Low Saturation State Research Articles

Mitigation of hypoxia and ocean acidification on the inner East China Sea shelf impacted by the 2023 summer drought

Hypoxia and acidification are universal environmental issues in coastal seas, especially in large river dominated shelves, and the East China Sea shelf is a typical case among them. However, the responses of status of hypoxia and acidification in coastal seas to the extremes of river discharges are still to be revealed. This study surveyed the influences of a summer drought on the status of hypoxia and acidification on the inner East China Sea shelf off the Changjiang estuary. In August of 2023 during a summer drought, carbonate system parameters and dissolved oxygen (DO) were surveyed on the East China Sea shelf off the Changjiang estuary. As expected, dissolved inorganic carbon (DIC) removal (up to >40 μmol kg−1) and DO over-saturation (up to >110 %) accompanied by high pH (up to >8.15) in the surface water were observed. However, low DO (32–172 μmol kg−1), low pH (7.63–8.04) and low saturation state index of aragonite (ΩAr) (1.34–3.06) in the bottom water were observed. Relationships of Excess DIC with DO consumption, and pH and ΩAr with Excess DIC indicated that the hypoxia and acidification in the bottom water was due mainly to the remineralization of the marine-sourced organic matter. Nevertheless, both hypoxia and acidification were mitigated, i.e. the hypoxic area was smaller, the minimum DO concentration, pH and saturation state index of aragonite were higher in August of 2023 than under the general summer condition. The lower Changjiang discharge (∼60 % of the long-term monthly average) mitigated eutrophication of the East China Sea shelf and decreased the phytoplankton biomass in the surface water and subsequently the hypoxia and acidification in the bottom water. However, acidification of the bottom water on the East China Sea shelf was still severe even during the summer drought. Regulating the anthropogenic impact on the coastal marginal seas is still urgently needed to mitigate the acidification status.

Study of Interfacial Properties of Anionic–Nonionic Surfactants Based on Succinic Acid Derivatives via Molecular Dynamics Simulations and the IGMH Method

Surfactants are widely used in fields such as oil recovery and flotation. The properties and mechanisms of surfactants can be effectively studied using molecular dynamics (MD) simulations. Herein, the aggregation behavior of surfactants was studied at the oil–water interface by MD simulation, and the micro-morphology of surfactants was analyzed under a low concentration and saturated state at the oil–water interface, respectively. The visualization results of the MD simulation showed that DTOA was saturated at the oil–water interface at 120 surfactant molecules, whereas 160 surfactant molecules were required for BEMA. In addition, the effect of surfactant concentration on the interfacial thickness and hydrogen bond distribution was studied, with the inflection point of hydrogen bond distribution identified as a characteristic parameter for surfactant saturation at the oil–water interface. The aggregation behavior of their hydrophobic and hydrophilic chains at the oil–water interface was qualitatively assessed using order parameters. Finally, the aggregation state of surfactants in salt-containing systems was studied, and it was found that the surfactants could effectively adsorb magnesium ions and calcium ions at the oil–water interface. However, the curve of the number of hydrogen bonds varies greatly, with a possible reason being that BEMA has a different coordination manner with diverse metal ions. This study provides some original insights into both the theoretical study and practical application of anionic and nonionic surfactants.

Study of Sintering Behavior of Methane Hydrate Particles on the Wall Surface.

