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The authors have developed an active absorption system combining a molecular sieve with a pressure gradient as a way to overcome the shortcomings of the phosphoric acid solution displacement method. Taking advantage of the pressure gradient produced between the inside and outside of a bottle, as water moves through it, CO2 in the atmosphere can actively be absorbed onto a molecular sieve in its pathway. A comparative study showed that the technique was in agreement with the phosphoric acid displacement method, within error. We applied the new method to collect not only atmospheric CO2 samples, but also CO2 samples from soil respiration to verify its utility. Simple yet practical, our method is well suited to extended collection times in a variety of environments, and capable of providing relatively large amounts of carbon for high-precision accelerator mass spectrometry (AMS) 14C analyses of atmospheric samples. [ABSTRACT FROM AUTHOR]

Attempts to estimate the influence of erosion on the carbon (C) cycle are limited by difficulties in accounting for the fate of mobilized organic material and for the uncertainty associated with land management practices. This study proposes a method to quantify the uncertainty introduced by the influence of land management on soil organic C (SOC) generation and decomposition at eroding soils. The framework is implemented in tRIBS-ECO (Triangulated Irregular Network-based Real-time Integrated Basin Simulator-Erosion and Carbon Oxidation). tRIBS-ECO is a spatially and depth-explicit model of C dynamics coupled with a process-based hydro-geomorphic model. We assess the impact of soil erosion on the net soil-atmosphere CO2 exchange at the Calhoun Critical Zone Observatory, one of the most severely agriculturally eroded regions in the U.S. Measurements of SOC storage are used from different catena positions. We demonstrate that the spatiotemporal variations of land management practices introduce significant uncertainty in estimates of the erosion-induced CO2 exchange with the atmosphere. Observations and simulations suggest that a substantial portion of eroded organic material is buried in alluvial sediments at the study site. According to results, recent reforestation led to a partial decline in soil and SOC erosion rates. It is suggested that the representation of the fine spatiotemporal variability of the dynamics of eroded C is important in the computation of C budgets in regional and global scales. [ABSTRACT FROM AUTHOR]

Alkalinity measurements have used spectrophotometric methods to measure concentrations from small samples, especially for HCO 3 − concentrations in terrestrial water. Nevertheless, the methods still pose challenges such as experimental and calculation complexity, along with the necessity of considering atmospheric CO 2 when preparing standard solutions. This study improved theoretical aspects of the spectrophotometric method based on chemical equilibrium equations combined with PHREEQC, yielding a new approach to alkalinity measurement. The differences between the experimentally obtained HCO 3 − concentration and the calculated value based on the updated chemical equilibrium equation were 0.038–5.4 × 10−6 mg/L. PHREEQC quantified the leaching of atmospheric CO 2 into the samples during experimentation. The effect was negligible at 0.01–0.02 mg/L HCO 3 −. The effect of increased atmospheric CO 2 because of human respiration in the laboratory was estimated as 0.05 mg/L HCO 3 −. These results suggest that the laboratory's experimental and computational steps for atmospheric CO 2 correction can be omitted when natural terrestrial water is targeted. We applied our new approach to various terrestrially derived natural waters (limestone cave drip water, hot spring water, fresh submarine groundwater discharge, groundwater, and river water) for simulations at different titration endpoints (pH 4.8 and 4.3). Differences between the values obtained by hydrochloric acid titration of HCO 3 − concentrations and those calculated using PHREEQC were smaller: less than 1%–7% different concentration for most samples. This study established a method for analyzing small samples of various natural terrestrial waters. • A method for alkalinity measurements (as bicarbonate) was tested. • The method uses spectrophotometric analysis of water samples with small volume. • Correcting bicarbonate concentrations for atmospheric CO 2 in labs is unnecessary. • Necessary sample volumes were 0.1 mL or 0.3 mL, which are useful for many fields. [ABSTRACT FROM AUTHOR]

The authors evaluate the United Nations Intergovernmental Panel on Climate Change (IPCC) consensus that the increase of carbon dioxide in the Earth's atmosphere is of anthropogenic origin and is causing dangerous global warming, climate change and climate disruption. The totality of the data available on which that theory is based is evaluated. The data include: (a) Vostok ice-core measurements; (b) accumulation of CO2 in the atmosphere; (c) studies of temperature changes that precede CO2 changes; (d) global temperature trends; (e) current ratio of carbon isotopes in the atmosphere; (f) satellite data for the geographic distribution of atmospheric CO2; (g) effect of solar activity on cosmic rays and cloud cover. Nothing in the data supports the supposition that atmospheric CO2 is a driver of weather or climate, or that human emissions control atmospheric CO2. [ABSTRACT FROM AUTHOR]

