Deglaciation ages and meltwater routing in the Fort McMurray region,northeastern Alberta and northwestern Saskatchewan,Canada

A field-based reconstruction of the deglacial paleogeography in the Fort McMurray area permits: 1) constraining the timing of meltwater routing to the Arctic from the present Hudson Bay drainage basin; and 2) minimum-age estimates for ice-margin positions that can be used to constrain ice-sheet modeling results. A downslope recession of the Laurentide Ice Sheet resulted in a series of proglacial lakes forming between the ice margin and higher land to the southwest. The paleogeography of these lakes is poorly constrained in part from the masking effect of boreal forest vegetation and map-scale issues. However, recent space-shuttle based DEMs increase the number and spatial extent of moraines identified within the study area resulting in a coherent pattern of ice margin retreat focused on the Athabasca River valley. An intensive lake-coring program resulted in a minimum ten-fold increase in the radiocarbon database used to limit moraine ages. Results indicate that deglaciation in this region was younger than previously reported, and it is likely that the meltwater could not drain northward to the Arctic Ocean from any source southeast of the Fort McMurray area until approximately 9850–9660 ¹⁴C BP.     

Rapid nutrient load reduction during infiltration of managed aquifer recharge in an agricultural groundwater basin: Pajaro Valley,California

Artificial recharge of groundwater is an increasingly important method for augmenting groundwater supply and can have a positive or negative influence on the quality of water resources. We instrumented a managed aquifer recharge (MAR) pond in central coastal California to assess how patterns of infiltration and recharge affect the load of nitrate delivered to the underlying aquifer. The concentration of nitrate in infiltrating water consistently decreased during passage through the first metre of subsurface soils. Enrichment of ¹⁸O and ¹⁵ N in the residual nitrate in infiltrating water proceeded in a ratio of 1:2, indicating that denitrification plays a significant role in the quantitative reduction of nutrients exported during infiltration through shallow soils. The extent and rate of nitrate removal was spatially and temporally variable across the bottom of the recharge pond, with 30% to 60% of the nitrate load being removed over the first 6 weeks of managed aquifer recharge operation. During the period of highest N loading to the system, when the average infiltration rate was > 1 m/day, the recharge pond achieved a load reduction efficiency of 7 kg NO₃^?‐N/day/ha, which compares favourably to nitrate load reductions achieved by treatment wetlands. Groundwater mounding and water composition below the recharge pond suggest that recharge and subsequent lateral transport occur heterogeneously in the underlying aquifer. Nitrate concentrations in the aquifer following infiltration were lowered primarily by dilution, with little evidence for additional denitrification occurring in the aquifer in comparison to high rates documented during shallow infiltration. Copyright © 2011 John Wiley & Sons, Ltd.     

Co-management of sea turtle fisheries: Biogeography versus geopolitics

Co-management between local communities and government agencies is promoted as a strategy to improve fisheries management. This paper considers the potential for co-management of sea turtle fisheries within four UK Overseas Territories (OTs) in the Caribbean, and for co-ordinated management among those territories. We focus on fisher incentives for engaging in co-management and on the potential to scale up co-management to a regional level. This paper presents data from Anguilla, British Virgin Islands, Montserrat, and Turks and Caicos Islands, where 110 turtle fishers participated in a socio-economic survey undertaken as part of the ‘Turtles in the UK Overseas Territories in the Caribbean’ project. Based on three established criteria for co-management (perceived crisis in stock, willingness to participate and community cohesion), results suggest that fisher support for co-management exists within each OT, but the extent of support for and views of specific management interventions varies among OTs. The implications of results for co-management in each territory, and for establishing co-ordinated management regimes in the region, are discussed in the context of current debates about the nature of resources and scalar (mis)matches between resource and management regimes.     

Distribution of diffuse flow megafauna in two sites on the Eastern Lau Spreading Center, Tonga

