Surface heat flow and CO₂ emissions within the Ohaaki hydrothermal field,Taupo Volcanic Zone,New Zealand     

Clinton Rissmann  Bruce Christenson  Cynthia Werner  Matthew Leybourne  Jim Cole  Darren Gravley 《Applied Geochemistry》2012

Carbon dioxide emissions and heat flow have been determined from the Ohaaki hydrothermal field, Taupo Volcanic Zone (TVZ), New Zealand following 20 a of production (116 MW_e). Soil CO₂ degassing was quantified with 2663 CO₂ flux measurements using the accumulation chamber method, and 2563 soil temperatures were measured and converted to equivalent heat flow (W m⁻²) using published soil temperature heat flow functions. Both CO₂ flux and heat flow were analysed statistically and then modelled using 500 sequential Gaussian simulations. Forty subsoil CO₂ gas samples were also analysed for stable C isotopes. Following 20 a of production, current CO₂ emissions equated to 111 ± 6.7 T/d. Observed heat flow was 70 ± 6.4 MW, compared with a pre-production value of 122 MW. This 52 MW reduction in surface heat flow is due to production-induced drying up of all alkali–Cl outflows (61.5 MW) and steam-heated pools (8.6 MW) within the Ohaaki West thermal area (OHW). The drying up of all alkali–Cl outflows at Ohaaki means that the soil zone is now the major natural pathway of heat release from the high-temperature reservoir. On the other hand, a net gain in thermal ground heat flow of 18 MW (from 25 MW to 43.3 ± 5 MW) at OHW is associated with permeability increases resulting from surface unit fracturing by production-induced ground subsidence. The Ohaaki East (OHE) thermal area showed no change in distribution of shallow and deep soil temperature contours despite 20 a of production, with an observed heat flow of 26.7 ± 3 MW and a CO₂ emission rate of 39 ± 3 T/d. The negligible change in the thermal status of the OHE thermal area is attributed to the low permeability of the reservoir beneath this area, which has limited production (mass extraction) and sheltered the area from the pressure decline within the main reservoir. Chemistry suggests that although alkali–Cl outflows once contributed significantly to the natural surface heat flow (∼50%) they contributed little (<1%) to pre-production CO₂ emissions due to the loss of >99% of the original CO₂ content due to depressurisation and boiling as the fluids ascended to the surface. Consequently, the soil has persisted as the major (99%) pathway of CO₂ release to the atmosphere from the high temperature reservoir at Ohaaki. The CO₂ flux and heat flow surveys indicate that despite 20 a of production the variability in location, spatial extent and magnitude of CO₂ flux remains consistent with established geochemical and geophysical models of the Ohaaki Field. At both OHW and OHE carbon isotopic analyses of soil gas indicate a two-stage fractionation process for moderate-flux (>60 g m⁻² d⁻¹) sites; boiling during fluid ascent within the underlying reservoir and isotopic enrichment as CO₂ diffuses through porous media of the soil zone. For high-flux sites (>300 g m⁻² d⁻¹), the δ¹³CO₂ signature (−7.4 ± 0.3‰ OHW and −6.5 ± 0.6‰ OHE) is unaffected by near-surface (soil zone) fractionation processes and reflects the composition of the boiled magmatic CO₂ source for each respective upflow. Flux thresholds of <30 g m⁻² d⁻¹ for purely diffusive gas transport, between 30 and 300 g m⁻² d⁻¹ for combined diffusive–advective transport, and ?300 g m⁻² d⁻¹ for purely advective gas transport at Ohaaki were assigned. δ¹³CO₂ values and cumulative probability plots of CO₂ flux data both identified a threshold of ∼15 g m⁻² d⁻¹ by which background (atmospheric and soil respired) CO₂ may be differentiated from hydrothermal CO₂.  相似文献   

<Emphasis Type="Italic">HST</Emphasis>-COS observations of the transiting extrasolar planetary system HD 209458b     

Kevin France  Jeffrey L. Linsky  Hao Yang  John T. Stocke  Cynthia S. Froning 《Astrophysics and Space Science》2011,335(1):25-32

