Molecular formulae of marine and terrigenous dissolved organic matter detected by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry

The chemical structure of refractory marine dissolved organic matter (DOM) is still largely unknown. Electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR-MS) was used to resolve the complex mixtures of DOM and provide valuable information on elemental compositions on a molecular scale. We characterized and compared DOM from two sharply contrasting aquatic environments, algal-derived DOM from the Weddell Sea (Antarctica) and terrigenous DOM from pore water of a tropical mangrove area in northern Brazil. Several thousand molecular formulas in the mass range of 300-600 Da were identified and reproduced in element ratio plots. On the basis of molecular elemental composition and double-bond equivalents (DBE) we calculated an average composition for marine DOM. O/C ratios in the marine samples were lower (0.36 ± 0.01) than in the mangrove pore-water sample (0.42). A small proportion of chemical formulas with higher molecular mass in the marine samples were characterized by very low O/C and H/C ratios probably reflecting amphiphilic properties. The average number of unsaturations in the marine samples was surprisingly high (DBE = 9.9; mangrove pore water: DBE = 9.4) most likely due to a significant contribution of carbonyl carbon. There was no significant difference in elemental composition between surface and deep-water DOM in the Weddell Sea. Although there were some molecules with unique marine elemental composition, there was a conspicuous degree of similarity between the terrigenous and algal-derived end members. Approximately one third of the molecular formulas were present in all marine as well as in the mangrove samples. We infer that different forms of microbial degradation ultimately lead to similar structural features that are intrinsically refractory, independent of the source of the organic matter and the environmental conditions where degradation took place.     

Effect of Surface Heterogeneity on the Boundary-Layer Height: A Case Study at a Semi-Arid Forest

We investigate the effects of an isolated meso-\(\gamma \)-scale surface heterogeneity for roughness and albedo on the atmospheric boundary-layer (ABL) height, with a case study at a semi-arid forest surrounded by sparse shrubland (forest area: \(28~\text{ km }^2\), forest length in the main wind direction: 7 km). Doppler lidar and ceilometer measurements at this semi-arid forest show an increase in the ABL height over the forest compared with the shrubland on four out of eight days. The differences in the ABL height between shrubland and forest are explained for all days with a model that assumes a linear growth of the internal boundary layer of the forest through the convective ABL upwind of the forest followed by a square-root growth into the stable free atmosphere. For the environmental conditions that existed during our measurements, the increase in ABL height due to large sensible heat fluxes from the forest (\(600~\text {W~m}^{-2}\) in summer) is subdued by stable stratification in the free atmosphere above the ABL, or reduced by high wind speeds in the mixed layer.     

Deriving characteristic parameters of the convective boundary layer from sodar measurements of the vertical velocity variance

This paper deals with the derivation of the convective mixing height and the characteristic convective velocity w _* from profiles of _w measured by sodar. The parameters were obtained by fitting an analytical profile to the observed data. Results were compared with values obtained by the meteorological preprocessor of a dispersion model and from noon radiosoundings. In addition, a Monte Carlo method was applied to study the influence of measurement errors. It turned out that it is inherently difficult to determine the depth of deep mixed layers from sodar measurements with a limited range, although the determination of w _* should be possible. However, a significant underestimation of _w , and thus w _*, was found, which is probably due to disproportional sampling of updrafts and downdrafts.     

Simulation of daily energy budget and mean soil temperatures at an arid site

Summary Soil temperature is often inadequately based upon relatively few measurements at widely dispersed locations. Within arid regions, such as the desert southwestern United States, soils, microclimates, and thus soil temperature may be markedly heterogeneous. Because extensive measurement of soil temperature is often not feasible, models are needed that simulate soil temperature based on readily available soil survey and above-ground weather information. This paper describes a simple energy-budget based model for simulating daily mean temperatures within a bare arid land soil. The model requires basic information on soil physical properties, and daily weather data including air temperature, windspeed, rainfall, and solar radiation to calculate daily surface energy budget components and surface temperature. One of two alternative numerical methods is then used to calculated subsurface temperatures. Tests of the model using 1987 daily temperature data from an arid site at Yuma, Arizona resulted in root mean square deviations within 1.4°C between daily modeled and measured temperatures at both 0.05 and 0.10 m depths. Sensitivity analysis showed modeled temperatures at 0.05 m depth to be most sensitive to parameters affecting the surface energy balance such as air temperature and solar radiation. Modeled temperatures at 1.0m depth were relatively more sensitive to initial temperature conditions and to parameters affecting distribution of energy within the profile such as thermal conductivity.With 3 Figures     

Climate change and coastal flooding in Metro Boston: impacts and adaptation strategies

Sea level rise (SLR) due to climate change will increase storm surge height along the 825 km long coastline of Metro Boston, USA. Land at risk consists of urban waterfront with piers and armoring, residential areas with and without seawalls and revetments, and undeveloped land with either rock coasts or gently sloping beachfront and low-lying coastal marshes. Risk-based analysis shows that the cumulative 100 year economic impacts on developed areas from increased storm surge flooding depend heavily upon the adaptation response, location, and estimated sea level rise. Generally it is found that it is advantageous to use expensive structural protection in areas that are highly developed and less structural approaches such as floodproofing and limiting or removing development in less developed or environmentally sensitive areas.     

