Deposition of talc — kerolite–smectite — smectite at seafloor hydrothermal vent fields: Evidence from mineralogical,geochemical and oxygen isotope studies     

Vesselin M. Dekov  Javier Cuadros  Wayne C. Shanks  Randolph A. Koski 《Chemical Geology》2008,247(1-2):171-194

Talc, kerolite–smectite, smectite, chlorite–smectite and chlorite samples from sediments, chimneys and massive sulfides from six seafloor hydrothermal areas have been analyzed for mineralogy, chemistry and oxygen isotopes. Samples are from both peridotite- and basalt-hosted hydrothermal systems, and basaltic systems include sediment-free and sediment-covered sites. Mg-phyllosilicates at seafloor hydrothermal sites have previously been described as talc, stevensite or saponite. In contrast, new data show tri-octahedral Mg-phyllosilicates ranging from pure talc and Fe-rich talc, through kerolite-rich kerolite–smectite to smectite-rich kerolite–smectite and tri-octahedral smectite. The most common occurrence is mixed-layer kerolite–smectite, which shows an almost complete interstratification series with 5 to 85% smectitic layers. The smectite interstratified with kerolite is mostly tri-octahedral. The degree of crystal perfection of the clay sequence decreases generally from talc to kerolite–smectite with lower crystalline perfection as the proportion of smectite layers in kerolite–smectite increases.Our studies do not support any dependence of the precipitated minerals on the type/subtype of hydrothermal system. Oxygen isotope geothermometry demonstrates that talc and kerolite–smectite precipitated in chimneys, massive sulfide mounds, at the sediment surface and in open cracks in the sediment near seafloor are high-temperature (> 250 °C) phases that are most probably the result of focused fluid discharge. The other end-member of this tri-octahedral Mg-phyllosilicate sequence, smectite, is a moderate-temperature (200–250 °C) phase forming deep within the sediment (～ 0.8 m). Chlorite and chlorite–smectite, which constitute the alteration sediment matrix around the hydrothermal mounds, are lower-temperature (150–200 °C) phases produced by diffuse fluid discharge through the sediment around the hydrothermal conduits. In addition to temperature, other two controls on the precipitation of this sequence are the silica activity and Mg/Al ratio (i.e. the degree of mixing of seawater with hydrothermal fluid). Higher silica activity favors the formation of talc relative to tri-octahedral smectite. Vent structures and sedimentary cover preclude complete mixing of hydrothermal fluid and ambient seawater, resulting in lower Mg/Al ratios in the interior parts of the chimneys and deeper in the sediment which leads to the precipitation of phyllosilicates with lower Mg contents. Talc and kerolite–smectite have very low trace- and rare earth element contents. Some exhibit a negative or flat Eu anomaly, which suggests Eu depletion in the original hydrothermal fluid. Such Eu depletion could be caused by precipitation of anhydrite or barite (sinks for Eu²⁺) deeper in the system. REE abundances and distribution patterns indicate that chlorite and chlorite–smectite are hydrothermal alteration products of the background turbiditic sediment.  相似文献   

Temporal variation and the effect of rainfall on metals flux from the historic Beatson mine,Prince William Sound,Alaska, USA     

Lisa L. Stillings  Andrea L. Foster  Randolph A. Koski  LeeAnn Munk  Wayne C. Shanks III 《Applied Geochemistry》2008

Several abandoned Cu mines are located along the shore of Prince William Sound, AK, where the effect of mining-related discharge upon shoreline ecosystems is unknown. To determine the magnitude of this effect at the former Beatson mine, the largest Cu mine in the region and a Besshi-type massive sulfide ore deposit, trace metal concentration and flux were measured in surface run-off from remnant, mineralized workings and waste. Samples were collected from seepage waters; a remnant glory hole which is now a pit lake; a braided stream draining an area of mineralized rock, underground mine workings, and waste piles; and a background location upstream of the mine workings and mineralized rock. In the background stream pH averaged ∼7.3, specific conductivity (SC) was ∼40 μS/cm, and the aqueous components indicative of sulfide mineral weathering, SO₄ and trace metals, were at detection limits or lower. In the braided stream below the mine workings and waste piles, pH usually varied from 6.7 to 7.1, SC varied from 40 to 120 μS/cm, SO₄ had maximum concentrations of 32 mg/L, and the trace metals Cu, Ni, Pb, and Zn showed maximum total acid extractable concentrations of 186, 5.9, 6.2 and 343 μg/L, respectively.  相似文献   

Mangrove Range Expansion Rapidly Increases Coastal Wetland Carbon Storage     

Cheryl?L.?DoughtyEmail author  J.?Adam?Langley  Wayne?S.?Walker  Ilka?C.?Feller  Ronald?Schaub  Samantha?K.?Chapman 《Estuaries and Coasts》2016,39(2):385-396

