http://hdl.handle.net/2122/179 Ricerca nel canale cerca http://www.earth-prints.org/simple-search http://hdl.handle.net/2122/5956 Titolo: BFM-SI: A new implementation of the biogeochemical flux model in sea ice<br/><br/>Autori: Tedesco, Letizia; CMCC; Vichi, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia<br/><br/>Abstract: This work describes a novel implementation of the Biogeochemical Flux Model (BFM) in a sea ice system (BFMSI). The chosen representative groups of the sea ice food web rely on the same dynamics as the BFM. The main differences between BFM and BFMSI stand in the type and number of functional groups, in the parameters assigned to several physiological and ecological processes and in the dimensional size classes they represent. The differential equations of BFMSI are written here according to the nomenclature associated to the new sea ice state variables. At the boundaries, the sea ice system is also coupled to the atmosphere and to the ocean through the exchange of organic and inorganic matter. This is done by computing the entrapment of particulate and dissolved matter and gases when sea ice grows and release to the ocean when sea ice melts to ensure mass conservation. The implementation of the BFM in sea ice and the coupling structure in General Circulation Models will add a new component that may provide new adequate estimate of the role and importance of sea ice biogeochemistry in the global carbon cycle. http://hdl.handle.net/2122/5760 Titolo: Particle fluxes in the deep Eastern Mediterranean basins: the role of ocean vertical velocities<br/><br/>Autori: Patara, L.; Centro Euro-Mediterraneo per i Cambiamenti Climatici (CMCC) Viale Aldo Moro, 44, 40127 Bologna; Pinardi, N.; Laboratorio SINCEM, Università di Bologna, Via San Alberto 163, 48100 Ravenna; Corselli, C.; Dipartimento di Scienze Geologiche e Geotecnologie, Universit`a Milano-Bicocca, Piazza della Scienza 4, 20126 Milan, Italy; Malinverno, E.; Dipartimento di Scienze Geologiche e Geotecnologie, Universit`a Milano-Bicocca, Piazza della Scienza 4, 20126 Milan, Italy; Tonani, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Santoleri, R.; Istituto di Scienze dell’Atmosfera e del Clima – C.N.R., Via del Fosso del Cavaliere 100, 00133 Rome, Italy; Masina, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia<br/><br/>Abstract: This paper analyzes the relationship betweendeep sedimentary fluxes and ocean current vertical velocitiesin an offshore area of the Ionian Sea, the deepestbasin of the Eastern Mediterranean Sea. Sediment trap dataare collected at 500m and 2800m depth in two successivemoorings covering the period September 1999–May 2001.A tight coupling is observed between the upper and deeptraps and the estimated particle sinking rates are more than200mday−1. The current vertical velocity field is computedfrom a 1/16 ×1/16 Ocean General Circulation Model simulationand from the wind stress curl. Current vertical velocitiesare larger and more variable than Ekman vertical velocities,yet the general patterns are alike. Current verticalvelocities are generally smaller than 1mday−1: we thereforeexclude a direct effect of downward velocities in determininghigh sedimentation rates. However we find that upwardvelocities in the subsurface layers of the water column arepositively correlated with deep particle fluxes. We thus hypothesizethat upwelling would produce an increase in upperocean nutrient levels – thus stimulating primary productionand grazing – a few weeks before an enhanced verticalflux is found in the sediment traps. High particle sedimentationrates may be attained by means of rapidly sinking fecalpellets produced by gelatinous macro-zooplankton. Othersedimentation mechanisms, such as dust deposition, are alsoconsidered in explaining large pulses of deep particle fluxes.The fast sinking rates estimated in this study might be an evi-Correspondence to: L. Patara(patara@bo.ingv.it)dence of the efficiency of the biological pump in sequesteringorganic carbon from the surface layers of the deep EasternMediterranean basins. http://hdl.handle.net/2122/5744 Titolo: Modelling approach to the assessment of biogenic fluxes at a selected Ross Sea site, Antarctica<br/><br/>Autori: Vichi, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Coluccelli, A.; UniPoliMa; Ravaioli, F.; CNR-ISMAR; Giglio, F.; CNR-ISMAR; Langone, L.; CNR-ISMAR; Azzaro, M.; CNR-IAMC; Azzaro, F.; CNR-IAMC; La Ferla, R.; CNR-IAMC; Catalano, G.; CNR-ISMAR; Cozzi, S.; CNR-ISMAR<br/><br/>Abstract: Several biogeochemical data have been collected in the last 10 years of Italian activity in Antarctica (ABIOCLEAR, ROSSMIZE, BIOSESO-I/II). A comprehensive 1-D