On the sensitivity of ecosystem box model simulations on mixed-layer depth estimates

doi:10.1016/0967-0637(96)00046-5

Deep Sea Research Part I: Oceanographic Research Papers

Volume 43, Issue 7, July 1996, Pages 1011-1027

https://doi.org/10.1016/0967-0637(96)00046-5 Get rights and content

Abstract

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 phytoplankton bloom during the Fladenground Experiment in spring 1976 (FLEX '76).

The time of establishment of the thermocline, the mean depth and the temporal variability of the mixed-layer depth differ substantially between the estimates under consideration. Exactly those features influence the model results fundamentally. All processes and state variables of the ecosystem model examined for a series of representations of mixed layer development during FLEX '76 differ widely from each other and from observations. Temporal variability of the mixed-layer depth causes a variability of the onset of the plankton bloom of about two weeks. Consequently, this class of ecological models cannot reproduce the dynamics of the spring bloom ecosystem appropriately; for this purpose vertical mixing processes need to be represented explicitly.

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Citation Excerpt :
No adequate climatology of Surface Mixed Layer (SML) thickness was available for this region, and so comparisons of simulated and observed SML thickness used FLEX observations from spring 1976 and PROVESS observations from autumn 1998. A time series of mixed layer depths during the FLEX was taken from Eigenheer et al. (1996), who defined the SML as the layer (next to the sea surface) in which the vertical gradient of daily mean temperature was less than 0.02 °C m− 1. In autumn 1998, regular CTD profiles were made by all ships visiting the PROVESS site, and the data assembled by Luyten et al. (2002).
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The simulated removal of nutrient up to the time of maximum chlorophyll was used to estimate values for diatoms and flagellates of the yield, q, of chlorophyll from nitrate or silicate. The silicate value (0.77 g chl (mol Si)⁻ ¹ in the best simulation) is novel. The yields from nitrate were 0.23–0.75 g chl (mol N)⁻ ¹, the range including both groups and all simulations. These were less than yields reported for inshore waters. Finally, the need for detailed study of the distributions of pelagic microflora and microfauna in late summer in the northern North Sea is pointed out.
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We have developed a general 1-D multi-component ecosystem model that incorporates a skillful upper ocean mixed layer model based on second moment closure of turbulence. The model is intended for eventual incorporation into coupled 3-D physical–biogeochemical ocean models with potential applications to modeling and studying primary productivity and carbon cycling in the global oceans as well as to promote the use of chlorophyll concentrations, in concert with satellite-sensed ocean color, as a diagnostic tool to delineate circulation features in numerical circulation models. The model is nitrogen-based and the design is deliberately general enough and modular to enable many of the existing ecosystem model formulations to be simulated and hence model-to-model comparisons rendered feasible. In its more general form (GEM10), the model solves for nitrate, ammonium, dissolved nitrogen, bacteria and two size categories of phytoplankton, zooplankton and detritus, in addition to solving for dissolved inorganic carbon and total alkalinity to enable estimation of the carbon dioxide flux at the air–sea interface. Dissolved oxygen is another prognostic variable enabling air–sea exchange of oxygen to be calculated. For potential applications to HNLC regions where productivity is constrained by the availability of a trace constituent such as iron, the model carries the trace constituent as an additional prognostic variable. Here we present 1-D model simulations for the Black Sea, Station PAPA and the BATS site. The Black Sea simulations assimilate seasonal monthly SST, SSS and surface chlorophyll, and the seasonal modulations compare favorably with earlier work. Station PAPA simulations for 1975–1977 with GEM5 assimilating observed SST and a plausible seasonal modulation of surface chlorophyll concentration also compare favorably with earlier work and with the limited observations on nitrate and pCO₂ available. Finally, GEM5 simulations at BATS for 1985–1997 are consistent with the available time series. The simulations suggest that while it is generally desirable to employ a comprehensive ecosystem model with a large number of components when accurate depiction of the entire ecosystem is desirable, as is the prevailing practice, a simpler formulation such as GEM5 (N²PZD model) combined with assimilation of remotely sensed SST and chlorophyll concentrations may suffice for incorporation into 3-D prediction models of primary productivity, upper ocean optical clarity and carbon cycling.
The PROWQM physical-biological model with benthicpelagic coupling applied to the northern North Sea
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Citation Excerpt :
Mills et al. (1994) suggested that the phytoplankton critical depth (Sverdrup, 1953) exceeded the depth of the water column prior to the start of stratification at station CS in the central North Sea. The FLEX observations summarised by Eigenheer et al. (1996) show some increase in chlorophyll and production, and a decrease in nitrate concentration, prior to stratification. In our standard simulation, the spring bloom, defined as occurring when chlorophyll concentration exceeded 1 mg m−3, started before the commencement of persistent stratification.
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On the sensitivity of ecosystem box model simulations on mixed-layer depth estimates

Abstract

Estuarine, Coastal and Shelf Science

Netherlands Journal of Sea Research

Netherlands Journal of Sea Research

Deep Sea Research

Netherlands Journal of Sea Research

Ecological Modelling

Deep-Sea Research I

Ecological modelling in coastal waters: towards predictive physical-chemical-biological simulation models

Ophelia

On the performance of a mixed-layer model based on the k-s turbulence closure

Journal of Geophysical Research

Bacterial production in fresh and saltwater ecosystems: a crosssystem overview

Marine Ecology Progress Series

Report of the Committee on Terms and Equivalents

Rapport et Proces Verbaux des Reunions

Supply of organic matter to the sediment in the northern North Sea during a spring phytoplankton bloom

Marine Biology

Simulationen der Plankton-Dynamik in der nördlichen Nordsee während FLEX '76 mit dem Modell von Fasham, Ducklow and McKelvie (1990), Diplomarbeit, Fachbereich Geowissenschaften der Universität Hamburg

Berichte aus dent ZMK, Hamburg

A model of annual plankton cycles

Biological Oceanography

Modelling the marine biota

The use of optimization techniques to model marine ecosystem dynamics at the JGOFS station at 47°N 20°W

Philosophical Transactions of the Royal Society of London

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Journal of Marine Research

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Fluctuations of dissolved amino acids: A comparison of natural and enclosed phytoplankton populations in the North Sea

Temporal and spatial scales in phytoplankton ecology. Mechanisms, methods, models, and management

Canadian Journal of Fisheries and Aquatic Sciences

On the succession of developmental stages of herbivorous zooplankton in the northern North Sea during FLEX '76,

Ein eindimensionales Stickstoff-basiertes physikalisch-biologisches Modell des pelagischen ökosystems

Berichte aus dent ZMK, Hamburg