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The direct and indirect effects of road verges and urban greening on butterflies in a tropical city-state
No full textRoad verges have considerable potential to benefit wildlife, but in highly urbanised areas management often limits their value for biodiversity. Evaluating how the management of road verges affects wildlife, both directly and indirectly, provides opportunities to integrate biodiversity into urban planning, design, and management. We studied butterfly pollinators next to main roads across Singapore, a highly urbanised tropical city-state that envisions itself as ‘A City in Nature’. Using structural equation models we quantified how road verge habitat quality (nectar-floral diversity, structural complexity, size, and plant richness) and surrounding landscapes (traffic density and greenness as a ratio of green to concreted areas) directly and indirectly affected butterflies. We found direct positive effects of nectar-floral diversity and structural complexity within road verges on butterfly diversity (abundance and richness). While road verge size and plant richness had no direct effects on butterfly diversity, both had indirect positive effects by increasing nectar-floral diversity and structural complexity. Greenness at a landscape (≥ 500 m radius) rather than local (≤ 250 m radius) scale positively affected butterfly diversity. Traffic density had a direct negative effect on butterfly diversity likely though increased mortality due to collisions. Our findings offer valuable insights for city planners and policymakers, and suggest that simple management decisions, such as improving resource quality within verges, can have positive benefits for biodiversity in highly urbanised areas. As cities around the world develop policy mechanisms to create greener environments, our results highlight opportunities to improve road verges to benefit butterflies, a commonly used flagship taxon for biodiversity
Glaciogenic structures at Ordovician tunnel valley margins and their implications for tunnel valley genesis in southern Jordan
No full textPenecontemporaneous deformation and erosional structures are described from the inclined bedrock margins of Late Ordovician (Hirnantian) tunnel valleys in southern Jordan. These include micro-faults, glacial striae and grooves, and newly described micro-slips. Together with the basal glacial diamictites, they indicate contact of the basal ice mass with the underlying Late Ordovician bedrock (the Tubayliyat Sandstone Formation) during erosion of the tunnel valleys. The striae/grooves are oriented parallel and at right angles to the tunnel axes; this latter sense of movement is supported by the associated micro-slips and the throw on the micro-faults. Two types of glacial margin are present: erosional or folded (ductile deformation). Locally preserved basal diamictites (tillites), including far-travelled granitoid and metamorphic clasts derived from the Arabian Shield, support a primary ice–bedrock erosional origin for the tunnel valleys. The presence of abundant erosional/deformational structures oriented towards the tunnel valley axes indicate subsequent movement of the basal ice mass towards the tunnel valley axes, possibly as a result of the collapse of sub-glacial streams during deglaciation. The deformational features are interpreted as the result of high hydrostatic groundwater pressure in the bedrock at the base of the ice sheet. The tunnel valleys were subsequently modified and infilled by two or more phases of fluvio-glacial siliciclastic sedimentation
Early Neoproterozoic (Tonian) subduction-related magmatism and tectonothermal activity in Shetland and northern mainland Scotland: implications for the tectonic evolution of NE Laurentia and Rodinia reconstructions
Get PDFThe tectonic setting of Tonian orogenic events recorded in the present-day circum-North Atlantic region is uncertain. U–Pb zircon geochronology shows that the Yell Sound and Westings groups (Shetland) and metasedimentary rocks of the Naver Nappe (northern mainland Scotland) were deposited between c. 1050 and 960 Ma and intruded by mafic, intermediate and felsic igneous rocks at c. 965–950 Ma. Chemical discrimination diagrams and Hf and Nd isotope data together suggest that the protoliths of the mafic meta-igneous rocks were emplaced as relatively juvenile crustal contributions in an active plate margin. Zircon growth at c. 920 Ma within the Yell Sound Group correlates with high-grade metamorphism documented previously in Shetland. Further zircon growth and Pb loss at c. 470–460 Ma indicates overprinting during the Ordovician Grampian orogenic event. Similar age successions of Ellesmere Island, Svalbard and East Greenland also contain evidence for Tonian magmatism (some calc-alkaline), deformation and metamorphism. The new data favour Rodinia reconstructions that incorporate subduction-related magmatism and associated tectonism along the margin of NE Laurentia during the Tonian. The Yell Sound Group and correlative peri-Laurentian successions were intruded by subduction-related magmas and deformed and metamorphosed during development of the Valhalla exterior accretionary orogen, part of a more extensive peri-Rodinian subduction system
Environmental degradation and fragmentation of microplastics: dependence on polymer type, humidity, UV dose and temperature
