Stable pCO2 Research Articles

Clumped isotope records of terrestrial temperatures during the Middle Jurassic (180–150 Ma) in East China

The Jurassic is a crucial greenhouse period that witnessed a transition from the relatively colder Triassic to the relatively warmer Cretaceous. However, previous studies based on marine sections suggest different long-term paleotemperature trends throughout the Jurassic. Oxygen isotope (ẟ18O) values of temperate belemnite and bivalve fossils suggest a general cooling followed by a general warming trend during the Jurassic, whereas TEX86H and clumped isotope sea surface temperature records available for parts of this period appear consistent with a relatively warm and stable climate. The paucity of Middle Jurassic paleotemperature estimates limits efforts to investigate the above disagreement. Here, we apply clumped isotope (Δ47) thermometry to paleosol carbonates from the central part of East China to reconstruct terrestrial paleotemperatures and paleoatmospheric CO2 (pCO2) in the Middle Jurassic. After evaluating potential burial diagenesis and seasonality of soil carbonate accumulation, we suggest that terrestrial mean annual temperatures ranged from 30 ± 4 °C to 34 ± 4 °C and the estimated mean pCO2 was 1219 ± 519 ppmv in mid-latitude East China during the Middle Jurassic. Based on the compiled marine temperatures and our results, we conclude that the paleoclimate was relatively warm and stable from the Middle Jurassic to at least the Earliest Cretaceous (ca. 180–135 Ma). Our estimated Middle Jurassic pCO2 aligns with previous records, revealing minimal variations compared to the pCO2 observed during the Early Cretaceous. These findings imply a link between the consistent temperatures and the relatively stable pCO2 levels from the Middle Jurassic through the Early Cretaceous.

Hypercapnia in hospitalized children and adolescents with anorexia nervosa as a predictive marker for readmission: a prospective study

PurposeTo determine whether hypercapnia is associated with risk of hospital readmission related to anorexia nervosa (AN) in children and adolescents.MethodsWe performed a prospective study of patients ≤ 18 years old admitted due to AN decompensation from November 2018 to October 2019. Both subtypes of AN, restricting subtype (AN-R) and binge-eating/purging subtype (AN-BP), were included. Study participants were evaluated upon admission, at discharge and six months after discharge. T-tests or Mann–Whitney U tests was used to compare means values. Pearson or Spearman correlations were used to measure the association between two variables. Logistic regression models were developed to evaluate the relationship between scoring methods and readmission.ResultsOf the 154 persons admitted during the study period, 131 met the inclusion criteria. Median age was 15.1 years. At admission, 71% of participants were malnourished and 33 (25%) had been previously admitted.We observed a marked decrease in venous pH and stable pCO2 elevation during follow-up period. Hypercapnia at discharge was associated with a twofold increased likelihood of readmission and the odds of readmission increased as discharge pCO2 rose. These findings did not depend on AN subtype or participant sex. Electrolytes persisted within the normal range.ConclusionHypercapnia and respiratory acidosis are common alterations in children and adolescents hospitalized due to AN decompensation. Hypercapnia persists for at least 6 months after discharge despite clinical improvement and is associated with higher odds of readmission. This is the first study to identify an abnormal laboratory finding as a potential predictor of readmission in AN.Level of evidenceIV: Multiple time series without intervention.

John W. Severinghaus, M.D., 1922 to 2021.

John W. Severinghaus, M.D., 1922 to 2021.

Diurnally fluctuatingpCO2 enhances growth of a coastal strain ofEmiliania huxleyiunder future-projected ocean acidification conditions

AbstractThe carbonate chemistry in coastal waters is more variable compared with that of open oceans, both in magnitude and time scale of its fluctuations. However, knowledge of the responses of coastal phytoplankton to dynamic changes in pH/pCO2 has been scarcely documented. Hence, we investigated the physiological performance of a coastal isolate of the coccolithophore Emiliania huxleyi (PML B92/11) under fluctuating and stable pCO2 regimes (steady ambient pCO2, 400 μatm; steady elevated pCO2, 1200 μatm; diurnally fluctuating elevated pCO2, 600–1800 μatm). Elevated pCO2 inhibited the calcification rate in both the steady and fluctuating regimes. However, higher specific growth rates and lower ratios of calcification to photosynthesis were detected in the cells grown under diurnally fluctuating elevated pCO2 conditions. The fluctuating pCO2 regime alleviated the negative effects of elevated pCO2 on effective photochemical quantum yield and relative photosynthetic electron transport rate compared with the steady elevated pCO2 treatment. Our results suggest that growth of E. huxleyi could benefit from diel fluctuations of pH/pCO2 under future-projected ocean acidification, but its calcification was reduced by the fluctuation and the increased concentration of CO2, reflecting a necessity to consider the influences of dynamic pH fluctuations on coastal carbon cycles associated with ocean global changes.

