Assessing selected natural and anthropogenic impacts on freshwater lens morphology on small barrier Islands: Dog Island and St. George Island, Florida, USA

Abstract The freshwater lens morphologies of the barrier islands Dog Island and St. George Island on the panhandle coast of Florida (FL), USA, are controlled to varying degrees by both natural and anthropogenic factors. Variable-density groundwater flow models confirm that spatial variability of recharge values can account for the observed lens asymmetry on these islands. The depth to the base of the lens does not vary significantly seasonally. Human development has altered recharge patterns in some areas, locally thinning the freshwater lens. Aqueduct water supply to St. George Island represents 7–25% of natural recharge; higher recharge rates are required to simulate the lens on St. George Island than on Dog Island. On both islands, coastal erosion rates are sufficiently rapid that the freshwater lens may not be in equilibrium with current boundary conditions.

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Resumen Las morfologías de los lentes de agua dulce en las islas de barrera: Islas Dog y St. George, en la costa alargada y estrecha de Florida, EUA, están controladas en diferentes grados por factores antropogénicos y naturales. Los modelos de flujo con densidad variable del agua subterránea, confirman que la variabilidad espacial de los valores de recarga, pueden ser la causa de la asimetría observada en los lentes de estas islas. La profundidad hasta la base de los lentes no varía significativamente con las estaciones climáticas. El desarrollo humano ha alterado las tendencias de recarga en algunas áreas, causando adelgazamiento local de los lentes de agua dulce. El abastecimiento de agua del acueducto en la Isla St. George, representa entre 7% y 25% de la recarga natural; por otro lado se necesitan cantidades mayores de recarga para simular los lentes en la Isla St. George que en la Isla Dog. En ambas islas, las tasas de erosión costera son tan rápidas, que las lentes de agua dulce podrían no estar en equilibrio con las condiciones actuales de frontera.

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Résumé La morphologie des lentilles deau douce des îles de Dog et de St. George, situés dans le district côtier de Florida-Etats Unis est contrôlé dans une mesure variable par des facteurs naturelles et humaines. Les modèles découlement à densité variable des eaux souterraines confirment que la variation spatiale de la recharge peut expliquer les asymétries observées des lentilles des cettes îles. La profondeur des lentilles ne présente pas des variations saisonnières importantes. Les activités humaines ont modifié la recharge dans certaines zones en amincissant localement les lentilles deau douce. Lalimentation en eaux de lîle de St. George représente 7–25% de la recharge naturelle; pour simuler les lentilles de lîle de Dog il a été nécessaire dintroduire des valeurs plus élevées de la recharge par rapport aux ceux utilisés pour lîle de St. George. Pour les deux îles lérosion côtière est assez rapide ainsi que les lentilles de eau douce ne sont pas en équilibre avec les conditions à la frontière.

     

Early Holocene brackish closed basin conditions in Georgian Bay, Ontario, Canada: microfossil (thecamoebian and pollen) evidence

Microfossils have been critical in unravelling the complex postglacial history of Georgian Bay. Thecamoebians (testate amoebae/rhizopods) record paleolimnological conditions, and pollen stratigraphy allows correlation across the basin, where sedimentation has been spatially and temporally discontinuous. Because parts of Georgian Bay have been non-depositional or erosional since the end of the Nipissing transgression (~5,000 (5,800 cal) BP), early Holocene features are exposed on the lakebed. Among these are shoreline features, such as submerged beaches and relict channels, associated with low-level Lake Hough that was driven far below the level of basin overflow. Cores taken throughout Georgian Bay record the existence of closed basin conditions that persisted several centuries around 7,500 (8,300 cal) BP, corresponding to the late Lake Hough lowstand. Evidence for hydrologic closure includes a low-diversity centropyxid-dominated thecamoebian fauna around the boundary between pollen subzones 2a and 2b in the Flowerpot Beach core, Flowerpot and Killarney basins, and in Severn Sound. This low-diversity centropyxid-dominated fauna is interpreted as recording the development of slightly brackish conditions as a result of a hydrologic deficit associated with relatively arid conditions in the Great Lakes basin during the early Holocene pine zone (~8,800–7,200 (9,900–8,050 cal) BP). The rest of the Holocene record in Georgian Bay (where it is preserved) is more diverse and dominated by difflugiid thecamoebians: predominantly Difflugia oblonga prior to human settlement, and Cucurbitella tricuspis since high-density human occupation and agriculture (and resulting eutrophication) began with the Wendat First Nations people around Severn Sound about 750 years ago. The implication that water budget fluctuations leading to discernible variations in lake level and water chemistry occurred in the relatively recent geologic past is significant to studies of global climate change and resource management in the Great Lakes, one of the world’s largest freshwater resources.     

Climate change, adaptation and economic growth

This paper explores the links between economic growth and the impacts of climate change. Inclusive, pro-poor growth is central to the development of low-income countries. There is also a broad consensus that growth and development are important to reduce vulnerability to climate change. Growth does not automatically reduce vulnerability, only the right kind of growth does. The paper aims to develop a better understanding of what the ??right kind of growth?? may be. We find that many growth policies, such as investment in skills and access to finance, indeed reduce vulnerability to climate change. However, climate change calls for some adjustments in growth policy. In particular, investment in infrastructure and efforts to stimulate entrepreneurship and competitive markets must take more of a risk management perspective and recognise climate risks.     

