CO2 Signal Research Articles

The evolution and diurnal expression patterns of photosynthetic pathway genes of the invasive alien weed, Mikania micrantha

Mikania micrantha is a fast-growing global invasive weed species that causes severe damage to natural ecosystems and very large economic losses of forest and crop production. It has advantages in photosynthesis, including a similar net photosynthetic rate as C4 plants and a higher carbon fixation capacity. We used a combination of genomics and transcriptomics approaches to study the evolutionary mechanisms and circadian expression patterns of M. micrantha. In M. micrantha, 16 positive selection genes focused on photoreaction and utilization of photoassimilates. In different tissues, 98.1% of the genes associated with photoresponse had high expression in stems, and more than half of the genes of the C4 cycle had higher expression in stems than in leaves. In stomatal opening and closing, 2 genes of carbonic anhydrase (CAs) had higher expression at 18:00 than at 8:00, and the slow anion channel 1 (SLAC1) and high-leaf-temperature 1 kinase (HT1) genes were expressed at low levels at 18:00. In addition, genes associated with photosynthesis had higher expression levels at 7:00 and 17:00. We hypothesized that M. micrantha may undergo photosynthesis in the stem and flower organs and that some stomata of the leaves were opening at night by CO2 signals. In addition, its evolution may attenuate photoinhibition at high light intensities, and enhance more efficient of photosynthesis during low light intensity. And the tissue-specific photosynthetic types and different diurnal pattern of photosynthetic-related genes may contribute to its rapid colonization of new habitats of M. micrantha.

Light-independent regulation of algal photoprotection by CO2 availability

Photosynthetic algae have evolved mechanisms to cope with suboptimal light and CO2 conditions. When light energy exceeds CO2 fixation capacity, Chlamydomonas reinhardtii activates photoprotection, mediated by LHCSR1/3 and PSBS, and the CO2 Concentrating Mechanism (CCM). How light and CO2 signals converge to regulate these processes remains unclear. Here, we show that excess light activates photoprotection- and CCM-related genes by altering intracellular CO2 concentrations and that depletion of CO2 drives these responses, even in total darkness. High CO2 levels, derived from respiration or impaired photosynthetic fixation, repress LHCSR3/CCM genes while stabilizing the LHCSR1 protein. Finally, we show that the CCM regulator CIA5 also regulates photoprotection, controlling LHCSR3 and PSBS transcript accumulation while inhibiting LHCSR1 protein accumulation. This work has allowed us to dissect the effect of CO2 and light on CCM and photoprotection, demonstrating that light often indirectly affects these processes by impacting intracellular CO2 levels.

Fingerprint of Climate Change on Southern Ocean Carbon Storage

AbstractThe Southern Ocean plays a critical role in the uptake, transport, and storage of carbon by the global oceans. It is the ocean's largest sink of CO2, yet it is also among the regions with the lowest storage of anthropogenic carbon. This behavior results from a unique combination of high winds driving the upwelling of deep waters and the subduction and northward transport of surface carbon. Here we isolate the direct effect of increasing anthropogenic CO2 in the atmosphere from the indirect effect of climate variability and climate change on the reorganization of carbon in the Southern Ocean interior using a combination of modeling and observations. We show that the effect of climate variability and climate change on the storage of carbon in the Southern Ocean is nearly as large as the effect of anthropogenic CO2 during the period 1998–2018 compared with the climatology around the year 1995. We identify a distinct climate fingerprint in dissolved inorganic carbon (DIC), with elevated DIC concentration in the ocean at 300–600 m that reinforces the anthropogenic CO2 signal, and reduced DIC concentration in the ocean around 2,000 m that offsets the anthropogenic CO2 signal. The fingerprint is strongest at lower latitudes (30°–55°S). This fingerprint could serve to monitor the highly uncertain evolution of carbon within this critical ocean basin, and better identify its drivers.

Observing System Choice Can Minimize Interference of the Biosphere in Studies of Urban CO2 Emissions

