Acidity of twelve northern New England (U.S.A.) lakes in recent centuries     

Ronald B. Davis  Dennis S. Anderson  Stephen A. Norton  Mark C. Whiting 《Journal of Paleolimnology》1994,12(2):103-154

Studies of sediment cores from 12 acidic lakes in granitic, forested and uninhabited catchments in northern New England, U.S.A. produced diatom-inferred pH (IpH) 5.2 to 5.8 and alkalinity (Ialk) –12 to 31 µeq l^–1, with slowly declining values at some lakes, for one to four centuries prior to logging. Increases of IpH (0.05 to 0.60) and Ialk (5 to 40 µeq l^–1) correlate with logging in the catchments in the early-1800s to early-1900s. Recovery to pre-logging IpH and Ialk correlates with forest succession toward conifers, and is completed in the late-1800s to mid-1900s. Beginning at 1915–1920 (4 lakes), 1930–1950 (4 lakes) and 1965–1970 (4 lakes), IpH and Ialk start decreasing below pre-logging values due to atmospheric acidic deposition, leading to respective total decreases of 0.10 to 0.45 (X=0.25) and 5 to 25 µeq l^–1 (X=15). Inputs of anthropogenic Pb, Zn, V, polycyclic aromatic hydrocarbons, and soot from the atmosphere are first detectable in early- to late-1800s sediment, and Cu in late-1800s sediment, increase rapidly in the late-1800s to mid-1900s, and level off or decrease since the 1960s — partly due to emission controls. Decreasing Ca, Mn, and possibly Zn relative to other metals and normalized to organic content, and increasing flux of Fe to the lakes, indicate soil and water acidification after 1900.This is the fourteenth of a series of papers to be published by this journal which is a contribution of the Paleoecological Investigation of Recent Lake Acidification (PIRLA) project. Drs. D. F. Charles and D. R. Whitehead are guest editors for this series.  相似文献   

Exploring former subglacial Hodgson Lake,Antarctica Paper I: site description,geomorphology and limnology     

Dominic A. Hodgson  Stephen J. Roberts  Michael J. Bentley  James A. Smith  Joanne S. Johnson  Elie Verleyen  Wim Vyverman  Andy J. Hodson  Melanie J. Leng  Andreas Cziferszky  Adrian J. Fox  David C.W. Sanderson 《Quaternary Science Reviews》2009,28(23-24):2295-2309

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A paleolimnological record of anthropogenic disturbances at Holmes Lake,Adirondack Mountains,New York     

Thomas E. Rhodes 《Journal of Paleolimnology》1991,5(3):255-262

Holmes Lake, Adirondack Mountains, New York, is a clear-water acidic lake that was treated with lime in 1983 to permit stocking of trout. Diatom assemblages in dated sediments reflect three anthropogenic modifications of the lake ecosystem: 1) assemblages from the mid- and late 1800's are associated with historical and sedimentary records of forest clearance, and indicate slightly increased pH; 2) acidobiontic species increase in sediments from the mid-1900's, a period of local reforestation and regionally increasing anthropogenic acid loading; 3) liming caused large increases of circumneutral periphytic species in the first growing season, and decreases of acidobiontic species by the second.  相似文献   

Coupling of deformation and reactions during mid-crustal shear zone development: an in situ frictional–viscous transition     

J. H. MARSH  S. E. JOHNSON  M. G. YATES  D. P. WEST JR 《Journal of Metamorphic Geology》2009,27(8):531-553

A well preserved strain and reaction gradient records the progressive transformation of a megacrystic Kfs+Cpx+Opx+Bt₁±Qtz syenitic pluton to a strongly sheared Kfs+Act+Bt₂+Ab+Qtz tectonite within the exhumed Norumbega Fault System, Maine, USA. Detailed microstructural analysis indicates that fracturing and localized fluid infiltration initiated the deconstruction of the existing K-feldspar and two-pyroxene load-bearing framework, and that feedback among metamorphic reactions, fabric development and enhanced permeability during progressive shearing led to the development of an interconnected, biotite- and actinolite-rich foliation. The activation of dislocation creep in biotite and quartz, and dissolution–precipitation creep in actinolite and feldspar, with increasing strain ultimately resulted in a transition from dominantly frictional to dominantly viscous deformation processes. Petrological data show that various scales of geochemical disequilibrium exist across the strain and reaction gradient, and that reaction progress was limited by slow chemical diffusion during the early stages of deformation. Petrological modelling results indicate that the existing plutonic assemblage was metastable at mid-crustal conditions, and that fluid infiltration and deformation allowed the product assemblage to advance towards chemical equilibration. Comparison of the observed microstructures and deformation mechanisms with experimental and numerical modelling results suggest that the development of an interconnected biotite-dominated fabric probably caused a major (up to three fold) reduction in bulk rock strength and localization of strain into the foliated margin.  相似文献   

Seasonal air temperature variations retrieved from a Geladaindong ice core, Tibetan Plateau     

ZHANG Yongjun  KANG Shichang  QIN Dahe  REN Jiawen  ZHANG Yulan  Bjorn GRIGHOLM  Paul MAYEWSKI 《地理学报》2007,17(4):431-441

