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Coral reefs are iconic ecosystems with immense ecological, economic and cultural value, but globally their carbonate‐based skeletal construction is threatened by ocean acidification (OA). Identifying coral species that have specialised mechanisms to maintain high rates of calcification in the face of declining seawater pH is of paramount importance in predicting future species composition, and growth of coral reefs. Here, we studied multiple coral species from two distinct volcanic CO2 seeps in Papua New Guinea to assess their capacity to control their calcifying fluid (CF) chemistry. Several coral species living under conditions of low mean seawater pH, but with either low or high variability in seawater pH, were examined and compared with those living in 'normal' (non‐seep) ambient seawater pH. We show that when mean seawater pH is low but highly variable, corals have a greater ability to maintain constant pHcf in their CF, but this characteristic was not linked with changes in abundance. Within less variable low pH seawater, corals with limited reductions in pHcf at the seep sites compared with controls tended to be more abundant at the seep site than at the control site. However, this finding was strongly influenced by a single species (Montipora foliosa), which was able to maintain complete pHcf homeostasis. Overall, although our findings indicate that there might be an association between ecological success and greater pHcf homeostasis, further research with additional species and at more sites with differing seawater pH regimes is required to solidify inferences regarding coral ecological success under future OA. [ABSTRACT FROM AUTHOR]

Much dissolved inorganic carbon (DIC) may exist in lacustrine carbonates in the terminal lakes of closed basins in arid areas, and inorganic carbon sinks in arid regions are an important hypothesis of global carbon cycle research in recent years. Previous studies have made significant progress in estimating the inorganic carbon content. However, the source of inorganic carbon sinks remains unclear. Here, we choose four typical arid closed basins in North China to investigate the provenance of inorganic carbon sinks. The results show that CO2 absorbed by saline‐alkaline soil is the main source of groundwater DIC in the study area, with a contribution rate of approximately 50%. Forty‐three groundwater radiocarbon ages from arid closed basins indicate that the DIC in groundwater is transported along the direction of water flow and deposited in terminal lakes, forming inorganic carbon sinks. Our study suggests that the total inorganic carbon contents of Zhuye Lake, Yanchi Lake, Huahai Lake, and Qinghai Lake in the Holocene are 0.318 Pg, 0.003 Pg, 0.160 Pg, and 3.289 Pg, respectively. The results demonstrate that inorganic carbon sinks are much larger than lake organic carbon storage, thereby serving as an important carbon cycle factor in arid regions. Plain Language Summary: As observation methods and experimental technologies have advanced, research on the global carbon cycle has penetrated all links of the Earth's surface system. The long‐neglected arid zone ecosystem exerts a significant impact on the interannual changes in global terrestrial carbon sinks. Despite this, research on the source of inorganic carbon sinks in arid areas is still insufficient. Therefore, age measurements and isotopic analyses are conducted in groundwater, river water and sediments in four arid closed basins of North China, and the main sources of inorganic carbon sinks in arid closed basins are explored. The results show that groundwater dissolved inorganic carbon is mainly derived from the CO2 absorbed by the saline‐alkaline soil through river leakage and irrigation and finally reaches the terminal lakes. Taken together, soil CO2 is one of the leading sources of inorganic carbon sinks in closed basins. Key Points: CO2 absorbed by saline‐alkaline soil is the main source of groundwater dissolved inorganic carbon (DIC) with a contribution rate of about 50%The DIC formed by the carbon absorption of saline‐alkaline soils becomes an inorganic carbon sinkThe rate of Holocene inorganic carbon sinks from lacustrine carbonates is much higher than that of organic carbon accumulation [ABSTRACT FROM AUTHOR]

Kuwait, being one of the leading oil producers in the world, is enriched with CO2 in the atmosphere, despite the frequent dust storms. Rainwater dissolves the atmospheric CO2 that acts as a carbon sink. The different sources for the contribution of CO2 in an arid region like Kuwait were determined by collecting 50 rainwater samples from November 2018 to December 2019. Total CO2, dissolved inorganic carbon (DIC) and pCO2 calculated from the analytical values of rainwater chemistry were distributed spatially to identify the specific areas enriched with CO2. Shuaiba, an industrial region, observed acidic pH (5.69) that led to the highest pCO2 (388ppmV) while Ishbiliya, the residential area, had alkaline pH with the highest DIC and total CO2 as 1147.9 µmole/L and 50.4 mg/L, respectively. The carbonate dust and major neutralizing ions were inferred to govern the DIC and the total CO2 in rainwater. Comparing the rainwater values to that of the groundwater and the seawater reflects similar pCO2 values, but the seawater has very high DIC. The biotic respiration and phytoplankton community influence pCO2 at the ocean-atmospheric interface. This phenomenon alters the transfer of CO2 to the atmospheric sink, thereby CO2 concentration in the rain showers. The statistical analysis of the rainwater chemistry data for samples from both residential and industrial regions predominantly indicated the influence of natural than anthropogenic sources. Samples of the study area and those from different parts of the world were represented in a bivariate plot using Total CO2 and (HCO3−/Ca2+ + Mg2+) variables. It was inferred from the graph that the samples of GCC region fall in a definite range. [ABSTRACT FROM AUTHOR]

We report results for the concentrations and radiocarbon (14C) compositions of dissolved inorganic carbon (DIC) in water samples collected from a north‐south transect in the western North Pacific (NP) Ocean in November 2019 and compare our results with values previously reported for similar transects during the WOCE and CLIVAR projects decades ago. We show that the strong bomb 14C penetration signal in the upper waters has gradually been reduced and diluted by deep water depleted in 14C‐DIC over the last 30 years. The rate of decrease in Δ14C‐DIC values in surface waters was greater from 2005 to 2019 than from 1993 to 2005, and the rates of decrease from 2005 to 2019 were fastest (5.4–7.0‰ yr−1) between 25° and 32°N and slowest (2.1–2.8‰ yr−1) between 13°N and 16°N. The downwelling of the water mass could have accelerated the transport of bomb 14C in the NP subtropical gyre (25°–32°N). The different decadal changes in Δ14C‐DIC in the North Pacific Intermediate Water (NPIW) from north to south prove that bomb 14C is transported southward to the southwestern NP and that the bomb 14C peak likely penetrates the ocean interior gradually. Changes in isopycnic circulation and advection diffusion in deep waters might have resulted in shifts in the baseline Δ14C‐DIC signature. Plain Language Summary: Dissolved inorganic carbon (DIC) in the ocean is the largest pool of exchangeable carbon in the world and plays dominant roles in the global carbon cycle. The North Pacific (NP) Ocean is an important, highly dynamic region that accounts for ∼25% of the annual CO2 global ocean sink from the atmosphere. To study the sources and cycling of DIC in the western NP, we measured radiocarbon, a powerful tracer, in DIC in water samples collected from 26 stations along a transect in the western NP in November 2019. We compared our results with data reported for similar transects in the NP sampled during the World Ocean Circulation Experiment (WOCE) and the Climate Variation and Predictability Program (CLIVAR) decades ago. The large data set enables us to evaluate the decadal changes in DIC concentrations and radiocarbon compositions in the western NP and to gain fresh knowledge about the carbon cycles linked to water circulation and mixing processes in the western NP. Key Points: Strong bomb 14C signals are well mixed into the upper 200–500 m water depth through air‐sea exchange long a transect in the western NP OceanDistribution of radiocarbon in DIC in the Kuroshio Extension region was influenced strongly by Oyashio Currents carrying low Δ14C valuesBomb 14C penetration signal in the NP has been reduced and diluted by deep waters carrying depleted 14C‐DIC over the last 30 years [ABSTRACT FROM AUTHOR]

The Canadian Arctic is warming at three times the rate of the rest of the planet and the effects of climate change on the Arctic marine carbon cycle remains unconstrained. Baffin Bay is a semi-enclosed, Arctic basin that connects the Arctic Ocean to the north to the Labrador Sea to the south. While the physical oceanography of surface Baffin Bay is well characterized, less is known about deep water formation mechanisms within the Basin. Only a few residence-time estimates for Baffin Bay Deep Water (BBDW) exist and range from 20 to 1450 years. Better residence time estimates are needed to understand the oceanographic significance of Baffin Bay. Here we report stable carbon (δ13C) and radiocarbon (Δ14C) values of dissolved inorganic carbon (DIC) collected aboard the CCGS Amundsen in 2019. DIC δ13C and Δ14C values between ranged between -0.7‰ to +1.9‰ and -90.0‰ to +29.8‰, respectively. Surface DIC δ13C values were between +0.7‰ to +1.9‰, while deep (>100m) values were 0.0 to -0.7‰. Surface DIC Δ14C values ranged between -5.4‰ to +22.9‰, while deep DIC (>1400m) DIC Δ14C averaged -82.2 ± 8.5‰ (n = 9). To constrain natural DIC Δ14C values, we quantified the amount of atmospheric “bomb” 14C in DIC (Δ14Cbomb; using the potential alkalinity method; Palk) and anthropogenic DIC (DICanth; using the ΔC* method). Both proxies indicate an absence of Δ14Cbomb and DICanth below 1000m. Using two previously proposed deep water formation mechanisms and our corrected DIC Δ14Cnatural values, we estimated a 14C-based residence time of 360-690 years for BBDW. Based on these residence times, we infer carbon is likely stored for centuries in deep Baffin Bay.

