International Pellet Watch: Global monitoring of persistent organic pollutants (POPs) in coastal waters. 1. Initial phase data on PCBs, DDTs, and HCHs   总被引：1，自引：0，他引：1  

Yuko Ogata  Kaoruko Mizukawa  Satoru Iwasa  Yukie Mato  Keiji Okuda  Michio Murakami  Ruchaya Booyatumanondo  Le Quang Dung  Carlos Miguez  Charles Moore  Steven Weerts  Erick Burres  Michael Van Velkenburg  Richard C. Lang  Brenda Danner  Richard C. Thompson 《Marine pollution bulletin》2009,58(10):1437-1446

Samples of polyethylene pellets were collected at 30 beaches from 17 countries and analyzed for organochlorine compounds. PCB concentrations in the pellets were highest on US coasts, followed by western Europe and Japan, and were lower in tropical Asia, southern Africa and Australia. This spatial pattern reflected regional differences in the usage of PCBs and was positively correlated with data from Mussel Watch, another monitoring approach. DDTs showed high concentrations on the US west coast and in Vietnam. In Vietnam, DDT was predominant over its metabolites (DDE and DDD), suggesting the principal source may be current usage of the pesticide for malaria control. High concentrations of pesticide HCHs were detected in the pellets from southern Africa, suggesting current usage of the pesticides in southern Africa. This study demonstrates the utility and feasibility of the International Pellet Watch approach to monitor POPs at a global scale.  相似文献   

A submillimetre survey for protostellar accretion discs using the JCMT–CSO interferometer     

David W. Brown  Claire J. Chandler  John E. Carlstrom  Richard E. Hills  Oliver P. Lay  Brenda C. Matthews  John S. Richer  Christine D. Wilson 《Monthly notices of the Royal Astronomical Society》2000,319(1):154-162

We present a submillimetre continuum survey for accretion discs around seven embedded protostars in the Perseus and Serpens molecular clouds. Observations were made at frequencies between 339 and 357 GHz using the James Clerk Maxwell Telescope–Caltech Submillimeter Observatory single-baseline interferometer on Mauna Kea, Hawaii. All the objects in our survey show compact dust emission on scales ≲1 arcsec, assumed to arise in a circumstellar accretion disc. We compare the properties of this compact component with evolutionary indicators, such as the ratio of compact to extended emission, and bolometric temperature. We find that discs of mass ∼0.01 M_⊙ have formed by the Class 0 stage, and that similar mass discs are observed in Class I and Class II sources. A trend is observed whereby the ratio of compact to extended emission in our sources increases from Class 0 to Class II sources. For three of the objects in the survey, NGC 1333 IRAS2:CR1 and SVS13 in Perseus, and FIRS1 in Serpens, the signal-to-noise ratio is sufficient to allow us to model the brightness distributions with elliptical Gaussian and power-law disc models. The Gaussian fits give semimajor half-power radii of approximately 90 to 140 au, at the assumed distance of 350 pc to the Perseus and Serpens clouds.  相似文献   

Preface     

George H. Denton  & Brenda L. Hall 《Geografiska Annaler: Series A, Physical Geography》2000,82(2-3):139-141

  相似文献   

A comparison of sample handling and analytical methods for determination of acid volatile sulfides in sediment   总被引：2，自引：0，他引：2  

Brenda Lasorsa  Atina Casas   《Marine Chemistry》1996,52(3-4)

Proper sample storage and analytical techniques are required when analyzing anoxic sediment for acid volatile sulfide (AVS), because a change in redox state may alter sediment parameters. The goal of this study was to determine the optimum sample handling, storage, and analytical techniques to adopt when determining AVS concentrations in sediment. To determine the correct handling and storage protocols for use with anoxic sediment, samples of three different AVS levels were manipulated under a combination of the following handling and storage plans: handled on benchtop or under nitrogen atmosphere; preserved with zinc acetate (ZnAc) or not preserved, and stored at 4 °C or frozen (< − 20 °C). The data indicate that sulfide levels are best maintained when samples are handled under a nitrogen atmosphere, stored at 4 °C or frozen, and analyzed within 2 weeks of collection. To determine the best analytical procedure for the determination of AVS in sediment, the following methods were compared: colorimetric, gravimetric, ion-selective electrode, and photoionization detection. The colorimetric method was preferred.  相似文献   

The Wasatch Environmental Observatory: A mountain to urban research network in the semi-arid western US     

Jennifer J. Follstad Shah  Ryan Bares  Brenda B. Bowen  Gabriel J. Bowen  David R. Bowling  David P. Eiriksson  Benjamin Fasoli  Richard P. Fiorella  Anna Gannet Hallar  Sarah J. Hinners  John D. Horel  Alexander A. Jacques  Logan R. Jamison  John C. Lin  Daniel L. Mendoza  Logan E. Mitchell  Diane E. Pataki  Sarah McKenzie Skiles  Rose M. Smith  Margaret A. Wolf  Paul D. Brooks 《水文研究》2021,35(9):e14352