AbstractCities around the world have introduced initiatives to reduce CO2 emissions. Atmospheric observations can provide evaluation and assessment of these initiatives by quantifying emissions, considering local sources and sinks. The relative importance of the urban biosphere, which can act as both a source (respiration) and sink (photosynthesis) of CO2, has previously been suggested to strongly impact urban CO2 measurements, confounding the ability to use observations to study fossil emissions. However, if using an observing framework that measures a local urban background and the direct urban core outflow, for example, along a downwind airborne transect, the biosphere’s role may be minimized. Here, we combine real, airborne observations of CO2 downwind of select cities in the Northeast US with high‐resolution, back‐trajectory modeling and spatially and temporally resolved surface biosphere and fossil fuel fluxes to characterize the relative biosphere importance to urban CO2 profiles. We show the biosphere influence using this urban observing system to be small, averaging only 15% of the local CO2 enhancement annually, <10% outside of summer, and with a maximum influence of 29% in summer when the biosphere drawdown is most pronounced. Furthermore, when considering two biosphere models that differ by >80%, the impact on observed urban CO2 signals is reduced to only 12% on average. Urban observing frameworks that utilize this local background approach—including those via aircraft or satellite observations—can minimize the biosphere's influence and thus help facilitate robust assessments of urban fossil fuel CO2 emissions.

Atmospheric verification of emissions reductions on paths to deep decarbonization

A central challenge for sustaining international cooperation to cut global greenhouse gas emissions is confidence that national policy efforts are leading to a meaningful impact on the climate. Here, we apply a detection protocol to determine when the measurable signal of atmospheric CO2 can be distinguished from the noise of the carbon cycle and uncertainties in emission trends. We test that protocol with a database of 226 emission mitigation scenarios—the universe of scenarios vetted by the Intergovernmental Panel on Climate Change. These scenarios are descriptive of ‘baseline’ trajectories of emissions trends in the absence of new policies along with trajectories that reflect substantial policy efforts to stop warming at 1.5 °C–2 °C above pre-industrial levels, as embodied in the Paris Agreement. The most aggressive mitigation scenarios (i.e. 1.5 °C) require 11–16 years to detect a signal of demonstrable progress from the noise; 2 °C scenarios lengthen detection by at least a decade. As more climate policy analysts face the reality that goals of 1.5 °C–2 °C seem infeasible, they have developed ‘overshoot’ scenarios with emissions that rise above the agreed goal and then, later on, fall aggressively to achieve it. These pathways come at the political cost of a 1–2 decade delay in detection, even for the 1.5 °C scenarios. The Paris Agreement requires a global ‘stocktake’ that interrogates national mitigation efforts; our results suggest that this effort must grapple with the question of when the world can gain confidence that the diplomacy on climate is demonstrably making an impact.

Using carpet plots to analyze blood transit times in the brain during hypercapnic challenge magnetic resonance imaging.

Blood arrival time and blood transit time are useful metrics in characterizing hemodynamic behaviors in the brain. Functional magnetic resonance imaging in combination with a hypercapnic challenge has been proposed as a non-invasive imaging tool to determine blood arrival time and replace dynamic susceptibility contrast (DSC) magnetic resonance imaging, a current gold-standard imaging tool with the downsides of invasiveness and limited repeatability. Using a hypercapnic challenge, blood arrival times can be computed by cross-correlating the administered CO2 signal with the fMRI signal, which increases during elevated CO2 due to vasodilation. However, whole-brain transit times derived from this method can be significantly longer than the known cerebral transit time for healthy subjects (nearing 20s vs. the expected 5-6s). To address this unrealistic measurement, we here propose a novel carpet plot-based method to compute improved blood transit times derived from hypercapnic blood oxygen level dependent fMRI, demonstrating that the method reduces estimated blood transit times to an average of 5.32s. We also investigate the use of hypercapnic fMRI with cross-correlation to compute the venous blood arrival times in healthy subjects and compare the computed delay maps with DSC-MRI time to peak maps using the structural similarity index measure (SSIM). The strongest delay differences between the two methods, indicated by low structural similarity index measure, were found in areas of deep white matter and the periventricular region. SSIM measures throughout the remainder of the brain reflected a similar arrival sequence derived from the two methods despite the exaggerated spread of voxel delays computed using CO2 fMRI.

Simultaneous detection of multi-component greenhouse gases based on an all-fibered near-infrared single-channel frequency-division multiplexing wavelength-modulated laser heterodyne radiometer