biogeochemical model was implemented as a tool to link observations with processes and to investigate the mechanisms that regulate the flux of biogenic material through the water column. The model is ideally located at station B (175° E–74° S) and was set up to reproduce the seasonal cycle of phytoplankton and organic matter fluxes as forced by the dominant water column physics over the period 1990–2001. Austral spring-summer bloom conditions are assessed by comparing simulated nutrient drawdown, primary production rates, bacterial respiration and biomass with the available observations. The simulated biogenic fluxes of carbon, nitrogen and silica have been compared with the fluxes derived from sediment traps data. The model reproduces the observed magnitude of the biogenic fluxes, especially those found in the bottom sediment trap, but the peaks are markedly delayed in time. Sensitivity experiments have shown that the characterization of detritus, the choice of the sinking velocity and the degradation rates are crucial for the timing and magnitude of the vertical fluxes. An increase of velocity leads to a shift towards observation but also to an overestimation of the deposition flux which can be counteracted by higher bacterial remineralization rates. Model results suggest that the timing of the observed fluxes depends first and foremost on the timing of surface production and on a combination of size-distribution and quality of the autochtonous biogenic material. It is hypothesized that the bottom sediment trap collects material originated from the rapid sinking of freshly-produced particles and also from the previous year's production period. http://hdl.handle.net/2122/5701 Titolo: On the corrections of ERA-40 surface flux products consistent with the Mediterranean heat and water budgets and the connection between basin surface total heat flux and NAO<br/><br/>Autori: Pettenuzzo, D.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Large, W.G.; National Center for Atmospheric Research, Boulder, Colorado; Pinardi, N.; Bologna University, Corso di Scienze Ambientali, Ravenna, Italy<br/><br/>Abstract: This is a study of heat fluxes and heat budget of the Mediterranean Sea using the European Centre for Medium-Range Weather Forecasts (ECMWF) 45 year reanalysis data set ERA-40. The simple use of the ERA-40 surface flux components fails to close the budget and, in particular, the shortwave radiation flux is found to be underestimated with respect to observed data by about 10%. The heat flux terms are recomputed and corrected in order to close the heat and freshwater budgets of the Mediterranean basin over the period 1958 to 2001, thus producing a corrected ERA-40 surface flux data set. Various satellite and in situ observational data are used to construct spatially varying corrections to the ERA-40 products needed to compute the air-sea fluxes. The corrected interannual and climatological net surface heat and freshwater fluxes are and , respectively, which are regarded as satisfactorily closing the Mediterranean heat and water budgets. It is also argued that there is an important contribution from large heat losses associated with a few severe winters over the Mediterranean Sea. This is shown to be related to wind regime anomalies, which strongly affect the latent heat of evaporation that is the main responsible for the interannual modulation of the total heat flux. Furthermore, the surface total heat flux anomaly time series is compared with the North Atlantic Oscillation (NAO) index, and the result is a positive correlation with ocean warming for positive NAO index and cooling associated to negative index periods. http://hdl.handle.net/2122/5699 Titolo: Is the southeastern Adriatic Sea coastal strip 1 an eutrophic area?<br/><br/>Autori: Marini, M.; Institute of Marine Science, National Research Council, Ancona, Italy; Grilli, F.; 1Institute of Marine Science, National Research Council, Ancona, Italy; Guarnieri, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Jones, B.; University of Southern California, Los Angeles, USA; Klajic, Z.; Institute of Marine Biology Kotor, Montenegro; Pinardi, N.; CIRSA, University of Bologna, Ravenna, Italy; Sanxhaku, M.; Institute of Hydrometeorology, Tirana, Albania<br/><br/>Abstract: The aim of the present study is to understand and assess the eutrophic state of the Buna-Bojana river delta coastal strip, in the southeastern Adriatic Sea, and contrast it with the northern Po river dominated shelf area. We present and compare observations of chemical and physical state variables from the two areas of the Adriatic Sea and we also use a numerical model output to depict the circulation