The sintering of hydrate aggregates on the pipe wall is a major form of hydrate deposition. Understanding the sintering behavior of hydrates on the wall is crucial for promoting hydrate safety management and preventing pipeline blockage. However, limited research currently exists on this topic. In this study, the cohesive force strength of hydrate particles on the wall surface under different conditions was directly measured using a high-pressure micromechanical force device (HP-MMF). Subsequently, the effects of subcooling and glycine on the cohesive force were investigated. The results indicate that the cohesive force is influenced by different growth states during the process of free water on the wall surface gradually growing into hydrate. Three states with larger measured values during the growth process were selected for research. Observation showed that increased subcooling strengthened sintering by accelerating the growth rate of the hydrate film, resulting in a significant increase in cohesive force. The role of glycine in the methane hydrate system was then evaluated. Glycine was found to reduce the degree of sintering by reducing the growth rate of the hydrate film, thereby decreasing the cohesive force. The optimal concentration in the system was determined to be 0.25 wt %. Moreover, compared with low subcooling (1 °C), glycine had a better effect at high subcooling (5 °C). At 5 °C subcooling and the optimal concentration, the cohesive force in the wall droplet state decreases from 677.38 to 489.02 mN/m, the cohesive force at the low-saturation state decreases from 951.79 to 543.32 mN/m, and the cohesive force at the high-saturation state decreases from 1194.95 to 641.76 mN/m. These findings contribute to a better understanding of the cohesive force behavior of gas hydrate on the inner wall of the pipeline and provide basic data for reducing the risk of hydrate blockage.

Calcification and trophic responses of mesophotic reefs to carbonate chemistry variability

Mesophotic coral ecosystems (MCEs) are extensions of adjacent shallow water coral reefs. Accessibility to these ecosystems is challenging due to their depth limits (~ 30 – 150 m) and as a result, scientific knowledge of these reef systems is limited. It has been posited that the depth limits of MCEs diminish anthropogenic effects experienced by shallow reef systems. A lack of empirical measurements to date has made this hypothesis impossible to determine for mesophotic reef metabolism. The alkalinity anomaly technique was utilized to determine rates of net ecosystem calcification (NEC) and net ecosystem production (NEP) from 30, 40 and 60 m mesophotic reefs during a 15-month period. Seawater chemistry was determined to be chemically conducive for calcification (average aragonite saturation Ωaragonite of 3.58, average calcite saturation Ωcalcite of 5.44) with estimates of NEC indicating these reef systems were net accretive and within global average values for shallow coral reefs (< 30 m). The strongest periods of calcification occurred in late summer and were coupled with strong autotrophic signals. These episodes were followed by suppressed calcification and autotrophy and in the case of the 60 m reefs, a switch to heterotrophy. Whilst there was variability between the three reefs depths, the overall status of the mesophotic system was net autotrophic. This determination was the opposite of trophic status estimates previously described for adjacent shallow reefs. Whilst there were periods of net dissolution, the mesophotic reef system was net accretive (i.e., gross calcification > gross CaCO3 dissolution). The measured inorganic carbon chemistry and estimates of NEC and NEP represent the first such biogeochemical measurements for MCEs. The values established by this study demonstrate just how close these understudied ecosystems are in terms of the known boundary thresholds for low saturation state reefs. Making predictions on how these ecosystems will respond to future climatic conditions, will require greater sampling effort over long times scales to decouple the environmental controls exerted on such ecosystems.

Thermal conductivity of dried biocemented sand at higher calcification

Thermal conductivity of dried biocemented sand at higher calcification

Impact of dissolved CO2 on calcification in two large, benthic foraminiferal species.

Rising atmospheric CO2 shifts the marine inorganic carbonate system and decreases seawater pH, a process often abbreviated to 'ocean acidification'. Since acidification decreases the saturation state for crystalline calcium carbonate (e.g., calcite and aragonite), rising dissolved CO2 levels will either increase the energy demand for calcification or reduce the total amount of CaCO3 precipitated. Here we report growth of two large benthic photosymbiont-bearing foraminifera, Heterostegina depressa and Amphistegina lessonii, cultured at four different ocean acidification scenarios (400, 700, 1000 and 2200 ppm atmospheric pCO2). Using the alkalinity anomaly technique, we calculated the amount of calcium carbonate precipitated during the incubation and found that both species produced the most carbonate at intermediate CO2 levels. The chamber addition rates for each of the conditions were also determined and matched the changes in alkalinity. These results were complemented by micro-CT scanning of selected specimens to visualize the effect of CO2 on growth. The increased chamber addition rates at elevated CO2 concentrations suggest that both foraminifera species can take advantage of the increased availability of the inorganic carbon, despite a lower saturation state. This adds to the growing number of reports showing the variable response of foraminifera to elevated CO2 concentrations, which is likely a consequence of differences in calcification mechanisms.