Gradual rise in levels of atmospheric carbon dioxide (CO2) due to burning of fossil fuels has become a matter of environmental concern in the recent years. In this alarming situation capturing CO2 and storing it to restrict its release to the atmosphere could be an attractive approach toward mitigation. Photosynthesis has been recognized as the most sustainable means to arrest CO2 from the atmosphere and microalgae; a photosynthetic microorganism has been identified as the potential sequestering candidate with the highest carbon fixing capabilities. Cyanobacteria and algae have developed their own exclusive editions of photosynthetic carbon concentrating mechanisms (CCMs) to aid ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) in efficient CO2 capture. Carbonic anhydrase (CA), a zinc-containing metallo-enzyme has been observed to play a key role in the CCM by catalysing the reversible hydration of CO2 into bicarbonate and a proton thereby helping in fixation of atmospheric CO2. This review gives an account of the importance of the different types of CA enzymes along with its locations, mechanism of action and the various studies on biosequestration of CO2 through microalgae. © 2016 American Institute of Chemical Engineers Environ Prog, 35: 1605-1615, 2016 [ABSTRACT FROM AUTHOR]

In this paper, we estimate the trends and variability in Advanced Very High Resolution Radiometer (AVHRR)-derived terrestrial net primary productivity (NPP) over India for the period 1982–2006. We find an increasing trend of 3.9% per decade (r = 0.78, R2 = 0.61) during the analysis period. A multivariate linear regression of NPP with temperature, precipitation, atmospheric CO2 concentration, soil water and surface solar radiation (r = 0.80, R2 = 0.65) indicates that the increasing trend is partly driven by increasing atmospheric CO2 concentration and the consequent CO2 fertilization of the ecosystems. However, human interventions may have also played a key role in the NPP increase: non-forest NPP growth is largely driven by increases in irrigated area and fertilizer use, while forest NPP is influenced by plantation and forest conservation programs. A similar multivariate regression of interannual NPP anomalies with temperature, precipitation, soil water, solar radiation and CO2 anomalies suggests that the interannual variability in NPP is primarily driven by precipitation and temperature variability. Mean seasonal NPP is largest during post-monsoon and lowest during the pre-monsoon period, thereby indicating the importance of soil moisture for vegetation productivity.

Meta-analysis is extensively used to synthesise the results of free air CO2 enrichment (FACE) studies to produce an average effect size, which is then used to model likely plant response to rising [CO2]. The efficacy of meta-analysis is reliant upon the use of data that characterises the range of responses to a given factor. Previous meta-analyses of the effect of FACE on plants have not incorporated the potential impact of reporting bias in skewing data. By replicating the methodology of these meta-analytic studies, we demonstrate that meta-analysis of FACE has likely exaggerated the effect size of elevated [CO2] on plants by 20 to 40%; having significant implications for predictions of food security and vegetation response to climate change. Incorporation of the impact of reporting bias did not affect the significance or the direction of the [CO2] effect.

Abstract Current terrestrial ecosystem models are usually driven with global average annual atmospheric carbon dioxide (CO2) concentration data at the global scale. However, high‐precision CO2 measurement from eddy flux towers showed that seasonal, spatial surface atmospheric CO2 concentration differences were as large as 35 ppmv and the site‐level tests indicated that the CO2 variation exhibited different effects on plant photosynthesis. Here we used a process‐based ecosystem model driven with two spatially and temporally explicit CO2 data sets to analyze the atmospheric CO2 fertilization effects on the global carbon dynamics of terrestrial ecosystems from 2003 to 2010. Our results demonstrated that CO2 seasonal variation had a negative effect on plant carbon assimilation, while CO2 spatial variation exhibited a positive impact. When both CO2 seasonal and spatial effects were considered, global gross primary production and net ecosystem production were 1.7 Pg C·yr−1 and 0.08 Pg C·yr−1 higher than the simulation using uniformly distributed CO2 data set and the difference was significant in tropical and temperate evergreen broadleaf forest regions. This study suggests that the CO2 observation network should be expanded so that the realistic CO2 variation can be incorporated into the land surface models to adequately account for CO2 fertilization effects on global terrestrial ecosystem carbon dynamics.

Global atmospheric CO2 distributions were simulated with a chemical transport model (GEOS-Chem) and compared with space-borne observations of CO2 column density by GOSAT from April 2009 to January 2010. The GEOS-Chem model simulated 3-D global atmospheric CO2 at 2°×2.5° horizontal resolution using global CO2 surface sources/sinks as well as 3-D emissions from aviation and the atmospheric oxidation of other carbon species. The seasonal cycle and spatial distribution of GEOS-Chem CO2 columns were generally comparable with GOSAT columns over each continent with a systematic positive bias of ~1.0%. Data from the World Data Center for Greenhouse Gases (WDCGG) from twelve ground stations spanning 90°S-82°N were also compared with the modeled data for the period of 2004-2009 inclusive. The ground-based data show high correlations with the GEOS-Chem simulation (0.66≤R2≤0.99) but the model data have a negative bias of ~1.0%, which is primarily due to the model initial conditions. Together these two comparisons can be used to infer that GOSAT CO2 retrievals underestimate CO2 column concentration by ~2.0%, as demonstrated in recent validation work using other methods. We further estimated individual source/sink contributions to the global atmospheric CO2 budget and trends through 7 tagged CO2 tracers (fossil fuels, ocean exchanges, biomass burning, biofuel burning, net terrestrial exchange, shipping, aviation, and CO oxidation) over 2004-2009. The global CO2 trend over this period (2.1 ppmv/year) has been mainly driven by fossil fuel combustion and cement production (3.2 ppmv/year), reinforcing the fact that rigorous CO2 reductions from human activities are necessary in order to stabilize atmospheric CO2 levels.

