Lunar motion: Theory and observations     

Jean Chapront  Michelle Chapront-Touzé 《Celestial Mechanics and Dynamical Astronomy》1996,66(1):31-38

Results of several fits of the lunar theory ELP 2000-82B and of Moons' theory of libration are presented. The theories are fitted both to JPL numerical integrations and to LLR observations  相似文献   

On the in situ aqueous alteration of soils on Mars     

Ronald Amundson  Stephanie Ewing  Brad Sutter  Oliver Chadwick  Michelle Walvoord 《Geochimica et cosmochimica acta》2008,72(15):3845-3864

Early (>3 Gy) wetter climate conditions on Mars have been proposed, and it is thus likely that pedogenic processes have occurred there at some point in the past. Soil and rock chemistry of the Martian landing sites were evaluated to test the hypothesis that in situ aqueous alteration and downward movement of solutes have been among the processes that have transformed these portions of the Mars regolith. A geochemical mass balance shows that Martian soils at three landing sites have lost significant quantities of major rock-forming elements and have gained elements that are likely present as soluble ions. The loss of elements is interpreted to have occurred during an earlier stage(s) of weathering that may have been accompanied by the downward transport of weathering products, and the salts are interpreted to be emplaced later in a drier Mars history. Chemical differences exist among the sites, indicating regional differences in soil composition. Shallow soil profile excavations at Gusev crater are consistent with late stage downward migration of salts, implying the presence of small amounts of liquid water even in relatively recent Martian history. While the mechanisms for chemical weathering and salt additions on Mars remain unclear, the soil chemistry appears to record a decline in leaching efficiency. A deep sedimentary exposure at Endurance crater contains complex depth profiles of SO₄, Cl, and Br, trends generally consistent with downward aqueous transport accompanied by drying. While no model for the origin of Martian soils can be fully constrained with the currently available data, a pedogenic origin is consistent with observed Martian geology and geochemistry, and provides a testable hypothesis that can be evaluated with present and future data from the Mars surface.  相似文献   

Distribution and Trophic Importance of Anthropogenic Nitrogen in Narragansett Bay: An Assessment Using Stable Isotopes     

Autumn Oczkowski  Scott Nixon  Kelly Henry  Peter DiMilla  Michael Pilson  Stephen Granger  Betty Buckley  Carol Thornber  Richard McKinney  Joaquin Chaves 《Estuaries and Coasts》2008,31(1):53-69

Narragansett Bay has been heavily influenced by human activities for more than 200 years. In recent decades, it has been one of the more intensively fertilized estuaries in the USA, with most of the anthropogenic nutrient load originating from sewage treatment plants (STP). This will soon change as tertiary treatment upgrades reduce nitrogen (N) loads by about one third or more during the summer. Before these reductions take place, we sought to characterize the sewage N signature in primary (macroalgae) and secondary (the hard clam, Mercenaria mercenaria) producers in the bay using stable isotopes of N (δ¹⁵N) and carbon (δ¹³C). The δ¹⁵N signatures of the macroalgae show a clear gradient of approximately 4‰ from north to south, i.e., high to low point source loading. There is also evidence of a west to east gradient of heavy to light values of δ¹⁵N in the bay consistent with circulation patterns and residual flows. The Providence River Estuary, just north of Narragansett Bay proper, receives 85% of STP inputs to Narragansett Bay, and lower δ¹⁵N values in macroalgae there reflected preferential uptake of ¹⁴N in this heavily fertilized area. Differences in pH from N stimulated photosynthesis and related shifts in predominance of dissolved C species may control the observed δ¹³C signatures. Unlike the macroalgae, the clams were remarkably uniform in both δ¹⁵N (13.2 ± 0.54‰ SD) and δ¹³C (−16.76 ± 0.61‰ SD) throughout the bay, and the δ¹⁵N values were 2–5‰ heavier than in clams collected outside the bay. We suggest that this remarkable uniformity reflects a food source of anthropogenically heavy phytoplankton formed in the upper bay and supported by sewage derived N. We estimate that approximately half of the N in the clams throughout Narragansett Bay may be from anthropogenic sources.  相似文献   

Coastal Habitat Use and Residency of Juvenile Atlantic Sharpnose Sharks (Rhizoprionodon terraenovae)     

John K. Carlson  Michelle R. Heupel  Dana M. Bethea  Lisa D. Hollensead 《Estuaries and Coasts》2008,31(5):931-940