Finite element method-based resistivity simulation and water saturation calculation of irregular laminated shaly sandstone

Shaly sandstone reservoir is one of the most significant targets in petroleum and gas exploration. However, the influences of various factors on the resistivity of irregular laminated shaly sandstone are yet to be determined, and it is extremely challenging to accurately calculate the water saturation. By considering shaly sandstone in Zhujiang Formation of Neogene in Pearl River Mouth Basin as an example, this research extracts the shale distribution form and the pore structure by image processing, simulates the resistivity of rock by finite element method, analyzes the influence of shale parameters on resistivity, and deduces the water saturation equation of shaly sandstone. Results show that, in shaly sandstone, shale distributes in irregular laminated patterns on a millimeter scale. The other clean sandstone areas have high porosity and the capacity to reserve oil and gas. At high water saturation states, the shaly sandstone mainly conducts electricity in the clean sandstone area and various shale parameters have minor influences on the resistivity of shaly sandstone. At low water saturation states, the shaly sandstone mainly conducts electricity in the shale area, the resistivity of shaly sandstone is very close to the resistivity of the water layer, and the reservoir is the so-called low resistivity reservoir. The conductive form of clean sandstone area and shale laminae tends to parallel but remains a noticeable difference from total parallel. The simulation results deduced that the water saturation equation of shaly sandstone is more accurate than other equations, which provides an innovative mindset to calculate the water saturation of shaly sandstone.

Acidification impacts and acclimation potential of Caribbean benthic foraminifera assemblages in naturally discharging low-pH water

Abstract. Ocean acidification (OA) is expected to negatively affect many ecologically important organisms. Here we report the response of Caribbean benthic foraminiferal assemblages to naturally discharging low-pH waters with a composition similar to that expected for the end of the 21st century. At low pH ∼ 7.8 and low saturation state with respect to calcite (Ωcalcite < 4), the relative abundance of hyaline, agglutinated, and symbiont-bearing species increased, indicating higher resistance to potential carbonate chemistry changes. Diversity and other taxonomical metrics (i.e., richness, abundance, and evenness) declined steeply with decreasing pH despite exposure of this ecosystem to low-pH conditions for millennia, suggesting that tropical foraminiferal communities will be negatively impacted under acidification scenarios SSP3-7.0 (Shared Socioeconomic Pathways) and SSP5-8.5. The species Archaias angulatus, a major contributor to sediment production in the Caribbean, was able to calcify at more extreme conditions (7.1 pH) than those projected for the late 21st century, but the calcified tests had a lower average density than those exposed to higher-pH conditions (7.96), indicating that reef foraminiferal carbonate production might decrease this century. Smaller foraminifera were particularly sensitive to low pH, and our results demonstrate their potential use to monitor OA conditions.

Tracking the Space‐Time Evolution of Ocean Acidification Extremes in the California Current System and Northeast Pacific

AbstractOcean acidification is punctuated by episodic extremes of low pH and saturation state with regard to aragonite (ΩA). Here, we use a hindcast simulation from 1984 to 2019 with a high‐resolution regional ocean model (ROMS‐BEC) to identify and track ocean acidification extremes (OAX) in the northeast Pacific and the California current system (CCS). In the first step, we identify all grid‐cells whose pH and ΩA are simultaneously below their first percentile over the analysis period (1984–2019). In the second step, we aggregate all neighboring cells with extreme conditions into three‐dimensional time evolving events, permitting us to track them in a Lagrangian manner over their lifetime. We detect more than 22 thousand events that occur at least once in the upper 100 m during their lifetime, with broad distributions in terms of size, duration, volume, and intensity, and with 26% of them harboring corrosive conditions (ΩA < 1). By clustering the OAXs, we find three types of extremes in the CCS. Near the coast, intense, shallow, and short‐lasting OAXs dominate, caused by strong upwelling. A second type consists of large and long‐lasting OAX events that are associated with westward propagating cyclonic eddies. They account for only 3% of all extremes, but are the most severe events. The third type is small extremes at depth arising from pycnocline heave. OAXs potentially have deleterious effects on marine life. Marine calcifiers, such as pteropods, might be especially impacted by the long‐lasting events with corrosive conditions.