Tropical precipitation, SSTs and the surface energy budget: a zonally symmetric perspective

The relative importance of sea surface temperatures (SSTs) and the surface energy budget to tropical precipitation is examined by comparing models with zonally symmetric climates, both fixed SST and coupled to a slab mixed layer ocean. Two models are considered with differing surface flux formulations and in each case solutions that are symmetric about the equator are perturbed to create interhemispheric asymmetry. When SSTs are prescribed in the two models with different flux formulations, the magnitude of tropical precipitation response to identical SST anomalies is significantly different, but the differences can be understood in terms of the altered surface fluxes. In contrast, when the net surface energy fluxes are constrained to be identical in mixed layer simulations of the two different models, the response of tropical precipitation to perturbations in the surface energy balance is very similar. Both perspectives predict qualitatively the same precipitation response, but the energy budget better predicts the magnitude of the precipitation response. Thus, we argue that the atmospheric energy budget, controlled in these experiments primarily by the surface energy budget, is more fundamental to the control of tropical precipitation than the SSTs, in these simulations with axisymmetric climates. We touch briefly on a complication in the interpretation of the model results due to the fact that fixed SST and slab-ocean versions of the model can produce different Hadley cell strengths for the same SSTs.     

Envisioning carbon capture and storage: expanded possibilities due to air capture,leakage insurance,and C-14 monitoring

In order to meet the challenge of climate change while allowing for continued economic development, the world will have to adopt a net zero carbon energy infrastructure. Due to the world’s large stock of low-cost fossil fuels, there is strong motivation to explore the opportunities for capturing the CO₂ that is produced in the combustion of fossil fuels and keeping it out of the atmosphere. Three distinct sets of technologies are needed to allow for climate neutral use of fossil fuels: (1) capture of CO₂ at concentrated sources like electric power plants, future hydrogen production plants and steel and cement plants; (2) capture of CO₂ from the air; and (3) the safe and permanent storage of CO₂ away from the atmosphere. A strong regime of carbon accounting is also necessary to gain the public’s trust in the safety and permanence of CO₂ storage. This paper begins with an extensive overview of carbon capture and storage technologies, and then presents a vision for the potential implementation of carbon capture and storage, drawing upon new ideas such as air capture technology, leakage insurance, and monitoring using a radioactive isotope such as C-14. These innovations, which may provide a partial solution for managing the risks associated with long-term carbon storage, are not well developed in the existing literature and deserve greater study.     

Potential impacts of global climate change on the hydrology and ecology of ephemeral freshwater systems of the forests of the northeastern United States

Global, national, and regional assessments of the potential effects of Global Climate Change (GCC) have been recently released, but not one of these assessments has specifically addressed the critical issue of the potential impacts of GCC on ephemeral freshwater systems (EFS). I suggest that this is a major oversight as EFS occur in various forms across the globe. In the northeastern United States, these systems, whether ephemeral (“vernal”) pools or ephemeral or intermittent headwater streams are abundant and provide unique habitats critical to the maintenance of forest biodiversity. Since the hydrology of these waterbodies is strongly affected by weather patterns (in the short-term) or climate (long-term), they are especially sensitive to climate change. In this essay, I review the literature on relationships between climate and hydrology of EFS and on relationships between hydrology and ecology of these systems. I then conclude with my assessment of potential impacts of GCC on the hydrology of EFS and implications for their ecology. The focus of this essay will be on EFS of the forests of the northeastern United States, but will include literature from other regions as they relate to the general relationships between GCC and EFS.     

A dark matter disc in three cosmological simulations of Milky Way mass galaxies

Making robust predictions for the phase-space distribution of dark matter at the solar neighbourhood is vital for dark matter direct-detection experiments. To date, almost all such predictions have been based on simulations that model the dark matter alone. Here, we use three cosmological hydrodynamic simulations of bright, disc-dominated galaxies to include the effects of baryonic matter self-consistently for the first time. We find that the addition of baryonic physics drastically alters the dark matter profile in the vicinity of the solar neighbourhood. A stellar/gas disc, already in place at high redshift, causes merging satellites to be dragged preferentially towards the disc plane where they are torn apart by tides. This results in an accreted dark matter disc that contributes ∼0.25–1.5 times the non-rotating halo density at the solar position. The dark disc, unlike dark matter streams, is an equilibrium structure that must exist in disc galaxies that form in a hierarchical cosmology. Its low rotation lag with respect to the Earth significantly boosts Weakly Interacting Massive Particle (WIMP) capture in the Earth and Sun, boosts the annual modulation signal and leads to distinct variations in the flux as a function of recoil energy that allow the WIMP mass to be determined.     

Grooves on small saturnian satellites and other objects: Characteristics and significance

High-resolution images from the Cassini Imaging Science Subsystem (ISS) show parallel sets of grooves on Epimetheus and Pandora. Grooves have previously been observed on other satellites and asteroids, including Phobos, Gaspra, Ida, Eros, and minor occurrences on Phoebe. Sets of parallel grooves are so far observed only on satellites known or likely to be subject to significant tidal stresses, such as forced librations. Grooves on asteroids and on satellites not subject to significant forced librations occur in more globally disorganized patterns that may reflect impacts, varying internal structures, or even thermal stresses. The patterns and individual morphologies of grooves on the tidally-affected satellites suggest fracturing in weak materials due to tidal stresses and forced librations.