Accounting for unpredictable spatial variability in plankton ecosystem models

Limitations on our ability to predict fine-scale spatial variability in plankton ecosystems can<br/>seriously compromise our ability to predict coarse-scale behaviour. Spatial variability which<br/>is deterministically unpredictable may distort parameter estimates when the ecosystem model<br/>is fitted to (or assimilates) ocean data, may compromise model validation, and may produce<br/>mean-field ecosystem behaviour discrepant with that predicted by the model. New statistical<br/>methods are investigated to mitigate these effects and thus improve understanding and prediction<br/>of coarse-scale behaviour e.g. in response to climate change. First, the standard model<br/>fitting technique is generalised to allow model-data ‘phase errors’ in the form of time lags,<br/>as has been observed to approximate mesoscale plankton variability in the open ocean. The<br/>resulting ‘variable lag fit’ is shown to enable ‘Lagrangian’ parameter recovery with artificial<br/>ecosystem data. A second approach employs spatiotemporal averaging, fitting a ‘weak prior’<br/>box model to suitably-averaged data from Georges Bank (as an example), allowing liberal<br/>biological parameter adjustments to account for mean effects of unresolved variability. A<br/>novel skill assessment technique is used to show that the extrapolative skill of the box model<br/>fails to improve on a strictly empirical model. Third, plankton models where horizontal variability<br/>is resolved ‘implicitly’ are investigated as an alternative to coarse or higher explicit<br/>resolution. A simple simulation study suggests that the mean effects of fine-scale variability<br/>on coarse-scale plankton dynamics can be serious, and that ‘spatial moment closure’ and<br/>similar statistical modelling techniques may be profitably applied to account for them.

Name dc:type.qualificationname

Ph.D.

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

University of Southampton

Year dc:date.issued

2008

Author dc:creator

• Wallhead, Philip John