Atmospheric CO2 Partial Pressure Research Articles

Elevated pCO2 may increase the edible safety risk of clams exposed to toxic Alexandrium spp.

Toxic harmful algal blooms (HABs) have received increasing attention owing to their threat to the health of aquatic life and seafood consumers. This study evaluated the impacts of elevated atmospheric partial pressure of CO2 (pCO2) on the production of paralytic shellfish toxins (PSTs) in different Alexandrium spp. strains, together with its further effects on the bioaccumulation/elimination dynamics of PSTs in bivalves contaminated with PSTs from toxic dinoflagellates. Our results showed that elevated pCO2 stimulated the growth of the two Alexandrium spp. (A. catenella and A. pacificum) isolated from the northern and southern coastal areas of China, respectively, and affected PST production including content and toxicity of the two strains differently. Further PSTs bioaccumulation/elimination in PSTs-contaminated Manila clam, Ruditapes philippinarum under high pCO2 also occurred. It is worth noting the biotransformation of neosaxitoxin (NEO) with high toxicity through trophic transfer with effect of elevated pCO2. When in microalgae cultured under the control (410 ppm) and elevated pCO2 conditions (495 and 850 ppm), the proportion of NEO in the PST content produced by A. catenella was reduced from 11.1 to 6.4 and 2.6 %, while the proportion of NEO in A. pacificum was increased from 3.1 to 3.6 and 4.7 %, respectively. NEO accounted for >50 % of total PST contents in clams, which were biotransformed via transfer from dinoflagellates and higher pCO2 enhanced this biotransformation leading to increased NEO accumulation. The negatively affected elimination of PSTs, especially NEO, in clams fed with A. catenella or A. pacificum, indicates that the detoxification of PSTs-contaminated clams may be more difficult under elevated pCO2. This study provides reference for developing models to assess the safety of bivalves under the co-stress of environmental change and toxic HABs, suggesting that ocean acidification may lead to the higher safety risk of Manila clams exposed to toxic HAB dinoflagellates.

Unidirectional ice-templating for aerogel adsorbents: Excellent pore structure and high CO2 capture performance for direct air capture

The ultralow atmospheric partial pressure of CO2 (∼40 Pa) presents a significant challenge for direct air capture (DAC). In this study, high-performance porous aerogel adsorbents are prepared using the unidirectional freezing–ice-templating method. The dispersion of the mixed solution is effectively improved by particle size modulation, and functionalized materials with abundant gas channels are constructed by the rapid cooling of liquid N2. The adsorbents feature a cross-structure comprising monolayer active components and nanoscale layered carriers. The unique micro/mesoporous composite structure of the adsorbents facilitates gas-phase transport. When the functional group efficiency is increased by 5.8 times, the prepared adsorbents demonstrate excellent CO2 capture capacity (1.17 mmol/g and 148 mol/m3) and a low adsorption half-time (1.28 min). The unique cross-structure of the adsorbents renders them hydrophobic; thus, they show higher adsorption capacity at high humidity than other moisture swing adsorbents. At the molecular scale, quantum chemical calculations show that appropriate coordination between the active components and carriers enhance the water vapor hindering ability of the adsorbents. The developed aerogel adsorbents significantly expand the application scenarios for moisture swing adsorbents and enhance the efficiency of DAC.

