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Hamerlynck E.P.,U.S. Department of Agriculture | Scott R.L.,U.S. Department of Agriculture | Sanchez-Canete E.P.,CSIC - Estacion Experimental De Zonas Aridas | Sanchez-Canete E.P.,Centro Andaluz Of Medio Ambiente | Barron-Gafford G.A.,University of Arizona
Journal of Geophysical Research: Biogeosciences | Year: 2013

Despite their prevalence, little attention has been given to quantifying arid land soil and ecosystem carbon fluxes over prolonged, annually occurring dry periods. We measured soil [CO2] profiles and fluxes (F s) along with volumetric soil moisture and temperature in bare interplant canopy soils and in soils under plant canopies over a three-month hot and dry period in a Chihuahuan Desert shrubland. Nocturnal Fs was frequently negative (from the atmosphere into the soil), a form of inorganic carbon exchange infrequently observed in other deserts. Negative Fs depended on air-soil temperature gradients and were more frequent and stronger in intercanopy soils. Daily integrated ecosystem-level Fs was always positive despite lower daily Fs in intercanopy soils due to nocturnal uptake and more limited positive response to isolated rains. Subsurface [CO2] profiles associated with negative Fs indicated that sustained carbonate dissolution lowered shallow-soil [CO2] below atmospheric levels. In the morning, positive surface Fs started earlier and increased faster than shallow-soil Fs, which was bidirectional, with upward flux toward the surface and downward flux into deeper soils. These dynamics are consistent with carbonate precipitation in conjunction with convection-assisted CO2 outgassing from warming air and soil temperatures and produced a pronounced diurnal Fs temperature hysteresis. We concluded that abiotic nocturnal soil CO2 uptake, through a small carbon sink, modulates dry season ecosystem-level carbon dynamics. Moreover, these abiotic carbon dynamics may be affected by future higher atmospheric carbon dioxide levels and predictions of more prolonged and regular hot and dry periods. Keypoints Desert soils had temperature gradient-dependent nocturnal carbon dioxide uptake Shallow subsurface soil carbon dioxide fluxes were sometimes bidirectional Inorganic carbon dynamics showed clockwise diurnal temperature hysteresis ©2013. American Geophysical Union. All Rights Reserved.

Sanchez-Canete E.P.,EEZA | Sanchez-Canete E.P.,Centro Andaluz Of Medio Ambiente | Serrano-Ortiz P.,EEZA | Serrano-Ortiz P.,Centro Andaluz Of Medio Ambiente | And 5 more authors.
Geophysical Research Letters | Year: 2011

Recent studies of carbonate ecosystems suggest a possible contribution of subterranean ventilation to the net ecosystem carbon balance. However, both the overall importance of such CO2 exchange processes and their drivers remain unknown. Here we analyze several dry-season episodes of net CO 2 emissions to the atmosphere, along with soil and borehole CO 2 measurements. Results highlight important events where rapid decreases of underground CO2 molar fractions correlate well with sizeable CO2 release to the atmosphere. Such events, with high friction velocities, are attributed to ventilation processes, and should be accounted for by predictive models of surface CO2 exchange. © 2011 by the American Geophysical Union.

Scott R.L.,U.S. Department of Agriculture | Serrano-Ortiz P.,CSIC - Estacion Experimental De Zonas Aridas | Serrano-Ortiz P.,Centro Andaluz Of Medio Ambiente | Domingo F.,CSIC - Estacion Experimental De Zonas Aridas | And 3 more authors.
Journal of Arid Environments | Year: 2012

