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  • 1
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    When is a biogeochemical model too complex? Objective model reduction for North Atlantic time-series sites (2013)
    Elsevier
    In:  Progress in Oceanography, 116 . pp. 49-65.
    Details
    Publication Date: 2019-07-30
    Description: Highlights • We objectively identify and remove unconstrained parameters from a marine ecosystem model. • Optimal model complexity is identified using three model selection metrics. • As many as 14 of the model’s 30 parameters can be removed, with no significant reduction in model-data misfit. • Optimal model structures and parameters are different at two different North Atlantic locations. • The specialised structures and parameters at each site may be unsuitable for new environments The degree of structural complexity that should be incorporated in marine biogeochemical models is unclear. We know that the marine ecosystem is complex, and that its observed behaviour is attributable to the interaction of a large number of separate processes, but observations are scarce and often insufficient to constrain more than a small number of model parameters. This issue is addressed using a novel algorithm that systematically removes model processes that are not constrained by observations. The algorithm is applied to a one-dimensional, eight component ecosystem-biogeochemistry model at two North Atlantic time-series sites. Between 11 and 14 of the 30 model parameters can be removed at each site with no significant reduction in the model’s ability to fit upper ocean (0–200 m) biogeochemical tracer and productivity data. The statistically optimal model structures and parameters provide estimates of the most likely state variables and fluxes at each site. Differences in these estimates between the two sites indicate that the optimal models are specialised to both the physical environment and the assimilated observations. At each site the heavily reduced models may thus be suitable for diagnostic purposes but may not be sufficiently complex for more general applications, such as in global ocean general circulation models, or for predicting the response of marine systems to environmental change.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.pocean.2013.06.002
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    Phytoplankton growth conditions during autumn and winter in the Irminger Sea, North Atlantic (2007)
    Inter Research
    In:  Marine Ecology Progress Series, 334 . pp. 47-61.
    Details
    Publication Date: 2015-09-22
    Description: Physical and chemical properties of the water column, along with meteorological conditions were examined for their relationship with phytoplankton biomass in the Irminger Sea during late autumn and early winter. Data were collected during 2 cruises to the region in November and December 2001 and November 2002. Phytoplankton biomass was approximated by (chl a) concentrations within the water column. When examined during autumn and winter alone, the Irminger Sea was suitably described as one biogeochemical region responding to varying meteorological forcing. Hydrographic differences within the region were not observed to have a significant effect on phytoplankton growth during this period. Strong correlations with latitude were seen in chl a concentrations, physical conditions (including mixed layer depth) and meteorological forcing (including net heat flux). Variability in autumn/winter phytoplankton growth conditions appears to be driven by light limitation modulated by meteorological forcing. The temporal and spatial scales of locations sampled in 2001 represent a progression in the physical and biological conditions from late autumn to early winter. Along this ‘virtual transect’, a baseline value of approximately 0.1 mg m–3 is seen in the mean chl a concentrations within the mixed layer. We postulate that convection provides a mechanism for reduction of net losses of phytoplankton, by helping to keep phytoplankton within the mixed layer. Under such conditions, a deeper and therefore more accurate estimation of the critical depth would be valid. Evidence of the extended maintenance of phytoplankton within the mixed layer is presented in the form of the relative dominances of different phytoplankton groups.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.3354/meps334047
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Considering the Role of Adaptive Evolution in Models of the Ocean and Climate System (2019)
    AGU (American Geophysical Union)
    In:  Journal of Advances in Modeling Earth Systems, 11 (11). pp. 3343-3361.