We summarize results from deep spectroscopic observations of the HD 209458 planetary system, carried out with the Hubble Space Telescope—Cosmic Origins Spectrograph. Orbitally resolved observations are used to show that hot gas emission lines, arising only in the stellar atmosphere, are not variable, while lower ionizations species found in the upper atmosphere of the hot Jupiter HD 209458b absorb stellar photons during transit. For both C II and Si III, we find mean transit attenuation of ～8%. The firm detection of silicon is in direct conflict with previous low-resolution studies, which we attribute to long-term variability in the system. We also use these observations to search for auroral emission from the planet, detecting a statistically significant emission feature at 1582 Å that is consistent with H₂ photoexcited by stellar O I photons.  相似文献   

Sediment quality of the lower St. Johns River, Florida: an integrative assessment of benthic fauna, sediment-associated stressors, and general habitat characteristics     

Cooksey C  Hyland J 《Marine pollution bulletin》2007,54(1):9-21

Sediment quality of the lower St. Johns River (LSJR) estuary, Florida was evaluated using synoptic data on benthic community structure, levels of potential stressors (chemical contaminants, ammonia and sulfide), and other basic habitat characteristics (depth, dissolved oxygen, salinity, temperature) collected at seven stations, three times a year from July 2000-July 2002. Un-ionized ammonia and hydrogen sulfide were detected at toxic levels on at least one sampling occasion at four stations. Chemical contamination of sediment at probable bioeffect levels also was observed at four stations. Concentrations of pesticides or other chemical substances typically associated with human activities (e.g., PCBs) were detectable at all stations, though not always present at concentrations likely of causing significant bioeffects. A total of 251 taxa and 9783 individuals were identified and enumerated from the benthic infaunal samples. Polychaete worms and molluscs dominated the benthic fauna at all seven stations. The opportunistic and pollution-tolerant polychaete Streblospio benedicti was the most abundant species overall (from all samples combined), appearing as a dominant at five of the seven stations. Overall, the sites sampled as part of this study indicate a highly stressed benthos resulting from multiple anthropogenic impacts.  相似文献   

Historical problems of travel for women geologists     

Cynthia V. Burek  & Martina Kölbl-Ebert 《Geology Today》2007,23(1):30-32

From unsuitable clothes to lack of chaperones, from harassment to lack of proper funding, throughout history women geologists have encountered difficulties travelling to their field locations or working in the field, whether these locations were close by or abroad. Most early female geologists were able to avoid many difficulties because they were protected through working locally, where their high social standing was known and respected, or because they worked in a team with husband, father or brother. However, the problem was to grow in the second half of the nineteenth century, when women started to appear as students and professionally trained geologists. This feature explores the difficulties of female geologists undertaking fieldwork from the late nineteenth to the mid-twentieth century.  相似文献   

Are Groundwater Level Data Collected by Citizen Scientists Trustworthy? A Cautionary Tale     

Alex K. Manda  J. Randall Etheridge  Cynthia Grace-McCaskey  Thomas R. Allen  Robert Howard 《Ground water》2021,59(1):123-130

Public participation in groundwater projects is increasing, however, the efficacy of the data collected in such studies, is not well-documented in the literature. In this study, the authors describe a citizen science project focused on measuring and recording groundwater levels in an aquifer and evaluate whether the groundwater data collected by the participants are trustworthy. A total of 31 participants were initially recruited to measure and record groundwater levels from 29 monitoring wells on a barrier island. Following recruitment, the authors provided training to the citizen scientists by introducing groundwater concepts, and showing the participants how to measure, record and report groundwater level data (over an 81-day period) with an electronic water level meter. The water level data recorded by the citizen scientists (i.e., 35 time series datasets with over 450 unique measurements) were then compared to high frequency data recorded by automated water level loggers that were already deployed in the groundwater monitoring wells to assess the trustworthiness of the data. Trustworthiness was evaluated using measures of reliability (i.e., consistency in measuring the same thing), validity (i.e., degree to which results are truthful), and other standard graphical and statistical techniques. The results suggest that with proper training, guidance, and motivation, citizen scientists can collect trustworthy groundwater level data that could be useful for monitoring the sustainability of aquifers and managing of groundwater levels. It is noted however, that such positive outcomes require significant investments of time and effort on the part of the project managers.  相似文献   

Harmful algal bloom species and phosphate-processing effluent: field and laboratory studies   总被引：1，自引：0，他引：1  

Garrett M  Wolny J  Truby E  Heil C  Kovach C 《Marine pollution bulletin》2011,62(3):596-601