The East Sea (also known as the Japan Sea; hereafter, EJS) has its own deep overturning circulation, that operates over a centurial timescale compared with a millennial timescale in the ocean. This allows the EJS to be used as a natural laboratory for investigating potential future changes in the oceanic system. Dissolved inorganic carbon (DIC), total alkalinity (TA), and pH were measured in 2019 in a wide area of the EJS to investigate the characteristics and changes of the carbonate system since the last extensive survey in 1999. In the layer below ∼1,000 m, DIC and apparent oxygen utilization (AOU) was uniform implying rapid horizontal mixing within a few years. Since 1999, DIC concentration increased by ∼11 μmol kg–1 in the layer deeper than 500 m. This increase accompanied a commensurate increase in AOU with the canonical ratio of 1.3, indicating that the accumulation of DIC was supplied from organic matter decomposition. This observation is consistent with a previous study suggesting that the slowed deep water ventilation was the cause of the increase in AOU and fast acidification. In the EJS, increase in DIC from the surface water to deep waters is much higher than that in TA, which is caused by high primary productivity and export production together with low rates of CaCO3 export. Thus, the DIC/TA ratio of deep waters, an indicator of vulnerability to acidification, is high. A recently reported change in deep water ventilation, namely, re-initiation of deep water formation reaching deeper depths to the Deep Water and the Bottom Water, implies that unexpected changes in the carbonate system may be detected in the future, which needs to be further monitored.

We measured the carbonate system (between 2015 and 2018) in an isolated and a well‐connected temperate estuary, both known for shellfish growth. We evaluated end‐member model estimates of inorganic carbon, alkalinity, pH, mineral saturation states (Ωa), and pH sensitivity (βDIC). We find winter conditions are estimated within observational uncertainty. Spring‐summer primary productivity elevates observed pH and Ωa above theoretical lines, beyond uncertainty. Both estuaries are sensitive in winter and likely to experience rapid pH changes with increased inorganic carbon inputs. Summer pH sensitivity is reduced by productivity and is least sensitive in the midsalinity region. We estimate carbon increased by up to 49 μmol kg−1, since the pre‐industrial period resulting in significant decreases in pH (0.2) and Ωa (0.5). The largest pH decrease occurred outside the minimum buffer zone, at higher salinities where carbon increase was greatest. The largest pH decrease occurred in winter, but the largest Ωa decrease occured in summer. Plain Language Summary: The ocean has absorbed about a third of human carbon dioxide emissions, increasing its acidity. Increasing acidity negatively affects marine organisms such as shellfish and fish that build calcium carbonate structures because they must spend more energy building and maintaining these structures. Most farmed and wild shellfish live in estuarine environments where acidification has not been widely studied. We made complete carbon system measurements over several years and across all seasons, in two distinct estuaries with significant aquaculture, where no previous carbon data existed. We estimated key acidification parameters and evaluated our ability to predict these parameters using only salinity, once properties in the freshest and saltiest water in the systems were well defined in all seasons. Our simple "mixing model" estimates winter conditions well, but during summer, phytoplankton blooms take up carbon and make conditions more favorable than predicted. We found that both estuaries are sensitive to future increases in carbon and are likely to experience rapid changes in chemistry. We estimate that human activity has already caused significant increases in inorganic carbon and associated acidification. The largest change critical to shell‐building organisms has occurred during the summer, and at higher salinities that are typical of grow sites. Key Points: End‐member mixing estimates winter pH and mineral saturation states in temperate estuaries within measurement uncertaintySeasonal productivity keeps pH and mineral saturation states above theoretical mixing curves by up to ∼1 pH and ∼2.5 Ωa, respectivelySince the preindustrial period nearshore estuarine pH declined by 0.05–0.2 with largest decline outside the minimum buffer zone [ABSTRACT FROM AUTHOR]

It is necessary to generate a sustainable strategy for evaluation of carbon leaching risk and organic fertilizer application by studying the effects of different fertilization practices on dissolved carbon leaching along soil profile in the area of lime concretion black soils. Aiming to analyze the contents and distribution of physicochemical, microbial properties, dissolved organic carbon (DOC), and dissolved inorganic carbon (DIC) contents in soil profile based on a 33-year long-term fertilization experiment to select an environmentally friendly organic amendments, five treatments were designed, including mineral fertilization (MF), mineral fertilization combined with low amount wheat straw (MFL), mineral fertilization combined with high amount wheat straw (MFH), mineral fertilization combined with pig manure (MFP), and mineral fertilization combined with cattle manure (MFC), respectively. Results showed that the contents of soil organic carbon, microbial biomass carbon (MBC), and microbial biomass nitrogen (MBN) in the profile at 0-60 cm soil depth were substantiality increased, whereas the values of soil total nitrogen, bulk density and pH value were mainly influenced at 0-20 cm soil depth in the organic amendments treatments compared with MF treatment. Compared with the MF treatment, soil DOC contents at 0-20 cm and >20-40 cm soil depths under long-term organic amendments application treatments were significantly (P<0.05) increased, whereas the values were not significantly increased at >40-60 cm soil depths. In contrast, soil DIC contents under long-term organic amendments application treatments at 0-60 cm depth were significantly (P<0.05) increased compared with the MF treatment. Both the values of UV280 absorption and aromaticity index (AI) at 0-60 cm soil depth were significantly (P<0.05) increased under long-term organic amendments application treatments, especially for the MFC treatment. The values of AI at the 0-20, >20-40, and >40-60 cm soil depths under the MFC treatment were significantly increased by 71.2%, 153.3%, and 38.1%, respectively. It was indicated that soil DOC chemical structure in the whole profile at 0-60 cm soil depth under long-term organic amendments application was greatly influenced and the contents of aromatic compound were increased, which suggested that soil DOC chemical structure under long-term organic amendments application were more complex. Furthermore, stepwise lineal regression showed that the DOC and DIC contents in the profile at 0-60 cm soil depth were regulated by soil pH value and MBC, and the strength of influence soil pH value was larger than soil MBC. Soil DOC chemical structure in the soil profile were mainly influenced by soil MBC. Generally, the type and amount of exogenous organic amendments were the two major factors influencing the characteristics of soil dissolved carbon distribution. The risk of dissolved carbon leaching was aggravated after long-term organic amendments application, especially for pig and cattle manure. Crop straw application is a recommended organic agricultural practice deceasing dissolved carbon leaching risk. [ABSTRACT FROM AUTHOR]

Ocean acidification typically reduces the calcification rates of massive Porites spp. corals, but increasing seawater temperatures (below the stress and bleaching threshold) can offset this effect. Here, we use δ11B to reconstruct the pH of the calcification media (pHECM) used to precipitate the skeleton in poritid corals cultured over a range of seawater pCO2 and at 25 °C and 28 °C. Increasing temperature had no significant effect on pHECM at high pCO2 although corals increased their calcification rates. pHECM was reduced at 28 °C compared to 25 °C at low seawater pCO2, although calcification rates remained constant. Increasing calcification rates could reflect the positive influence of temperature on aragonite precipitation rate, an increase in calcification media saturation state or a change in the concentration/behaviour of the skeletal organic matrix. The two temperatures utilized in this study were within the seasonal range at the coral collection site and do not represent a heat stress scenario. Increasing seawater temperatures may promote calcification in some corals in the future but are unlikely to benefit the majority of corals, which are already living close to their maximum thermal tolerance limits. [ABSTRACT FROM AUTHOR]

Based on long-term dynamic tracing of dissolved inorganic carbon (DIC) and stable carbon isotope (δ13CDIC) in produced water from 20 coalbed methane (CBM) wells in western Guizhou, the spatial-temporal dynamic variations of δ13CDIC of the GP well group produced in multi-layer commingled manner were analyzed, and the relationship between the value of δ13CDIC and CBM productivity was examined. The produced water samples of typical wells in the GP well group were amplified and sequenced using 16S rDNA, and a geological response model of δ13CDIC in produced water from CBM wells with multi-coal seams was put forward. The research shows that: δ13CDIC in produced water from medium-rank coal seams commonly show positive anomalies, the produced water contains more than 15 species of methanogens, and Methanobacterium is the dominant genus. The dominant methanogens sequence numbers in the produced water are positively correlated with δ13CDIC, and the positive anomaly of δ13CDIC is caused by reduction of methanogens, and especially hydrogenotrophic methanogens. Vertical segmentation of sedimentary facies and lithology in stratum with multi-coal seams will result in permeability and water cut segmentation, which will lead to the segmentation of δ13CDIC and archaea community in produced water, so in the strata with better permeability and high water cut, the δ13CDIC of the produced water is abnormally enriched, and the dominant archaea is mainly Methanobacterium. In the strata with weak permeability and low water cut, the δ13CDIC of the produced water is small, and the microbial action is weak. The shallow layer close to the coal seam outcrop is likely to be affected by meteoric precipitation, so the δ13CDIC of the produced water is smaller. The geological response model of δ13CDIC in produced water from multi-coal seams CBM wells in the medium-rank coal reveals the geological mechanism and microbial action mechanism of the δ13CDIC difference in the produced water from the multi-coal seams CBM wells. It also provides effective geochemical evidence for the superimposed fluid system controlled by sedimentary facies, and can also be used for the contribution analysis of the produced gas and water by the multi-layer CBM wells.

