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Relative sea level rise (RSLR) due to climate change and geodynamics represents the main threat for the survival of Venice,
emerging today only 90 cm above the Northern Adriatic mean sea level (msl). The 25 cm RSLR occurred over the 20th century,
consisting of about 12 cm of land subsidence and 13 cm of sea level rise, has increased the flood frequency by more than seven
times with severe damages to the urban heritage. Reasonable forecasts of the RSLR expected to the century end must be investigated
to assess the suitability of the Mo.S.E. project planned for the city safeguarding, i.e., the closure of the lagoon inlets
by mobile barriers. Here we consider three RSLR scenarios as resulting from the past sea level rise recorded in the Northern
Adriatic Sea, the IPCC mid-range A1B scenario, and the expected land subsidence. Available sea level measurements show that
more than 5 decades are required to compute a meaningful eustatic trend, due to pseudo-cyclic 7–8 year long fluctuations.
The period from 1890 to 2007 is characterized by an average rate of 0.12 ± 0.01 cm/year. We demonstrate that linear regression
is the most suitable model to represent the eustatic process over these 117 year. Concerning subsidence, at present Venice
is sinking due to natural causes at 0.05 cm/year. The RSLR is expected to range between 17 and 53 cm by 2100, and its repercussions
in terms of flooding frequency are associated here to each scenario. In particular, the frequency of tides higher than 110 cm,
i.e., the value above which the gates would close the lagoon to the sea, will increase from the nowadays 4 times per year
to a range between 20 and 250. These projections provide a large spread of possible conditions concerning the survival of
Venice, from a moderate nuisance to an intolerable aggression. Hence, complementary solutions to Mo.S.E. may well be investigated. 相似文献
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Mullan Donal Swindles Graeme Patterson Tim Galloway Jennifer Macumber Andrew Falck Hendrik Crossley Laura Chen Jie Pisaric Michael 《Theoretical and Applied Climatology》2017,129(3-4):1089-1108
Theoretical and Applied Climatology - Climate models project that the northern high latitudes will warm at a rate in excess of the global mean. This will pose severe problems for Arctic and... 相似文献
67.
Laura M. Kracker 《The Professional geographer》1999,51(3):440-450
Rather than seeing the oceans as an expansive void, researchers using acoustic technologies can detect the heterogeneity of biological resources and view the marine environment as a three-dimensional landscape. Underwater remote sensing, using acoustics, provides high resolution maps of the spatial distribution of organisms in aquatic ecosystems. Analyzing the spatial pattern of species distribution within the water column and the impact of that organization on ecological processes bridges the fields of fisheries and spatial analysis. Tools and concepts familiar to geographers, such as remote sensing, GIS, and landscape ecology, contribute to the investigation of large lake and marine ecosystems. 相似文献
68.
Deep-sea corals have been shown to be useful archives of rapid changes in ocean chemistry during the last glacial cycle. Their aragonitic skeleton can be absolutely dated by U-Th data, freeing radiocarbon to be used as a water-mass proxy. For certain species of deep-sea corals, the growth rate allows time resolution that is comparable to ice cores. An additional proxy is needed to exploit this opportunity and turn radiocarbon data into rates of ocean overturning in the past.Neodymium isotopes in seawater can serve as a quasi-conservative water-mass tracer and initial results indicate that deep-sea corals may be reliable archives of seawater Nd isotopes. Here we present a systematic study exploring Nd isotopes as a water-mass proxy in deep-sea coral aragonite. We investigated five different genera of modern deep-sea corals (Caryophyllia, Desmophyllum, Enallopsamia, Flabellum, Lophelia), from global locations covering a large potential range of Nd isotopic compositions. Comparison with ambient seawater measurements yields excellent agreement and suggests that deep-sea corals are reliable archives for seawater Nd isotopes.A parallel study of Nd concentrations in these corals yields distribution coefficients for Nd between seawater and coral aragonite of 1-10, omitting one particular genus (Enallopsamia). The corals and seawater did however not come from exactly the same location, and further investigations are needed to reach robust conclusions on the incorporation of Nd into deep-sea coral aragonite.Lastly, we studied the viability of extracting the Nd isotope signal from fossil deep-sea corals by carrying out stepwise cleaning experiments. Our results show that physical removal of the ferromanganese coating and chemical pre-cleaning have the highest impact on Nd concentrations, but that oxidative/reductive cleaning is also needed to acquire a seawater Nd isotope signal. 相似文献
69.
