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The CO2 characteristics of the Semarang Bay system on the Northern coast of Java were investigated to understand the roles in carbon dioxide flux. The flux of carbon dioxide at the sea surface between seawater and atmosphere is essential for mitigating atmospheric CO2. The aims of this study were to assess the variation of CO2 partial pressure seawater (pCO2sea) and CO2 flux and to analyse the water quality variable which has the larger influence on CO2 flux in the waters of Semarang Bay. The variables in this study were temperature, pH, salinity, and DO. Different methods were adopted in the analysis of water samples: spectrophotometric to measure chlorophyll-a and phosphate and titration method to measure Total Alkalinity (TA) and Dissolved Inorganic Carbon (DIC). A CO2 meter was used to measure the CO2atm. The lowest CO2 flux value was (1.86 mmol CO2 m-2 day-1) during the morning period while the pCO2sea reached 461.04 µatm and CO2 flux 83.79 mmol CO2 m-2 day-1 at night. At noon time, with increased temperature, pCO2sea was 461.04 µatm, and CO2 flux was 83.79 mmol CO2 m-2 day-1. The high concentration of chlorophyll-a ranged between 3.55-4.11 mg.L-1. This chlorophyll-a concentration has a negative correlation with CO2 flux, and it was found that TA and DIC concentrations have no relationship with CO2 flux. Based on PCA analysis, it was found that the variability of CO2 flux in Semarang Bay is influenced by the variability of pCO2sea, sea surface temperature and kwa (affected by wind speed). [ABSTRACT FROM AUTHOR]

The response of coastal systems to global acidification depends strongly on river inputs, which can alter the total alkalinity (AT) and dissolved inorganic carbon (DIC) in seawater. The northern Adriatic Sea (NAd) is a shallow continental shelf region that currently receives about 15% of the total freshwater input in the Mediterranean Sea, where the role of riverine discharges on the carbonate system has been poorly studied. In particular, river discharges can alter the carbonate system in the sea, affecting both the equilibrium chemistry and biological processes. For the main rivers flowing into the NAd (the Po, Adige, Brenta, Piave, Livenza, Tagliamento, Isonzo, Timavo and Rižana), data were collected for the pH, concentrations of the total alkalinity (AT), Ca2+ and Mg2+ and the isotopic ratio of stable carbon in the dissolved inorganic carbon (δ13CDIC). The DIC fluxes were estimated using the THINCARB (THermodynamic modeling of INOrganic CARBon) model for the compilation of the AT and pH data. The results show that the total transport of the AT in the rivers was 205 Gmol yr−1 while the transport of the DIC was 213 Gmol yr−1, of which about 70% was from the Po River. About 97% of the DIC in the river waters was in the form of bicarbonates. The high Mg2+/Ca2+ ratios indicate that dolomite weathering is predominant in the Adige, Piave, and Livenza river basins, while lower ratios in the Timavo and Rižana rivers indicate a greater proportion of calcite. The mean δ13C-DIC value was estimated to be −10.0 ± 1.7 ‰, a value nowadays considered typical for the DIC flux inputs in oceanic carbon cycle modeling. The DIC flux depends on the mineral weathering and biological activity in each river basin. However, these natural processes can be modified by anthropogenic disturbances that should be better quantified. [ABSTRACT FROM AUTHOR]

Multi‐decadal trends of the total dissolved inorganic carbon (DIC) concentrations and consequent ocean acidification in surface seawater were investigated on the basis of data from shipboard measurements conducted since 1996 along the 165°E repeat line in the western North Pacific. The observed trends exhibited clear meridional variabilities, with higher rates in the subtropical and tropical zones and lower rates in the subarctic zone, with a DIC range from +0.09 ± 0.14 to +1.64 ± 0.16 μmol kg−1 yr−1 and pH range from −0.0023 ± 0.0034 to −0.0281 ± 0.0059 decade−1. DIC and acidification trends were consistent with those expected from the atmospheric CO2 concentrations at nearly all latitudinal zones, but were significantly different at some latitudes. We attribute the significantly lower rates observed in the central western Subarctic Gyre and southern Subtropical Gyres primarily to the variabilities in upward DIC supply from the subsurface associated with the variability in ocean circulation. However, the higher rate observed to the south of the Kuroshio Extension appears to have been caused by the change in winter vertical mixing related to the change in its stable/unstable paths. Plain Language Summary: CO2 uptake by the ocean leads to a change in the state of CO2 chemistry in seawater, commonly referred to as "ocean acidification," and also plays an important role in mitigating global warming by reducing the atmospheric CO2 concentration. To project future ocean acidification under different socio‐economic scenarios, we need to understand the current trends in oceanic CO2 concentrations and acidification and the impact of climate change on these trends. Based on the data obtained from shipboard observations extending from the subarctic to equatorial zones in the western North Pacific over the last 25 years, we observed a clear meridional variability in ocean acidification trends, which was generally consistent with the trends expected from the increase in the atmospheric CO2 concentration. However, in some regions, the trends in oceanic CO2 concentration and acidification in surface seawater are likely influenced by the temporal variability in ocean circulation, in addition to the atmospheric CO2. These results suggest that the sensitivity of ocean acidification trends to climate change varies greatly between oceanic regions within the western North Pacific. Key Points: Meridional variability was found in the trends of dissolved inorganic carbon in the surface layer along the 165°E repeat lineExtremely slow rates of increase observed in the subarctic and tropics are attributed to ocean circulation variabilityA fast increase in the south of the Kuroshio Extension is likely associated with the variability in its path [ABSTRACT FROM AUTHOR]

Inland surface water plays an important role in global carbon cycling, which responds to transformation between dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC). Studies have shown that algae in karst lakes and reservoirs can convert DIC to organic matter (OM) and form stable carbon sinks via photosynthesis. However, the pathways of conversion of inorganic carbon to organic carbon during algal growth remain unclear and need further investigation. In this study, spectroscopic techniques were applied to investigate the variations in algal organic matter (AOM) composition in the growth metabolism of Chlorella vulgaris and Scenedesmus obliquus under simulated karst water condition. The results showed that algal extracellular organic matter (EOM) contained high DIC concentration during the adaptation phase, which formed the carbon source for algal photosynthesis. In addition, DOC in algae increased after entering the stationary phase, while more OM was released into water. As algal growth proceeded, the amino groups in EOM were consumed to produce more aromatic protein-like material, while more lipid material was produced in intracellular organic matter (IOM). The spectral characterization results could intuitively determine AOM dynamics in different growth stages of algae, which can be used for establishing effective approaches for detecting organic carbon variations and responding to regional carbon cycling in karst water.

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. [ABSTRACT FROM AUTHOR]

We report on diurnal, tidal, and seasonal variations of dissolved inorganic carbon (DIC), water partial pressure of CO2 (pCO2), and associated water–air CO2 fluxes in a tidal creek of a temperate coastal lagoon with 70% of intertidal flats, during eight tidal/diurnal cycles and two consecutive years covering all seasons. Surface waters of the lagoon were always slightly oversaturated in CO2 with respect to the atmosphere with an average pCO2 value of 496 ± 36 ppmv. Seasonally, subsurface water pCO2 values were controlled by both temperature and biological/tidal advection effects that compensated each other and resulted in weak annual variations. High-resolution temporal pCO2 records reveal that the highest fluctuations (192 ppmv) occurred at the tidal/diurnal scale as a result of biological activity, advection from the tidal flat, and porewater pumping that all contributed to water pCO2 and carbonate chemistry variations. Total alkalinity (TA) versus salinity plots suggest a net production of alkalinity in the lagoon attributed to benthic carbonate dissolution and/or anaerobic degradation of organic matter. We specifically highlighted that for the same salinity range, during flooding, daytime pCO2 were generally lower than nighttime pCO2 values because of photosynthesis, whereas during ebbing, daytime pCO2 were higher than nighttime pCO2 values because of heating. Waters in the lagoon were a relatively weak CO2 source to the atmosphere over the year compared to other estuarine and lagoon waters elsewhere, and to sediment-air fluxes measured simultaneously by atmospheric Eddy Covariance (EC) in the Arcachon lagoon. Because of low values and small variations of the air-sea pCO2 gradient, the variability of fluxes calculated using the piston velocity parameterization was greatly controlled by the wind speed at the diurnal and, to a lesser extent, seasonal time scales. During the emersion, the comparison of these pCO2 data in the tidal creek with EC fluxes measured 1.8 km away on the tidal flat suggests high heterogeneity in air-sea CO2 fluxes, both spatially and at short time scales according to the inundation cycle and the wind speed. In addition to tidal pumping when the flat becomes emerged, our data suggest that lateral water movement during the emersion of the flat generates strong spatial heterogeneity in water–air CO2 flux. [ABSTRACT FROM AUTHOR]

