http://hdl.handle.net/2122/159 Search the Channel search http://www.earth-prints.org/simple-search http://hdl.handle.net/2122/3796 Title: Biogeographic validation of a global ocean biogeochemical model <br/> <br/>Authors: Vichi, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Allen, J. I.; PML, UK; Hardman-Mountford, N.; PML, UK <br/> <br/>Abstract: Currently biogeochemical models of the global ocean focus on simulating the coupling between prevalent physical conditions and the biogeochemical processes with the underlying assumption that coherent biological properties are a direct (or modulated) response to physics. This is one possible biogeographic characterisation of the pelagic environment, since biogeochemistry represents only one aspect of marine ecosystems. Several models are currently capable of simulating the chlorophyll distribution observed from space, though an objective validation with respect to relevant ecosystem properties is still lacking. In this paper we analyse the results of one of the most comprehensive models of ocean biogeochemistry with an emphasis on biogeographic validation sensu Longhurst (Ecological Geography of the Sea, 2007, 2nd edition, Academic Press). A set of multivariate statistical tools, Multi Dimensional Scaling (MDS) and Principal Components Analysis (PCA), are used to verify the existence of pre-defined biogeographic provinces and their statistical significance. The MDS ordination indicates that the given provinces are recognizable in the model on the basis of the selected variables. Analysis of Similarity (ANOSIM) shows that the provinces are statistically separable and they can be more easily distinguished in terms of their environmental features rather than their biology. The underlying relationships between the physical and biological properties are investigated through correlation analyses, thus providing some insights on how the model reproduces features characteristic of the various regions. Satellite chlorophyll data have been used to demonstrate external validation at the biogeographic level. The a priori provinces as characterised by chlorophyll values cannot be statistically separated in either the data or the model. It is likely this is related to the arbitrary choice of province boundaries, which are not necessarily the same as those derivable from non-interpolated SeaWiFS data. The PCA comparison of modelled and observed chlorophyll demonstrated some objective skill in the model as it generally captures the dominant mode of the data, although severe mismatch was identified in certain regions by visual comparison (Indian and Southern Oceans). The model also overestimated seasonal variability compared to the data. The method shows promise for helping overcome problems with model verification due to undersampling of most ocean biogeochemical variables. Mon, 29 Oct 2007 22:58:59 GMT http://hdl.handle.net/2122/3452 Title: A numerical simulation study of dissolved organic carbon accumulation in the northern Adriatic Sea <br/> <br/>Authors: Polimene, L.; Centro Interdipartimentale per la Ricerca sulle Scienze Ambientali, Università di Bologna, Ravenna, Italy; Pinardi, N.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Zavatarelli, M.; Centro Interdipartimentale per la Ricerca sulle Scienze Ambientali, Università di Bologna, Ravenna, Italy; Allen, J. I.; Plymouth Marine Laboratory, Plymouth, UK; Giani, M.; Istituto Centrale per la Ricerca scientifica e tecnologica Applicata al Mare (ICRAM) sts Chioggia, Chioggia, Italy; Vichi, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia <br/> <br/>Abstract: A mechanistic explanation for the accumulation of dissolved organic carbon (DOC), observed in coastal seas such as the Northern Adriatic Sea, is proposed here on the basis of numerical simulations of the marine ecosystem dynamics carried out with a coupled biogeochemical-circulation model. The biogeochemical model is based on the European Regional Seas Ecosystem Model (ERSEM) upgraded with a more detailed representation of the DOC-bacteria interactions and resolving different level of DOC lability/refractivity. The circulation model is the Adriatic Sea implementation of the Princeton Ocean Model. The analysis of simulations confirms the important role of the Po river nutrient input on the ecosystem dynamics and highlights the presence of a strong across-shelf trophic gradient that, affecting the Bacterial Growth Efficiency (BGE), could be a key factor for the DOC accumulation. The simulations show the importance of circulation features in modulating the exchanges between areas having different trophic structure such as the western coastal strip, strongly influenced by the Po river runoff, and the open sea areas in the centre of the northern Adriatic sub-basin. The DOC produced in the high