locally, basalt flows are imaged intruding sediment in this zone, and heat flow values locally exceed 100 mW/m2. Velocities within the entire crust range 4.0–6.7 km/s, which are typical for continental rocks and indicate that significant rift-related magmatic underplating may not be present. The characteristics of the pre-tectonic, syn-tectonic and post-tectonic sedimentary units allow us to infer the spatial and temporal evolution of active rifting. In the western part of the southern transect, thick postrift sediments were deposited in half grabens that are bounded by large fault blocks. Fault spacing and block size diminish to the east as crustal thinning increases. Recent tectonic activity is expressed by faults cutting the seafloor in the east, near the mainland of Italy. The two transects show the evolution from the less extended rift in the north with a fairly symmetric conjugate structure to the asymmetric margins farther south. This structural evolution is consistent with W-E rift propagation and southward increasing extension rates.
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  • 85
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    Seasonal variability of methyl iodide in the Kiel Fjord (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research: Oceans, 119 (3). pp. 1609-1620.
    Details
    Publication Date: 2019-09-23
    Description: From October 2008 to November 2010, CH3I concentrations were measured in the Kiel Fjord together with potentially related biogeochemical and physical parameters. A repeating seasonal cycle of CH3I was observed with highest concentrations in summer (ca. 8.3 pmol L−1; June and July) and lowest concentrations in winter (ca. 1.5 pmol L−1; December to February). A strong positive correlation at zero lag between [CH3I] and solar radiation (R2 = 0.93) was observed, whereas correlations with other variables (SST, Chlorophyll a) were weaker, and they lagged CH3I by ca. 1 month. These results appear consistent with the hypothesis that SSR is the primary forcing of CH3I production in surface seawater, possibly through a photochemical pathway. A mass balance of the monthly averaged data was used to infer mean rates of daily net production (Pnet) and losses for CH3I over the year. The sea-to-air flux of CH3I in the Kiel Fjord averaged 3.1 nmol m−2 d−1, the mean chemical loss rate was 0.047 pmol L−1 d−1, and Pnet varied systematically from winter to summer (from 0 to 0.6 pmol L−1 d−1). Pnet was correlated at zero lag with SST, SSR, and Chla (R2 = 0.55, 0.67, and 0.73, respectively, p 〈〈 0.01). The lagged cross-correlation analysis indicated that SSR led Pnet by 1 month, whereas the strongest cross correlations with Chla were at lags of 0 to +1 month, and SST lagged Pnet by 1 month. The broad seasonal peak of Pnet makes it difficult to determine the key factor controlling CH3I net production using in situ concentration data alone.
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  • 86
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    Interplate seismicity at the CRISP drilling site: The 2002 Mw=6.4 Osa Earthquake at the southeastern end of the Middle America Trench (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Geochemistry, Geophysics, Geosystems, 15 (7). pp. 3035-3050.
    Details
    Publication Date: 2018-02-28
    Description: We investigate potential relations between variations in seafloor relief and age of the incoming plate and interplate seismicity. Westward from Osa Peninsula in Costa Rica, a major change in the character of the incoming Cocos Plate is displayed by abrupt lateral variations in seafloor depth and thermal structure. Here a Mw 6.4 thrust earthquake was followed by three aftershock clusters in June 2002. Initial relocations indicate that the main shock occurred fairly trenchward of most large earthquakes along the Middle America Trench off central Costa Rica. The earthquake sequence occurred while a temporary network of OBH and land stations ∼80 km to the northwest were deployed. By adding readings from permanent local stations, we obtain uncommon P wave coverage of a large subduction zone earthquake. We relocate this catalog using a nonlinear probabilistic approach within both, a 1-D and a 3-D P wave velocity models. The main shock occurred ∼25 km from the trench and probably along the plate interface at 5–10 km depth. We analyze teleseismic data to further constrain the rupture process of the main shock. The best depth estimates indicate that most of the seismic energy was radiated at shallow depth below the continental slope, supporting the nucleation of the Osa earthquake at ∼6 km depth. The location and depth coincide with the plate boundary imaged in prestack depth-migrated reflection lines shot near the nucleation area. Aftershocks propagated downdip to the area of a 1999 Mw 6.9 sequence and partially overlapped it. The results indicate that underthrusting of the young and buoyant Cocos Ridge has created conditions for interplate seismogenesis shallower and closer to the trench axis than elsewhere along the central Costa Rica margin.