The intensively monitored plots in Europe have offered a lot of information with regard to the dynamics of forest ecosystems. A large stock of data is already available as an input to ecological models. The carbon sequestration challenge is a little different from others. It requires long-term studies and additional information from what already exists. So far, apart from the determination of organic C in soils, research in the intensively monitored plots has mainly focused on above ground processes, i.e., crown assessment, phenology, deposition, litterfall, tree growth, and foliar chemistry. All these parameters are valuable and will continue to be so. However, according to the latest literature reviews on the subject, the key to understanding the reaction of trees to climate change lies in the dynamics of belowground processes. Information is needed on nitrogen mineralization rates, soil respiration rates and labile carbon forms in soils. If we take into account that countries pay for their carbon emissions and are paid for carbon sequestration, a research like this can be worth doing. Most importantly, the ecological models can be enriched and therefore be more precise in predicting tree response to climate change.

Understanding what drives the interannual variability (IAV) of the land carbon sink is crucial for improving future predictions of this important, yet uncertain, component of the climate system. While drivers of global and hemispheric-scale net ecosystem exchange (NEE) IAV have been investigated, our understanding of the drivers of NEE IAV at regional scales (e.g. sub-continental, biome-level) is quite poor. Here we explore the biome-level attribution and drivers of North American NEE using inverse estimates derived from a dense network of atmospheric CO _2 observations. We find that deciduous broadleaf and mixed forests are the primary regions responsible for North American NEE IAV, which differs from the ecoregions identified for the globe and Northern Hemisphere. We also find that a suite of terrestrial biosphere models (TBMs) do not agree on the dominant biome contributing to NEE IAV, with TBMs falling along an apparent spectrum ranging between those with IAV dominated primarily by forested ecosystems to those with IAV dominated by non-forested ecosystems. Furthermore, this regional trade-off in TBM NEE IAV is found to be linked to differing regional responses to environmental drivers among TBMs. This work displays the importance of extra-tropical forests in driving continental NEE IAV and also highlights the challenges and limitations of using TBMs to inform regional-scale carbon flux dynamics.

Many studies on drought consider precipitation and potential evapotranspiration (PET) impacts. However, catchment water retention is a factor affecting the interception of precipitation and slowing down runoff which also plays a critical role in determining the risks of hydrological drought. The Budyko framework links retention to the partitioning of precipitation into runoff or evapotranspiration. Applied worldwide, we demonstrate that retention changes are the dominant contribution to measured runoff changes in 21 of 33 major catchments. Similarly, assessing climate simulations for the historical period suggests that models substantially underestimate observed runoff changes due to unrepresented water management processes. Climate models show that water retention (without direct water management) generally decreases by the end of the 21st century, except in dry central Asia and northwestern China. Such decreases raise runoff, mainly driven by precipitation intensity increases (RCP4.5 scenario) and additionally by CO _2 -induced stomata closure (RCP8.5). This mitigates runoff deficits (generally from raised PET under warming) by increasing global mean runoff from −2.77 mm yr ^−1 to +3.81 mm yr ^−1 (RCP4.5), and −6.98 mm yr ^−1 to +5.11 mm yr ^−1 (RCP8.5).

Increasing atmospheric CO2 over the next 200 years will cause the pH of ocean waters to decrease further. Many recent studies have examined the effect of decreasing pH on calcifying organisms in ocean waters and on other biological processes (photosynthesis, nitrogen fixation, elemental ratios, and community structure). In this review, we examine how pH will change the organic and inorganic speciation of metals in surface ocean waters, and the effect that it will have on the interactions of metals with marine organisms. We consider both kinetic and equilibrium processes. The decrease in concentration of OH- and CO32- ions can affect the solubility, adsorption, toxicity, and rates of redox processes of metals in seawater. Future studies are needed to examine how pH affects the interactions of metals complexed to organic ligands and with marine organisms.

The influence of heightened doses of the active UVB radiation at the wavelength λ ≤ 310 nm upon surface and aquatic ecosystems is examined in the article. We show that the CO2 growth in the atmosphere in the1980-90s up to 1.6 million a year occurred under regular growth of the UVB radiation in this period as a result of the ozonosphere continuous volcanogenic depression because of abnormally high frequency of volcano eruptions, spreading their products in the stratosphere. Not only the photosynthetic activity depression in surface and aquatic ecosystems but also the decrease of the ocean absorption property as a result of the essential temperature increasing of its surface approximately by 0.7ºC in this period because of intensive absorption of the rising UVB radiation by dissolved organic substance preditermine the CO2 acceleration of growth.