Spatial assessment of forest cover and land-use changes in the Hindu-Kush mountain ranges of northern Pakistan

Anthropogenic activities and natural processes are continuously altering the mountainous environment through deforestation, forest degradation and other land-use changes. It is highly important to assess, monitor and forecast forest cover and other land-use changes for the protection and conservation of mountainous environment. The present study deals with the assessment of forest cover and other land-use changes in the mountain ranges of Dir Kohistan in northern Pakistan, using high resolution multi-temporal SPOT-5 satellite images. The SPOT-5 satellite images of years 2004, 2007, 2010 and 2013 were acquired and classified into land-cover units. In addition, forest cover and land-use change detection map was developed using the classified maps of 2004 and 2013. The classified maps were verified through random field samples and Google Earth imagery (Quick birds and SPOT-5). The results showed that during the period 2004 to 2013 the area of forest land decreased by 6.4%, however, area of range land and agriculture land have increased by 22.1% and 2.9%, respectively. Similarly, barren land increased by 1.1%, whereas, area of snow cover/glacier is significantly decreased by 21.3%. The findings from the study will be useful for forestry and landscape planning and can be utilized by the local, provincial and national forest departments; and REDD+ policy makers in Pakistan.     

Trophic modeling of the Northern Humboldt Current Ecosystem, Part II: Elucidating ecosystem dynamics from 1995 to 2004 with a focus on the impact of ENSO

The Northern Humboldt Current Ecosystem is one of the most productive in the world in terms of fish production. Its location near to the equator permits strong upwelling under relatively low winds, thus creating optimal conditions for the development of plankton communities. These communities ultimately support abundant populations of grazing fish such as the Peruvian anchoveta, Engraulis ringens. The ecosystem is also subject to strong inter-annual environmental variability associated with the El Niño Southern Oscillation (ENSO), which has major effects on nutrient structure, primary production, and higher trophic levels. Here our objective is to model the contributions of several external drivers (i.e. reconstructed phytoplankton changes, fish immigration, and fishing rate) and internal control mechanisms (i.e. predator-prey) to ecosystem dynamics over an ENSO cycle. Steady-state models and time-series data from the Instituto del Mar del Perú (IMARPE) from 1995 to 2004 provide the base data for simulations conducted with the program Ecopath with Ecosim. In simulations all three external drivers contribute to ecosystem dynamics. Changes in phytoplankton quantity and composition (i.e. contribution of diatoms and dino- and silicoflagellates), as affected by upwelling intensity, were important in dynamics of the El Niño of 1997–98 and the subsequent 3 years. The expansion and immigration of mesopelagic fish populations during El Niño was important for dynamics in following years. Fishing rate changes were the most important of the three external drivers tested, helping to explain observed dynamics throughout the modeled period, and particularly during the post-El Niño period. Internal control settings show a mix of predator–prey control settings; however a “wasp-waist” control of the ecosystem by small pelagic fish is not supported.     

Experimental impact cratering: A summary of the major results of the MEMIN research unit

This paper reviews major findings of the Multidisciplinary Experimental and Modeling Impact Crater Research Network (MEMIN). MEMIN is a consortium, funded from 2009 till 2017 by the German Research Foundation, and is aimed at investigating impact cratering processes by experimental and modeling approaches. The vision of this network has been to comprehensively quantify impact processes by conducting a strictly controlled experimental campaign at the laboratory scale, together with a multidisciplinary analytical approach. Central to MEMIN has been the use of powerful two-stage light-gas accelerators capable of producing impact craters in the decimeter size range in solid rocks that allowed detailed spatial analyses of petrophysical, structural, and geochemical changes in target rocks and ejecta. In addition, explosive setups, membrane-driven diamond anvil cells, as well as laser irradiation and split Hopkinson pressure bar technologies have been used to study the response of minerals and rocks to shock and dynamic loading as well as high-temperature conditions. We used Seeberger sandstone, Taunus quartzite, Carrara marble, and Weibern tuff as major target rock types. In concert with the experiments we conducted mesoscale numerical simulations of shock wave propagation in heterogeneous rocks resolving the complex response of grains and pores to compressive, shear, and tensile loading and macroscale modeling of crater formation and fracturing. Major results comprise (1) projectile–target interaction, (2) various aspects of shock metamorphism with special focus on low shock pressures and effects of target porosity and water saturation, (3) crater morphologies and cratering efficiencies in various nonporous and porous lithologies, (4) in situ target damage, (5) ejecta dynamics, and (6) geophysical survey of experimental craters.