Rise In PCO2 Research Articles

Impact of warming and acidification of the Mediterranean Sea on statolith formation of the scyphozoan jellyfish Rhizostoma pulmo Macri (1778)

Ocean warming and acidification negatively affect organisms and biogeochemical cycles. To date, emphasis has been placed on the study of the impact on the structures of calcifying species; however, there is limited knowledge about the influence of the increase of these two variables on the solid structures of non-calcifying species as jellyfish. Here, we study the effects that the increase of temperature and acidity would cause on the statoliths of newly released ephyrae of the Mediterranean jellyfish Rhizostoma pulmo. Six combinations of temperature and PCO2 (18, 24 and 30ºC with a PCO2 of 500 and 1000 ppm each), according to the projections of the SSP5-8.5 (IPCC, 2021) scenario for the year 2100, were applied during 32 days to different groups of polyps randomly selected. Statoliths of the released ephyrae were counted and their size was measured. Our results show that, even though neither temperature nor PCO2 increase exerted a representative effect on the amount of statoliths synthesized in newly released ephyra from R. pulmo, it did exert an impact on the size of these structures: warming led to the formation of larger statoliths, while the rise in PCO2 induced the production of smaller structures. Under the simultaneous increase of both variables, acidification attenuated the effects of temperature, but still slightly larger statoliths were synthesized. The size differences observed in these structures could negatively impact the equilibrium system of this jellyfish species, potentially affecting its ability to survive.

Historic ocean acidification of Loch Sween revealed by correlative geochemical imaging and high-resolution boron isotope analysis of Boreolithothamniom cf. soriferum

Ocean Acidification (OA) arises from the increase in atmospheric carbon dioxide concentration following the industrial revolution. The ecological and socio-economic consequences of OA were first identified around 10–15 years ago but remain poorly understood. This is particularly true in coastal regions where local processes can have dramatic consequences on pH trends through time, obscuring and compounding the long-term effects from rising atmospheric CO2. Here we explore the possibility of generating long records of coastal ocean pH using the skeletons of widely distributed coralline algae (CA). The skeletons of these slow growing (<1 mm/year) taxa often contain micron-scale heterogeneities, making sampling for high-resolution climate reconstructions using bulk sampling techniques difficult. Here we use laser ablation coupled to inductively coupled plasma mass spectrometers to generate high-resolution 2D images of the element/calcium ratios and boron isotope composition (δ11B) of a sample of Boreolithothamniom cf. soriferum from Loch Sween in Scotland, UK where we have been monitoring temperature since 2004 and pH during 2014. By carefully correlating the geochemical images with a scanning electron microscopy image we can segment them to remove the marginal portions of the skeleton, isolating the central growth axis to generate an age model and growth rate. The δ11B-pH is significantly elevated above the seawater pH in Loch Sween (8.4 to 8.9 vs. 7.9 to 8.1) consistent with other CA that show internal pH elevation. On a seasonal scale, internal pH is negatively correlated with temperature and also exhibits a long-term decline. By removing this temperature effect, internal pH can be correlated to seawater pH during the 2014 monitoring period allowing us to reconstruct a seawater acidification trend from 2004 to 2018 of -0.018 pH units per year, 10x higher than open ocean trends but consistent with contemporaneous monitoring efforts of UK coastal waters. Reconstructed aqueous CO2 suggests that prior to ∼2008 Loch Sween was a sink of CO2 but after this date, particularly during the early summer, it was a substantial CO2 source. Comparison of reconstructed aqueous CO2 with a record of calcification rate of our sample of Boreolithothamniom cf. soriferum suggests this acidification and associated rise in local seawater pCO2 may have freed this sample from carbon limitation leading to a recent increase in calcification.

