Lake Sapanca is located on a strand of the Northern Anatolian Fault Zone (NAFZ, Turkey), where a series of strong earthquakes (Ms >6.0) have occurred over the past hundred years. Identifying prehistoric earthquakes in and around Lake Sapanca is key to a better understanding of plate movements along the NAFZ. This study contributes to the development of palaeolimnological tools to identify past earthquakes in Lake Sapanca. To this end several promising proxies were investigated, specifically lithology, magnetic susceptibility, grain size (thin-section and laser analysis), geochemistry, pollen concentration, diatom assemblages, 137Cs and 210Pb. Sedimentological indicators provided evidence for reworked, turbidite-like or homogeneous facies (event layers) in several short cores (<45 cm). Other indicators of sediment input and the historical chronicles available for the area suggest that three of these event layers likely originated from the AD 1957, 1967 and 1999 earthquakes. Recent changes in sediment deposition and nutrient levels have also been identified, but are probably not related to earthquakes. This study demonstrates that a combination of indicators can be used to recognize earthquake-related event layers in cores that encompass a longer period of time. 相似文献
We report the results of two soil CO2 efflux surveys by the closed chamber circulation method at the Puhimau thermal area in the upper East Rift Zone (ERZ) of
volcano, Hawaii. The surveys were undertaken in 1996 and 1998 to constrain how much CO2 might be reaching the ERZ after degassing beneath the summit caldera and whether the Puhimau thermal area might be a significant
contributor to the overall CO2 budget of . The area was revisited in 2001 to determine the effects of surface disturbance on efflux values by the collar emplacement
technique utilized in the earlier surveys. Utilizing a cutoff value of 50 g m−2 d−1 for the surrounding forest background efflux, the CO2 emission rates for the anomaly at Puhimau thermal area were 27 t d−1 in 1996 and 17 t d−1 in 1998. Water vapor was removed before analysis in all cases in order to obtain CO2 values on a dry air basis and mitigate the effect of water vapor dilution on the measurements. It is clear that Puhimau thermal
area is not a significant contributor to CO2 output and that most of CO2 (8500 t d−1) is degassed at the summit, leaving only magma with its remaining stored volatiles, such as SO2, for injection down the ERZ. Because of the low CO2 emission rate and the presence of a shallow water table in the upper ERZ that effectively scrubs SO2 and other acid gases, Puhimau thermal area currently does not appear to be generally well suited for observing temporal changes
in degassing at . 相似文献
In response to public concerns about discharges from large cruise ships, Alaska's Department of Environmental Conservation (ADEC) sampled numerous effluents in the summer of 2000. The data showed that basic marine sanitation device (MSD) technology for black water (sewage) was not performing as expected. Untreated gray water had high levels of conventional pollutants and surprisingly high levels of bacteria. Both black water and gray water discharges sometimes exceeded state water quality standards for toxicants. The state convened a Science Advisory Panel (the Panel) to evaluate impacts associated with cruise ship wastewater discharges. The effluent data received wide media coverage and increased public concerns. Consequently, legislative decisions were made at the State and Federal level, and regulations were imposed before the Panel completed its evaluation. The Panel demonstrated that following the rapid dilution from moving cruise ships, the effluent data from the Summer of 2000 would not have exceeded water quality standards, and environmental effects were not expected. 相似文献
We present quantitative morphology measurements of a sample of optically selected group galaxies at 0.3 < z < 0.55 using the Hubble Space Telescope ( HST ) Advanced Camera for Surveys (ACS) and the gim2d surface brightness fitting software package. The group sample is derived from the Canadian Network for Observational Cosmology Field Galaxy Redshift Survey (CNOC2) and follow-up Magellan spectroscopy. We compare these measurements to a similarly selected group sample from the Millennium Galaxy Catalogue (MGC) at 0.05 < z < 0.12 . We find that, at both epochs, the group and field fractional bulge luminosity (B/T) distributions differ significantly, with the dominant difference being a deficit of disc-dominated (B/T < 0.2) galaxies in the group samples. At fixed luminosity, z = 0.4 groups have ∼5.5 ± 2 per cent fewer disc-dominated galaxies than the field, while by z = 0.1 this difference has increased to ∼19 ± 6 per cent. Despite the morphological evolution we see no evidence that the group environment is actively perturbing or otherwise affecting the entire existing disc population. At both redshifts, the discs of group galaxies have similar scaling relations and show similar median asymmetries as the discs of field galaxies. We do find evidence that the fraction of highly asymmetric, bulge-dominated galaxies is 6 ± 3 per cent higher in groups than in the field, suggesting there may be enhanced merging in group environments. We replicate our group samples at z = 0.4 and 0 using the semi-analytic galaxy catalogues of Bower et al. This model accurately reproduces the B/T distributions of the group and field at z = 0.1 . However, the model does not reproduce our finding that the deficit of discs in groups has increased significantly since z = 0.4 . 相似文献
More than 400 km of high-resolution, partially digitally acquired seismic data were collected in a 30 × 60 km area offshore from the Dutch mesotidal barrier island shoreline, in order to analyze the Holocene transgressive sequence.
The investigated area was subaerially exposed during the most recent (Weichselian) Pleistocene lowstand and glaciated during the previous (Saale/Illinoian) glacial period. Sea level was probably at a level comparable to that of the present during the intervening Eem/Sangamonian highstand.