Hydrothermal vent environments are characterized by large gradients of toxic chemicals and high temperatures, which play a significant role in defining species’ distributions. We used high-resolution imagery and spatially explicit in-situ physico-chemical measurements analyzed within a Geographic Information System (GIS) in order to characterize the spatial relations among different groups of megafauna, temperature, and chemistry within two discrete vent communities (40 and 50 m²) on the Eastern Lau Spreading Center (ELSC). Chemical (sulfide and O₂ concentrations) and temperature data were obtained from approximately 75 different locations within each community using in-situ instruments. All data were integrated into a GIS, which served as a visualization tool and enabled the data to be analyzed in a spatial context. Our results confirm the importance of abiotic variables in defining the distributions of some fauna and elucidate several biological associations that are consistent between the two communities. The provannid snail, Alviniconcha spp., appears to actively avoid temperatures above 32–46 °C and/or sulfide concentrations exceeding approximately 260 μM. Slightly higher average sulfide concentrations and temperatures were measured among aggregations of Ifremeria nautilei compared to aggregations of the mussel Bathymodiolus brevior; however, the presence of mixed aggregations of the two species indicates an overlap in requirements. The brachyuran crab, Austinograea spp., was consistently observed directly on symbiont-containing species, particularly Alviniconcha spp. The solitary snail, Eosipho desbruyeresi, was rarely observed on biological substrata, but was often (60% of its population at the most active site) within 5 cm of symbiont-containing fauna, indicating a tolerance and preference for proximity to areas of high productivity. Densities and coverage of species differed substantially between the two communities despite high species overlap. Symbiont-containing species covered much larger areas at the more hydrothermally active site, ABE1, while shrimp and anemones occurred in relatively higher densities within the less-active site, TM1. This is the first study to thoroughly characterize realized distributions of megafauna at vent sites along the ELSC.     

Overwash sedimentation associated with a large-scale northeaster

The December 1, 1974 northeaster was a significant event in terms of sediment transport with 20 m³ of sand per meter of dune breach being carried onto the backdune area of Assateague Island, Maryland as overwash. Previous investigators have reported larger transport rates for landfall hurricanes, but this is the largest amount recorded for a winter northeaster. The Ash Wednesday Storm, March 6–8, 1962, was a much larger event, but no quantitative data exists for overwash deposition.The resulting sedimentary deposit can be interpreted by defining sedimentation units. Inverse sediment grading was predominant, but normal grading occurred when the material was monomineralic and the unit totally depositional in nature. The timing of the storm surge was recorded in some sections as a distinctive heavy mineral enrichment in the sediment.     

The response of vegetation cover and dune activity to rainfall,drought and fire observed by multitemporal satellite imagery

The stable longitudinal dunes in the northern Simpson Desert, Australia, were observed in satellite imagery to become more active after vegetation cover was reduced by fire and drought. Subsequent rainfall events also resulted in significant vegetation regrowth and dune stabilization. These switches between more active and stable conditions have not been previously described in the largely vegetated dune fields of central Australia. The observations, made on 12 dune sites, relied on high spatial resolution satellite imagery to observe dune crest activity, and seasonal Landsat fractional cover imagery to observe vegetation cover changes. The non-photosynthetic vegetation (NPV) component of the fractional vegetation cover images revealed significant changes in hummock grass cover on the dunes between 1988 and 2018, with a positive relationship with the three-year cumulative rainfall, disrupted by two periods of patchy burning. Only those sites that had burnt became active, and only after vegetation cover had remained low (NPV < 16%) during the ‘Millennium Drought’. There is no threshold in vegetation cover, below which dune crests become active, but active dune features require four-years of low NPV cover (< 16%) to develop. The large rainfall event that ended the drought increased NPV cover, stabilizing the dunes. Similar hummock grass covered dunes are present across large areas of the arid zone, and are likely to respond in similar ways, given that fire and drought are common occurrences in Australia. © 2019 John Wiley & Sons, Ltd. © 2019 John Wiley & Sons, Ltd.     

The kinematics of solar inner coronal transients

Solar Physics - The kinematic properties of a dozen ‘loop-like’ coronal transients have been examined over the range 1.2–2.4 R⊙ from Sun center. Values and trends of...     

On the distribution of material as a function of temperature in the post-flare loop system of 12 August 1970

Observations of the post-flare loop system formed after the east limb proton flare of 12 August 1970 include (a) sets of filtergrams from which photographic subtractions have been constructed and (b) spectra from which a distribution of electron density as a function of temperature for three coronal regions are derived. The filtergrams show no indications of radial velocities in excess of 80 km/s. The spectra indicate an increase in density at the tops of the loops with most of the material at a relatively cool temperature: N 6.0 × 10¹⁰, T = 3 × 10⁵K. The distribution functions obtained for areas just above and just below loops indicate a lower electron density and the presence of material at high temperatures, N 2.0 × 10¹⁰ and T 2.6 × 10⁶K (above the loops) and T _e > > 4.4 × 10⁶K for material below the loops.