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  • 1
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    Royal Society of London
    In:  Proceedings of the Royal Society B: Biological Sciences, 285 (1885). p. 20181203.
    Publication Date: 2019-04-05
    Description: Ocean plastic pollution has resulted in a substantial accumulation of microplastics in the marine environment. Today, this plastic litter is ubiquitous in the oceans, including even remote habitats such as deep-sea sediments and polar sea ice, and it is believed to pose a threat to ecosystem health. However, the concentration of microplastics in the surface layer of the oceans is considerably lower than expected, given the ongoing replenishment of microplastics and the tendency of many plastic types to float. It has been hypothesized that microplastics leave the upper ocean by aggregation and subsequent sedimentation. We tested this hypothesis by investigating the interactions of microplastics with marine biogenic particles collected in the southwestern Baltic Sea. Our laboratory experiments revealed a large potential of microplastics to rapidly coagulate with biogenic particles, which substantiates this hypothesis. Together with the biogenic particles, the microplastics efficiently formed pronounced aggregates within a few days. The aggregation of microplastics and biogenic particles was significantly accelerated by microbial biofilms that had formed on the plastic surfaces. We assume that the demonstrated aggregation behaviour facilitates the export of microplastics from the surface layer of the oceans and plays an important role in the redistribution of microplastics in the oceans.
    Type: Article , PeerReviewed
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  • 2
    Publication Date: 2019-01-08
    Description: A central aspect of coastal biogeochemistry is to determine how nutrients, lithogenic- and organic matter are distributed and transformed within coastal and estuarine environments. Analyses of the spatio-temporal changes of total suspended matter (TSM) concentration indicate strong and variable linkages between intertidal fringes and pelagic regions. In particular, knowledge about the organic fraction of TSM provides insight to how biogenic and lithogenic particulate matter are distributed in suspension. In our study we take advantage of a set of over 3000 in situ Loss on Ignition (LoI) data from the Southern North Sea that represent fractions of particulate organic matter (POM) relative to TSM (LoI $\equiv$ POM:TSM). We introduce a parameterization (POM-TSM model) that distinguishes between two POM fractions incorporated in TSM. One fraction is described in association with mineral particles. The other represents a seasonally varying fresh pool of POM. The performance of the POM-TSM model is tested against data derived from MERIS/ENVISAT-TSM products of the German Bight. Our analysis of remote sensing data exhibits specific qualitative features of TSM that can be attributed to distinct coastal zones. Most interestingly, a transition zone between the Wadden Sea and seasonally stratified regions of the Southern North Sea is identified where mineral associated POM appears in concentrations comparable to those of freshly produced POM. We will discuss how this transition is indicative for a zone of effective particle interaction and sedimentation.The dimension of this transition zone varies between seasons and with location. Our proposed POM-TSM model is generic and can be calibrated against in situ data of other coastal regions.
    Type: Article , PeerReviewed
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  • 3
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    PANGAEA
    In:  Supplement to: Slavik, Kaela; Lemmen, Carsten; Zhang, Wenyan; Kerimoglu, Onur; Klingbeil, Knut; Wirtz, Kai W (accepted): The large scale impact of offshore windfarm structures on pelagic primary productivity in the southern North Sea. Hydrobiologia, https://doi.org/10.1007/s10750-018-3653-5
    Publication Date: 2018-12-01
    Description: The increasing demand for renewable energy is projected to result in a 40-fold increase in offshore wind electricity in the European Union by 2030. Despite a great number of local impact studies for selected marine populations, the regional ecosystem impacts of offshore wind farm structures are not yet well assessed nor understood. The study resulting from this dataset investigates whether the accumulation of epifauna, dominated by the filter feeder Mytilus edulis (blue mussel), on turbine structures affects pelagic primary production in the southern North Sea.
    Type: Dataset
    Format: application/zip, 816.0 kBytes
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  • 4
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    PANGAEA
    In:  Supplement to: Lemmen, Carsten; Wirtz, Kai W (2014): On the sensitivity of the simulated European Neolithic transition to climate extremes. Journal of Archaeological Science, 51, 65-72, https://doi.org/10.1016/j.jas.2012.10.023
    Publication Date: 2019-02-12
    Description: Was the spread of agropastoralism from the Fertile Crescent throughout Europe influenced by rapid climatic shifts? We here generate idealized climate events using palaeoclimate records. In a mathematical model of regional sociocultural development, these events disturb the subsistence base of simulated forager and farmer societies. We evaluate the regional simulated transition timings and durations against a published large set of radiocarbon dates for western Eurasia; the model is able to realistically hindcast much of the inhomogeneous space-time evolution of regional Neolithic transitions. Our study shows that the inclusion of climate events improves the simulation of typical lags between cultural complexes, but that the overall difference to a model without climate events is not significant. Climate events may not have been as important for early sociocultural dynamics as endogenous factors.