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  • 87
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    Seismic structure of the north-central Chilean convergent margin: Subduction erosion of a paleomagmatic arc (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Geophysical Research Letters, 41 (5). pp. 1523-1529.
    Details
    Publication Date: 2017-04-10
    Description: We study the erosive convergent margin of north-central Chile (at similar to 31 degrees S) by using high-resolution bathymetric, wide-angle refraction, and multichannel seismic reflection data to derive a detailed tomographic 2-D velocity-depth model. In the overriding plate, our velocity model shows that the lowermost crustal velocities beneath the upper continental slope are 6.0-6.5km/s, which are interpreted as the continental basement composed by characteristic metamorphic and igneous rocks of the Coastal Cordillera. Beneath the lower and middle continental slope, however, the presence of a zone of reduced velocities (3.5-5.0km/s) is interpreted as the outermost fore arc composed of volcanic rocks hydrofractured as a result of frontal and basal erosion. At the landward edge of the outermost fore arc, the bathymetric and seismic data provide evidence for the presence of a prominent trenchward dipping normal scarp (similar to 1km offset), which overlies a strong lateral velocity contrast from similar to 5.0 to similar to 6.0km/s. This pronounced velocity contrast propagates deep into the continental crust, and it resembles a major normal listric fault. We interpret this seismic discontinuity as the volcanic-continental basement contact of the submerged Coastal Cordillera characterized by a gravitational collapse of the outermost fore arc. Subduction erosion has, most likely, caused large-scale crustal thinning and long-term subsidence of the outermost fore arc.
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  • 88
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    A conceptual model of community dynamics during the transport stage of the invasion process: a case study of ships’ ballast (2014)
    Wiley
    In:  Diversity and Distributions, 20 (2). pp. 236-244.
    Details
    Publication Date: 2014-12-09
    Description: Aim: After J. L. Lockwood, P. Cassey and T. Blackburn (2009, Diversity and Distributions, 15, 904–910) first described a theoretical relationship between propagule pressure and colonization pressure, two empirical studies demonstrated that the transport stage of the invasion process can profoundly influence the strength of the relationship among multiple events, as well as predictions of introduction risk. However, studies exploring dynamics of transported communities are rare, as repeated-measures sampling during transportation by any vector is logistically difficult. We constructed a conceptual model of community dynamics during transportation and supported it by empirical data for propagule pressure and colonization pressure of plankton. Location: Global. Methods: A conceptual model of community dynamics was developed based on lognormal species abundance distribution and the simulation model of J. L. Lockwood, P. Cassey and T. Blackburn (2009, Diversity and Distributions, 15, 904–910). We considered four cases: case ‘A’ – no reduction in propagule nor colonization pressure; case ‘B’ – strong reduction in propagule and mild reduction in colonization pressure; case ‘C’ – mild reduction in propagule and strong reduction in colonization pressure; and case ‘D’ – strong reduction in both propagule and colonization pressures. Results: The cases ‘B’, ‘C’ and ‘D’ were supported by empirical data for invertebrates, dinoflagellates and diatoms from ships’ ballast tanks, respectively. Propagule pressure of invertebrates, dinoflagellates and diatoms decreased 99.95%, 80% and 94% in 25 days, respectively, while colonization pressure decreased 34%, 57% and 64%. Main conclusions: Transport affects both propagule pressure and colonization pressure of taxa, with the magnitude of change dependent on length of transport and taxon-specific survival and reproduction. Our model demonstrates that introduction risk varies substantially across and within taxa depending on the occurrence and severity of selection pressures during transportation which serve to change species abundance distributions.