Contrasting intensity of aragonite dissolution and dolomite cementation in glacial versus interglacial intervals of a subtropical carbonate succession

AbstractAragonite and high‐Mg calcite are abundant in modern, neritic carbonate systems but almost absent in their fossil counterparts. Dissolution of these metastable mineral phases commonly leaves no visible trace in the sedimentary record, compromising the derivation of palaeoenvironmental information from the rock record. The upper 25 m of Integrated Ocean Drilling Program (IODP) Site U1460 on the outer ramp of the western Australian Shelf were investigated to study shallow burial (tens of metres) marine diagenesis in organic‐carbon poor sediments using microscopic, total organic carbon, biomarkers and mineralogical analysis in combination with porewater geochemistry. Aragonite dissolution is negligible at the seafloor but intensifies ca 5 m below, even though bulk porewaters are supersaturated for aragonite. This apparent contradiction likely results from dissolution in undersaturated microenvironments. Aragonite dissolution below 5 to 6 m is on average more intense in interglacial compared to glacial intervals. The presence of disseminated framboidal pyrite and porewater results indicate that minor sulphate reduction is active at IODP Site U1460. Sulphate reduction is probably limited by the low organic matter content (ca 0.2%). It is well‐known from the literature that incipient sulphate reduction can lead to a drop in pH and consequently to carbonate dissolution. It is therefore assumed that the slightly higher concentration of organic matter in the interglacial intervals allowed increased aragonite dissolution during sulphate reduction compared to glacial beds. Low amounts of dolomite cement (<15%) start to form at the same depth (5 to 6 m) as aragonite dissolution intensifies. Dolomite formation and aragonite dissolution also show covariance on a metre‐scale below 5 to 6 m, indicating that a low carbonate saturation state might enhance dolomite formation. This mechanism provides an indirect link between dolomite formation, aragonite dissolution and orbital cycles. The outcome of this study, therefore, contributes to a better understanding of differential diagenesis in marine carbonates.

Contrasting land-uses in two small river basins impact the colored dissolved organic matter concentration and carbonate system along a river-coastal ocean continuum

Human activities have led to an increase in land use change, with effects on the structure and functioning of ecosystems. The impact of contrasting land uses along river basins on the concentration of colored dissolved organic matter (CDOM) reaching the coastal zone, and its relationship with the carbonate system of the adjacent coastal ocean, is poorly known. To understand the relationship between land use change, CDOM and its influence on the carbonate system, two watersheds with contrasting land uses in southern Chile were studied. The samples were collected at eight stations between river and adjacent coastal areas, during three sampling campaigns in the austral summer and spring. Chemical and biological samples were analyzed in the laboratory according to standard protocols. Landsat 8 satellite images of the study area were used for identification and supervised classification using remote sensing tools. The Yaldad River basin showed 82% of native forest and the Colu River basin around 38% of grassland (agriculture). Low total alkalinity (AT) and Dissolved Inorganic Carbon (DIC), but high CDOM proportions were typically observed in freshwater. A higher CDOM and humic-like compounds concentration was observed along the river-coastal ocean continuum in the Yaldad basin, characterized by a predominance of native forests. In contrast, nutrient concentrations, AT and DIC, were higher in the Colu area. Low CaCO3 saturation state (ΩAr < 2) and even undersaturation conditions were observed at the coastal ocean at Yaldad. A strong negative correlation between AT, DIC and ΩAr with CDOM/fDOM, suggested the influence of terrestrial material on the seawater carbon chemistry. Our results provide robust evidence that land uses in river basins can influence CDOM/fDOM proportion and its influence on the carbonate chemistry of the adjacent coastal, with potential implications for the shellfish farming activity in this region.

