Quaternary interaction of cryospheric and oceanographic processes along the central‐east Greenland margin     

Lara F. Prez  Tove Nielsen  Tine L. Rasmussen  Monica Winsborrow 《Boreas: An International Journal of Quaternary Research》2019,48(1):72-91

The east Greenland margin has been influenced by oceanographic and cryospheric processes since the late Miocene, when the southwards flow of the East Greenland Current (EGC) initiated and ice sheets first advanced across the margin. However, the relative importance of these processes, and their influence on the sedimentation of the margin through time remains poorly understood. High‐resolution single‐channel seismic, chirp sub‐bottom profiles and swath bathymetry data were acquired along the middle/lower slope and proximal basinal area off Liverpool Land, central‐east Greenland margin. In this study, seismic‐stratigraphical and morphological analyses allowed us to distinguish between the major sedimentary processes that influenced this margin during the Quaternary. The stratigraphical architecture reveals mass transport deposits (MTDs) related to glacially influenced down‐slope sedimentation. These are intercalated with buried contourite systems associated with bottom‐current controlled along‐slope sedimentation. The distribution of the MTDs suggests the influence of two distinct ice‐stream systems. Initial phases of down‐slope deposition during the early‐middle Quaternary appears to be related to distal deposition fed by an ice stream from the Scoresby Sund area in the south. Shallow sedimentary processes, together with morphological analysis of the sea floor, show that the most recent activity of down‐slope processes during the latest Quaternary has occurred in the north, linked to an ice stream from the Kong Oscar Fjord area. These observations document a temporal shift in the relative dominance of the Scoresby Sund and Kong Oscar Fjord ice‐stream systems. The glacial influence on the margin has been interrupted by periods of stronger activity of along‐slope bottom‐current flow, demonstrating that the EGC periodically controlled sedimentation on the continental margin.  相似文献   

Net autotrophy in a fluvial lake: the relative role of phytoplankton and floating-leaved macrophytes     

Monica Pinardi  Marco Bartoli  Daniele Longhi  Pierluigi Viaroli 《Aquatic Sciences - Research Across Boundaries》2011,73(3):389-403

This study combined water- and sediment flux measurements with mass balances of dissolved gas and inorganic matter to determine the importance of pelagic and benthic processes for whole-system metabolism in a eutrophic fluvial lake. Mass balances of dissolved O₂, inorganic carbon (DIC), nitrogen (DIN), phosphorous (SRP), particulate N (PN) and P (PP) and Chl a were calculated at a nearly monthly frequency by means of repeated sampling at the lake inlet and outlet. Simultaneously, benthic fluxes of gas and nutrients, including denitrification rates, and the biomass of the dominant pleustophyte (Trapa natans) were measured, and fluxes of O₂ and CO₂ across the water–atmosphere interface were estimated from diel changes in outlet concentrations. On an annual scale, Middle Lake exhibited CO₂ supersaturation, averaging 313% (range 86–562%), but was autotrophic with a net O₂ production (6.35 ± 2.05 mol m⁻² y⁻¹), DIC consumption (−31.18 ± 18.77 mol m⁻² y⁻¹) and net export of Chl a downstream (8.38 ± 0.95 mol C m⁻² y⁻¹). Phytoplankton was the main driver of Middle Lake metabolism, with a net primary production estimated at 33.24 mol O₂ m⁻² y⁻¹, corresponding to a sequestration of 4.18 and 0.26 mol m⁻² y⁻¹ of N and P, respectively. At peak biomass, T. natans covered about 18% of Middle Lake’s surface and fixed 2.46, 0.17 and 0.02 mol m⁻² of C, N and P, respectively. Surficial sediments were a sink for O₂ (−14.47 ± 0.65 mol O₂ m⁻² y⁻¹) and a source of DIC and NH₄ ⁺ (18.84 ± 2.80 mol DIC m⁻² y⁻¹ and 0.83 ± 0.16 mol NH₄ ⁺ m⁻² y⁻¹), and dissipated nitrate via denitrification (1.44 ± 0.11 mol NO₃ ⁻ m⁻² y⁻¹). Overall, nutrient uptake by primary producers and regeneration from sediments were a minor fraction of external loads. This work suggests that the creation of fluvial lakes can produce net autotrophic systems, with elevated rates of phytoplanktonic primary production, largely sustained by allochtonous nutrient inputs. These hypereutrophic aquatic bodies are net C sinks, although they simultaneously release CO₂ to the atmosphere.  相似文献   