Volcanic and orbitally forced carbon release during the Middle Eocene Climatic Optimum

The drivers of the Middle Eocene Climatic Optimum (MECO) remain enigmatic. Here we report a high-resolution terrestrial MECO record from the Bohai Bay Basin, eastern China. The record shows episodic Hg enrichments and a volcanogenic Δ199Hg signature during the MECO, and an abrupt chemical weathering enhancement and negative δ13Corg excursion (CIE) during the MECO peak warmth. A high-resolution age model constrains the MECO to ca. 40.59−40.18 Ma with the onset in the first ∼320 k.y. Peak warmth and the CIE initiated at 40.27 Ma, corresponding to 405 k.y. and 100 k.y. eccentricity maxima, and lasted for ∼90 k.y., reminiscent of the early Eocene hyperthermals. Our findings suggest that episodic volcanism contributed to gradual atmospheric pCO2 rise, leading to the long duration of the MECO onset. Orbital forcing at 40.27 Ma, on top of CO2 forcing, caused the peak warmth and a positive carbon cycle feedback. The regional increase in weathering is inconsistent with evidence for weakened global continental weathering, suggesting strong spatial heterogeneity in the weathering response to MECO warming.

Pliocene CO2 rise due to sea-level fall as a mechanism for the delayed ice age

Global sea level fell progressively during the Pliocene in response to the growth of ice sheets at high northern latitudes. However, not until ∼2.7 Ma did the climate system actually generate and maintain major ice sheets in the Northern Hemisphere. A decline in atmospheric CO2 levels (pCO2) is thought to be responsible for the Pleistocene ice ages. However, the link between pCO2 and Pliocene glaciations, or their delay, is not well understood, mainly because the magnitude of pCO2 remains uncertain beyond the maximum age of ice cores (∼0.8 Ma). Here, we develop a carbonate clumped isotope (∆47) geothermometer specifically for pedogenic carbonate in Chinese loess, which we use to reconstruct temperatures in northern China, and pCO2, for the past 7.24 Ma. The palaeotemperature results show an oscillatory cooling trend over time in the East Asian monsoon region, in good agreement with coeval tropical sea surface temperature records. The pCO2 reconstruction using the pedogenic carbonate palaeobarometer reveals low values (150–325 ppmv) during the intervals of 7.24–4.3 Ma and 2.6–0 Ma. In contrast, there is a three-step rise in pCO2 up to 535 ppmv from 4.3 to 2.6 Ma, coincident with an oscillatory decrease in sea level and in benthic δ13C. We suggest that the Pliocene CO2 rise was causally related to the sea-level fall and associated organic carbon oxidation on exposed continental shelves, thereby delaying the onset of the ice age. This implies a negative feedback mechanism induced by long-term cooling since the Late Miocene, which may have delayed the onset of the ice age but did not prevent it.

Early Eocene biotic assemblage from the sedimentary deposits of the Tarkeshwar Lignite Mine, Gujarat and its palaeoenvironmental implications

The Palaeogene biota and the palaeoenvironmental history from the low latitudes are remarkably well–preserved in theopen–cast lignite deposits from Western India. Lignite sequences of the Cambay Shale Formation (Gujarat) have been a majorsource to understand the concept of early evolution of fossils including flora, arthropods, vertebrates fauna, and several aquaticforms during the Early Eocene. The study deals with an extensive record of amber inclusions and extracted pollen, vertebratefragments, dinoflagellate cysts and Carbon isotopes from the lignite and associated sediments from the Tarkeshwar Lignite Mineto add insights into the palaeoenvironment and depositional conditions of the Cambay Basin during the Early Eocene period. Thecurrent study demonstrates that throughout the late Palaeocene and early Eocene epoch, the palaeoenvironment changed fromlow land, marshy (lower portion), to shallow marine environment, presumably due to hyperthermal event PETM (middle part).Age diagnostic taxa, viz. Auxiodinium longispinosum, Apectodinium parvum and early wetzelielloid (Vallodinium? sp.) excursionprovide late Palaeocene–early Eocene period (~56–53 Ma) for the dinocyst interval in the middle part of the section. A pronouncednegative Carbon Isotope Excursion (CIE) in the middle part is correlated to the second Eocene Thermal maximum (53.7 Ma),which is a globally recorded hyperthermal event. During the ETM–2 warming, the rise in pCO2 caused warm, humid conditionsas well as a rise in sea level, which may have contributed to the establishment of constrained shallow marine environments in theexamined middle unit sedimentary succession. Floral (spore–pollens, leaf, wood, seed, fruits) and faunal assemblages (Crocodiles,fish remains, amber insects) revealed the prevalence of a dense tropical luxurious rain forest (floral and faunal) near shore duringthe ETM–2 in the Tarkeshwar Lignite Mines, Cambay Basin.