Comparing biosphere-atmosphere carbon exchange across monsoon (warm-season rainfall) and Mediterranean (cool-season rainfall) regimes can yield information about the interaction between energy and water limitation. Using data collected from eddy covariance towers over grass and shrub ecosystems in Arizona, USA and Almeria, Spain, we used net ecosystem carbon dioxide exchange (NEE), gross ecosystem production (GEP), and other meteorological variables to examine the effects of the different precipitation seasonality. Considerable crossover behavior occurred between the two rainfall regimes. As expected in these usually water-limited ecosystems, precipitation magnitude and timing were the dominant drivers of carbon exchange, but temperature and/or light also played an important role in regulating GEP and NEE at all sites. If significant rainfall occurred in the winter at the Arizona sites, their behavior was characteristically Mediterranean whereby the carbon flux responses were delayed till springtime. Likewise, the Spanish Mediterranean sites showed immediate pulse-like responses to rainfall events in non-winter periods. The observed site differences were likely due to differences in vegetation, soils, and climatology. Together, these results support a more unified conceptual model for which processes governing carbon cycling in semiarid ecosystems need not differ between warm-season and cool-season rainfall regimes. © 2012.

Cuezva S.,University of Alicante | Fernandez-Cortes A.,CSIC - National Museum of Natural Sciences | Porca E.,Institute Recursos Naturales y Agrobiologia | Pasic L.,University of Ljubljana | And 7 more authors.
FEMS Microbiology Ecology | Year: 2012

The walls and ceiling of Altamira Cave, northern Spain, are coated with different coloured spots (yellow, white and grey). Electron microscopy revealed that the grey spots are composed of bacteria and bioinduced CaCO 3 crystals. The morphology of the spots revealed a dense network of microorganisms organized in well-defined radial and dendritic divergent branches from the central area towards the exterior of the spot, which is coated with overlying spheroidal elements of CaCO 3 and CaCO 3 nest-like aggregates. Molecular analysis indicated that the grey spots were mainly formed by an unrecognized species of the genus Actinobacteria. CO 2 efflux measurements in rocks heavily covered by grey spots confirmed that bacteria-forming spots promoted uptake of the gas, which is abundant in the cave. The bacteria can use the captured CO 2 to dissolve the rock and subsequently generate crystals of CaCO 3 in periods of lower humidity and/or CO 2. A tentative model for the formation of these grey spots, supported by scanning electron microscopy and transmission electron microscopy data, is proposed. © 2012 Federation of European Microbiological Societies. Published by Blackwell Publishing Ltd. All rights reserved.

Foyo-Moreno I.,University of Granada | Foyo-Moreno I.,Centro Andaluz Of Medio Ambiente | Alados I.,University of Malaga | Anton M.,University of Extremadura | And 6 more authors.
Journal of Geophysical Research: Atmospheres | Year: 2014

Under cloudless conditions aerosols are the main atmospheric components responsible for direct effects on solar radiation. Measurements of aerosol optical properties along with simultaneous measurements of solar irradiances (global -G- and diffuse -D-) were recorded at an urban site (Granada, Spain) to characterize the radiative effect of atmospheric aerosols from 2006 to 2008. The selection of cloudless conditions was made considering cases with 0 oktas. To avoid cloud contamination, a restricted data set with clearness index larger than 0.65 and maximum D of 200-W/m2 was used. The analysis was performed evaluating G, D, and IN (direct normal irradiance) and the ratios between them in association with aerosol optical depth (AOD) at 675-nm. Results show an aerosol forcing efficiency of -279-±-21-W/m2 per unit of AOD at 675-nm at 15° solar zenith angle and a maximum value in June for monthly mean aerosol radiative forcing of -23-±-7-W/m 2. Large dependency was shown of the ratios D/G and D/IN which increased with increasing AOD, while IN/G decreased. On the other hand, the ratio D/IN was the most reliable parameter to estimate AOD with a coefficient of determination of 0.94; the empirical relationship obtained was validated using an independent data set obtaining 2.5% mean bias deviation and 13.5% root-mean-square deviation. This relationship constitutes an alternative tool for estimating AOD from routine irradiance measurements available from numerous radiometric stations worldwide. Key Points Estimate of aerosol optical depth from available radiometric measurements Combined characterization of irradiance and aerosol data at an urban location Aerosol radiative forcing is calculated only from global irradiance data © 2014. American Geophysical Union. All Rights Reserved.

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