pCO2 Variability Research Articles

Seasonal cycle of surface ocean pCO2 and pH in the northern Indian Ocean and their controlling factors

This paper examines the seasonal variability of surface ocean pCO2and pH in the northern Indian Ocean. It aims to identify their controlling factors using a high-resolution, regional ocean-ecosystem model simulation and available surface ocean carbon observations. The seasonal variability of pCO2 and pH of the northern Indian Ocean is attributed to the changes in surface temperature (T), dissolved inorganic carbon (DIC), total alkalinity (ALK), and salinity (S). The western Arabian Sea has an enormous seasonal variance of pCO2 due to coastal upwelling dynamics. In contrast, the seasonal variance of pCO2 in the Bay of Bengal is governed by the upper ocean mixed layer dynamics, albeit with smaller amplitudes. The contribution of T (DIC) in the seasonal variance of pCO2 and pH at the western Arabian Sea is ±90 (∓100) μatm and ±0.18 (∓0.20) pH units, respectively. The contribution of ALK and S is complementary to each other in inducing seasonal variances of pCO2 and pH in the southeastern Arabian Sea with a magnitude of ±5∼10 μatm and ±0.02 pH units, respectively. In the northern Bay of Bengal, salinity plays a significant role in controlling seasonal variability of pCO2 and pH with amplitudes of roughly ±20 µatm and ±0.18 pH units, respectively, along the pathways of freshwater spreading. The maxima of seasonal amplitudes of pCO2 and pH occur during April-May and August-September for both basins. This study highlights the hotspots of pCO2 and pH in the northern Indian Ocean, where observational efforts to monitor pCO2 and pHbecome an essential requirement.

Spatiotemporal Dynamics of CO2 Gas Exchange From Headwater Mountain Streams

AbstractMountain streams play an important role in the global carbon cycle by transporting, metabolizing, and exchanging carbon they receive from the terrestrial environment. The rates at which these processes occur remain highly uncertain because of a paucity of observations and the difficulty of measuring gas exchange rates in steep, turbulent mountain streams. This uncertainty is compounded by large temporal and spatial variability in stream carbon dioxide (CO2) concentrations in mountain environments. In this study, we measured diel, seasonal, and annual variations in CO2 partial pressure (pCO2) in seven headwater streams and a groundwater spring in the Colorado Rocky Mountains to determine how CO2 exchange fluxes () vary with time, annual precipitation, and landscape characteristics. Our results show that temporal variability in pCO2 and in mountain streams is large and is strongly influenced by solar radiation, the accumulation and melting of seasonal snowpacks, and interannual variations in precipitation. Spatial variations in pCO2 and were related to landscape characteristics, with soil organic matter, wetlands, and likely groundwater discharge zones having a positive influence. Periglacial features, such as ice and rock glaciers, had a negative influence on stream pCO2 and . Estimated from streams in an alpine/subalpine region of Colorado was 3.4 kg C m−2 yr−1 normalized to stream surface area (95% CI: 2.1–5.0 kg C m−2 yr−1), consistent with recent work on CO2 exchange from mountain streams in the Swiss Alps. Our results highlight the importance of mountain streams as substantial contributors in the global carbon cycle.

Diel pCO2 fluctuations alter the molecular response of coral reef fishes to ocean acidification conditions.

Environmental partial pressure of CO2 (pCO2 ) variation can modify the responses of marine organisms to ocean acidification, yet the underlying mechanisms for this effect remain unclear. On coral reefs, environmental pCO2 fluctuates on a regular day-night cycle. Effects of future ocean acidification on coral reef fishes might therefore depend on their response to this diel cycle of pCO2 . To evaluate the effects on the brain molecular response, we exposed two common reef fishes (Acanthochromis polyacanthus and Amphiprion percula) to two projected future pCO2 levels (750 and 1,000µatm) under both stable and diel fluctuating conditions. We found a common signature to stable elevated pCO2 for both species, which included the downregulation of immediate early genes, indicating lower brain activity. The transcriptional programme was more strongly affected by higher average pCO2 in a stable treatment than for fluctuating treatments, but the largest difference in molecular response was between stable and fluctuating pCO2 treatments. This indicates that a response to a change in environmental pCO2 conditions is different for organisms living in a fluctuating than in stable environments. This differential regulation was related to steroid hormones and circadian rhythm (CR). Both species exhibited a marked difference in the expression of CR genes among pCO2 treatments, possibly accommodating a more flexible adaptive approach in the response to environmental changes. Our results suggest that environmental pCO2 fluctuations might enable reef fishes to phase-shift their clocks and anticipate pCO2 changes, thereby avoiding impairments and more successfully adjust to ocean acidification conditions.