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). [ABSTRACT FROM AUTHOR]

The lack of strong geothermal manifestations and limited fumarolic activity has sparked widespread debate about the presence of active magma reservoirs beneath the Wudalianchi volcanic field (WVF). Helium (He) in hydrological systems is sensitive and responsive to the mixture of mantle-derived He, making it an excellent tool for deciphering mantle-derived magmatic processes. Through investigating dissolved He and inorganic carbon (DIC) in shallow groundwater of the WVF, we found that He captures mantle characteristics with R/Ra ratios (R equals to 3He/4He ratios, Ra is atmospheric 3He/4He ratio of 1.39 × 10−6) ranging from 0.07 to 2.27 and the highest proportion of mantle-derived He is 30.38 %. In contrast, DIC shows minimal mantle influence, with low concentrations (1.91–7.39 mmol/L) and depleted δ13C-DIC values ranging from −17.9 ‰ to −13.6 ‰. The calculated mantle 4He fluxes in groundwater are 2–3 orders of magnitude higher than that in stable continents and show the signature of volcanic degassing. The high mantle He fluxes and high upward flow rates suggest the efficient release and transfer of mantle-derived He into shallow groundwater through magma degassing. Magma-aging model effectively constraints the period of magmatic activity to within the last 47 ka. These findings, consistent with seismic noise imaging results, support the presence of magma reservoirs in the upper–middle crust. The absence of magmatic carbon signature in groundwater suggests the decoupling of magmatic He and magmatic CO 2. Magmatic CO 2 may be removed during ascent, possibly being trapped through dissolution or precipitation processes within the low-resistivity bodies identified at ∼2.5 km depth by magnetotelluric imaging. These findings not only contribute to resolving the controversy surrounding the existence of magma reservoirs beneath the WVF but also have broader implications in guiding the exploration and validation of hidden magmatic systems. • Shallow groundwater (depth < 200 m) in the Wudalianchi volcanic field captured identifiable magmatic helium. • Shallow magma reservoirs at a depth of ∼7.5 km exist beneath the Wudalianchi volcanic field. • The removal of magmatic CO 2 leads to limited bubbling activity in the Wudalianchi volcanic field. [ABSTRACT FROM AUTHOR]

The acidification of the marginal seawater was a more intricate process than the ocean. Although some studies have been done on seasonal acidification in the bottom water of Chinese marginal seas, research on surface water acidification has still been insufficient. We analyzed the acidification properties and controlling factors in the Bohai Sea (BS) and Yellow Sea (YS) surface water during April 2023. The observation showed that the average surface water pH of the BS, North Yellow Sea (NYS), and South Yellow Sea (SYS) were 8.09 ± 0.06, 8.13 ± 0.05, and 8.15 ± 0.05. Phytoplankton significantly impacted pH and Ω arag , while riverine inputs and biological activity played a vital role in controlling DIC and TA. The Yellow River significantly impacted the BS. The North Yellow Sea Cold Water Mass had a limited impact on acidification, while the South Yellow Sea Cold Water Mass significantly affected the SYS. Regarding seasonal fluctuations, Ω arag was significantly higher in summer than in other seasons. DIC and TA showed different patterns in both the BS and YS, with a minimal fluctuation in pH. Over the last two decades, the pH in the BS showed a slight annual decline, and the rate of change was (−1.45 ± 2.19) × 10−5 yr−1. In contrast, the NYS and SYS have slightly risen, with rates of change of (2.39 ± 1.24) × 10−5 and (1.23 ± 0.76) × 10−5 yr−1. We believed that surface water acidification in the BS and YS did not follow the expected trend of significant acidification observed in open oceanic regions. Instead, the acidification process in these marginal seas was dominated by local factors such as riverine inputs, biological activity, and cold water masses, resulting in minimal pH changes over the last two decades. [Display omitted] • River inputs and phytoplankton influenced BS and YS surface seawater acidification. • Summarizing data of past 20 years on surface water acidification in BS and YS. • The BS and YS surface water may not be acidified. [ABSTRACT FROM AUTHOR]

[Display omitted] • p CO 2 shows pulsatile features in karst urban river after receiving WWTP effluents. • WWTP effluents influences DIC weathering end-members discrimination in karst rivers. • Identified geochemical controls on DIC in a karst stream impacted by WWTP effluents. • WWTP effluents are one of essential contributors to karst river DIC pool. Wastewater treatment plants (WWTPs) are an important manifestation of the impact of urbanization on aquatic ecosystems, and the influences of effluents discharge from WWTPs on receiving river carbon biogeochemical cycle processes has been a research hotspot. However, our knowledge about potential impacts of WWTP effluents on dissolved inorganic carbon (DIC) cycle in karst rivers is rather limited. This study investigates the water chemistry and carbon isotope composition (δ13C DIC) in the urbanized reach of a river that drains the world's largest continuous karst region in Southwest China, in an attempt to determine the effects of WWTP effluents on karst river DIC cycle and source discrimination. The results reveal: (1) Partial pressure of dissolved carbon dioxide (p CO 2) levels in the river increased noticeably during the dry and normal seasons after receiving WWTP effluents; (2) There existed an ionic ratio overlap between end-members of silicate rock weathering and WWTP effluents which requires caution in identifying end-members of rock weathering in urbanized karst rivers; (3) DIC in the highly urbanized karst rivers was affected by complex geochemical processes and these processes varied in different seasons; (4) The contribution of WWTP effluents to the riverine DIC pool was 21±13 %, 58±21 % and 66±33 % in the wet, dry, and normal seasons, respectively. These findings highlight the interference of WWTP effluents with DIC carbon cycling in the receiving karst rivers. Since DIC from WWTPs do not relate with consuming atmospheric or soil CO 2 , it is important to exclude their contribution from the watershed's rock weathering carbon sink budget. Based on these findings, we insist that the role and effect of WWTP effluents should be carefully considered when examining DIC carbon source and cycling in rivers that drain urbanized watersheds with abundant wastewater treatment plants. [ABSTRACT FROM AUTHOR]