Equilibration times of dissolved inorganic carbon (DIC) depend on conversion reactions between CO2(aq) and the dissociation products of carbonic acid [S = (H2CO3) + (HCO3−) + (CO32−)]. Here, we develop analytical equations and a numerical model to calculate chemical equilibration times of DIC during pH transitions in buffered and unbuffered solutions. We approximate the equilibration degree of the DIC reservoir by the smaller of the CO2(aq) and S pools at the new pH, since the smaller pool is always farther from equilibrium during the chemical evolution. Both the amount of DIC converted and the rate of conversion differ between a pH increase and decrease, leading to distinct equilibration times for these general cases. Alkalinity perturbations in unbuffered solutions initially drive pH overshoots (increase or decrease) relative to the new equilibrium pH. The increased rates of DIC conversion associated with the pH overshoot yield shorter equilibration times compared to buffered solutions. Salinity has opposing effects on buffered and unbuffered solutions, decreasing and increasing equilibration times, respectively.

Mangroves are carbon-rich ecosystems that store large quantities of carbon, mostly in soils. Early carbon (C) budgets indicated that >50% of mangrove C fixation was unaccounted for. This ‘missing C’ has now been discovered to be a large release (423 Tg C a−1) of porewater dissolved DIC (dissolved inorganic carbon), dissolved organic carbon (DOC), and total alkalinity (17 TMOL a−1) via lateral export derived from bacterial decomposition of soil organic matter. This large export originates from DIC produced over at least a 1.0–1.5 m soil profile (280–420 Tg C a−1) via decomposition of autochthonous and allochthonous inputs and/or likely mineralization in deep (≥1 m) ancient soils. DOC and DIC export from mangroves equate to 41% and ≈100% of export from the world’s tropical rivers, respectively. A newly revised blue carbon budget for the world’s mangroves indicates a mean ecosystem gross primary production (GPPE) to ecosystem respiration (RE) ratio of 1.35 and a net ecosystem production (NEP) of 794 g C m−2 a−1 (= global NEP of 117 Tg C a−1), reflecting net autotrophy. CORG burial is 5% and 9% of GPPE and NEPE, respectively. Mean RE/GPPE is 0.74 and carbon use efficiency averages 0.57, higher than for tropical humid forests (0.35).

Diagenesis is a double-edged sword of geochemical recordings. It makes us always doubt about the representativeness of many geochemical indicators, especially the isotope and mineral related. It also provides a window to explore the biogeochemical processes at the water–rock interface, which are related to the interactions between the hydrosphere, biosphere, and lithosphere. In this study, we identified microbial early diagenesis in lacustrine ostracods from the Songliao Basin 91.35 million years ago by using in situ mineralogical and carbon isotope analytical methods. Our results suggest multiple biological early-diagenesis processes and the formation of a ferric and methane transition zone (FMTZ) in the sulfate-poor pore water, which are conducive to the formation of dolomite and ankerite. These secondary carbonate minerals related to dissimilatory iron reduction and methanogenesis have heavier carbon isotopic compositions than the calcified ostracod shell in the water column and might bring interferences to the geochemical parameters of ostracods.

Anaerobic oxidation of methane (AOM) is one of the major processes limiting the release of the greenhouse gas methane from natural environments. In Lake Kinneret sediments, iron-coupled AOM (Fe-AOM) was suggested to play a substantial role (10-15% relative to methanogenesis) in the methanic zone (>20 cm sediment depth), based on geochemical profiles and experiments on fresh sediments. Apparently, the oxidation of methane is mediated by a combination of mcr gene bearing archaea and aerobic bacterial methanotrophs. Here we aimed to investigate the survival of this complex microbial interplay under controlled conditions. We followed the AOM process during long19 term (~ 18 months) anaerobic slurry experiments of these methanic sediments with two stages of incubations and additions of 13C-labeled methane, multiple electron acceptors and inhibitors. After these incubation stages carbon isotope measurements in the dissolved inorganic pool still showed considerable AOM (3-8% relative to methanogenesis). Specific lipid carbon isotope measurements and metagenomic analyses indicate that after the prolonged incubation aerobic methanotrophic bacteria were no longer involved in the oxidation process, whereas mcr gene bearing archaea were most likely responsible for oxidizing the methane. Humic substances and iron oxides are likely electron acceptors to support this oxidation, whereas sulfate, manganese, nitrate, and nitrite did not support the AOM in these methanic sediments. Our results suggest in the natural lake sediments methanotrophic bacteria are responsible for part of the methane oxidation by the reduction of combined micro levels of oxygen and iron oxides in a cryptic cycle, while the rest of the methane is converted by reverse methanogenesis. After long-term incubation, the latter prevails without bacterial methanotropic activity and with a different iron reduction pathway. [ABSTRACT FROM AUTHOR]

Subarctic catchments underlain by permafrost sequester a major stock of frozen organic carbon (C), which may be mobilized as the Arctic warms. Warming can impact C export from thawing soils by altering the depth and timing of runoff related to changing storm and fire regimes and altered soil thaw depths. We investigated C export in a first order headwater stream (West Twin Creek) and its receiving third order river (Beaver Creek) in interior Alaska using discrete sampling of dissolved organic and inorganic C (DOC and DIC) and 15‐min collection of specific conductance (SC), fluorescent dissolved organic matter (fDOM) and water discharge (Q). Storm SC‐Q relationships displayed negative slopes, indicating solute limitation and limited influence of seasonal soil thaw on storm runoff chemistry. Concurrently, fDOM‐Q displayed positive slopes that decreased over the summer, indicating flushing of a limited fDOM pool. Baseflow DIC increased over the season concurrent with soil thaw, with higher DIC at the larger scale indicating greater influence of deeper, mineral‐rich flow paths. Storm and seasonal trends were generally similar at both scales. The biggest difference was in fDOM, which displayed higher concentrations and slower depletion in the first order stream. Improved process understanding from this study can be used to better predict carbon export and cycling by stream networks as northern forests and arctic regions continue to warm. Plain Language Summary: As permafrost thaws in high‐latitude environments, carbon may be released from soils and transported to streams or converted to gas and emitted to the atmosphere. We investigated the carbon export to streams by collecting samples and using sensors to monitor carbon continuously in a small stream and larger river. Storms flushed carbon from shallow soils, delivering high loads of organic carbon to streams. The amount of organic carbon that was flushed from catchments generally declined through the summer, but with different trends in the small stream and larger river. The larger river also showed dampened responses and greater inorganic carbon, associated with greater influence of groundwater, multiple contributing catchments, and a large vegetated floodplain. These findings shed light on the disconnect between storm and intra‐storm carbon fluxes that improve our ability to predict future exports with continued arctic thaw. Key Points: Multiple years of discharge, dissolved carbon, specific conductance, and fluorescent dissolved organic matter in nested, subarctic streamsStorms were major sources of dissolved organic and inorganic carbon, with decreasing yields as the summer progressedTrends were similar at the first and third order, with diverse sources, less source limitation, and more groundwater at the larger scale [ABSTRACT FROM AUTHOR]

The atmospheric partial pressure of CO2 (pCO2) has been increasing dramatically since the beginning of the industrial revolution and about 30% of the CO2 produced by anthropogenic activities was absorbed by the ocean. This led to a perturbation of the seawater carbonate chemistry resulting in a decrease of the average surface ocean pH by 0.1 and termed ocean acidification (OA). Projections suggest that pCO2 may reach 900 μatm by the end of the twenty-first century lowering the average pH of the surface ocean by 0.4 units. The negative impacts of OA on many species of marine invertebrates such as mollusks, echinoderms, and crustaceans are well documented. However, less attention has been paid to the impacts of low pH on fitness and immune system in crustaceans. Here, we exposed Pacific white shrimps to 3 different pHs (nominal pH 8.0, 7.9, and 7.6) over a 100-days experiment. We found that, even though there were no significant effects on fitness parameters (survival, growth and allometries between length and weight), some immune markers were modified under low pH. A significant decrease in total hemocyte count and phenoloxidase activity was observed in shrimps exposed to pH 7.6 as compared to pH 8.0; and phagocytosis rate significantly decreased with decreasing pH. A significant increase in superoxide production was also observed at pH 7.6 as compared to pH 8.0. All these results suggest that a 100-days exposure to pH 7.6 did not have a direct effect on fitness but lead to a modulation of the immune response.

