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Parameter set used,for all model runs. Bold$gures denote mod$ed values, and the original values from Fashum (1993) are given in brackets
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A certain class of pelagic ecosystem box models uses the mixed layer depth as the main physical forcing. This paper investigates the influence of the definition and derivation of the mixed layer depth on the simulation results. For this investigation the model of Fasham et al. (1990) (Journal of Marine Research, 48, 591–639) is used to simulate the...
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... addition we incorporated the MichaelisMenten-like formulation of phytoplankton and zooplankton loss terms used by Fasham (1993). Most of the parameters were taken from Fasham (1993); some of them, however, we modified in order to take account of the knowledge of the North Sea ecosystem (bold figures in Table 2). ...Citations
... However, it can be difficult to implement realistically for longer seasonal to annual time scales. In those cases, seasonal changes in mixed layer depth, mixing rate, and vertical gradient all need to be specified and errors in the specifications can have a large impact on the simulations (Eigenheer et al. 1996 ). Moreover, the instantaneously mixed representation of the mixed layer is only a rough approximation of the real physics of the mixed layer. ...
There is rising interest from oceanic and atmospheric scientists in the potential role of dimethylsulphide (DMS) in regulating global climate. The increased availability of field observations of DMS and related compounds (DMS(P)) and of their transformation rates in the ocean has stimulated the development of ecosystem models of marine sulfur cycling. The models cover a wide range of complexity levels and spatial/temporal scales, from zero-dimensional local simulations spanning a few days to regional/global simulations driven by ocean general circulation models. The degree of complexity required to model DMS(P) dynamics, particularly the differentiation into phyto plankton species or groups, remains an important open question. First attempts to drive these models with vertically resolved turbulence models suggest interesting interactions between DMS(P) dynamics and fine-scale ocean mixing that can modify fluxes of DMS to the atmosphere. Recent models also bring into focus the strong affinities between the cycling of DMS(P) and that of dissolved organic carbon in the surface ocean. Formal parameter estimation techniques, which are increasingly used in ecosystem modelling of carbon and nitrogen dynamics, should play a stronger role in the development of DMS sulfur modelling. Extrapolation of DMS cycling and fluxes to the global scale presently relies largely on empirical approach. A semiempirical approach, based on a simple ecosystem model, is shown to reproduce gross features of the global distribution of DMS in the surface ocean. This shows promise for the continuing development of ecosystem models for global modelling of marine sulfur fluxes to the atmosphere.
... [20] The biogeochemical model is embedded in a onedimensional (1-D) vertical physical frame. The model therefore neglects horizontal transport processes and takes into account only vertical processes, i.e. advection (equation (A80)) and diffusion (equation (A81)), which are considered the main driving forces of ecosystem dynamics in the upper ocean [Eigenheer et al., 1996;Denman and Peña, 1999]. As in the models of Lefevre et al. [2002] and Cropp et al. [2004], vertical mixing in the current version of DMOS is parameterized using a prescribed turbulent diffusion coefficient (kz, Table 1) following the approach used by Cropp et al. [2004]. ...
A new one-dimensional model of DMSP/DMS dynamics (DMOS) is developed and applied to the Sargasso Sea in order to explain what drives the observed dimethylsulfide (DMS) summer paradox: a summer DMS concentration maximum concurrent with a minimum in the biomass of phytoplankton, the producers of the DMS precursor dimethylsulfoniopropionate (DMSP). Several mechanisms have been postulated to explain this mismatch: a succession in phytoplankton species composition towards higher relative abundances of DMSP producers in summer; inhibition of bacterial DMS consumption by ultraviolet radiation (UVR); and direct DMS production by phytoplankton due to UVR-induced oxidative stress. None of these hypothetical mechanisms, except for the first one, has been tested with a dynamic model. We have coupled a new sulfur cycle model that incorporates the latest knowledge on DMSP/DMS dynamics to a preexisting nitrogen/carbon-based ecological model that explicitly simulates the microbial-loop. This allows the role of bacteria in DMS production and consumption to be represented and quantified. The main improvements of DMOS with respect to previous DMSP/DMS models are the explicit inclusion of: solar-radiation inhibition of bacterial sulfur uptakes; DMS exudation by phytoplankton caused by solar-radiation-induced stress; and uptake of dissolved DMSP by phytoplankton. We have conducted a series of modeling experiments where some of the DMOS sulfur paths are turned ''off'' or ''on,'' and the results on chlorophyll-a, bacteria, DMS, and DMSP (particulate and dissolved) concentrations have been compared with climatological data of these same variables. The simulated rate of sulfur cycling processes are also compared with the scarce data available from previous works. All processes seem to play a role in driving DMS seasonality. Among them, however, solar-radiation-induced DMS exudation by phytoplankton stands out as the process without which the model is unable to produce realistic DMS simulations and reproduce the DMS summer paradox.