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  • 89
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    The influence of natural and anthropogenic factors on major stratospheric sudden warmings (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research: Atmospheres, 119 (13). pp. 8117-8136.
    Details
    Publication Date: 2019-06-28
    Description: Major stratospheric sudden warmings are prominent disturbances of the Northern Hemisphere polar winter stratosphere. Understanding the factors controlling major warmings is required, since the associated circulation changes can propagate down into the troposphere and affect the surface climate, suggesting enhanced prediction skill when these processes are accurately represented in models. In this study we investigate how different natural and anthropogenic factors, namely, the quasi-biennial oscillation (QBO), sea surface temperatures (SSTs), anthropogenic greenhouse gases, and ozone-depleting substances, influence the frequency, variability, and life cycle of major warmings. This is done using sensitivity experiments performed with the National Center for Atmospheric Research's Community Earth System Model (CESM). CESM is able to simulate the life cycle of major warmings realistically. The QBO strengthens the climatological stratospheric polar night jet (PNJ) and significantly reduces the frequency of major warmings through reduction of planetary wave propagation into the PNJ region. Variability in SSTs weakens the PNJ and significantly increases the major warming frequency due to enhanced wave forcing. Even extreme climate change conditions (RCP8.5 scenario) do not influence the total frequency but determine the prewarming phase of major warmings. The amplitude and duration of major warmings seem to be mainly determined by internal stratospheric variability. We also suggest that SST variability, two-way ocean/atmosphere coupling, and hence the memory of the ocean are needed to reproduce the observed tropospheric negative Northern Annular Mode pattern after major warmings.
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  • 90
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    Global patterns of phytoplankton nutrient and light colimitation inferred from an optimality-based model (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Global Biogeochemical Cycles, 28 (7). pp. 648-661.
    Details
    Publication Date: 2019-09-23
    Description: The widely used concept of constant ”Redfield” phytoplankton stoichiometry is often applied for estimating which nutrient limits phytoplankton growth in the surface ocean. Culture experiments, in contrast, show strong relations between growth conditions and cellular stoichiometry with often substantial deviations from Redfield stoichiometry. Here we investigate to what extent both views agree by analyzing remote sensing and in situ data with an optimality-based model of nondiazotrophic phytoplankton growth in order to infer seasonally varying patterns of colimitation by light, nitrogen (N), and phosphorus (P) in the global ocean. Our combined model-data analysis suggests strong N and N-P colimitation in the tropical ocean, seasonal light, and N-P colimitation in the Northern Hemisphere, and strong light limitation only during winter in the Southern Ocean. The eastern equatorial Pacific appears as the only ocean area that is essentially not limited by N, P, or light. Even though our optimality-based approach specifically accounts for flexible stoichiometry, inferred patterns of N and P limitation are to some extent consistent with those obtained from an analysis of surface inorganic nutrients with respect to the Redfield N:P ratio. Iron is not part of our analysis, implying that we cannot accurately predict N cell quotas in high-nutrient, low-chlorophyll regions. Elsewhere, we do not expect a major effect of iron on the relative distribution of N, P, and light colimitation areas. The relative importance of N, P, and light in limiting phytoplankton growth diagnosed here by combining observations and an optimal growth model provides a useful constraint for models used to predict future marine biological production under changing environmental conditions.
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  • 91
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    Quantifying tidally-driven benthic oxygen exchange across permeable sediments: An aquatic eddy correlation study (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research: Oceans, 119 (10). pp. 6918-6932.