Atmospheric carbon dioxide (CO 2) concentrations increase due to volcanic emissions, diffuse degassing from fault zones, and various human-caused gas emissions, especially in densely populated urban zones, which play a pivotal role in the ongoing climate change. This study aims to examine changes in the concentration and stable isotopic composition of atmospheric CO 2. A laser-based analyzer provided the δ13C and δ18O values based on concentration measurements for various CO 2 isotopologues. Multiple linear regression (MLR) showed that almost 30% of the atmospheric CO 2 changes are caused by weather variations, while ∼70% of the changes involve CO 2 from various gas sources related to human activities. The Keeling plot approach was used to identify the isotopic signature of the extra CO 2 , which points to the gas produced by hydrocarbon combustion. An isotopic mass balance model was designed to show the relation between excess atmospheric CO 2 and the flux of human-related gas emissions. Calculating the CO 2 flux in the atmosphere based on this isotopic mass balance model showed that several tons of CO 2 move daily between geospheres. This study shows that surveying atmospheric CO 2 in urban zones allows quantifying the CO 2 emissions from various sources. • Anthropogenic CO 2 flux can be estimated by stable isotopic surveying. • Gas emissions from human activities force the atmospheric CO 2. • The monitoring of stable isotopes allows identifying the CO 2 sources in the air. • Several tons per day of CO 2 flow through the geosphere in urban zones. • Transient in the air CO 2 occurs owing to changes in weather variables. [ABSTRACT FROM AUTHOR]

The plastid ndh genes have hovered frequently on the edge of dispensability. They are absent in the plastid DNA of many algae and certain higher plants and present editing sites requiring C-to-U corrections of primary transcripts. The evolutionary origin of editing sites and their loss due to C-to-T reversions at the DNA level are unknown and must be related to the dispensability of the ndh genes in specific environments. In order to better understand the evolution of ndh gene editing sites, we have created expandable data banks with the 12 editing sites of the ndhB gene (600 GenBank sequences) and both editing sites of the ndhF gene (1,600 GenBank sequences). Since their origin via T-to-C mutations that probably occurred between 300 and 200 Myr BP (Permian-Triassic), ndh editing sites have undergone independent and random C-to-T reversions in the different angiosperm lineages. Some of these reversions appear early in angiosperm diversification. Old C-to-T reversions can be traced back to radiation steps that gave origin to main classes, orders and some families.

Abstract Understanding urban carbon cycling is essential given that cities sustain 54% of the global population and contribute 70% of anthropogenic CO2 emissions. When combined with CO2 concentration measurements ([CO2]), stable carbon isotope analyses (δ13C) can differentiate sources of CO2, including ecosystem respiration and combustion of fossil fuels, such as petroleum and natural gas. In this study, we used a wavelength scanned-cavity ringdown spectrometer to collect ∼2x106 paired measurements for [CO2] and δ13C values in Evanston, IL for August 2011 through February 2012. Evanston is located immediately north of Chicago, IL, the third largest city in the United States. The measurements represent one of the longest records of urban [CO2] and δ13C values thus far reported. We also compiled local meteorological information, as well as complementary [CO2] and δ13C data for background sites in Park Falls, WI and Mauna Loa, HI. We use the dataset to examine how ecosystem processes, fossil fuel usage, wind speed, and wind direction control local atmospheric [CO2] and δ13C in a midcontinent urban setting on a seasonal to daily basis. On average, [CO2] and δ13C values in Evanston were 16–23 ppm higher and 0.97–1.13‰ lower than the background sites. While seasonal [CO2] and δ13C values generally followed broader northern hemisphere trends, the difference between Evanston and the background sites was larger in winter versus summer. Mixing calculations suggest that ecosystem respiration and petroleum combustion equally contributed CO2 in excess of background during the summer and that natural gas combustion contributed 80%–94% of the excess CO2 in winter. Wind speed and direction strongly influenced [CO2] and δ13C values on an hourly time scale. The highest [CO2] and lowest δ13C values occurred at wind speeds

This paper presents the comparison of two CO2 datasets from the National Institute for Environmental Studies (NIES) of Japan and the Atmospheric CO2 Observations from Space (ACOS) of NASA for three years (2010 to 2012). Both CO2 datasets are retrieved from the Greenhouse gases Observing SATellite (GOSAT) short-wavelength infrared spectra over High gain surface land. In this three-year period, the yield of the NIES CO2 column averaged dry air mole fractions (XCO2) is about 71% of ACOS retrievals. The overall bias is 0.21 ± 1.85 ppm and -0.69 ± 2.13 ppm for ACOS and NIES XCO2, respectively, when compared with ground-based Fourier Transform Spectrometer (FTS) observations from twelve Total Carbon Column Observing Network (TCCON) sites. The differences in XCO2 three-year means and seasonal means are within about 1 to 2 ppm. Strong consistency is obtained for the ACOS and NIES XCO2 monthly averages time series over different regions, with the greatest mean difference of ACOS to NIES monthly means over China (1.43 ± 0.60 ppm) and the least over Brazil (-0.03 ± 0.64 ppm). The intercomparison between the two XCO2 datasets indicates that the ACOS XCO2 is globally higher than NIES by about 1 ppm and has smaller bias and better consistency than NIES data. [ABSTRACT FROM AUTHOR]