Get PDFDepending on the environmental compartment, plastics are subjected to various stressors, including UV light, water, microbial exudates (enzymes), and temperature. Among these, stress on plastics from photo-chemical processes was identified as a leading exposure pathway of plastics, e.g., in the atmosphere or on the water surface. While the focus of earlier studies mainly was on deterioration of the chemical and mechanical properties, more recent studies demonstrate how photo-oxidation leads to fragmentation and release of secondary micro- and nanoplastic fragments, as well as low-molecular weight species. These studies tend to focus on a single exposure condition and a limited number of polymer types. Therefore, this study focuses on systematically evaluating the influence of temperature and relative humidity during simulated UV exposure on the fragmentation and degradation of five types of pristine microplastic powders: polypropylene, low density polyethylene, polyamide 6, high impact polystyrene and thermoplastic polyurethane. We quantified the dose-dependent release of water-soluble organics, as well as secondary micro- and nanoplastics (including their particle size distributions) and found that the polymer identity dictated the type and quantity of species released rather than the aging protocol. With this systematic assessment the generated data can be used in mechanistic microplastic fragmentation models to determine fragmentation rates and fragment size distributions
Giant pit craters on the modern seafloor above magma-induced hydrothermal vent complexes of Scotia Sea, offshore Antarctica
Get PDFMassive injection of 13 C depleted carbon to the ocean and atmosphere coincided with major environmental upheaval multiple times in the geological record. For several events, the source of carbon has been attributed to explosive venting of gas produced when magmatic sills intruded organic-rich sediment. The concept mostly derives from studies of a few ancient sedimentary basins with numerous hydrothermal vent complexes (HTVCs) where craters appear to have formed across large areas of the seafloor at the same time, but good examples remain rare in strata younger than the Early Eocene. We present geophysical data documenting at least 150 large (km-scale) craters on the modern seafloor across ∼148,000 km 2 of Scan Basin in the southern Scotia Sea, a remote region offshore Antarctica. Seismic and bathymetric information reveals the craters relate to vertical fluid pipes extending above dome-shaped forced folds and saucer-shaped igneous sills. Presumably, magmatic intrusions deform overlying sediment and produce thermogenic gas, where buoyant hydrothermal fluids migrate upwards from sill flanks through V-shaped gas chimneys to the seafloor. Fluid expulsion, driven by excess pore pressure, enhances vertical conduits and creates collapse structures on the seafloor. Age estimates for sill emplacement and crater formation come from correlations of seismic reflectors with bore hole data collected on IODP Expedition 382. Sills intruded into sediment at least two times, first about 12–13 Ma (Middle Miocene), which occurred with deep intrusions of stacked composite sills, and once about 0.9 Ma and associated with volcanism along Discovery Bank, which may have reactivated previous fluid venting. Crater reactivation has occurred since 0.9 Ma, although probably episodically. Importantly, at present-day, numerous craters related to sills and fluid pipes populate the seafloor above a young sedimentary basin, and the ocean and atmosphere are receiving massive quantities of 13 C depleted carbon. The two phenomena are unrelated but, with changes in global climate and sedimentation, the craters could be filled simultaneously and give an impression in the rock record of rapid and coeval formation coincident with carbon emission. Interpretations of ancient HTVCs and their significance to global carbon cycling needs revision with consideration of modern seafloor regions with HTVCs, notably Scan Basin
The influence of subglacial lake discharge on Thwaites Glacier ice-shelf melting and grounding-line retreat
Get PDFThe retreat of the Antarctic Ice Sheet is conventionally attributed to increased ocean melting of ice shelves, potentially enhanced by internal instability from grounding lines near retrograde bed slopes. Ocean melting is enhanced by increased intrusion of modified Circumpolar Deep Water (mCDW) into ice shelf cavities. Upwelling from the release of subglacial meltwater can enhance mCDW’s melting ability, though its efficacy is not well understood and is not represented in current ice sheet loss projections. Here we quantify this process during an exceptional subglacial lake drainage event under Thwaites Glacier. We found that the buoyant plume from the subglacial discharge temporarily doubled the rate of ocean melting under Thwaites, thinning the ice shelf. These events likely contributed to Thwaites’ rapid thinning and grounding line retreat during that period. However, simulations and observations indicate that a steady subglacial water release would more efficiently enhance basal melt rates at Thwaites, with melt rate increasing like the square root of the subglacial discharge. Thus, it remains unclear whether increased subglacial flooding events provide a stabilizing influence on West Antarctic ice loss by reducing the impact of subglacial water on ocean melting, or a destabilizing influence by triggering rapid changes at the grounding zone
The importance of ditches and canals in global inland water CO2 and N2O budgets