The performance of an all fibered near-infrared (NIR) single-channel frequency-division multiplexing wavelength-modulated laser heterodyne radiometer (FDM WM-LHR) is demonstrated in ground-based solar occultation mode. The system modulates the laser through the high-frequency signal output by the lock-in amplifier to replace the traditional chopper modulation, making it more stable and compact. Moreover, personal computers are used to simultaneously control the operating current of two distributed feedback (DFB) lasers through a general purpose interface bus-universal serial bus (GPIB-USB), thereby controlling the central wavelength of the laser at 1602.88 and 1653.727 nm, which serve as the absorption lines for the local oscillator detection of the two main greenhouse gases: CO2 and CH4. Firstly, the performance of traditional laser heterodyne radiometer (LHR) and the wavelength-modulated laser heterodyne radiometer (WM-LHR) are compared. The results reveal that both the radiometers have an optimized 2f signal when the modulation amplitude m = 2.2. In the actual measurement, 0.25 V and 0.21 V are selected as the modulation amplitude of the laser for the detection of CH4 and CO2. Under the same experimental parameters, at 1602.88 nm, the signal-to-noise ratio (SNR) for the 2f signal of CO2 in the WM-LHR system is 500.24, while that for the direct absorption signal (DAS) of CO2 in the traditional LHR system is 337.94. At 1653.727 nm, the SNR for the 2f signal in the WM-LHR system and the DAS of CH4 in the traditional LHR system are 512.04 and 389.58, respectively. Obviously, the SNR for the WM-LHR system is greatly improved. Finally, the application of frequency-division multiplexing (FDM) technology in the WM-LHR system is discussed. The modulation frequency of the two lasers should be appropriately selected to avoid interference between the signals. Overall, the results show that the FDM WM-LHR system can not only detect multiple gases simultaneously but also reduce the implementation cost of the ground-based radiometer. In addition, this study provides useful insights on planetary atmosphere exploration.

Diurnal variability of atmospheric O2, CO2, and their exchange ratio above a boreal forest in southern Finland

Abstract. The exchange ratio (ER) between atmospheric O2 and CO2 is a useful tracer for better understanding the carbon budget on global and local scales. The variability of ER (in mol O2 per mol CO2) between terrestrial ecosystems is not well known, and there is no consensus on how to derive the ER signal of an ecosystem, as there are different approaches available, either based on concentration (ERatmos) or flux measurements (ERforest). In this study we measured atmospheric O2 and CO2 concentrations at two heights (23 and 125 m) above the boreal forest in Hyytiälä, Finland. Such measurements of O2 are unique and enable us to potentially identify which forest carbon loss and production mechanisms dominate over various hours of the day. We found that the ERatmos signal at 23 m not only represents the diurnal cycle of the forest exchange but also includes other factors, including entrainment of air masses in the atmospheric boundary layer before midday, with different thermodynamic and atmospheric composition characteristics. To derive ERforest, we infer O2 fluxes using multiple theoretical and observation-based micro-meteorological formulations to determine the most suitable approach. Our resulting ERforest shows a distinct difference in behaviour between daytime (0.92 ± 0.17 mol mol−1) and nighttime (1.03 ± 0.05 mol mol−1). These insights demonstrate the diurnal variability of different ER signals above a boreal forest, and we also confirmed that the signals of ERatmos and ERforest cannot be used interchangeably. Therefore, we recommend measurements on multiple vertical levels to derive O2 and CO2 fluxes for the ERforest signal instead of a single level time series of the concentrations for the ERatmos signal. We show that ERforest can be further split into specific signals for respiration (1.03 ± 0.05 mol mol−1) and photosynthesis (0.96 ± 0.12 mol mol−1). This estimation allows us to separate the net ecosystem exchange (NEE) into gross primary production (GPP) and total ecosystem respiration (TER), giving comparable results to the more commonly used eddy covariance approach. Our study shows the potential of using atmospheric O2 as an alternative and complementary method to gain new insights into the different CO2 signals that contribute to the forest carbon budget.

Efficacy of the CO Tracer Technique in Partitioning Biogenic and Anthropogenic Atmospheric CO2 Signals in the Humid Subtropical Eastern Highland Rim City of Cookeville, Tennessee

Accurate accounting of the partition between anthropogenic and biogenic carbon dioxide mixing ratios (CO2Anth and CO2Bio) in urban-based CO2 measurements is key to developing effective emission reduction strategies since such measurements can provide an independent catalogue of local and regional CO2 emission inventories. In an attempt to delineate the contribution of CO2Bio to the overall urban CO2 mixing ratio enhancements, carbon monoxide (CO) was utilized as a tracer, following CO2 and CO mixing ratio measurements using a wavelength-scanned cavity ring-down spectrometer (CRDS). These measurements were performed in Cookeville, TN, (36.1628° N, 85.5016° W), a medium-sized city within the Eastern Highland Rim region of the United States. Between the years 2017 and 2019, the average seasonal wintertime CO2Bio mixing ratios varied between −0.65 ± 3.44 ppm and 0.96 ± 2.66 ppm. During the springtime, the observed CO2Bio signals were largely negative while the CO2Anth values were generally lower than the wintertime values. The contribution of CO from the isoprene oxidation reaction with the hydroxyl radical (OH) (COisoprene) to the overall CO enhancement during the growing season was estimated to be ~17–27 ppb, underscoring the importance of considering the contribution of COisoprene to untangling different CO2Anth and CO2Bio sources and sinks in high isoprene-emitting urban environments.