THE MIDDLE EOCENE CLIMATIC OPTIMUM (MECO) IMPACT ON THE BENTHIC AND PLANKTIC FORAMINIFERAL RESILIENCE FROM A SHALLOW-WATER SEDIMENTARY RECORD

We present here new quantitative analyses of planktic and benthic foraminifera to assess the impact of the Middle Eocene Climatic Optimum (MECO, ~40 Ma) on these biotic groups studied along a shallow-water succession rich in larger benthic foraminifera (Sealza, Liguria, NW Italy). The MECO is one of the major Eocene global warming events, characterized by ~4–6°C warming, shifts in the global carbon cycle, and rise in atmospheric pCO2. The Sealza succession is interpreted as the product of a drowning ramp influenced by tectonic activity and provides an exceptional chance to compare biotic variations in shallow-water assemblages with deep-water communities across the MECO. In the section, the MECO interval is tentatively constrained by stable isotope oxygen data and calcareous plankton biostratigraphy. The marked decline in abundance of the epifaunal benthic Cibicidoides across the lower-middle part of the MECO suggests a decrease in oxygenation at the seafloor. Further evidence of oxygen depletion is the increase in organic matter content (TOC) of the sediment and the presence of infaunal genera Uvigerina and Bolivina. The planktic foraminiferal assemblages record the MECO warming in the upper water column as the mixed-layer warm index genera Acarinina and Morozovelloides markedly increase in abundance. In the post-MECO interval, here poorly exposed, cooler conditions are indicated by the dominance of the cold-water index genus Subbotina. Remarkably, Acarinina decline in abundance in the upper MECO interval and never recover. The MECO perturbance permanently impacted the benthic and planktic communities at Sealza that exceeded the tipping point to move to a new regime, thus proving the fauna to be not resilient, but also not recording any extinctions.

Kungurian (Cisuralian) conifers and environmental changes: a negative δ13C shift in the flora of Tregiovo (Northern Italy)

The Le Fraine fossil locality, near the Tregiovo village (Trento Province, northern Italy) yields two of the best documented Kungurian (early Permian) plant fossil assemblages of eastern palaeoequatorial Pangea. Both plant assemblages (Tregiovo A and B) are dominated by walchian and voltzian conifers but differ in the relative abundance of the major plant groups. Analyses of the δ13C of the bulk organic carbon throughout the entire stratigraphic succession of Tregiovo show a negative trend towards the upper part of the succession. Several conifer taxa are recognized and taxon-specific δ13C analyses of the conifer remains in both plant fossil assemblages shows the same trend in all taxa. This correlation between the negative shift of the bulk organic carbon and the taxon-specific δ13C analysis shows that the negative δ13C shift recorded along the stratigraphic section is not the result of change in relative abundance within the plant assemblages but instead has an external cause, likely the δ13C values of atmospheric CO2. These results agree well with a negative shift observed in other Kungurian continental successions (e.g., China, South Africa, Australia), supporting a global perturbation in the carbon cycle. The negative shift in δ13C could very well record the last deglaciation phases of the Late Paleozoic Ice Age and the rise of the atmospheric pCO2.

Remote sensing and machine learning method to support sea surface pCO2 estimation in the Yellow Sea