Cenozoic Carbon Dioxide: The 66 Ma Solution

The trend in partial pressure of atmospheric CO2, P(CO2), across the 66 MYr of the Cenozoic requires elucidation and explanation. The Null Hypothesis sets sea surface temperature (SST) as the baseline driver for Cenozoic P(CO2). The crystallization and cooling of flood basalt magmas is proposed to have heated the ocean, producing the Paleocene–Eocene Thermal Maximum (PETM). Heat of fusion and heat capacity were used to calculate flood basalt magmatic Joule heating of the ocean. Each 1 million km3 of oceanic flood basaltic magma liberates ~5.4 × 1024 J, able to heat the global ocean by ~0.97 °C. Henry’s Law for CO2 plus seawater (HS) was calculated using δ18O proxy-estimated Cenozoic SSTs. HS closely parallels Cenozoic SST and predicts the gas solute partition across the sea surface. The fractional change of Henry’s Law constants, Hn−HiHn−H0 is proportional to ΔP(CO2)i, and Hn−HiHn−H0×∆P(CO2)+P(CO2)min, where ΔP(CO2) = P(CO2)max − P(CO2)min, closely reconstructs the proxy estimate of Cenozoic P(CO2) and is most consistent with a 35 °C PETM ocean. Disparities are assigned to carbonate drawdown and organic carbon sedimentation. The Null Hypothesis recovers the glacial/interglacial P(CO2) over the VOSTOK 420 ka ice core record, including the rise to the Holocene. The success of the Null Hypothesis implies that P(CO2) has been a molecular spectator of the Cenozoic climate. A generalizing conclusion is that the notion of atmospheric CO2 as the predominant driver of Cenozoic global surface temperature should be set aside.

Boron isotopic compositions of middle Miocene to recent shallow-water carbonates from the South China Sea: Assessing diagenetic effects and implications for paleoclimate changes

The partial pressure of atmospheric CO2 (pCO2) significantly influences global climate change and biological evolution through geological history. Boron isotopic composition (δ11B) in carbonates has been used to reconstruct the paleo-pH of seawater, providing insight into atmospheric pCO2 levels. However, the fidelity of δ11B records in marine carbonates due to diagenesis remains uncertain. Here, to understand how diagenetic processes influence B isotopic records in marine carbonates, we examined B concentrations and δ11B values of modern corals (from Hainan Island), unconsolidated shallow pushcores (Jiuzhang A and Jiuzhang B from Nansha Islands, South China Sea), and a long drillcore (XK-1 from Xisha Islands, South China Sea) covering the Late Miocene to Holocene periods. Our coral samples show a uniform δ11B range (20.16 ± 0.85%), consistent with previously published values for modern corals in other open oceans. The δ11B values of the unlithified carbonate sediments from Jiuzhang A and B pushcores vary within a narrow range (18.70 ± 0.84%), yielding pH and CO2 concentrations consistent with the range between modern and pre-industrial values. Since we did not observe any statistically significant covariations between traditionally established diagenetic proxies (such as δ13C, δ18O, Mn/Sr, and Al/Ca) and δ11B values for non-dolomitized samples in the XK-1 drillcore, we suggest that δ11B values of bulk limestones are not significantly affected by typical diagenesis (meteoric, mixed-diagenetic, and marine diagenetic processes), likely due to limited post-depositional recrystallization of our study carbonates. In contrast, dolomitization significantly decreases δ11B values of bulk carbonates, rendering dolomites unsuitable as archives for reconstructing seawater δ11Bborate values. Our study supports that marine limestone with limited recrystallization or dolomitization have the potential to record ambient seawater pH values with high resolution. The established secular seawater pH variations based on XK-1 δ11B records provide information about ocean acidification over the past 5.1 million years.

Carbon Cycle Instability for High-CO2 Exoplanets: Implications for Habitability

Implicit in the definition of the classical circumstellar habitable zone (HZ) is the hypothesis that the carbonate-silicate cycle can maintain clement climates on exoplanets with land and surface water across a range of instellations by adjusting atmospheric CO2 partial pressure (pCO2). This hypothesis is made by analogy to the Earth system, but it is an open question whether silicate weathering can stabilize climate on planets in the outer reaches of the HZ, where instellations are lower than those received by even the Archean Earth and CO2 is thought likely to dominate atmospheres. Since weathering products are carried from land to ocean by the action of water, silicate weathering is intimately coupled to the hydrologic cycle, which intensifies with hotter temperatures under Earth-like conditions. Here, we use global climate model simulations to demonstrate that the hydrologic cycle responds counterintuitively to changes in climate on planets with CO2-H2O atmospheres at low instellations and high pCO2, with global evaporation and precipitation decreasing as pCO2 and temperatures increase at a given instellation. Within the Maher & Chamberlain (or MAC) weathering formulation, weathering then decreases with increasing pCO2 for a range of instellations and pCO2 typical of the outer reaches of the HZ, resulting in an unstable carbon cycle that may lead to either runaway CO2 accumulation or depletion of CO2 to colder (possibly snowball) conditions. While the behavior of the system has not been completely mapped out, the results suggest that silicate weathering could fail to maintain habitable conditions in the outer reaches of the nominal HZ.