Integrating High-Resolution Coastal Acidification Monitoring Data Across Seven United States Estuaries.

Beginning in 2015, the United States Environmental Protection Agency’s (EPA’s) National Estuary Program (NEP) started a collaboration with partners in seven estuaries along the East Coast (Barnegat Bay; Casco Bay), West Coast (Santa Monica Bay; San Francisco Bay; Tillamook Bay), and the Gulf of Mexico (GOM) Coast (Tampa Bay; Mission-Aransas Estuary) of the United States to expand the use of autonomous monitoring of partial pressure of carbon dioxide (pCO2) and pH. Analysis of high-frequency (hourly to sub-hourly) coastal acidification data including pCO2, pH, temperature, salinity, and dissolved oxygen (DO) indicate that the sensors effectively captured key parameter measurements under challenging environmental conditions, allowing for an initial characterization of daily to seasonal trends in carbonate chemistry across a range of estuarine settings. Multi-year monitoring showed that across all water bodies temperature and pCO2 covaried, suggesting that pCO2 variability was governed, in part, by seasonal temperature changes with average pCO2 being lower in cooler, winter months and higher in warmer, summer months. Furthermore, the timing of seasonal shifts towards increasing (or decreasing) pCO2 varied by location and appears to be related to regional climate conditions. Specifically, pCO2 increases began earlier in the year in warmer water, lower latitude water bodies in the GOM (Tampa Bay; Mission-Aransas Estuary) as compared with cooler water, higher latitude water bodies in the northeast (Barnegat Bay; Casco Bay), and upwelling-influenced West Coast water bodies (Tillamook Bay; Santa Monica Bay; San Francisco Bay). Results suggest that both thermal and non-thermal influences are important drivers of pCO2 in Tampa Bay oxygen, National Estuary Program and Mission-Aransas Estuary. Conversely, non-thermal processes, most notably the biogeochemical structure of coastal upwelling, appear to be largely responsible for the observed pCO2 values in West Coast water bodies. The co-occurrence of high salinity, high pCO2, low DO, and low temperature water in Santa Monica Bay and San Francisco Bay characterize the coastal upwelling paradigm that is also evident in Tillamook Bay when upwelling dominates freshwater runoff and local processes. These data demonstrate that high-quality carbonate chemistry observations can be recorded from estuarine environments using autonomous sensors originally designed for open-ocean settings.

Increase in CO2 Uptake Capacity in the Arctic Chukchi Sea During Summer Revealed by Satellite‐Based Estimation

AbstractThe capacity of CO2 uptake in the Chukchi Sea is particularly sensitive to rapid physical and biological changes. However, scarce field observations pose a challenge in understanding the long‐term trend of CO2 uptake capacity on this continental shelf. We adopted a machine‐learning‐based approach to construct a 17‐years (2003–2019) long‐term time series of summer sea surface partial pressure of CO2 (pCO2) from remote sensing products. We show that the long‐term increase in CO2 uptake capacity can be attributed to strong and enhanced biological uptake. In addition, the intraseasonal variability of surface pCO2 in early summer confirms the crucial role of sea ice melt and the subsequently enhanced photosynthesis as soon as the surface ocean converts into an open system. Our results thus highlight the use of remote sensing data in interpolating/extrapolating the highly dynamic carbonate system in the continental shelf sea and shed light into future studies involving machine learning or algorithms.

A semi‐empirical mathematical model to specify the pH of bicarbonate‐buffered cell culture medium formulations

AbstractThe carbon dioxide/bicarbonate system is routinely used as a buffer in mammalian cell culture medium. However, due to the continuous degassing of carbon dioxide and its dependence on temperature, it is difficult to achieve the target pH during preparation at ambient temperature and without control of dissolved carbon dioxide, and even more so at cell culture operating conditions. These problems were amplified when preparing multiple (e.g., 20) customized preparations of an in‐sourced proprietary medium during research and process development of mammalian cell culture systems. Thus, a mathematical model was created to specify the amount of acid or base to add during preparation so as to achieve the target pH of each medium at process conditions without having to do titration. The relationship between gaseous carbon dioxide and the dissolved carbon dioxide in the proprietary medium containing unknown species was specified using a modified Henry's law equation (as done in prior work). Further, to allow medium preparation without doing titration, the acid/base properties of the proprietary medium were fitted by a parameter related to its Net Medium Acids during specification of model parameters. A subset of the solutions was prepared and tested in bioreactors with controlled CO2 flow to validate the model. Then, the model was used to assess the equivalence of the pHs of the customized medium formulations despite variations in pCO2 that occurred during incubation and sampling.