Continuous Monitoring and Future Projection of Ocean Warming, Acidification, and Deoxygenation on the Subarctic Coast of Hokkaido, Japan

As the ocean absorbs excessive anthropogenic CO2 and ocean acidification proceeds, it is thought to be harder for marine calcifying organisms, such as shellfish, to form their skeletons and shells made of calcium carbonate. Recent studies have suggested that various marine organisms, both calcifiers and non-calcifiers, will be affected adversely by ocean warming and deoxygenation. However, regardless of their effects on calcifiers, the spatiotemporal variability of parameters affecting ocean acidification and deoxygenation has not been elucidated in the subarctic coasts of Japan. This study conducted the first continuous monitoring and future projection of physical and biogeochemical parameters of the subarctic coast of Hokkaido, Japan. Our results show that the seasonal change in biogeochemical parameters, with higher pH and dissolved oxygen (DO) concentration in winter than in summer, was primarily regulated by water temperature. The daily fluctuations, which were higher in the daytime than at night, were mainly affected by daytime photosynthesis by primary producers and respiration by marine organisms at night. Our projected results suggest that, without ambitious commitment to reducing CO2 and other greenhouse gas emissions, such as by following the Paris Agreement, the impact of ocean warming and acidification on calcifiers along subarctic coasts will become serious, exceeding the critical level of high temperature for 3 months in summer and being close to the critical level of low saturation state of calcium carbonate for 2 months in mid-winter, respectively, by the end of this century. The impact of deoxygenation might often be prominent assuming that the daily fluctuation in DO concentration in the future is similar to that at present. The results also suggest the importance of adaptation strategies by local coastal industries, especially fisheries, such as modifying aquaculture styles.

Spatial variability of summertime aragonite saturation states and its influencing factor in the Bering Sea

The Bering sea is susceptible to ocean acidification driven by both human activities (anthropogenic CO2) and distinctive natural processes. To assess the situation of ocean acidification, we investigated the spatial variability of aragonite saturation states (ΩAr) in July 2010 during the 4th Chinese National Arctic Research Expedition (CHINARE). The surface waters were all oversaturated with respect to aragonite (ΩAr > 1) due to high biological removal, and ΩAr ranged from 1.43 to 3.17. The relatively low ΩAr values were found in the western Bering Strait and eastern nearshore region of the Bering Sea Shelf, which were associated with the upwelling and riverine input, respectively. In the subsurface, the ΩAr decreased to generally low saturation states and were observed to be strongly undersaturated (ΩAr < 1) in the bottom waters with a lowest value of 0.45, which might be caused by remineralization. However, unlike prior studies, the low ΩAr values in the shallow nearshore region were still above the saturation horizon throughout the water column, which were probably counteracted by high local primary production. In the context of climate change and increasing anthropogenic CO2 absorption, the suppression and undersaturation of ΩAr in the Bering Sea are not only attributed to the natural processes but also the accumulation of anthropogenic CO2.

