Northern Hemisphere Temperature Variability for the Past Three Centuries: Tree-Ring and Model Estimates     

Rosanne D'Arrigo  Gordon Jacoby  Melissa Free  Alan Robock 《Climatic change》1999,42(4):663-675

We compare Northern Hemisphere energy-balance-model temperature calculations to an annual temperature reconstruction based on 20 tree-ring width records from latitudinal and elevational treeline sites in northern North America, Scandinavia, Siberia and Mongolia for the past three centuries. The energy-balance model uses three primary forcings; solar, volcanic, and anthropogenic trace gas and aerosol variations. Several different parameterizations of the forcings are compared. The best agreement (r = 0.8) is found when the annual reconstruction is compared to a version of the model using (1) the Dust Veil Index of Lamb, (2) a solar parameterization which includes the length of the solar cycle, and (3) anthropogenic forcing. The implication is that all three forcings are important in explaining the temperature variations. The general similarity in low-frequency trends between the two independently-derived time series supports the validity of both the model estimates and the tree-ring reconstruction.  相似文献   

Diatom assemblages and water depth in Lake 239 (Experimental Lakes Area,Ontario): implications for paleoclimatic studies   总被引：3，自引：0，他引：3  

Melissa?T. MoosEmail author  Kathleen R.?Laird  Brian?F.?Cumming 《Journal of Paleolimnology》2005,34(2):217-227

Diatom assemblages in surface sediments were sampled along three transects in Lake 239, from the Experimental Lakes Area (NW Ontario), and analyzed in order to explore the relationship between modern species distributions and water depth. Approximately 170 diatom species were identified in surficial sediments at lake depths from 2 to 30 m. The species composition varied with sample depth but remained highly similar across all three transects. The main patterns of variation in the diatom assemblages across transects, derived from a detrended correspondence analysis (DCA), showed that assemblages were highly correlated (r = 0.97 to 0.98). At depths > 8 m the pattern of predominantly benthic composition changed to a planktonic assemblage dominated by Cyclotella stelligera. This depth currently corresponds to the depth of 1% light penetration as assessed from extinction coefficient measurements. Diatom species diversity increases with the switch to the near-shore benthic taxa in all three transects. Additionally, there is a large decrease in the ratio of chrysophyte scales to diatoms at depths < 8 m. Light transmission data from wet and dry periods over the last 35 years suggests that during dry periods the extent of the littoral zone should change by over 2 m. We suggest that cores along a transect from 8 to 14 m should provide a highly sensitive location for detailed paleoclimatic study.  相似文献   

Anaerobic biodegradation of TCE in laboratory columns of fractured saprolite     

Lenczewski ME  McKay LD  Layton A 《Ground water》2004,42(4):534-541

An experiment was conducted to determine if biodegradation of trichloroethylene (TCE) can occur in previously uncontaminated ground water in saturated fractured saprolite (highly weathered material derived from sedimentary rocks). Two undisturbed columns (0.23 m diameter by 0.25 m long) of fractured saprolite were collected from approximately 2 m depth at an uncontaminated site on the Oak Ridge Reservation, Oak Ridge, Tennessee. Natural, uncontaminated ground water from the site, which was degassed and spiked with dissolved phase TCE, was continuously pumped through one column containing the natural microbial communities (the biotic column). In a second column, the microorganisms were inhibited and the dissolved phase TCE was added under aerobic conditions (dissolved oxygen conditions > 2 ppm). In effluent from the biotic column, reducing conditions rapidly developed and evidence of anaerobic biodegradation of TCE, by the production of cDCE, first appeared approximately 31 days after addition of TCE. Reductive dechlorination of TCE occurred after iron-reducing conditions were established and about the same time that sulfate reduction began. There was no evidence of methanogenesis. Analyses using polymerase chain reaction with specific primers sets detected the bacteria Geothrix, Geobacter, and Desulfococcus-Desulfonema-Desulfosarcina in the effluent of the biotic column, but no methanogens. The presence of these bacteria is consistent with iron- and sulfate-reducing conditions. In the inhibited column, there were no indicators of TCE degradation. Natural organic matter that occurs in the saprolite and ground water at the site is the most likely primary electron donor for supporting reductive dechlorination of TCE. The relatively rapid appearance of indicators of TCE dechlorination suggests that these processes may occur even in settings where low oxygen conditions occur seasonally due to changes in the water table.  相似文献   

Rhenium–osmium systematics of the Mount Isa copper orebody and the Eastern Creek Volcanics,Queensland, Australia: implications for ore genesis     

Melissa J. Gregory  Bruce F. Schaefer  Reid R. Keays  Andy R. Wilde 《Mineralium Deposita》2008,43(5):553-573