Meta-analysis is extensively used to synthesize the results of free air CO2 enrichment (FACE) studies to produce an average effect size, which is then used to model likely plant response to rising [CO2]. The efficacy of meta-analysis is reliant upon the use of data that characterizes the range of responses to a given factor. Previous meta-analyses of the effect of FACE on plants have not incorporated the potential impact of reporting bias in skewing data. By replicating the methodology of these meta-analytic studies, we demonstrate that meta-analysis of FACE has likely exaggerated the effect size of elevated [CO2] on plants by 20 to 40%; having significant implications for predictions of food security and vegetation response to climate change. Incorporation of the impact of reporting bias did not affect the significance or the direction of the [CO2] effect. [ABSTRACT FROM AUTHOR]

Dendrochronological studies of tree rings in a 250-year-old Qinghai spruce (Picea crassifolia) forest in the Qilian Mountains of northwestern China indicate a 60 % sustained increase in tree-ring growth between 1980 and 2009 compared with any time since 1785. Over the same period, the maximum, minimum, and average temperatures all increased by nearly 2 °C during the growing season (May through September), the frequency of frost decreased 18 days, precipitation remained unchanged, while atmospheric concentrations of CO2 increased by 48 ppm. To explain how the changes in climatic variables might cause the increase in tree growth, we parameterized a process-based growth model (3-PG, physiological processes predicting growth) with values from the literature and performed a series of sensitivity tests. The results of our analysis indicated that a reduction in frost frequency during the growing season, which allows stomata to remain open, enhanced gross photosynthesis by 42 %. Up to a 20 % increase in PG could be attributed to rising atmospheric CO2 between 1980 and 2009, with half of this attributed to increased light interception from a simulated 0.4 increase in canopy leaf area index. The increase in average and maximum temperatures had little direct effect on gross photosynthesis with the optimum temperature set between 9 and 10 °C. Indirectly, the increase in monthly average minimum temperature during the growing season, although small, crossed a threshold that reduced the impact of frost. Our analyses show the value of combining dendrochronological measurements with a process-based model to gain a more holistic understanding of how environmental factors interact to affect tree growth. [ABSTRACT FROM AUTHOR]

Respiratory CO2 emissions from laboratory freshwater microcosms enriched with organic C (glucose and amino acids) and kept in the dark at 24°C were compared to control microcosms without C enrichment for two different freshwater pond sources. The purpose was to estimate experimentally the rate of respiratory CO2 emission from organically polluted freshwater ecosystems compared to non-enriched water. Experiment One, used pond water collected at the Lamont-Doherty Earth Observatory campus; and Experiment Two used pond water, inoculated with natural detritus, obtained from North Carolina. At peak respiration, the net efflux of CO2 (enriched minus control) to the atmosphere was ~ 90 nmol min-1 L-1 (Day 7, Experiment One) and ~ 240 nmol min-1 L-1 (Day 3, Experiment Two). The corresponding net efflux of C to the atmosphere was 25 nmol C min-1 L-1 (Day 7, Experiment One) and 65 nmol C min-1 L-1 (Day 3, Experiment Two). Peak CO2 emissions from the organic-enriched microcosms expressed as μmol m-2 s-1 (as more typically reported for natural bodies of water) were 0.20 for Experiment One, and 0.42 for Experiment Two, at a surface layer depth of approx. 20 cm, i.e. the microcosm depth. There was a relatively large correlation between respiratory CO2 emission and bacterial densities in the organic-C enriched microcosms (r = 0.76), but a smaller correlation (r = 0.32) in the non-enriched, control microcosm. Further broad scale research, robustly sampling natural bodies of organically polluted water, is needed to confirm and better establish the results of the research reported here using microcosms. [ABSTRACT FROM AUTHOR]

Current terrestrial ecosystem models are usually driven with global average annual atmospheric carbon dioxide (CO2) concentration data at the global scale. However, high-precision CO2 measurement from eddy flux towers showed that seasonal, spatial surface atmospheric CO2 concentration differences were as large as 35 ppmv and the site-level tests indicated that the CO2 variation exhibited different effects on plant photosynthesis. Here we used a process-based ecosystem model driven with two spatially and temporally explicit CO2 data sets to analyze the atmospheric CO2 fertilization effects on the global carbon dynamics of terrestrial ecosystems from 2003 to 2010. Our results demonstrated that CO2 seasonal variation had a negative effect on plant carbon assimilation, while CO2 spatial variation exhibited a positive impact. When both CO2 seasonal and spatial effects were considered, global gross primary production and net ecosystem production were 1.7 Pg C·yr-1 and 0.08 Pg C·yr-1 higher than the simulation using uniformly distributed CO2 data set and the difference was significant in tropical and temperate evergreen broadleaf forest regions. This study suggests that the CO2 observation network should be expanded so that the realistic CO2 variation can be incorporated into the land surface models to adequately account for CO2 fertilization effects on global terrestrial ecosystem carbon dynamics. [ABSTRACT FROM AUTHOR]

