ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    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
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 2
    Publication Date: 2018-05-23
    Description: Author Posting. © The Author(s), 2018. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Ecological Modelling 376 (2018): 54-67, doi:10.1016/j.ecolmodel.2018.03.003.
    Description: The present study describes the responses of summer phytoplankton biomass to changes in top-down forcing (expressed as zooplankton mortality) in three ecosystems (the North Sea, the Baltic Sea and the Nordic Seas) across different 3D ecosystem models. In each of the model set-ups, we applied the same changes in the magnitude of mortality (±20%) of the highest trophic zooplankton level (Z1). Model results showed overall dampened responses of phytoplankton relative to Z1 biomass. Phytoplankton responses varied depending on the food web structure and trophic coupling represented in the models. Hence, a priori model assumptions were found to influence cascades and pathways in model estimates and, thus, become highly relevant when examining ecosystem pressures such as fishing and climate change. Especially, the different roles and parameterizations of additional zooplankton groups grazed by Z1, and their importance for the outcome, emphasized the need for better calibration data. Spatial variability was high within each model indicating that physics (hydrodynamics and temperature) and nutrient dynamics also play vital roles for ecosystem responses to top-down effects. In conclusion, the model comparison indicated that changes in top-down forcing in combination with the modelled food-web structure affect summer phytoplankton biomass and, thereby, indirectly influence water quality of the systems.
    Description: The work was supported by the EU grant “Vectors of Change in Oceans and Seas, Marine Life, Impact and Economic Sectors” (Vectors, FP7/2010-2013) and The Danish Council for Strategic Research to the project “Integrated Management of Agriculture, Fishery, Environment and Economy” (IMAGE, grant no. 09-067259).
    Keywords: Plankton functional types ; Trophic cascades ; Zooplankton mortality ; Phytoplankton ; Ensemble modelling
    Repository Name: Woods Hole Open Access Server
    Type: Preprint
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 3
    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 , NonPeerReviewed
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 4
    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 , NonPeerReviewed
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 5
    Publication Date: 2019-08-29
    Description: This dataset contains a model simulation of the environmental conditions close to the sea-floor from January 1948-April 2015. The simulations relies on the coupled physcial-biogeochemical HYCOM-ECOSMO and has been forced by a Global High Resolution Climate Reconstruction (ECHAM6). The dataset is monthly, it consist of temperature, salinity, currents, oxygen, nitrate, phosphate and silicate all interpolated to 1 meter above the sea floor. Additionally the dataset contains gross primary and secondary production integrated over the water column.
    Type: Dataset
    Format: text/tab-separated-values, 55 data points
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 6
    Publication Date: 2012-12-01
    Description: This article presents some advantages using a shape-preserving total variation diminishing (TVD) advection scheme in an ecosystem model. The superbee flux-limiter has been used to the second-order Lax–Wendroff advection scheme to make it TVD. We performed simulations for three shelf sea regions with different characteristic time scales, namely, the North Sea, the Barents Sea, and the Baltic Sea. To explore the advantages, we also performed reference runs with the much simpler and computationally cheaper upwind advection scheme. Frontal structures are much better resolved with the TVD scheme. The bottom salinity in the Baltic Sea stays at realistic values throughout the 10-year simulation with the TVD scheme, while with the upwind scheme, it drifts towards lower values and the permanent haline stratification in the Baltic is almost completely eroded within one seasonal cycle. Only when applying TVD for both the vertical and horizontal advections the model succeeded to preserve haline stratification in the decadal simulation. Lower trophic level patterns are far better reproduced with the TVD scheme, and for the estimated cod larval survival, the advantages seem to be even stronger. Simulations using the TVD-derived prey fields identified distinct regions such as Dogger Bank to favor potential larvae survival (PLS), which did not appear as particularly favorable in the upstream simulations. The TVD scheme needs about 25 % more time on the central processing unit (CPU) in case of a pure hydrodynamic setup with only two scalar state variables (Barents Sea application). The additional CPU time cost increases for a coupled physical–biological model application with a large number of state variables. However, this is more than compensated by all the advantages found, and, hence, we conclude that it is worthwhile to use the TVD scheme in our ecosystem model. ©2012 Springer-Verlag Berlin Heidelberg
    Print ISSN: 1616-7341
    Electronic ISSN: 1616-7228
    Topics: Geosciences , Physics
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 7
    Publication Date: 2014-05-07
    Print ISSN: 1354-1013
    Electronic ISSN: 1365-2486
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Published by Wiley
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 8
    Publication Date: 2019-10-07