structures of the two areas. The area affected by the Po River discharge extends at least one hundred kilometres southward of the delta and approximately twenty kilometres offshore. Maximum chlorophyll concentrations follow closely the river waters. Similarly to the northern Adriatic Sea, the Buna/Bojana river discharge extends northward along the coasts for one hundred kilometres and shows large maxima in chlorophyll. The two coastal areas have opposite dominant dynamical processes: while the Po river affected area is a downwelling region, the Buna/Bojana is characterized by upwelling favourable winds. However, during the period of study, upwelling is not a dominant feature of the circulation and both the shelf slope current and the along shore currents in the southeastern Adriatic Sea are northward, the along shore current probably dominated by the river runoff. Under these conditions, primary productivity is high in both areas which allows us to conclude that river plume dynamics with the associated nutrient inputs control the eutrophication state of the coastal strip, regardless of the general hydrodynamics regime of the southeastern Adriatic Sea area http://hdl.handle.net/2122/4515 Titolo: Temporal Changes in Fluid Chemistry and Energy Profiles in the Vulcano Island Hydrothermal System<br/><br/>Autori: Rogers, K. L.; Department of Earth and Planetary Sciences, Washington University, St. Louis, Missouri.; Amend, J. P.; Department of Earth and Planetary Sciences, Washington University, St. Louis, Missouri.; Gurrieri, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia<br/><br/>Abstract: In June 2003, the geochemical composition of geothermal fluids was determined at 9 sites in the Vulcano hydrothermal system, including sediment seeps, geothermal wells, and submarine vents. Compositional data were combined with standard state reaction properties to determine the overall Gibbs free energy (deltaGr) for 120 potential lithotrophic and heterotrophic reactions. Lithotrophic reactions in the H-O-N-S-C-Fe system were considered, and exergonicreactions yielded up to 120 kJ per mole of electrons transferred. The potential for heterotrophy was characterized by energy yields from the complete oxidation of 6 carboxylic acids—formic, acetic, propanoic, lactic, pyruvic, and succinic—with the following redox pairs:O2/H2O, SO4 2-/H2S, NO3-/NH4+, S0/H2S, and Fe3O4/Fe2+. Heterotrophic reactions yielded 6–111 kJ/mol e-. Energy yields from both lithotrophic and heterotrophic reactions were highly dependent on the terminal electron acceptor (TEA); reactions with O2 yielded the most energy, followed by those with NO3-, Fe(III), SO4 2-, and S0. When only reactions with complete TEA reduction were included, the exergonic lithotrophic reactions followed a similar electron tower. Spatial variability in deltaGr was significant for iron redox reactions, owing largely to the wide range in Fe2+ and H+ concentrations. Energy yields were compared to those obtained for samples collected in June 2001. The temporal variations in geochemicalcomposition and energy yields observed in the Vulcano hydrothermal system between 2001and 2003 were moderate. The largest differences in deltaGr over the 2 years were from iron redox reactions, due to temporal changes in the Fe2+ and H+ concentrations. The observed variations in fluid composition across the Vulcano hydrothermal system have the potential to influence not only microbial diversity but also the metabolic strategies of the resident microbialcommunities. http://hdl.handle.net/2122/4504 Titolo: A process-oriented model study of equatorial Pacific phytoplankton: the role of iron supply and tropical instability waves<br/><br/>Autori: Vichi, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Masina, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Nencioli, F.; Università di Bologna e Università di Santa Barbara, US<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 biogeochemical 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. The presence of a continental iron source is necessary for the maintenance of the observed subsurface iron maximum in the EUC core. In the eastern Pacific region, phytoplankton production is enhanced when additional iron is available in the EUC. Simulated 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 factors. When the iron nutricline is sufficiently shallow to be reached by the wave vertical scale, the effect of the waves is to enhance iron availability in the euphotic zone leading to a net local increase of phytoplankton biomass. We therefore suggest that the local maxima of phytoplankton observed in moorings off the Equator in the eastern Pacific might be not only the result of concentration mechanisms, but also the result of an increase in local production sustained by advected iron. http://hdl.handle.net/2122/3822 Titolo: Particle fluxes in the deep Eastern Mediterranean basins: the role of ocean vertical velocities<br/><br/>Autori: Patara, L.; Centro Euro-Mediterraneo per i Cambiamenti Climatici; Pinardi, N.