The Mississippi River (MR) discharges on average 474 km3 of water annually into the Northern Gulf of Mexico (NGOM) with a large quantity of carbon, playing a vital role in the ecosystem’s food chain and water quality. In this study, we analyzed exports of dissolved inorganic (DIC) and organic carbon (DOC) from January 2021 to December 2021, during which the contiguous United States experienced one of the coldest winters as well as the hottest summer on record. Bi-weekly in situ river measurements and water sampling were conducted in the lower MR at Baton Rouge in Louisiana, USA, approximately 368 km from the river’s mouth. We found that the MR transported 12.61 Tg C of DIC and 4.54 Tg C of DOC into the NGOM during the study period. Much of the DOC mass export occurred during the winter (~38%), while much of the DIC mass export took place in the spring months (~35%). The seasonality of DOC and DIC exports was affected by their concentrations, water temperature, and discharge. DIC concentrations were significantly higher in the fall (32.0 mg L−1) than those during the winter (20.4 mg L−1), while DOC concentrations were highest during the winter months (11.3 mg L−1) and varied seasonally, however, not significantly. Partial pressure of dissolved carbon dioxide (pCO2) in the MR averaged 1703 ± 646 µatm peaking in the summer at 2594 µatm and reaching a low in the winter at 836 µatm. Outgassing of CO2 (FCO2) peaked in the spring averaging 3.43 g C m2 d−1 and was lowest in the winter at 1.62 g C m2 y−1. Our findings validate our initial hypotheses that seasonal variability and weather extremes strongly affect terrestrial-aquatic carbon transfer, and that climate change will likely intensify carbon export from the Mississippi River Basin.

Rivers are important sites for carbon (C) transport and critical components of the global C cycle that is currently not well constrained. However, little is known about C species’ longitudinal and temporal changes in large tropical rivers. The Usumacinta River is Mexico’s main lotic system and the tenth largest in North America. Being a tropical river, it has a strong climatic seasonality. This study aims to evaluate how organic (DOC and POC) and inorganic (DIC and PIC) carbon change spatially and seasonally along the Usumacinta River (medium and lower basin) in rainy (RS-2017) and dry (DS-2018) seasons and to estimate C fluxes into the southern Gulf of Mexico. Concentrations of DOC, POC, DIC, and PIC ranged from 0.88 to 7.11 mg L−1, 0.21 to 3.78 mg L−1, 15.59 to 48.27 mg L−1, and 0.05 to 1.51 mg L−1, respectively. DOC was the dominant organic species (DOC/POC > 1). It was ~doubled in RS and showed a longitudinal increase, probably through exchange with wetlands and floodplains. Particulate carbon showed a positive relationship with the total suspended solids, suggesting that in RS, it derived from surface erosion and runoff in the watershed. DIC is reported for the first time as the highest concentration measured in tropical rivers in America. It was higher in the dry season without a longitudinal trend. The C mass inflow–outflow balance in the RS suggested net retention (DOC and POC sink) in floodplains. In contrast, in the DS, the balance suggested that floodplains supply (C source) autochthonous DOC and POC. The lower Usumacinta River basin is a sink for DIC in both seasons. Finally, the estimated annual C export for the Usumacinta-Grijalva River was 2.88 (2.65 to 3.14) Tg yr−1, of which DIC was the largest transported fraction (85%), followed by DOC (10%), POC (4%), and PIC (

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Previous research has indicated that a potentially large portion of root‐respired CO2 can move internally through tree xylem, but these reports are relatively scarce and have generally been limited to short observations. Our main objective was to provide a continuous estimate of the quantity and variability of root‐respired CO2 that moves either internally through the xylem (FT) or externally through the soil to the atmosphere (FS) over most of a growing season. Nine trees were measured in a Populus deltoides stand for 129 days from early June to mid‐October. We calculated FT as the product of sap flow and dissolved [CO2] in the xylem (i.e., [CO2*]) and calculated FS using the [CO2] gradient method. During the study, stem and soil CO2 concentrations, temperature, and sap flow were measured continuously. We determined that FT accounted for 33% of daily total belowground CO2 flux (i.e., FS + FT; FB) during our observation period that spanned most of a growing season. Cumulative daily FT was lower than FS 74% of the time, equivalent to FS 26% of the time, and never exceeded FS. One‐third of the total CO2 released by belowground respiration over most of the growing season in this forest stand followed the FT pathway rather than diffusing into the soil. The magnitude of FT indicates that measurements of FS alone substantially underestimate total belowground respiration in some forest ecosystems by systematically underestimating belowground autotrophic respiration. The variability in FT observed during the growing season demonstrated the importance of making long‐term, high‐frequency measurements of different flux pathways to better understand physiological and ecological processes and their implications to global change. [ABSTRACT FROM AUTHOR]

The tropical Indian Ocean is a net sink for the carbon dioxide (CO2) in the atmosphere and phytoplankton production plays a crucial role in CO2 fixation and determines the direction of CO2 flux at the sea-to-air interface. In order to assess the influence of phytoplankton composition and primary production on pCO2 levels in the Indian Ocean, sampling was conducted at 25 stations during the spring intermonsoon period under the auspices of the Indian GEOTRACES program. The pCO2 was significantly correlated with salinity due to the discharge of low pCO2 water by major rivers to the Bay of Bengal (BoB). The stronger negative correlation observed between pCO2 and major phytoplankton marker pigments, net primary production and oxygen saturation levels suggesting significant influence of biological processes on pCO2 levels in the Indian Ocean. This study indicates that pCO2 levels are strongly modulated by biological processes than hitherto hypothesized as solubility pump in the Indian Ocean. Research highlights: Surface pCO2 levels are undersaturated in the Indian Ocean compared to atmosphere, except Arabian Sea. Oligotrophic conditions prevailed in the entire tropical Indian Ocean. Picophytoplankton (cyanobacteria) is the dominant phytoplankton in the Indian Ocean. 4.Significant relation between phytoplankton groups and pCO2 indicates strong biological control on surface pCO2. [ABSTRACT FROM AUTHOR]

Copyright of Environmental Science & Technology (10036504) is the property of Editorial Board of Environmental Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The stable isotope ratio of dissolved inorganic carbon (δ13CDIC) in rivers reflects the dominant vegetation type in the surrounding watershed, rates of chemical weathering, atmospheric CO2 fluxes, and the relative rates of photosynthesis and respiration. Reconstructing past δ13CDIC values may reveal changes in these characteristics before watersheds experience land‐use change and/or climate change. This study uses freshwater mussels, Elliptio complanata, and coeval environmental data to assess how high‐resolution changes in the oxygen and carbon isotope ratios of shell carbonate (δ18Oshell and δ13Cshell, respectively) can be used as proxies of paleotemperature and paleo‐DIC in rivers. To test our hypotheses, we analyzed time‐series δ18Oshell and δ13Cshell values, δ13C values in bivalve tissues, and environmental data collected fortnightly from the Neuse River, North Carolina. Shell microsamples milled every 150 μm along the maximum growth axis represent an average of 12 ± 5 days (n = 524; excluding periods of growth cessation of >30 days), which is similar to the environmental data resolution (∼14 days). Serially sampled δ18Oshell and δ13Cshell values did not capture the full range of environmental conditions due to growth cessation during winter shutdown and extreme weather events. Low water temperature and elevated turbidity appear to be significant drivers of growth cessation. Spatial and temporal differences in the amount of metabolic carbon incorporated in the shell (∼0%–44%) likely occur due to variable mussel metabolic rates within and among study sites. Though high‐resolution δ13Cshell values did not reflect variations in δ13CDIC values, average δ13Cshell values were indicative of average δ13CDIC values in the Neuse River. Plain Language Summary: Recently, extreme weather and land‐use change, such as urbanization and agriculture, have transported carbon from land to rivers. Many of these watersheds are affected by pollution, making them unsuitable for recreational activities, including swimming, boating, and fishing. Therefore, understanding carbon transfer from land to rivers is essential for maintaining healthy ecosystems. This study investigates how to reconstruct the carbon sources to rivers before human modification of watersheds. If live freshwater mussel shells record the carbon sources in modern rivers, then historical and fossil shells can be used to reconstruct carbon sources in the past. We compare chemical variations in freshwater mussel shells to chemical variations in the water in which they grew. We found that mussels shells cease growth in winter when the water temperature is cold or during extreme weather events when waters are turbid. Because the mussels do not grow for much of the year, the shells were not reliable recorders of seasonal carbon sources. However, there were similarities the carbon sources measured by the mussel shells and the waters in which they grew during summer months. Therefore, we can use historical and fossil mussel shells to observe broad trends in carbon fluxes in past rivers. Key Points: This study tests the utility of stable isotope ratios in freshwater mussel shells as proxies of paleotemperature and paleo‐dissolved inorganic carbon in riversDespite long periods of shell growth cessation, δ18O values in mussel shells can be used to reconstruct summer water temperaturesThe average δ13C values in mussel shells approximate the average δ13C values of dissolved inorganic carbon in the Neuse River, North Carolina [ABSTRACT FROM AUTHOR]