    Type: Dataset
    Format: application/x-gzip, 681.0 kBytes
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  • 5
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    PANGAEA
    In:  Supplement to: Lemmen, Carsten; Gronenborn, D; Wirtz, Kai W (2011): A simulation of the Neolithic transition in Western Eurasia. Journal of Archaeological Science, 38(12), 3459-3470, https://doi.org/10.1016/j.jas.2011.08.008
    Publication Date: 2019-02-12
    Description: Farming and herding were introduced to Europe from the Near East and Anatolia; there are, however, considerable arguments about the mechanisms of this transition. Were it the people who moved and either outplaced, or admixed with, the indigenous hunter-gatherer groups? Or was it material and information that moved---the Neolithic Package---consisting of domesticated plants and animals and the knowledge of their use? The latter process is commonly referred to as cultural diffusion and the former as demic diffusion. Despite continuous and partly combined efforts by archaeologists, anthropologists, linguists, palaeontologists and geneticists, a final resolution of the debate has not yet been reached. In the present contribution we interpret results from the Global Land Use and technological Evolution Simulator (GLUES). GLUES is a mathematical model for regional sociocultural development, embedded in the geoenvironmental context, during the Holocene. We demonstrate that the model is able to realistically hindcast the expansion speed and the inhomogeneous space-time evolution of the transition to agropastoralism in western Eurasia. In contrast to models that do not resolve endogenous sociocultural dynamics, our model describes and explains how and why the Neolithic advanced in stages. We uncouple the mechanisms of migration and information exchange and also of migration and the spread of agropastoralism. We find that: (1) An indigenous form of agropastoralism could well have arisen in certain Mediterranean landscapes, but not in Northern and Central Europe, where it depended on imported technology and material. (2) Both demic diffusion by migration and cultural diffusion by trade may explain the western European transition equally well. (3) Migrating farmers apparently contribute less than local adopters to the establishment of agropastoralism. Our study thus underlines the importance of adoption of introduced technologies and economies by resident foragers.
    Type: Dataset
    Format: application/octet-stream, 141.0 kBytes
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  • 6
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    Geophysical Research Abstracts Vol. 20, EGU2018-7790, 2018
    Publication Date: 2018-05-25
    Description: Field data collected for the North Sea indicate a prominent seasonal variation in the vertical distribution of total organic carbon (TOC) and macrobenthic biomass in sediments. The vertical TOC profiles classify into three modes, with maximum at surface, middle and deep part of sediments, respectively. We here present a mechanistic model to quantify, for the first time, the dynamic interaction between sedimentary TOC and benthic fauna. The major model principles include that (i) the vertical distribution of macrobenthic biomass is a trade-off between nutritional benefit (quantity and quality of TOC) and the costs of burial (respiration) and mortality, and (ii) the vertical transport of TOC is in turn modulated by macrobenthos through bioturbation. A novelty of our model is that bioturbation is resolved dynamically depending on variation of local food resources and macrobenthic biomass. This allows capturing of the benthic response to both depositional and erosional conditions and improving estimates of the material exchange flux at the sediment-water interface. The coupling of the TOC-benthos model with 3D hydrodynamic-ecological simulations reveals that the three profile modes of sedimentary TOC (in both quantify and quality) can be explained as a combined response to pelagic conditions (shear stress and primary production) and the synergy between bioturbation, vertical redistribution of higher quality TOC and vertical positioning of benthic organisms. A model reconstruction of the benthic status in the North Sea from 1950s to 2010s indicates that despite a relatively stable pattern at decadal and regional scales, significant variations exist at smaller scales characterized by seasons and local areas. In addition, inter-annual and multi-year cycle-like variations are also prominent especially in coastal areas.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
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  • 7
    ISSN: 1574-6941
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: An integrated modeling framework was developed to assess physical, biological and chemical processes in the sediment and at the sediment–water interface. Special focus is laid on the description of different functional groups of bacteria as defined according to their metabolic pathways, including fermentation, methanogenesis and oxidation of high and low molecular mass dissolved organic carbon, ammonium as well as other reduced compounds. The model is subjected to a new validation method which allows for an appropriate representation of remaining uncertainties. It is also able to reproduce two-dimensional gradients in all state variables induced by a pore-water velocity field typical for permeable sediments. Another improvement with respect to many classical models follows from the simulation of adaptive changes in dormancy and motility strategies. Within an extensive analysis stage, the evolutionary stability of these strategies is investigated under a variable hydrodynamical regime. The results show that optimal behavior in terms of adhesion and readiness to dormancy shifts differ between functional groups. This pattern is compared to recent empirical findings and discussed in relation to the confidence limits of the overall methodology. In the numerical experiments, also the effect of variable microbial strategies on the total carbon mineralization of the sediment is determined.
    Type of Medium: Electronic Resource
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  • 8
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    Association for the Sciences of Limnology and Oceanography
    In:  Limnology and Oceanography, 56 (6). pp. 2080-2094.