MICA-Based fMRI Analysis of Specific CO2-Level-Dependent BOLD Signal Changes in the Human Brainstem

Noninvasive studies of the central respiratory control are of key importance to understanding the physiopathology of central apneas and periodic breathing. The study of the brainstem and cortical-subcortical centers may be achieved by using functional magnetic resonance imaging (fMRI) during gas challenges (hypercapnia). Nonetheless, disentangling specific from non-specific effects of hypercapnia in fMRI is a major methodological challenge, as CO2 vasodilatory effects and physiological noise do strongly impact the BOLD signal. This is particularly true in deep brainstem regions where chemoreceptors and rhythm pattern generators are located. One possibility to detect the true neural-related activation is given by the presence of a supralinear relation between CO2 changes and BOLD signal related to neurovascular coupling in overactive neural areas. Here, we test this hypothesis of a supralinear relationship between CO2 and BOLD signal, as a marker of specificity. We employed a group-masked Independent Component Analysis (mICA) approach and we compared activation levels across different mixtures of inspired CO2 using polynomial regression. Our results highlight key nodes of the central breathing control network, also including dorsal pontine and medullary regions. The suggested methodology allows a voxel-wise parametrization of the response, targeting an issue that affects many fMRI studies employing hypercapnic challenges.

General Circulation Model Constraints on the Detectability of the CO2-CH4 Biosignature Pair on TRAPPIST-1e with JWST

Terrestrial exoplanets such as TRAPPIST-1e will be observed in a new capacity with the JWST/Near Infrared Spectrograph (NIRSpec), which is expected to be able to detect CO2, CH4, and O2 signals, if present, with multiple coadded transit observations. The CO2-CH4 pair in particular is theorized to be a potential biosignature when inferred to be in chemical disequilibrium. Here, we simulate TRAPPIST-1e’s atmosphere using the ExoCAM general circulation model, assuming an optimistic haze-free, tidally locked planet with an aquaplanet surface, with varying atmospheric compositions from 10−4 bar to 1 bar of partial CO2 pressure with 1 bar of background N2. We investigate cases both with and without a modern Earth-like CH4 mixing ratio to examine the effect of CO2 and CH4 on the transmission spectrum and climate state of the planet. We demonstrate that in the optimistic haze-free cloudy case, H2O, CO2, and CH4 could all be detectable in less than 50 transits within an atmosphere of 1 bar N2 and 10 mbar CO2 during JWST’s lifespan with NIRSpec as long as the noise floor is ≲10 ppm. We find that in these optimistic cases, JWST may be able to detect potential biosignature pairs such as CO2-CH4 in TRAPPIST-1e’s atmosphere across a variety of atmospheric CO2 content, and that temporal climate variability does not significantly affect spectral feature variability for NIRSpec PRISM.

Carbon isotope study of conodont elements: Applications and limitations

Conodont elements composed of protein-apatite nanocomposites are considered a promising geochemical archive due to their high resistivity to weathering and diagenetic processes. This article introduces some possible applications and limitation of the carbon isotope investigations in conodont research. It is based on the author's collections of conodonts comprising stratigraphic interval from the Upper Devonian to the Mississippian. Total number of the studied conodont elements is 282. The data obtained suggest that isotopic compositions of carbon of conodont elements probably reflect isotopic composition of the conodont diet with some insignificant taphonomical and histological biases. The variations in δ13Ccon were probably controlled by changes in the C-isotope composition of the phytoplankton as the main part of conodont food, which, in turn, was affected by global and local changes in the pelagic ecosystem. Decrease in δ13Ccon may be provoked by shortening of the food chains, enhancing of C-isotope fractioning by phytoplankton, and a decrease in δ13C of atmospheric CO2. Significant changes in δ13Ccon mark probable perturbations in the pelagic ecosystems. Decoupling carbon isotope composition of carbonates and conodont elements is a proxy of the water temperature, CO2 concentration in atmosphere and hydrosphere, and phytoplankton growth rate. It is likely that the CO2 concentration was a leading factor affecting decoupling carbon isotope composition of carbonates and conodont elements in the late Famennian – Tournaisian interval. However, the CO2 signal can be obscured by variations in primary bioproductivity. Fluctuations in decoupling carbon isotope composition of carbonates and conodont elements reflect global and local changes in pelagic marine ecosystems, and prominent excursions can be used as stratigraphic markers.