The 2085 km² Jordan River Basin, and its seven sub-catchments draining the Central Wasatch Range immediately east of Salt Lake City, UT, are home to an array of hydrologic, atmospheric, climatic and chemical research infrastructure that collectively forms the Wasatch Environmental Observatory (WEO). WEO is geographically nested within a wildland to urban land-use gradient and built upon a strong foundation of over a century of discharge and climate records. A 2200 m gradient in elevation results in variable precipitation, temperature and vegetation patterns. Soil and subsurface structure reflect systematic variation in geology from granitic, intrusive to mixed sedimentary clastic across headwater catchments, all draining to the alluvial or colluvial sediments of the former Lake Bonneville. Winter snowfall and spring snowmelt control annual hydroclimate, rapid population growth dominates geographic change in lower elevations and urban gas and particle emissions contribute to episodes of severe air pollution in this closed-basin. Long-term hydroclimate observations across this diverse landscape provide the foundation for an expanding network of infrastructure in both montane and urban landscapes. Current infrastructure supports both basic and applied research in atmospheric chemistry, biogeochemistry, climate, ecology, hydrology, meteorology, resource management and urban redesign that is augmented through strong partnerships with cooperating agencies. These features allow WEO to serve as a unique natural laboratory for addressing research questions facing seasonally snow-covered, semi-arid regions in a rapidly changing world and an excellent facility for providing student education and research training.  相似文献   

A new hammer-driven freeze corer   总被引：1，自引：0，他引：1  

Brenda M. Miskimmin  P. Jefferson Curtis  David W. Schindler  Nestor Lafaut 《Journal of Paleolimnology》1996,15(3):265-269

A shortcoming of freeze corers has been the inability to collect long cores in stiff sediments. We describe a hammerdriven freeze corer that collects undisturbed sediment cores up to 1.3 m in length in stiff or soft lake sediments. The corer was tested in prairie, montane and alpine lakes of western Canada. For these stiff sediments, conventional (gravity-only) freeze coring methods collected cores ranging from 25–59 cm compared with 100–124 cm for our hammer-driven device. The maximum length of cores could exceed 1.3 m if a longer core barrel was constructed.  相似文献   

Climate change in lowland Central America during the late deglacial and early Holocene     

Michael B. Hillesheim  David A. Hodell  Barbara W. Leyden  Mark Brenner  Jason H. Curtis  Flavio S. Anselmetti  Daniel Ariztegui  David G. Buck  Thomas P. Guilderson  Michael F. Rosenmeier  Douglas W. Schnurrenberger 《第四纪科学杂志》2005,20(4):363-376

The transition from arid glacial to moist early Holocene conditions represented a profound change in northern lowland Neotropical climate. Here we report a detailed record of changes in moisture availability during the latter part of this transition (～11 250 to 7500 cal. yr BP) inferred from sediment cores retrieved in Lake Petén Itzá, northern Guatemala. Pollen assemblages demonstrate that a mesic forest had been largely established by ～11 250 cal. yr BP, but sediment properties indicate that lake level was more than 35 m below modern stage. From 11 250 to 10 350 cal. yr BP, during the Preboreal period, lithologic changes in sediments from deep‐water cores (>50 m below modern water level) indicate several wet–dry cycles that suggest distinct changes in effective moisture. Four dry events (designated PBE1‐4) occurred centred at 11 200, 10 900, 10 700 and 10 400 cal. yr BP and correlate with similar variability observed in the Cariaco Basin titanium record and glacial meltwater pulses into the Gulf of Mexico. After 10 350 cal. yr BP, multiple sediment proxies suggest a shift to a more persistently moist early Holocene climate. Comparison of results from Lake Petén Itzá with other records from the circum‐Caribbean demonstrates a coherent climate response during the entire span of our record. Furthermore, lowland Neotropical climate during the late deglacial and early Holocene period appears to be tightly linked to climate change in the high‐latitude North Atlantic. We speculate that the observed changes in lowland Neotropical precipitation were related to the intensity of the annual cycle and associated displacements in the mean latitudinal position of the Intertropical Convergence Zone and Azores–Bermuda high‐pressure system. This mechanism operated on millennial‐to‐submillennial timescales and may have responded to changes in solar radiation, glacial meltwater, North Atlantic sea ice, and the Atlantic meridional overturning circulation (MOC). Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Geological features indicative of processes related to the hematite formation in Meridiani Planum and Aram Chaos, Mars: a comparison with diagenetic hematite deposits in southern Utah, USA     