Luciano Cortesogno Laura Gaggero Alberto Zanetti 《Contributions to Mineralogy and Petrology》2000,139(4):373-393
SIMS analyses have been carried out on clinopyroxenes, plagioclases and amphiboles of six gabbroic samples from Holes 921–924
of the Ocean Drilling Program Leg 153 sited in the MARK area of the Mid-Atlantic Ridge at the ridge–transform intersection,
to investigate the rare earth, trace and volatile element distribution in the lower ocean crust during igneous crystallization
and higher grade metamorphic conditions. The metagabbros underwent granulite to subgreenschist facies conditions through three
main tectono-metamorphic phases: (1) ductile regime (750 < T < 1000 °C and P ≈ 0.3 GPa); (2) transitional regime (600 < T < 700 °C
and P ≈ 0.2 GPa); (3) brittle regime (350 ≤ T < 600 °C and P < 0.2 GPa). Igneous clinopyroxenes show C1-chondrite normalized
patterns depleted in LREE, and nearly flat for HREE. The rare earth and trace element distributions in igneous clinopyroxenes
and plagioclases indicate that these minerals act as REE reservoirs, and comprise the main contribution to the overall rock
content. The abundances in igneous minerals reflect the degree of fractionation of the parent liquids. In metamorphic clinopyroxenes
recrystallized in anhydrous assemblages, the REE and trace elements patterns mimic those of the primary ones. Conversely,
clinopyroxene re-equilibrated in amphibole-bearing assemblages shows a significant increase in REE, Ti, Zr, Y and V, a negative
Eu anomaly, and slight decreases in Sr and Ba. An overall increase of REE and some trace elements is evident in hydrous assemblages,
with preferential partitioning in the amphibole. It shows high Ti (18196–22844 ppm), LREE depleted patterns and LaN/SmN=0.10–0.33, LaN/YbN=0.10–0.30. Amphiboles from granoblastic assemblages show homogeneous patterns with no or a positive anomaly for TiN and negative anomalies for SrN and ZrN. Volatiles in amphibole are low, with Cl/F < 1; H2O% is significantly lower than the stoichiometric ratio (1.33–1.53%). The composition of the clinopyroxene and amphibole recrystallized
in low-strain domains records evidence of incomplete re-equilibration, and element diffusion and partitioning is in part controlled
by the textural site. The possible origins of the fluids involved in the metamorphic recrystallization are discussed: (1)
remobilization from igneous amphibole; (2) exsolution from evolved melts; (3) introduction of seawater-derived fluids modified
in rock-dominated systems; (4) injection of highly evolved hydrous melts during the metamorphic process.
Received: 6 September 1999 / Accepted: 6 March 2000 相似文献
70.
This article is intended to explain the snow avalanche occurrence, as a natural phenomenon directly influenced by the local natural conditions, for the well-delimited area represented by the Piatra Mica massif, belonging to the Piatra Craiului mountain range (southern Carpathians). In this respect, depending on the factors that may trigger or encourage the avalanches, some vulnerable areas with avalanche occurring conditions have been identified, based on the analysis of the relationships among the factors controlling the avalanche vulnerability in the study area. These factors are mainly represented by the slope aspect, which induces from the very beginning some specific features for each type of slope (north-, east-, south and west-facing slopes), the geological structure, slope gradient and topography. At the same time, the general climatic and biological features have been taken into account, from the point of view of their importance for avalanche occurrence and distribution. Depending on the microrelief exhibited by the avalanche chutes, one can establish distinct dynamical features for each of the four major slopes of the massif. It is worth mentioning that for this study area, this is the first paper dealing with avalanche phenomenon, vulnerable space, control factors and landscape dynamics. In accomplishing this demarche, we used detailed mappings in the field in several stages, the processing of satellite images, analytical (declivities, the exposure of slopes, etc.) and synthetic maps from which the dynamic of sectors with avalanches resulted. The findings of this investigation may further be employed for solving the problems raised by avalanche-prone areas, as well as for devising a better strategy for the effective management of the mountain realm. 相似文献