CO2 dynamics and heterogeneity in a cave atmosphere: role of ventilation patterns and airflow pathways

Understanding the dynamics and distribution of CO2 in the subsurface atmosphere of carbonate karst massifs provides important insights into dissolution and precipitation processes, the role of karst systems in the global carbon cycle, and the use of speleothems for paleoclimate reconstructions. We discuss long-term microclimatic observations in a passage of Postojna Cave, Slovenia, focusing on high spatial and temporal variations of pCO2. We show (1) that the airflow through the massif is determined by the combined action of the chimney effect and external winds and (2) that the relationship between the direction of the airflow, the geometry of the airflow pathways, and the position of the observation point explains the observed variations of pCO2. Namely, in the terminal chamber of the passage, the pCO2 is low and uniform during updraft, when outside air flows to the site through a system of large open galleries. When the airflow reverses direction to downdraft, the chamber is fed by inlets with diverse flow rates and pCO2, which enter via small conduits and fractures embedded in a CO2-rich vadose zone. If the spatial distribution of inlets and outlets produces minimal mixing between low and high pCO2 inflows, high and persistent gradients in pCO2 are formed. Such is the case in the chamber, where vertical gradients of up to 1000 ppm/m are observed during downdraft. The results presented in this work provide new insights into the dynamics and composition of the subsurface atmosphere and demonstrate the importance of long-term and spatially distributed observations.

Constraining fluid-rock interactions during eogenetic karst and their impacts on carbonate reservoirs: Insights from reactive transport modeling

Eogenetic karst has been regarded as a dominant origin of hydrocarbon reservoirs, whereas quantifying the fluid-rock interactions and their impacts on porosity evolution during the palaeokarst process remain persistent challenges that limit the accuracy of reservoir quality prediction. This study investigates the dissolution of carbonate rocks with potential controlling factors by reactive transport modeling that couples fluid flow, mineral reactions and porosity changes in a one-dimensional vadose meteoric water-rock system. Simulation results of base case scenario and sensitivity analyses show that the duration of subaerial exposure and recharge capacity of rainwater significantly determine the karst-affected depth and porosity increment. The amount of calcite dissolution is also affected by a downward decrease in calcite solubility (temperature-dependent) and the enrichment of Ca2+ and HCO3− in the lower part. The atmospheric carbon dioxide concentration has a minor impact on the vertical extent of karst, while it facilitates the dissolution rate under high pCO2 conditions. The influence of atmospheric pCO2 variation over geological time on the porosity increment was reconstructed under hydrogeological conditions of the base case scenario (exposure time = 130 ka; rainfall = 628 mm/a). The differences in the dissolution rates and extent of karst between limestone and dolostone can be interpreted as the results of different rate-determining reaction mechanisms, i.e., thermodynamically controlled calcite and kinetically controlled dolomite.

Variations in Seawater pCO2 Associated With Vertical Mixing During Tropical Cyclone Season in the Northwestern Subtropical Pacific Ocean

This study examines interannual variations in the seawater CO2 partial pressure (pCO2) for months (August–October) with frequent tropical cyclone (TC) events in the northwestern subtropical Pacific Ocean (22°N–28°N, 135°E–145°E) between 2007 and 2017. The temperature-normalized pCO2 averaged over August–October showed a year-to-year variation ranging from 346 to 359 μatm over the 11 study years, which appeared to be related to the variation in vertical mixing that likely results from the TC activity in these months. Sea surface temperature and wind data consistently supported the association between mixing and TC intensity. Nonetheless, the pCO2 reduction caused by negative sea-surface temperature anomalies found over the TC season (July–October) shifted the study area from a CO2 source to a CO2 sink over these months. In the south (17°N–22°N) of the study area, mixing-driven variations in pCO2 were smaller during the same months, which appeared to be caused by the relatively deeper mixed layer depth and the more homogenous profile of CO2 in this tropical region. These results suggest that more extensive pCO2 measurements are required to fully resolve the effect of TCs on the carbonate system from the regional- to the basin-scale in the western Pacific Ocean, where TC intensity is expected to increase in the future.