Estuaries are among the most productive and economically important marine ecosystems at the land-ocean interface and contribute significantly to exchange of CO2 with the atmosphere. Estuarine microbial communities are major links in the biogeochemical C cycle and flow of C in food webs from primary producers to higher consumers. Considerable attention has been given to bacteria and autotrophic eukaryotes in estuarine ecosystems, but less research has been devoted to the role of heterotrophic eukaryotic microbes. Current research is reviewed here on the role of heterotrophic eukaryotic microbes in C biogeochemistry and ecology of estuaries, with particular attention to C budgets, trophodynamics, and the metabolic fate of C in microbial communities. Some attention is given to the importance of these processes in climate change and global warming, especially in relation to sources and sinks of atmospheric CO2, while also documenting the current paucity of research on the role of eukaryotic microbes that contribute to this larger question of C biogeochemistry and the environment. Some recommendations are made for future directions of research and opportunities of applying newer technologies and analytical approaches to a more refined analysis of the role of C in estuarine microbial community processes and the biogeochemical C cycle. [ABSTRACT FROM AUTHOR]

Soil erosion, particularly that caused by agriculture, is closely linked to the global carbon (C) cycle. There is a wide range of contrasting global estimates of how erosion alters soil-atmosphere C exchange. This can be partly attributed to limited understanding of how geomorphology, topography, and management practices affect erosion and oxidation of soil organic C (SOC). This work presents a physically based approach that stresses the heterogeneity at fine spatial scales of SOC erosion, SOC burial, and associated soil-atmosphere C fluxes. The Holcombe's Branch watershed, part of the Calhoun Critical Zone Observatory in South Carolina, USA, is the case study used. The site has experienced some of the most serious agricultural soil erosion in North America. We use SOC content measurements from contrasting soil profiles and estimates of SOC oxidation rates at multiple soil depths. The methodology was implemented in the tRIBS-ECO (Triangulated Irregular Network-based Real-time Integrated Basin Simulator-Erosion and Carbon Oxidation), a spatially and depth-explicit model of SOC dynamics built within an existing coupled physically based hydro-geomorphic model. According to observations from multiple soil profiles, about 32% of the original SOC content has been eroded in the study area. The results indicate that C erosion and its replacement exhibit significant topographic variation at relatively small scales (tens of meters). The episodic representation of SOC erosion reproduces the history of SOC erosion better than models that use an assumption of constant erosion in space and time. The net atmospheric C exchange at the study site is estimated to range from a maximum source of 14.5 g m−2 yr−1 to a maximum sink of −18.2 g m−2 yr−1. The small-scale complexity of C erosion and burial driven by topography exerts a strong control on the landscape's capacity to serve as a C source or a sink. [ABSTRACT FROM AUTHOR]

Nitrogen (N) deposition and changing climate patterns in the northeastern USA can influence forest productivity through effects on plant nutrient relations and water use. This study evaluates the combined effects of N fertilization, climate and rising atmospheric CO2 on tree growth and ecophysiology in a temperate deciduous forest. Tree ring widths and stable carbon (δ13C) and oxygen (δ18O) isotopes were used to assess tree growth (basal area increment, BAI) and intrinsic water use efficiency (iWUE) of Quercus velutina Lamb., the dominant tree species in a 20+ year N fertilization experiment at Harvard Forest (MA, USA). We found that fertilized trees exhibited a pronounced and sustained growth enhancement relative to control trees, with the low- and high-N treatments responding similarly. All treatments exhibited improved iWUE over the study period (1984–2011). Intrinsic water use efficiency trends in the control trees were primarily driven by changes in stomatal conductance, while a stimulation in photosynthesis, supported by an increase in foliar %N, contributed to enhancing iWUE in fertilized trees. All treatments were predominantly influenced by growing season vapor pressure deficit (VPD), with BAI responding most strongly to early season VPD and iWUE responding most strongly to late season VPD. Nitrogen fertilization increased Q. velutina sensitivity to July temperature and precipitation. Combined, these results suggest that ambient N deposition in N-limited northeastern US forests has enhanced tree growth over the past 30 years, while rising ambient CO2 has improved iWUE, with N fertilization and CO2 having synergistic effects on iWUE. [ABSTRACT FROM AUTHOR]

Explanations of the glacial-interglacial variations in atmospheric pCO2 invoke a significant role for the deep ocean in the storage of CO2. Deep-ocean density stratification has been proposed as a mechanism to promote the storage of CO2 in the deep ocean during glacial times. A wealth of proxy data supports the presence of a "chemical divide" between intermediate and deep water in the glacial Atlantic Ocean, which indirectly points to an increase in deep-ocean density stratification. However, direct observational evidence of changes in the primary controls of ocean density stratification, i.e., temperature and salinity, remain scarce. Here, we use Mg/Ca-derived seawater temperature and salinity estimates determined from temperature-corrected δ18O measurements on the benthic foraminifer Uvigerina spp. from deep and intermediate water-depth marine sediment cores to reconstruct the changes in density of sub-Antarctic South Atlantic water masses over the last deglaciation (i.e., 22-2 ka before present).We find that a major breakdown in the physical density stratification significantly lags the breakdown of the deep-intermediate chemical divide, as indicated by the chemical tracers of benthic foraminifer δ13C and foraminifer/ coral 14C. Our results indicate that chemical destratification likely resulted in the first rise in atmospheric pCO2,whereas the density destratification of the deep South Atlantic lags the second rise in atmospheric pCO2 during the late deglacial period. Our findings emphasize that the physical and chemical destratification of the ocean are not as tightly coupled as generally assumed. [ABSTRACT FROM AUTHOR]