Research on the ionic chemistry of rivers and weathering types provides the basis for elucidating the dynamics of river chemistry and exploring carbon cycling in river systems. There is a lack of water chemistry study in the river systems in the Tibet Plateau, especially in the streams/rivers flowing from and through glaciers and permafrost. Samples in the rivers flowing through different land covers (lakes, glaciers, permafrost, grasslands, peatlands) were collected in different months (April, June, August and October) in 2016, covering various hydrological regimes. The temporal and spatial dynamic variations of major ions and the underlying causes were explored. The results revealed that in the headwater region Ca2+ and HCO3− were the dominant ions, derived primarily from the dissolution of carbonatites and evaporates. However, the concentrations of ions from different land covers were vastly different.The high concentrations of Na+ and K+ in the lakes sample were mainly affected by evaporation and precipitation. The acid deposition caused by atmospheric pollutants resulted in high concentration of SO42− in glacial and permafrost streams. K+ concentration was high in the grassland region with frequent agricultural activities such as the planting and fertilization of highland barleys that applied nitrogen and potassium fertilizers. Although Total Dissolved Load (TDS) was higher for the lakes and streams/rivers from glaciers and permafrost, and its average (287.28 ± 40 mg/L) over the headwater region was lower than that in the middle and lower reaches of the Yellow River because of low temperature. The current study provided the basis of and reference for the overall water chemistry characteristics and carbon cycling processes of the entire Yellow River. [ABSTRACT FROM AUTHOR]

We report marine dissolved organic carbon (DOC) concentrations, and DOC Δ14C and δ13C values in seawater collected from the Southern Ocean and eastern Pacific GOSHIP cruise P18 in 2016/2017. The aging of 14C in DOC in circumpolar deep water northward from 69°S to 20°N was similar to that measured in dissolved inorganic carbon in the same samples, indicating that the transport of deep waters northward is the primary control of 14C in DIC and DOC. Low DOC ∆14C and δ13C measurements between 1,200 and 3,400 m depth may be evidence of a source of DOC produced in nearby hydrothermal ridge systems (East Pacific Rise). Plain Language Summary: Dissolved organic carbon (DOC) is the most abundant form of reduced carbon in the ocean, and is believed to originate mostly from photosynthesis in surface waters. Yet, the 14C age of DOC is thousands of years old, leaving a gap in our understanding of how long DOC persists in the deep ocean. We find aging of DOC and dissolved inorganic carbon (DIC) in the deep ocean from 69°S to 20°N is equal. We hypothesize that the transport and mixing of deep waters northward is the primary control of 14C in DIC and DOC in circumpolar deep water. Key Points: Dissolved organic carbon (DOC) ages similarly to dissolved inorganic carbon (DIC) in deep water as it flows north from the Southern Ocean to the east PacificThe lowest DOC ∆14C value yet obtained (–578‰) may be the result of input of ancient DOC produced in hydrothermal systemsDeep DOC δ13C are variable and lower close to the East Pacific Rise, supporting that hydrothermal input of DOC is feasible [ABSTRACT FROM AUTHOR]

Radiocarbon (14C) is useful for estimating groundwater ages for transport and water resource exploitation assessment. If the 14C content of dissolved inorganic carbon (14CDIC) is known, the age of groundwater can be estimated by applying a radiocarbon decay equation combined with an appropriate geochemical correction model. However, age determinations are subject to uncertainties caused by parameters which need to be estimated or assumed. Here, we discuss the principles of 14C-based groundwater age estimations and the corrections and errors that affect age determinations differently. Generally, the two factors that impact the results of 14C groundwater age are Type-1 and Type-2 errors. Type-1 errors are pulse-type changes on derived groundwater ages that are independent of the water age. Type-2 errors cause gradual changes on derived groundwater 14C ages that depend on the water age. The cumulative impact of these errors substantively reduces the accuracy and confidence of 14C age determinations and corrections. When using 14C for groundwater age, consideration of both error types along with the use of samples having a range of 14CDIC contents helps practitioners recognize and minimize 14C age uncertainty, especially for groundwater ages of <1000 and >30,000 years B.P. [ABSTRACT FROM AUTHOR]

Ocean acidification (OA) is a global environmental concern, and submarine groundwater discharge (SGD) is a potentially process that enhances OA. This review summarizes the relationship between two types of constituents carried by SGD into China's seawater and OA. 1) Current research predominantly concentrates on constituent fluxes from SGD, neglecting its ecological impacts on carbon and nutrients budgets, as well as the mechanisms between carbon and nutrients. 2) Uncertainties persist in SGD research methods and acidification characterization. 3) There's a need to enhance quantitative research methods of SGD-OA, particularly in areas with intricate biogeochemical processes. Effective identification methods are crucial to quantify SGD's contribution to OA. Investigating core scientific questions, including SGD's impact on OA rates and scales, is paramount. While the primary focus is on SGD-OA research in China, insights gained from novel perspectives could have broader value for coastal management globally. [Display omitted] • Uncertainties exist in SGD and coastal acidification characterization. • Relative paucity of studies on SGD input carbon at different scales in China. • Consider coupling of SGD-carried nutrients and carbon to coastal acidification. • Consider conducting qualitative and quantitative studies on SGD and acidification. [ABSTRACT FROM AUTHOR]

• Unveiling the dissolved inorganic carbon cycle in a karst reservoir through hydrodynamic modeling and δ13C. • The DIC retention capacity is more pronounced under weak hydraulic conditions in HJD. • Significant CO 2 emissions during periods of intense hydrodynamics necessitate close monitoring. • Quantification of DIC flux across diverse hydrodynamic scenarios in a deep subtropical reservoir. • The method (hydrodynamic model and δ13C) is applicable to karst canyon-type reservoir worldwide. Dam construction significantly impacts river hydrodynamics, subsequently influencing carbon biogeochemical processes. However, the influence of hydrodynamic conditions on the migration and transformation of Dissolved Inorganic Carbon (DIC) remains uncertain. To bridge this knowledge gap, we integrated hydrochemistry, isotopic composition (δ13C DIC), and a hydrodynamic model (CE-QUAL-W2) to examine the distinctions, control mechanisms, and environmental effects of DIC biogeochemical processes in a typical large and deep reservoir (Hongjiadu Reservoir) under different hydrodynamic conditions. We evaluated hydrodynamic alterations through the Schmidt stability index and relative water column stability. The analysis disclosed that during weak hydrodynamics periods, the energy necessary for complete mixing the surface and deep water was 34 times higher (3615.32 J/m2 vs.106.86 J/m2), and stability was 13 times greater (312.96 vs. 24.69) compared to periods of strong hydrodynamics. Additionally, the spatiotemporal heterogeneity of DIC concentrations (1.4 % to -9.1 %) and δ13C DIC (-1.7 % to -19.5 %) from the dry to wet seasons reflected disparities in DIC control mechanisms under varied hydrodynamic conditions. Based on model simulations, our calculations indicate that during weak hydrodynamics periods, the enhancement of the biological carbon pump effect resulted in substantial sequestration of DIC, reaching up to 379.6 t-DIC·d−1 in the water. Conversely, during strong hydrodynamics periods, DIC retention capacity decreased by 69.2 t·d−1, resulting in reservoir CO 2 emissions of 22.7 × 104 t, which were more than 7 times higher than during weak hydrodynamics periods (3.2 × 104 t). Our findings emphasize the discernible impact of hydrodynamic conditions on reservoir biogeochemical processes related to DIC. Considering the increasing construction of reservoirs globally, understanding and controlling hydrodynamic conditions are crucial for mitigating CO 2 emissions and optimizing reservoir management. [Display omitted] [ABSTRACT FROM AUTHOR]