Ocean acidification may mitigate negative effects of warming on carbon burial potential in subtidal unvegetated estuarine sediments

AbstractEstuarine sediments make an important contribution to the global carbon cycle, but we do not know how this will change under a future climate, which is expected to have lower pH oceans and frequent high‐temperature days. Six combinations of warming and partial pressures of CO2(pCO2) were chosen to investigate the combined and individual effects of short‐term pressures on the diel metabolic response of shallow unvegetated sediments ex‐situ. Whereas warming significantly increased respiration, making sediments more heterotrophic, high‐pCO2increased net primary productivity, resulting in less heterotrophic sediments. As a result, warming decreased the carbon burial potential of estuarine sediments and high‐pCO2had the opposite effect. High‐pCO2mitigates the negative effects of warming on benthic metabolism under the combined scenario, with carbon burial similar to that expected under high‐pCO2conditions alone. Climate scenarios also changed the diurnalpCO2variation, with ranges increasing by 33% with warming, and almost doubling under high‐pCO2conditions. An additive response inpCO2variability was observed under the combined scenario, increasing to 2.3× the current diel‐pCO2range, highlighting the reduced buffering capacity of the water associated with a high CO2climate. Future carbon burial and export under increased frequencies of unseasonably warm days projected for mid and end of century (30% and 50% of days‐per‐year, respectively) were estimated with and without ocean acidification. By 2100, warming alone could decrease annual estuarine sediment burial potential by 25%. However, ocean acidification could mitigate the negative effects of more frequent high‐temperature days and increase carbon burial potential over current conditions by ~18%.

Wastewater-boosted biodegradation amplifying seasonal variations of pCO2 in the Mekong–Tonle Sap river system

Wastewater-boosted biodegradation amplifying seasonal variations of pCO2 in the Mekong–Tonle Sap river system

Reduced Ocean Carbon Sink in the South and Central North Sea (2014–2018) Revealed From FerryBox Observations

AbstractSurface seawater carbon dioxide partial pressure (pCO2) in the south‐central North Sea was measured between 2014 and 2018 using FerryBox‐integrated membrane sensors on ships‐of‐opportunity. Average annual pCO2 variability was biologically controlled, with thermal effects modulating its amplitude. Deseasonalized winter trends of seawater pCO2 were positive (4.4 ± 2.0–8.4 ± 2.9 µatm yr−1), biogeochemically driven, stronger than the atmospheric pCO2 trend, and more pronounced than previous analyses. The trends calculated including all deseasonalized monthly averages were even higher (9.7 ± 2.8–12.2 ± 1.4 µatm yr−1). During our investigation, the southern study area became a stronger source and the northern part became a weaker sink for atmospheric carbon. Overall, average sea‐air CO2 flux in our study area, from the Skagerrak to the Southern Bight (53°N), changed from −0.75 ± 0.61 mmol m−2 day−1 in 2014 to +0.20 ± 0.96 mmol m−2 day−1 in 2018.