    Details
    Publication Date: 2018-02-26
    Description: Continental shelves are predominately (~70%) covered with permeable, sandy sediments. While identified as critical sites for intense oxygen, carbon, and nutrient turnover, constituent exchange across permeable sediments remains poorly quantified. The central North Sea largely consists of permeable sediments and has been identified as increasingly at risk for developing hypoxia. Therefore, we investigate the benthic O2 exchange across the permeable North Sea sediments using a combination of in situ microprofiles, a benthic chamber, and aquatic eddy correlation. Tidal bottom currents drive the variable sediment O2 penetration depth (from ~3 to 8 mm) and the concurrent turbulence-driven 25-fold variation in the benthic sediment O2 uptake. The O2 flux and variability were reproduced using a simple 1-D model linking the benthic turbulence to the sediment pore water exchange. The high O2 flux variability results from deeper sediment O2 penetration depths and increased O2 storage during high velocities, which is then utilized during low-flow periods. The study reveals that the benthic hydrodynamics, sediment permeability, and pore water redox oscillations are all intimately linked and crucial parameters determining the oxygen availability. These parameters must all be considered when evaluating mineralization pathways of organic matter and nutrients in permeable sediments.
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  • 92
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    AssessingSymbiodiniumdiversity in scleractinian corals via next-generation sequencing-based genotyping of the ITS2 rDNA region (2014)
    Wiley
    In:  Molecular Ecology, 23 (17). pp. 4418-4433.
    Details
    Publication Date: 2019-09-23
    Description: The persistence of coral reef ecosystems relies on the symbiotic relationship between scleractinian corals and intracellular, photosynthetic dinoflagellates in the genus Symbiodinium. Genetic evidence indicates that these symbionts are biologically diverse and exhibit discrete patterns of environmental and host distribution. This makes the assessment of Symbiodinium diversity critical to understanding the symbiosis ecology of corals. Here, we applied pyrosequencing to the elucidation of Symbiodinium diversity via analysis of the internal transcribed spacer 2 (ITS2) region, a multicopy genetic marker commonly used to analyse Symbiodinium diversity. Replicated data generated from isoclonal Symbiodinium cultures showed that all genomes contained numerous, yet mostly rare, ITS2 sequence variants. Pyrosequencing data were consistent with more traditional denaturing gradient gel electrophoresis (DGGE) approaches to the screening of ITS2 PCR amplifications, where the most common sequences appeared as the most intense bands. Further, we developed an operational taxonomic unit (OTU)-based pipeline for Symbiodinium ITS2 diversity typing to provisionally resolve ecologically discrete entities from intragenomic variation. A genetic distance cut-off of 0.03 collapsed intragenomic ITS2 variants of isoclonal cultures into single OTUs. When applied to the analysis of field-collected coral samples, our analyses confirm that much of the commonly observed Symbiodinium ITS2 diversity can be attributed to intragenomic variation. We conclude that by analysing Symbiodinium populations in an OTU-based framework, we can improve objectivity, comparability and simplicity when assessing ITS2 diversity in field-based studies.
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  • 93
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    Potential of full pattern fit methods for the texture analysis of geological materials: implications from texture measurements at the recently upgraded neutron time-of-flight diffractometer SKAT (2014)
    Wiley
    In:  Journal of Applied Crystallography, 47 (5). pp. 1520-1534.
    Details
    Publication Date: 2018-06-08
    Description: The application of Rietveld texture analysis (RTA) to time-of-flight (TOF) neutron diffraction data allows complex materials with many diffraction peaks to be investigated, for example, rocks composed of different minerals. At the recently upgraded SKAT texture diffractometer at the JINR in Dubna (Russia), which provides three alternative multidetector systems, resolution and accessible range of lattice d spacings can be adapted to sample requirements. In order to infer the optimum experimental setup and the reliability of texture estimates from complicated TOF patterns, the influence of counting statistics and various spectral resolutions on texture deconvolution was investigated. Comparing the results obtained at different resolutions and from different sections of the d patterns indicates that the textures of a four-phase sample can be determined, but using a section at small d spacings with a larger number of peak overlaps leads to smoother textures. A complex seven-phase sample shows orientation differences in addition to the smoothing effect. Weak textures and textures of the minor rock constituents are inaccurate owing to multiple peak overlaps. Consequently, good resolution is essential for RTA on such samples. Grid thinning tests confirmed that no more than 150 diffraction spectra are needed to characterize the texture of a monomineralic sample, and approximately 350 spectra are sufficient for a four-phase sample. The irregular grid point arrangement caused by the SKAT geometry has no negative consequences.