The climate change-induced expansion of mangroves into salt marshes could significantly alter the carbon (C) storage capacity of coastal wetlands, which have the highest average C storage per land area among unmanaged terrestrial ecosystems. Mangrove range expansion is occurring globally, but little is known about how these rapid climate-driven shifts may alter ecosystem C storage. Here, we quantify current C stocks in ecotonal wetlands across gradients of marsh- to mangrove-dominance, and use unique chronological maps of vegetation cover to estimate C stock changes from 2003 to 2010 in a 567-km² wildlife refuge in the mangrove-salt marsh ecotone. We report that over the 7-yr. period, total wetland C stocks increased 22 % due to mangrove encroachment into salt marshes. Newly established mangrove stands stored twice as much C on a per area basis as salt marsh primarily due to differences in aboveground biomass, and mangrove cover increased by 69 % during this short time interval. Wetland C storage within the wildlife refuge increased at a rate of 2.7 Mg C ha^?1 yr.^?1, more than doubling the naturally high coastal wetland C sequestration rates. Mangrove expansion could account for a globally significant increase of terrestrial C storage, which may exert a considerable negative feedback on warming.  相似文献   

Energy partitioning at treeline forest and tundra sites and its sensitivity to climate change     

Peter M. Lafleur  Wayne R. Rouse 《大气与海洋》2013,51(1):121-133

Abstract

Summertime energy budgets of contiguous wetland tundra and forest near Churchill, Manitoba along the coast of Hudson Bay were measured over a five year period, 1989–1993. An examination of differences in energy budgets between the two sites showed that net radiation was similar in all years. Soil heat flux was greater at the tundra site in most, but not all, years. However, sensible heat flux was always larger at the forest site and latent heat flux was always greater at the tundra site. Mean daily Bowen ratios at both sites were less than unity in all years. Average Bowen ratios for the five years were 0.45 for tundra and 0.66 for forest. Wind direction is used as an analogue for changing climatic conditions where onshore winds are cooler and moister than offshore winds. Sensible and latent heat fluxes at both sites varied significantly between onshore and offshore wind regimes. However, differences between onshore and offshore fluxes at the tundra site were larger than for the forest. Thus, Bowen ratios also varied more at the tundra site. We have plotted the ratio of tundra‐to‐forest Bowen ratios as a measure of the relative sensitivity of energy partitioning to climatic change. The ratio decreases with increasing vapour pressure deficit (and increasing air temperature). We interpret these results as suggesting that energy partitioning over the wetland tundra is more sensitive to changes in climate than the treeline forest environment. Thus, as the climate warms and becomes drier, more additional energy goes into evaporation of water from the wetland tundra than from the forest.  相似文献   

Nonlinear convection in an imposed horizontal magnetic field     

Wayne Arter† 《地球物理与天体物理流体动力学》2013,107(4):259-292

Abstract

Nonlinear two-dimensional magnetoconvection, with a Boussinesq fluid driven across the field-lines, is taken as a model for giant-cell convection in the sun and late-type stars. A series of numerical experiments shows the sensitivity of the horizontal scale of convection to the applied field and to the Rayleigh number R. Overstable oscillations occur in cells as broad as they are deep, but increasing R leads to steady motions of much greater wavelength. Purely geometrical effects can cause oscillation: this work implies that strong horizontal field will in general lead to time-dependent convection.  相似文献   

The Arctic Coastal Dynamics Database: A New Classification Scheme and Statistics on Arctic Permafrost Coastlines     

Hugues Lantuit  Pier Paul Overduin  Nicole Couture  Sebastian Wetterich  Felix Aré  David Atkinson  Jerry Brown  Georgy Cherkashov  Dmitry Drozdov  Donald Lawrence Forbes  Allison Graves-Gaylord  Mikhail Grigoriev  Hans-Wolfgang Hubberten  James Jordan  Torre Jorgenson  Rune Strand ?deg?rd  Stanislav Ogorodov  Wayne H. Pollard  Volker Rachold  Sergey Sedenko  Steve Solomon  Frits Steenhuisen  Irina Streletskaya  Alexander Vasiliev 《Estuaries and Coasts》2012,35(2):383-400

Arctic permafrost coasts are sensitive to changing climate. The lengthening open water season and the increasing open water area are likely to induce greater erosion and threaten community and industry infrastructure as well as dramatically change nutrient pathways in the near-shore zone. The shallow, mediterranean Arctic Ocean is likely to be strongly affected by changes in currently poorly observed arctic coastal dynamics. We present a geomorphological classification scheme for the arctic coast, with 101,447?km of coastline in 1,315 segments. The average rate of erosion for the arctic coast is 0.5?m? year^?1 with high local and regional variability. Highest rates are observed in the Laptev, East Siberian, and Beaufort Seas. Strong spatial variability in associated database bluff height, ground carbon and ice content, and coastline movement highlights the need to estimate the relative importance of shifting coastal fluxes to the Arctic Ocean at multiple spatial scales.  相似文献   

Optical spectra of supernova remnant candidates in the Sculptor Group galaxy NGC 300     

