Abstract
Abstract. Now that regional circulation patterns can be reasonably well reproduced by ocean circulation models, significant effort is being directed toward incorporating complex food webs into these models, many of which now routinely include multiple phytoplankton (P) and zooplankton (Z) compartments. This study quantitatively assesses how the number of phytoplankton and zooplankton compartments affects the ability of a lower-trophic-level ecosystem model to reproduce and predict observed patterns in surface chlorophyll and particulate organic carbon. Five ecosystem model variants are implemented in a one-dimensional assimilative (variational adjoint) model testbed in the Mid-Atlantic Bight. The five models are identical except for variations in the level of complexity included in the lower trophic levels, which range from a simple 1P1Z food web to a considerably more complex 3P2Z food web. The five models assimilated satellite-derived chlorophyll and particulate organic carbon concentrations at four continental shelf sites, and the resulting optimal parameters were tested at five independent sites in a cross-validation experiment. Although all five models showed improvements in model–data misfits after assimilation, overall the moderately complex 2P2Z model was associated with the highest model skill. Additional experiments were conducted in which 20% random noise was added to the satellite data prior to assimilation. The 1P and 2P models successfully reproduced nearly identical optimal parameters regardless of whether or not noise was added to the assimilated data, suggesting that random noise inherent in satellite-derived data does not pose a significant problem to the assimilation of satellite data into these models. However, the most complex model tested (3P2Z) was sensitive to the level of random noise added to the data prior to assimilation, highlighting the potential danger of over-tuning inherent in such complex models.
Highlights
In spite of recent advances in marine ecosystem modeling that allow for the incorporation of multiple plankton functional types and/or size classes (e.g., Follows et al, 2007; Kishi et al, 2007; Salihoglu and Hofmann, 2007), it remains ambiguous as to whether models with additional plankton compartments necessarily perform better than models characterized by relatively simple structures
This study examines how model skill, skill in reproducing surface chlorophyll and particulate organic carbon concentrations, is affected by manipulating the complexity of the planktonic food web without altering other underlying formulations and assumptions in the model
The model estimates of the peak chlorophyll during the fall bloom ranged from 2 mg Chl m−3 to > 5 mg Chl m−3 at the CV5 site
Summary
In spite of recent advances in marine ecosystem modeling that allow for the incorporation of multiple plankton functional types and/or size classes (e.g., Follows et al, 2007; Kishi et al, 2007; Salihoglu and Hofmann, 2007), it remains ambiguous as to whether models with additional plankton compartments necessarily perform better than models characterized by relatively simple structures. The use of a single plankton compartment may fail to resolve key processes in a given ecosystem (e.g., Ward et al, 2013), the inclusion of additional complexity in plankton structure comes with a substantial cost: significant uncertainties will inevitably be associated with the additional state variables and required parameters (Anderson, 2005; Flynn, 2005). These trade-offs in model structure selection pose a challenging question: how does one determine how many phytoplankton and zooplankton compartments need to be included in a given application of a lower trophic model?. Friedrichs: Effects of increasing the complexity of planktonic food web models
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