With global climate changing, the carbon dioxide (CO2) absorption rates increased in marginal seas. Due to the limited availability of in-situ spatial and temporal distribution data, the current status of the sea surface carbon dioxide partial pressure (pCO2) in the Yellow Sea is unclear. Therefore, a pCO2 model based on a random forest algorithm has been developed, which was trained and tested using 14 cruise data sets from 2011 to 2019, and remote sensing satellite sea surface temperature, chlorophyll concentration, diffuse attenuation of downwelling irradiance, and in-situ salinity were used as the input variables. The seasonal and interannual variations of modeled pCO2 were discussed from January 2003 and December 2021 in the Yellow Sea. The results showed that the model developed for this study performed well, with a root mean square difference (RMSD) of 43 μatm and a coefficient of determination (R2) of 0.67. Moreover, modeled pCO2 increased at a rate of 0.36 μatm year-1 (R2 = 0.27, p &amp;lt; 0.05) in the YS, which is much slower than the rate of atmospheric pCO2 (pCO2air) rise. The reason behind it needs further investigation. Compared with pCO2 from other datasets, the pCO2 derived from the RF model exhibited greater consistency with the in-situ pCO2 (RMSD = 55 μatm). In general, the RF model has significant improvement over the previous models and the global data sets.

Diagnosis of Nocturnal Hypoventilation in Pediatric Neuromuscular Disorders: A Survey of Clinical Practice in Australia and New Zealand

Objectives: Nocturnal hypoventilation is a complication of neuromuscular disorders. There are various recommendations for measuring pCO&lt;sub&gt;2&lt;/sub&gt; during polysomnography and numerous national and international definitions of hypoventilation that could contribute to significant variations in clinical practice. We therefore aimed to determine clinical practices implemented by Australasian pediatric sleep physicians.Methods: Pediatric sleep physicians completed an electronic survey for information regarding pCO&lt;sub&gt;2&lt;/sub&gt; measurements and definitions of hypoventilation that are followed for children with neuromuscular disorders.Results: It was found that transcutaneous measurement of pCO&lt;sub&gt;2&lt;/sub&gt; was performed in all centers, with 25% of the centers simultaneously performing capnography. Twelve definitions of hypoventilation were used, including published definitions from the American Academy of Sleep Medicine (AASM) manual and recommendations of the pediatric Australasian Sleep Association/Australasian Sleep Technologists Association. The most commonly used definition of hypoventilation (9/17, 53%) was the 2012 pediatric AASM definition (pCO&lt;sub&gt;2&lt;/sub&gt; &gt;50 mmHg for &gt;25% of the total sleep time). There was a discrepancy between centers and individuals within the same center when defining hypoventilation. Answers stating the use of the Australasian definitions (rise in pCO&lt;sub&gt;2&lt;/sub&gt; ≥10 mmHg from wake to sleep, average rise in pCO&lt;sub&gt;2&lt;/sub&gt; ≥3 mmHg from non rapid eye movement to rapid eye movement sleep) were more frequent when asked specifically via a checkbox (yes/no) compared to free text.Conclusions: These results confirm the heterogeneity and lack of standardization of clinical practice within Australasia when measuring pCO&lt;sub&gt;2&lt;/sub&gt; during polysomnography and defining hypoventilation. The Australasian definitions were not used as frequently as anticipated.

Deoxygenation enhances photosynthetic performance and increases N2 fixation in the marine cyanobacterium Trichodesmium under elevated pCO2.

Effects of changed levels of dissolved O2 and CO2 on marine primary producers are of general concern with respect to ecological effects of ongoing ocean deoxygenation and acidification as well as upwelled seawaters. We investigated the response of the diazotroph Trichodesmium erythraeum IMS 101 after it had acclimated to lowered pO2 (~60 μM O2) and/or elevated pCO2 levels (HC, ~32 μM CO2) for about 20 generations. Our results showed that reduced O2 levels decreased dark respiration significantly, and increased the net photosynthetic rate by 66 and 89% under the ambient (AC, ~13 μM CO2) and the HC, respectively. The reduced pO2 enhanced the N2 fixation rate by ~139% under AC and only by 44% under HC, respectively. The N2 fixation quotient, the ratio of N2 fixed per O2 evolved, increased by 143% when pO2 decreased by 75% under the elevated pCO2. Meanwhile, particulate organic carbon and nitrogen quota increased simultaneously under reduced O2 levels, regardless of the pCO2 treatments. Nevertheless, changed levels of O2 and CO2 did not bring about significant changes in the specific growth rate of the diazotroph. Such inconsistency was attributed to the daytime positive and nighttime negative effects of both lowered pO2 and elevated pCO2 on the energy supply for growth. Our results suggest that Trichodesmium decrease its dark respiration by 5% and increase its N2-fixation by 49% and N2-fixation quotient by 30% under future ocean deoxygenation and acidification with 16% decline of pO2 and 138% rise of pCO2 by the end of this century.

