A meta‐analysis of reef island response to environmental change on the Great Barrier Reef

Reef islands on the Great Barrier Reef are influenced by a range of environmental factors. A meta‐analysis of 103 islands is presented to express variation in island size (area and volume) as a function of latitudinal and cross shelf gradients in regional oceanographic factors (exposure to incident waves, tidal range and tropical cyclone frequency) and local physical factors (position on the shelf, area, length and depth of supporting reef platform, vegetative cover). Models performed well for unvegetated sandcays (R² = 0.89), vegetated sandcays (R² = 0·72) and low wooded islands (R² = 0.78), with a moderate level of variation explained when all islands were simultaneously regressed (R² = 0.58). Future island dynamics were simulated for anticipated changes in cyclone regime, wave activity and sea level. For 38 islands mapped on the 1973 Royal Society and Universities of Queensland Expedition to the Northern Great Barrier Reef, change over the same 22 year period (1973–1995) was determined and the relative magnitude of observed and modelled changes was compared and found to be consistent through rank correlation analysis (Γ = 0.84 for unvegetated sandcays, Γ = 0.81 for vegetated sandcays). Simulations of island area or volume change from 2000 to 2100 indicated that under a 30% decrease in tropical cyclone activity, unvegetated sandcays continue to accrete at a lower rate, whereas all island types erode under a 38% increase in tropical cyclone activity. Vegetated sandcays initially accrete at higher levels of cyclone activity, entering an erosive state with a 60% increase in activity. Low wooded islands are unresponsive to environmental changes modelled. A sensitivity analysis of vegetated and unvegetated sandcays indicated that the presence of vegetation increases the tropical cyclone activity threshold at which islands begin to erode. Greatest sedimentary losses occur within the central band of high cyclone activity between Cooktown and Mackay. Copyright © 2015 John Wiley & Sons, Ltd.     

Late Holocene relative sea level rise and the Neoglacial history of the Greenland ice sheet

In West Greenland, early and mid Holocene relative sea level (RSL) fall was replaced by late Holocene RSL rise during the Neoglacial, after 4–3 cal. ka BP (thousand calibrated years before present). Here we present the results of an isolation basin RSL study completed near to the coastal town of Sisimiut, in central West Greenland. RSL fell from 14 m above sea level at 5.7 cal. ka BP to reach a lowstand of ?4.0 m at 2.3–1.2 cal. ka BP, before rising by an equivalent amount to present. Differences in the timing and magnitude of the RSL lowstand between this and other sites in West and South Greenland record the varied interplay of local and non‐Greenland RSL processes, notably the reloading of the Earth's crust caused by a Neoglacial expansion of the Greenland Ice Sheet (GIS) and the subsidence associated with the collapse of the Laurentide Ice Sheet forebulge. This means that the timing of the sea level lowstand cannot be used to infer directly when the GIS advanced during the Neoglacial. The rise in Late Holocene RSL is contrary to recently reported bedrock uplift in the Sisimiut area, based on repeat GPS surveys. This indicates that a belt of peripheral subsidence around the current ice sheet margin was more extensive in the late Holocene, and that there has been a switch from subsidence to uplift at some point in the last thousand years or so. Copyright © 2008 John Wiley & Sons, Ltd.     

Soil aggregate fraction 1-5 mm: An indicator for soil quality in rangelands

Aggregate size distribution affects the soil’s physical quality and fertility. Widely used aggregation indices include the size fractions <0.25 mm, >2 mm, and >8 mm, and the mean weight diameter of aggregates. A recent study from the semi-arid hilly rangeland of the Negev desert, Israel revealed considerable impact of the type of surface cover (shrub patches, trampling routes, and the remainder of the interpatch spaces) on these indices, but only limited impact of hillside aspect (north- vs. south-facing) and a small impact of livestock grazing. The aim of this study was to address the impact of these factors on the poorly studied mid-size aggregate fraction of 1-5 mm as a complementary index of the soil’s physical quality. The content and mean weight diameter of this fraction were analyzed by using the same set of soil samples. As a general trend, compared with the widely used aggregation indices, the content of this fraction was found to be more responsive to livestock grazing. Furthermore, both the content and mean weight diameter of this fraction were found to be highly responsive to type of cover. These effects reveal positive relationships between this fraction and the soil’s physical quality.     

Determining effective wellbore permeability from a field pressure test: a numerical analysis of detection limits

We propose a simple pressure test that can be used in the field to determine the effective permeability of existing wellbores. Such tests are motivated by the need to understand and quantify leakage risks associated with geological storage of CO₂ in mature sedimentary basins. If CO₂ is injected into a deep geological formation, and the resulting CO₂ plume encounters a wellbore, leakage may occur through various pathways in the “disturbed zone” surrounding the well casing. The effective permeability of this composite zone, on the outside of the well casing, is an important parameter for models of leakage. However, the data that exist on this key parameter do not exist in the open literature, and therefore specific field tests need to be done in order to reduce the uncertainty inherent in the leakage estimates. The test designed and analyzed herein is designed to measure effective wellbore permeability within a low-permeability caprock, bounded above and below by permeable reservoirs, by pressurizing the reservoir below and measuring the response in the reservoir above. Alternatively, a modified test can be performed within the caprock without directly contacting the reservoirs above and below. We use numerical simulation to relate pressure response to effective well permeability and then evaluate the range of detection of the effective permeability based on instrument measurement error and limits on fracture pressure. These results can guide field experiments associated with site characterization and leakage analysis.     