The history of life on Earth is punctuated by a series of mass extinction episodes that vary widely in their magnitude, duration, and cause. Biomarkers are a powerful tool for the reconstruction of historical environmental conditions and can therefore provide insights into the cause and responses to ancient extinction events. In examining the five largest mass extinctions in the geological record, investigators have used biomarkers to elucidate key processes such as eutrophy, euxinia, ocean acidification, changes in hydrological balance, and changes in atmospheric CO2. By using these molecular fossils to understand how Earth and its ecosystems have responded to unusual environmental activity during these extinctions, models can be made to predict how Earth will respond to future changes in its climate. [ABSTRACT FROM AUTHOR]

The elevation and extent of coastal marshes are dictated by the interplay between the rate of relative sea-level rise (RRSLR), surface accretion by inorganic sediment deposition, and organic soil production by plants. These accretion processes respond to changes in local and global forcings, such as sediment delivery to the coast, nutrient concentrations, and atmospheric CO2, but their relative importance for marsh resilience to increasing RRSLR remains unclear. In particular, marshes up-take atmospheric CO2 at high rates, thereby playing a major role in the global carbon cycle, but the morphologic expression of increasing atmospheric CO2 concentration, an imminent aspect of climate change, has not yet been isolated and quantified. Using the available observational literature and a spatially explicit ecomorphodynamic model, we explore marsh responses to increased atmospheric CO2, relative to changes in inorganic sediment availability and elevated nitrogen levels. We find that marsh vegetation response to foreseen elevated atmospheric CO2 is similar in magnitude to the response induced by a varying inorganic sediment concentration, and that it increases the threshold RRSLR initiating marsh submergence by up to 60% in the range of forcings explored. Furthermore, we find that marsh responses are inherently spatially dependent, and cannot be adequately captured through 0-dimensional representations of marsh dynamics. Our results imply that coastal marshes, and the major carbon sink they represent, are significantly more resilient to foreseen climatic changes than previously thought. [ABSTRACT FROM AUTHOR]

The elevation and extent of coastal marshes are dictated by the interplay between the rate of relative sea-level rise (RRSLR), surface accretion by inorganic sediment deposition, and organic soil production by plants. These accretion processes respond to changes in local and global forcings, such as sediment delivery to the coast, nutrient concentrations, and atmospheric CO2, but their relative importance for marsh resilience to increasing RRSLR remains unclear. In particular, marshes up-take atmospheric CO2 at high rates, thereby playing a major role in the global carbon cycle, but the morphologic expression of increasing atmospheric CO2 concentration, an imminent aspect of climate change, has not yet been isolated and quantified. Using the available observational literature and a spatially explicit ecomorphodynamic model, we explore marsh responses to increased atmospheric CO2, relative to changes in inorganic sediment availability and elevated nitrogen levels. We find that marsh vegetation response to foreseen elevated atmospheric CO2 is similar in magnitude to the response induced by a varying inorganic sediment concentration, and that it increases the threshold RRSLR initiating marsh submergence by up to 60% in the range of forcings explored. Furthermore, we find that marsh responses are inherently spatially dependent, and cannot be adequately captured through 0-dimensional representations of marsh dynamics. Our results imply that coastal marshes, and the major carbon sink they represent, are significantly more resilient to foreseen climatic changes than previously thought. [ABSTRACT FROM AUTHOR]

Active remote sensing of atmospheric XCO2 has several advantages over existing passive remote sensors, including global coverage, a smaller footprint, improved penetration of aerosols, and night observation capabilities. China is planning to launch a multi-functional atmospheric observation satellite equipped with a CO2-IPDA (integrated path differential absorption Lidar) to measure columnar concentrations of atmospheric CO2 globally. As space and power are limited on the satellite, compromises have been made to accommodate other passive sensors. In this study, we evaluated the sensitivity of the system’s retrieval accuracy and precision to some critical parameters to determine whether the current configuration is adequate to obtain the desired results and whether any further compromises are possible. We then mapped the distribution of random errors across China and surrounding regions using pseudo-observations to explore the performance of the planned CO2-IPDA over these regions. We found that random errors of less than 0.3% can be expected for most regions of our study area, which will allow the provision of valuable data that will help researchers gain a deeper insight into carbon cycle processes and accurately estimate carbon uptake and emissions. However, in the areas where major anthropogenic carbon sources are located, and in coastal seas, random errors as high as 0.5% are predicted. This is predominantly due to the high concentrations of aerosols, which cause serious attenuation of returned signals. Novel retrieving methods must, therefore, be developed in the future to suppress interference from low surface reflectance and high aerosol loading.