CO2 enrichment accelerates alpine plant growth via increasing water-use efficiency

Phenological changes in global vegetation are often attributed to climate warming. However, climate warming and elevated atmospheric CO2 concentration (eCO2) are two co-occurring global change factors, and how eCO2 would affect vegetation phenology has received less attention. The partial pressure of atmospheric CO2 on the Tibetan Plateau (TP) is lower than that in regions of lower altitudes. Consequently, the growth and phenology of alpine plants in this region could be more sensitive to eCO2, but this hypothesis is not yet supported by empirical evidence. Here we explored the effect of eCO2 on plant phenology (including phenophases of green-up, budding, and flowering) through a 5-year field manipulation experiment in a high-altitude (4600 m above sea level) alpine grassland on the TP. Our results showed that eCO2 significantly advanced the spring phenology of an early-flowering species (Kobresia pygmaea), while it had no impact on the phenology of two mid-flowering species (Potentilla saundersiana and Potentilla cuneata). Compared to other low-altitude regions, plant phenology on the TP underwent greater alterations under eCO2, which supports our hypothesis that the growth of high-altitude plants is more sensitive to eCO2. Furthermore, we found that eCO2 significantly reduced the overlapping of flowering between contrasting plant species, mainly due to the phenological advancement of the K. pygmaea induced by eCO2. The observed advancement of the spring phenology in K. pygmaea under eCO2 was associated with increasing ecosystem water-use efficiency (WUE), thereby advancing its subsequent phenological development, such as budding and flowering. Our findings provide experimental evidence that atmospheric CO2 enrichment can accelerate plant growth processes in high-altitude regions, and suggest that large-scale model simulations should consider the effects of elevated atmospheric CO2 concentration on plant growth and phenology.

Diagenetic effects on strontium isotopes in shallow-water carbonate sediments from Middle Miocene to Recent

Seawater 87Sr/86Sr ratios have been used as a proxy for continental weathering flux and the partial pressure of atmospheric CO2 (pCO2) in Earth's past, but the fidelity of 87Sr/86Sr records in marine carbonates under diagenesis remains controversial. To investigate this issue, we undertook an integrated chemostratigraphic study of 87Sr/86Sr, δ13C, and δ18O in bulk carbonate from three cores of the South China Sea region: lithified bulk carbonate of Late Miocene to Holocene age in the 607-m-long Xike-1 core (0–11,942 kyr B.P.) from the Paracel (Chinese: Xisha) Islands, and unlithified carbonate sediment in two shallow (<5-m deep) pushcores from the Spratly (Chinese: Nansha) Islands, Jiuzhang A (0–680 yr B.P.) and Jiuzhang B (0–350 yr B.P.). The carbonate sediment of the Jiuzhang cores yielded 87Sr/86Sr signatures matching those of modern seawater, confirming that carbonate sediments can be faithful archives of contemporaneous oceanic Sr-isotopic compositions. Four diagenetic zones were identified in the Xike-1 core based on δ13C and δ18O patterns: meteoric (Unit I, 0–161 m), mixed-diagenetic (Unit II, 161–215 m), and marine diagenetic zones (Unit III, 215–577 m), along with a second meteoric zone (Unit IV, 577–607 m). The bulk‑carbonate 87Sr/86Sr profile was not strongly altered by dolomitization or other processes in any of the diagenetic zones (although minor effects were observed in the marine zone). This study concludes that marine carbonates are likely to retain primary seawater Sr isotopic signatures even after undergoing multiple stages of diagenesis. This study provides detailed 87Sr/86Sr secular variations and continental weathering history since 12 Ma.

