Resilience to change in two coastal communities: Using the maximum dexterity fleet

Using whole-ecosystem dynamic simulation models fitted to local data, two coastal communities are described (temperate, northern British Columbia, Canada; tropical, Raja Ampat, Indonesia) where relatively poor fishers’ livelihoods are threatened by climate change and overfishing. A novel theoretical minimum bycatch scenario, the ‘maximum dexterity fleet’, is combined with a search algorithm specifying optimal fisheries to achieve economic and biodiversity goals. Potential gains made by approaching an optimal fleet configuration prove robust against increased risks from climate variability. Although fish, gear and way of life differ greatly, in both communities it is suggested that dexterity (adroitness in adapting fishing gear) could lead to improved benefits from fishing.     

Characterizing supraglacial meltwater channel hydraulics on the Greenland Ice Sheet from in situ observations

Supraglacial rivers on the Greenland Ice Sheet (GrIS) transport large volumes of surface meltwater toward the ocean, yet have received relatively little direct research. This study presents field observations of channel width, depth, velocity, and water surface slope for nine supraglacial channels on the south‐western GrIS collected between July 23 and August 20, 2012. Field sites are located up to 74 km inland and span 494–1485 m elevation, and contain measured discharges larger than any previous in situ study: from 0.006 to 23.12 m³/s in channels 0.20 to 20.62 m wide. All channels were deeply incised with near vertical banks, and hydraulic geometry results indicate that supraglacial channels primarily accommodate greater discharges by increasing velocity. Smaller streams had steeper water surface slopes (0.74–8.83%) than typical in terrestrial settings, yielding correspondingly high velocities (0.40–2.60 m/s) and Froude numbers (0.45–3.11) with supercritical flow observed in 54% of measurements. Derived Manning's n values were larger and more variable than anticipated from channels of uniform substrate, ranging from 0.009 to 0.154 with a mean value of 0.035 ± 0.027 despite the absence of sediment, debris, or other roughness elements. Ubiquitous micro‐depressions in shallow sections of the channel bed may explain some of these roughness values. However, we find that other, unobserved sources of flow resistance likely contributed to these elevated Manning's n values: future work should explicitly consider additional sources of flow resistance beyond bed roughness in supraglacial channels. We conclude that hydraulic modeling for these channels must allow for both subcritical and supercritical flow, and most importantly must refrain from assuming that all ice‐substrate channels exhibit similar hydraulic behavior, especially for Froude numbers and Manning's n. Finally, this study highlights that further theoretical and empirical work on supraglacial channel hydraulics is necessary before broad scale understanding of ice sheet hydrology can be achieved. Copyright © 2016 John Wiley & Sons, Ltd.     

The Ballybofey Anticline: A solution of the general structure of parts of Donegal and Tyrone

A tight early fold, the Ballybofey anticline, trends south-eastwards across central Donegal. South-west of its axial trace the Dalradian strata are inverted so that the rocks high in the Series occur at the lowest structural level, next to, and facing downwards, the supposedly Moinian psammites in the core of the Lough Derg antiform. Rapid facies changes occur in the Dalradian rocks across the Caledonian strike.     

Uncertainties in climate stabilization

The atmospheric composition, temperature and sea level implications out to 2300 of new reference and cost-optimized stabilization emissions scenarios produced using three different Integrated Assessment (IA) models are described and assessed. Stabilization is defined in terms of radiative forcing targets for the sum of gases potentially controlled under the Kyoto Protocol. For the most stringent stabilization case (“Level 1” with CO₂ concentration stabilizing at about 450 ppm), peak CO₂ emissions occur close to today, implying (in the absence of a substantial CO₂ concentration overshoot) a need for immediate CO₂ emissions abatement if we wish to stabilize at this level. In the extended reference case, CO₂ stabilizes at about 1,000 ppm in 2200—but even to achieve this target requires large and rapid CO₂ emissions reductions over the twenty-second century. Future temperature changes for the Level 1 stabilization case differ noticeably between the IA models even when a common set of climate model parameters is used (largely a result of different assumptions for non-Kyoto gases). For the Level 1 stabilization case, there is a probability of approximately 50% that warming from pre-industrial times will be less than (or more than) 2°C. For one of the IA models, warming in the Level 1 case is actually greater out to 2040 than in the reference case due to the effect of decreasing SO₂ emissions that occur as a side effect of the policy-driven reduction in CO₂ emissions. This effect is less noticeable for the other stabilization cases, but still leads to policies having virtually no effect on global-mean temperatures out to around 2060. Sea level rise uncertainties are very large. For example, for the Level 1 stabilization case, increases range from 8 to 120 cm for changes over 2000 to 2300.     