Coastal habitat use and residency of a coastal bay by juvenile Atlantic sharpnose sharks, Rhizoprionodon terraenovae, were examined by acoustic monitoring, gillnet sampling, and conventional tag–recapture. Acoustic monitoring data were used to define the residency and movement patterns of sharks within Crooked Island Sound, Florida. Over 3 years, sharks were monitored for periods of 1–37 days, with individuals regularly moving in and out of the study site. Individual sharks were continuously present within the study site for periods of 1–35 days. Patterns of movement could not be correlated with time of day. Home range sizes were typically small (average?=?1.29 km²) and did not vary on a yearly basis. Gillnet sampling revealed that juvenile Atlantic sharpnose sharks were present in all habitat types found within Crooked Island Sound, and peaks in abundance varied depending on month within a year. Although telemetry data showed that most individuals remained within the study site for short periods of time before emigrating, conventional tag–recapture data indicates some individuals return to Crooked Island Sound after extended absences (maximum length?=?1,352 days). Although conventional shark nursery theory suggests small sharks remain in shallow coastal waters to avoid predation, juvenile Atlantic sharpnose sharks frequently exited from protected areas and appear to move through deeper waters to adjacent coastal bays and estuaries. Given the high productivity exhibited by this species, the benefit gained through a nursery that reduces predation may be limited for this species.  相似文献   

Magnetic fabrics and rock magnetism of Proterozoic dike swarm from the southern São Francisco Craton, Minas Gerais State, Brazil     

Maria Irene Bartolomeu Raposo  Alexandre O. Chaves  Paulo Lojkasek-Lima  Manoel Souza D'Agrella-Filho  Wilson Teixeira   《Tectonophysics》2004,378(1-2):43-63

Magnetic fabric and rock magnetism studies were performed on 32 mafic dikes of a Proterozoic dike swarm from the southern São Francisco Craton (SFC; Minas Gerais State, SE Brazil). Magnetic anisotropies were determined by applying anisotropy of low-field magnetic susceptibility (AMS) and anisotropy of remanent magnetization (ARM). The latter was performed imposing both anhysteretic (total (AAR) and partial pAAR)) and isothermal remanence magnetizations (AIRM). Partial anhysteretic remanence anisotropy was performed based on remanent coercivity spectra from a pilot specimen of each site. In most sites, AMS is dominantly carried by ferromagnetic minerals, however, in some sites, the paramagnetic contribution exceeds 70% of bulk susceptibility. Rock magnetism and thin section analysis allow classifying the dikes as non-hydrothermalized and hydrothermalized. Magnetic measurement shows that the mean magnetic susceptibility is usually lower than 5×10⁻³ (SI). Ti-poor titanomagnetites up to pure magnetite pseudo-single-domain (PSD) grain sizes carry the majority of magnetic fabrics for non-hydrothermalized dikes whereas coarse to fine grained Ti-poor titanomagnetites carry the majority of magnetic fabrics for hydrothermalized dikes.Three primary AMS fabrics are recognized which are coaxial with ARM fabric, except for two dikes, from both non-hydrothermalized and hydrothermalized dikes. Normal AMS fabric surprisingly is not dominant (31%). The parallelism between AMS, pAAR_0–30, pAAR_30–60 and pAAR_60–90 fabrics in the hydrothermalized dikes indicates that magnetic grains formed due to late-stage crystallization or to remobilization of iron oxides due to hydrothermal alteration after dike emplacement have acquired a mimetic fabric coaxial with the primary fabric given by coarse-grained early crystallized Ti-poor titanomagnetites. This fabric is interpreted as magma flow in which the analysis of K_max inclination permitted the inference that the dikes were fed by horizontal or subhorizontal fluxes (K_max<30°). Intermediate AMS fabric is the most important (41%) in the investigated swarm. It is interpreted as due to vertical compaction of a static magma column with the minimum stress along the dike strike. ARM determinations for these sites also remained intermediate except for two dikes. In one of them, AIRM fabric resulted in normal AMS fabric while for the other AAR fabric resulted in inverse AMS fabric. A combination of AMS and ARM fabrics suggest that magmatic fabric for both dikes were overprinted by some late local event, probably related to Brasiliano orogenic processes after dike emplacement. InverseInverse AMS fabric is a minority (four dikes). ARM determinations also remained inverse suggesting a primary origin for inverse AMS fabric.  相似文献   