The combined effect of pH and dissolved inorganic carbon concentrations on the physiology of plastidic ciliate Mesodinium rubrum and its cryptophyte prey

Ocean acidification is caused by rising atmospheric partial pressure of CO2 (pCO2) and involves a lowering of pH combined with increased concentrations of CO2 and dissolved in organic carbon in ocean waters. Many studies investigated the consequences of these combined changes on marine phytoplankton, yet only few attempted to separate the effects of decreased pH and increased pCO2. Moreover, studies typically target photoautotrophic phytoplankton, while little is known of plastidic protists that depend on the ingestion of plastids from their prey. Therefore, we studied the separate and interactive effects of pH and DIC levels on the plastidic ciliate Mesodinium rubrum, which is known to form red tides in coastal waters worldwide. Also, we tested the effects on their prey, which typically are cryptophytes belonging to the Teleaulax/Plagioslemis/Geminigera species complex. These cryptophytes not only serve as food for the ciliate, but also as a supplier of chloroplasts and prey nuclei. We exposed M. rubrum and the two cryptophyte species, T. acuta, T. amphioxeia to different pH (6.8 - 8) and DIC levels (∼ 6.5 - 26 mg C L-1) and assessed their growth and photosynthetic rates, and cellular chlorophyll a and elemental contents. Our findings did not show consistent significant effects across the ranges in pH and/or DIC, except for M. rubrum, for which growth was negatively affected only by the lowest pH of 6.8 combined with lower DIC concentrations. It thus seems that M. rubrum is largely resilient to changes in pH and DIC, and its blooms may not be strongly impacted by the changes in ocean carbonate chemistry projected for the end of the 21st century.

Atmospheric CO2 Depletion Near the Surface in the Martian Polar Regions

AbstractThe kinetic temperature of the Martian seasonal caps is controlled by the partial pressure of atmospheric CO2 at the surface. When carbon dioxide condenses, typically near the poles, light non‐condensable species (Ar, N2, CO, etc.) accumulate in the atmosphere, resulting in a decrease of the CO2 partial pressure and depressing the local frost point temperature. The buoyant air should mix laterally and vertically within the polar vortices. Observations show that the Martian seasonal caps' kinetic temperatures are ∼0–4 K below the expected CO2 frost point, depending on latitude and season, indicating atmospheric CO2 gas depletion at the surface/atmosphere interface. In the North and South, we find relatively similar non‐condensable peak enhancement factors (e.g., EFNC ∼ 6–8, up to ∼8.7 in the North) at most latitudes, confirming the efficient meridional mixing within the polar vortices, despite steep surface condensation gradients. In the South, this surface enhancement is similar to column‐integrated values derived from Gamma Ray Spectrometer data, indicating efficient vertical mixing. But in the North, the surface depletion is much larger than in the entire column, suggesting poor vertical mixing. Reduced infrared emission of the seasonal caps stemming from CO2 depletion is not a major energy balance factor. This work illustrates how the atmosphere's composition at the surface can be significantly different from column‐integrated values.

Contrasting Sea‐Air CO2 Exchanges in the Western Tropical Atlantic Ocean

AbstractThe western Tropical Atlantic Ocean is a biogeochemically complex region due to the structure of the surface current system and the large freshwater input from the Amazon River coupled with the dynamics of precipitation. Such features make it difficult to understand the dynamics of the carbon cycle, leading to contrasting estimates in sea‐air CO2 exchanges in this region. Here, we demonstrate that these contrasting estimates occur because the western Tropical Atlantic Ocean can be split into three distinct sub‐regions in terms of the sea‐air CO2 exchanges. The sub‐region under the North Brazil Current domain acts as a weak annual CO2 source to the atmosphere, with low interannual variability. The sub‐region under the North Equatorial Current influence acts as an annual CO2 sink, with great temporal variability. The third sub‐region under the Amazon River plume influence shows greater interannual variability of CO2 exchanges, but it always acts as a net oceanic sink for CO2. Despite this large spatial variability, the entire region acts as a net annual CO2 sink of −1.6 ± 1.0 mmol m−2 day−1. Importantly, the Amazon River plume waters drive 87% of the CO2 uptake in the western Tropical Atlantic Ocean. In addition, we found a significant increasing trend in sea surface CO2 partial pressure in the North Brazil Current and North Equatorial Current waters. Such trends are more pronounced than the increase in atmospheric CO2 partial pressure, revealing the sensitivity of carbon dynamics in these sub‐regions to global climate change.