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  • 94
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    Major role of the equatorial current system in setting oxygen levels in the eastern tropical Atlantic Ocean: a high-resolution model study (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Geophysical Research Letters, 41 . pp. 2033-2040.
    Details
    Publication Date: 2019-09-23
    Description: Understanding the causes of the observed expansion of tropical ocean's oxygen minimum zones (OMZs) is hampered by large biases in the representation of oxygen distribution in climate models, pointing to incorrectly represented mechanisms. Here we assess the oxygen budget in a global biogeochemical circulation model, focusing on the Atlantic Ocean. While a coarse (0.5°) configuration displays the common bias of too large and too intense OMZs, the oxygen concentration in an eddying (0.1°) configuration is higher and closer to observations. This improvement is traced to a stronger oxygen supply by a more realistic representation of the equatorial and off-equatorial undercurrents, outweighing the concurrent increase in oxygen consumption associated with the stronger nutrient supply. The sensitivity of the eastern tropical Atlantic oxygen budget to the equatorial current intensity suggests that temporal changes in the eastward oxygen transport from the well-oxygenated western boundary region might partly explain variations in the OMZs.
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  • 95
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    Seismic structure of the Central Tyrrhenian basin: Geophysical constraints on the nature of the main crustal domains (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research: Solid Earth, 119 (1). pp. 52-70.
    Details
    Publication Date: 2018-02-27
    Description: In this work we investigate the crustal and tectonic structures of the Central Tyrrhenian back-arc basin combining refraction and wide-angle reflection seismic (WAS), gravity, and multichannel seismic (MCS) reflection data, acquired during the MEDOC (MEDiterráneo OCcidental)-2010 survey along a transect crossing the entire basin from Sardinia to Campania at 40°N. The results presented include a ~450 km long 2-D P wave velocity model, obtained by the traveltime inversion of the WAS data, a coincident density model, and a MCS poststack time-migrated profile. We interpret three basement domains with different petrological affinity along the transect based on the comparison of velocity and velocity-derived density models with existing compilations for continental crust, oceanic crust, and exhumed mantle. The first domain includes the continental crust of Sardinia and the conjugate Campania margin. In the Sardinia margin, extension has thinned the crust from ~20 km under the coastline to ~13 km ~60 km seaward. Similarly, the Campania margin is also affected by strong extensional deformation. The second domain, under the Cornaglia Terrace and its conjugate Campania Terrace, appears to be oceanic in nature. However, it shows differences with respect to the reference Atlantic oceanic crust and agrees with that generated in back-arc oceanic settings. The velocities-depth relationships and lack of Moho reflections in seismic records of the third domain (i.e., the Magnaghi and Vavilov basins) support a basement fundamentally made of mantle rocks. The large seamounts of the third domain (e.g., Vavilov) are underlain by 10–20 km wide, relatively low-velocity anomalies interpreted as magmatic bodies locally intruding the mantle.
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    P and S wave velocity measurements of water-rich sediments from the Nankai Trough, Japan (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research: Solid Earth, 119 (2). pp. 787-805.