Sinkholes play a critical role in groundwater systems by facilitating both recharge and discharge of groundwater, serving as indicators of underlying geologic processes, shaping subsurface hydrology, and influencing water quality. Therefore, studying karst groundwater systems is essential for effective groundwater management, especially in areas with limestone sequences. Spatial variations of water isotopes (δ2H, δ18O), dissolved inorganic and organic carbon (DIC and DOC), including their isotopes alone with pH, EC, alkalinity and chloride were determined in surface- and groundwater of the Mulankavil karst aquifer basin in the northwest of Sri Lanka. Twenty-seven groundwater wells, one offshore spring and two sinkholes were selected for sampling. The contribution of sinkhole water and seawater to karst aquifers was calculated using δ18O and chloride as tracers. In addition, deuterium excess (d-excess) values were used to determine groundwater evaporative loss before infiltration. Near the Mulankavil sinkhole area, the mixing of surface water and infiltrating rainwater was found to vary between 26 and 60%, with an average of 56%. In contrast, surface water mixing in the Nagapadduvan and Vellankulam sinkholes was about 41–59% and 33–70%, respectively. In near coastal wells, these values fell to 20% due to the influence of seawater intrusion. During the dry season, groundwater d-excess varied between −5.0 and + 10.8‰, while surface water in sinkholes showed values between +1.8 and −9.4‰. Groundwater wells near the Mulankavil sinkhole showed lower DIC (<5.5 mmol/L) with enriched δ13C DIC (>-14‰). The karst aquifer systems in northern Sri Lanka exhibit two main recharge mechanisms: (a) selective recharge by surface water at sinkholes and (b) diffuse recharge by direct rainfall over the study area. Seawater intrusion near the coast can be prevented by artificially recharging rainwater during the monsoon season. [Display omitted] • The Mulankavil Karst groundwater basin is a vital freshwater reserve in Sri Lanka. • A geochemical proxy approach was used to quantify water fluxes from different sources. • The mixing of evaporated sinkholes and seawater determines the geochemistry of groundwater. • Conversion of DOC to DIC was evident in the studies of karst aquifer systems. [ABSTRACT FROM AUTHOR]

Rainfall-driven riverine dissolved carbon (DC) transport is crucial for research on the carbon cycle. However, the relationship between river DC and discharge during rainfall events in the vegetation restoration area remains unclear. This study aims to elucidate the evolving patterns of DC concentrations in rivers of small watersheds undergoing vegetation restoration on the Loess Plateau during rainfall events. It quantified the relationship between rainfall, floods, and river DC using high-frequency sampling, continuous hydrology, and climate monitoring, along with hysteresis analysis. Results indicated that disparities in carbon sources and previous hydrological conditions mainly influenced the trends and hysteresis patterns of river dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC) concentrations. During intermittent rainfall, depletion of proximal DOC sources in preceding events led to scarcity in subsequent events, while activation of DIC sources replenished the river in subsequent events. Rainfall significantly affected river DC flux in the vegetation restoration watersheds. The output flux range for DOC and DIC was 0.37–9.12 kg/h and 2.21–39.95 kg/h, respectively. Thus, measures must be implemented to mitigate the additional carbon losses resulting from revegetation. These research findings can serve as a scientific basis for ecological environmental protection in the Loess Plateau and for predicting river carbon flux during vegetation restoration. [Display omitted] • Rainfall impacts river dissolved carbon in restoration watersheds. • Vegetation restoration affects riverine dissolved carbon dynamics. • DOC and DIC concentrations vary with rainfall events. • High-frequency sampling reveals carbon source depletion patterns. • Study informs ecological protection on the Loess Plateau. [ABSTRACT FROM AUTHOR]

To clarify the impacts of tidal hydrological process shifts caused by sea level rise on the blue carbon cycle, a typical coastal wetland in Jiaozhou Bay was selected for this study. The soils of Suaeda salsa (SS) and Phragmites australis (PA) wetlands were collected to simulate the effects of three types of tidal hydrological processes (Neap tide group, NT; Middle tide group, MT; Spring tide group, ST) on the soil-water dissolved inorganic carbon (DIC) dynamic. The results showed that the concentration of water dissolved inorganic carbon (WDIC) increased rapidly (115% higher) at early stage (days 0–4) under the influence of the tidal hydrological processes. Significant differences were found in WDIC concentration during different tidal hydrological processes (P < 0.05), which were expressed as MT (52.7 ± 13.3 mg L−1) > ST (52.5 ± 12.9 mg L−1) > NT (48.4 ± 10.1 mg L−1). After experiencing the tidal hydrological processes, the soil DIC content showed a net accumulation (55.1 ± 1.29 mg L−1 vs. 46.7 ± 1.76 mg L−1, P < 0.001), whereas the soil inorganic carbon (SIC) decreased (2.73 ± 1.64 mg L−1 vs. 4.61 ± 1.71 mg L−1), which may be attributed to the dissolution of SIC caused by the uptake of CO 2 to form DIC. The accumulation of soil DIC was directly related to the SIC (λ = 1.03, P < 0.01), and indirectly related to soil nutrients (SOC substrate, λ = −0.003) and microbes (microbial biomass, λ = −0.10), and was mainly dominated by abiotic processes (abiotic: 58.1 ± 1.8% to 82.7 ± 2.46% vs. biotic: 17.4 ± 2.46% to 41.9 ± 1.76%). The increase of tidal frequency generally inhibited the accumulation of soil DIC content and promoted the output of WDIC. However, the response of soil DIC in different wetland types to tidal frequency was divergent, which was mainly regulated by the trade-off between soil nutrients and SIC content. Taken together, tidal hydrological processes and their frequency changes reshaped DIC dynamics, promoted the dissolution of SIC and the potential uptake of CO 2. These findings enhance the comprehension of the inorganic carbon cycle within coastal wetlands, particularly amidst the backdrop of climate change and the rising sea levels. [Display omitted] • Tidal hydrological processes cause the continuous outflow of DIC in water. • Tidal hydrological processes significantly enhance the accumulation of soil DIC. • Abiotic processes dominate the formation of DIC rather than biotic processes. • Tidal frequency shapes the DIC dynamics in different wetland types. [ABSTRACT FROM AUTHOR]

The Hirnantian carbon isotopic excursion (HICE) was characterized by a positive δ13C excursion (up to ∼ + 7‰) of oceanic dissolved inorganic carbon (DIC). However its mechanism remains controversial, impeding our understanding of this global event and its environmental significance. Here, we conducted a comprehensive analysis of global carbon-isotope records, based on 65 paleogeographically-widely distributed sections (4612 carbon-isotope data), documenting a steep oceanic DIC δ13C water-depth gradient (e.g., a 4.6‰ offset in the HICE excursion magnitude within Laurentia) during the Hirnantian Stage. We propose a hybrid hypothesis that the HICE records a shift toward more positive values owing to a large glacio-eustatic fall (>100 m) under the herein-identified steep δ13C water-depth gradient, with potential contributions from global-ocean δ13C DIC changes and authigenic carbonates. This study provides the first large-data evidence for a widely density-stratified ocean during the Hirnantian Glaciation, with implications for reconstructions of ocean circulation and the carbon cycle during the Early Paleozoic. [ABSTRACT FROM AUTHOR]

Rivers are important routes for material and energy transport between terrestrial and marine ecosystems. Recent global-scale assessments of carbon (C) have suggested that C emission fluxes to the atmosphere are comparable to the fluvial C fluxes to the ocean. However, many previous studies only collected data from inland rivers in low altitude regions. Therefore, it remains unclear how plateau rivers affect C flux. In this study, 20 monitoring sites were set up along the Yarlung Tsangpo (YT) River on the Tibetan Plateau and detailed observations were carried out in the wet and dry seasons. The riverine CO2 fluxes exhibited significant seasonal patterns which ranged from 597.12 ± 292.63 μatm in the wet season to 368.72 ± 123.50 μatm in the dry season. The CO2 emission flux (FCO2) obtained from floating chamber method, ranging from 8.44 ± 6.94 mmol m−2 d−1 in sunmmer to 3.62 ± 6.32 mmol m−2 d−1 in winter, with an average value of 6.03 mmol m−2 d−1. Generally, the river was a weak carbon source with respect to the atmosphere. However, the pCO2 and FCO2 were much lower than that for other large rivers around the globe, which were obviously restrained by the weak microbial activities due to the low primary productivity and carbonate buffer activities in the carbonate background. Carbon loss via atmosphere exchange in the YT River on the plateau accounted for 2.2% and 10.6% of the riverine dissolved carbon fluxes (67.77 × 109 mol a−1) according to the floating chamber and thin boundary layer methods, respectively. The YT River probably acts as a “pipeline” to transport weathered nutrients from the plateau to downstream areas. Our results demonstrated the characteristics of a “weak outgassing effect and a high transport flux of carbon” for the plateau river, which is different from rivers on plains. Considering the global relevance of Tibetan Plateau, further studies with enhanced spatiotemporal resolution are needed to better understand the important role of plateau rivers on carbon budgets and climate change over both regional and global cycles.