Contrasting effects of constant and fluctuating pCO2 conditions on the exercise physiology of coral reef fishes

Ocean acidification (OA) is predicted to affect the physiology of some fishes. To date, most studies have investigated this issue using stable pCO2 levels based on open ocean projections. Yet, most shallow, nearshore systems experience temporal and spatial pCO2 fluctuations. For example, pCO2 on coral reefs is highest at night and lowest during the day, but as OA progresses, both the average pCO2 and magnitude of fluctuations are expected to increase. We exposed four coral reef fishes – Lutjanus fulviflamma, Caesio cuning, Abudefduf whitleyi, and Cheilodipterus quinquelineatus – to ambient, stable elevated, or fluctuating elevated pCO2 conditions for 9–11 days. Then, we measured swimming performance, oxygen uptake rates, and haematological parameters during the day and at night. When compared to ambient pCO2 conditions, L. fulviflamma, C. cuning, and A. whitleyi exposed to fluctuating elevated pCO2 increased swimming performance, maximum oxygen uptake rates, and aerobic scope, regardless of time of day; whereas, the only nocturnal species studied, C. quinquelineatus, decreased maximum oxygen uptake rates and aerobic scope. Our findings suggest that exposure to fluctuating or stable elevated pCO2 can physiologically benefit some coral reef fishes; however, other species, such as the cardinalfish examined here, may be more sensitive to future OA conditions.

The effects of constant and fluctuating elevated pCO2 levels on oxygen uptake rates of coral reef fishes

Ocean acidification, resulting from increasing atmospheric carbon dioxide (CO2) emissions, can affect the physiological performance of some fishes. Most studies investigating ocean acidification have used stable pCO2 treatments based on open ocean predictions. However, nearshore systems can experience substantial spatial and temporal variations in pCO2. Notably, coral reefs are known to experience diel fluctuations in pCO2, which are expected to increase on average and in magnitude in the future. Though we know these variations exist, relatively few studies have included fluctuating treatments when examining the effects of ocean acidification conditions on coral reef species. To address this, we exposed two species of damselfishes, Amblyglyphidodon curacao and Acanthochromis polyacanthus, to ambient pCO2, a stable elevated pCO2 treatment, and two fluctuating pCO2 treatments (increasing and decreasing) over an 8 h period. Oxygen uptake rates were measured both while fish were swimming and resting at low-speed. These 8 h periods were followed by an exhaustive swimming test (Ucrit) and blood draw examining swimming metrics and haematological parameters contributing to oxygen transport. When A. polyacanthus were exposed to stable pCO2 conditions (ambient or elevated), they required more energy during the 8 h trial regardless of swimming type than fish exposed to either of the fluctuating pCO2 treatments (increasing or decreasing). These results were reflected in the oxygen uptake rates during the Ucrit tests, where fish exposed to fluctuating pCO2 treatments had a higher factorial aerobic scope than fish exposed to stable pCO2 treatments. By contrast, A. curacao showed no effect of pCO2 treatment on swimming or oxygen uptake metrics. Our results show that responses to stable versus fluctuating pCO2 differ between species - what is stressful for one species many not be stressful for another. Such asymmetries may have population- and community-level impacts under higher more variable pCO2 conditions in the future.

Increase of the transient climate response to cumulative carbon emissions with decreasing CO2 concentration scenarios

Near-constancy of the transient climate response to cumulative carbon emissions (TCRE) facilitates the development of future emission pathways compatible with temperature targets. However, most studies have explored TCRE under scenarios of temperature increase. We used an Earth system model (MIROC-ESM) to examine TCRE in scenarios with increasing and stable CO2 concentrations, as well as overshoot pathways in which global mean temperatures peak and decline. Results showed that TCRE is stable under scenarios of increasing or stable CO2 concentration at an atmospheric CO2 concentration (pCO2) double the pre-industrial level. However, in the case of overshoot pathways and a stable pCO2 scenario at a quadrupled pCO2 level, the TCRE increases by 10%–50%, with large increases over a short period just after pCO2 starts to decrease. During the period of pCO2 increase, annual ocean heat uptake (OHU) and ocean carbon storage (CO) (or cumulative ocean carbon uptake from the start of the experiment) exhibit similar changes, resulting in a stable TCRE. During the pCO2 decrease period, after a sudden TCRE increase when pCO2 starts to decrease, the OHU decreases and CO increases (relative to the pCO2 increase period) balance each other out, resulting in a stable TCRE. In overshoot pathways, the temperature distribution when the global mean temperature anomaly cools to 1.5 °C reveals small warming over land and large warming over the oceans relative to the 1% per annum pCO2 increasing scenario, particularly in some high-latitude areas of both hemispheres. The increase in TCRE with overshoot pathways decreases the carbon budget for the temperature anomaly targets in such scenarios. Our analysis showed a 16%–35% decrease in the remaining carbon budget for the 1.5 °C global warming target, in comparison with the reference scenario with a 1% per year pCO2 increase, for pathways peaking at the doubled pCO2 level followed by decline to the pre-industrial level.