    Publication Date: 2017-05-02
    Description: On the basis of the assumption that natural selection should tend to produce organisms optimally adapted to their environments, we consider optimality as a guiding concept for abstracting the behavior of aquatic microorganisms (plankton) to develop models to study and predict the behavior of planktonic organisms and communities. This is closely related to trait-based ecology, which considers that traits and functionality can be understood as the result of the optimization inherent in natural selection, subject to constraints imposed by fundamental processes necessary for life. This approach is particularly well suited to plankton because of their long evolutionary history and the ease with which they can be manipulated in experiments. We review recent quantitative modeling studies of planktonic organisms that have been based on the assumption that adaptation of species and acclimation of organisms maximize growth rate. Compared with mechanistic models not formulated in terms of optimality, this approach has in some cases yielded simpler models, and in others models of greater generality. The evolutionary success of any given species must depend on its interactions with both the physical environment and other organisms, which depend on the evolving traits of all organisms concerned. The concept of an evolutionarily stable strategy (ESS) can, at least in principle, constrain the choice of goal functions to be optimized in models. However, the major challenge remains of how to construct models at the level of organisms that can resolve short-term dynamics, e.g., of phytoplankton blooms, in a way consistent with ESS theory, which is formulated in terms of a steady state.
    Type: Article , PeerReviewed
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  • 9
    Publication Date: 2017-02-03
    Description: Chlorophyll (chl a) concentration in coastal seas exhibits variability on various spatial and temporal scales. Resuspension of particulate matter can somewhat limit algal growth, but can also enhance productivity because of the intrusion of nutrient-rich pore water from sediments or bottom water layers into the whole water column. This study investigates whether characteristic changes in net phytoplankton growth can be directly linked to resuspension events within the German Bight. Satellite-derived chl a were used to derive spatial patterns of net rates of chl a increase/decrease (NR) in 2003 and 2004. Spatial correlations between NR and mean water column irradiance were analysed. High correlations in space and time were found in most areas of the German Bight (R2 〉 0.4), suggesting a tight coupling between light availability and algal growth during spring. These correlations were reduced within a distinct zone in the transition between shallow coastal areas and deeper offshore waters. In summer and autumn, a mismatch was found between phytoplankton blooms (chl a 〉 6 mg m−3) and spring-tidal induced resuspension events as indicated by bottom velocity, suggesting that there is no phytoplankton resuspension during spring tides. It is instead proposed here that frequent and recurrent spring-tidal resuspension events enhance algal growth by supplying remineralized nutrients. This hypothesis is corroborated by a lag correlation analysis between resuspension events and in-situ measured nutrient concentrations. This study outlines seasonally different patterns in phytoplankton productivity in response to variations in resuspension, which can serve as a reference for modelling coastal ecosystem dynamics.
    Type: Article , PeerReviewed
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  • 10
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    Frontiers
    In:  Frontiers in Marine Science, 4 (Art.No. 131).
    Publication Date: 2019-02-01
    Description: Autotrophic organisms reveal an astounding flexibility in their elemental stoichiometry, with potentially major implications on biogeochemical cycles and ecological functioning. Notwithstanding, stoichiometric regulation, and co-limitation by multiple resources in autotrophs were in the past often described by heuristic formulations. In this study, we present a mechanistic model of autotroph growth, which features two major improvements over the existing schemes. First, we introduce the concept of metabolic network independence that defines the degree of phase-locking between accessory machines. Network independence is in particular suggested to be proportional to protein synthesis capability as quantified by variable intracellular N:C. Consequently, the degree of co-limitation becomes variable, contrasting with the dichotomous debate on the use of Liebig's law or the product rule, standing for constantly low and high co-limitation, respectively. Second, we resolve dynamic protein partitioning to light harvesting, carboxylation processes, and to an arbitrary number of nutrient acquisition machineries, as well as instantaneous activity regulation of nutrient uptake. For all regulatory processes we assume growth rate optimality, here extended by an explicit consideration of indirect feed-back effects. The combination of network independence and optimal regulation displays unprecedented skill in reproducing rich stoichiometric patterns collected from a large number of published chemostat experiments. This high skill indicates (1) that the current paradigm of fixed co-limitation is a critical short-coming of conventional models, and (2) that stoichiometric flexibility in autotrophs possibly reflects an optimality strategy. Numerical experiments furthermore show that regulatory mechanisms homogenize the effect of multiple stressors. Extended optimality alleviates the effect of the most limiting resource(s) while down-regulating machineries for the less limiting ones, which induces an ubiquitous response surface of growth rate over ambient resource levels. Our approach constitutes a basis for improved mechanistic understanding and modeling of acclimative processes in autotrophic organisms. It hence may serve future experimental and theoretical investigations on the role of those processes in aquatic and terrestrial ecosystems.
    Type: Article , PeerReviewed
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