Active fault zones provide favorable channels for the discharge of carbon-bearing fluids from Earth’s interior. Earthquakes, as a common fault-related dynamic process, can disturb the circulation of subsurface fluids and their interactions with country rocks and sediments on short timescales, which may cause changes in carbon mobilization processes and carbon sources of the discharged fluids. However, quantitative research on earthquake-induced changes in carbon mobilization at deep and shallow levels remains lacking. Here, we present a quantitative study on stable carbon isotopes (δ13C) and radiocarbon values (Δ14C) of dissolved inorganic carbon (DIC) in subsurface fluid samples from the surface rupture zone formed by the Mw 7.4 Maduo earthquake (22 May 2021) and the East Kunlun fault, NE Tibetan Plateau. Our results show that δ13CDIC values vary from –11.6‰ to 0.1‰, while Δ13CDIC values have a range of –980‰ to –46‰. Using a mass balance model based on δ13CDIC and DIC concentrations, we calculated the proportions of source components involved in DIC, including organic carbon, carbonates, and deeply-sourced carbon. On average, waters discharging from the surface rupture zone have higher inputs from organic carbon (28.1%) than those from the East Kunlun fault (18.6%), with the latter showing higher deeply-sourced carbon contributions (45.7% vs. 30.7%). This is consistent with the lower average Δ14CDIC value (–544‰) observed from the East Kunlun fault, suggesting more inputs from carbon source components that are devoid of 14C (i.e., deeply-sourced carbon and carbonates). These findings indicate that seismic events can significantly affect the carbon mobilization processes at variable depths, especially the shallow soil organic carbon in the case of the 2021 Maduo earthquake. The potential effects of earthquake-induced changes in carbon mobilization processes should be taken into account in the modeling of tectonic carbon dioxide degassing and carbon cycle on longer timescales.

Spatial variability in carbon dioxide (CO2) and oxygen (O2) was assessed within an Indigenous Hawaiian fishpond undergoing active ecosystem restoration. The brackish, tidal fishpond is located within Kāne‘ohe Bay, Hawai‘i. Following a year of monthly discrete sampling, a significant shift in DIC and percent O2 saturation was observed along the North-South axis within the pond. The south end of the pond was higher in DIC (+35 μmol·kg⁻¹) and lower in percent O2 saturation (-19%) than the north end, which exhibited values similar to those observed in water entering the fishpond from the bay. Water quality parameters and inequal proximity to water flux sites suggested that a difference in residence time may exist along the north-south axis. In addition, ΔTA/ΔDIC relationships revealed a respiration signal in south end of the pond, which was enhanced at depth. While physical processes strongly affect CO2 and O2 across various temporal scales, spatial patterns in biological processes may also affect variability within the fishpond. These findings demonstrate that changes in water chemistry within the fishpond are the result of ecosystem restoration efforts. In turn, future management decisions at the fishpond will play an important role in preserving its viability as a healthy habitat for the intended marine species.

The 2011 off the Pacific coast of Tohoku Earthquake occurred off southern Sanriku, Japan, on March 11 and generated strong shaking and huge tsunami along the entire eastern coast of Tohoku. The mainshock and numerous large aftershocks caused mass-wasting sedimentation events on the continental shelf, slope, and trench bottom. To investigate the impacts of the 2011 Tohoku Earthquake on the deep-sea bottom-water environment off Sanriku, we conducted shipboard surveys up to ~ 2000 dbar during 2011–2018 and long-term monitoring of the seafloor on the continental slope using a deep-sea station (~ 1000 dbar) off Otsuchi Bay during 2012–2018. The high turbidity (maximum ~ 6%) was observed for the bottom water deeper than 500 dbar on the continental slope of the entire area off Sanriku during 2012–2018. This high turbidity was caused by sporadic sediment resuspension induced by frequent large aftershocks. Furthermore, dissolved oxygen concentrations in the bottom layer from 1000 to 1500 dbar dropped significantly by about 10% after the earthquake, while nutrients and dissolved inorganic carbon showed no significant changes but exhibited wide variations. The high turbidity was associated with the increase in the concentrations of phosphate, dissolved inorganic carbon, and methane, as well as the decrease in those of dissolved oxygen and nitrate. This suggests that remineralization of suspended organic matter resulting from the respiration and denitrification of microbial communities after the earthquake caused the chemical properties of the deep-sea bottom-water. The deep-sea bottom-water environment change was maintained by sporadic sediment resuspension due to continued large aftershocks and was likely caused by variations in dissolved inorganic carbon and phosphate. There are two peaks in the concentration and carbon isotope ratio of methane on the deeper slope from 1000 to 2000 dbar near the hypocenter, which were advected along isopycnal surfaces of 27.38σθ (1000 dbar) and 27.56σθ (1500 dbar). The source of the shallower peak of chemical input is considered to be the sediment resuspension from the shallow sediment on the continental slope induced by the mainshock and large aftershocks. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Epiphytic bacteria develop complex interactions with their host macrophytes and play an important role in the ecological processes in freshwater habitats. However, how dominant and rare taxa respond to elevated atmospheric CO2 remains unclear. A manipulated experiment was carried out to explore the effects of elevated CO2 on the diversity or functional characteristics of leaf epiphytic dominant and rare bacteria from a submerged macrophyte. Three levels (high, medium, normal) of dissolved inorganic carbon (DIC) were applied to the overlying water. The physicochemical properties of the overlying water were measured. Elevated atmospheric CO2 significantly decreased the pH and dissolved oxygen (DO) of overlying water. Proteobacteria, Cyanobacteria, Bacteroidetes, Planctomycetes, and Actinobacteria are the dominant phyla of leaf epiphytic bacteria from Myriophyllum spicatum, occupying over 90% of the accumulated relative abundances. The aquatic DIC level and further pH significantly drove the epiphytic community composition differences among the three DIC levels. For dominant epiphytic bacteria, the functional potential of nutrient processes and mutualistic relationships were strongly affected by a high DIC level, while responses of rare epiphytic bacteria were more related to trace element processes, pathogens, and defense strategies under a high DIC level. Our results showed the responses of epiphytic bacteria to elevated CO2 varied across dominant and rare taxa. [ABSTRACT FROM AUTHOR]

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 (<1%). This investigation is the first to present the C loads in a Mexican river. [ABSTRACT FROM AUTHOR]