Dissolved carbon (DC) in forest streams plays a crucial role in maintaining the structure and productivity of adjoining aquatic ecosystems as well as informing biogeochemical links between mountain forests and adjoining rivers. Nevertheless, the functions of forest stream DC dynamics are rarely incorporated into river management. To better understand the biogeochemical links between subalpine forests and adjoining streams, the seasonal dynamics of DC in 15 representative forest streams were investigated in a geographically fragile subalpine-gorge catchment in the upper reaches of the Yangtze River. Depending on stream characteristics and critical periods, the DC stocks in the streams ranged from 0.22 to 2.35 mg m−2 for total DC, from 0.10 to 1.66 mg m−2 for dissolved inorganic carbon (DIC), and from 0.12 to 1.27 mg m−2 for dissolved organic carbon (DOC). Moreover, the annual stocks of DC, DIC, and DOC were 1.01, 0.56, and 0.45 mg m−2, respectively. Correspondingly, the averaged export rates for DC, DIC, and DOC from the forest streams ranged from 0.27 to 1.98 mg s−1, from 0.24 to 1.48 mg s−1, and from 0.18 to 0.90 mg s−1, respectively, in the subalpine forest catchment. The annual export rates of total DC, DIC, and DOC were 1.06, 0.75, and 0.31 mg C s−1, respectively. In particular, the highest rates of export were 4.67, 3.53, and 1.34 mg s−1 for DC, DIC, and DOC, respectively, in the snowmelt period. The average ratios of DOC to DIC stock in the export water ranged from 0.23–2.41 for the 15 streams, and the average value was 0.85 during this one-year investigation. In addition, the maximum and minimum values of the DC stocks, their exports, and the DIC:DOC ratio were consistently observed during the snowmelt season and the late growing period. In summary, precipitation, temperature, water discharge rate, and sediment depth regulated the stocks and export rates of DC and its components. In general, forest streams are important links between the carbon biogeochemical cycle of subalpine forests and adjoining streams.

Large rivers export a large amount of dissolved inorganic carbon (DIC) and nutrients to continental shelves; and subsequent river-to-sea mixing, eutrophication, and seasonal hypoxia (dissolved oxygen < 2 mg⋅L–1) can further modify DIC and nutrient distributions and fluxes. However, quantitative studies of seasonal carbonate variations on shelves are still insufficient. We collected total alkalinity (TA), DIC, and NO3– data from nine cruises conducted between 2006 and 2010 on the northern Gulf of Mexico continental shelf, an area strongly influenced by the Mississippi and Atchafalaya Rivers. We applied a three-end-member model (based on salinity and potential alkalinity) to our data to remove the contribution of physical mixing to DIC and nitrate distribution patterns and to derive the net in situ removal of DIC and nitrate (ΔDIC and ΔNO3–, respectively). Systematic analyses demonstrated that the seasonal net DIC removal in the near-surface water was strong during summer and weak in winter. The peak in net DIC production in the near-bottom, subsurface waters of the inner and middle sections of the shelf occurred between July and September; it was coupled, but with a time lag, to the peak in the net DIC removal that occurred in the near-surface waters in June. A similar 2-month delay (i.e., January vs. November) could also be observed between their minima. A detailed examination of the relationship between ΔDIC and ΔNO3– demonstrates that net biological activity was the dominant factor of DIC removal and addition. Other effects, such as air–sea CO2 gas exchange, wetland exports, CaCO3 precipitation, and a regional variation of the Redfield ratio, were relatively minor. We suggest that the delayed coupling between eutrophic surface and hypoxic bottom waters reported here may also be seen in the carbon and nutrient cycles of other nutrient-rich, river-dominated ocean margins worldwide.

Climate change globally accelerates the shrinkage of inland lakes, resulting in increases in both water salinity and dissolved inorganic carbon (DIC). The increases of salinity and DIC generate contrasting effects on microbial primary producers and primary production, however, their combined effects remain unclear in aquatic ecosystems. We hypothesized that increased DIC mitigates the constraints of enhanced salinity on microbial primary producers and primary production. To test this, we employed isotope labeling and molecular methods to explore primary production and four dominant types of microbial primary producers (form IA, IB, IC and ID) in lakes on the Tibetan Plateau. Results showed that DIC was positively correlated with the abundance of the form IAB and ID microbial primary producers and primary production (all P < 0.001) and offset salinity constraints. Structural equation models elucidated that DIC substantially enhanced primary production by stimulating the abundance of form ID microbial primary producers. The abundance of form ID primary producers explained more variations (14.6%) of primary production than form IAB (6%) and physicochemical factors (6.8%). Diatoms (form ID) played a determinant role in primary production in the lakes by adapting to high DIC and high salinity. Our findings suggest that inland lakes may support higher primary productivity in future climate change scenarios. [ABSTRACT FROM AUTHOR]

The formation of H 2 CO 3 and HCO 3 − from CO 2 is common in aqueous environmental systems and occurs via the CO 2 hydration and hydroxylation reactions. The reactions are especially important in the context of CaCO 3 mineral precipitation. The reactions carry with them equilibrium and kinetic isotope fractionations that impact paleoclimate proxy records. Herein, quantum mechanical calculations of dissolved inorganic carbon species embedded in H 2 O clusters are analyzed under a transition state theory framework to predict kinetic isotope fractionations associated with the reactions. Experimental measurements of reaction energetics and equilibrium isotope fractionations are well-reproduced by the models which suggests the computational methods are justified. The CO 2 hydration reaction discriminates against 13C by 19–23‰ and against 18O by 14–15‰ at 25 °C. The CO 2 hydroxylation reaction discriminates against 13C by 26–31‰ and against 18O by 27–30‰ at 25 °C. Our analyses of the model isotopic fractionations lead to the conclusion that hydrogen-bonds and C(CO 2)-O(H 2 O or OH−) distances influence the calculated values. We infer that when the model H-bond patterns more realistically represent the aqueous species, the accuracy and precision of equilibrium fractionation factor prediction is improved. Implications for coral carbonate paleothermometry are discussed. Results indicate that hydration and hydroxylation δ13C-δ18O slopes bound the values of slopes form corals and abiotic precipitation experiments, albeit with key uncertainties related to precipitation fractionations. The process of regressing molecular model fractionation results against H-bond patterns as presented here is a promising way to improve isotope fractionation calculations in aqueous systems. [ABSTRACT FROM AUTHOR]

The Canadian Arctic is warming at an unprecedented rate. Warming-induced permafrost thaw can lead to mobilization of aged carbon from stores in soils and rocks. Tracking the carbon pools supplied to surrounding river networks provides insight on pathways and processes of greenhouse gas release. Here, we investigated the dual-carbon isotopic characteristics of the dissolved inorganic carbon (DIC) pool in the main stem and tributaries of the Mackenzie River system. The radiocarbon ( 14 C) activity of DIC shows export of "old" carbon (2,380 ± 1,040 14 C years BP on average) occurred during summer in sampling years. The stable isotope composition of river DIC implicates degassing of aged carbon as CO 2 from riverine tributaries during transport to the delta; however, information on potential drivers and fluxes are still lacking. Accounting for stable isotope fractionation during CO 2 loss, we show that a large proportion of this aged carbon (60 ± 10%) may have been sourced from biospheric organic carbon oxidation, with other inputs from carbonate weathering pathways and atmospheric exchange. The findings highlight hydrologically connected waters as viable pathways for mobilization of aged carbon pools from Arctic permafrost soils., (© The Author(s) 2024. Published by Oxford University Press on behalf of National Academy of Sciences.)