    Details
    Publication Date: 2022-01-31
    Description: Numerical models have been highly successful in simulating global carbon and nutrient cycles in today's ocean, together with observed spatial and temporal patterns of chlorophyll and plankton biomass at the surface. With this success has come some confidence in projecting the century-scale response to continuing anthropogenic warming. There is also increasing interest in using such models to understand the role of plankton ecosystems in past oceans. However, today's marine environment is the product of billions of years of continual evolution—a process that continues today. In this paper, we address the questions of whether an assumption of species invariance is sufficient, and if not, under what circumstances current model projections might break down. To do this, we first identify the key timescales and questions asked of models. We then review how current marine ecosystem models work and what alternative approaches are available to account for evolution. We argue that for timescales of climate change overlapping with evolutionary timescales, accounting for evolution may to lead to very different projected outcomes regarding the timescales of ecosystem response and associated global biogeochemical cycling. This is particularly the case for past extinction events but may also be true in the future, depending on the eventual degree of anthropogenic disruption. The discipline of building new numerical models that incorporate evolution is also hugely beneficial in itself, as it forces us to question what we know about adaptive evolution, irrespective of its quantitative role in any specific event or environmental changes.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2018MS001452
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    Modelling spatial and temporal patterns in size-structured marine plankton communities: top-down and bottom-up controls (2014)
    Oxford University Press
    Details
    Publication Date: 2014-01-10
    Description: Idealized equilibrium models have attributed the observed size structure of marine communities to the interactions between nutrient and grazing control. Here, we examine this theory in a more realistic context using a size-structured global ocean food-web model, together with a much simplified version of the same model for which equilibrium solutions are readily obtained. Both models include the same basic assumptions: allometric scaling of physiological traits and size-selective zooplankton grazing. According to the equilibrium model, grazing places a limit on the phytoplankton biomass within each size-class, while the supply rate of essential nutrients limits the number of coexisting size classes, and hence the total biomass, in the system. The global model remains highly consistent with this conceptual view in the large-scale, annual average sense, but reveals more complex behaviour at shorter timescales, when phytoplankton and zooplankton growth may become decoupled. In particular, we show temporal and spatial scale dependence between total phytoplankton biomass and two key ecosystem properties: the zooplankton-to-phytoplankton ratio, and the partitioning of biomass among different size classes.
    Print ISSN: 0142-7873
    Electronic ISSN: 1464-3774
    Topics: Biology
    Published by Oxford University Press
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  • 5
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    When everything is not everywhere but species evolve: an alternative method to model adaptive properties of marine ecosystems (2015)
    Oxford University Press
    Details
    Publication Date: 2015-01-23
    Description: The functional and taxonomic biogeography of marine microbial systems reflects the current state of an evolving system. Current models of marine microbial systems and biogeochemical cycles do not reflect this fundamental organizing principle. Here, we investigate the evolutionary adaptive potential of marine microbial systems under environmental change and introduce explicit Darwinian adaptation into an ocean modelling framework, simulating evolving phytoplankton communities in space and time. To this end, we adopt tools from adaptive dynamics theory, evaluating the fitness of invading mutants over annual timescales, replacing the resident if a fitter mutant arises. Using the evolutionary framework, we examine how community assembly, specifically the emergence of phytoplankton cell size diversity, reflects the combined effects of bottom-up and top-down controls. When compared with a species-selection approach, based on the paradigm that "Everything is everywhere, but the environment selects", we show that (i) the selected optimal trait values are similar; (ii) the patterns emerging from the adaptive model are more robust, but (iii) the two methods lead to different predictions in terms of emergent diversity. We demonstrate that explicitly evolutionary approaches to modelling marine microbial populations and functionality are feasible and practical in time-varying, space-resolving settings and provide a new tool for exploring evolutionary interactions on a range of timescales in the ocean.
    Print ISSN: 0142-7873
    Electronic ISSN: 1464-3774
    Topics: Biology
    Published by Oxford University Press
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  • 6
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    Marine mixotrophy increases ecological efficiency [Environmental Sciences] (2016)
    National Academy of Sciences
    Details
    Publication Date: 2016-03-16
    Description: Mixotrophic plankton, which combine the uptake of inorganic resources and the ingestion of living prey, are ubiquitous in marine ecosystems, but their integrated biogeochemical impacts remain unclear. We address this issue by removing the strict distinction between phytoplankton and zooplankton from a global model of the marine plankton food web....
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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