High sensitivity of a keystone forage fish to elevated CO2 and temperature.

Sand lances of the genus Ammodytes are keystone forage fish in coastal ecosystems across the northern hemisphere. Because they directly support populations of higher trophic organisms such as whales, seabirds or tuna, the current lack of empirical data and, therefore, understanding about the climate sensitivity of sand lances represent a serious knowledge gap. Sand lances could be particularly susceptible to ocean warming and acidification because, in contrast to other tested fish species, they reproduce during boreal winter months, and their offspring develop slowly under relatively low and stable pCO2 conditions. Over the course of 2 years, we conducted factorial pCO2 × temperature exposure experiments on offspring of the northern sand lance Ammodytes dubius, a key forage species on the northwest Atlantic shelf. Wild, spawning-ripe adults were collected from Stellwagen Bank National Marine Sanctuary (Cape Cod, USA), and fertilized embryos were reared at three pCO2 conditions (400, 1000 and 2100 μatm) crossed with three temperatures (5, 7 and 10 ˚C). Exposure to future pCO2 conditions consistently resulted in severely reduced embryo survival. Sensitivity to elevated pCO2 was highest at 10 ˚C, resulting in up to an 89% reduction in hatching success between control and predicted end-of-century pCO2 conditions. Moreover, elevated pCO2 conditions delayed hatching, reduced remaining endogenous energy reserves at hatch and reduced embryonic growth. Our results suggest that the northern sand lance is exceptionally CO2-sensitive compared to other fish species. Whether other sand lance species with similar life history characteristics are equally CO2-sensitive is currently unknown. But the possibility is a conservation concern, because many boreal shelf ecosystems rely on sand lances and might therefore be more vulnerable to climate change than currently recognized. Our findings indicate that life history, spawning habitat, phenology and developmental rates mediate the divergent early life CO2 sensitivities among fish species.

Diel CO2 cycles reduce severity of behavioural abnormalities in coral reef fish under ocean acidification

Elevated CO2 levels associated with ocean acidification (OA) have been shown to alter behavioural responses in coral reef fishes. However, all studies to date have used stable pCO2 treatments, not considering the substantial diel pCO2 variation that occurs in shallow reef habitats. Here, we reared juvenile damselfish, Acanthochromis polyacanthus, and clownfish, Amphiprion percula, at stable and diel cycling pCO2 treatments in two experiments. As expected, absolute lateralization of A. polyacanthus and response to predator cue of Am. percula were negatively affected in fish reared at stable, elevated pCO2 in both experiments. However, diel pCO2 fluctuations reduced the negative effects of OA on behaviour. Importantly, in experiment two, behavioural abnormalities that were present in fish reared at stable 750 µatm CO2 were largely absent in fish reared at 750 ± 300 µatm CO2. Overall, we show that diel pCO2 cycles can substantially reduce the severity of behavioural abnormalities caused by elevated CO2. Thus, past studies may have over-estimated the impacts of OA on the behavioural performance of coral reef fishes. Furthermore, our results suggest that diel pCO2 cycles will delay the onset of behavioural abnormalities in natural populations.

Long-term spatial and temporal variation of CO<sub>2</sub> partial pressure in the Yellow River, China

Abstract. Carbon transport in river systems is an important component of the global carbon cycle. Most rivers of the world act as atmospheric CO2 sources due to high riverine CO2 partial pressure (pCO2). By determining the pCO2 from alkalinity and pH, we investigated its spatial and temporal variation in the Yellow River watershed using historical water chemistry records (1950s–1984) and recent sampling along the mainstem (2011–2012). Except the headwater region where the pCO2 was lower than the atmospheric equilibrium (i.e. 380 μatm), river waters in the remaining watershed were supersaturated with CO2. The average pCO2 for the watershed was estimated at 2810 ± 1985 μatm, which is 7-fold the atmospheric equilibrium. As a result of severe soil erosion and dry climate, waters from the Loess Plateau in the middle reaches had higher pCO2 than that from the upper and lower reaches. From a seasonal perspective, the pCO2 varied from about 200 μatm to > 30 000 μatm with higher pCO2 usually occurring in the dry season and lower pCO2 in the wet season (at 73% of the sampling sites), suggesting the dilution effect of water. While the pCO2 responded exponentially to total suspended solids (TSS) export when the TSS concentration was less than 100 kg m−3, it decreased slightly and remained stable if the TSS concentration exceeded 100 kg m−3. This stable pCO2 is largely due to gully erosion that mobilizes subsoils characterized by low organic carbon for decomposition. In addition, human activities have changed the pCO2 dynamics. Particularly, flow regulation by dams can diversely affect the temporal changes of pCO2, depending on the physiochemical properties of the regulated waters and adopted operation scheme. Given the high pCO2 in the Yellow River waters, large potential for CO2 evasion is expected and warrants further investigation.