The syn-tectonic breccia-hosted Mount Isa Cu deposit in northwest Queensland is the largest sediment-hosted Cu deposit in Australia. Whole-rock samples of chalcopyrite-rich Cu ore form an isochron with a Re–Os age of 1,372 ± 41 Ma. This age is more than 100 Ma younger than the previously accepted age of Cu ore formation, an Ar–Ar mineral age for biotite separated from the host rocks within the alteration envelope to the Cu orebody. This discrepancy cannot be unequivocally resolved due to a lack of other absolute geochronological constraints for Cu mineralisation or the deformation event associated with Cu emplacement. The 1,372 ± 41 Ma date may reflect (a) the time of Cu deposition, (b) the time of a hydrothermal event that reset the Re–Os signature of the Cu ore or (c) mixing of the Re–Os isotope systematics between the host rocks and Cu-bearing fluids. However, a range of published Ar–Ar and Rb–Sr dates for potassic alteration associated with Cu mineralisation also records an event between 1,350 and 1,400 Ma and these are consistent with the 1,372 Ma Re–Os age. The 1.8 Ga Eastern Creek Volcanics are a series of tholeiitic basalts with a primary magmatic Cu enrichment which occur adjacent to the Mount Isa Cu deposit. The whole-rock Os isotopic signature of the Eastern Creek Volcanics ranges from mantle-like values for the upper Pickwick Member, to more radiogenic/crustal values for the lower Cromwell Member. The Re–Os isotope signature of the Cu ores overlaps with those calculated for the two volcanic members at 1,372 Ma; hence, the Os isotope data are supportive of the concept that the Os in the Cu ores was sourced from the Eastern Creek Volcanics. By inference, it is therefore postulated that the Eastern Creek Volcanics are the source of Cu in the Mount Isa deposit, as both Os and Cu are readily transported by oxidised hydrothermal fluids, such as those that are thought to have formed the Cu orebody. The Pickwick Member yields a Re–Os isochron age of 1,833 ± 51 Ma, which is within error of previously reported age constraints. The initial ¹⁸⁷Os/¹⁸⁸Os isotopic ratio of 0.114 ± 0.067 (γOs = −0.7) is slightly subchondritic, and together with other trace element geochemical constraints, is consistent with a subcontinental lithospheric mantle source. The Pickwick Member records a minimum age of ca. 1.95 Ga for melt depletion in the subcontinental lithospheric mantle beneath the Mount Isa Inlier prior to the extraction of the magmas which formed the Eastern Creek Volcanics. This corresponds with the end of subduction-related magmatism along the eastern margin of the Northern Australian Craton, which included the Mount Isa Inlier.  相似文献   

Historicizing climate change—engaging new approaches to climate and history     

Sverker Sörlin  Melissa Lane 《Climatic change》2018,149(1):1-11

This introduction to a special issue of Climatic Change argues that it is timely and welcome to intensify historical research into climate change and climate as factors of history. This is also already an ongoing trend in many disciplines. The article identifies two main strands in historical work on climate change, both multi-disciplinary: one that looks for it as a driver of historical change in human societies, the other that analyzes the intellectual and scientific roots of the climate system and its changes. In presenting the five papers in this special issue the introduction argues that it is becoming increasingly important to also situate “historicizing climate change” within the history of thought and practice in wider fields, as a matter of intellectual, political, and social history and theory. The five papers all serve as examples of intellectual, political, and social responses to climate-related phenomena and their consequences (ones that have manifested themselves relatively recently and are predominantly attributable to anthropogenic climate change). The historicizing work that these papers perform lies in the analysis of issues that are rising in societies related to climate change in its modern anthropogenic version. The history here is not so much about past climates, although climate change itself is always directly or indirectly present in the story, but rather about history as the social space where encounters take place and where new conditions for humans and societies and their companion species and their life worlds in natures and environments are unfolding and negotiated. With climate change as a growing phenomenon historicizing climate change in this version will become increasingly relevant.  相似文献   

Natural Resource Access Rights and Wrongs: Nontimber Forest Products Gathering in Urban Environments     

Susan Charnley  Rebecca J. McLain  Melissa R. Poe 《社会与自然资源》2018,31(6):734-750

This article uses research about non-timber forest products (NTFP) gathering in Seattle, Washington, USA to examine how people gain access to natural resources in urban environments. Our analysis focuses on gathering in three spaces: parks, yards, and public rights of way. We present a framework for conceptualizing access, and highlight cognitive mechanisms of access associated with foragers’ internal moral judgments about harvesting. Key findings are: (1) internal moral calculations about whether it is right or wrong to harvest a particular NTFP in a particular place are an important but previously unacknowledged mechanism governing resource access; and (2) these calculations may help prevent over-harvesting of NTFPs, which are common pool resources, in urban environments where social and environmental conditions lend themselves to a de facto situation of open access. Our findings suggest that voluntary codes of conduct may be the best way to manage NTFP access in cities.  相似文献   

Kāhuli: Uncovering Indigenous Ecological Knowledge to Conserve Endangered Hawaiian Land Snails     

Aimee You Sato  Melissa Renae Price  Mehana Blaich Vaughan 《社会与自然资源》2018,31(3):320-334