Measurements of pH and nitrate from the Southern Ocean Carbon and Climate Observations and Modeling array of profiling floats were used to assess the ratios of dissolved inorganic carbon (DIC) and nitrate (NO3) uptake during the spring to summer bloom period throughout the Southern Ocean. Two hundred and forty‐three bloom periods were observed by 115 floats from 30°S to 70°S. Similar calculations were made using the Takahashi surface DIC and nitrate climatology. To separate the effects of atmospheric CO2 exchange and mixing from phytoplankton uptake, the ratios of changes in DIC to nitrate of surface waters (ΔDIC/ΔNO3) were computed in the Biogeochemical Southern Ocean State Estimate (B‐SOSE) model. Phytoplankton uptake of DIC and nitrate are fixed in B‐SOSE at the Redfield Ratio (RR; 6.6 mol C/mol N). Deviations in the B‐SOSE ΔDIC/ΔNO3 must be due to non‐biological effects of CO2 gas exchange and mixing. ΔDIC/ΔNO3 values observed by floats and in the Takahashi climatology were corrected for the non‐biological effects using B‐SOSE. The corrected, in situ biological uptake ratio (C:N) occurs at values similar to the RR, with two major exceptions. North of 40°S biological DIC uptake is observed with little or no change in nitrate giving high C:N. In the latitude band at 55°S, the Takahashi data give a low C:N value, while floats are high. This may be due to a change in CO2 air‐sea exchange in this region from uptake during the Takahashi reference year of 2005 to outgassing of CO2 during the years sampled by floats. Plain Language Summary: Phytoplankton take up dissolved inorganic carbon (DIC) and nitrate as they grow. This results in a decrease in DIC and nitrate during the spring through summer bloom periods each year. The ratio of DIC to nitrate uptake is typically near 6.6 mol C/mol N, a value termed the Redfield Ratio (RR). Here, we used sensor data from an array of profiling floats deployed by the Southern Ocean Carbon and Climate Observations and Modeling program in the Southern Ocean to examine the ratio of C:N uptake by phytoplankton during 243 bloom periods from October through February. We find uptake occurred at values near the RR throughout the Southern Ocean, with two exceptions. North of 40°S, C:N ratios exceed the Redfield value, most likely due to phytoplankton production of a gel‐like organic matter deficient in nitrogen. Near 55°S in the Antarctic Southern Zone, an apparent increase in the C:N ratio over the past decade may reflect a change from an air‐sea flux of CO2 into the ocean to a flux out of the ocean. Key Points: Carbon:nitrate uptake ratios by phytoplankton are near the Redfield Ratio in Southern Ocean waters south of 40°SCarbon:nitrate uptake ratios north of 40°S are much higher, likely due to production of dissolved organic matter with little nitrogenA change in air‐sea CO2 flux during October to February from a sink in 2005 to a source in recent years may have occurred near 55°S [ABSTRACT FROM AUTHOR]

The importance of studying the radiocarbon content of dissolved inorganic carbon (DI14C) in the oceans has been recognized for decades. Starting with the GEOSECS program in the 1970s, 14C sampling has been a part of most global survey programs. Early results were used to study air-sea gas exchange while the more recent results are critical for helping calibrate ocean general circulation models used to study the effects of climate change. Here we summarize the major programs and discuss some of the important insights the results are starting to provide. [ABSTRACT FROM AUTHOR]

Submarine groundwater discharge (SGD) has been widely recognized as an important source of dissolved nutrients in coastal waters and affects nutrient biogeochemistry. In contrast, little information is available on SGD impacts on coastal carbon budgets. Here, we assessed the SGD and associated carbon (dissolved inorganic carbon [DIC] and total alkalinity [TA]) fluxes in Liaodong Bay (the largest bay of the Bohai Sea, China) and discussed their border implications for coastal DIC budget and buffering capacity. Based on 223Ra and 228Ra mass balance models, the SGD flux was estimated to be (0.92–1.43) × 109 m3 d−1. SGD was the largest contributor of DIC, accounting for 55%–77% of the total DIC sources. The low ratio (<1) of SGD‐derived TA to DIC fluxes and negative correlation between radium isotopes and pH in seawater implied that SGD would potentially reduce seawater pH in Liaodong Bay. Combining the groundwater carbon data in Liaodong Bay with literature data, we found that the SGD‐derived DIC flux off China was 4–9 times greater than those from rivers. By analyzing the TA/DIC ratios in groundwater along the Chinese coast and related carbon fluxes, SGD was thought to partially reduce the CO2 buffer capacity in receiving seawater. These results obtained at the bay scale and national scale suggest that SGD is a significant component of carbon budget and may play a critical role in modulating coastal buffering capacity and atmospheric CO2 sequestration. Plain Language Summary: Submarine groundwater discharge (SGD) is an important process of land‐sea interaction, but its significance on coastal carbon budgets is still poorly understood. In this study, the SGD and associated carbon flux were quantified based on high‐resolution radium and carbon data in an urbanized bay (Liaodong Bay, China). By reviewing the coastal groundwater carbon data in the existing literature, this study provided a first approximation of SGD‐derived carbon fluxes at the shelf‐scale along the Chinese coastlines. The results suggested that SGD is an important component of dissolved inorganic carbon (DIC) budgets at the bay scale and shelf‐scale. SGD with low total alkalinity/DIC ratio would potentially reduce seawater pH and CO2 buffering capacity in receiving coastal waters. This study highlights the important but easily overlooked implications of SGD for coastal carbon budget and carbonate system. Key Points: Submarine groundwater discharge and associated carbon fluxes were estimated in the largest bay of the Bohai Sea, ChinaSubmarine groundwater discharge was an important component of coastal carbon budgets at the bay scale and shelf‐scaleGroundwater carbon inputs to ocean would modify local seawater pH and partially influence CO2 buffering capacity in receiving coastal waters [ABSTRACT FROM AUTHOR]

The evasion of CO2 from inland waters, a major carbon source to the atmosphere, depends on dissolved inorganic carbon (DIC) concentrations. Our understanding of DIC dynamics across gradients of climate, geology, and vegetation conditions however have remained elusive. To understand its large‐scale patterns and drivers, we collated instantaneous and mean (multiyear average) DIC concentrations from about 100 rivers draining minimally‐impacted watersheds in the contiguous United States. Within individual sites, instantaneous concentrations (C) measured at daily to seasonal scales exhibit a near‐universal response to changes in river discharge (Q) in a negative power law form. High concentrations occur at low discharge when DIC‐enriched groundwater dominates river discharge; low concentrations occur under high flow when relatively DIC‐poor shallow soil water predominates river discharge. Such patterns echo the widely observed increase of soil CO2 and DIC with depth and the shallow‐and‐deep hypothesis that emphasizes the importance of flow paths and source water chemistry. Across sites, mean concentrations (Cm) decrease with increasing mean discharge (Qm), a long‐term climate measure, and reachs maxima at around 200 mm/yr. A parsimonious model reveals that high mean DIC arises from soil CO2 accumulation when rates of DIC‐generating reactions are relatively high compared to its export fluxes in arid climates. Although instantaneous and mean DIC concentrations similarly decrease with increasing discharge, results here highlight their distinct drivers: daily to seasonal‐scale instantaneous concentration variations (C) are controlled by subsurface CO2 distribution over depth (from below), whereas long‐term mean concentrations (Cm) are regulated by climate (from above). The results emphasize the significance of land‐river connectivity via subsurface flow paths. They also underscore the importance of characterizing subsurface CO2 distribution to illuminate belowground processes in order to project the future of water and carbon cycles in a warming climate. Key Points: Within individual sites, instantaneous dissolved inorganic carbon (DIC) (C) exhibits a near‐universal dilution pattern with lower concentrations at high discharge (Q)Across sites, DIC (Cm) similarly exhibits a dilution pattern with a lower mean concentration at high mean discharge (Qm) in humid climatesAlbeit similar patterns, results highlight distinct drivers of instantaneous and mean concentrations by subsurface CO2 profiles and climate, respectively [ABSTRACT FROM AUTHOR]