Determination of carbonate content in barite ore by headspace gas chromatography.

This paper reports a method for determining the carbonate content in barite ore using headspace gas chromatography. Based on the acidification reaction, the carbonate in the barite ore was converted to CO2 in a closed headspace vial. When the carbonate content was significant, the pressure caused changes in the CO2 and O2 signals and affected the measurement accuracy. It was found that carbonate content is proportional to the intensity ratio of the CO2 to O2 signals. Thus, the carbonate content in barite ore can be measured indirectly using a theoretical model. The results showed that the carbonate in 3g of barite ore sample with a particle size of 74μm could react completely with a hydrochloric acid solution (2mol/L) at 65°C for 5min. The method described herein had good precision (relative standard deviation<4.14%) and accuracy (relative differences<6.12%). Further, the limit of quantification was 0.07mol/L. Owing to its simplicity and speed, this method can be used for the batch determination of carbonate content in barite ore.

Elevated CO2 induces rapid dephosphorylation of plasma membrane H+ -ATPase in guard cells.

Light induces stomatal opening, which is driven by plasma membrane (PM) H+ -ATPase in guard cells. The activation of guard-cell PM H+ -ATPase is mediated by phosphorylation of the penultimate C-terminal residue, threonine. The phosphorylation is induced by photosynthesis as well as blue light photoreceptor phototropin. Here, we investigated the effects of cessation of photosynthesis on the phosphorylation level of guard-cell PM H+ -ATPase in Arabidopsis thaliana. Immunodetection of guard-cell PM H+ -ATPase, time-resolved leaf gas-exchange analyses and stomatal aperture measurements were carried out. We found that light-dark transition of leaves induced dephosphorylation of the penultimate residue at 1 min post-transition. Gas-exchange analyses confirmed that the dephosphorylation is accompanied by an increase in the intercellular CO2 concentration, caused by the cessation of photosynthetic CO2 fixation. We discovered that CO2 induces guard-cell PM H+ -ATPase dephosphorylation as well as stomatal closure. Interestingly, reverse-genetic analyses using guard-cell CO2 signal transduction mutants suggested that the dephosphorylation is mediated by a mechanism distinct from the established CO2 signalling pathway. Moreover, type 2C protein phosphatases D6 and D9 were required for the dephosphorylation and promoted stomatal closure upon the light-dark transition. Our results indicate that CO2 -mediated dephosphorylation of guard-cell PM H+ -ATPase underlies stomatal closure.

A novel capnogram analysis to guide ventilation during cardiopulmonary resuscitation: clinical and experimental observations

BackgroundCardiopulmonary resuscitation (CPR) decreases lung volume below the functional residual capacity and can generate intrathoracic airway closure. Conversely, large insufflations can induce thoracic distension and jeopardize circulation. The capnogram (CO2 signal) obtained during continuous chest compressions can reflect intrathoracic airway closure, and we hypothesized here that it can also indicate thoracic distension.ObjectivesTo test whether a specific capnogram may identify thoracic distension during CPR and to assess the impact of thoracic distension on gas exchange and hemodynamics.Methods(1) In out-of-hospital cardiac arrest patients, we identified on capnograms three patterns: intrathoracic airway closure, thoracic distension or regular pattern. An algorithm was designed to identify them automatically. (2) To link CO2 patterns with ventilation, we conducted three experiments: (i) reproducing the CO2 patterns in human cadavers, (ii) assessing the influence of tidal volume and respiratory mechanics on thoracic distension using a mechanical lung model and (iii) exploring the impact of thoracic distension patterns on different circulation parameters during CPR on a pig model.Measurements and main results(1) Clinical data: 202 capnograms were collected. Intrathoracic airway closure was present in 35%, thoracic distension in 22% and regular pattern in 43%. (2) Experiments: (i) Higher insufflated volumes reproduced thoracic distension CO2 patterns in 5 cadavers. (ii) In the mechanical lung model, thoracic distension patterns were associated with higher volumes and longer time constants. (iii) In six pigs during CPR with various tidal volumes, a CO2 pattern of thoracic distension, but not tidal volume per se, was associated with a significant decrease in blood pressure and cerebral perfusion.ConclusionsDuring CPR, capnograms reflecting intrathoracic airway closure, thoracic distension or regular pattern can be identified. In the animal experiment, a thoracic distension pattern on the capnogram is associated with a negative impact of ventilation on blood pressure and cerebral perfusion during CPR, not predicted by tidal volume per se.