P138 Inter-observer agreement and sensitivity of definitions for hypoventilation in children with neuromuscular disorders

Abstract Background hypoventilation occurs in neuromuscular disorders with respiratory muscle weakness. There are numerous definitions of hypoventilation. This study aimed to determine which definitions of hypoventilation had the highest inter-observer agreement and sensitivity in children with neuromuscular disorders. Methods twenty polysomnograms from children with neuromuscular disorders were examined by six paediatric sleep physicians to determine whether hypoventilation was present and which definitions of hypoventilation were used. Inter-observer agreement for the diagnosis of hypoventilation was calculated, with sensitivity determined in an exploratory analysis. Results mean inter-observer agreement was excellent at 82% (κ=0.533), higher for the absence (84%) than the presence (70%) of hypoventilation. Some physicians used more than one definition to diagnose hypoventilation for the same polysomnogram. Even when agreement was substantial, the definitions chosen varied between physicians.The objective defiitions used most frequently when inter-observer agreement was substantial that hypoventilation was present were; average increase in pCO2 ≥3mmHg from NREM to REM (n=15), increase of ≥10mmHg from awake to asleep (n=10) and pCO2 &amp;gt;50mmHg &amp;gt;25% total sleep time (n=8). The sensitivity for these definitions was 83%, 67% and 50%. Conclusions even when inter-observer agreement was high that hypoventilation was present, there was a lack of consistency between physicians when defining hypoventilation. An average increase in pCO2 ≥3mmHg from NREM to REM sleep had the highest inter-observer agreement and sensitivity. Alternative definitions in cases without a rise of pCO2 in REM are pCO2 &amp;gt;50mmHg for 25% total sleep time and/or an increase of ≥10mmHg from awake to asleep.

On the significance of long-term trends in tree-ring N isotopes – The interplay of soil conditions and regional NOx emissions

As anthropogenic nitrogen (N) emissions have been rising for decades, it is critical to develop natural archives that help understand how natural processes were modified in the past. Tree-ring δ15N values may represent such an indicator but its validity as faithful record of N cycling changes is still debated. Here we produce long-tree-ring δ15N series for five white spruce stands from two boreal regions submitted to moderate industrial N inputs. The obtained δ15N series show sharp differences among stands, even from the same region, despite the fact that they show similar increases in intrinsic water use efficiency (iWUE), a proxy for foliar strategies derived from δ13C values. The statistical modeling of these series and the basal area increment (BAI) of the trees allow to suggest that the mechanisms controlling the isotopic fractionation of N assimilated by tree rings are decoupled from the foliar strategies under the anthropogenic N emissions. The iWUE trends mainly reflect rise of pCO2 and changes in air quality. The long-term δ15N trends echo different biogeochemical processes responding to N deposition due to distinct original soil pH at the various sites. We contend that tree-ring δ15N series can record changes in the forest N cycle, but their rigorous interpretation requires laborious work, particularly an understanding of the biogeochemistry in the soil immediately around the investigated trees.“Seek simplicity and distrust it”, Alfred North Whitehead.

Monsoon- and ENSO-driven surface-water pCO2 variation in the tropical West Pacific since the Last Glacial Maximum