    Details
    Publication Date: 2018-02-27
    Description: Acoustic velocities were measured during triaxial deformation tests of silty clay and clayey silt core samples from the Nankai subduction zone (Integrated Ocean Drilling Program Expeditions 315, 316, and 333). We provide a new data set, continuously measured during pressure increase and subsequent axial deformation. A new data processing method was developed using seismic time series analysis. Compressional wave velocities (V-p) range between about 1450 and 2200 m/s, and shear wave velocities (V-s) range between about 150 and 800 m/s. V-p slightly increases with rising effective confining pressure and effective axial stress. Samples from the accretionary prism toe show the highest Vp, while fore-arc slope sediments show lower Vp. Samples from the incoming plate, slightly richer in clay minerals, have the lowest values for V-p. V-s increases with higher effective confining pressures and effective axial stress, irrespective of composition and tectonic setting. Shear and bulk moduli are between 0.2 and 1.3 GPa, and 3.85 and 8.41 GPa, respectively. Elastic moduli of samples from the accretionary prism toe and the footwall of the megasplay fault (1.50 and 3.98 GPa) are higher than those from the hanging wall and incoming plate (0.59 and 0.88 GPa). This allows differentiation between normal and overconsolidated sediments. The data show that in a tectonosedimentary environment of only subtle compositional differences, acoustic properties can be used to differentiate between stronger (accretionary prism toe) and weaker (fore-arc slope, incoming plate) sediments. Especially V-p/V-s ratios may be instrumental in detecting zones of low effective stress and thus high pore fluid pressure
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    The seawater neodymium and lead isotope record of the final stages of Central American Seaway closure (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Paleoceanography, 29 (7). pp. 715-729.
    Details
    Publication Date: 2019-09-23
    Description: Key Points: Seawater Nd and Pb isotope records for the Pliocene Caribbean and EEP Caribbean Nd isotope composition became more UNADW-like during the Pliocene Short term changes support link between CAS closure and strength of AMOC The shoaling and final closure of the Central American Seaway (CAS) resulted in a major change of the global ocean circulation and has been suggested as an essential driver for strengthening of Atlantic Meridional Overturning Circulation (AMOC). The exact timing of CAS closure is key to interpreting its importance. Here we present a reconstruction of deep and intermediate water Nd and Pb isotope compositions obtained from fossil fish teeth and the authigenic coatings of planktonic foraminifera in the eastern equatorial Pacific (ODP Site 1241) and the Caribbean (ODP Sites 998, 999 and 1000) covering the final stages of CAS closure between 5.6 and 2.2 Ma. The data for the Pacific site indicate no significant Atlantic/Caribbean influence over this entire period. The Caribbean sites show a continuous trend to less radiogenic Nd isotope compositions during the Pliocene, consistent with an enhancement of Upper North Atlantic Deep Water (UNADW) inflow and a strengthening of the AMOC. Superimposed onto this long-term trend, shorter-term changes of intermediate Caribbean Nd isotope signatures approached more UNADW-like values during intervals when published reconstructions of seawater salinity suggested complete closure of the CAS. The data imply that significant deep water exchange with the Pacific essentially stopped by 7 Ma and that shallow exchange, which still occurred at least periodically until approximately 2.5 Ma, may have been linked to the strength of the AMOC but did not have any direct effect on the intermediate and deep Caribbean Nd isotope signatures through mixing with Pacific waters.
    Type: Article , PeerReviewed
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    Observations of Stratospheric Sudden Warmings in Earth Rotation Variations (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research: Atmospheres, 119 (16). pp. 9666-9678.
    Details
    Publication Date: 2018-02-06
    Description: Stratospheric sudden warmings (SSWs) are extreme events in the polar stratosphere that are both caused by and have effects on the tropospheric flow. This means that SSWs are associated with changes in the angular momentum of the atmosphere, both before and after their onset. Because these angular momentum changes are transferred to the solid Earth, they can be observed in the rate of the Earth's rotation and the wobble of its rotational pole. By comparing observed Earth rotation variations to reanalysis data, we find that an anomaly in the orientation of the Earth's rotational pole, up to 4 times as large as the annual polar wobble, typically precedes SSWs by 20-40 days. The polar motion signal is due to pressure anomalies that are typically seen before SSW events and represents a new type of observable that may aid in the prediction of SSWs. A decline in the length of day is also seen, on average, near the time of the SSW wind reversal and is found to be due to anomalous easterly winds generated in the tropical troposphere around this time, though the structure and timing of this signal seems to vary widely from event to event.
