Soil pore space CO2, O2, and apparent respiratory quotient (ARQ) data collected from experimental soil wetting experiments

Soil pore space CO2, O2, and apparent respiratory quotient (ARQ) data are from experimental soil wetting experiments. These laboratory wetting experiments were designed to test how calcite dissolution and precipitation can obscure the CO2 produced by soil respiration in response to rainfall events. Natural soil samples were collected from the University of Texas Stengl Lost Pines Biological Station (Latitude: 30.096°; Longitude -97.171°, Elevation: 145 m a.s.l.). Collected soil was sieved and filled to 25 cm depth into two separate tubs (49 cm long x 34 cm wide x 29 cm high) in the laboratory. Approximately 20 weight percent calcite was mixed into the treatment soil, and the other soil was left untreated. Soil gas samples were collected every four hours from a perforated horizontal gas well installed at 20 cm depth using an automated manifold system. Soil gas samples were dried and then the O2 and CO2 concentrations were measured using a Sable Systems (Las Vegas, Nevada, USA) Field Metabolic System. Temperature drift in the raw O2 data was corrected for by normalizing ambient air O2 measurements to 20.95%. W ARQ values were calculated as the relative difference in soil gas concentrations between the soil and ambient air corrected by a constant that accounts for faster diffusion of O2 through soil pore spaces (ARQ = -0.76*ΔCO2/ΔO2). Rain events were simulated by adding the equivalent of 2 cm and 1 cm of water at the beginning of the experiment and 9 days later

Production-Diffusion modeling results using a Monte Carlo approach to simulate carbon isotope excursions in organic matter and paleosol carbonate during the PETM

Production-Diffusion modeling results using a Monte Carlo approach to simulate carbon isotope excursions in organic matter and paleosol carbonate during the Paleocene-Eocene Thermal Maximum. These modeling experiments were designed to test the effects soil methane oxidation and increased soil respiration rates can have on the carbon isotope values of pedogenic carbonate. The results from four modeling experiments are included. Three methane oxidation experiments that simulate a large methane release over 100, 1000, and 10000 years, respectively, and one soil respiration experiment

Best of Karst

The “Best of Karst” is an annually event organized by the Karst Research Group at the University of South Florida, during which a highly esteemed karst scientist from the US or overseas is presenting a series of lectures, followed by 2 days of field trips highlighting the karst and caves of Central and North Florida. Due to the pandemic, the event went virtual in 2021 and in celebration of the International Year of Caves and Karst we decided to invite five distinguished scientists

Impact of commercial natural gas production on geochemistry and microbiology in a shale-gas reservoir

We consider the effect that commercial gas production has had on microbiology and water and gas geochemistry in the northern producing trend of the Antrim Shale, an unconventional gas reservoir in the Michigan Basin, USA. We analyzed gas, water, and microbial biomass samples collected from seven wells in 2009 and compared our findings to the result of analyses performed as early as 1991 on samples collected from the same wells. We also examined production records associated with six wells. Water production has decreased sharply over time and is currently at 0.2 to 14.6% of peak levels. While this has happened, the chemical and isotopic composition of gas and water produced from the wells has shifted. The proportion of CO[subscript 2] has increased by as much as 15 mole% while CH[subscript 4] content has correspondingly decreased. Isotopically, the δ[superscript 13]C and δD values of CH[subscript 4] decreased for most wells by averages of 1.3‰ and 9‰, respectively, while δ[superscript 13]C values of CO[subscript 2] increased for most wells by an average of 1.7‰. Alkalinity in the water from each well decreased by 10 mM on average and SO[subscript 4][superscript 2−] content increased from below 50 μM to over 200 μM on average in water from each well with initial values. Microorganisms most closely related to CO[subscript 2]-reducing methanogens were the most abundant group in archaeal clone libraries and SO[subscript 4][superscript 2−] reducers were the most abundant group in bacterial libraries. In contrast, no SO[subscript 4][superscript 2−] reducers were identified in a nucleic acid-based analysis of a sample collected in 2002 from one of the wells we sampled . Our results show that commercial gas production has not only caused chemical and isotopic changes in water and gas in the Antrim Shale but also an increase in the abundance of SO[subscript 4][superscript 2−]-reducing microorganisms, a change that can ultimately have a negative impact on biogenic CH[subscript 4] formation. Processes that can explain these changes include ongoing biogeochemical reactions, groundwater flow, gas desorption, and open-system degassing

Best of Karst

The “Best of Karst” is an annually event organized by the Karst Research Group at the University of South Florida, during which a highly esteemed karst scientist from the US or overseas is presenting a series of lectures, followed by 2 days of field trips highlighting the karst and caves of Central and North Florida. Due to the pandemic, the event went virtual in 2021 and in celebration of the International Year of Caves and Karst we decided to invite five distinguished scientists

Intensified aridity in northern China during the middle Piacenzian warm period

Dryland areas are predicted to expand significantly due to global climate change and such expansion would reduce carbon sequestration and enhance warming, forming a positive feedback. However, a contrasting theory is that Earth's thermal equator will move northward in a warm climate, resulting in precipitation increase and dryland shrinking. A study of past warm periods analogous to future climate can help distinguish between these predictions. The middle Piacenzian warm period during similar to 3.3-3 Ma is the best pre-Quaternary analog to late 21st century climate, but Pliocene terrestrial paleoclimatic records that can resolve orbital-timescale variations are scarce. Here we present a pedogenic carbonate oxygen isotope record spanning the entire Pliocene from the Chinese Loess Plateau. The record reveals intensified evaporation-induced aridity during the warm phases of the middle Piacenzian period. These records provide the first evidence demonstrating that intensified evaporation in northern China counteracted any precipitation increase associated with thermal equator migration during the warm periods. These results suggest that Asian drylands will likely expand with future warming, requiring a revision of model simulation which predicts increases in humidity

Quantifying soil-respired CO2 on the Chinese Loess Plateau

Soil respiration is one of the dominant fluxes of CO2 from terrestrial ecosystems to the atmosphere. Accurate quantification of soil respiration is essential for robust projection of future climate variation and for reliable estimation of paleoatmospheric CO2 levels using soil carbonates. Soil-respired CO2, which is the most uncertain factor in estimating atmospheric CO2 concentration, has been calculated from modern observations of surface soils and from proxy indicators of paleosols formed during time periods of known atmospheric CO2. However, these estimations provide a wide range of S(z) values from past to present. To directly compare modern observation with past estimation, here we first monitored soil CO2 profiles in a Holocene profile on the western Chinese Loess Plateau (CLP) for two years, providing direct measurements of soil-respired (CO2 )at the depth where carbonate nodules likely formed. We then collected carbonate nodules below last interglacial paleosol (S1) from two N-S-aligned transects across the CLP to back-calculate soil-respired CO2. The mean back-calculated S(z) from S1 carbonate nodules vary from 539 +/- 87 ppm to 848 +/- 170 ppm in the sections on the northwestern and southeastern CLP, respectively. The mean value of directly measured soil-respired CO2 on the western CLP is 572 + 273 ppm before the onset of summer monsoon, consistent with the back-calculated S(z) in northwestern sections. Our results suggest that spatial S(z) variations are mainly controlled by monsoonal precipitation during the summer season on the CLP. To better constrain the high end of S(z), more monitoring work is needed in higher precipitation areas on the southeastern CLP