FC 025ACID BASE DISORDERS IN COVID-19

Background and AimsAcid-base disorders are common in severely ill patients and reflect the severity of the underlying pathologic process. The incidence and effects of acid-base derangement in COVID-19 patients have been poorly evaluated until now. Tropism of the virus for the lungs and kidneys may theoretically lead to frequent acid-base alterations due to pneumonia and kidney injury, respectively. To verify the derangement of acid-base disorders in COVID-19, we investigated the distribution and the impact of acid-base disorders on the survival of symptomatic patients with a diagnosis of COVID-19.MethodWe retrospectively collected data from electronic charts of all COVID-19 patients hospitalized at the University Hospital of Modena from 4 March to 20 June 2020.Arterial blood gas (ABG) analysis was required to monitor pulmonary gas exchange and acid-base status. A pH of less than 7.37 was categorized as acidemia and a pH of more than 7.42 was categorized as alkalemia.211 patients were included in the study population. In patients with multiple ABG analyses, we selected only the first measurement.ResultsThe estimated mean age of the population was 64.7 ±15,3 years with a high predominance of males (71.6%). Half of the population referred dyspnea and 61.4% at physical examination. Most patients (82.6%) were on oxygen therapy when ABG analysis was performed. Overall, ABG analyses revealed acute respiratory compromise manifesting with a low arterial partial pressure of oxygen (P02, 70.2±25.1 mmHg), oxygen saturation (SO2, 92%) and a mild reduction of PO2/FiO2 ratio (231±129).Acid-base disturbance was found in the 79.7% of the patients, and contrary to our expectation, metabolic alkalosis (33.6%) was the main alteration followed by respiratory alkalosis (30.3%), combined alkalosis (9.4%) respiratory acidosis (3.3%) metabolic acidosis (2.8%) and other compensated acid-base disturbances (3.6%). ANOVA with post hoc Tukey, revealed statistically significant differences in age, sex, serum level of K, Na, bicarbonate, creatinine of PCO2, PO2/FiO2 ratio, CKD, symptoms (caught, diarrhea) and fatality rate among groups.Metabolic acidosis was associated with death (HR=8.2; CI 95%, 1,93-32,39; P<0.004), after adjustment for lung injury (PaO2/FiO2 ratio) tissue hypoperfusion (lactate) and renal involvement (estimated as GFR< 60 ml/min or development of acute kidney injury), Pathological pH (alkalosis or acidosis), variations of PCO2 or hypobicarbonatemia were not associated with mortality in our study population. Metabolic acidosis occurred in patients with a mean creatinine of 4.5±4.5 mg/dl. Notably, 33.3% of patients were on hemodialysis, 33.3% developed COVID-19-associated acute kidney injury and 33.3% had a GFR <60 ml/min. Patients with metabolic acidosis had the highest death-fatality rate (100%) after 7±5.6 days from admission, 50% died of acute respiratory distress syndrome and 50% of septic shock.ConclusionIn conclusion, all kinds of acid-base alterations were found in patients with COVID-19. Metabolic and respiratory alkalosis were the most common acid-base disorders, whereas metabolic acidosis was the only acid-base disturbance associate with poor outcome in our cohort of patients.

Distribution of pCO2 and air-sea CO2 flux in Devi estuary, eastern India

Carbon dioxide (CO2) super-saturation in estuaries and the associated efflux to the atmosphere is an important part of the global carbon cycle. However, the net global estuarine emission of CO2 is based on limited spatial data. In this study, alkalinity, pH, salinity and temperature data were used to quantify the CO2 dynamics in the Devi estuary formed by the main distributary of the Mahanadi river on the east coast of India. The samples were collected during summer, monsoon and winter of 2018–19 in order to understand the seasonal and spatial variability of pCO2 and CO2 efflux from the estuary. High pCO2 (1565 ± 782 μatm) in comparison to the atmosphere (389 μatm) was found in the estuary throughout the study period. The highest pCO2 was observed during winter season (2071 ± 828 μatm) and the lowest one during monsoon (951 ± 316 μatm). A decreasing trend in pCO2 from the upper estuary to lower estuary was observed. The mean dissolved oxygen saturation (DO%) was 137% throughout the study period indicating well-oxygenated waters. A decrease in DO% with increased pCO2 accompanied by a decrease in pH suggests that organic matter degradation is a major controlling factor of pCO2 in the estuary. Thus, heterotrophic environmental condition is prevalent in the estuary. Net annual CO2 efflux from the Devi river estuary was estimated to be 40.1 ± 7.5 mol C m−2 yr−1, and the highest efflux was observed during summer season (126 ± 69 mmol C m−2 d−1) due to higher temperature and wind speed. The net efflux from the Devi river estuary is about 0.003–0.006% of the total global CO2 emission from estuaries. This study highlights the importance of small-scale estuaries in emitting large flux of CO2 to the atmosphere. The results contribute to the increasing dataset of pCO2 and CO2 effluxes from estuaries worldwide in order to accurately estimate the role of estuaries in the global carbon budget.