Contrasting sources of Late Paleozoic rhyolite magma in the Polish Lowlands: evidence from U–Pb ages and Hf and O isotope composition in zircon

International Journal of Earth Sciences - The Polish Lowlands, located southwest of the Teisseyre–Tornquist Zone, within Trans-European Suture Zone, were affected by bimodal, but dominantly...     

Reconstructing the last Irish Ice Sheet 2: a geomorphologically-driven model of ice sheet growth,retreat and dynamics

The ice sheet that once covered Ireland has a long history of investigation. Much prior work focussed on localised evidence-based reconstructions and ice-marginal dynamics and chronologies, with less attention paid to an ice sheet wide view of the first order properties of the ice sheet: centres of mass, ice divide structure, ice flow geometry and behaviour and changes thereof. In this paper we focus on the latter aspect and use our new, countrywide glacial geomorphological mapping of the Irish landscape (>39 000 landforms), and our analysis of the palaeo-glaciological significance of observed landform assemblages (article Part 1), to build an ice sheet reconstruction yielding these fundamental ice sheet properties. We present a seven stage model of ice sheet evolution, from initiation to demise, in the form of palaeo-geographic maps. An early incursion of ice from Scotland likely coalesced with local ice caps and spread in a south-westerly direction 200 km across Ireland. A semi-independent Irish Ice Sheet was then established during ice sheet growth, with a branching ice divide structure whose main axis migrated up to 140 km from the west coast towards the east. Ice stream systems converging on Donegal Bay in the west and funnelling through the North Channel and Irish Sea Basin in the east emerge as major flow components of the maximum stages of glaciation. Ice cover is reconstructed as extending to the continental shelf break. The Irish Ice Sheet became autonomous (i.e. separate from the British Ice Sheet) during deglaciation and fragmented into multiple ice masses, each decaying towards the west. Final sites of demise were likely over the mountains of Donegal, Leitrim and Connemara. Patterns of growth and decay of the ice sheet are shown to be radically different: asynchronous and asymmetric in both spatial and temporal domains. We implicate collapse of the ice stream system in the North Channel – Irish Sea Basin in driving such asymmetry, since rapid collapse would sever the ties between the British and Irish Ice Sheets and drive flow configuration changes in response. Enhanced calving and flow acceleration in response to rising relative sea level is speculated to have undermined the integrity of the ice stream system, precipitating its collapse and driving the reconstructed pattern of ice sheet evolution.     

A Snapshot of the Sun Near Solar Minimum: The Whole Heliosphere Interval

We present an overview of the data and models collected for the Whole Heliosphere Interval, an international campaign to study the three-dimensional solar?Cheliospheric?Cplanetary connected system near solar minimum. The data and models correspond to solar Carrington Rotation 2068 (20 March??C?16 April 2008) extending from below the solar photosphere, through interplanetary space, and down to Earth??s mesosphere. Nearly 200 people participated in aspects of WHI studies, analyzing and interpreting data from nearly 100 instruments and models in order to elucidate the physics of fundamental heliophysical processes. The solar and inner heliospheric data showed structure consistent with the declining phase of the solar cycle. A closely spaced cluster of low-latitude active regions was responsible for an increased level of magnetic activity, while a highly warped current sheet dominated heliospheric structure. The geospace data revealed an unusually high level of activity, driven primarily by the periodic impingement of high-speed streams. The WHI studies traced the solar activity and structure into the heliosphere and geospace, and provided new insight into the nature of the interconnected heliophysical system near solar minimum.     

A scoping review on the multiplicity of scale in spatial analysis

Journal of Geographical Systems - Scale is a central concept in the geographical sciences and is an intrinsic property of many spatial systems. It also serves as an essential thread in the fabric...     

Vulnerability and adaptation to climate-related fire impacts in rural and urban interior Alaska

This paper explores whether fundamental differences exist between urban and rural vulnerability to climate-induced changes in the fire regime of interior Alaska. We further examine how communities and fire managers have responded to these changes and what additional adaptations could be put in place. We engage a variety of social science methods, including demographic analysis, semi-structured interviews, surveys, workshops and observations of public meetings. This work is part of an interdisciplinary study of feedback and interactions between climate, vegetation, fire and human components of the Boreal forest social–ecological system of interior Alaska. We have learned that although urban and rural communities in interior Alaska face similar increased exposure to wildfire as a result of climate change, important differences exist in their sensitivity to these biophysical, climate-induced changes. In particular, reliance on wild foods, delayed suppression response, financial resources and institutional connections vary between urban and rural communities. These differences depend largely on social, economic and institutional factors, and are not necessarily related to biophysical climate impacts per se. Fire management and suppression action motivated by political, economic or other pressures can serve as unintentional or indirect adaptation to climate change. However, this indirect response alone may not sufficiently reduce vulnerability to a changing fire regime. More deliberate and strategic responses may be required, given the magnitude of the expected climate change and the likelihood of an intensification of the fire regime in interior Alaska.