... and diffusion (eq(2.81)), which are considered the main driving forces of ecosystem dynamics in the upper ocean [Eigenheer et al., 1996;Denman and na, 1999]. As in the models of Lefèvre et al. [2002] and Cropp et al. [2004], vertical mixing in the current version of DMOS is parameterized using a prescribed turbulent diffusion coefficient (kz, Table 2.1) following the approach used by Cropp et al. [2004]. ...
... by Eigenheer et al. (1996). Here the observed salinity at 10 m depth deviated substantially from the simulated salinity from 9 to 19 June. ...
... The chlorophyll concentrations exhibited the observed bloom periods with an overestimation of the simulated spring bloom. Deficits in the physical simulation may cause the other deficits, as biological dynamics sensitively depend on the physical development, as shown byEigenheer et al. (1996).Lee et al. (2002) reduced the model COHERENS to a one-dimensional version, called PROWQM, then extending this model version by new pelagic and benthic components for coupling the physical and microbiological processes in the water column with sedimentation/resuspension and benthic mineralisation processes. They compared their simulations for the northern North Sea extensively with several new and historic data sets as well as model results, concluding that resuspension, pelagic and benthic mineralisation and denitrification were important processes which need further 32/70 investigations for being properly modelled. ...
The aim of this review is to provide an overview of the status of validation of eleven biogeochemical and ecological models of the greater North Sea (COHERENS, CSM-NZB, DCM-NZB, DYMONNS, ECOHAM, ELISE, ERSEM, FYFY, GHER, NORWECOM, POLCOMS-ERSEM) showing the realism achieved as well as the problems hindering a better degree of validity of the models. Several of the models were able to reproduce observations of the state variables correctly within an order of magnitude, but all models are not capable of reproducing every simulated state variable in the range of observations. None of the models can be called a valid model. Comparison of results from different models with datasets are evaluated according to the different spatial and temporal scales, for which data products were available, namely for regional distributions, annual cycles, long-term developments and events. The higher the trophic level, the greater was the discrepancy with the data. Problems still exist in determining the necessary complexity of the ecosystem model. More complexity in the model does not necessarily improve the simulations. Special attention should be devoted to the regeneration mechanisms in the sediments. Species' groups have been simulated so far with rather limited success. The ecological model simulations did not reproduce fully the observed variability. Possible sources of lacking coincidence with observations originating from the spatial and temporal resolution of the internal dynamics, the trophic resolution, or the resolution of the forcing functions are discussed. Most of the models still need to be evaluated more intensively for their predictive potential to be judged. They have not yet been tested to a degree which is possible today using the various existing datasets from the northwest European shelf seas (presented in the Appendix). Common datasets for the necessary annual cycles of forcing functions are needed.
... This has led to a focus on the role of upper ocean ecosystems in shaping climate [3]. The vertical physical dynamics of the mixed layer are a critical driving force determining ecosystem dynamics in the upper ocean [4]; by comparison, horizontal advection is believed to have little influence on mixed layer ecosystems [5]. The mean irradiance field, controlled by the interaction of light penetration and the mixed layer depth, and the supply of nutrients into the mixed layer are important limiting factors on biological production [6]. ...
