http://hdl.handle.net/2122/153 2013-05-20T20:29:41Z http://hdl.handle.net/2122/8663 Title: Integrating geologic fault data into tsunami hazard studies Authors: Basili, R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Tiberti, M. M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Kastelic, V.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Romano, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Piatanesi, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Selva, J.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Lorito, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia Abstract: We present the realization of a fault-source data set designed to become the starting point in regional-scale tsunami hazard studies. Our approach focuses on the parametric fault characterization in terms of geometry, kinematics, and assessment of activity rates, and includes a systematic classification in six justification levels of epistemic uncertainty related with the existence and behaviour of fault sources. We set up a case study in the central Mediterranean Sea, an area at the intersection of the European, African, and Aegean plates, characterized by a complex and debated tectonic structure and where several tsunamis occurred in the past. Using tsunami scenarios of maximum wave height due to crustal earthquakes (Mw=7) and subduction earthquakes (Mw=7 and Mw=8), we illustrate first-order consequences of critical choices in addressing the seismogenic and tsunamigenic potentials of fault sources. Although tsunamis generated by Mw=8 earthquakes predictably affect the entire basin, the impact of tsunamis generated by Mw=7 earthquakes on either crustal or subduction fault sources can still be strong at many locales. Such scenarios show how the relative location/orientation of faults with respect to target coastlines coupled with bathymetric features suggest avoiding the preselection of fault sources without addressing their possible impact onto hazard analysis results. 2013-04-18T22:00:00Z http://hdl.handle.net/2122/8195 Title: Impacts of natural and anthropogenic climate variations on North Pacific plankton in an Earth System Model Authors: Patara, L.; CMCC; Vichi, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Masina, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia Abstract: The impacts of natural atmospheric variability and anthropogenic climate change on the spatial distribution, seasonality, structure, and productivity of North Pacific plankton groups are investigated by means of an Earth System Model (ESM) that contains a plankton model with variable stoichiometry. The ESM is forced with observed greenhouse gases for the 20th century and with the Intergovernmental Panel on Climate Change A1B Emission Scenario for the 21st century. The impacts of the two main modes of variability – connected with the Aleutian Low (AL) strength and with the North Pacific Oscillation (NPO) – are considered. When the AL is strong, primary productivity and chlorophyll concentrations are higher in the central Pacific, the seasonality of plankton is enhanced, and the classical grazing chain is stimulated, whereas in the Alaskan Gyre the model simulates a chlorophyll decrease and a shift toward smaller phytoplankton species. A stronger NPO increases productivity and chlorophyll concentration at ∼45°N. In the anthropogenic climate change scenario, simulated sea surface temperature is 4 °C higher with respect to contemporary conditions, leading to reduced mixing and nutrient supply at middle-subpolar latitudes. The seasonal phytoplankton bloom is reduced and occurs one month earlier, the flow of carbon to the microbial loop is enhanced, and phytoplanktonic stoichiometry is nutrient-depleted. Primary productivity is enhanced at subpolar latitudes, due to increased ice-free regions and possibly to temperature-related photosynthesis stimulation. This study highlights that natural climate variability may act alternatively to strengthen or to weaken the human-induced impacts, and that in the next decades it will be difficult to distinguish between internal and external climate forcing on North Pacific plankton groups. 2011-12-31T23:00:00Z http://hdl.handle.net/2122/8194 Title: Sensitivity of a marine coupled physical biogeochemical model to time resolution, integration scheme and time splitting method Authors: Butenschön, M.; University of Bologna; Zavatarelli, M.; University of Bologna; Vichi, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia Abstract: Coupled marine biogeochemical models are composed of a hydrodynamic component with a transport model for the ecological state variables and a model for the biogeochemical dynamics. The combination of these components involves the implementation of a numerical coupling method, that performs the spatial–temporal integration of the combined system, introducing an additional source of error to the system (splitting error). In this article we demonstrate the sensitivity of a comparatively complex 1D hydrodynamical biogeochemical model to the coupling method, showing that for an inadequate choice of the coupling method, the splitting error may dominate the numerical error of the system. It is demonstrated that for this type of system the tracer transport time scale clearly dominates over the scale of the biogeochemical processes, that maybe computed on significantly coarser time scales. In between the implemented coupling schemes Operator Splitting and Source Splitting, the Source Splitting method inserting the biogeochemical rates into the transport tracer integration is to be preferred for these type of models. 