PCO2 and CO2 evasion from two small suburban rivers: Implications of the watershed urbanization process

Rivers are widely reported as CO2-emitting hotpots and are attracting increasing attention worldwide. However, less attention has been given to the CO2 emission from the suburban rivers which are experiencing rapid watershed urbanization and increasing anthropogenic stress. Here, two small suburban rivers in Southwest China were studied, and seasonal sampling campaigns with high spatial resolution were carried out to explore the characterization of partial pressure (pCO2) and CO2 efflux and their possible controls. The results showed that, the pCO2 and estimated CO2 fluxes from the two suburban rivers ranged from 37 to 6466 μatm (mean of 1293 ± 1126 μatm) and −72–1569 mmol·m−2·d−1 (mean of 185 ± 240 mmol·m−2·d−1), respectively. And, both of them exhibited disproportionately high variability and acted as strong CO2 emitters to the atmosphere. The pCO2 in the two suburban rivers showed significant spatial variability, with urban sections having 2–2.5 times higher values than exurban sections, and, the urban land use proportion in the basins accounted for 35%–67% of such spatial variation in pCO2. The sewage-dominated urban tributaries had much higher pCO2 and acted as an obvious exciter to the high pCO2 in urban sections of suburban rivers. Carbon and nutrients concentrations also accounted for the spatial variation in pCO2 and fCO2 in the two suburban rivers, and acted as good indicators. The seasonal variation in pCO2, with the highest values in autumn and lowest values in spring, was controlled by the precipitation dilution effect and seasonal temperature as well as the boosted primary production at several urban sites. We highlighted that small suburban rivers showed disproportionally high spatial variability in pCO2 and CO2 fluxes in their limited basin areas due to the development of urbanization, and could be used as a good model for studying the complex impacts of anthropogenic disturbances on river carbon biogeochemical processes.

Seasonal and Interannual Variability of the CO2 System in the Eastern Mediterranean Sea: A Case Study in the North Western Levantine Basin

The seasonal variability of the carbonate system in the eastern Mediterranean Sea (EMed) was investigated based on discrete total alkalinity (AT), total dissolved inorganic carbon (CT), and pH measurements collected during three cruises around Crete between June 2018 and March 2019. This study presents a detailed description of this new carbonate chemistry dataset in the eastern Mediterranean Sea. We show that the North Western Levantine Basin (NWLB) is unique in terms of range of AT variation vs. CT variation in the upper water column over an annual cycle. The reasons for this singularity of the NWLB can be explained by the interplay between strong evaporation and the concomitant consumption of CT by autotrophic processes. The high range of AT variations, combined to temperature changes, has a strong impact on the variability of the seawater pCO2 (pCO2SW). Based on Argo float data, an entire annual cycle for pCO2SW in the NWLB has been reconstructed in order to estimate the temporal sequence of the potential “source” and “sink” of atmospheric CO2. By combining this dataset with previous observations in the NWLB, this study shows a significant ocean acidification and a decrease in the oceanic surface pHT25 of −0.0024 ± 0.0004 pHT25 units.a–1. The changes in the carbonate system are driven by the increase of atmospheric CO2 but also by unexplained temporal changes in the surface AT content. If we consider that the EMed will, in the future, encounter longer, more intense and warmer summer seasons, this study proposes some perspectives on the carbonate system functioning of the “future” EMed.

The Effect of CO2 on Resting-State Functional Connectivity: Isocapnia vs. Poikilocapnia.

The normal variability in breath size and frequency results in breath-to-breath variability of end-tidal PCO2 (PETCO2), the measured variable, and arterial partial pressure of carbon dioxide (PaCO2), the independent variable affecting cerebral blood flow (CBF). This study examines the effect of variability in PaCO2 on the pattern of resting-state functional MRI (rs-fMRI) connectivity. A region of interest (ROI)-to-ROI and Seed-to-Voxel first-level bivariate correlation, hemodynamic response function (hrf)-weighted analysis for measuring rs-fMRI connectivity was performed during two resting-state conditions: (a) normal breathing associated with breath-to-breath variation in PaCO2 (poikilocapnia), and (b) normal breathing with breath-to-breath variability of PETCO2 dampened using sequential rebreathing (isocapnia). End-tidal PCO2 (PETCO2) was used as a measurable surrogate for fluctuations of PaCO2. During poikilocapnia, enhanced functional connections were found between the cerebellum and inferior frontal and supramarginal gyrus (SG), visual cortex and occipital fusiform gyrus; and between the primary visual network (PVN) and the hippocampal formation. During isocapnia, these associations were not seen, rather enhanced functional connections were identified in the corticostriatal pathway between the putamen and intracalacarine cortex, supracalcarine cortex (SCC), and precuneus cortex. We conclude that vascular responses to variations in PETCO2, account for at least some of the observed resting state synchronization of blood oxygenation level-dependent (BOLD) signals.