Several findings suggest that CO2 emissions in lakes are not always directly linked to changes in metabolism but can be associated with interactions with the dissolved inorganic carbon equilibrium. Alkalinity has been described as a determining factor in regulating the relative contributions of biological and inorganic processes to carbon dynamics in lakes. Here we analyzed the relationship between metabolic changes in dissolved oxygen (DO) and dissolved inorganic carbon (DIC) at different timescales in eight lakes covering a wide range in alkalinity. We used high-frequency data from automatic monitoring stations to explore the sensitivity of DIC to metabolic changes inferred from oxygen. To overcome the problem of noisy data, commonly found in high-frequency measurements datasets, we used Singular Spectrum Analysis to enhance the diel signal-to-noise ratio. Our results suggest that in most of the studied lakes, a large part of the measured variability in DO and DIC reflects non-metabolic processes. Furthermore, at low alkalinity, DIC dynamics appear to be mostly driven by aquatic metabolism, but this relationship weakens with increasing alkalinity. The observed deviations from the metabolic 1:1 stoichiometry between DO and DIC were strongly correlated with the deviations expected to occur from calcite precipitation, with a stronger correlation when accounting also for the benthic contribution of calcite precipitation. This highlights the role of calcite precipitation as an important driver of CO2 supersaturation in lakes with alkalinity above 1 meq L−1, which represents 57% of the global area of lakes and reservoirs around the world. [ABSTRACT FROM AUTHOR]

Increasing attention has recently been drawn to oxygen depletion and ocean acidification in coastal seas and their impacts on the marine ecosystem. Intensive organic matter degradation combined with weak water exchange is considered to be mainly responsible for bottom water oxygen depletion and acidification. Hypoxia and acidification in the bottom water of Bohai Sea have been frequently observed in summer seasons over the past decade. In this study, monthly surveys were conducted along an inshore-offshore transect in the north Bohai Sea from May to August in 2017 and 2018. The physical structure of the water column in the study area was characterized by a well-mixed surface layer and an essentially homogeneous deep layer that were separated by a strong pycnocline over the period from mid-Jun to late August in both years. Dissolved oxygen (DO), pH, and dissolved inorganic carbon (DIC) in the water column were also split into two layers by the pycnocline and varied little in each layer. No significant interannual variations were observed for the temporal progressions of DO, pH and DIC in the bottom water. Average DO concentration and pH in the bottom water linearly decreased with time from May to August while DIC presented an opposite trend. DO became increasingly unsaturated from mid-June to late August when DO decreased to 96 μmol L–1 and pH to 7.74. The molar ratio of net oxygen consumption to DIC production was 1.42, similar to the Redfield ratio (1.30). Pelagic respiration (>60%) linked to degradation of fresh organic matter prevailed over sediment respiration (

Methane transport from subsurface reservoirs to shallow marine sediment is characterized by unique biogeochemical interactions significant for ocean chemistry. Sulfate-Methane Transition Zone (SMTZ) is an important diagenetic front in the sediment column that quantitatively consumes the diffusive methane fluxes from deep methanogenic sources toward shallow marine sediments via sulfate-driven anaerobic oxidation of methane (AOM). Recent global compilation from diffusion-controlled marine settings suggests methane from below and sulfate from above fluxing into the SMTZ at an estimated rate of 3.8 and 5.3 Tmol year–1, respectively, and wider estimate for methane flux ranges from 1 to 19 Tmol year–1. AOM converts the methane carbon to dissolved inorganic carbon (DIC) at the SMTZ. Organoclastic sulfate reduction (OSR) and deep-DIC fluxes from methanogenic zones contribute additional DIC to the shallow sediments. Here, we provide a quantification of 8.7 Tmol year–1 DIC entering the methane-charged shallow sediments due to AOM, OSR, and the deep-DIC flux (range 6.4–10.2 Tmol year–1). Of this total DIC pool, an estimated 6.5 Tmol year–1 flows toward the water column (range: 3.2–9.2 Tmol year–1), and 1.7 Tmol year–1 enters the authigenic carbonate phases (range: 0.6–3.6 Tmol year–1). This summary highlights that carbonate authigenesis in settings dominated by diffusive methane fluxes is a significant component of marine carbon burial, comparable to ∼15% of carbonate accumulation on continental shelves and in the abyssal ocean, respectively. Further, the DIC outflux through the SMTZ is comparable to ∼20% of global riverine DIC flux to oceans. This DIC outflux will contribute alkalinity or CO2 in different proportions to the water column, depending on the rates of authigenic carbonate precipitation and sulfide oxidation and will significantly impact ocean chemistry and potentially atmospheric CO2. Settings with substantial carbonate precipitation and sulfide oxidation at present are contributing CO2 and thus to ocean acidification. Our synthesis emphasizes the importance of SMTZ as not only a methane sink but also an important diagenetic front for global DIC cycling. We further underscore the need to incorporate a DIC pump in methane-charged shallow marine sediments to models for coastal and geologic carbon cycling.

Cultivation of flooded rice has developed in wetlands of the Cerrado Biome as a result of the expansion of the Brazilian agricultural frontier. Changes in soil moisture content due to agricultural practices associated with flood irrigation may induce geochemical transformations in the soil. The present study aimed at investigating the effect of flood irrigation on inorganic carbon cycling through the determination of dissolved inorganic carbon (DIC) concentrations. Incubation experiments under anoxic and reducing conditions were carried out in laboratory with samples of horizons A, AB, Bf1 and Bf2 of Plinthosols profiles from areas under 20 and 30 year of flood irrigation and natural area of the Irrigation Project Luiz Alves do Araguaia, GO, Brazil. Soil samples under flooding were incubated for 1, 7, 15, 30, 60 and 120 days to simulate the effect of prolonged flooding and after incubation the liquid fraction was analyzed for DIC. Higher concentrations of DIC were found in the A horizon (up to 37.2 mg/L) from soil profiles under cultivation, which may be associated with liming or desorption processes of carbon species. DIC correlated with soil electrical conductivity and Eh. It is concluded that solubilization of inorganic carbon is favored by flood irrigation, especially in Plinthosols that have received liming, as well as by the reducing state of the soil and higher concentrations of ions in solution.

Based on long-term dynamic tracing of dissolved inorganic carbon (DIC) and stable carbon isotope (δ 13C DIC) in produced water from 20 coalbed methane (CBM) wells in western Guizhou, the spatial-temporal dynamic variations of δ 13C DIC of the GP well group produced in multi-layer commingled manner were analyzed, and the relationship between the value of δ 13C DIC and CBM productivity was examined. The produced water samples of typical wells in the GP well group were amplified and sequenced using 16S rDNA, and a geological response model of δ 13C DIC in produced water from CBM wells with multi-coal seams was put forward. The research shows that: δ 13C DIC in produced water from medium-rank coal seams commonly show positive anomalies, the produced water contains more than 15 species of methanogens, and Methanobacterium is the dominant genus. The dominant methanogens sequence numbers in the produced water are positively correlated with δ 13C DIC , and the positive anomaly of δ 13C DIC is caused by reduction of methanogens, and especially hydrogenotrophic methanogens. Vertical segmentation of sedimentary facies and lithology in stratum with multi-coal seams will result in permeability and water cut segmentation, which will lead to the segmentation of δ 13C DIC and archaea community in produced water, so in the strata with better permeability and high water cut, the δ 13C DIC of the produced water is abnormally enriched, and the dominant archaea is mainly Methanobacterium. In the strata with weak permeability and low water cut, the δ 13C DIC of the produced water is small, and the microbial action is weak. The shallow layer close to the coal seam outcrop is likely to be affected by meteoric precipitation, so the δ 13C DIC of the produced water is smaller. The geological response model of δ 13C DIC in produced water from multi-coal seams CBM wells in the medium-rank coal reveals the geological mechanism and microbial action mechanism of the δ 13C DIC difference in the produced water from the multi-coal seams CBM wells. It also provides effective geochemical evidence for the superimposed fluid system controlled by sedimentary facies, and can also be used for the contribution analysis of the produced gas and water by the multi-layer CBM wells. [ABSTRACT FROM AUTHOR]

The Paleocene–Eocene Thermal Maximum (PETM) (55.6 Mya) was a geologically rapid carbon-release event that is considered the closest natural analog to anthropogenic CO2 emissions. Recent work has used boron-based proxies in planktic foraminifera to characterize the extent of surface-ocean acidification that occurred during the event. However, seawater acidity alone provides an incomplete constraint on the nature and source of carbon release. Here, we apply previously undescribed culture calibrations for the B/Ca proxy in planktic foraminifera and use them to calculate relative changes in seawater-dissolved inorganic carbon (DIC) concentration, surmising that Pacific surface-ocean DIC increased by +1,010+1,415−646 µmol/kg during the peak-PETM. Making reasonable assumptions for the pre-PETM oceanic DIC inventory, we provide a fully data-driven estimate of the PETM carbon source. Our reconstruction yields a mean source carbon δ13C of −10‰ and a mean increase in the oceanic C inventory of +14,900 petagrams of carbon (PgC), pointing to volcanic CO2 emissions as the main carbon source responsible for PETM warming. [ABSTRACT FROM AUTHOR]

To meet the global energy demands, the exploitation of coalbed methane has received increasing attention. Biogeochemical parameters of co-produced water from coalbed methane wells were performed in the No. 3 coal seam in the Shizhuangnan block of the southern Qinshui Basin (China). These biogeochemical parameters were firstly utilized to assess coal reservoir environments and corresponding coalbed methane production. A high level of Na+ and HCO3– and deuterium drift were found to be accompanied by high gas production rates, but these parameters are unreliable to some extent. Dissolved inorganic carbon (DIC) isotopes δ13CDIC from water can be used to distinguish the environmental redox conditions. Positive δ13CDIC values within a reasonable range suggest reductive conditions suitable for methanogen metabolism and were accompanied by high gas production rates. SO42–, NO3– and related isotopes affected by various bacteria corresponding to various redox conditions are considered effective parameters to identify redox states and gas production rates. Importantly, the combination of δ 13CDIC and SO42– can be used to evaluate gas production rates and predict potentially beneficial areas. The wells with moderate δ 13CDIC and negligible SO42– represent appropriate reductive conditions, as observed in most high and intermediate production wells. Furthermore, the wells with highest δ 13CDIC and negligible SO42– exhibit low production rates, as the most reductive environments were too strict to extend pressure drop funnels. [ABSTRACT FROM AUTHOR]