Jens Ormö  Goro Komatsu  Brenda Beitler 《Icarus》2004,171(2):295-316

In order to understand the formation of the few but large, hematite deposits on Mars, comparisons are often made with terrestrial hematite occurrences. In southern Utah, hematite concretions have formed within continental sandstones and are exposed as extensive weathered-out beds. The hematite deposits are linked to geological and geomorphological features such as knobs, buttes, bleached beds, fractures and rings. These terrestrial features are visible in aerial and satellite images, which enables a comparison with similar features occurring extensively in the martian hematite-rich areas. The combination of processes involved in the movement and precipitation of iron in southern Utah can provide new insights in the context of the hematite formation on Mars. Here we present a mapping of the analogue geological and geomorphological features in parts of Meridiani Planum and Aram Chaos. Based on mapping comparisons with the Utah occurrences, we present models for the formation of the martian analogues, as well as a model for iron transport and precipitation on Mars. Following the Utah model, high albedo layers and rings in the mapped area on Mars are due to removal or lack of iron, and precipitation of secondary diagenetic minerals as fluids moved up along fractures and permeable materials. Hematite was precipitated intraformationally where the fluid transporting the reduced iron met oxidizing conditions. Our study shows that certain geological/geomorphological features can be linked to the hematite formation on Mars and that pH differences could suffice for the transport of the iron from an orthopyroxene volcanoclastic source rock. The presence of organic compounds can enhance the iron mobilization and precipitation processes. Continued studies will focus on possible influence of biological activity and/or methane in the formation of the hematite concretions in Utah and on Mars.  相似文献   

Geochemistry and Provenance of Springs in a Baja California Sur Mountain Catchment     

Jory C. Lerback  Brenda B. Bowen  C. E. Humphrey  Diego. P. Fernandez  Jeremiah A. Bernau  Shane J. Macfarlan  Eric Schniter  J. J. Garcia 《Ground water》2022,60(2):295-308

Fractured rock aquifers cover much of Earth's surface and are important mountain sites for groundwater recharge but are poorly understood. To investigate groundwater systematics of a fractured-dominated aquifer in Baja California Sur, Mexico, we examined the spatial patterns of aquifer recharge and connectivity using the geochemistry of springs. We evaluate a range of geochemical data within the context of two endmember hypotheses describing spatial recharge patterns and fracture connectivity. Hypothesis 1 is that the aquifer system is segmented, and springs are fed by local recharge. Hypothesis 2 is that the aquifer system is well connected, with dominant recharge occurring in the higher elevations. The study site is a small <15 km² catchment. Thirty-four distinct springs and two wells were identified in the study area, and 24 of these sites were sampled for geochemical analyses along an elevation gradient and canyon transect. These analyses included major ion composition, trace element and strontium isotopes, δ¹⁸O and δ²H isotopes, radiocarbon, and tritium. δ¹⁸O and δ²H isotopes suggest that the precipitation feeding the groundwater system has at least two distinct sources. Carbon isotopes showed a change along the canyon transect, suggesting that shorter flowpaths feed springs in the top of the transect, and longer flowpaths discharge near the bottom. Geochemical interpretations support a combination of the two proposed hypotheses. Understanding of the connectivity and provenance of these springs is significant as they are the primary source of water for the communities that inhabit this region and may be impacted by changes in recharge and use.  相似文献   

Late Pleistocene snowline fluctuations at Nevado Coropuna (15°S), southern Peruvian Andes     

Gordon R.M. Bromley  Brenda L. Hall  Kurt M. Rademaker  Claire E. Todd  Adina E. Racovteanu 《第四纪科学杂志》2011,26(3):305-317

Deposits preserved on peaks in the southern Peruvian Andes are evidence for past glacial fluctuations and, therefore, serve as a record of both the timing and magnitude of past climate change. Moraines corresponding to the last major expansion of ice on Nevado Coropuna date to 20‐25 ka, during the last glacial maximum. We reconstructed the snowline at Coropuna for this period using a combined geomorphic‐numeric approach to provide a first‐order estimate of the magnitude of late‐Pleistocene climate change. Our reconstructions show that snowline was approximately 550‐770 m lower during the last glacial maximum than during the late Holocene maximum, which ended in the 19^th century, and ～750 m lower than today. While these values are similar to data from nearby Nevado Solimana, reconstructions from the neighbouring peak of Nevado Firura reveal a smaller snowline depression, suggesting the glacial response to climate forcing in the tropics is strongly influenced by non‐climatic factors. These data constitute some of the first directly dated palaeo‐snowline data from the arid tropics and suggest that the magnitude of the last glaciation in at least parts of the tropical Andes was similar to late‐Pleistocene events at higher latitudes. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献