Structural and Hydrogeological Controls on Hydrocarbon and Brine Migration into Drinking Water Aquifers in Southern New York

Environmental concerns regarding the potential for drinking water contamination in shallow aquifers have accompanied unconventional energy development in the northern Appalachian Basin. These activities have also raised several critical questions about the hydrogeological parameters that control the naturally occurring presence and migration of hydrocarbon gases in shallow aquifers within petroliferous basins. To interrogate these factors, we analyzed the noble gas, dissolved ion, and hydrocarbon gas (molecular and isotopic composition) geochemistry of 98 groundwater samples from south‐central New York. All samples were collected ?1km from unconventional drilling activities and sample locations were intentionally targeted based on their proximity to various types of documented fault systems. In agreement with studies from other petroliferous basins, our results show significant correlations between elevated levels of radiogenic [⁴He], thermogenic [CH₄], and dissolved ions (e.g., Cl, Br, Sr, Ba). In combination, our data suggest that faults have facilitated the transport of exogenous hydrocarbon‐rich brines from Devonian source rocks into overlying Upper Devonian aquifer lithologies over geologic time. These data conflict with previous reports, which conclude that hydrodynamic focusing regulates the occurrence of methane and salt in shallow aquifers and leads to elevated levels of these species in restricted flow zones within valley bottoms. Instead, our data suggest that faults in Paleozoic rocks play a fundamental role in gas and brine transport from depth, regulate the distribution of their occurrence in shallow aquifers, and influence the geochemistry of shallow groundwater in this petroliferous basin.     

Climate change, water resources, and the politics of adaptation in the Middle East and North Africa

Through an examination of global climate change models combined with hydrological data on deteriorating water quality in the Middle East and North Africa (MENA), we elucidate the ways in which the MENA countries are vulnerable to climate-induced impacts on water resources. Adaptive governance strategies, however, remain a low priority for political leaderships in the MENA region. To date, most MENA governments have concentrated the bulk of their resources on large-scale supply side projects such as desalination, dam construction, inter-basin water transfers, tapping fossil groundwater aquifers, and importing virtual water. Because managing water demand, improving the efficiency of water use, and promoting conservation will be key ingredients in responding to climate-induced impacts on the water sector, we analyze the political, economic, and institutional drivers that have shaped governance responses. While the scholarly literature emphasizes the importance of social capital to adaptive governance, we find that many political leaders and water experts in the MENA rarely engage societal actors in considering water risks. We conclude that the key capacities for adaptive governance to water scarcity in MENA are underdeveloped.     

Climate deterioration in the Eastern Mediterranean as revealed by ion microprobe analysis of a speleothem that grew from 2.2 to 0.9 ka in Soreq Cave, Israel

Analysis of oxygen isotope ratios (δ¹⁸O) by ion microprobe resolves a sub-annual climate record for the Eastern Mediterranean from a Soreq Cave stalagmite that grew between 2.2 and 0.9 ka. In contrast to conventional drill-sampling methods that yield a total variation of 1.0‰ in δ¹⁸O_calcite values across our sample, the methods described here reveal up to 2.15‰ variation within single annual growth bands. Values of δ¹⁸O measured by ion microprobe vary in a regular saw-tooth pattern that correlates with annual, fluorescent growth banding where calcite grades from light to dark fluorescence. Modern records of precipitation and of cave dripwater indicate that variable δ¹⁸O_calcite values record regular seasonal differences in δ¹⁸O_rainfall modified by mixing in the vadose zone. Large differences in δ¹⁸O values measured across a single band (i.e., between the dark and light fluorescent calcite, or Δ¹⁸O_dark-light) are interpreted to indicate wetter years, while smaller differences represent drier years. Oxygen isotopes record: 1) month-scale growth increments, 2) changes in Δ¹⁸O_dark-light that represent seasonality, 3) a systematic, long-term decrease in maximum Δ¹⁸O_dark-light values, and 4) an overall increase in average δ¹⁸O_calcite values through time. These results suggest a drying of regional climate that coincides with the decline of the Roman and Byzantine Empires in the Levant region.     