The Effect of Ocean Acidification on Skeletal Structures

It is well known that the increasing partial pressure of atmospheric CO2 (pCO2) is reducing surface ocean pH, a process known as ocean acidification (OA) [...]

How Well Do We Understand the Land‐Ocean‐Atmosphere Carbon Cycle?

AbstractFossil fuel combustion, land use change and other human activities have increased the atmospheric carbon dioxide (CO2) abundance by about 50% since the beginning of the industrial age. The atmospheric CO2 growth rates would have been much larger if natural sinks in the land biosphere and ocean had not removed over half of this anthropogenic CO2. As these CO2 emissions grew, uptake by the ocean increased in response to increases in atmospheric CO2 partial pressure (pCO2). On land, gross primary production also increased, but the dynamics of other key aspects of the land carbon cycle varied regionally. Over the past three decades, CO2 uptake by intact tropical humid forests declined, but these changes are offset by increased uptake across mid‐ and high‐latitudes. While there have been substantial improvements in our ability to study the carbon cycle, measurement and modeling gaps still limit our understanding of the processes driving its evolution. Continued ship‐based observations combined with expanded deployments of autonomous platforms are needed to quantify ocean‐atmosphere fluxes and interior ocean carbon storage on policy‐relevant spatial and temporal scales. There is also an urgent need for more comprehensive measurements of stocks, fluxes and atmospheric CO2 in humid tropical forests and across the Arctic and boreal regions, which are experiencing rapid change. Here, we review our understanding of the atmosphere, ocean, and land carbon cycles and their interactions, identify emerging measurement and modeling capabilities and gaps and the need for a sustainable, operational framework to ensure a scientific basis for carbon management.

Marine anoxia linked to abrupt global warming during Earth’s penultimate icehouse

Piecing together the history of carbon (C) perturbation events throughout Earth’s history has provided key insights into how the Earth system responds to abrupt warming. Previous studies, however, focused on short-term warming events that were superimposed on longer-term greenhouse climate states. Here, we present an integrated proxy (C and uranium [U] isotopes and paleo CO2) and multicomponent modeling approach to investigate an abrupt C perturbation and global warming event (∼304 Ma) that occurred during a paleo-glacial state. We report pronounced negative C and U isotopic excursions coincident with a doubling of atmospheric CO2 partial pressure and a biodiversity nadir. The isotopic excursions can be linked to an injection of ∼9,000 Gt of organic matter–derived C over ∼300 kyr and to near 20% of areal extent of seafloor anoxia. Earth system modeling indicates that widespread anoxic conditions can be linked to enhanced thermocline stratification and increased nutrient fluxes during this global warming within an icehouse.

Freshwater and Evaporite Brine Compositions on Hadean Earth: Priming the Origins of Life.