Water column baseline assessment for offshore Carbon Dioxide Capture and Storage (CCS) sites: Analysis of field data from the Goldeneye storage complex area

Monitoring operations at the seafloor above a storage complex area are required to demonstrate that offshore storage of CO2 in the deep subsurface is safe and effective. Within the framework of the STEMM-CCS project, the Goldeneye area was identified as an offshore experimental site for CO2 storage. In this work, the physico-chemical characteristics of the water column at the Goldeneye site were determined by an in-depth analysis of measurements collated from CTD casts, discrete water samples and seafloor landers. The results showed a clear tidal, seasonal and inter-annual variability in the measured parameters within the monitoring period (Oct 2017- May 2019). Variations in pH and pCO2 over a single tidal cycle were in the order of ±0.008 and ±1.5 μatm, respectively. The temporal variability of water column carbonate chemistry parameters was further defined with the aim to provide a solid background for the discrimination from natural changes of potential impacts of CO2 emissions at the potential storage site. Here, we demonstrated how the combination of new and existing methods and technologies could be used for an effective assessment of water column conditions at a potential offshore carbon storage site.

Controlling factors of seasonal and spatial variation of riverine CO2 partial pressure and its implication for riverine carbon flux

Global carbon cycle is closely related to the earth's energy budget, because CO2 plays an active role in the global climate change. The higher CO2 partial pressure (pCO2) in inland water in comparison with atmosphere, causing a CO2 evasion from water to the air. However, the relationship between CO2 evasion, riverine carbon export, and hydrochemistry in watershed has remained largely unknown. This study collected 84 river water samples in Jiulongjiang River, to further address this subject on a small watershed scale. Water temperature fluctuation, riverine photosynthesis, and acidic matter input could not account for the seasonal variation of pCO2 in Jiulongjiang River. The spatial shifts of pCO2 were derived from the mixing process between headwater and soil influx. The soil influx with high pCO2 compensated the CO2 lost from evasion and caused pCO2 in Jiulongjiang River higher than the atmospheric level. The seasonal variation of pCO2 was caused by the precipitation difference between the wet season and dry season. The addition of rainwater significantly decreased the riverine pCO2 and HCO3− concentration in the wet season. The CO2 evasion rate in Jiulongjiang River was clearly higher than that in most worldwide large rivers. The annual CO2 evasion flux in Jiulongjiang River Basin was estimated about 2.48 × 105 T C/year, which was higher than the riverine total carbon export. The CO2 evasion rate exhibited significantly positive relationship with water surface area, indicating that the global CO2 evasion flux may be roughly estimated based on the observed regression relationship. Overall, our study indicated that it still requires collaborative effects to investigate the carbon dynamics in river water, more estimations of CO2 outgassing flux from river water under different hydrologic and geologic conditions are necessary.

Sea surface pCO2 variability and air-sea CO2 exchange in the coastal Sudanese Red Sea

The dynamics of sea surface pCO2 (pCO2w) and air–sea CO2 exchange of the Sudanese coastal Red Sea has for the first time been studied over a full annual cycle (October 2014–October​ 2015) based on semi-continuous measurements from moored autonomous sensors. pCO2w showed a seasonal amplitude of approximately 70 μatm, overlaid by a high frequency (3-4 days) signal of around 10 μatm. The highest values, of about 440 μatm occurred during summer and fall, while the lowest values of about 370 μatm occurred during winter. The monthly pCO2w change was primarily driven by temperature, i.e., heating and cooling of the water surface. Additionally, Dissolved Inorganic Carbon (DIC) and Total Alkalinity (AT) contributed significantly to the observed change in pCO2w as a consequence of along-coast advection and upwelling of CO2-rich deep water, and likely biological production, and uptake of atmospheric CO2. The area is a net annual source for atmospheric CO2 of 0.180 ± 0.009 mol CO2 m−2 y−1. Based on a compilation of historic and our new data, altogether covering the years 1977 to 2015, long term trends of pCO2w were determined for the seasons winter–spring (1.75 ± 0.72 μatm y−1) and summer -fall (180 ± 0.41 μatm y−1), both weaker than the atmospheric trend (1.96 ± 0.02 μatm y−1). We are suggesting that the study region has transformed from being a source of CO2 to the atmosphere throughout the year to becoming a sink of CO2 during parts of the year. The long term pCO2w trend was to a large degree driven by increasing DIC, but increasing AT and temperature also played a role.