Complementing XCO2 imagery with ground-based CO2 and 14CO2 measurements to monitor CO2 emissions from fossil fuels on a regional to local scale

Abstract. Various satellite imagers of the vertically integrated column of carbon dioxide (XCO2) are under development to enhance the capabilities for the monitoring of fossil fuel (FF) CO2 emissions. XCO2 images can be used to detect plumes from cities and large industrial plants and to quantify the corresponding emission using atmospheric inversions techniques. However, this potential and the ability to catch the signal from more diffuse FF CO2 sources can be hampered by the mix between these FF signals and a background signal from other types of CO2 surface fluxes, and in particular of biogenic CO2 fluxes. The deployment of dense ground-based air-sampling networks for CO2 and radiocarbon (14CO2) could complement the spaceborne imagery by supporting the separation between the fossil fuel and biogenic or biofuel (BF) CO2 signals. We evaluate this potential complementarity with a high-resolution analytical inversion system focused on northern France, western Germany, Belgium, Luxembourg, and a part of the Netherlands and with pseudo-data experiments. The inversion system controls the FF and BF emissions from the large urban areas and plants, in addition to regional budgets of more diffuse emissions or of biogenic fluxes (NEE, net ecosystem exchange), at an hourly scale over a whole day. The system provides results corresponding to the assimilation of pseudo-data from a single track of a 300 km swath XCO2 imager at 2 km resolution and from surface ground-based CO2 and/or 14CO2 networks. It represents the diversity of 14CO2 sources and sinks and not just the dilution of radiocarbon-free FF CO2 emissions. The uncertainty in the resulting FF CO2 emissions at local (urban area/plant) to regional scales is directly derived and used to assess the potential of the different combinations of observation systems. The assimilation of satellite observations yields estimates of the morning regional emissions with an uncertainty down to 10 % (1σ) in the satellite field of view, from an assumed uncertainty of 15 % in the prior estimates. However, it does not provide direct information about emissions outside the satellite field of view or about afternoon or nighttime emissions. The co-assimilation of 14CO2 and CO2 surface observations leads to a further reduction of the uncertainty in the estimates of FF emissions. However, this further reduction is significant only in administrative regions with three or more 14CO2 and CO2 sampling sites. The uncertainty in the estimates of 1 d emission in North Rhine-Westphalia, a region with three sampling sites, decreases from 8 % to 6.6 % when assimilating the in situ 14CO2 and CO2 data in addition to the satellite data. Furthermore, this additional decrease appears to be larger when the ground stations are close to large FF emission areas, providing an additional direct constraint for the estimate of these sources rather than supporting the characterization of the background signal from the NEE and its separation from that of the FF emissions. More generally, the results indicate no amplification of the potential of each observation subsystem when they are combined into a large observation system with satellite and surface data.

Carbon Fluxes during Dansgaard–Oeschger Events as Simulated by an Earth System Model

Abstract The Community Earth System Model with marine and terrestrial biogeochemistry is configured to simulate glacial climate. The integration shows transitions from warm to cold states—interstadials to stadials—and back. The amplitude of the associated Greenland and Antarctica temperature changes and the atmospheric CO2 signal are consistent with ice-core reconstructions, and so are the time lags between termination of a stadial, Antarctic temperature reversal, and the decline of the atmospheric CO2 concentration (for brevity’s sake simply referred to as CO2 from here on). The present model results stand out because the transitions occur spontaneously (without forcing changes like hosing) and because they reproduce the observed features above in a configuration that uses the same parameterizations as climate simulations for the present day (i.e., no retuning has been done). During stadials, precipitation shifts lead to reduced growth on land, which dominates the CO2 increase; the ocean acts as a minor carbon sink during the stadials. After the end of the stadials, however, the sudden reversal of the stadial anomalies in temperature, wind, and precipitation turns the ocean into a carbon source, which accounts for the continued rise of CO2 for several hundred years into the interstadial. The simulations also provide a novel possible interpretation for the observed correlation between CO2 and Antarctic temperature: rather than both being controlled by Southern Ocean processes, they are both controlled by the North Atlantic Ocean, and most of the extra CO2 may not be of Southern Hemisphere origin. If the stadials are prolonged through North Atlantic hosing, the upper ocean comes to an equilibrium, and the CO2 response is dominated by a single process: reduced export production in the North Atlantic as result of the collapsed overturning circulation. This is in contrast to the unforced simulation where the net ocean carbon flux anomaly is the sum of several regional responses of both signs and similar magnitudes. Reducing the aeolian iron deposition by half, to account for the observed reduction of Southern Hemisphere dust fluxes during stadials, reduces biological productivity and export production so that the Southern Ocean emerges as an important carbon source, at least for the three centuries up until a new equilibrium for the upper ocean is reached. Significance Statement The last ice age featured millennial-scale oscillations in CO2 and temperature, the latter being anticorrelated between Greenland and Antarctica. This is often referred to as the bipolar seesaw. Here, an Earth system model is described that reproduces these signals, and its results are used to explain the observed correlation between temperature and CO2. In contrast to previous idealized studies it is found that all ocean basins and the land each contribute equally to the CO2 signal.