Quantitative paleoecological reconstructions using biological proxies, such as diatoms, Cladocera, and chironomids, have revolutionized paleolimnology and have greatly contributed to the understanding of the past local and regional environmental changes, as well as to nature conservation. While macrophytes are good ecological indicators, they have rarely been used to reconstruct past lake-water chemistry. The present study investigates which environmental variable best explains aquatic plant community composition in Finnish, Polish, and Swedish lakes for its further use in quantitative paleoenvironmental reconstructions. The method involved the creation of a modern macrophyte-environment calibration dataset, calculation of modern calibration functions using simple averaging regression, and final reconstruction of past environmental conditions in Lake Linówek (NE Poland) from a fossil assemblage using weighted averaging calibration. The data demonstrate that conductivity and alkalinity best explained macrophyte community composition in our dataset. Species "optima" for alkalinity were influenced by the presence/absence of carbon concentrating mechanisms (CCMs), enabling the utilization of HCO 3 - as a carbon source. Quantitative paleoenvironmental reconstruction indicates that past water conductivity and alkalinity fluctuated depending on internal lake processes and the supply of basic ions to the lake from the catchment related to climate and soil development in the watershed during the late Glacial (∼14,500-11,700 calibrated years before the present; cal BP) and the Holocene (11,700 cal BP-recent). We conclude that macrophytes can be successfully used for past lake-water chemistry reconstruction. Furthermore, calculated modern calibration functions for conductivity and alkalinity can be used in nature conservation for determining habitat requirements of numerous endangered macrophyte species as a basis for successful (re)introductions., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Algae play critical roles in the carbon dioxide (CO 2 ) exchange between the water bodies and the atmosphere. However, the effects of prokaryotic and eukaryotic algae on carbon utilization, CO 2 flux, and the underlying mechanisms remain poorly understood. Therefore, this study investigated the differences in carbon preferences and CO 2 fluxes under different algal dominance days. Our research revealed that dissolved inorganic carbon (DIC) concentration fluctuations had a limited effect on the relative abundance of algae. However, shifts in dominant algal phyla induced changes in DIC, with Cyanobacteria preferring HCO 3 - and Chlorophyta preferring CO 2 . Analysis of the water chemistry balance indicated that the growth of Chlorophyta had a 15.59 times greater effect on CO 2 sinks compared with that of Cyanobacteria. During the Cyanobacteria dominance days, the lower DIC concentration did not result in a reduction in CO 2 emissions. However, increases in the dissolved organic carbon concentration provided a favorable environment for Cyanobacteria, which promoted CO 2 emissions. The CCM model indicated that the growth of Chlorophyta resulted in CO 2 uptake rates at least 3.57 times higher and CO 2 leakage rates up to 0.97 times lower compared to Cyanobacteria, accelerating CO 2 transport into the cell. Overall, CO 2 sink was stronger on Chlorophyta dominance days than on Cyanobacteria dominance days. This study emphasized the influence of algal phyla on CO 2 fluxes, revealing the significant CO 2 sink associated with Chlorophyta. Further research should investigate how to manipulate environmental factors to favor Chlorophyta growth and effectively reduce CO 2 emissions., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

In karst areas, the dissolved inorganic carbon (DIC) concentrations in aquatic systems are typically higher than that in non-karst areas due to intensive carbonate rock weathering. Understanding the sources and input fluxes of DIC in karst reservoirs is crucial for regional carbon cycle studies. This study utilized dual carbon isotopes (δ 13 C DIC and Δ 14 C DIC ) to estimate the contribution rates and input fluxes of DIC from various sources in Aha Reservoir (AHR), located in southwestern China. Our results indicated that the DIC concentrations (22.33-32.79 mg L -1 ) and δ 13 C DIC values (-10.02‰ to -8.55‰) were nearly homogeneous both vertically and laterally in the reservoir (p > 0.05). The Δ 14 C DIC values (-246.31‰ to -137.86‰) were homogeneous along the vertical profile (p > 0.05), but showed significant horizontal variation (p < 0.05), with values decreasing from -149.57 ± 10.27‰ to -232.85 ± 2.37‰ at the mouths of the inflowing rivers. We found that the inflowing rivers were the primary DIC sources to AHR, contributing 70% of the total input, while groundwater and atmospheric CO 2 contributions were relatively minor, at 18% and 12%, respectively. The Jinzhong River (JZR), influenced by industrial and domestic wastewater discharge, contributed the largest DIC input flux at 2.01 t/(km 2 ·mon). In contrast, the Youyu River (YYR), influenced by acidic mine drainage, and the Baiyan River (BYR), influenced by agricultural activities, contributed relatively smaller DIC input fluxes of 1.29 t/(km 2 ·mon) and 1.03 t/(km 2 ·mon), respectively. This study highlights the significant impact of anthropogenic activities on DIC input in AHR, with industrial and domestic wastewater discharges having a greater influence than agricultural activities and acidic mine wastewater inputs. These findings underscore the critical need to manage and mitigate the impacts of human activities on karst reservoir ecosystems., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Carbon dioxide (CO 2 ) stands as the primary driver of Earth's greenhouse effect, and it's suggested that the global contribution of CO 2 emissions from lakes cannot be ignored. Despite the numerous estimations of CO 2 fluxes from lakes, limited focus has been directed towards the carbon isotopes (δ 13 C) of dissolved CO 2 in lake water. Particularly, the potential use of δ 13 C values in tracing the CO 2 concentrations in lake water remains as an understudied area, warranting further exploration and investigation. In this study, we conducted an analysis of the concentrations and δ 13 C values of dissolved CO 2 in 33 lakes located at the Tibetan Plateau, Chinese Loess Plateau, and Yangtze Plain (among which high-resolution spatial investigations were performed in 6 lakes through in-situ continuous monitoring). Our findings revealed spatial variations in both the CO 2 concentrations and δ 13 C values in lakes. Additionally, notable differences are observed among lakes in different regions of China, with lakes in the Yangtze Plain exhibiting considerably higher CO 2 concentrations, and the overall CO 2 δ 13 C values in lakes on the Tibetan Plateau tend to be more positive, while those in lakes on the Chinese Loess Plateau tend to be more negative. The pH values, dissolved oxygen, and dissolved organic carbon are likely crucial factors influencing the CO 2 concentrations and δ 13 C values in the lakes. Furthermore, lake water CO 2 concentrations are negatively correlated with δ 13 C values of CO 2 and dissolved inorganic carbon (DIC) both within a single lake with high spatial resolutions or in lake groups across different regions. These results highlight that the CO 2 /DIC δ 13 C values can be applied to trace the concentration variations of dissolved CO 2 in lakes., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

The uptake of atmospheric CO2 and the cycle of dissolved inorganic carbon (DIC) in the ocean are the major mechanisms and pathways controlling global climate change and carbon cycling. The stable carbon isotope (δ13C) of DIC, therefore, provides an important tracer for processes such as air-sea exchange, photosynthesis, and water dynamics in the ocean. Here, we present new δ13C-DIC data on water samples collected from a north-south transect (13°N–40°N, 150°E) in the western North Pacific (NP) Ocean in November 2019 and compare the results with those previously reported for similar transects (149.3°E) during WOCE and CLIVAR projects over the past three decades. The values of δ13C-DIC, ranging from -0.83‰ to 0.86‰, were higher in the surface waters and decreased with depth. The high δ13C-DIC values in the surface waters were influenced primarily by isotopic fractionation during air-sea exchange and photosynthesis. With depth, the movement of different water masses and mixing, as well as bathypelagic respiration in the dark water of the ocean, all play important roles in influencing the distribution and isotopic signatures of δ13C-DIC in the western NP Ocean. The δ13C-DIC values of the 0–200 m water layer varied from -0.17‰ to 0.86‰, with lower values at high latitudes, affected by the low δ13C-DIC values carried by the Oyashio Current to the Kuroshio Extension (KE) region. A downward trend was present in the δ13C-DIC signature from north to south in the North Pacific Intermediate Water (NPIW) and Pacific Deep Water (PDW) in the western NP, which reflected the remineralization of organic matter with a horizontal transport of NPIW and PDW. We found a strong 13C Suess Effect in the upper 2,000 m in the western NP Ocean, and δ13C-DIC at the surface (

