Spatio-temporal variability and vertical distribution of a low rocky subtidal assemblage in the north-west Mediterranean     

David Balata  Stefano Acunto  Francesco Cinelli 《Estuarine, Coastal and Shelf Science》2006,67(4):553-561

Natural assemblages show large variability at multiple scales in space and time as a consequence of several abiotic and biological factors. This study was conducted in conditions of high turbidity of the water and examined the spatio-temporal variability and the vertical distribution at two different depths of a low rocky subtidal assemblage. Algal and invertebrate organisms were sampled at a range of spatial scales extending from meters to a few kilometers, over a period of 21 months. Results indicated that patterns of distribution and abundance of organisms differed between the two depths and at the smallest spatial scales examined. These differences were due to differences in relative abundance rather than differences in composition of taxa. Results showed that assemblages varied largely among dates of sampling, suggesting that temporal variability of these organisms may be more important than previously stated. The patchy distribution and the peculiar life traits of most taxa of these assemblages allowed the concept of metapopulation and metacommunity to be applied to this system. This might have implications for predictions of the responses of subtidal assemblages to environmental changes due to anthropogenic activities.  相似文献   

Carbon and nitrogen isotope excursions in mid-Pleistocene sapropels from the Tyrrhenian Basin: Evidence for climate-induced increases in microbial primary production     

Philip A. Meyers  Stefano M. Bernasconi 《Marine Geology》2005,220(1-4):41-58

The modern Mediterranean Sea is oligotrophic, yet its sediment record contains layers of organic-carbon-rich sapropels at 21 ky (precessional) spacing that imply periods of elevated paleoproductivity that approached the high productivities of modern upwelling systems. Resolution to this paradox is provided by lines of evidence suggesting that the mode of primary productivity changed from one dominated by algae to one during times of sapropel deposition in which photosynthetic bacteria were important. We have made a high-resolution comparison of the organic carbon and nitrogen isotopic compositions of three sapropels and their background sediments in a 3-m sequence that corresponds to 1001 to 946 ka. Organic δ¹³C values systematically increase from − 26‰ to − 21‰ and δ¹⁵N values systematically decrease from 4‰ to < 0‰ as organic carbon mass accumulation rates increase in the sapropel layers. The increase in carbon isotope values mirrors the increases in primary productivity and associated organic matter export indicated by the increased mass accumulation rates. The decrease in nitrogen isotope values implies major contributions of nitrogen-fixing cyanobacteria to the total marine productivity. The precessional minima with which sapropels coincide were times of wetter climate that stratified the surface Mediterranean Sea, increased delivery of soil-derived phosphorus, and evidently amplified microbial primary production. Our high-resolution study reveals several relatively rapid excursions into and out of the high-productivity mode that suggest that sapropel deposition was a climate-sensitive surface-driven phenomenon that was not accompanied by basin-wide stagnation.  相似文献   

PAssive COastal TOMography: an Innovative Approach for the Remote Monitoring of Sea Temperature     

Enrico De  Marinis  Paola Picco  Alessandro Crise  Otello Gasparini  Stefano Salon 《Marine Ecology》2002,23(S1):122-137

Abstract. This paper describes a new Ocean Acoustic Tomography (OAT) methodology - a passive tomography - presently in an advanced development phase. This technique has been developed for long-term, extensive, remote monitoring of the seawater temperature spatial distribution, which is estimated from the received noise emitted from ships of opportunity. To test the passive tomographic processor under controlled conditions, the components of the naval noise from different kinds of vessels was analysed and realistic naval noise was simulated. The feasibility of the proposed methodology was confirmed by test-runs on semi-synthetic data; its capability to resolve temperature profiles will be better assessed with the use of real acoustic and environmental data collected during the INTIMATE00 experiment performed in October 2000 in the Atlantic Ocean off the Portuguese coast. An analysis of the space and time variability of the Empirical Orthogonal Function (EOF) decomposition of the sound speed (SSP) in the Mediterranean Sea has been carried out to identify areas where acoustic tomography can be successfully applied. Results from simulations in the South Adriatic Sea, which was identified as a region with a high sound speed variability associated with the seasonal cycle and with the main oceanographic processes, are reported.  相似文献   

The role of the European Community in the Mediterranean coastal zone management     

Stefano Belfiore 《Ocean & Coastal Management》1996,31(2-3)

The objective of this paper is to focus on the role of the European Community (EC) in the management of the coastal zones of the Mediterranean. The EC performs this role at two levels of involvement: with respect to its Mediterranean member states and through the Euro-Mediterranean co-operation, in co-ordination with international and regional initiatives, such as those of the United Nations (Mediterranean Action Plan (MAP)) and the World Bank. According to this, the coastal policy of the EC is considered with special attention to past and current developments, and the main policy objectives and instruments are discussed. This review is followed by a brief analysis of the EC Mediterranean coastal zone: the general use and development patterns, the main pressures bearing upon it, and its definition from a legal and administrative perspective. An evaluation of the role of the EC in the Mediterranean context then follows, with particular reference to the ongoing developments of the Euro-Mediterranean co-operation within MAP and the Barcelona Convention system. On this basis, conclusions are drawn on the need to improve the EC Mediterranean coastal policy through a strengthened integration between the various EC sectoral policies, and between these policies and the policies of the member states, and through an optimised co-ordination with MAP.  相似文献   