Under natural conditions, the dissolved inorganic carbon (DIC) in river water is dominantly derived from carbonate or silicate dissolution by carbonic acid. However, sulfuric and nitric acids produced by human activities provide additional acidity for chemical weathering, which would affect the DIC flux and change its isotopic composition. To identify the natural and anthropogenic impacts on DIC, the major ion concentrations and stable carbon isotopes of the DIC (δ13C-DIC) of river waters were measured in the Pearl River Delta (PRD) region, which is one of the most developed and populated areas in China. The mass balance calculations for DIC-apportionment showed that carbonate dissolution by carbonic acid was the dominant origin of DIC in the Beijiang (BJ) River (67%) and Xijiang (XJ) River (78%) and silicate dissolution by carbonic acid was the dominant origin of DIC in the Guangzhou (GZ) Channel (37%) and Dongjiang (DJ) River (50%), which was related to the lithology of the catchment. The contribution of carbonate dissolution by sulfuric and nitric acids, which represented the contribution of human activities to the total DIC concentrations in river water, showed high proportions in the GZ Channel and DJ River, with averages of 42% and 34%, respectively, which were associated with a high degree of urbanization. Evidence of hydrochemical parameters and δ13C-DIC signatures indicated that human activities had impacts on the DIC pool. Carbonate dissolution by sulfuric and nitric acids caused by human activities changed DIC apportionments rather than the DIC flux, and this part of DIC would ultimately become a source of CO2 to the atmosphere on the geological timescale and affects the CO2 budget. An increase in nutrient concentration due to increased sewage discharge in the urbanized area could promote phytoplankton photosynthesis, which could change the DIC pool and increase the δ13C-DIC value. This study quantitatively highlights the influence of human activities on DIC apportionment in river water, suggesting that anthropogenic impacts should be seriously considered when evaluating the evolution of DIC. [ABSTRACT FROM AUTHOR]

One of the most important questions in the science of global carbon cycle is how to balance the atmospheric CO2 budget. However, there is a large terrestrial carbon sink is missing. The locations, magnitudes, variations, and mechanisms responsible for this terrestrial missing carbon sink are uncertain and the focus of much continuing debate. In order to provide a basis for the assessment of carbonate weathering-related carbon sink, this study investigated the spatial and temporal variations of dissolved inorganic carbon (DIC) and particulate organic carbon (POC), and used stable carbon isotopes and hydrochemical data to quantitatively estimate the proportion of DIC transformation to POC and analyze the potential influence of the transformation of DIC into OC on the carbon isotope composition in the Lijiang River (typical karst surface water), Southwest China. The results showed that DIC concentrations are high in winter and low in summer and increase from upstream to downstream. POC concentrations are high in summer and low in spring. δ13CPOC and δ13CDIC are negatively correlated in the Lijiang River. The δ13CDIC values are high in spring and low in summer, compared with the estimated δ13CDIC(cal.); the observed δ13CDIC values have a maximum positive shift in spring and similar in the summer; the δ13CPOC values decrease from upstream to downstream, and are high in summer and low in spring. These observations indicate that the isotopic compositions of both DIC and POC are significantly affected by aquatic photosynthesis that transforms DIC into OC. In-river primary production contribute 12–54% of POC, and the contributions of carbonate rock-sourced DIC to the riverine POC range from 7 to 30%, which suggests an important sink of atmospheric CO2 in river systems and should be taken into account in global carbon cycle. [ABSTRACT FROM AUTHOR]

Autonomous continuous analysis of oceanic dissolved inorganic carbon (DIC) concentration with depth is of great significance with regard to ocean acidification and climate change. However, miniaturisation of in situ analysis systems is hampered by the size, cost and power requirements of traditional optical instrumentation. Here, we report a low-cost microfluidic alternative based on CO2 separation and conductance measurements that could lead to integrated lab-on-chip systems for ocean float deployment, or for moored or autonomous surface vehicle applications. Conductimetric determination of concentration, in the seawater range of 1000–3000 µmol kg−1, has been achieved using a microfluidic thin-film electrode conductivity cell and a membrane-based gas exchange cell. Sample acidification released CO2 through the membrane, reacting in a NaOH carrier, later drawn through a sub-µL conductivity cell, for impedance versus time measurements. Precision values (relative standard deviations) were ~ 0.2% for peak height measurements at 2000 µmol kg−1. Comparable precision values of ~ 0.25% were obtained using a C4D electrophoresis headstage with similar measurement volume. The required total sample and reagent volumes were ~ 500 µL for the low volume planar membrane gas exchange cell. In contrast, previous conductivity-based DIC analysis systems required total volumes between 5000 and 10,000 µL. Long membrane tubes and macroscopic wire electrodes were avoided by incorporating a planar membrane (PDMS) in the gas exchange cell, and by sputter deposition of Ti/Au electrodes directly onto a thermoplastic (PMMA) manifold. Future performance improvements will address membrane chemical and mechanical stability, further volume reduction, and component integration into a single manifold. [ABSTRACT FROM AUTHOR]

We propose an alternative scheme for the use of 224Ra/228Th disequilibria to investigate carbon and nutrient export from a permeable sandy seabed. Sediment profiles of dissolved 224Ra, total 224Ra and 228Th were determined at two different intertidal sand systems - an intertidal sandy beach near Weitou Bay in Fujian (China), and a tidal sand flat in the Wadden Sea near Cuxhaven (Germany). Dramatic deficit of total 224Ra relative to 228Th was identified in the upper 20 or 30 cm sand layer over the sand systems. We construct a simple two-dimensional advective cycling model to simulate interfacial fluid transport in a sand system that is subject to periodic tidal inundation and swash actions. Based on the 224Ra/228Th disequilibria in the sediment, the model gives estimates of 20.3, 9.1, and 1.9 L m−2 h−1 for water exchange flux at the high tide, mid-tide, and low tide position over the sandy beach at Weitou Bay, respectively. In comparison, the model provides an estimate of 7.2 L m−2 h−1 for water exchange flux at the tidal sand flat in the Wadden Sea. The production of dissolved inorganic carbon (DIC) in porewater is the rate-limiting step for DIC export from the sandy beach into the sea, and can be reasonably simulated as a first-order kinetic reaction. The pattern of interfacial fluid transport over the beach facilitates a horizontal zonation of redox condition in the sediment, which evolves progressively from a fully oxic state at the high tide position to a suboxic state at the low tide position. There is clear evidence of nitrogen loss via denitrification in the suboxic status, and we estimate a nitrogen removal rate of 3.3 mmolN m−2 d−1 at this site. For the two intertidal sand systems, DIC export fluxes range from 20.1 to 89.4 mmolC m−2 d−1, comparable in magnitude to fluxes determined in organic rich estuarine sediments. In the meantime, export fluxes of dissolved inorganic nitrogen (DIN) change from 0.8 to 18.6 mmolN m−2 d−1. Overall, this study suggests that the role of sandy sediments in the biogeochemical cycling of carbon and nutrients needs to be revisited. [ABSTRACT FROM AUTHOR]

Streams in hot, arid environments often exist as a series of isolated pools along main channels. During these periods, shallow alluvial through flow may strongly influence key ecological processes within pools. We measured diel changes in δ13C values of dissolved inorganic carbon (DIC) and dissolved oxygen (DO) in two pools of ephemeral, dryland streams. We quantified alluvial water connectivity through stable isotope analysis (δ18O and δ2H) of pool and alluvial water. We also estimated gross primary productivity (GPP) and ecosystem respiration (ER) rates across a wider set of pools in both streams. δ13CDIC values displayed regular diel cycles, where both pools displayed small but similar daily amplitude (0.7–0.9‰) despite contrasting amplitudes of change in DO (0.8 mg L−1 vs. 2.8 mg L−1) and contrasting alluvial water connectivity (connected vs. disconnected). Water temperature was the strongest predictor of both δ13CDIC values and rates of change in δ13CDIC across both pools. Across both streams, all pools were net heterotrophic. GPP (0.35–1.73 g O2 m−2 d−1) and ER (0.49–2.64 g O2 m−2 d−1) rates were linked to aquatic vegetation cover. The disconnect between diurnal amplitudes of δ13C values and DO concentrations thus suggests that ecological drivers of gas exchange became increasingly localised as pools contracted. [ABSTRACT FROM AUTHOR]