Sickle cell cerebrovascular reactivity to a CO2 stimulus: Too little, too slow.

Background: Despite increased cerebral blood flow (CBF), cerebral infarcts occur in patients with sickle cell disease (SCD). This suggests increased CBF does not meet metabolic demand possibly due to compromised cerebral vasodilatory response. Hypothesis: In adult SCD patients, cerebrovascular reactivity (CVR) and speed of vasodilatory response (tau) to a standardized vasodilatory stimulus, are reduced compared to normal subjects. Methods: Functional brain imaging performed as part of routine care in adult SCD patients without known large vessel cerebral vasculopathy was reviewed retrospectively. CVR was calculated as the change in CBF measured as the blood-oxygenation-level-dependent (BOLD)-magnetic resonance imaging signal, in response to a standard vasoactive stimulus of carbon dioxide (CO2). The tau corresponding to the best fit between the convolved end-tidal partial pressures of CO2 and BOLD signal was defined as the speed of vascular response. CVR and tau were normalized using a previously generated atlas of 42 healthy controls. Results: Fifteen patients were included. CVR was reduced in grey and white matter (mean Z-score for CVR −0.5 [−1.8 to 0.3] and −0.6 [−2.3 to 0.7], respectively). Tau Z-scores were lengthened in grey and white matter (+0.9 [−0.5 to 3.3] and +0.8 [−0.7 to 2.7], respectively). Hematocrit was the only significant independent predictor of CVR on multivariable regression. Conclusion: Both measures of cerebrovascular health (CVR and tau) in SCD patients were attenuated compared to normal controls. These findings show that CVR represents a promising tool to assess disease state, stroke risk, and therapeutic efficacy of treatments in SCD and merits further investigation.

(Digital Presentation) Mass Spectroscopic Products Analysis during Charging of Li-O2 Cell with Tegdme Based Electrolyte

Rechargeable lithium-air battery (LAB) is considered to be one of the most promising energy storage devices because of its large theoretical energy density. Despite significant efforts by many research groups, LAB is still far from practical use and many problems must be overcome [1]. The first problem is associated with the use of air as it contains many components other than oxygen including N2, water, and CO2, which interfere battery reactions. Thus, most of the fundamental studies are not on LAB but on Lithium-oxygen battery (LOB), which uses pure oxygen as an active material. Even LOB has many serious problems, including low cyclability caused by (1) high charging overpotential, which induces degradation of positive electrode (carbon) and electrolyte solution, and (2) degradation/dendrite formation of negative Li metal electrode. To improve the cyclability, it is essential to clarify the mechanism of degradation of electrodes and electrolyte.Here we employed mass spectroscopy to follow products generation during charging so that we can clarify the degradation mechanisms of electrodes and electrolyte. Porous carbon sheet (KJCNT from KJ Specialty Paper), lithium metal (Honjo Metal), 1 M LiTFSI TEGDME (both from Sigma-Aldrich) solution, PE separator (W-Scope), and stainless steel mesh (Hohsen) were used as positive electrode, negative electrode, electrolyte, separator, and gas diffusion layer, respectively. Isotope exchanged TEGDME, i.e., 13CH3-TEGDME and CD3-TEGDME, which were synthesized in our laboratory, and 18O2 (Taiyo Nippon Sanso) were used for mass spectroscopy for precise products assignments. Details of set-up for mass analysis have been reported elsewhere [2]. We carried out online QMS (Quadrupole Mass Spectrometer) measurement for mass numbers of decomposition products between 12-90 during the potential sweep from OCP to 4.8 V (0.05 mV/s).Figure 1 shows the current and mass signals of m/z = 18 (H2O), 32 (O2), and 44 (CO2) as a function of potential. It is clear that current increased immediately as potential was scanned from OCP (~2.8 V ), reached a maximum at 3.3 V, decreased gradually, reached a minimum at 4.0 V, increased again to reach a maximum at 4.4 V, decreased to reach a minimum at 4.6 V and increased again. The potential dependence of O2 signal is very similar to that of current as the main battery reaction is Li2O2 → 2Li+ + O2 + 2e-. Two clear peaks were observed at around 3.3 V and 4.4V, showing the presence of two kinds of Li2O2 [3]. The H2O signal started to increase just after the 1st current/O2 peaks where the current efficiency for O2 generation current efficiency started to decrease, suggesting the H2O formation is related to the decrease of the current efficiency. The CO2 signal started to be significant at 4.1 V where current and the O2 signals started to increase again and reached a maximum at ca. 4.5 V, which is more positive than those of current and O2 signal but equal to H2O peak. Although current increased again significantly at potentials more positive than 4.65 V, no mass signals of O2, H2O and CO2 increased. Instead signals such as m/z = 15, 29, 31, 45, and 60, which are related to organic molecules derived from TEGDME, became significant. Figure 2 shows the online QMS results at 4.65 V. We can see that various mass signals such as 15, 29, etc. were observed at this potential. By careful analysis of the results with the assistance of isotopes 18O2, 13CH3-TEGDME, and CD3-TEGDME, presence of CH3OH, HCHO and other organic molecules with high vapor pressure originated from TEGDME were confirmed. Additionally, we detected molecules with low vapor pressure such as CH3O(CH2)2OH, CH3OCH2COCH3, etc., which were derived from TEGDME by GC/MS analysis of samples collected every 1hr. Based on the products detected by online QMS and GC/MS, possible degradation mechanism of electrolyte can be deduced. I will discuss the degradation mechanism of electrolyte based on the above results.[1] Liu T., et al. Current challenges and routes forward for nonaqueous lithium–air batteries. Chemical reviews, 2020, 120(14): 6558-6625.[2] Ue, M., et al. Material balance in the O2 electrode of Li–O2 cells with a porous carbon electrode and TEGDME-based electrolytes, RSC Advances, 2020, 10(70): 42971 - 42982.[3] Nishioka K, et al. Isotopic depth profiling of discharge products identifies reactive interfaces in an aprotic Li–O2 battery with a redox mediator. Journal of the American Chemical Society, 2021, 143(19): 7394-7401. Figure 1