Impact of methane seeps on the local carbon‐isotope record: a case study from a Late Jurassic hemipelagic section     

Beat Louis‐Schmid  Pauline Rais  Dmitry Logvinovich  Stefano M. Bernasconi  Helmut Weissert 《地学学报》2007,19(4):259-265

An Oxfordian (Late Jurassic) hemipelagic succession from Beauvoisin (SE France) contains a pronounced, short‐lived negative excursion in the bulk‐carbonate carbon‐isotope record, with an amplitude of 4‰. It was shown previously that the Beauvoisin paleoenvironment was impacted by hydrocarbon seepage. New isotopic data corroborate that methane was a significant constituent of these hydrocarbons. The negative excursion was caused by transient enhanced precipitation of ¹³C‐depleted carbonate, mediated by anaerobic oxidation of methane. Despite its local diagenetic origin, the Beauvoisin excursion is similar in shape and duration to globally recognized negative C‐isotope excursions that have been related to catastrophic, massive dissociation of methane hydrate. Shape and duration of negative excursions therefore cannot be used as an argument when determining their origin if they have not been shown to represent a global perturbation of the carbon cycle.  相似文献   

Spectral measurements of aerosol particle extinction in the 0.4–3.7 μm wavelength range, performed at Sagres with the IR‐RAD sun‐radiometer     

Vito Vitale  Claudio Tomasi  Wolfgang Von Hoyningen&#;huene  Ubaldo Bonafe  Stefano Marani  Angelo Lupi  Alessandra Cacciari  Pietro Ruggeri 《Tellus. Series B, Chemical and physical meteorology》2000,52(2):716-733

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20 My of nitrogen fixation during deposition of mid-Cretaceous black shales on the Demerara Rise,equatorial Atlantic Ocean     

Philip A. Meyers  Stefano M. Bernasconi  Jong-Gwon Yum 《Organic Geochemistry》2009,40(2):158-166

Thick sequences of dark colored, organic carbon rich, finely laminated Santonian–Cenomanian claystones and homogeneous Albian siltstones were recovered from Ocean Drilling Program Sites 1257, 1258 and 1260 on the Demerara Rise in the western equatorial Atlantic Ocean. Total organic carbon (TOC) concentrations vary from 2 to over 20 wt% in the sequences of “black shales” that were deposited over a period of ～20 million years. Similarly long periods of elevated marine productivity implied by the high TOC concentrations are uncommon in the geological record and must have required unusual paleoceanographic conditions. The importance of nitrogen fixing bacteria to sustaining the amplified export production of organic matter is indicated by δ¹⁵N values that remain between ?4‰ and 0‰, a range that is notably less positive than the average of +5‰ for modern ocean sediments. Although containing mostly marine organic matter, the black shales have TOC/TN molar ratios between 20 and 40 that mimic those of land plant organic matter. The anomalously large TOC/TN ratios suggest selective organic matter degradation, probably associated with low oxygen conditions in the water column, that favored preservation of nitrogen poor forms of organic matter relative to nitrogen rich components. Deposition of black shales on the Demerara Rise was likely a consequence of the mid-Cretaceous warm and wet greenhouse climate that strengthened thermohaline stratification of this part of the Atlantic Ocean, which in turn encouraged bacterial nitrogen fixation, enhanced primary production, magnified organic matter export, and ultimately established anoxic conditions at the seafloor that improved preservation of organic matter for much of the 20 My period represented by these thick sequences.  相似文献   

Lethal and estrogenic effects of 4-nonylphenol in the cockle Cerastoderma glaucum     

Marin MG  Rigato S  Ricciardi F  Matozzo V 《Marine pollution bulletin》2008,57(6-12):552-558