The chemical composition of aqueous solutions during the Hadean era determined the availability of essential elements for prebiotic synthesis of the molecular building blocks of life. Here we conducted quantitative reaction path modeling of atmosphere-water-rock interactions over a range of environmental conditions to estimate freshwater and evaporite brine compositions. We then evaluated the solution chemistries for their potential to influence ribonucleotide synthesis and polymerization as well as protocell membrane stability. Specifically, solutions formed by komatiite and tonalite (primitive crustal rocks) weathering and evaporation-rehydration (drying-wetting) cycles were studied assuming neutral atmospheric composition over a wide range of values of atmospheric partial pressure of CO2 (PCO2) and temperatures (T). Solution pH decreased and total dissolved concentrations of inorganic P, Mg, Ca, Fe, and C (PT, MgT, CaT, FeT, and CT) increased with increasing PCO2. The PCO2 and T dictated how the solution evolved with regard to minerals precipitated and ions left in solution. At T = 75°C and PCO2 < 0.05 atm, the concentration ratio of magnesium to calcium ion concentrations (Mg2+/Ca2+) was < 1 and predominantly metal aluminosilicates (including clays), dolomite, gibbsite, and pyrite (FeS2) precipitated, whereas at PCO2 > 0.05 atm, Mg2+/Ca2+ was > 1 and mainly magnesite, dolomite, pyrite, chalcedony (SiO2), and kaolinite (Al2Si2O5) precipitated. At T = 75°C and PCO2 > 0.05 atm, hydroxyapatite (HAP) precipitated during weathering but not during evaporation, and so, PT increased with each evaporation-rehydration cycle, while MgT, CaT, and FeT decreased as other minerals precipitated. At T = 75°C and PCO2 ∼5 atm, reactions with komatiite provided end-of-weathering solutions with high enough Mg2+ concentrations to promote RNA-template directed and montmorillonite-promoted nonenzymatic RNA polymerization, but incompatible with protocell membranes; however, montmorillonite-promoted RNA polymerization could proceed with little or no Mg2+ present. Cyclically evaporating/rehydrating brines from komatiite weathering at T = 75°C and PCO2 ∼5 atm yielded the following: (1) high PT values that could promote ribonucleotide synthesis, and (2) low divalent cation concentrations compatible with amino acid-promoted, montmorillonite-catalyzed RNA polymerization and with protocell membranes, but too low for template-directed nonenzymatic RNA polymerization. For all PCO2 values, Mg2+ and PT concentrations decreased, whereas the HCO3- concentration increased within increasing temperature, due to the retrograde solubility of the minerals controlling these ions' concentrations; Fe2+ concentration increased because of prograde pyrite solubility. Tonalite weathering and cyclical wetting-drying reactions did not produce solution compositions favorable for promoting prebiotic RNA formation. Conversely, the ion concentrations compatible with protocell emergence, placed constraints on PCO2 of early Earth's atmosphere. In summary: (1) prebiotic RNA synthesis and membrane self-assembly could have been achieved even under neutral atmosphere conditions by atmosphere-water-komatiite rock interactions; and (2) constraints on element availability for the origins of life and early PCO2 were addressed by a single, globally operating mechanism of atmosphere-water-rock interactions without invoking special microenvironments. The present results support a facile origins-of-life hypothesis even under a neutral atmosphere as long as other favorable geophysical and planetary conditions are also met.

Eutrophication Amplifies the Diel Variability of Carbonate Chemistry in an Equatorial, Semi-Arid, and Negative Estuary

This study presents high-resolution data on diel variations of carbonate chemistry in a semi-arid estuary (Jaguaribe River) in NE Brazil, which has witnessed decreasing annual rainfall and freshwater inputs due to climate change and river damming. In addition, the estuary has been suffering with increasing discharges from shrimp farm and urban effluents. We monitored surface water and atmospheric CO2 partial pressure (pCO2), temperature, salinity, and wind speed with continuous real-time measurements during two eulerian surveys in October 2017 (33 h) and September 2018 (44 h), during spring tides in the dry season. Additionally, pH, total alkalinity (TA), dissolved inorganic carbon (DIC), carbonate (CO32–), and saturation state of calcite (Ωcal) and aragonite (Ωara) were monitored hourly. Higher salinity (&amp;gt;38) during ebb tides confirmed the hypersalinity and negative estuarine circulation. TA and DIC concentrations in the estuary were higher than in the adjacent coastal ocean due to evaporation, showing positive correlation with salinity and negative correlation with tidal height. Measured TA and DIC concentrations were slightly higher than those calculated by the conservative evaporation model, suggesting their production in the estuary by aerobic and anaerobic processes. CO32–, Ωcal, and Ωara showed a clear semi-diurnal (tidal-driven) and diel (24 h; biological-driven) patterns: lowest values occurred at flood tide during night-time (respectively, 185 μmol kg–1, 4.3 and 2.8), whereas highest occurred during ebb tide and daytime (respectively, 251 μmol kg–1, 5.7 and 3.8). DIC/TA ratios were higher at night-time supporting a diel control (linked to solar irradiance) of the carbonate buffering capacity. pCO2 was oversaturated comparing to the atmosphere (512–860 μatm) and the estuary was a source of CO2, with fluxes ranging from 2.2 to 200.0 mmol C m–2 d–1 (51.9 ± 26.7 mmol C m–2 d–1), which are higher than emissions normally found in low-inflow, marine-dominated estuaries. The diel variability of DIC indicated a net heterotrophic metabolism averaging −5.17 ± 7.39 mmol C m–2 h–1. Eutrophication amplifies the diel variability of the CO2 system generating large differences between daytime and night-time. The results highlight the importance of considering diel variability when estimating CO2 fluxes and carbonate chemistry in eutrophic, semi-arid, and tidally dominated estuaries under rapid environmental changes, and may represent future conditions in estuaries worldwide experiencing warming, increasing aridity and eutrophication.

