Formation and Fluxes of Soil Trace Gases

Trace gas cycling is an important feature of the soil system [...]

Carbon gas cycling in supraglacial debris covers

<p>Debris-covered glaciers extend over 4000 km2 in the high Asian Mountains and are significant and expanding features of most of the World’s glacierized mountain ranges. Within supraglacial debris covers, a combination of fresh mechanically-weathered rock and an abundance of water and energy during melt seasons provides an ideal environment for chemical rock weathering and microbial activity. These processes involve exchange of carbon dioxide CO2 and methane CH4 with the atmosphere, while daytime heating of debris leads to evaporation of meltwater from the debris matrix. Debris-covered glaciers may therefore play an important role in regional and global cycling of major greenhous gases. This new project aims to address 2 key questions: (i) What are the important chemical and microbiological processes affecting carbon gas exchange within supraglacial debris covers? (ii) What are the rates and controls on gas exchange and how do these rates vary in time and space? Initial direct measurements of CO2 flux have been made using an eddy covariance (EC) and gas analyser system installed over debris cover at Miage glacier in the Italian Alps, during the melt season. Under fine weather conditions, there is a strong daily cycle in downwardly-directed CO2 flux, closely linked to variation in energy input to the debris, driven by the flux of shortwave radiation. In contrast, rainfall is associated with short pulses of upwardly-directed CO2 flux to the atmosphere. In common with previously published findings, these data indicate that supraglacial debris covers are a strong summer sink of CO2. At Miage glacier the mean summer (June-August) flux is almost 0.5 g carbon per day per square metre of debris, more than 2 orders of magnitude higher than reported fluxes over cryoconite. Current gas flux data are limited to a few points and this project will extend measurements to varying lithologies, elevations and glaciers in different climatic environments using portable greenhouse gas analysers in conjunction with the EC system. Direct flux measurements will be supported by in-field analysis of debris strucure and composition and subsequent laboratory analysis to determine the minerals, carbon content and microbial communities present in debris covers to uncover controlling processes and determine the relative roles of chemical weathering and microbial activity in carbon gas cycling.</p>

Where now for forest trace gas research?

<p>Forests play an important role in the exchange of radiatively important trace gases with the atmosphere. The past decade has seen remarkable growth in interest in this research area with studies yielding ever-greater insight into both the importance of these exchanges and the fundamental processes of exchange in ecosystems that are vulnerable and highly responsive to agents of global change. I will provide an overview of previous studies that are now global in coverage, which have shown that in both temperate and tropical wetland and upland forests, tree stems constitute significant surfaces of exchange of both methane (CH4) and nitrous oxide (N2O). Considering studies spanning diverse forest biomes across the full latitudinal range of forest extent, leads to emergent questions that this new and developing pan-disciplinary coalition of researchers are increasingly well able to address. Given that forests are both sensitive and highly responsive to agents of global change at a range of scales, there is a need to further characterise the fundamental functioning of exchange processes in forests e.g. with respect to hydrology, climate and the biology of microbes and the trees and soils they inhabit. Such insight will help with planning the next generation of integrative studies, at scale, to enable the role of forests in trace gas cycling in a changing world to be characterised.</p>

Outflows in star-forming galaxies: Stacking analyses of resolved winds and the relation to their hosts’ properties

ABSTRACT Outflows form an integral component in regulating the gas cycling in and out of galaxies, although their impact on the galaxy hosts is still poorly understood. Here we present an analysis of 405 high mass (log M*/M⊙ ≥ 10), star-forming galaxies (excluding AGN) with low inclinations at z ∼ 0, using stacking techniques of the Na D λλ5889, 5895 Å neutral gas tracer in IFU observations from the MaNGA DR15 survey. We detect outflows in the central regions of 78/405 galaxies and determine their extent and power through the construction of stacked annuli. We find outflows are most powerful in central regions and extend out to ∼1Re, with declining mass outflow rates and loading factors as a function of radius. The stacking of spaxels over key galaxy quantities reveals outflow detections in regions of high ΣSFR (≳0.01 M⊙ yr−1 kpc−2) and $\Sigma _{M_{*}}$ (≳107 M⊙ kpc−2) along the resolved main sequence. Clear correlations with ΣSFR suggest it is the main regulator of outflows, with a critical threshold of ∼0.01 M⊙ yr−1 kpc−2 needed to escape the weight of the disc and launch them. Furthermore, measurements of the Hδ and Dn4000 indices reveal virtually identical star formation histories between galaxies with outflows and those without. Finally, through stacking of H i 21 cm observations for a subset of our sample, we find outflow galaxies show reduced H i gas fractions at central velocities compared to their non-detection control counterparts, suggestive of some removal of H i gas, likely in the central regions of the galaxies, but not enough to completely quench the host.