Karst ecological stresses are harmful to plant growth, especially high bicarbonate concentrations, drought, high pH, etc. In this study, the effects of 0, 2.0, 7.0 and 12.0 mmol L−1 sodium bicarbonate concentrations on the biomass, electrophysiological properties, intracellular water metabolism, nutrient transport, photosynthesis and chlorophyll fluorescence of Coix lacryma-jobi L. were investigated. The results show that 2.0 mmol L−1 sodium bicarbonate effectively improved the biomass formation of Coix lacryma-jobi L., notably increased its intrinsic capacitance (IC) and decreased its intrinsic resistance (IR), intrinsic impedance (IZ), intrinsic capacitive reactance (IXc) and intrinsic inductive reactance (IXL) as well as reliably enhanced its intracellular water metabolism, nutrient transport and photosynthetic capacities. However, 7.0 and 12.0 mmol L−1 sodium bicarbonate concentrations exhibited marked inhibitory effects on the plants’ photosynthetic rate, stomatal conductance, transpiration rate and dry weight, whereas they did not significantly change the intracellular water metabolism or the nutrient transport capacity of Coix lacryma-jobi L. This study highlights that appropriate bicarbonate levels could enhance the intracellular water metabolism, nutrient transport, photosynthesis and growth of Coix lacryma-jobi L., which can be rapidly monitored by the plant’s electrophysiological properties. Importantly, plant electrophysiological measurement is significantly superior to photosynthesis measurement. In the future, plant electrophysiological measurement can be used as a means to quickly and effectively evaluate the physiological response of plants to the external environment.

In deep karst reservoirs, the internal environment is complex, and thermal stratification isnot the only factor controlling the vertical distribution of the DIC concentration. Previous studies have not fully understood the migration and transformation of DIC in a deep-water reservoir. In this study, a deep-water reservoir in southwest China was chosen, and the spatial and temporal characteristics of the DIC concentration, pCO2, δ13CDIC value, and SIc were investigated. It was found that the Pingzhai Reservoir is a double temperature leapfrog reservoir. The DIC concentration, pCO2, Sic, and δ13CDICvalues showed annual cycle variation. During the thermal stratification phase, the DIC concentration, pCO2, Sic, and δ13CDICvalues were significantly different between the surface layer and the lower layer. However, during the mixing and mixed phases, the differences were not significant. The vertical divergence of the DIC in the Pingzhai Reservoir was influenced by the subtemperate layer, human activities, and sources. The formation of the subtemperate layer was due to the submerged flow formed when river water enteredthe reservoir, which provides a channel for DIC from the river to enter the lower layer of the reservoir. Human activities increased the solubility of carbonate rocks in the reservoir, and the source of DIC was one of the factors contributing to the concentration stratification of DIC in the reservoir.

Global change is modifying meteorological and hydrological factors that influence the thermal regime of water bodies. These modifications can lead to longer stratification periods with enlarged hypolimnetic anoxic periods, which can promote heterotrophic anaerobic processes and alter reservoir carbon cycling. Here, we quantified aerobic and anaerobic heterotrophic processes (aerobic respiration, denitrification, iron and manganese reduction, sulfate reduction, and methanogenesis) on dissolved inorganic carbon (DIC) production in the hypolimnion of a Mediterranean reservoir (El Gergal, Spain) under two contrasting hydrological conditions: a wet year with heavy direct rainfall and frequent water inputs from upstream reservoirs, and a dry year with scarce rainfall and negligible water inputs. During the wet year, water inputs and rainfall induced low water column thermal stability and earlier turnover. By contrast, thermal stratification was longer and more stable during the dry year. During wet conditions, we observed lower DIC accumulation in the hypolimnion, mainly due to weaker sulfate reduction and methanogenesis. By contrast, longer stratification during the dry year promoted higher hypolimnetic DIC accumulation, resulting from enhanced methanogenesis and sulfate reduction, thus increasing methane emissions and impairing reservoir water quality. Aerobic respiration, denitrification and metal reduction produced a similar amount of DIC in the hypolimnion during the two studied years. All in all, biological and geochemical (calcite dissolution) processes explained most of hypolimnetic DIC accumulation during stratification regardless of the hydrological conditions, but there is still ~ 30% of hypolimnetic DIC production that cannot be explained by the processes contemplated in this study and the assumptions made. [ABSTRACT FROM AUTHOR]

Permafrost-affected soils contain large quantities of soil organic carbon (SOC). Changes in the SOC pool of a particular ecosystem can be related to its net ecosystem carbon balance (NECB) in which the balance of carbon (C) influxes and effluxes is expressed. For polygonal tundra landscapes, accounts of ecosystem carbon balances in the literature are often solely based on estimates of vertical carbon fluxes. To fill this gap, we present data regarding the lateral export rates of dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) from a polygonal tundra site in the North-Siberian Lena River Delta, Russia. We use water discharge observations in combination with concentration measurements of water-borne carbon to derive the lateral carbon fluxes from one season (2 June-8 September 2014 for DOC, 8 June-8 September 2014 for DIC). To put the lateral C fluxes into context, we furthermore present the surface-atmosphere eddy covariance fluxes of carbon dioxide CO2) and methane (CH4) from this study site. The results show cumulative annual lateral DIC and DOC fluxes of 0.31-0.38 g m-2 and 0.06-0.08 g m-2, respectively. Vertical turbulent fluxes of CO2-C and CH4-C accumulated to -19.0 ± 1.2 g m-2 and 1.0 ± 0.02 g m-2 during the 93-day observation period (8 June-8 September 2014). Thus, the lateral C export represented about 2% of the net ecosystem exchange CO2 (NEE). However, the relationship between lateral and surface-atmosphere fluxes changed over the observation period. the beginning of the growing season (early June), the lateral C flux outpaced the surface-directed net vertical turbulent CO2 flux, causing the polygonal tundra landscape to be a net carbon source during this time of the year. Later in the growing season, the vertical turbulent CO2 flux dominated the NECB. Notably, the surface-atmosphere C flux served as a good approximation the NECB at our study site during the growing season. [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. [ABSTRACT FROM AUTHOR]

The carbon isotope values (δ13C) of aquatic plants are of great significance for recognizing carbon cycles and tracing environmental changes in lakes. Yet, the influence of δ13C values of their utilizing carbon sources (especially in the case of CO2 separated from the HCO3– in water) on their δ13C differences have never been evaluated, which is mainly due to the lack of CO2 δ13C investigations in lake water. In this study, we used a newly developed fast-response automated gas equilibrator for real-time concentration and δ13C determination of dissolved CO2 in the surface and bottom lake water of Lake Tuosu, Lake Qinghai and Lake Keluke, China. Moreover, we determined the corresponding δ13C values of total organic carbon (TOC) of a submerged plant (Potamogeton) and an alga (Cladophora), as well as the δ13C values of dissolved inorganic carbon (DIC) in bottom lake water. The results showed that the CO2 δ13C values of bottom and surface water in these three lakes did not show significant differences and the δ13C values of CO2 at different water depths also did not show significant differences. However, Potamogeton had higher TOC δ13C values (average 14–16‰) than Cladophora in these lakes. Although Potamogeton and Cladophora could utilize HCO3– as an additional carbon source whose δ13C values were more positive (ca. 7–8‰) than CO2, this effect on their δ13C values was no >4‰ after evaluation. Thus, our results show that the δ13C values of carbon sources (including CO2 and HCO3–) are not the main factors in determining the TOC δ13C difference between Potamogeton and Cladophora, which could be primarily related to the biosynthetic fractionation for different aquatic plant species. Our results benefit further understanding and interpretations of δ13C variations in carbon cycles and paleoenvironment reconstructions for lakes.