Limitation of C4 photosynthesis by low carbonic anhydrase activity increases with temperature but does not influence mesophyll CO2 conductance.

The CO2-concentrating mechanism (CCM) in C4 plants is initiated by the uptake of bicarbonate (HCO3-) via phosphoenolpyruvate carboxylase (PEPC). Generation of HCO3- for PEPC is determined by the interaction between mesophyll CO2 conductance and the hydration of CO2 to HCO3- by carbonic anhydrase (CA). Genetic reduction of CA was previously shown not to limit C4 photosynthesis under ambient atmospheric partial pressures of CO2 (pCO2). However, CA activity varies widely across C4 species and it is unknown if there are specific environmental conditions (e.g. high temperature) where CA may limit HCO3- production for C4 photosynthesis. Additionally, CA activity has been suggested to influence mesophyll conductance, but this has not been experimentally tested. We hypothesize that CA activity can limit PEPC at high temperatures, particularly at low pCO2, but does not directly influence gm. Here we tested the influence of genetically reduced CA activity on photosynthesis and gm in the C4 plant Zea mays under a range of pCO2 and temperatures. Reduced CA activity limited HCO3- production for C4 photosynthesis at low pCO2 as temperatures increased, but did not influence mesophyll conductance. Therefore, high leaf CA activity may enhance C4 photosynthesis under high temperature when stomatal conductance restricts the availability of atmospheric CO2.

Decrease in volume and density of foraminiferal shells with progressing ocean acidification

Rapid increases in anthropogenic atmospheric CO2 partial pressure have led to a decrease in the pH of seawater. Calcifying organisms generally respond negatively to ocean acidification. Foraminifera are one of the major carbonate producers in the ocean; however, whether calcification reduction by ocean acidification affects either foraminiferal shell volume or density, or both, has yet to be investigated. In this study, we cultured asexually reproducing specimens of Amphisorus kudakajimensis, a dinoflagellate endosymbiont-bearing large benthic foraminifera (LBF), under different pH conditions (pH 7.7–8.3, NBS scale). The results suggest that changes in seawater pH would affect not only the quantity (i.e., shell volume) but also the quality (i.e., shell density) of foraminiferal calcification. We proposed that pH and temperature affect these growth parameters differently because (1) they have differences in the contribution to the calcification process (e.g., Ca2+-ATPase and Ω) and (2) pH mainly affects calcification and temperature mainly affects photosynthesis. Our findings also suggest that, under the IPCC RCP8.5 scenario, both ocean acidification and warming will have a significant impact on reef foraminiferal carbonate production by the end of this century, even in the tropics.