2011-12-31T23:00:00Z http://hdl.handle.net/2122/8193 Title: Global response to solar radiation absorbed by phytoplankton in a coupled climate model Authors: Patara, L.; CMCC; Vichi, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Masina, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Fogli, P. G.; CMCC; Manzini, E.; MPI Abstract: The global climate response to solar radiation absorbed by phytoplankton is investigated by performing multi-century simulations with a coupled ocean–atmosphere-biogeochemistry model. The absorption of solar radiation by phytoplankton increases radiative heating in the near-surface ocean and raises sea surface temperature (SST) by overall ~0.5°C. The resulting increase in evaporation enhances specific atmospheric humidity by 2–5%, thereby increasing the Earth’s greenhouse effect and the atmospheric temperatures. The Hadley Cell exhibits a weakening and poleward expansion, therefore reducing cloudiness at subtropical-middle latitudes and increasing it at tropical latitudes except near the Equator. Higher SST at polar latitudes reduces sea ice cover and albedo, thereby increasing the high-latitude ocean absorption of solar radiation. Changes in the atmospheric baroclinicity cause a poleward intensification of mid-latitude westerly winds in both hemispheres. As a result, the North Atlantic Ocean meridional overturning circulation extends more northward, and the equatorward Ekman transport is enhanced in the Southern Ocean. The combination of local and dynamical processes decreases upper-ocean heat content in the Tropics and in the subpolar Southern Ocean, and increases it at middle latitudes. This study highlights the relevance of coupled ocean–atmosphere processes in the global climate response to phytoplankton solar absorption. Given that simulated impacts of phytoplankton on physical climate are within the range of natural climate variability, this study suggests the importance of phytoplankton as an internal constituent of the Earth’s climate and its potential role in participating in its long-term climate adjustments. 2011-12-31T23:00:00Z http://hdl.handle.net/2122/8168 Title: Process studies on the ecological coupling between sea ice algae and phytoplankton Authors: Tedesco, L.; Marine Research Centre, Finnish Environment Institute; Vichi, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Thomas, D.; Marine Research Centre, Finnish Environment Institute Abstract: The seasonal dynamics of pelagic and sea ice communities are closely related in ice-covered waters, however, modelling works that analyse such interactions are scarce. We use the Biogeochemical Flux Model in Sea Ice (BFM-SI) coupled to the pelagic Biogeochemical Flux Model (BFM) in a study area in Greenland to quantitatively investigate: (1) the significance of photoacclimation/photoadaptation strategies of autotrophs, (2) the fate of the sea ice biomass in case of algae seeding, algae aggregation and at different mixed layer depths and (3) the changes in community production under a climate change scenario. The results show that sea ice algae need to be both photoacclimated and photoadapted to the sea ice environment in order to grow, while phytoplankton may adopt different strategies for optimising their growth. The seeding of the phytoplankton bloom shows to be driven, both in timing and magnitude, by the viability of sea ice algae and by the degree of aggregation of algae released from the ice, which also affects the sinking rate to the sea floor. Under a mild climate change scenario (SRES B2, 2071–2090) the sea ice community is projected to be generally more productive, whereas phytoplankton growth will be reduced because the melt of sea ice will occur earlier in the season when light is less favourable to sustain the growth. While it is generally anticipated that the melting of multi-year ice in the Arctic Ocean will cause an increase in marine production, this study shows that seasonal ice-covered seas in the Northern hemisphere may actually be less productive and may shift to more oligotrophic conditions within the next 100 years. 2011-12-31T23:00:00Z http://hdl.handle.net/2122/7755 Title: MyOcean Architetture & Design Document for Production Center sub system Authors: Drudi, Massimiliano; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Fratianni, Claudia; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Teruzzi, Anna; OGS, Trieste; Salon, Stefano; OGS, Trieste; Korres, Gerasimos; HCMR, Athens; Grandi, Alessandro; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Marino, Stefano; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Tonani, Marina; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia 2010-11-29T23:00:00Z http://hdl.handle.net/2122/7625 Title: Impact of appendicularians on detritus and export fluxes: a model approach at Dyfamed site Authors: Berline, L.; LOB; Stemman, L.; LOB; Vichi, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Lombard, F.; LOPB; Gorsky, G.; LOB Abstract: So far, the role of appendicularians in the biogeochemical cycling of organic matter has been largely overlooked. Appendicularians represent only a fraction of total mesozooplankton biomass, however these ubiquitous zooplankters have very high filtration and growth rates compared to copepods, and produce numerous fecal pellets and filtering houses contributing to export production by aggregating small marine particles. To study their quantitative impact on biogeochemical flux, we have included this group in the biogeochemical flux model, using a recently developed ecophysiological model. One-dimensional annual simulations of the pelagic ecosystem including appendicularians were conducted with realistic surface forcing for the year 2000, using data from the DyFAMed open ocean station. The appendicularian grazing impact was generally low, but appendicularians increased detritus production by 8% and export production by 55% compared to a simulation without appendicularians. Therefore, current biogeochemical models lacking appendicularians probably under, or misestimate the detritus and export production by omitting the pathway from small-sized plankton to fast sinking detritus. Detritus production and export rates are 60% lower than the estimates from mesotrophic sites, showing that appendicularians’ role is lower but still significant in oligotrophic environments. The simulated annual export at 200 m exceeds sediment trap values by 44%, suggesting an intense degradation during the sinking of appendicularian detritus, supported by observations made at other sites. Thus, degradation and grazing of appendicularian detritus need better quantification if we are to accurately assess the role of appendicularia in export flux. 2010-12-31T23:00:00Z http://hdl.handle.net/2122/7588 Title: Assimilating Along-Track Altimetric Observations through Local Hydrostatic Adjustment in a Global Ocean Variational Assimilation System Authors: Storto, A.; Centro Euro-Mediterraneo per i Cambiamenti Climatici, Bologna, Italy; Dobricic, S.; Centro Euro-Mediterraneo per i Cambiamenti Climatici, Bologna, Italy; Masina, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Di Pietro, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia Abstract: A global ocean three-dimensional variational data assimilation system was developed with the aim of assimilating along-track sea level anomaly observations, along with in situ observations from bathythermographs and conventional sea stations. All the available altimetric data within the period October 1992–January 2006 were used in this study. The sea level corrections were covariated with vertical profiles of temperature and salinity according to the bivariate definition of the background-error vertical covariances. Sea level anomaly observational error variance was carefully defined as a sum of instrumental, representativeness, observation operator, and mean dynamic topography error variances. The mean dynamic topography was computed from the model long-term mean sea surface height and adjusted through an optimal interpolation scheme to account for observation minus first-guess biases. Results show that the assimilation of sea level anomaly observations improves the model sea surface height skill scores as well as the subsurface temperature and salinity fields. Furthermore, the estimate of the tropical and subtropical surface circulation is clearly improved after assimilating altimetric data. Nonnegligible impacts of the mean dynamic topography used have also been found: compared to a gravimeter-based mean dynamic topography the use of the mean dynamic topography discussed in this paper improves both the consistency with sea level anomaly observations and the verification skill scores of temperature and salinity in the tropical regions. Furthermore, the use of a mean dynamic topography computed from the model long-term sea surface height mean without observation adjustments results in worsened verification skill scores and highlights the benefits of the current approach for deriving the mean dynamic topography. 2011-02-28T23:00:00Z http://hdl.handle.net/2122/7562 Title: Global ocean re-analyses for climate applications Authors: Masina, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Di Pietro, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Storto, A.; Centro Euro-Mediterraneo per i Cambiamenti Climatici, Bologna, Italy; Navarra, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia Abstract: One of the main objectives of the global ocean modelling activities at Centro Euro-Mediterraneo per i Cambiamenti Climatici (CMCC) is the production of global ocean re-analyses over multidecadal periods to reconstruct the state of the ocean and the large scale cir- culation over the recent past. The re-analyses are used for climate applications and for the assessment of the benefits of assimilating ocean observations on seasonal and longer predictions. Here we present the main characteristics of an optimal interpola- tion based assimilation system used to produce a set of global ocean re-analyses validated against a set of high quality in situ observa- tions and independent data. Differences among the experiments of the set are analyzed in terms of improvements in the method used to assimilate the data and the quality of observations them- selves. For example, the integrated ocean heat content, which can be taken as an indicator of climate changes, is examined to detect possible sources of uncertainty of its long-term changes. Global and basin scale upper ocean heat content exhibits warming trends over the last few decades that still depend in a significant way on the assimilated observations and the formulation of the background covariances. However, all the re-analyses show a global warming trend of the oceanic uppermost 700 m over the last five decades that falls within the range of the most recent observation-based estimates. The largest discrepancies between our estimates and observational based ones are confined in the upwelling regions of the PacificandAtlanticOceans.Finally,theresultsshow that the climatological heat and salt transports as a function of latitude also fall within the range of the estimates based on observations and atmospheric re-analyses. 2011-08-31T22:00:00Z http://hdl.handle.net/2122/6871 Title: Challenges of modeling depth-integrated marine primary productivity over multiple decades: A case study at BATS and HOT Authors: Saba, V.; VIMS; Friedrichs, M.A.M.; VIMS; et al.; including; Vichi, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia Abstract: The performance of 36 models (22 ocean color models and 14 biogeochemical ocean circulation models (BOGCMs)) that estimate depth-integrated marine net primary productivity (NPP) was assessed by comparing their output to in situ 14C data at the Bermuda Atlantic Time series Study (BATS) and the Hawaii Ocean Time series (HOT) over nearly two decades. Specifically, skill was assessed based on the models' ability to estimate the observed mean, variability, and trends of NPP. At both sites, more than 90% of the models underestimated mean NPP, with the average bias of the BOGCMs being nearly twice that of the ocean color models. However, the difference in overall skill between the best BOGCM and the best ocean color model at each site was not significant. Between 1989 and 2007, in situ NPP at BATS and HOT increased by an average of nearly 2% per year and was positively correlated to the North Pacific Gyre Oscillation index. The majority of ocean color models produced in situ NPP trends that were closer to the observed trends when chlorophyll-a was derived from high-performance liquid chromatography (HPLC), rather than fluorometric or SeaWiFS data. However, this was a function of time such that average trend magnitude was more accurately estimated over longer time periods. Among BOGCMs, only two individual models successfully produced an increasing NPP trend (one model at each site). We caution against the use of models to assess multiannual changes in NPP over short time periods. Ocean color model estimates of NPP trends could improve if more high quality HPLC chlorophyll-a time series were available 2009-12-31T23:00:00Z