In 2002, the Florida Department of Environmental Protection began discharging phosphate-processing effluent into Bishop Harbor, an estuary within Tampa Bay. Because of concerns that the effluent would serve as a nutrient source for blooms of the toxic dinoflagellate Karenia brevis, a field monitoring program was established and laboratory bioassays were conducted. Several harmful algal bloom (HAB) species, including Prorocentrum minimum and Heterosigma akashiwo, were observed in bloom concentrations adjacent to the effluent discharge site. Blooms of diatoms were widespread throughout Bishop Harbor. K. brevis was observed with cell concentrations decreasing with increasing proximity to the effluent discharge site. Bioassays using effluent as a nutrient source for K. brevis resulted in decreased cell yields, increased growth rates, and increased time to log-phase growth. The responses of HAB species within Bishop Harbor and of K. brevis to effluent in bioassays suggested that HAB species differ in their response to phosphate-processing effluent.  相似文献   

Architecture,structural and tectonic significance of the Seagap fault (offshore Tanzania) in the framework of the East African Rift     

David Iacopini  Stefano Tavani  Sara Pentagallo  Vittorio Maselli  Marina Dottore Stagna  Cynthia Ebinger  David Reynolds  Arjan van Vliet 《Basin Research》2023,35(1):387-412

The Southeastern portion of the East African Rift System reactivates Mesozoic transform faults marking the separation of Madagascar from Africa in the Western Indian Ocean. Earlier studies noted the reactivation of the Davie Fracture Zone in oceanic lithosphere as a seismically active extensional fault, and new 3D seismic reflection data and exploration wells provide unprecedented detail on the kinematics of the sub-parallel Seagap fault zone in continental/transitional crust landward of the ocean-continent transition. We reconstruct the evolution of the seismically active Seagap fault zone, a 400-km-long crustal structure affecting the Tanzania margin, from the late Eocene to the present day. The Seagap fault zone is represented by large-scale localized structures affecting the seafloor and displaying growth geometries across most of the Miocene sediments. The continuous tectonic activity evident by our seismic mapping, as well as 2D deep seismic data from literature, suggests that from the Middle-Late Jurassic until 125 Ma, the Seagap fault acted as a regional structure parallel to, and coeval with, the dextral Davie Fracture Zone. The Seagap fault then remained active after the cessation of both seafloor spreading in the Somali basin and strike-slip activity on the Davie Fracture Zone, till nowaday. Its architecture is structurally expressed through the sequence of releasing and restraining bends dating back at least to the early Neogene. Seismic sections and horizon maps indicate that those restraining bends are generated by strike-slip reactivation of Cretaceous structures till the Miocene. Finally based on the interpretation of edge-enhanced reflection seismic surfaces and seafloor data, we shows that, by the late Neogene, the Seagap fault zone switched to normal fault behaviour. We discuss the Seagap fault's geological and kinematic significance through time and its current role within the microplate system in the framework of the East African rift, as well as implications for the evolution and re-activation of structures along sheared margins. The newly integrated datasets reveal the polyphase deformation of this margin, highlighting its complex evolution and the implications for depositional fairways and structural trap and seal changes through time, as well as potential hazards.  相似文献   

Earth observations during space shuttle flight STS‐35: Columbia's mission to planet earth,December 2–10, 1990     

Kamlesh P. Lulla  Cynthia A. Evans  Michael R. Helfert  Vance D. Brand  Guy S. Gardner  John M. Lounge 《国际地球制图》2013,28(4):71-80

The article describes methodology of space monitoring of the existing landscapes as it is practised in the CIS (former USSR). Different points of mew are presented concerning environmental monitoring as well as the aspects of its practical organization. The objectives of automation of the ecological data acquisition, storage and processing are also dealt with; necessity of geographic information systems creation is substantiated. Experience gained in the operation of geoinformation systems is considered with plans on geo‐information base development for the needs of geographical and ecological studies of the CIS landscapes. Practical experience with case studies on identifying and mapping the ecological disaster zones is described in the Aral Sea basin and the Kyzyl Kum desert.  相似文献   

Earth observations during space shuttle mission sts‐69 Endeavour's Images of Earth (September 7–18, 1995)     

Susan Runco  Kamlesh Lulla  David L. Amsbury  Cynthia Evans  M. Justin Wilkinson  Kim Willis 《国际地球制图》2013,28(1):91-104

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Climate Change and Extreme Weather Events; Implications for Food Production, Plant Diseases, and Pests   总被引：8，自引：0，他引：8  

Cynthia Rosenzweig  Ana Iglesias  X.B. Yang  Paul R. Epstein  Eric Chivian 《Global Change & Human Health》2001,2(2):90-104

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