Impacts of the Wenchuan earthquake on tree mortality and biomass carbon stock     

Shuai Qiu  Ming Xu  Yunpu Zheng  Renqiang Li  Michelle Hang Gi Wong  Liyun Zhang  Lixiang Liu  Changhong Lai  Wen Zhang 《Natural Hazards》2015,77(2):1261-1274

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Can spatial statistics help decipher impact crater saturation?          下载免费PDF全文

Michelle R. Kirchoff 《Meteoritics & planetary science》2018,53(4):874-890

Impact crater saturation equilibrium is a state where a surface is so densely cratered that a new crater cannot form without removing older craters and the observed crater density is in (quasi-)equilibrium. Whether densely cratered surfaces throughout the solar system are saturated for large, kilometer-sized craters has been debated for decades. This work explores if spatial statistics can provide insight if these crater distributions are in saturation equilibrium. The supposition is that crater distributions become more spatially uniform (more evenly spaced) as they reach saturation (Squyres et al. 1997 ). A numerical simulation of crater saturation is combined with observations of cratered terrains throughout the solar system to assess the utility of using spatial statistics. The numerical simulations examine spatial statistics and saturation equilibrium for crater distributions for various input population size-frequency distribution (SFD) slopes, along with a range in the effective crater erasure size, effectiveness of smaller craters erasing the rims of larger craters, and the amount of rim needed to recognize a crater. Simulations show that saturated terrains do become more spatially uniform, and that the degree of uniformity appears to be most dependent on the input SFD slope. When simulation results are compared to observed crater distributions, I find that large, kilometer-sized craters on densely cratered terrains throughout the solar system are likely in saturation equilibrium.  相似文献   

Soil paludification and Sphagnum bog initiation: the influence of indurated podzolic soil and fire     

Alice Schaffhauser  Serge Payette  Michelle Garneau  Élisabeth C. Robert 《Boreas: An International Journal of Quaternary Research》2017,46(3):428-441

The initiation and growth of boreal peatlands developed on well‐drained, sandy landforms are closely associated with podzolic soil paludification processes. The origin of Sphagnum bogs extending on large deltaic plains was examined to test the hypothesis of the dual impact of indurated (ortstein) podzols and fire on forest soil paludification and concurrent peatland initiation and expansion. Mineral soil, basal organic matter and peat monoliths were sampled for soil and macrofossil analyses along an 800‐m toposequence starting from a mixed‐wood boreal forest to a Sphagnum bog (Lebel bog, eastern Quebec, Canada), and ending at a peat dome in the thickest section of the peatland. Mineral soils along the toposequence are ortstein humo‐ferric podzols distributed in the forest environment and beneath Sphagnum peat in the bog, except at the peat dome. Initial peatland growth occurred c. 6000 cal. a BP. Soil paludification coincided with the cessation of fire occurrence as recorded in the organic and mineral layers preceding Sphagnum expansion. Unlike most temperate and boreal raised bogs, the Sphagnum bog developed directly from a forest environment without passing through a transitional fen stage. Conifer forests regenerated successively after several fires between 4200 and 1600 cal. a BP before bog expansion. Pre‐bog forests were composed of fire‐prone black spruce (Picea mariana) and jack pine (Pinus banksiana) trees, and ericaceous species. Given the distribution and thickness of ortstein horizons progressively decreasing and disappearing towards the peatland dome, growth and expansion of the Sphagnum bog was not caused by soil induration processes, which could have potentially impeded vertical and horizontal drainage. The development of indurated podzols outside and several hundred metres inside the peatland preceded the initiation and expansion of the Sphagnum bog. Cessation of fire activity appears to be a key factor facilitating the lateral expansion of the Sphagnum bog under wet soil conditions.  相似文献   

Particulate air pollution from wildfires in the Western US under climate change     

Jia Coco Liu  Loretta J. Mickley  Melissa P. Sulprizio  Francesca Dominici  Xu Yue  Keita Ebisu  Georgiana Brooke Anderson  Rafi F. A. Khan  Mercedes A. Bravo  Michelle L. Bell 《Climatic change》2016,135(3-4):655-668

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Adaptation and Indigenous peoples in the United Nations Framework Convention on Climate Change     

James Ford  Michelle Maillet  Vincent Pouliot  Thomas Meredith  Alicia Cavanaugh  IHACC Research Team 《Climatic change》2016,139(3-4):429-443

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