Carbonate Chemistry Dynamics of Surface Waters in the Northern Gulf of Mexico     

Nina Keul  John W. Morse  Rik Wanninkhof  Dwight K. Gledhill  Thomas S. Bianchi 《Aquatic Geochemistry》2010,16(3):337-351

This paper presents the results of two cruises in the Northern Gulf of Mexico in 2008 that investigated local and short-term factors influencing the carbonate chemistry dynamics and saturation state with respect to aragonite (Ω_aragonite) of surface seawater in this region. One cruise covered much of the northern half of the Gulf, and the other focused on the coastal zone west of the Atchafalaya Bay outlet of the Mississippi River—the region where the hypoxic “dead zone” occurs on the Louisiana shelf. Offshore waters (>100 m depth) exhibited only small variations in CO₂ fugacity (fCO₂), total alkalinity (TA) and Ω_aragonite. Values were close to those typically observed in subtropical Atlantic Ocean and Caribbean Sea waters of similar salinity. However, inner shelf waters (<50 m depth) exhibited large variations in fCO₂, TA, and Ω_aragonite that were not directly related to salinity or distance from the Mississippi River plume. Changes in TA values were not the result of simple mixing of end-member freshwater and seawater TA concentrations but exhibited a minimum in values near salinity of 25. This minimum could be the result of microbial recycling across salinity gradients, biological removal of alkalinity by formation of calcium carbonate or mixing of a third end-member with a low alkalinity such as Terrebonne Bay. All waters were supersaturated with respect to aragonite. Offshore waters had an average Ω_aragonite of 3.86 with a standard deviation of only ±0.06 and inner shelf waters had a range in Ω_aragonite values from 3.9 to 9.7 with a median of 4.3. Shelf water Ω_aragonite values were elevated relative to the offshore as a consequence of both high TA input from Mississippi River and biological drawdown of CO₂. A dominant factor controlling Ω_aragonite distribution in offshore waters with relatively constant temperatures was fCO₂, with higher supersaturation occurring in areas with low fCO₂.  相似文献   

Much damage for little advantage: Field studies and morphodynamic modelling highlight the environmental impact of an apparently minor coastal mismanagement     

Roberta LasagnaMonica Montefalcone  Giancarlo AlbertelliNicola Corradi  Marco FerrariCarla Morri  Carlo Nike Bianchi 《Estuarine, Coastal and Shelf Science》2011,94(3):255-262

While coastal management activities have long been known to exert a strong influence on the health of marine ecosystems, neither scientists nor administrators have realized that small interventions may lead to disproportionately larger impacts. This study investigated the broad and long-lasting environmental consequences of the construction of an ill-planned, although small (only 12 m long) jetty for pleasure crafts on the hydrodynamic conditions and on the meadow of the seagrass Posidonia oceanica of an embayed cove in the Ligurian Sea (NW Mediterranean). There, P. oceanica used to develop on a high (>1.5 m) matte (a lignified terrace causing seafloor elevation) in which the leaves reach the surface and form a compact natural barrier to waves in front of the beach. Such a so-called ‘fringing reef’ of P. oceanica is today recognized of high ecological value and specific conservation efforts are required. The construction of the jetty implied the cutting of the matte, which directly destroyed part of the fringing reef. In addition, meadow mapping and sedimentological analyses coupled with morphodynamic modelling showed that the ecosystem of the whole cove had been greatly altered by the jetty. We used the geometric planform approach, a proper tool in the study of headland-controlled embayment, both to characterise the present situation of Prelo cove and to simulate the original one, before the jetty was built. In the long term, such a small jetty completely altered the configuration and the hydrodynamic conditions of the whole cove, splitting the original pocket beach into two smaller ones and creating strong rip-currents flowing seaward along the jetty. These rip-currents enhanced erosion of residual shallow portions of the meadow and further modified the sedimentary fluxes in shallow waters. A century after the construction of the jetty, an irreversible environmental damage has occurred, as the slow growing rate of P. oceanica implies that the high matte terrace and the fringing reef will hardly form again, even after the removal of the jetty. The lesson learnt from this study is that even such small, and therefore reputed intrinsically ‘innocent’, interventions on the coastal zone require accurate planning based on interdisciplinary studies to understand and respect the delicate interplay among morphological, hydrodynamic and ecological components.  相似文献   