The East Asian monsoon (EAM) and El Niño-Southern Oscillation (ENSO) are large-scale oceanic-atmospheric fluctuations that dominate climate variability in the tropical Pacific Ocean. Although the effects of EAM and ENSO on physical and biological processes are increasingly understood, little is known about their influence on seawater carbonate chemistry in the tropical Pacific, especially in the geological past. Here, we present reconstructed variations in surface-water pCO2 (pCO2(sw)) and their deviation from atmospheric pCO2 (ΔpCO2(sw-atm)) in the western Philippine Sea (WPS) since 27 ka. Our record displays covariation between ΔpCO2(sw-atm) and the intensity of the East Asian summer monsoon (EASM) since the Last Glacial Maximum (LGM), suggesting that EASM-driven upwelling controls long-term changes in surface-water carbonate chemistry and air-sea CO2 fluxes. Rapid changes in ΔpCO2(sw-atm) were linked to the ENSO-like state and, to a lesser extent, the East Asian winter monsoon (EAWM) during the Last Deglaciation, with low values corresponding to La Niña-like phases and strong EAWM during Heinrich Event 1, the Allerød and the Younger Dryas, and high values corresponding to El Niño-like phases and weak EAWM during the Bølling and Pre-Boreal. This interpretation is supported by the relationship of EAM and ENSO to modern surface-water carbonate chemistry in the WPS. Our new record, combined with previously published data, suggests that the tropical Pacific played a minimal role in sequestering CO2(atm) during the LGM. Tropical Pacific surface waters overall became a pronounced CO2 source to the atmosphere during the Last Deglaciation, possibly making a substantial contribution to the deglacial pCO2(atm) rise. We infer that this flux was mainly due to ENSO-related patterns of vertical stratification or lateral advection, perhaps in addition to equatorial upwelling of southern-sourced waters already enriched in dissolved inorganic carbon. Our findings indicate that tropical conditions (i.e., EAM and ENSO-like state) played a crucial role in glacial-interglacial pCO2(atm) changes, suggesting that this is an important area for future research into the causes of glacial pCO2(atm) cycles.

Astronomically paced climate evolution during the Late Paleozoic icehouse-to-greenhouse transition

Late Paleozoic deglaciation is Earth's first icehouse-to-greenhouse transition with extensive vegetation, but the response of tropical climate to this transition has not yet been fully addressed. Here, cyclostratigraphic analysis was conducted on the magnetic susceptibility (MS) record of a deep marine carbonate succession in South China to construct the astrochronology of late Cisuralian (Early Permian), and decipher the evolutionary response to the climate transition in the MS and δ13Ccarb time series. The constructed astronomical time scale indicates an age of 272.83 ± 0.2 Ma for the Cisuralian–Guadalupian boundary in South China. Synchronizing global records demonstrates a complicated linkage between low and high latitudes, involving secular changes in atmospheric pCO2, ice volume, tropical climate and carbon cycling. In the final stage of the Early Permian icehouse (~290–288.2 Ma), the delivery of moisture from low to high latitudes was reduced in comparison with that in the icehouse apex. A more humid climate facilitated the development of tropical coal forests and more storage of 12C on land. In a full greenhouse condition (~281–272 Ma), the tropical responses to a rise in atmospheric pCO2 involved continental drying and ocean stagnation. On a shorter time scale, the nodes of 1.36 Myr obliquity cycles triggered ice-sheet expansion and enhanced tropical precipitation during an icehouse condition. With the gradual transition to an arid greenhouse, the insolation-climate relationship began to change at ~285.1 Ma, and the obliquity nodes became associated instead with terrestrial aridity and marine anoxia. These results bring into a focus pattern of shifting dynamics involving Earth's astronomical parameters and climate change for icehouse and greenhouse worlds in the Late Paleozoic Era.

Elevated pCO2 changes community structure and function by affecting phytoplankton group-specific mortality

The rise of atmospheric pCO2 has created a number of problems for marine ecosystem. In this study, we initially quantified the effects of elevated pCO2 on the group-specific mortality of phytoplankton in a natural community based on the results of mesocosm experiments. Diatoms dominated the phytoplankton community, and the concentration of chlorophyll a was significantly higher in the high-pCO2 treatment than the low-pCO2 treatment. Phytoplankton mortality (percentage of dead cells) decreased during the exponential growth phase. Although the mortality of dinoflagellates did not differ significantly between the two pCO2 treatments, that of diatoms was lower in the high-pCO2 treatment. Small diatoms dominated the diatom community. Although the mortality of large diatoms did not differ significantly between the two treatments, that of small diatoms was lower in the high-pCO2 treatment. These results suggested that elevated pCO2 might enhance dominance by small diatoms and thereby change the community structure of coastal ecosystems.