Dimethylsulphide (DMS) is produced by upper ocean ecosystems and emitted to the atmosphere where it may have an important role in climate regulation. Several attempts to quantify the role of DMS in climate change have been undertaken in modeling studies. We examine a model of biogenic DMS production and describe its endogenous dynamics and sensitivities. We extend the model to develop a one-dimensional version that more accurately resolves the important processes of the mixed layer in determining the ecosystem dynamics. Comparisons of the results of the one-dimensional model with vertical profiles of DMS in the upper ocean measured at the Bermuda Atlantic Time Series suggest that the model represents the interaction between the biological and physical processes well. Our analysis of the model confirms its veracity and provides insights into the important processes determining DMS concentration in the oceans.
... This has led to a focus on the role of upper ocean ecosystems in shaping climate [Gabric et al., 2001a]. [3] The vertical physical dynamics of the mixed layer are a critical driving force determining ecosystem dynamics in the upper ocean [Eigenheer et al., 1996] ; by comparison , horizontal advection is believed to have little influence on mixed layer ecosystems [Denman and Pena, 1999] . The mean irradiance field, controlled by the interaction of light penetration and the mixed layer depth, and the supply of nutrient into the mixed layer are important limiting factors on biological production [Doney et al., 1996]. ...
Dimethylsulphide (DMS) is produced by upper ocean ecosystems and emitted to the atmosphere, where it may have an important role in climate regulation. Several attempts to quantify the role of DMS in climate change have been undertaken in modeling studies. We examine a model of biogenic DMS production and describe its endogenous dynamics and sensitivities. We extend the model to develop a one-dimensional version that more accurately resolves the important processes of the mixed layer in determining the ecosystem dynamics. Comparisons of the results of the one-dimensional model with an empirical relationship that describes the global distribution of DMS, and also with vertical profiles of DMS in the upper ocean measured at the Bermuda Atlantic Time Series, suggest that the model represents the interaction between the biological and physical processes well on local and global scales. Our analysis of the model confirms its veracity and provides insights into the important processes determining DMS concentration in the oceans. Yes Yes
... Zero-dimensional models are always subject to the criticisms that they neglect processes occurring below the mixed layer and that their results may depend on the definition of MLD adopted (Eigenheer et al., 1996). A vertical one-dimensional model, in which the seasonal cycle of the vertical diffusion coefficient is prescribed, was used by Frost (1993). ...
A review of ecosystem modeling is presented, classifying the models on the basis of the problems they address. The problems
are chosen mainly from those concerning the North Pacific and encompass: limiting factors in high-nutrient/low-chlorophyll
(HNLC) regions; nutrient supply to the subtropical gyre; long-term variation; parameter optimization; oceanic provinces. A
future research direction should be to sort out priorities of various biogeochemical and ecological processes with the long-term
variation problem being the axis, while keeping the model complexity at a minimum and invoking the parameter optimization
technique.
... It is, however, not only the circulation, i.e. the flow pattern, that influences the development of the ecosystem in nature. Vertical mixing and stratification have a decisive influence on the phytoplankton dynamics (Radach and Moll, 1993;Eigenheer et al., 1996). In ERSEM these features are represented by relatively coarse parametrisations. ...
The ecosystem model ERSEM II has been used to hindcast the development of the ecosystem of the North Sea during the years 1955 to 1993. The simulation was driven by the box-aggregated output from a general circulation model of the North Sea of corresponding duration; radiation, river inputs, atmospheric input and boundary conditions at the borders to the Atlantic Ocean and to the Baltic Sea were applied as realistically as possible. The general features of the eutrophication process are reproduced in the hindcast: the coastal areas show strong changes in nutrient concentrations in the hindcast as well as in the observations. Eutrophication not only shows up in the nutrient concentrations, but also in primary production. The simulated spatial distributions of phosphate, nitrate and primary production compare well with the observed ones. In addition, the hindcast simulates considerable trend-like changes of the nutrients in the southern part of the North Sea, where the nutrients are transported from the continental coastal strip to the southern central North Sea. The line from the river Humber to southern Norway separates the region of noticeable anthropogenic influence of riverine and atmospheric input from the northern area, which is mainly influenced by the Atlantic nutrient inflow. The observed annual cycles in the central and northern North Sea are quite well reproduced by the hindcast. The comparison of the hindcast with the long-term observations at two sites in the continental coastal zone of the North Sea shows that the long-term behaviour of phosphate, nitrate and silicate is simulated well. Primary production is increased in summers during the main period of eutrophication, 1975 to 1989, in the hindcast and in the observations. The flagellates at Helgoland, however, experience much more pronounced annual cycles with much less interannual variability in the hindcast than in the observations.