Spatial gradient of temperature and potential vegetation feedback across Europe during the late Quaternary

After the last glacial maximum (LGM; 18,000 years. bp) plants migrated onto areas made free by the retreating ice sheets. Pollen records document changes in ecosystems and are an important proxy for the reconstruction of climate parameters. Here, we quantify changes in January temperature (Tjan) over the past 14,000 years using 216 European pollen records. We used functional principal component analysis to evaluate the patterns of change over this period of time. Between 14 and 12 ka, Tjan records show comparable changes across Europe. After this time period, northwest and southeast Europe experienced differing trends in Tjan, trends that became pronounced by 9 ka. The spatial gradient of Tjan records is well-correlated with the overall change from steppe to increasingly diverse forest ecosystems. In particular, differential incorporation of conifer vs. deciduous species into forest ecosystems, based on differential colonization out of refugia, likely resulted in albedo gradients over Europe that affected regional Tjan.     

Critical phenomena in the rheology of partially melted rocks

Theoretical considerations and exploratory experiments indicate that most of the extreme change of large-strain “viscosities” between the solidus and the liquidus of rocks is concentrated about a non-zero rheological critical melt percentage (RCMP). Usually the RCMP is within the range of 20 ± 10 vol%. Below it, both bulk shear and segregative-compactive filter pressing are drastically slowed down, requiring strains in the solid fraction and squeezing of thin melt films. Many geological consequences of these critical phenomena may be far reaching. In particular, most of the upper-mantle low-velocity zone (LVZ), if partially melted, is likely to be stabilized somewhat below the RCMP, with runaway excesses of heat, melt and shear strain creating local excursions over the RCMP. Flow may be thus concentrated in narrow high-melt channels, within a relatively unsheared LVZ.     

Sea-land oxygen isotopic relationships from planktonic foraminifera and speleothems in the Eastern Mediterranean region and their implication for paleorainfall during interglacial intervals

The oxygen and carbon stable isotope compositions of cave speleothems provide a powerful method for understanding continental climate change. Here, we examine the question of the regionality of this isotopic record and its linkage with the marine isotopic record in the Eastern Mediterranean (EM) region. The study presents a new, accurately dated 250-kyr δ¹⁸O and δ¹³C record determined from speleothems of the Peqiin Cave, Northern Israel. Its comparison with the continuous 185-kyr isotopic record of the Soreq Cave speleothems from Central Israel reveals striking similarities. Thus, a strong regional climatic signal, brought about by variations in temperature and rainfall amount, is reflected in both cave records. Low δ¹⁸O minima in the Peqiin profile for the last 250- to 185-kyr period (interglacial marine isotopic stage 7) match the timing of sapropels 9 to 7 and are indicative of high rainfall in the EM region at these times. The combined Soreq and Peqiin δ¹⁸O record for the last 250 kyr excellently matches the published Globigerinoides ruber (G. ruber) marine δ¹⁸O record for the EM Sea, with the isotopic compositional difference Δ_{G.ruber-speleothems} remaining relatively constant at −5.6 ± 0.7‰, thus establishing for the first time a robust, exploitable link between the land and the marine isotopic records. The correspondence of low δ¹⁸O speleothem values and high cave water stands with low G. ruber δ¹⁸O values during interglacial sapropel events indicates that these periods were characterized by enhanced rainfall in the EM land and sea regions. By use of sea surface temperatures derived from alkenone data as a proxy for land temperatures at the Soreq Cave, we calculate the paleorainfall δ¹⁸O values and its amounts. Maximum rainfall and lowest temperature conditions occurred at the beginning of the sapropel events and were followed by decrease in rainfall and increase in temperatures, leading to arid conditions. The record for the last 7000 yr shows a trend toward increasing aridity and agrees well with climatic and archeological data from North Africa and the Middle East.     