Trends and Rhythms in Climate Change During the Early Permian Icehouse

AbstractLate Paleozoic deglaciation is the first icehouse‐to‐greenhouse transition in a world with expansive tropical forests, but the detailed process of this climatic upheaval is still debated due to lack of high‐precision global correlation. Here, based on the cyclostratigraphic analysis of a deep‐marine succession of Naqing in South China, chronostratigraphic correlation was achieved between Paleo‐Tethyan deep‐marine carbonate cyclicity and U‐Pb zircon age‐calibrated cyclothems from the Pangaean paleotropics. Refining the global chronostratigraphy indicates ages of 294.1 ± 0.2 Ma and 290.1 ± 0.2 Ma for the base of the Sakmarian and Artinskian stages, respectively. We juxtapose the climatic proxies and indicators across blocks and latitudes to decipher the trends and rhythms in climate change during a period from the apex of the Late Paleozoic ice age (LPIA) to the initial deglaciation. On the multiple‐million‐year time scale, the polar and equatorial climates were linked through the atmospheric pCO2 control. A rise in pCO2 promoted Gondwanan deglaciation and tropical aridification. The disparity in the inferred polarity of tropical climate changes during glacials and interglacials has been confirmed on the million‐year time scale. The meridional flux of moisture was enhanced during the minima of the ∼1.2 Myr obliquity cycle, periodically resulting in Gondwanan glaciation, glacio‐eustatic sea‐level lowerings, and reduced moisture availability in the tropical Pangaean and Paleo‐Tethyan regions. Our study provides an improved temporal resolution and understanding of the apex of the LPIA.

Contracting eastern African C4 grasslands during the extinction of Paranthropus boisei

The extinction of the Paranthropus boisei estimated to just before 1 Ma occurred when C4 grasslands dominated landscapes of the Eastern African Rift System (EARS). P. boisei has been characterized as an herbivorous C4 specialist, and paradoxically, its demise coincided with habitats favorable to its dietary ecology. Here we report new pedogenic carbonate stable carbon (δ13CPC) and oxygen (δ18OPC) values (nodules = 53, analyses = 95) from an under-sampled interval (1.4–0.7 Ma) in the Turkana Basin (Kenya), one of the most fossiliferous locales of P. boisei. We combined our new results with published δ13CPC values from the EARS dated to 3–0 Ma, conducted time-series analysis of woody cover (ƒWC), and compared the EARS ƒWC trends to regional and global paleo-environmental and -climatic datasets. Our results demonstrate that the long-term rise of C4 grasslands was punctuated by a transient but significant increase in C3 vegetation and warmer temperatures, coincident with the Mid-Pleistocene Transition (1.3–0.7 Ma) and implicating a short-term rise in pCO2. The contraction of C4 grasslands escalated dietary competition amongst the abundant C4-feeders, likely influencing P. boisei’s demise.

Atmospheric carbon dioxide variations across the middle Miocene climate transition

Abstract. The middle Miocene climate transition ∼ 14 Ma marks a fundamental step towards the current “ice-house” climate, with a ∼ 1 ‰ δ18O increase and a ∼ 1 ‰ transient δ13C rise in the deep ocean, indicating rapid expansion of the East Antarctic Ice Sheet associated with a change in the operation of the global carbon cycle. The variation of atmospheric CO2 across the carbon-cycle perturbation has been intensely debated as proxy records of pCO2 for this time interval are sparse and partly contradictory. Using boron isotopes (δ11B) in planktonic foraminifers from Ocean Drilling Program (ODP) Site 1092 in the South Atlantic, we show that long-term pCO2 varied at 402 kyr periodicity between ∼ 14.3 and 13.2 Ma and follows the global δ13C variation remarkably well. This suggests a close link to precessional insolation forcing modulated by eccentricity, which governs the monsoon and hence weathering intensity, with enhanced weathering and decreasing pCO2 at high eccentricity and vice versa. The ∼ 50 kyr lag of δ13C and pCO2 behind eccentricity in our records may be related to the slow response of weathering to orbital forcing. A pCO2 drop of ∼ 200 µatm before 13.9 Ma may have facilitated the inception of ice-sheet expansion on Antarctica, which accentuated monsoon-driven carbon cycle changes through a major sea-level fall, invigorated deep-water ventilation, and shelf-to-basin shift of carbonate burial. The temporary rise in pCO2 following Antarctic glaciation would have acted as a negative feedback on the progressing glaciation and helped to stabilize the climate system on its way to the late Cenozoic ice-house world.