• High atmospheric p CO 2 levels, constrained by the paired C-isotopic compositions of carbonate and organic carbon from ∼1.6 Ga Gaoyuzhuang Formation, could have played an important role in compensating for the low solar luminosity and maintaining the temperature of the Mesoproterozoic Earth's surface. It is hypothesized that the Mesoproterozoic was characterized by a prevailing warm climate and a high atmospheric p CO 2 level. However, quantitative constraints on Mesoproterozoic atmospheric p CO 2 are scarce. Here, we report high-resolution organic and inorganic carbon isotope records from sediment samples aged ∼1.6 Ga, collected from Hebei Province in North China. The δ13C org values of these Mesoproterozoic samples vary from −28.4‰ to −34.3‰, and the δ13C carbonate values range from −2.1‰ to 0.4‰. The paired carbonate and organic carbon isotope records can be used as a proxy to quantify the atmospheric CO 2 concentration during the Mesoproterozoic. According to the calibration between the photosynthetic isotopic effect and atmospheric CO 2 , atmospheric CO 2 concentrations are estimated to be within the range of 910–18,800 ppmv, ∼2–50 times greater than the present atmospheric level. The results support the previous hypothesis which suggests that high levels of atmospheric CO 2 prevailed in the Early Mesoproterozoic. High atmospheric pCO 2 levels could have played an important role in compensating for the possible lower solar luminosity and maintaining the temperature of the Mesoproterozoic Earth's surface. [ABSTRACT FROM AUTHOR]

This study documents new stromatolite deposits from the Anisian succession of the Guanling Formation in the Boyun section of eastern Yunnan Province, southwestern China. The Boyun stromatolites are characterized by undulating laminations, which yield a variety of biostructures and abiotic grains, such as cyanobacteria Bevocastria and Renalcis , microclots, fecal pellets, coccoid-like spheroids, and authigenic quartz. Filamentous cyanobacteria Bevocastria are likely the major builder constructing the Boyun stromatolite build-ups. Stromatolites in the Boyun section likely grew in an open, oxic marine environment, differing from the Lower Triassic stromatolites that were mostly formed in relatively oxygen-poor conditions of shallow marine settings, strengthening the view that stromatolites are not necessarily indicative of harsh environments. In addition, the global dataset of cyanobacteria filament sizes through the Triassic deciphers that a pronounced increase in the diameter of filamentous cyanobacteria through the Early-Middle Triassic, followed by a decline during the Late Triassic. The developments of marine deoxygenation in the Early Triassic and Rhaetian broadly coincided with the reduction in cyanobacteria filament diameter, suggesting a possible causal link between the two. Our data also show that the diversity of cyanobacteria does not show a significant correlation relationship with any modeled estimates of CO 2 , indicating that their might be more complex when CO 2 levels below ∼2800 ppm (10 times present atmospheric level). • New Anisian (Middle Triassic) stromatolites from Yunnan Province, Southwest China are reported. • Filamentous cyanobacteria Bevocastria are major builder constructing the Boyun stromatolites. • Cyanobacteria filaments diameter increase through the Early-Middle Triassic, followed by a decline during the Late Triassic. [ABSTRACT FROM AUTHOR]

A geological history of pedogenic salts and their microbiomes can now be reconstructed from a review of thousands of described paleosols ranging in age back 3700 Ma. The current diversity of evaporite minerals within paleosol gypsic (By) horizons may have begun with kieserite (MgSO 4.H 2 O at 3700 Ma), then barite (BaSO 4 at 3458 Ma), and gypsum (CaSO 4.2H 2 O at 3217 Ma). Pedogenic carbonate of calcic (Bk) horizons appeared later, first nahcolite (NaHCO 3 at 3016 Ma), then dolomite ((Mg,Ca)(CO 3) 2 at 2403 Ma), and low-magnesium calcite (CaCO 3 at 1460 Ma). The earliest occurrence of each salt is shallow in paleosol profiles (12–25 cm), but deeper (50–100 cm) salt horizons (By and Bk) horizons appear later in the Proterozoic and Paleozoic. These changes can be normalized for estimated differences in mean annual precipitation in the same paleosol from both depth to salts and from chemical composition, which demonstrated that depth to salts and soil productivity measured as respired carbon dioxide showed unchanged relationship with mean annual precipitation in deep time. Stepwise increases in soil respiration through time inferred from depth of soil salts reflects evolving soil microbiomes and atmospheric composition cued to major advances in the evolution of life on land, such as the evolution of anaerobic, then aerobic photosynthetic microbes, then land plants, and trees. [Display omitted] • Archean paleosols contain desert roses of kieserite (3700 Ma), barite (3458 Ma), gypsum (3217 Ma). • Pedogenic carbonate appeared later: nahcolite (3016 Ma), dolomite (2403 Ma), and calcite (1460 Ma). • The earliest occurrence of each salt is shallow (12–25 cm) in paleosol profiles. • Deeper salt horizons appear later with Paleozoic non-vascular land plants and then trees. • The fossil record of soil salts reflects evolving soil microbiomes and evolution of life on land. [ABSTRACT FROM AUTHOR]