Fe xxv and Fe xxvi lines from low-velocity, photoionized gas in the X-ray spectra of active galactic nuclei     

Stefano Bianchi  Giorgio Matt  Fabrizio Nicastro  Delphine Porquet  Jacques Dubau 《Monthly notices of the Royal Astronomical Society》2005,357(2):599-607

We have calculated the equivalent widths of the absorption lines produced by Fe  xxv and Fe  xxvi in a Compton-thin, low-velocity photoionized material illuminated by the nuclear continuum in active galactic nuclei. The results, plotted against the ionization parameter and the column density of the gas, are a complement to those presented by Bianchi & Matt for the emission lines from the same ionic species. As an extension to the work by Bianchi & Matt, we also present a qualitative discussion on the different contributions to the He-like iron emission line complex in the regimes where recombination or resonant scattering dominates, providing a useful diagnostic tool to measure the column density of the gas. Future high-resolution missions (e.g. Astro-E2 ) will allow us to fully take advantage of these plasma diagnostics. In the meantime, we compare our results with an up-to-date list of Compton-thick and unobscured (at least at the iron line energy) Seyfert galaxies with emission and/or absorption lines from H- and He-like iron observed with Chandra and XMM–Newton .  相似文献   

A multiwavelength map of the nuclear region of NGC 7582     

Stefano Bianchi  Marco Chiaberge  Enrico Piconcelli  Matteo Guainazzi 《Monthly notices of the Royal Astronomical Society》2007,374(2):697-702

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On the origin of soft X-rays in obscured AGN: answers from high-resolution spectroscopy with XMM–Newton     

Matteo Guainazzi  Stefano Bianchi 《Monthly notices of the Royal Astronomical Society》2007,374(4):1290-1302

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Perfluorinated compounds in blood of Caretta caretta from the Mediterranean Sea     

Cristiana Guerranti  Stefania Ancora  Nicola Bianchi  Guido Perra  Emiliano Leonida Fanello  Simonetta Corsolini  Maria Cristina Fossi  Silvano Ettore Focardi 《Marine pollution bulletin》2013

Perfluorinated compounds (PFCs), widely used for their hydro-oil repellent properties, are almost non-degradable in the environment; there is scientific evidence that indicate bioaccumulation. They represent a threat to many organisms, because they are toxic and are endocrine disruptors. Scientific studies have demonstrated the presence of PFCs in blood and liver samples of fish, turtles, birds and mammals of marine ecosystems in different geographical areas. The aim of this study was to determine the distribution of PFOS and PFOA in blood samples of the marine turtle Caretta caretta, using a minimally invasive sampling procedure. 49 blood samples of marine turtle, taken from several Italian marine turtle rescue centers, were analyzed. While PFOA was never detected, measurable concentrations of PFOS were found in 15 blood samples; the values show a range from 1.14 ng/g to 28.51 ng/g (wet wt.). No differences between groups of samples taken from different areas were found.  相似文献   

NGC 3147: a 'true' type 2 Seyfert galaxy without the broad-line region     

S. Bianchi  A. Corral  F. Panessa  X. Barcons  G. Matt  L. Bassani  F. J. Carrera  E. Jiménez-Bailón 《Monthly notices of the Royal Astronomical Society》2008,385(1):195-199

We report on simultaneous optical and X-ray observations of the Seyfert galaxy, NGC 3147. The XMM–Newton spectrum shows that the source is unabsorbed in the X-rays  ( N _H < 5 × 10²⁰ cm⁻²)  . On the other hand, no broad lines are present in the optical spectrum. The origin of this optical/X-rays misclassification (with respect to the Unification Model) cannot be attributed to variability, since the observations in the two bands are simultaneous. Moreover, a Compton-thick nature of the object can be rejected on the basis of the low-equivalent width of the iron Kα line (≃130 eV) and the large ratio between the 2–10 keV and the [O  iii ] fluxes. It seems therefore inescapable to conclude that NGC 3147 intrinsically lacks the Broad-Line Region, making it the first 'true' type 2 Seyfert galaxy.  相似文献   