0502 Harmony in the Sleep Lab: A Focus on Recognition of Hypoventilation and Direct Feedback Improves Quality of Pediatric Titrations

Abstract Introduction Over 350 pediatric polysomnogram titrations (T-PSGs) are performed each year at the Sleep Laboratory at Children’s Hospital of Philadelphia in three locations by 24 different polysomnography technologists (PSGTs) on a diverse patient population, typically performed as outpatient procedures and occasionally at the bedside as inpatients. PSGTs are responsible for titration of continuous or bilevel positive airway pressure based on flow, work of breathing, arousals, and/or gas exchange. PSGTs have varying degrees of experience; thus, maintaining quality of T-PSGs is challenging. We hypothesized that a quality improvement (QI) approach to reviewing T-PSGs with interdisciplinary education and regular feedback would improve T-PSGs. Our goal was to have &amp;gt;/= 80% of titrations of optimal quality. Methods Each T-PSG record was reviewed by a sleep physician for optimal quality, defined as appropriate signal integrity, titration, and documentation to permit definitive interpretation. Exclusion: RAM cannula use, illness, or external signal interference. Titration QI (T-QI) comments were reviewed by the sleep lab QI team bi-weekly to plan feedback. Improvement interventions for PSGTs included didactic education: lectures, presentations, and cases focusing on recognition of hypoventilation; direct feedback with teaching points by sleep physician and small group sessions with clinical supervisors to review areas for improvement; and communication of specific titration goals. Satisfaction surveys regarding recognition/titration for OSA/hypoventilation, transcutaneous CO2 signal integrity, and documentation were administered to sleep physicians. Results From September 2020-November 2021, PSGT education included: 1 synchronous and 2 asynchronous didactic presentations; 1:1 review of didactics with each night PSGT (n=24); T-QI feedback (2/week); and small group review sessions (4/week). 408 titrations were completed; 42 (10.3%, 2.8/month) were excluded; 366 (89.7%, 24.4/month) were reviewed for T-QI. 54.8% [50,71%] were deemed optimal during the first three months (pre-intervention) vs. 80.1% [63,96%] during the intervention period. QI satisfaction survey showed improvement in 3 of 4 domains. Conclusion Quality of T-PSG is enhanced by QI review of each titration, highlighting teaching points and areas for improvement via direct feedback and small group review. Education and communication among physicians, supervisors and technologists are important to support development which can result in better titrations and satisfaction. Support (If Any) none