Regional modeling of climate change impacts on smallholder agriculture and ecosystems in Central America

Climate change will have serious repercussions for agriculture, ecosystems, and farmer livelihoods in Central America. Smallholder farmers are particularly vulnerable due to their reliance on agriculture and ecosystem services for their livelihoods. There is an urgent need to develop national and local adaptation responses to reduce these impacts, yet evidence from historical climate change is fragmentary. Modeling efforts help bridge this gap. Here, we review the past decade of research on agricultural and ecological climate change impact models for Central America. The results of this review provide insights into the expected impacts of climate change and suggest policy actions that can help minimize these impacts. Modeling indicates future climate-driven changes, often declines, in suitability for Central American crops. Declines in suitability for coffee, a central crop in the regional economy, are noteworthy. Ecosystem models suggest that climate-driven changes are likely at low- and high-elevation montane forest transitions. Modeling of vulnerability suggests that smallholders in many parts of the region have one or more vulnerability factors that put them at risk. Initial adaptation policies can be guided by these existing modeling results. At the same time, improved modeling is being developed that will allow policy action specifically targeted to vulnerable groups, crops, and locations. We suggest that more robust modeling of ecological responses to climate change, improved representation of the region in climate models, and simulation of climate influences on crop yields and diseases (especially coffee leaf rust) are key priorities for future research.     

Binary evolution with relativistic jets

Relativistic jets can extract mass–energy from a black hole. In semi-detached black hole binaries the jet ejection process constitutes a ‘consequential angular momentum loss' (CAML) process. The effect of this jet-induced CAML is to lower the transfer rate below the value set by systemic driving and to stabilize otherwise unstable systems. Implications of jet-induced CAML for GRO J1655−40 are discussed.     

Hydrogen peroxide production rates in clean and polluted coastal marine waters of the Mediterranean, Red and Baltic Seas

The main aim of this study was to assess the hydrogen peroxide (HP) production rates (HPPR) related to anthropogenic pollution in coastal waters by laboratory and field experiments. HPPR's were assessed by simultaneous measurements of HP concentrations, cumulative solar UV irradiation and dissolved organic matter (DOM) fluorescence in the seawater samples at clean and polluted sites in the Mediterranean, Red and the Baltic Seas. The natural HP concentrations at all sites (8–100 nM) fall within the normal range recorded elsewhere, and follows a diurnal pattern. The polluted stations in the Mediterranean and Baltic Seas showed higher HPPR (3.2–16.6 nM m² W⁻¹ h⁻¹) than the clean stations, while in the Red Sea no significant differences were found because the station that was considered a priori polluted was actually rather clean (2–3 nM m² W⁻¹ h⁻¹). Laboratory experiments demonstrated that HPPR was positively linearly correlated to DOM fluorescence, however, this relationship was not found in the natural seawater samples examined in the field. The lack of relationship between HPPR and DOM in the field was attributed to enzymatic breakdown of HP as observed in dark decay experiments. HP dark decay rates were highest in polluted stations, probably due to larger bacterioplankton populations in these samples. Moreover, the HP dark decay rates were much lower in filtered than in non-filtered samples. Sun incubation of filtered (0.2 μm) seawater samples were performed to assess whether elimination of particles would yield higher HPPRs than in non-filtered samples. In the Baltic Sea (low UV irradiation) HPPR was higher in the filtered samples, while at sites with relatively high UV irradiation (Mediterranean and Red Seas), filtration of seawater did not stimulate HPPRs, probably due to UV-damage to planktonic microorganisms.     

The sublimation of falling snow over the Mackenzie River Basin

The sublimation of falling snow may be an important component of the atmospheric water budget of the Mackenzie River Basin and many parts of the Arctic. To investigate this issue, a simple sublimation model is used along with surface precipitation observations and sonde data obtained during the autumn 1994 Beaufort and Arctic Storms Experiment (BASE). Model results are then compared with actual precipitation measurements at Inuvik and Tuktoyaktuk, sites in Northern Canada, to approximate mass loss due to sublimation. The sublimation results are found to vary in concert with cloud base height, precipitation intensity aloft and the nature of the precipitation. Atmospheric conditions are furthermore examined over a wide range of the Arctic, especially the Mackenzie River Basin, to assess to what degree the results can be generalized. The presence of a relatively dry near-surface layer, a favourable environment for sublimation, is a key feature of most sites during the early autumn storm period. Estimates of sublimational mass losses are found over Inuvik and Tuktoyaktuk using sonde derived cloud base heights and temperature and humidity profiles. Sublimation losses for such sites are found to be of the order of 40–60%, which shows that sublimation is indeed a significant process over the Mackenzie Basin and needs to be well handled in climate models. However, increasing the vertical resolution of the sublimation model to that of climate scales can dramatically affect predicted sublimation amounts; how to properly account for sublimation then remains a difficult task.     

下地壳拆沉作用及大陆地壳演化

讨论了下地壳拆沉作用的地球化学示踪方法,并以近来对秦岭－大别造山带和美国西部内华达岩基地区的研究成果为例,说明了下地壳拆沉在两地区壳－幔演化方面可能起的重要作用。     

Henry's law constant and hydrolysis of peroxyacetyl nitrate (PAN)

The effect of temperature on the solubility of PAN and on its hydrolysis rate in near-neutral and slightly acidic water were studied in a bubble column apparatus. The results obtained are a Henry's law coefficient H=10^–9.04±0.6 exp[(6513±376)/T] M atm^–1, and a first-order hydrolysis rate constant k=10^6.60±1.0 exp[(–6612±662)/T] s^-1, which was independent of pH in the range 3.2pH6.7. The products formed are nitrite and nitrate in approximately equal proportions under near-neutral conditions. At a pH<4, nitrite is oxidized in a secondary reaction, and nitrate becomes the only product at low pH. Previously measured deposition velocities of PAN on stagnant water surfaces are shown to be hydrolysis rate limited.     

Lava morphology mapping by expert system classification of high-resolution side-scan sonar imagery from the East Pacific Rise, 9°–10°N

Fine-scale lava morphology has been classified on the ridge crest of the East Pacific Rise between 9°15′N and 10°02′N using an expert system classification method. This method establishes the means to classify complicated seafloor environments by integrating textural and geometric feature attributes from a high-resolution side-scan sonar dataset where ground-reference data are available from near-bottom visual observations. The classification in this study focuses upon mapping the lava morphology distribution of sheet, lobate, and pillow flows along the East Pacific Rise. The reliability of the classification has been evaluated using an accuracy assessment. The study region yields a coverage area of 37,814 m² (44%) for lobate flows; 10,421 m² (12%) for pillow flows; 15,096 m² (18%) for sheet flows; 19,679 m² (23%) for fissured areas; and 2,967 m² (3%) for shadows or no data. The systematic distribution of lava morphology along the ridge found in this study supports the idea of using the regional distribution of surface morphology as an indicator of emplacement dynamics and supports an organization of the volcanic plumbing system at a third order segmentation scale beneath mid-ocean ridges.