    Description: The Öresund (the Sound), which is a part of the Danish straits, is linking the marine North Sea and the brackish Baltic Sea. It is a transition zone where ecosystems are subjected to large gradients in terms of salinity, temperature, carbonate chemistry, and dissolved oxygen concentration. In addition to the highly variable environmental conditions, the area is responding to anthropogenic disturbances in, e.g., nutrient loading, temperature, and pH. We have reconstructed environmental changes in the Öresund during the last ca. 200 years, and especially dissolved oxygen concentration, salinity, organic matter content, and pollution levels, using benthic foraminifera and sediment geochemistry. Five zones with characteristic foraminiferal assemblages were identified, each reflecting the environmental conditions for the respective period. The largest changes occurred around 1950, when the foraminiferal assemblage shifted from a low diversity fauna dominated by the species Stainforthia fusiformis to higher diversity and abundance and dominance of the Elphidium species. Concurrently, the grain-size distribution shifted from clayey to sandier sediment. To explore the causes of the environmental changes, we used time series of reconstructed wind conditions coupled with large-scale climate variations as recorded by the North Atlantic Oscillation (NAO) index as well as the ECOSMO II model of currents in the Öresund area. The results indicate increased changes in the water circulation towards stronger currents in the area after the 1950s. The foraminiferal fauna responded quickly (
    Print ISSN: 1726-4170
    Electronic ISSN: 1726-4189
    Topics: Biology , Geosciences
    Published by Copernicus on behalf of European Geosciences Union (EGU).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 9
    Publication Date: 2019-05-06
    Description: Coupled physical–biological models usually resolve only parts of the trophic food chain; hence, they run the risk of neglecting relevant ecosystem processes. Additionally, this imposes a closure term problem at the respective “ends” of the trophic levels considered. In this study, we aim to understand how the implementation of higher trophic levels in a nutrient–phytoplankton–zooplankton–detritus (NPZD) model affects the simulated response of the ecosystem using a consistent NPZD–fish modelling approach (ECOSMO E2E) in the combined North Sea–Baltic Sea system. Utilising this approach, we addressed the above-mentioned closure term problem in lower trophic ecosystem modelling at a very low computational cost; thus, we provide an efficient method that requires very little data to obtain spatially and temporally dynamic zooplankton mortality. On the basis of the ECOSMO II coupled ecosystem model we implemented one functional group that represented fish and one group that represented macrobenthos in the 3-D model formulation. Both groups were linked to the lower trophic levels and to each other via predator–prey relationships, which allowed for the investigation of both bottom-up processes and top-down mechanisms in the trophic chain of the North Sea–Baltic Sea ecosystem. Model results for a 10-year-long simulation period (1980–1989) were analysed and discussed with respect to the observed patterns. To understand the impact of the newly implemented functional groups for the simulated ecosystem response, we compared the performance of the ECOSMO E2E to that of a respective truncated NPZD model (ECOSMO II) applied to the same time period. Additionally, we performed scenario tests to analyse the new role of the zooplankton mortality closure term in the truncated NPZD and the fish mortality term in the end-to-end model, which summarises the pressure imposed on the system by fisheries and mortality imposed by apex predators. We found that the model-simulated macrobenthos and fish spatial and seasonal patterns agree well with current system understanding. Considering a dynamic fish component in the ecosystem model resulted in slightly improved model performance with respect to the representation of spatial and temporal variations in nutrients, changes in modelled plankton seasonality, and nutrient profiles. Model sensitivity scenarios showed that changes in the zooplankton mortality parameter are transferred up and down the trophic chain with little attenuation of the signal, whereas major changes in fish mortality and fish biomass cascade down the food chain.
    Print ISSN: 1991-959X
    Electronic ISSN: 1991-9603
    Topics: Geosciences
    Published by Copernicus on behalf of European Geosciences Union (EGU).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 10
    Publication Date: 2017-04-13
    Description: Here we present results from a long-term model simulation of the 3d coupled ecosystem model ECOSMO II for a North and Baltic Sea setup. The model allows both multi-decadal hindcast simulation of the marine system and specific process studies under controlled environmental conditions. Model results have been analysed with respect to long-term multi decadal variability in both physical and biological parameters with the help of empirical orthogonal function (EOF) analysis. The analysis of a 61-year (1948–2008) long hind cast reveals a quasi-decadal variation on salinity, temperature and current fields in the North Sea in addition to singular events of major changes during restricted time frames. These changes in hydrodynamic variables where found to be associated to changes in ecosystem productivity that are temporally aligned with the timing of reported regime shifts in the areas. Our results clearly indicate that for analysing ecosystem productivity spatially explicit methods are indispensable. Especially in the North Sea a correlation analysis between atmospheric forcing and primary production (PP) reveals significant correlations for NAO and wind forcing for the central part of the region, while AMO and air temperature are correlated to long-term changes in the southern North Sea frontal areas. Since correlations cannot serve to identify causal relationship we performed scenario model runs with perturbing the temporal variability in forcing condition emphasizing specifically the role of solar radiation, wind and eutrophication. The results revealed that, although all parameters are relevant for the magnitude of PP in the North Sea and Baltic Sea, the dominant impact on long-term variability and major shifts in ecosystem productivity was introduced by modulations of the wind fields.
    Electronic ISSN: 2190-4995
    Topics: Geosciences
    Published by Copernicus on behalf of European Geosciences Union (EGU).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...