The lethal and sublethal effects of the xenoestrogen 4-nonylphenol (NP) were evaluated in the cockle Cerastoderma glaucum. In a 96-h lethality test, bivalves were exposed to 0, 0+ acetone, 0.19, 0.38, 0.75, 1.5 and 3.0 mg NP/l. The 96-h LC(50) value was 0.3mg NP/l. No mortality was observed at 0.1 mg NP/l. The potential estrogenicity of NP was studied in both sexually undifferentiated (resting phase) and differentiated (pre-spawning phase) cockles, exposed for 7 and 14 days to 0, 0+ acetone, 0.0125, 0.025, 0.05, and 0.1 mg NP/l. Vitellogenin (Vg)-like protein levels were determined in both haemolymph and digestive gland by the alkali-labile phosphate (ALP) assay. In the resting phase, exposure for 7 days to 0.1 mg NP/l resulted in significant increases in ALP in both haemolymph and digestive gland, compared with controls. A significant increase was also observed in digestive gland of animals exposed to 0.0125 mg NP/l-exposed animals. After 14 days of exposure, haemolymph ALP levels were significantly increased in exposed animals at all NP concentrations tested, whereas no difference was recorded in digestive gland. In the pre-spawning phase, exposure for 7 days to NP significantly increased ALP levels in haemolymph from males exposed at all NP concentrations tested, whereas no significant variations were found in haemolymph from females. NP (0.05 and 0.1 mg/l) was also shown to increase ALP concentrations significantly in digestive gland of males, but not in those of females. Likewise, after 14 days' exposure, ALP levels significantly increased in haemolymph from males only at 0.1 mg NP/l. Conversely, NP caused significant increases in ALP levels in digestive gland from both males (at all NP concentrations tested) and females (at 0.025 and 0.1 mg NP/l). These results demonstrate that NP induces Vg synthesis in C. glaucum. Interestingly, males were more responsive to NP than females.  相似文献   

Dynamics and driving factors of late Holocene gullying in the Main Ethiopian Rift (MER)   总被引：1，自引：0，他引：1  

Stefano Carnicelli  Marco Benvenuti  Giovanni Ferrari  Mario Sagri   《Geomorphology》2009,103(4):541-554

The issue of determining the driving factors in gullying, apart from land use, is somewhat lagging in comparison with the study of their physical modelling and control technology. Available information focuses on the basic ideas of climatic control, anthropic determinism and internal “authigenic” dynamics. High resolution chronology of cyclic systems, common in extensively gullied areas, can provide a clue to the weight of each factor. This paper reports a study of this kind, focusing on two gully catchments in the Main Ethiopian Rift (MER), but backed by an extensive regional survey. By integrating tracing and correlation of unconformity-bounded stratigraphic units and soils with radiocarbon dating, a detailed chronology was obtained for the last 5000 years. This could be compared with proxy climate reconstructions of similar detail. Clear evidence of climatic control emerged; gully filling is triggered by decreased stream transport capacity and increased sediment supply during transitions towards drier climate phases, while gully entrenchment appears to take place at the start of moist intervals, for the reverse reasons. A broader consideration of geological setting, however, puts forward a more general interpretation. These gullies actually formed, in the beginning, as part of the land surface response to sudden, very recent tectonic events, which created accommodation space for temporary sediment stores. They should then be seen in the frame of the Discontinuous Ephemeral Stream (DES) concept; as such, they are intrinsically non-linear and complex phenomena, whose response is linearized by a strong climatic–vegetational forcing, acting on both channel flow and sediment supply.  相似文献   

Stratigraphic evolution of the Triassic–Jurassic succession in the Western Southern Alps (Italy): the record of the two-stage rifting on the distal passive margin of Adria     

Fabrizio Berra  Maria Teresa Galli  Federico Reghellin  Stefano Torricelli†  Roberto Fantoni† 《Basin Research》2009,21(3):335-353

The Triassic–Lower Jurassic succession of the Southern Alps is characterized by rapid thickness changes, from an average of about 5000 m east of Lago Maggiore to about 500 m in the Western Southern Alps. The stratigraphy reflects the Triassic evolution of the Tethyan Gulf and the Early Jurassic rifting responsible for the Middle Jurassic break‐up of Adria from Europe. The succession of the Western Southern Alps starts with Lower Permian volcanics directly covered by Anisian sandstones. The top of the overlying Ladinian dolostones (300 m) records subaerial exposure and karstification. Locally (Gozzano), Upper Sinemurian sediments cover the Permian volcanics, documenting pre‐Sinemurian erosion. New biostratigraphic data indicate a latest Pliensbachian–Toarcian age for the Jurassic synrift deposits that unconformably cover Ladinian or Sinemurian sediments. Therefore, in the Western Southern Alps, the major rifting stage that directly evolved into the opening of the Penninic Ocean began in the latest Pliensbachian–Toarcian. New data allowed us to refine the evolution of the two previously recognized Jurassic extensional events in the Southern Alps. The youngest extensional event (Western Southern Alps) occurred as tectonic activity decreased in the Lombardy Basin. During the Sinemurian the Gozzano high represents the western shoulder of a rift basin located to the east (Lombardy). This evolution documents a transition from diffuse early rifting (Late Hettangian–Sinemurian), controlled by older discontinuities, to rifting focused along a rift valley close to the Pliensbachian–Toarcian boundary. This younger rift bridges the gap between the Hettangian–Sinemurian diffuse rifting and the Callovian–Bathonian break‐up. The late Pliensbachian–Toarcian rift, which eventually lead to continental break‐up, is interpreted as the major extensional episode in the evolution of the passive margin of Adria. The transition from diffuse to focused extension in the Southern Alps is comparable to the evolution of the Central Austroalpine during the Early Jurassic and of the Central and Northern Atlantic margins.  相似文献