Evaluating the Glacial‐Deglacial Carbon Respiration and Ventilation Change Hypothesis as a Mechanism for Changing Atmospheric CO2

AbstractThe prevailing hypothesis to explain pCO2 rise at the last glacial termination calls upon enhanced ventilation of excess respired carbon that accumulated in the deep sea during the glacial. Recent studies argue lower [O2] in the glacial ocean is indicative of increased carbon respiration. The magnitude of [O2] depletion was 100–140 µ mol/kg at the glacial maximum. Because respiration is coupled to δ13C of dissolved inorganic carbon (DIC), [O2] depletion of 100–140 µ mol/kg from carbon respiration would lower deep water δ13CDIC by ∼1‰ relative to surface water. Prolonged sequestration of respired carbon would also lower the amount of 14C in the deep sea. We show that Pacific Deep Water δ13CDIC did not decrease relative to the surface ocean and Δ14C was only ∼50‰ lower during the late glacial. Model simulations of the hypothesized ventilation change during deglaciation lead to large increases in δ13CDIC, Δ14C, and ε14C that are not recorded in observations.

Efficacy and safety of oxygen-sparing nasal reservoir cannula for treatment of pediatric hypoxemic pneumonia in Uganda: a pilot randomized clinical trial

BackgroundOxygen is an essential therapy for hypoxemia but is scarce in low-income settings. Oxygen conserving devices optimize delivery, but to date have been designed for adults in high-income settings. Here we present the development and clinical pilot study of an oxygen-sparing nasal reservoir cannula (OSNRC) for pediatric use in low-income settings.Methods(1) Pre-clinical development of a novel OSNRC using a simulated respiratory circuit with metabolic simulator and anatomically accurate face-airway models. Simulated breathing waveforms were designed based on airway resistance, lung compliance, respiratory rate, and tidal volume of spontaneous breathing for three disease conditions. (2) Pilot, randomized, controlled, non-blinded, cross-over study of the OSNRC vs standard nasal cannula (SNC) among children hospitalized with hypoxemic pneumonia in Uganda. Eight children were randomized to OSNRC followed by SNC, and eight were randomized to SNC followed by OSNRC.ResultsThe laboratory simulation showed that the OSNRC provided the same or higher fraction of inspired oxygen at approximately 2.5-times lower flow rate compared to SNC. The flow savings ratio exhibited a linear relationship with the OSNRC volume to tidal volume ratio with a slope that varied with breathing waveforms. The range of performance from different breathing waveforms defined a performance envelope of the OSNRC. Two mask sizes (30 mL and 50 mL) provided sufficient coverage for patients between the 3rd and 97th percentile in our targeted age range. In the clinical pilot study, the rise in capillary blood pCO2 was similar in the OSNRC and SNC groups, suggesting that the OSNRC was not associated with CO2 retention. There were no significant differences between OSNRC and SNC with respect to clinical adverse events, lactate levels, pH, and SpO2. The OSNRC group had a higher mean SpO2 than the SNC group (adjusted mean difference, 1.4, 95% confidence interval 1.1 to 1.8), showing oxygen delivery enhancement.ConclusionThe OSNRC enhances oxygen delivery without causing CO2 retention and appears to be well-tolerated by pediatric patients. If safety, efficacy and tolerability are confirmed in larger trials, this device has the potential to optimize oxygen delivery in children in low-resource settings, reducing the global burden of pediatric pneumonia.Trial registrationThe trial was retrospectively registered (International Standard Registered Clinical/Social Study Number (ISRCTN): 15216845; Date of registration: 15 July 2020).