Fluvial morphometry of supraglacial river networks on the southwest Greenland Ice Sheet

Extensive, complex supraglacial river networks form on the southwest Greenland ice sheet (GrIS) surface each melt season. These networks are the dominant pathways for surface meltwater transport on this part of the ice sheet, but their fluvial morphometry has received little study. This paper utilizes high-resolution (2 m) WorldView-1/2 images, digital elevation models, and GIS tools to present a detailed morphometric characterization (river number, river length, Strahler stream order, width, depth, bifurcation ratio, braiding index, drainage density, slope, and relief ratio) for 523 GrIS supraglacial river networks. A new algorithm is presented to determine Strahler stream order in supraglacial environments. Results show that (1) Supraglacial river networks are broadly similar to terrestrial landscapes in that they follow Horton’s laws (river number, mean river length, and slope versus stream order), widen downstream, and have comparable mean bifurcation ratios (3.7 ± 1.9) and braiding indices; (2) unlike terrestrial systems, supraglacial drainage densities (0.90–4.75 km/km²) have no correlation with elevation relief, but instead display a weakly inverse correlation with ice surface elevation; (3) both well-developed (e.g., fifth-order) and discrete (e.g., first-order) supraglacial river networks form on the ice sheet, with the latter associated with short flow distances upstream of a terminal moulin; (4) mean river flow widths increase substantially, but flow depths only modestly, with increasing stream order. Viewed collectively, the 523 supraglacial river networks studied here display fluvial morphometries both similar and dissimilar to terrestrial systems, with moulin capture an important physical process driving the latter.     

Saldanha Bay,South Africa III: new production and carrying capacity for bivalve aquaculture

Measurements of NH₄, NO₃, urea and HCO₃ uptake using 15N and 13C stable isotope tracers were undertaken in Saldanha Bay, South Africa, between January 2012 and January 2013. These studies provide the first direct measurements of N utilisation by the plankton in the bay. Primary production in the bay is driven predominantly by the advection of nutrients from the neighbouring shelf environment during upwelling events, with terrestrial and other sources providing minor inputs. New production (NO₃-based) was calculated from the f-ratio and total primary production and was used to provide estimates of potential carrying capacity for bivalve culture. Despite the apparent light limitation of NO3 uptake in the winter, the availability of NO₃ appeared to exert the major influence on new production throughout the year. In addition, new production was modulated by NH₄ availability as shown by the suppression of NO₃ uptake by concentrations higher than 1?1.5?mmol m^?3. The estimated areal new production of 0.60?g C m^?2 d^?1 yielded a bay-wide annual estimate of 9 811 t C ha^?1 y^?1, slightly higher than previous calculations based on physical models. It is estimated that the total annual production of mussels and oysters, respectively, for a 1 000-ha cultivation area is approximately 40 000–53 000 t y^?1 (mainly Mytilus galloprovincialis) and 4 600–6 000 t y^?1 (Crassotrea gigas). The combined total production figures constitute only 24–31% of the surplus new production. A combined harvestable carrying capacity of 74 000–82 000 t y^?1 can be calculated from this surplus. However, from a management and ecological perspective, bivalve culture should be limited to well below this theoretical maximum. Even with this constraint, there appears to be considerable scope for expansion of bivalve farming over the modest, present levels with little jeopardy to ecological integrity.