Impacts of pH on the Fitness and Immune System of Pacific White Shrimp

The atmospheric partial pressure of CO2 (pCO2) has been increasing dramatically since the beginning of the industrial revolution and about 30% of the CO2 produced by anthropogenic activities was absorbed by the ocean. This led to a perturbation of the seawater carbonate chemistry resulting in a decrease of the average surface ocean pH by 0.1 and termed ocean acidification (OA). Projections suggest that pCO2 may reach 900 μatm by the end of the twenty-first century lowering the average pH of the surface ocean by 0.4 units. The negative impacts of OA on many species of marine invertebrates such as mollusks, echinoderms, and crustaceans are well documented. However, less attention has been paid to the impacts of low pH on fitness and immune system in crustaceans. Here, we exposed Pacific white shrimps to 3 different pHs (nominal pH 8.0, 7.9, and 7.6) over a 100-days experiment. We found that, even though there were no significant effects on fitness parameters (survival, growth and allometries between length and weight), some immune markers were modified under low pH. A significant decrease in total hemocyte count and phenoloxidase activity was observed in shrimps exposed to pH 7.6 as compared to pH 8.0; and phagocytosis rate significantly decreased with decreasing pH. A significant increase in superoxide production was also observed at pH 7.6 as compared to pH 8.0. All these results suggest that a 100-days exposure to pH 7.6 did not have a direct effect on fitness but lead to a modulation of the immune response.

The Paleoclimate Significance of the δ13C Composition of Individual Hydrocarbon Compounds in the Maoming Oil Shales, China

Maoming oil shales are typical low-altitude lacustrine sediments that were deposited during the late Paleogene. The hydrocarbon composition and compound-specific stable carbon isotopic composition (δ13C) of organic matter in the profile samples of the oil shales have been analyzed. The results show that algae and aquatic plants are major parent sources of the organic matter in the oil shales associated with a small portion of terrestrial higher plant input. The δ13C composition of the bulk organic matter and the n-alkanes varies greatly on the profile from −26.9 to −15.8‰ and −31.7 to −16.2‰, respectively. While a good positive correlation among the δ13C composition of individual n-alkanes implies that these n-alkanes were originated from the similar source input. The δ13C composition of n-alkanes on the profile displays a positive excursion trend from the bottom to the top, and this excursion was likely related to the general decreasing trend of the partial pressure of atmospheric CO2 (pCO2) during the late Paleogene. The δ13C composition of the C30-4-methyl steranes ranges from −11.9 to −6.3‰, which is suggestive of Dinoflagellates-related source input. Coincidently, the high abundance C33-botryococcanes were detected in the samples on the top section of the profile and display an extremely positive carbon isotopic composition of −4.5 to −8.4‰, suggesting that the lower partial pressure of atmospheric CO2 had triggered a bicarbonate consumption mechanism for Botryococcus braunii B. Therefore, the δ13C composition of n-alkanes and C33-botryococcanes and their profile variation suggest that a general declining process associated with fluctuation in the partial pressure of atmospheric CO2 is likely the major reason for the rapid climatic changes toward the end of the late Paleogene.

Intraspecific variation in multiple trait responses of Alexandrium ostenfeldii towards elevated pCO2

Dissolved oceanic CO2 concentrations are rising as result of increasing atmospheric partial pressure of CO2 (pCO2), which has large consequences for phytoplankton. To test how higher CO2 availability affects different traits of the toxic dinoflagellate Alexandrium ostenfeldii, we exposed three strains of the same population to 400 and 1,000 µatm CO2, and measured traits including growth rate, cell volume, elemental composition, 13C fractionation, toxin content, and volatile organic compounds (VOCs). Strains largely increased their growth rates and particulate organic carbon and nitrogen production with higher pCO2 and showed significant changes in their VOC profile. One strain showed a significant decrease in both PSP and cyclic imine content and thereby in cellular toxicity. Fractionation against 13C increased in response to elevated pCO2, which may point towards enhanced CO2 acquisition and/or a downscaling of the carbon concentrating mechanisms. Besides consistent responses in some traits, other traits showed large variation in both direction and strength of responses towards elevated pCO2. The observed intraspecific variation in phenotypic plasticity of important functional traits within the same population may help A. ostenfeldii to negate the effects of immediate environmental fluctuations and allow populations to adapt more quickly to changing environments.