Get PDFDitches and canals are omitted from global budgets of inland water emissions, despite research showing them to be emitters of greenhouse gases (GHGs). Here, we synthesize data across climate zones and land use types to show, for the first time, that global ditches emit notable amounts of carbon dioxide (CO2) and nitrous oxide (N2O). Ditches had higher per‐area emissions of CO2 and N2O than ponds, lakes, and reservoirs, likely due to high nutrient inputs. Preliminary upscaling showed that the inclusion of ditches would increase global inland water CO2 emissions by 0.6%–1% and N2O emissions by 3%–9%. Trophic state and climate influenced N2O emissions, while CO2 emissions had complex drivers difficult to disentangle at the global scale. This research highlights the importance of including ditches in global inland water GHG budgets and informs more accurate reporting of anthropogenic emissions in national inventories
Antarctic Waters
No full textHere, we summarize the diatom research topics and applications that have the broadest relevance and importance for Antarctic studies. From the Southern Ocean we focus on biogeography, sea surface temperature (SST) and sea-ice reconstructions (including frontal migrations) and biostratigraphy. We also include the significance of studying laminated diatomaceous sediments and how diatoms are used as bottom water tracers in the global ocean circulation. Diatoms from Antarctic lake sediments and ice cores are also briefly introduced
Assessing the suitability of sites near Pine Island Glacier for subglacial bedrock drilling aimed at detecting Holocene retreat–readvance
Get PDFUnambiguous identification of past episodes of ice sheet thinning below the modern surface and grounding line retreat inboard of present requires recovery and exposure dating of subglacial bedrock. Such efforts are needed to understand the significance and potential future reversibility of ongoing and projected change in Antarctica. Here we evaluate the suitability for subglacial bedrock drilling of sites in the Hudson Mountains, which are located in the Amundsen Sea sector of West Antarctica. We use an ice sheet model and field data – geological observations, glaciological observations and bedrock samples from nunataks, and ground-penetrating radar from subglacial ridges – to rate each site against four key criteria: (i) presence of ridges extending below the ice sheet, (ii) likelihood of increased exposure of those ridges if the grounding line was inboard of present, (iii) suitability of bedrock for drilling and geochemical analysis, and (iv) accessibility for aircraft and drilling operations. Our results demonstrate that although no site in the Hudson Mountains is perfect for this study when assessed against all criteria, the accessibility, N–S orientation and basaltic bedrock lithology of Winkie Nunatak's southernmost ridge (74.86° S, 99.77° W) make it a feasible site both for drilling and subsequent cosmogenic nuclide analysis. Furthermore, the ridge is strewn with glacial erratics at all elevations, providing valuable constraints on its early Holocene deglacial history. Based on our experiences during this study, we conclude with a series of recommendations for assessing site suitability for future bedrock drilling campaigns. We emphasise the importance of consulting a range of expertise prior to drilling and ensuring that sufficient field reconnaissance is undertaken (including obtaining detailed grids of radar survey data and bedrock samples)
Twenty‐thousand‐year gap between deglaciation and peat formation on sub‐Antarctic Marion Island attributed to climate and sea level change
Get PDFRadiocarbon dating of basal peats has been a key factor in determining minimum ages for deglaciation on sub-Antarctic islands. On Marion Island, peat bogs dominate the landscape below 300 m a.s.l., and palynological assessments of peat cores have been used to assess the vegetation history and succession rates as well as the sensitivity of the indigenous flora to climatic change. Initiation of peat on the sub-Antarctic islands signifies a major landscape change which has previously been linked to the retreat of glaciers. Here we test this hypothesis by comparing previously published and new basal peat ages from Marion Island with cosmogenic isotope dates for deglaciation, and local and regional palaeo-environmental changes. Results show that, in common with other sub-Antarctic islands, peat initiation occurred after the Antarctic Cold Reversal (15–13 ka) and through the early Holocene climate optimum. This substantially post-dates cosmogenic isotope evidence for deglaciation from the basalts which shows that the areas where the peatlands dominate were ice-free from the start of Marine Isotope Stage (MIS) 2 (~31 ka). This suggests that environmental conditions controlled peat initiation rather than deglaciation. Regional climatic proxies show that during and after MIS 2, extremely low temperatures, extensive sea ice conditions and depressed sea surface temperatures together with lower sea levels at an island scale could have maintained conditions unfavourable for peat initiation at their current locations. On Marion Island, the significant gap of ~20 000 years between the timing of deglaciation and peat formation indicates that the use of peat basal ages as a proxy for the minimum age of deglaciation in the sub-Antarctic should be used with extreme caution
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