Stable isotopic compositions of waters in the karst environments of China: Climatic implications

A total of 117 water samples, including cave water, ground water, spring water and river water, collected from the monsoonal area of China have been analyzed for their H- and O-isotope composition. Overall, a δ¹⁸O–δD correlation is observed of δD = −4.45 + 6.6δ¹⁸O (R² = 0.90) and a significant evaporation effect observed for the southern sites. Average δ¹⁸O and δD site values generally correspond to those of precipitation in nearby cities, with correlations of δD = 2.18 + 7.23δ¹⁸O (R² = 0.95) for the sample sites and δD = 11.05 + 7.95δ¹⁸O (R² = 0.95) for the cities. The effects of rainfall amount and temperature on precipitation δ¹⁸O were calculated using a simplified theoretical model derived from the Rayleigh distillation equation, which demonstrated that the sign of δ¹⁸O_pvs. T correlation is dependent on precipitation intensity. The mean δ¹⁸O value of cave waters exhibit decreasing trends with increasing latitude and reveal a spatial pattern of positive correlation with annual mean temperature and precipitation, mainly reflecting isotopic fractionations in the moisture source traveling from the ocean side to the inland continent. This spatial pattern implies that the δ¹⁸O values recorded in the proxy climate records derived from speleothems might be influenced by shifts in monsoon boundary during the past, especially between glacial and interglacial intervals.     

Formation processes of cemented features in karstic cave sites revealed using stable oxygen and carbon isotopic analyses: A case study at middle paleolithic Amud Cave,Israel

Hearths are important archaeological features, serving to infer past practices related to hominin subsistence and social behaviors. The identification of hearths is not always straightforward due to post‐depositional processes. In karstic cave environments in particular it is not always easy to distinguish, in the field or in the laboratory, between geogenic and anthropogenic cemented features because both are composed of calcite. Here we present a novel study in which bulk oxygen and carbon isotopic analyses were used in order to unequivocally identify anthropogenic calcite derived from hearths in the Neanderthal site of Amud Cave (Israel). We demonstrate that the isotopic composition of wood ash is distinctively different from that of geogenic calcite. The linear relationship observed between carbon and oxygen isotopic compositions of the various sediment types in Amud Cave is interpreted as a mixing line between wood ash and geogenic calcite, thus enhancing our understanding of the origins of sedimentological variability at the site and showing that not all of the cemented sediments in Amud Cave should be regarded as hearths. Our study suggests that the relative abundance of validated hearths in the various areas of the cave may be associated with Neanderthal use of space in Amud Cave. © 2008 Wiley Periodicals, Inc.     

Evaluating salinity sources of groundwater and implications for sustainable reverse osmosis desalination in coastal North Carolina, USA

The natural and pumping-induced controls on groundwater salinization in the coastal aquifers of North Carolina, USA, and the implications for the performance of a reverse osmosis (RO) desalination plant have been investigated. Since installation of the well field in the Yorktown aquifer in Kill Devil Hills of Dare County during the late 1980s, the groundwater level has declined and salinity of groundwater has increased from ??1,000 to ??2,500 mg/L. Geochemical and boron isotope analyses suggest that the salinity increase is derived from an upflow of underlying saline groundwater and not from modern seawater intrusion. In the groundwater of four wells supplying the plant, elevated boron and arsenic concentrations were observed (1.3?C1.4 mg/L and 8?C53 ??g/L, respectively). Major ions are effectively rejected by the RO membrane (96?C99% removal), while boron and arsenic are not removed as effectively (16?C42% and 54?C75%, respectively). In coming decades, the expected rise of salinity will be associated with higher boron content in the groundwater and consequently also in the RO-produced water. In contrast, there is no expectation of an increase in the arsenic content of the salinized groundwater due to the lack of increase of arsenic with depth and salinity in Yorktown aquifer groundwater.