Physiological response of Crocosphaera watsonii to enhanced and fluctuating carbon dioxide conditions.

We investigated the effects of elevated pCO2 on cultures of the unicellular N2-fixing cyanobacterium Crocosphaera watsonii WH8501. Using CO2-enriched air, cultures grown in batch mode under high light intensity were exposed to initial conditions approximating current atmospheric CO2 concentrations (∼400 ppm) as well as CO2 levels corresponding to low- and high-end predictions for the year 2100 (∼750 and 1000 ppm). Following acclimation to CO2 levels, the concentrations of particulate carbon (PC), particulate nitrogen (PN), and cells were measured over the diurnal cycle for a six-day period spanning exponential and early stationary growth phases. High rates of photosynthesis and respiration resulted in biologically induced pCO2 fluctuations in all treatments. Despite this observed pCO2 variability, and consistent with previous experiments conducted under stable pCO2 conditions, we observed that elevated mean pCO2 enhanced rates of PC production, PN production, and growth. During exponential growth phase, rates of PC and PN production increased by ∼1.2- and ∼1.5-fold in the mid- and high-CO2 treatments, respectively, when compared to the low-CO2 treatment. Elevated pCO2 also enhanced PC and PN production rates during early stationary growth phase. In all treatments, PC and PN cellular content displayed a strong diurnal rhythm, with particulate C:N molar ratios reaching a high of 22∶1 in the light and a low of 5.5∶1 in the dark. The pCO2 enhancement of metabolic rates persisted despite pCO2 variability, suggesting a consistent positive response of Crocosphaera to elevated and fluctuating pCO2 conditions.

Responses of calcification of massive and encrusting corals to past, present, and near-future ocean carbon dioxide concentrations

In this study, we report the acidification impact mimicking the pre-industrial, the present, and near-future oceans on calcification of two coral species (Porites australiensis, Isopora palifera) by using precise pCO2 control system which can produce acidified seawater under stable pCO2 values with low variations. In the analyses, we performed Bayesian modeling approaches incorporating the variations of pCO2 and compared the results between our modeling approach and classical statistical one. The results showed highest calcification rates in pre-industrial pCO2 level and gradual decreases of calcification in the near-future ocean acidification level, which suggests that ongoing and near-future ocean acidification would negatively impact coral calcification. In addition, it was expected that the variations of parameters of carbon chemistry may affect the inference of the best model on calcification responses to these parameters between Bayesian modeling approach and classical statistical one even under stable pCO2 values with low variations.

Habitat traits and food availability determine the response of marine invertebrates to ocean acidification

Energy availability and local adaptation are major components in mediating the effects of ocean acidification (OA) on marine species. In a long-term study, we investigated the effects of food availability and elevated pCO2 (ca. 400, 1000 and 3000μatm) on growth of newly settled Amphibalanus (Balanus) improvisus to reproduction, and on their offspring. We also compared two different populations, which were presumed to differ in their sensitivity to pCO2 due to differing habitat conditions: Kiel Fjord, Germany (Western Baltic Sea) with naturally strong pCO2 fluctuations, and the Tjärnö Archipelago, Sweden (Skagerrak) with far lower fluctuations. Over 20weeks, survival, growth, reproduction and shell strength of Kiel barnacles were all unaffected by elevated pCO2 , regardless of food availability. Moulting frequency and shell corrosion increased with increasing pCO2 in adults. Larval development and juvenile growth of the F1 generation were tolerant to increased pCO2 , irrespective of parental treatment. In contrast, elevated pCO2 had a strong negative impact on survival of Tjärnö barnacles. Specimens from this population were able to withstand moderate levels of elevated pCO2 over 5weeks when food was plentiful but showed reduced growth under food limitation. Severe levels of elevated pCO2 negatively impacted growth of Tjärnö barnacles in both food treatments. We demonstrate a conspicuously higher tolerance to elevated pCO2 in Kiel barnacles than in Tjärnö barnacles. This tolerance was carried over from adults to their offspring. Our findings indicate that populations from fluctuating pCO2 environments are more tolerant to elevated pCO2 than populations from more stable pCO2 habitats. We furthermore provide evidence that energy availability can mediate the ability of barnacles to withstand moderate CO2 stress. Considering the high tolerance of Kiel specimens and the possibility to adapt over many generations, near future OA alone does not seem to present a major threat for A. improvisus.