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Corselli, C.; Universita' di Milano-Bicocca; Malinverno, E.; Universita' di Milano-Bicocca; Tonani, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Santoleri, R.; Istituto di Scienze Atmosferiche e del Clima, Roma; Masina, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia<br/><br/>Abstract: This paper analyzes the relationship between deep sedimentary fluxes and ocean current vertical velocities in an offshore area of the Ionian Sea, the deepest basin of the Eastern Mediterranean Sea. Sediment trap data are collected at 500 m and 2800 m depth in two successive moorings covering the period September 1999 – May 2001. A tight coupling is observed between the upper and deep traps and the deduced particle settling rates are larger than 200 m/day. The current vertical velocity field is computed from a high resolution Ocean General Circulation Model (OGCM) simulation and from the wind stress curl. Values are generally smaller than 1 m/day: we therefore exclude a direct effect of downward vertical velocities in determining sedimentation rates. However we find that upward vertical velocities in the subsurface layers of the water column are significantly correlated with deep particle fluxes. We thus hypothesize that upwelling would produce an increase in upper ocean nutrient levels - thus stimulating primary productivity and grazing - a few weeks before an enhanced vertical flux is found in the sediment traps. The role of ocean vertical velocities on deep particle fluxes would therefore be indirect. High particle sedimentation rates may be attained by means of rapidly sinking fecal pellets produced by gelatinous macro-zooplankton organisms. Other sedimentation mechanisms, such as dust deposition, are also taken into account in explaining large pulses of deep particle fluxes. http://hdl.handle.net/2122/3796 Titolo: Biogeographic validation of a global ocean biogeochemical model<br/><br/>Autori: 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. http://hdl.handle.net/2122/3453 Titolo: Modelling approach to the assessment of biogenic fluxes at a selected Ross Sea site, Antarctica<br/><br/>Autori: Vichi, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Coluccelli, A.; UNIVPM, Italy; Ravaioli, M.; CNR-ISMAR; Giglio, F.; CNR-ISMAR; Langone, L.; CNR-ISMAR; Azzaro, M.; CNR-IAMC; Azzaro, F.; CNR-IAMC; La Ferla, R.; CNR-IAMC; Cozzi, S.; CNR-ISMAR; Catalano, G.; CNR-ISMAR<br/><br/>Abstract: Abstract Several biogeochemical data have been collected in the last 10 years of Italian activity in Antarctica (ABIOCLEAR, ROSSMIZE, BIOSESO-I/II). A comprehensive 1-D biogeochemical model was implemented as a tool to link observations with processes and to investigate the mechanisms that regulate the flux of biogenic material through the water column. The model is ideally located at station B (175^{o}E - 74^{o}S) and was set up to reproduce the seasonal cycle of phytoplankton and organic matter fluxes as forced by the dominant water column physics over the period 1990-2001. Austral spring-summer bloom conditions are assessed by comparing simulated nutrient drawdown, primary production rates, bacterial respiration and biomass with the available observations. The simulated biogenic fluxes of carbon, nitrogen and silica have been compared with the fluxes derived from sediment traps data. The model reproduces quite well the magnitude of the biogenic fluxes, expecially those observed in the bottom sediment trap, but the peaks are delayed in time. Sensitivity experiments have shown that the characterization of detritus, the choice of the sinking velocity and the degradation rates are crucial for the timing and magnitude of the vertical fluxes. An increase of velocity leads to a shift towards observation but also to an overestimation of the deposition flux which can be counteracted by higher bacterial remineralization rates. Model results suggest that observed fluxes could be explained by the size-distribution and quality of the locally-produced biogenic material. It is hypothesized that the bottom sediment trap collects material originated from rapid sinking of particles and also from previous years production periods, likely modulated by advective and aggregation mechanisms which are still not resolved by the model.