energy system of the Po runoff coastal strip, characterized by high BGE, is transported toward the open areas, which is a more oligotrophic environment with lower BGE. In this area the DOC turnover time is strongly increased giving rise to the DOC accumulation. Tue, 06 Mar 2007 22:58:59 GMT http://hdl.handle.net/2122/3438 Title: A generalized model of pelagic biogeochemistry for the global ocean ecosystem. Part II: Numerical simulations <br/> <br/>Authors: Vichi, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Masina, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Navarra, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia <br/> <br/>Abstract: This paper presents a global ocean implementation of a multi-component model of marine pelagic biogeochemistry coupled on-line with an ocean general circulation model forced with climatological surface fields (PELAgic biogeochemistry for Global Ocean Simulations, PELAGOS). The final objective is the inclusion of this model as a component in an Earth System model for climate studies. The pelagic model is based on a functional stoichiometric representation of marine biogeochemical cycles and allows simulating the dynamics of C, N, P, Si, O and Fe taking into account the variation of their elemental ratios in the functional groups. The model also includes a parameterization of variable chlorophyll/carbon ratio in phytoplankton, carrying chl as a prognostic variable. The first part of the paper analyzes the contribution of non-local advective–diffusive terms and local vertical processes to the simulated chl distributions. The comparison of the three experiments shows that the mean chl distribution at higher latitudes is largely determined by mixing processes, while vertical advection controls the distribution in the equatorial upwelling regions. Horizontal advective and diffusive processes are necessary mechanisms for the shape of chl distribution in the sub-tropical Pacific. In the second part, the results have been compared with existing datasets of satellite-derived chlorophyll, surface nutrients, estimates of phytoplankton community composition and primary production data. The agreement is reasonable both in terms of the spatial distribution of annual means and of the seasonal variability in different dynamical oceanographic regions. Results indicate that some of the model biases in chl and surface nutrients distributions can be related to deficiencies in the simulation of physical processes such as advection and mixing. Other discrepancies are attributed to inadequate parameterizations of phytoplankton functional groups. The model has skill in reproducing the overall distribution of large and small phytoplankton but tends to underestimate diatoms in the northern higher latitudes and overestimate nanophytoplankton with respect to picoautotrophs in oligotrophic regions. The performance of the model is discussed in the context of its use in climate studies and an approach for improving the parameterization of functional groups in deterministic models is outlined. Fri, 29 Dec 2006 22:58:59 GMT http://hdl.handle.net/2122/3434 Title: A process-oriented model study of equatorial Pacific phytoplankton: the role of iron supply and tropical instability waves <br/> <br/>Authors: Vichi, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Nencioli, F.; Centro Interdipartimentale di Ricerca per le Scienze Ambientali, Ravenna, Italy; Masina, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia <br/> <br/>Abstract: The response of phytoplankton growth to iron supply and its modulation by large scale circulation and tropical instability waves (TIWs) in the eastern equatorial Pacific has been investigated with an ocean biogeochemistry model. This process study shows that iron can be efficiently advected from the New Guinea shelf through the Equatorial Undercurrent (EUC) to the eastern Pacific. In this region phytoplankton production is enhanced when an additional source of iron is applied in the New Guinea shelf and advected in the model by the EUC. In the eastern Pacific, phytoplankton variability is linked to TIWs activity, as revealed by a wavelet analysis of the total autotrophic carbon. The net local effect of the waves on phytoplankton can be either positive or negative depending on several fac- tors. In some cases the effect of the waves is to enhance iron availability in the euphotic zone leading to a net local increase of phytoplankton biomass, provided that the iron nu- tricline is sufficiently shallow to be reached by the wave vertical scale. In these cases it is also suggested that local maxima of phytoplankton observed in moorings off equator are sustained by advected iron and subsequent local production instead of being the result of concentration mechanisms. Sun, 29 Oct 2006 22:58:59 GMT