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    The SPARC Data Initiative: Comparison of upper troposphere/lower stratosphere ozone climatologies from limb-viewing instruments and the nadir-viewing Tropospheric Emission Spectrometer (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research: Atmospheres, 119 (11). pp. 6971-6990.
    Details
    Publication Date: 2018-02-06
    Description: We present the first comprehensive intercomparison of currently available satellite ozone climatologies in the upper troposphere/lower stratosphere (UTLS) (300-70hPa) as part of the Stratosphere-troposphere Processes and their Role in Climate (SPARC) Data Initiative. The Tropospheric Emission Spectrometer (TES) instrument is the only nadir-viewing instrument in this initiative, as well as the only instrument with a focus on tropospheric composition. We apply the TES observational operator to ozone climatologies from the more highly vertically resolved limb-viewing instruments. This minimizes the impact of differences in vertical resolution among the instruments and allows identification of systematic differences in the large-scale structure and variability of UTLS ozone. We find that the climatologies from most of the limb-viewing instruments show positive differences (ranging from 5 to 75%) with respect to TES in the tropical UTLS, and comparison to a zonal mean ozonesonde climatology indicates that these differences likely represent a positive bias for p100hPa. In the extratropics, there is good agreement among the climatologies regarding the timing and magnitude of the ozone seasonal cycle (differences in the peak-to-peak amplitude of 〈15%) when the TES observational operator is applied, as well as very consistent midlatitude interannual variability. The discrepancies in ozone temporal variability are larger in the tropics, with differences between the data sets of up to 55% in the seasonal cycle amplitude. However, the differences among the climatologies are everywhere much smaller than the range produced by current chemistry-climate models, indicating that the multiple-instrument ensemble is useful for quantitatively evaluating these models.
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    Biology of Green Sulfur Bacteria (2014)
    Wiley
    In:  In: eLS (Encyclopedia of Life Sciences). Wiley, Chichester, UK, ..
    Details
    Publication Date: 2017-03-22
    Description: Abstract: Green sulfur bacteria have gained much attention because of a number of highly interesting features including unique structures of the photosynthetic apparatus and the presence of chlorosomes as very powerful light antenna that can capture minute amounts of light. This has important ecological consequences, because the efficient light-harvesting determines the ecological niche of these bacteria at the lowermost part of stratified environments where the least of light is available. Furthermore, the strict dependency on photosynthesis to provide energy for growth and the obligate phototrophy of green sulfur bacteria together with their characteristic sulfur metabolism have provoked much interest in their physiology, ecology and genomics. The oxidation of sulfide as their outmost important photosynthetic electron donor involves the deposition of elemental sulfur globules outside the cells and separates the process of sulfide oxidation to sulfate into two parts. This is the basis for stable syntrophic associations between green sulfur bacteria and sulfur- and sulfate-reducing bacteria in which the sulfur compounds are recycled. The green sulfur bacteria are distantly related to other bacteria and represent the phylum Chlorobi, though the known representatives are taxonomically treated as Chlorobiaceae with the genera Chlorobium, Chlorobaculum, Prosthecochloris and Chloroherpeton. Key Concepts: Green sulfur bacteria depend on light for life due to their obligate phototrophic metabolism. Green sulfur bacteria perform a highly efficient photosynthesis due to the presence of light harvesting organelles, the chlorosomes, which are filled with special bacteriochlorophyll molecules. Green sulfur bacteria inhabit the lowermost part of the photic environments due to their efficient light capture. Green sulfur bacteria inhabit the lowermost part of the chemocline in the stratified environment due to their sensitivity to oxygen, their high sulfide tolerance and their dependence in light. Green sulfur bacteria are important drivers of oxidation of reduced sulfur compounds in the stratified, sulfide-containing environment receiving low irradiation.
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