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  • Articles  (5)
  • 1
    Publication Date: 2019-06-14
    Description: Benthic fluxes of dissolved nutrients and oxygen measured in the southern North Sea using ex situ incubation chambers indicate a prominent annual cycle characterized by low level from mid-autumn (Oct) to early spring (Mar) and enhanced values from mid-spring (Apr) to early autumn (Sep) with peak in late summer (late Aug/early Sep). The same cycle is also shown in the budget of total organic carbon (TOC) and macrobenthic biomass in surface sediments. The significant positive correlations between the benthic nutrient fluxes, oxygen, sedimentary TOC and macrobenthos suggest that their variation might respond to a common source, i.e. the primary production. However, the linkages between these quantities and pelagic primary production, which exhibits a dominant bloom in early spring (Mar/Apr) and a secondary bloom in early summer (Jun/Jul) in the study area, is not straightforward. We present a numerical study to unravel the complex linkages. A 3-D coupled hydrodynamic-biogeochemical model (ECOSMO) was used to provide benthic boundary conditions for a 1-D biogeochemical model in the sediment (TOCMAIM) that mechanistically resolves the interaction between macrobenthos and organic matter through bioturbation. Simulation results based on a satisfactory hindcast from 1948 to 2015 reveal that although the spring algal bloom normally starts in late winter (Feb) and peaks in early spring (Mar/Apr), deposition of labile OC to seafloor is limited in this period due to energetic hydrodynamic conditions. Sedimentation and accumulation of labile OC (originated from fresh planktonic detritus) in seafloor surface sediments are facilitated in summer when wind-waves become weak enough. This drives the blooming of macrobenthos, with peak of biomass in late summer (Aug). Bioturbation intensity, which is dependent upon macrobenthic biomass, community structure as well as local food resource, peaks also in later summer. Enhanced bioturbation and benthic metabolism result in an increased oxygen flux into sediments, promoting remineralization of OC and release of nutrients. The following period (late Sep/Oct) is characterized by low level of pelagic primary production in combination with enhanced wind-waves, which not only reduce the input of labile OC into sediments substantially but also remobilize surface material (sediments and OC) on a major part of the shallow coastal seafloor. Depletion of labile OC in the uppermost centimeters of sediments by a combined effect of erosion, macrobenthic uptake and downward mixing (through bioturbation) accounts for the rapid decline of benthic nutrient fluxes in Oct, which remain low through the stormy winter until the next spring.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
    Location Call Number Limitation Availability
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  • 2
    Publication Date: 2019-08-13
    Description: The importance of macrobenthos in benthic‐pelagic coupling and early diagenesis of organic carbon (OC) has long been recognized but has not been quantified at a regional scale. By using the southern North Sea as an exemplary area we present a modelling attempt to quantify the budget of total organic carbon (TOC) reworked by macrobenthos in seafloor surface sediments. Vertical profiles in sediments collected in the field indicate a significant but nonlinear correlation between TOC and macrobenthic biomass. A mechanistic model is used to resolve the bi‐directional interaction between TOC and macrobenthos. A novelty of this model is that bioturbation is resolved dynamically depending on variations in local food resource and macrobenthic biomass. The model is coupled to 3D hydrodynamic‐biogeochemical simulations to hindcast the mutual dependence between sedimentary TOC and macrobenthos from 1948 to 2015. Agreement with field data reveals a satisfactory model performance. Our simulations show that the preservation of TOC in the North Sea sediments is not only determined by pelagic conditions (hydrodynamic regime and primary production) but also by the vertical distribution of TOC, bioturbation intensity, and the vertical positioning of macrobenthos. Macrobenthos annually ingest 20%–35% and in addition vertically diffuse 11%–22% of the total budget of TOC in the upper‐most 30 cm sediments in the southern North Sea. This result indicates a central role of benthic animals in modulating the OC cycling at the sediment‐water interface of continental margins.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 3
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    Geophysical Research Abstracts Vol. 20, EGU2018-7790, 2018
    In:  EPIC3EGU General Assembly 2018, Vienna, 2018-04-07-2018-04-13Geophysical 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 , notRev
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  • 4
    Publication Date: 2020-01-14
    Description: Coastal morphodynamic and hydrodynamic processes impose a first-order control on biogeochemical cycling and distribution of benthic habitats. However, little is known on how biota in turn affect sediment transport, biogeochemical cycling and morphodynamics at a regional scale and long-term. Here we firstly present a mini-review of recent progress on numerical modeling of interactions between benthic biota, biogeochemical cycling and coastal morphodynamics. Special focus is laid on 1) the synergetic effects of dominant benthic functional groups on sedimentation process, and 2) the macrobenthic response to changing morphological, hydrodynamic and biogeochemical conditions. In a second part we present preliminary results from a case study area (Jade Bay, Wadden Sea) based on simulations using a coupled hydrodynamic-biogeochemical-morphodynamic model and comparison with biogeochemical and taxonomic field monitoring data. The aim is to understand benthic ecosystem functioning and to identify the main drivers of coastal ecosystem changes for better prediction of their future development.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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  • 5
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    ELSEVIER SCIENCE BV
    In:  EPIC3Earth-Science Reviews, ELSEVIER SCIENCE BV, 221(103803), ISSN: 0012-8252
    Publication Date: 2022-08-21
    Description: Benthic organisms and their bioturbation activities have a profound effect on a multitude of sediment properties. While many studies have already explored benthic impacts at small temporal and spatial scales, little is known on how the small-scale effects accumulate and interactively guide large-scale (km-scale) morphological evolution. Here we firstly summarize the most important processes of benthos affecting sediment stability and then explore existing biomorphodynamic modeling studies both at small- and large-scales. In general, microbenthos (body size 〈0.1 mm) mainly stabilizes sediments while meio- (0.1–1 mm) and macrobenthos (〉1 mm) may stabilize or destabilize sediments. Among all types of sediment, fine-grained fraction (silt and clay) is most sensitive to the impact of benthos. Benthic organisms have the capability to mediate sediment transport and sedimentation patterns beyond their habitats on the long-term and over a large-scale. However, so far, numerical models evaluating benthic impact are limited to explorative studies and have not reached a stage where they can be used for predictive modeling. The barriers hindering a further development of biomorphodynamic models include not only limited understanding of fundamental biological/bio-physical processes affecting morphological development and dynamic feedback loops among them but also a shortage of data for model calibration and confirmation of simulation results. On the other hand, thriving for higher model complexity does not necessarily lead to better performance. Before conducting biomorphodynamic modeling, researchers must figure out which questions can be answered in a meaningful sense with simulation results that can be compared with observations and which level of modeling complexity is sufficient for that purpose.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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