The area's seismic signature is characterized by several levels of channelization, separated by major, area-wide high-amplitude reflectors. The lowermost aerial reflector represents the Saale boulder clay. The largest channel system, which cuts this reflector, was incised during the Older Dryas cooling event and filled during the Allerød warming period. It was subsequently re-incised during the Younger Dryas and refilled during the early Holocene. The most pronounced and extensive reflector represents the base of the Holocene, and almost everywhere equals the planed-off top of the Eem highstand section. This reflector is overlain by aggradational facies, separated by one level of channelization and one planed-off (ravinement?) surface. The most prominent type of seismic facies above the lowermost level of channelization is a set of progradational clinoforms, which is interpreted as a preserved ebb-tidal delta system. This system is associated with the first Holocene shoreline of ca. 7500 yrs BP.
The eastern part of the study area contains sand ridges with a complex pattern of internal cross-stratification. Ridge-crest sediments are very well-sorted with a mean grain size of 2.8-2.6 φ (ca. 0.15 mm), whereas sediments in the troughs are well-sorted with a mean grain size of 1.8-0.8 φ (0.25–0.5 mm). Origin of these ridges is tentatively thought to be related to reworking since 5000 yrs BP, when the dynamic regime was more or less similar to that of the present and sediment supply had decreased substantially. 相似文献
Tree rings representing the period from the mid-1950s up to 2001 were studied as part of an investigation of anthropogenic radionuclide input to terrestrial systems. A live specimen of Pinus sylvestris from the east coast of Ireland was felled, sampled and analysed for comparison with a similar tree felled close to the Atlantic seaboard on the west coast of Ireland. Data for the tree ring sequences were examined relative to the radionuclide content of peat profiles sampled in close proximity to the locations of the studied Pine trees.The data indicate that 14C concentrations in tree ring sequences from the east and west coasts of Ireland are virtually identical. The sequences show maximum 14C concentrations (185 and 189 pMC at east and west coast sites, respectively) that correspond closely with published data for atmospheric levels during the height of the nuclear weapons test period (1945-1980). The tree ring count for the specimen from the east coast places the 14C peak precisely at 1964, the year following the known peak in atmospheric concentrations due to above ground testing of nuclear weapons. However, 14C data show that simple ring counting of the west coast tree did not provide an accurate chronology. The data demonstrate the importance of applying dendrodating techniques using replicated site chronologies, and the value of the 14C bomb fallout curve for the construction of recent chronologies. Data show no evidence of enhanced uptake at the east coast that might suggest incorporation of output from the Sellafield nuclear complex or from the release of radioactivity resulting from an accidental fire at the plant in 1957. 相似文献
Coral reefs are highly vulnerable to the impacts of rising marine temperatures and marine heatwaves. Mitigating dangerous climate change is essential and urgent, but many reef systems are already suffering on current levels of warming. Geoengineering options are worth exploring to protect the Great Barrier Reef (GBR) from extreme warming conditions, but we contend that they require strong governance and public consultation from the outset. Australian governments are currently funding feasibility testing of three geoengineering proposals for the GBR. Each proposal involves manipulating ocean or atmospheric conditions to lower water temperatures and thereby reduce the threat of mass coral bleaching events. Innovative strategies to protect the GBR and field testing of these is essential, but current laws do not guarantee robust governance for field testing of these technologies. Nor do they provide the foundation for a more coherent national policy on climate intervention technologies more generally. Responsible governance frameworks, including detailed risk assessment and early public consultation, are necessary for geoengineering research to build legitimacy and promote scientific progress.
Key policy insights
Marine heatwaves pose a serious threat to coral reefs, including Australia’s iconic Great Barrier Reef.
Australian governments have recognized the threats of warming waters, and are funding research of geoengineering options for the Great Barrier Reef.
The limited earlier field testing of geoengineering demonstrates the need for specific governance to manage risks, build legitimacy and maintain public support.
Australia requires a framework to govern geoengineering research and development before deployment of such technologies.
A stage-structured population model has been developed for the estuarine amphipod Leptocheirus plumulosus to provide interpretive guidance for sediment toxicity tests with this species. This time-varying, field-based model includes several matrices to reflect seasonal changes in demographics. In this paper, we conduct sensitivity analysis of the model to identify which life history parameters have the greatest potential impact on population growth rate (lambda). Results indicate seasonal variability in the relative demographic importance of vital rates. Over winter, annual population growth is most sensitive to the persistence of juveniles and adults and growth from the juvenile to the adult stage. In spring and fall, changes in fecundity are likely to have large effects on population dynamics. In addition, we demonstrate the applicability of the model by using it to interpret toxicological data from an assessment of sediment contamination in Baltimore Harbor, MD. The model was parameterized with survival data from acute toxicity tests with L. plumulosus to project effects on population growth rate (lambda). Results of these model simulations indicate that relatively small changes in survival can result in large changes in lambda, indicating high risk to benthic populations. Furthermore, population projections mirror observed abundances of L. plumulosus at the test sites. These analyses provide a first indication of the usefulness of the Leptocheirus population model as a tool for exploring ecological effects of sediment contamination. 相似文献