Abiotic and Biotic Links Work Two Ways: Effects on the Deposit at the Cliff Foot Induced by Mechanical Action of Date Mussel Harvesting (<Emphasis Type="Italic">Lithophaga lithophaga</Emphasis>)   总被引：1，自引：0，他引：1  

Alessio Rovere  Stefano Bellati  Valeriano Parravicini  Marco Firpo  Carla Morri  Carlo Nike Bianchi 《Estuaries and Coasts》2009,32(2):333-339

The existence of linkages between ecological and geomorphological processes and the influence of human activities both on the biota and on geomorphology is well known for terrestrial environments, while it has been seldom reported for submerged ones. A survey in the Noli-Bergeggi area (NW Mediterranean Sea) has been carried out to test the hypothesis that the harvesting of Lithophaga lithophaga has an impact not only on the hammered rock, but also on the sediments at the cliff foot. Size and roundness of pebbles have been measured at different stations and statistical analyses have been used to test the differences between impact and control situations. Results show a dependence of the roundness of pebbles on the date mussel harvesting, indicating a decrease both of the roundness index and of its variability at the cliff foot in impacted sites. Conclusions stress the biogeomorphological nature of this activity, not limited to the present location.  相似文献   

Can plankton communities be considered as bio-indicators of water quality in the Lagoon of Venice?   总被引：4，自引：0，他引：4  

Bianchi F  Acri F  Aubry FB  Berton A  Boldrin A  Camatti E  Cassin D  Comaschi A 《Marine pollution bulletin》2003,46(8):964-971

This study examines whether plankton of the Lagoon of Venice could be considered as a bio-indicator of areas subjected to various anthropogenic influences. This study was a two year hydrochemical and biological survey in five areas of the Lagoon of Venice, each with different environmental conditions due to pollution from urban, industrial, thermal and agricultural wastes. Phytoplankton associations did not show any promising species. In the different lagoonal areas, this community was differentiated into its major groups. In contrast, the copepod Acartia tonsa Dana could be considered as a target species in highly eutrophic areas.  相似文献   

Novel decomposition products of chlorophyll-a in continental shelf (Louisiana shelf) sediments: formation and transformation of carotenol chlorin esters     

Nianhong Chen  Thomas S. Bianchi 《Geochimica et cosmochimica acta》2003,67(11):2027-2042

In April 2000, we collected box cores from five stations along a cross-shelf transect on the Louisiana (LA) continental shelf. Novel esters of carotenols and chlorins (carotenoid chlorin esters, CCEs), which are highly specific grazing markers, were identified in surface and deep sediments (>10 cm) from the LA shelf. Chlorophyll-a inventory indicated that CCEs are one of the major decay products of chlorophyll-a in shelf sediments. Abundances of total CCEs (9-18%) in surface sediments along the cross-shelf transect were comparable to the abundance of pheophytin-a, pyropheophytin-a, and total steryl chlorin esters (SCEs). Prior work has identified four CCEs which have dehydrated fucoxanthin/fucoxanthinol as a substitute alcohol of phytol. We report on four newly identified CCEs associated with nondehydrated fuxocanthin/fucoxanthinol esterified to (pyro)pheophorbide-a. These nondehydrated CCEs were generally present in lower concentrations than their dehydrated counterparts, but were detectable by atmospheric pressure chemical ionization (APCI) mass spectrometry coupled with high-performance liquid chromatography (HPLC). We attributed differences between this study and previous work to the time allowed for predepositional decay and grazing processes to occur. The rapid sedimentation of CCEs in the shallow water column (ca. 10 m) on the LA shelf allowed for effective burial of all CCEs compared to the deeper water column regions sampled by previous work. This speculation is supported by the fact that the concentrations of CCEs with nondehydrated fucoxanthin/fucoxanthinol were extremely low in sediments from the site on the outer LA shelf with a deeper (253 m) water column. We also tentatively identified an additional CCE and its isomer as fucoxanthinol didehydrate pyropheophorbide-a ester. We suggest that the formation and transformation of CCEs are primarily controlled by the following three biologically mediated reactions: demethoxycarbonylation, dehydration, and deacetylation. Our laboratory copepod grazing experiment also confirmed that CCEs can be excellent class-specific biomarkers of zooplankton grazing on phytoplankton.  相似文献