William C. Millar  Graeme L. White  Miroslav D. Filipović  Jeffrey L. Payne  Evan J. Crawford  Thomas G. Pannuti  Wayne D. Staggs 《Astrophysics and Space Science》2011,332(2):221-239

We present moderate-resolution (<5 Å) long-slit optical spectra of 51 nebular objects in the nearby Sculptor Group galaxy NGC 300 obtained with the 2.3 meter Advanced Technology Telescope at Siding Spring Observatory, Australia. Adopting the criterion of [S?ii]_Total:Hα≥0.4 to confirm supernova remnants (SNRs) from optical spectra, we find that of 28 objects previously proposed as SNRs from optical observations, 22 meet this criterion with six showing [S?ii]_Total:Hα of less than 0.4. Of 27 objects suggested as SNRs from radio data, four are associated with the 28 previously proposed SNRs. Of these four, three (included in the 22 above) meet the criterion. In all, 22 of the 51 nebular objects meet the [S ii]_Total:Hα criterion as SNRs while the nature of the remaining 29 objects remains undetermined by these observations.  相似文献   

Impact of two DNA repair pathways, homologous recombination and non-homologous end joining, on bacterial spore inactivation under simulated martian environmental conditions     

Ralf Moeller  Andrew C. Schuerger  Wayne L. Nicholson 《Icarus》2011,215(1):204-210

Spores of Bacillus subtilis were used as a model system to study the impact of the two major DNA double-strand break (DSB) repair mechanisms [homologous recombination (HR) and non-homologous end-joining (NHEJ)] on the survivability of air-dried mono- and multilayers of bacterial spores under a simulated martian environment; i.e., an environment with low temperature (−10 °C), pure CO₂ atmosphere (99.99% CO₂), 200-1100 nm UV-VIS-NIR radiation, and 0.69 kPa pressure. Spores in multilayers exhibited low inactivation rates compared to monolayers, mainly due to shadowing effects of overlying spores. Simulated martian UV irradiation reduced dramatically spore viability, whereas when shielded from martian UV radiation, spores deficient in NHEJ- and HR-mediated DNA repair were significantly more sensitive to simulated martian environmental conditions than were wild-type spores. In addition, NHEJ-deficient spores were consistently more sensitive than HR-deficient spores to simulated Mars environmental conditions, suggesting that DSBs were an important type of DNA damage. The results indicated that both HR and NHEJ provide an efficient set of DNA repair pathways ensuring spore survival after exposure to simulated martian environmental conditions.  相似文献   

Analytical Expression for Vertical Stress within an Inclined Mine Stope with Non-parallel Walls   总被引：1，自引：0，他引：1  

Ching Hung Ting  Nagaratnam Sivakugan  Wayne Read  Sanjay Kumar Shukla 《Geotechnical and Geological Engineering》2014,32(2):577-586

Arching is a phenomenon that occurs in many situations in geotechnical engineering. When underground mine stopes are backfilled, a significant fraction of the self-weight of the backfill is carried by the side walls. As a result, the vertical stress at the bottom of the stope is significantly less than its overburden pressure. Few analytical expressions published in the literature can be used to determine the vertical stresses of stope with parallel walls. The objective of this paper is to extend the analytical solution previously developed by the authors to long plane-strain stopes with non-parallel walls with both slopes leaning to the same side. Different combinations of wall inclination are examined using the new analytical expression developed. To validate the analysis, the proposed results are compared with numerical model results. The results show that the proposed analytical expression is capable of estimating the vertical stress within mine stopes when the inclination of the hangingwall to the horizontal (α) is less than that of footwall (β). An important behavioural trend for the stress distribution is observed, where with the same overburden pressure and base width, the stress magnitude experienced by fill material significantly varies depending on the wall inclination.  相似文献   

Energy balance of the intertidal zone of Western Hudson bay I: Ice‐free period     

Arvids Silis  Wayne R. Rouse  Steve Hardill 《大气与海洋》2013,51(2):327-345

Abstract

This study reports on tower measurements from the intertidal zone taken during the ice‐free period between August 1 and September 20, 1985. Sea and air temperatures showed ranges of 8 and 14°C, respectively, and both were colder during onshore than during offshore winds. Onshore winds were associated with a nearly saturated atmosphere whereas offshore ones were quite dry. Surface albedo was twice as great for low tide as for high tide. The ratio net/solar radiation was 13% less at low tide owing to both the larger albedo and the stronger long‐wave radiation loss. Heat fluxes into the bottom sediments were small with net gains in August and net losses in September. During the day, heat storage in the water was large and positive. This occurred even with the tide out, when the ponded water continued to warm. At night the water gave up heat, both for low and high tide, and especially late in the season. The latent heat flux was always positive and was largest by day during low tide and by night during high tide. The sensible heat flux was positive for onshore winds and often negative for offshore winds. Under all wind directions heat storage constituted 60% of net radiation, the latent heat flux 35% and the remainder was proportioned equally between the sensible heat flux and the flux into the bottom sediments.  相似文献