High-temperature vesuvianite: crystal chemistry and surface considerations     

Chiara Elmi  Maria Franca Brigatti  Luca Pasquali  Monica Montecchi  Angela Laurora  Daniele Malferrari  Stefano Nannarone 《Physics and Chemistry of Minerals》2011,38(6):459-468

A multi-methodical approach has been applied for characterizing the bulk and surface crystal chemical features of a high-temperature vesuvianite crystal from skarns of Mount Somma-Vesuvius Volcano (Naples, Italy). Vesuvianite belongs to the space group P4/nnc with unit cell parameters a = 15.633(1) Å, c = 11.834(1) Å and chemical formula (Ca_18.858 Na_0.028 Ba_0.004 K_0.006 Sr_0.005 □_0.098)_19.000 (Al_8.813 Ti_0.037 Mg_2.954 Mn_0.008 Fe_0.114²⁺ Fe_1.375³⁺ Cr_0.008 B_0.202)_13.511 Si_18.000(O_0.261 F_0.940 OH_7.799)_9.000. Structure refinement, which converges at R = 0.0328, demonstrates a strong positional disorder down the fourfold axes, indicating that the Y1 site is split into two positions (Y1A and Y1B) alternatively occupied. However, because of X4 proximity to Y1B and Y1A, X4 cannot be occupied if Y1B or Y1A are. Overall Y1 occupancy (Y1A + Y1B) reaches approximately 0.5, as common in vesuvianite and occupancy of Y1B site is extremely limited. Moreover, T1 position, limitedly occupied, accommodates the excess of cations generally related to Y position. A small quantity (0.202 apfu) of boron is sited at the T2 site that, like T1, is poorly occupied. The determination of the amount of each element on the (100) vesuvianite surface, obtained through X-ray photoelectron spectroscopy high-resolution spectra in the region of the Si_2p, Al_2p, Mg_1s, and Ca_2p core levels, evidences that a greater amount of aluminum and a smaller amount of calcium characterize the surface with respect to the bulk. Although both of these features require further investigation, we may consider the Al increase can be related to preferential orientation of Al-rich sites on the (100) plane. Furthermore, the surface structure of vesuvianite suggests that Al, Ca, and Mg cations maintain coordination features at the surface similar to the bulk. Silica, however, while presenting fourfold coordination, shows also a [1]-fold small coordinated component at binding energy 99.85 eV, due to broken Si–O bonds at the surface. The presence of eight- and nine-coordinated Ca cations is suggested by a large XPS feature resulting from the merging of Ca_2p3/2 and Ca_2p1/2 peaks at 348.45 and 352.05 eV, respectively.  相似文献   

Quantitative comparison of impeller-flowmeter and particle-size-distribution techniques for the characterization of hydraulic conductivity variability   总被引：1，自引：0，他引：1  

Marco Barahona-Palomo  Monica Riva  Xavier Sanchez-Vila  Enric Vazquez-Sune  Alberto Guadagnini 《Hydrogeology Journal》2011,19(3):603-612

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On the migration of precursors of strong earthquakes     

F. Bella  P.F. Biag  M. Caputo  G. Della Monica  A. Ermini  V. Sgrigna 《地学学报》1992,4(6):676-681

It is found that perturbations presumedly associated with swarms, the B patterns and the BG pattern precursors of strong earthquakes in New Zealand, California and Apennines, propagate in the crust of the Earth with a velocity of the order of cm¹. The hypothesis that a single travelling elastic perturbation causes a set of precursors of the same strong earthquake is discussed and it is concluded that each precursor is associated with a different perturbation.  相似文献   

The effect of star formation on the evolution of Blue Compact Dwarf galaxies     

Simone Recchi  Francesca Matteucci  Annibale D'Ercole  Monica Tosi 《Astrophysics and Space Science》2003,284(2):623-626

We study the effect of different star formation regimes on the dynamical and chemical evolution of Blue Compact Dwarf galaxies. To do that, we adopt a 2-D hydrocode coupled with detailed chemical yields originating from SNeII, SNeIa and from intermediate-mass stars. We apply this kind of simulation to a model of galaxy resembling IZw18. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