... Radach and Lenhart (1995); Tett and Walne (1995)). Only a few vertically fully resolved coupled physical-biological models exist in the literature (Radach, 1983;Stramska and Dickey, 1993;Sharples and Tett, 1994;Eigenheer et al., 1996). None of them discusses the consequences of the timing of the onset and the extent of the stratification for the phytoplankton production, the succession and trophic interactions during a full growth season. ...
... None of them discusses the consequences of the timing of the onset and the extent of the stratification for the phytoplankton production, the succession and trophic interactions during a full growth season. Only one model (Eigenheer et al., 1996) shows the response of phytoplankton and nutrients for different types of stratification, but for the spring period only. Nevertheless, one may speculate that the timing of the onset of stratification in spring, when the succession of dominating phytoplankton species proceeds rapidly (X weeks) (Riegman et al., 1993), may determine the species composition for at least several months. ...
... The seasonal stratification dynamics are fairly well modelled with a mixed layer model with exceptions for periods in early spring and a period in August. Eigenheer et al. (1996) also concluded that a mixed layer model predicts a too early start of the stratification in spring when compared to observations of the FLEX-experiment (Weber, 1980) but also earlier than when using a turbulence closure model (Mellor and Yamada, 1982). A possible reason for this too early start could be that in this application and the one of Eigenheer et al. (1996) daily averaged forcing are used in which diurnal effects are neglected. ...
Local heating rate within the water column depends on energy input by solar radiation and on heat exchange across the surface as controlled by wind and convection. The heating results in thermal stratification of the water column, which in turn affects the vertical transport of, for example, nutrients. In this paper the implications of the stratification on the biota by focusing on the time of its onset and its variability in time and (vertical) space are evaluated. Especially the consequences of the stratification on the phytoplankton dynamics and the trophic interactions are shown. For this purpose, an integrated ecosystem model is developed which includes a physical submodel and an ecological model. The model is calibrated with data from a mooring project, during which a large number of physical and biological parameters have been measured at a site on the Oyster Grounds in the North Sea over a 15-month period. The physical model is a one-dimensional entrainment/detrainment model. The ecological model consists of submodels which are part of the ERSEM ecological model and which describe the biological and chemical processes in the water column and in the benthos. Results show that stratification has a major impact on the biota. Especially the timing of the onset of the stratification has major consequences for the production and succession of phytoplankton and the structure of the food web during the entire growing season.
... Radach and Lenhart (1995); Tett and Walne (1995)). Only a few vertically fully resolved coupled physical-biological models exist in the literature (Radach, 1983;Stramska and Dickey, 1993;Sharples and Tett, 1994;Eigenheer et al., 1996). None of them discusses the consequences of the timing of the onset and the extent of the stratification for the phytoplankton production, the succession and trophic interactions during a full growth season. ...
... None of them discusses the consequences of the timing of the onset and the extent of the stratification for the phytoplankton production, the succession and trophic interactions during a full growth season. Only one model (Eigenheer et al., 1996) shows the response of phytoplankton and nutrients for different types of stratification, but for the spring period only. Nevertheless, one may speculate that the timing of the onset of stratification in spring, when the succession of dominating phytoplankton species proceeds rapidly (X weeks) (Riegman et al., 1993), may determine the species composition for at least several months. ...
... The seasonal stratification dynamics are fairly well modelled with a mixed layer model with exceptions for periods in early spring and a period in August. Eigenheer et al. (1996) also concluded that a mixed layer model predicts a too early start of the stratification in spring when compared to observations of the FLEX-experiment (Weber, 1980) but also earlier than when using a turbulence closure model (Mellor and Yamada, 1982). A possible reason for this too early start could be that in this application and the one of Eigenheer et al. (1996) daily averaged forcing are used in which diurnal effects are neglected. ...