Indigenous knowledge is a multilayered knowledge system that can inform contemporary management in both natural observations and cultural value. Centuries old observations preserved within song, chant, and story has been globally recognized as a resource to integrate with conservation efforts for endangered species. In the case of the endemic land snails, kāhuli, of the Hawaiian archipelago, there is a prominent cultural presence preserved in oral tradition and written records in 19th and early 20th century’s Hawaiian language newspapers. As we witness the dramatic decimation of one of the greatest models of species radiation, the unveiling of the repositories of indigenous knowledge is crucial for conservation of these endemic land snails. This paper reports on indigenous knowledge that informs about the cultural significance (i.e., poetic device, metaphorical role, importance to hula) and ecology of kāhuli, and how indigenous knowledge can contribute to conservation efforts of rare and endangered species.  相似文献   

Biogeographic variability in the physiological response of the cold‐water coral Lophelia pertusa to ocean acidification          下载免费PDF全文

Samuel E. Georgian  Sam Dupont  Melissa Kurman  Adam Butler  Susanna M. Strömberg  Ann I. Larsson  Erik E. Cordes 《Marine Ecology》2016,37(6):1345-1359

While ocean acidification is a global issue, the severity of ecosystem effects is likely to vary considerably at regional scales. The lack of understanding of how biogeographically separated populations will respond to acidification hampers our ability to predict the future of vital ecosystems. Cold‐water corals are important drivers of biodiversity in ocean basins across the world and are considered one of the most vulnerable ecosystems to ocean acidification. We tested the short‐term physiological response of the cold‐water coral Lophelia pertusa to three pH treatments (pH = 7.9, 7.75 and 7.6) for Gulf of Mexico (USA) and Tisler Reef (Norway) populations, and found that reductions in seawater pH elicited contrasting responses. Gulf of Mexico corals exhibited reductions in net calcification, respiration and prey capture rates with decreasing pH. In contrast, Tisler Reef corals showed only slight reductions in net calcification rates under decreased pH conditions while significantly elevating respiration and capture rates. These differences are likely the result of environmental differences (depth, pH, food supply) between the two regions, invoking the potential for local adaptation or acclimatization to alter their response to global change. However, it is also possible that variations in the methodology used in the experiments contributed to the observed differences. Regardless, these results provide insights into the resilience of L. pertusa to ocean acidification as well as the potential influence of regional differences on the viability of species in future oceans.  相似文献   

Vegetation water sources in California's Sierra Nevada (USA) are young and change over time,a multi-isotope (δ18O, δ2H, 3H) tracer approach.     

Melissa Thaw  Ate Visser  Richard Bibby  Amanda Deinhart  Erik Oerter  Martha Conklin 《水文研究》2021,35(6):e14249

Sierra Nevada forests transpire a significant amount of California's water resources, sparking interest in applying forest management to improve California's water supply. Determining the source water of evapotranspiration enables forest managers to make informed decisions. To this end, a significant interest in critical zone science is to develop new methods to work across time scales to predict subsurface water storage and use. In this study, forest vegetation accessed young water and switched sources depending on availability, suggesting that forest drought vulnerability may depend on the range of water sources available (rain, snowmelt and deeply stored water). This finding also suggests that changes in transpiration rates may have immediate effects on water sources in close proximity to vegetation, and delayed effects on storage and runoff. New δ¹⁸O, δ²H and ³H data were used to track precipitation, runoff, evapotranspiration and storage through the critical zone seasonally, including seasons where evapotranspiration and snowmelt were in phase (winter snowmelt) and out of phase (seasonally dry summer). The main source of this headwater catchment's runoff is derived from its meadow saturated zone water, which was dominated by snowmelt. Water that originated as snowmelt contributed to transpiration, unless other sources, such as recent rain, became available. In cases where xylem δ¹⁸O and δ²H signatures matched those of deeper saturated zone water, ³H data showed that xylem water was distinctly younger than the deep saturated zone water. During 2016, which experienced relatively normal snowpack in winter and seasonally dry summer conditions, mean summer saturated zone water and vegetation water were similar in δ¹⁸O, −12.4 ± 0.04 ‰ and − 12.5 ± 0.3 ‰, respectively, but were distinctly different in ³H, 5.5 ± 0.2 pCi/L and 13.7 ± 1.1 pCi/L, respectively. While δ¹⁸O shows that vegetation and meadow saturated zone water have similar origins, ³H shows they have dissimilar ages.  相似文献   

A 1900‐year paleohurricane record from Wassaw Island,Georgia, USA     

Lawrence M Kiage  Daniel Deocampo  Terrence A. Mccloskey  Thomas A. Bianchette  Melissa Hursey 《第四纪科学杂志》2011,26(7):714-722

We present here the first paleotempestology record from Wassaw Island on the Georgia Bight, located in the south Atlantic coast of the United States. In the historical period, the Georgia Bight has experienced less frequent hits by hurricanes than other locations along the US Gulf and Atlantic coasts. The 1900‐year record inferred from the overwash sand layers from a back‐barrier marsh on Wassaw Island suggests that the island was directly struck by major storms on nine occasions during this interval. The Wassaw Island record shows alternating regimes, with periods of increased activity from >2000 a BP until ～1100 a BP, and ～100 a BP until the present, sandwiching a quiet period from ～1100 to 250 a BP. Storm deposits from the most recent active period are perhaps amalgamated, indicating that site‐specific conditions may result in event undercounting and suggests that the relative thickness of sand layers in the sedimentary record is not always indicative of hurricane strength. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献