A 70-year history of precipitation δ18O record has been retrieved using an ice core drilled from a plat portion of the firn area in the Guoqu Glacier (33o34′37.8″ N, 91o10′35.3″ E, 5720 m a.s.l.) on Mt. Geladaindong (the source region of Yangtze River) during October and November, 2005. Based on the seasonality of δ18O records and the significant positive rela-tionships between monsoon/non-monsoon δ18O values and summer/spring air temperature from the nearby meteorological stations, the history of summer and spring air temperature have been reconstructed for the last 70 years. The results show that both summer and spring air temperature variations present similar trends during the last 70 years. Regression analysis indicates that the slope of the temperature-δ18O relationship is 1.3℃/‰ for non-monsoon δ18O values and spring air temperature, and 0.4℃/‰ for monsoon δ18O values and summer air temperature. Variation of air temperature recorded in the ice core is consistent with that in the Northern Hemisphere (NH), however, the warming trend in the Geladaindong region is more intense than that in the NH, reflecting a higher sensitivity to global warming in the high elevation regions. In addition, warming trend is greater in spring than in summer.  相似文献   

A perturbation solution for dyke propagation in an elastic medium with graded density   总被引：1，自引：0，他引：1  

Zuan Chen  Z.-H. Jin  S. E. Johnson 《Geophysical Journal International》2007,169(1):348-356

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Climatic significance of δ~(18)O records from an 80.36 m ice core in the East Rongbuk Glacier, Mount Qomolangma (Everest)     

Paul A. Mayewski 《中国科学D辑(英文版)》2005,(2)

The δ18O variations in an 80.36 m ice core retrieved in the accumulation zone of the East Rongbuk Glacier, Mount Qomolangma (Everest), is not consistent with changes of air temperature from both southern and northern slopes of Himalayas, as well as these of the temperature anomalies over the Northern Hemisphere. The negative relationship between the δ18O and the net accumulation records of the ice core suggests the "amount effect" of summer precipitation on the δ18O values in the region. Therefore, the δ18O records of the East Rongbuk ice core should be a proxy of Indian Summer Monsoon intensity, which shows lower δ18O values during strong monsoon phases and higher values during weak phases.  相似文献   

Sea-salt aerosol transport patterns over the Northern Hemisphere inferred from two subarctic ice core records     

Yuping?Yan  Shichang?Kang  Junying?SunEmail author  Paul?A.?Mayewski  Dahe?Qin 《中国科学D辑(英文版)》2005,48(4):576-584

Ice core records provide the most direct, detailedand complete measure of past climate change[1,2]. Gla-ciochemical records have been used to investigate thechanges in atmospheric circulation patterns overGreenland Ice Sheet and West Antarctic[3—6]. Mostrecently, major ion series developed from new suban-nual scale sampling of GISP2 ice core from centralGreenland are calibrated with instrumental series ofsea level pressure (SLP) provide proxy records of ma-jor marine (Icelandic Low) and…  相似文献   

Solar variability and the levels of Lake Victoria,East Africa,during the last millenium   总被引：1，自引：0，他引：1  

J. Curt?StagerEmail author  David?Ryves  Brian F.?Cumming  L. David?Meeker  Juerg?Beer 《Journal of Paleolimnology》2005,33(2):243-251

A new diatom series with 1–6 year resolution from Lake Victoria, East Africa, shows that lake level minima occurred ca. 820–760, 680–660, 640–620, 370–340, and 220–150 calendar years BP. Inferred lake levels were exceptionally high during most of the Little Ice Age (ca. 600–200 calendar years BP). Synchrony between East African high lake levels and prolonged sunspot minima during much of the last millenium may reflect solar variabilitys effects on tropical rainfall, but those relationships reversed sign ca. 200 years ago. Historical records also show that Victoria lake levels rose during every peak of the ca. 11-year sunspot cycle since the late 19th century. These findings suggest that, if these apparent tropical sun–climate associations during the last millenium were real, then they were subject to abrupt sign reversals.Electronic Supplementary Material to this article is available at .  相似文献   

Identification of an E3 ubiquitin-protein ligase in the softshell clam (Mya arenaria).     

M L Kelley  R J Van Beneden 《Marine environmental research》2000,50(1-5):289-293

Softshell clams (Mya arenaria) were exposed to dioxin in controlled laboratory experiments in order to study their molecular response to dioxin exposure. A complementary DNA (cDNA) fragment with sequence similarity to E3 ubiquitin-protein ligase appeared to be upregulated in dioxin-exposed clams compared to controls. E3 covalently ligates ubiquitin onto a protein, targeting it for degradation. Our findings suggest that the ubiquitin-mediated proteolytic pathway in the softshell clam may be activated by dioxin exposure. Because the clam E3-predicted amino acid sequence is most similar to a specific vertebrate E3 protein (E6-AP), we hypothesize that dioxin may stimulate ubiquitin-mediated degradation of cell-cycle regulatory proteins, such as the tumor suppressor p53, which promotes cell proliferation. This pathway has been observed in human cervical cancer. Partial cDNA sequence of the clam E3 has been identified using the differential display polymerase chain reaction (ddPCR) and RACE (Rapid Amplification of cDNA Ends) PCR; the full-length sequence is currently being determined. Discovering the molecular mechanism(s) stimulated by dioxin exposure in this invertebrate model may contribute to a better understanding of the effects of dioxin on marine organisms.  相似文献