The carbon system in the eastern tropical Atlantic remains poorly known. The variability and drivers of the carbon system are assessed using surface dissolved inorganic carbon (DIC), alkalinity (TA) and fugacity of CO2 (fCO2) measured in the 12° N–12° S, 12° W–12° E region from 2005 to 2019. A relationship linking DIC to temperature, salinity and year has been determined, with salinity being the strongest predictor. The seasonal variations of DIC, ranging from 80 to 120 μμmol kg−1, are more important than the year-to-year variability that is less than 50 μμmol kg−1 over the 2010–2019 period. DIC and TA concentrations are lower in the northern part of the basin where surface waters are fresher and warmer. Carbon supply dominates over biological carbon uptake during the productive upwelling period from July to September. The lowest DIC and TA are located in the Congo plume. The influence of the Congo is still observed at the mooring at 6° S, 8° E as shown by large salinity and chlorophyll variations. Nevertheless, this site is a source of CO2 emissions into the atmosphere.

Under the influence of periodic temperature variations, biogeochemical cycling in water bodies is markedly affected by the periodic thermal stratification processes in subtropical reservoirs or lakes. In current studies, there is insufficient research on the influence and mechanism of dissolved inorganic carbon (DIC) distribution in karst carbon-rich groundwater-fed reservoirs under the coupled effects of thermal structure stratification and the biological carbon pump (BCP) effect. To address this issue, the Dalongdong (DLD) reservoir in the subtropical region of southern China was chosen as the site for long-term monitoring and research on relevant physicochemical parameters of water, DIC, and its stable carbon isotope (δ13C DIC), CO 2 emission flux, as well as the reservoir's thermal stratification index. The results show that: (1) the DLD reservoir is a typical warm monomictic reservoir, which exhibits regular variations of mixing period-stratification period-mixing period on a yearly scale due to thermal structure changes; (2) DIC was consumed by aquatic photosynthetic organisms in the epilimnion during the stratification period, leading to a decrease in DIC concentration, partial pressure of CO 2 (p CO 2) and CO 2 emission flux, and an increase in stable carbon isotope (δ13C DIC). During the mixing period, the trend was reversed; (3) During the thermal stratification, aquatic photosynthesis and water temperature were the primary factors controlling DIC variations in both the epilimnion and thermocline. Regarding the hypolimnion, calcite dissolution, organic matter decomposition, and water temperature were the dominant controlling factors. These results indicate that although carbon-rich karst groundwater provides a plentiful supply of DIC in the DLD reservoir, its availability is still influenced by variations in the reservoir's thermal structure and the metabolic processes of aquatic photosynthetic organisms. Therefore, to better estimate the regional carbon budget in a reservoir or lake, future studies should especially consider the combined effects of BCP and thermal structure variations on carbon variations. [Display omitted] • The distribution of DIC is mainly controlled by water temperature and metabolism. • The FCO 2 in the mixing period was higher than in the stratified period. • The BCP effect is expressed in the relationship between DIC and δ13C DIC. [ABSTRACT FROM AUTHOR]

Interest on the potential CO 2 sequestration of marine bivalve aquaculture has increased during the last decade. However, there is still some controversy about which biological processes are involved and how to estimate their contribution to the carbon footprint of bivalve aquaculture. This work considers the dissolved inorganic carbon, CO 2 and alkalinity fluxes linked to flesh and shell growth, calcification, respiration, faeces egestion, and ammonia excretion, accounting also for the RDOC production associated to these processes. We have developed an algorithm for a dynamic estimation of these fluxes based on a net production DEB growth model for mussels. The resulting model has been implemented in Python to create a toolbox with a graphical user interface. This toolbox allows the selection of different culture strategies, in terms of seeding date, seed size and culture length, and consequently analyzes the carbon footprint and impact on the carbonate chemistry of seawater of aquaculture management. • Mussel physiology is commonly ignored in carbon footprint estimates of mussel aquaculture. • MusselCF provides dynamic estimation of mussel culture carbon footprint and its impact on the seawater carbonate chemistry. • Hydrography, carbonate chemistry, seeding time and mussel seed and harvest size dictate the physiological carbon footprint. [ABSTRACT FROM AUTHOR]

This study combines measurements of dissolved inorganic carbon (DIC), total alkalinity (TA), pH, earth observation (EO), and ocean model products with deep learning to provide a good step forward in detecting changes in the ocean carbonate system parameters at a high spatial and temporal resolution in the North Atlantic region (Long. −61.00° to −50.04° W; Lat. 24.99° to 34.96° N). The in situ reference dataset that was used for this study provided discrete underway measurements of DIC, TA, and pH collected by M/V Equinox in the North Atlantic Ocean. A unique list of co-temporal and co-located global daily environmental drivers derived from independent sources (using satellite remote sensing, model reanalyses, empirical algorithms, and depth soundings) were collected for this study at the highest possible spatial resolution (0.04° × 0.04°). The resulting ANN-estimated DIC, TA, and pH obtained by deep learning shows a high correspondence when verified against observations. This study demonstrates how a select number of geophysical information derived from EO and model reanalysis data can be used to estimate and understand the spatiotemporal variability of the oceanic carbonate system at a high spatiotemporal resolution. Further methodological improvements are being suggested.

The present study reviewed the carbon-biogeochemistry-related observations concerning CO2 and CH4 dynamics in the estuaries adjoining the Indian Sundarbans mangrove ecosystem. The review focused on the partial pressure of CO2 and CH4 [pCO2(water) and pCH4(water)] and air–water CO2 and CH4 fluxes and their physical, biogeochemical, and hydrological drivers. The riverine-freshwater-rich Hooghly estuary has always exhibited higher CO2 emissions than the marine-water-dominated Sundarbans estuaries. The mangrove sediment porewater and recirculated groundwater were rich in pCO2(water) and pCH4(water), enhancing their load in the adjacent estuaries. Freshwater-seawater admixing, photosynthetically active radiation, primary productivity, and porewater/groundwater input were the principal factors that regulated pCO2(water) and pCH4(water) and their fluxes. Higher chlorophyll-a concentrations, indicating higher primary production, led to the furnishing of more organic substrates that underwent anaerobic degradation to produce CH4 in the water column. The northern Bay of Bengal seawater had a high carbonate buffering capacity that reduced the pCO2(water) and water-to-air CO2 fluxes in the Sundarbans estuaries. Several authors traced the degradation of organic matter to DIC, mainly following the denitrification pathway (and pathways between aerobic respiration and carbonate dissolution). Overall, this review collated the significant findings on the carbon biogeochemistry of Sundarbans estuaries and discussed the areas that require attention in the future.

The response of coastal systems to global acidification depends strongly on river inputs, which can alter the total alkalinity (AT) and dissolved inorganic carbon (DIC) in seawater. The northern Adriatic Sea (NAd) is a shallow continental shelf region that currently receives about 15% of the total freshwater input in the Mediterranean Sea, where the role of riverine discharges on the carbonate system has been poorly studied. In particular, river discharges can alter the carbonate system in the sea, affecting both the equilibrium chemistry and biological processes. For the main rivers flowing into the NAd (the Po, Adige, Brenta, Piave, Livenza, Tagliamento, Isonzo, Timavo and Rižana), data were collected for the pH, concentrations of the total alkalinity (AT), Ca2+ and Mg2+ and the isotopic ratio of stable carbon in the dissolved inorganic carbon (δ13CDIC). The DIC fluxes were estimated using the THINCARB (THermodynamic modeling of INOrganic CARBon) model for the compilation of the AT and pH data. The results show that the total transport of the AT in the rivers was 205 Gmol yr−1 while the transport of the DIC was 213 Gmol yr−1, of which about 70% was from the Po River. About 97% of the DIC in the river waters was in the form of bicarbonates. The high Mg2+/Ca2+ ratios indicate that dolomite weathering is predominant in the Adige, Piave, and Livenza river basins, while lower ratios in the Timavo and Rižana rivers indicate a greater proportion of calcite. The mean δ13C-DIC value was estimated to be −10.0 ± 1.7 ‰, a value nowadays considered typical for the DIC flux inputs in oceanic carbon cycle modeling. The DIC flux depends on the mineral weathering and biological activity in each river basin. However, these natural processes can be modified by anthropogenic disturbances that should be better quantified.