Results from the Eso Large Program on Transneptunian Objects and Centaurs     

Boehnhardt  Hermann  Barucci  Antonella  Delsanti  Audrey  De Bergh  Catherine  Doressoundiram  Alain  Romon  Jennifer  Dotto  Elisabetta  Tozzi  Gianpaolo  Lazzarin  Monica  Fornasier  Sonia  Peixinho  Nuno  Hainaut  Olivier  Davies  John  Rousselot  Philippe  Barrera  Luis  Birkle  Kurt  Meech  Karen  Ortiz  JoseLuis  Sekiguchi  Tomohiko  Watanabe  Jun-ichi  Thomas  Nick  West  Richard 《Earth, Moon, and Planets》2003,92(1-4):145-156

BVRI photometry of 107 TNOs and Centaurs establishes the range of spectral gradients to be between –5 to 55%/100 nm (with one exception). A cluster of very red Cubewanos is firmly identified in orbits of low inclination and eccentricity beyond 40 AU from the Sun. Further correlations between surface colours and dynamical parameters (inclination and perihelion distance) are suggested for Cubewanos and scattered disk objects, but lack complete confidence for their reality. Plutinos and Centaurs do not show any clear correlation between surface colours and orbital parameters. We present in this paper 12 spectra obtained in the visible region and nine of them for which we obtained also near infrared spectra up to 2.4 microns. A few other objects have been observed, but the data are still under reduction and analysis. The principal reported results obtained are: (i) a wide range of visible slopes; (ii) evidence for surface variations on 2001 PT₁₃; and (iii) possible detection of few percent of water ice (1999 TC_36}, 2000 EB₁₇₃, 1999 DE₉, 2001 PT₁₃, 2000 QC₂₄₃, 1998 SG₃₅).  相似文献   

Formation and evolution of late-type dwarf galaxies – I. NGC 1705 and NGC 1569     

Donatella Romano  Monica Tosi  Francesca Matteucci 《Monthly notices of the Royal Astronomical Society》2006,365(3):759-778

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Effect of particle characteristics on the evolution of particle size,particle morphology,and fabric of sands loaded under uniaxial compression     

Ganju  Eshan  Kılıç  Mustafa  Prezzi  Monica  Salgado  Rodrigo  Parab  Niranjan  Chen  Wayne 《Acta Geotechnica》2021,16(11):3489-3516

Acta Geotechnica - This paper presents the results and analyses of uniaxial compression experiments performed on three silica sands. The sands have comparable particle-size distributions, but their...  相似文献   

The role of magma mixing/mingling and cumulate melting in the Neapolitan Yellow Tuff caldera-forming eruption (Campi Flegrei,Southern Italy)     

Francesca?ForniEmail author  Eleonora?Petricca  Olivier?Bachmann  Silvio?Mollo  Gianfilippo?De Astis  Monica?Piochi 《Contributions to Mineralogy and Petrology》2018,173(6):45

Understanding the mechanisms responsible for the generation of chemical gradients in high-volume ignimbrites is key to retrieve information on the processes that control the maturation and eruption of large silicic magmatic reservoirs. Over the last 60 ky, two large ignimbrites showing remarkable zoning were emplaced during caldera-forming eruptions at Campi Flegrei (i.e., Campanian Ignimbrite, CI, ~?39 ka and Neapolitan Yellow Tuff, NYT, ~?15 ka). While the CI displays linear compositional, thermal and crystallinity gradients, the NYT is a more complex ignimbrite characterized by crystal-poor magmas ranging in composition from trachy-andesites to phonolites. By combining major and trace element compositions of matrix glasses and mineral phases from juvenile clasts located at different stratigraphic heights along the NYT pyroclastic sequence, we interpret such compositional gradients as the result of mixing/mingling between three different magmas: (1) a resident evolved magma showing geochemical characteristics of a melt extracted from a cumulate mush dominated by clinopyroxene, plagioclase and oxides with minor sanidine and biotite; (2) a hotter and more mafic magma from recharge providing high-An plagioclase and high-Mg clinopyroxene crystals and (3) a compositionally intermediate magma derived from remelting of low temperature mineral phases (i.e., sanidine and biotite) within the cumulate crystal mush. We suggest that the presence of a refractory crystal mush, as documented by the occurrence of abundant crystal clots containing clinopyroxene, plagioclase and oxides, is the main reason for the lack of erupted crystal-rich material in the NYT. A comparison between the NYT and the CI, characterized by both crystal-poor extracted melts and crystal-rich magmas representing remobilized portions of a “mature” (i.e., sanidine dominated) cumulate residue, allows evaluation of the capability of crystal mushes of becoming eruptible upon recharge.  相似文献