Arctic Ocean acidification over the 21st century co-driven by anthropogenic carbon increases and freshening in the CMIP6 model ensemble

Abstract. The uptake of anthropogenic carbon (Cant) by the ocean leads to ocean acidification, causing the reduction of pH and the saturation states of aragonite (Ωarag) and calcite (Ωcalc). The Arctic Ocean is particularly vulnerable to ocean acidification due to its naturally low pH and saturation states and due to ongoing freshening and the concurrent reduction in total alkalinity in this region. Here, we analyse ocean acidification in the Arctic Ocean over the 21st century across 14 Earth system models (ESMs) from the latest Coupled Model Intercomparison Project Phase 6 (CMIP6). Compared to the previous model generation (CMIP5), models generally better simulate maximum sea surface densities in the Arctic Ocean and consequently the transport of Cant into the Arctic Ocean interior, with simulated historical increases in Cant in improved agreement with observational products. Moreover, in CMIP6 the inter-model uncertainty of projected changes over the 21st century in Arctic Ocean Ωarag and Ωcalc averaged over the upper 1000 m is reduced by 44–64 %. The strong reduction in projection uncertainties of Ωarag and Ωcalc can be attributed to compensation between Cant uptake and total alkalinity reduction in the latest models. Specifically, ESMs with a large increase in Arctic Ocean Cant over the 21st century tend to simulate a relatively weak concurrent freshening and alkalinity reduction, while ESMs with a small increase in Cant simulate a relatively strong freshening and concurrent total alkalinity reduction. Although both mechanisms contribute to Arctic Ocean acidification over the 21st century, the increase in Cant remains the dominant driver. Even under the low-emissions Shared Socioeconomic Pathway 1-2.6 (SSP1-2.6), basin-wide averaged Ωarag undersaturation in the upper 1000 m occurs before the end of the century. While under the high-emissions pathway SSP5-8.5, the Arctic Ocean mesopelagic is projected to even become undersaturated with respect to calcite. An emergent constraint identified in CMIP5 which relates present-day maximum sea surface densities in the Arctic Ocean to the projected end-of-century Arctic Ocean Cant inventory is found to generally hold in CMIP6. However, a coincident constraint on Arctic declines in Ωarag and Ωcalc is not apparent in the new generation of models. This is due to both the reduction in Ωarag and Ωcalc projection uncertainty and the weaker direct relationship between projected changes in Arctic Ocean Cant and changes in Ωarag and Ωcalc.

Dynamic Transitions of Epilepsy Waveforms Induced by Astrocyte Dysfunction and Electrical Stimulation.

Experimental studies have shown that astrocytes participate in epilepsy through inducing the release of glutamate. Meanwhile, considering the disinhibition circuit among inhibitory neuronal populations with different time scales and the feedforward inhibition connection from thalamic relay nucleus to cortical inhibitory neuronal population, here, we propose a modified thalamocortical field model to systematically investigate the mechanism of epilepsy. Firstly, our results show that rich firing activities can be induced by astrocyte dysfunction, including high or low saturated state, high- or low-frequency clonic, spike-wave discharge (SWD), and tonic. More importantly, with the enhancement of feedforward inhibition connection, SWD and tonic oscillations will disappear. In other words, all these pathological waveforms can be suppressed or eliminated. Then, we explore the control effects after different external stimulations applying to thalamic neuronal population. We find that single-pulse stimulation can not only suppress but also induce pathological firing patterns, such as SWD, tonic, and clonic oscillations. And we further verify that deep brain stimulation can control absence epilepsy by regulating the amplitude and pulse width of stimulation. In addition, based on our modified model, 3 : 2 coordinated reset stimulation strategies with different intensities are compared and a more effective and safer stimulation mode is proposed. Our conclusions are expected to give more theoretical insights into the treatment of epilepsy.

Chemical Exposure Due to Anthropogenic Ocean Acidification Increases Risks for Estuarine Calcifiers in the Salish Sea: Biogeochemical Model Scenarios

Ocean acidification is projected to have profound impacts on marine ecosystems and resources, especially in the estuarine habitats. Here, we describe biological risks under current exposure of anthropogenic ocean acidification in the Salish Sea, an estuarine system that already experiences inherently low OA conditions. We used the PNNL/DOE Salish Sea biogeochemical model (SSM) informed by a selection of OA-related biological thresholds of ecologically and economically important calcifiers, pteropods and Dungeness crabs. The SSM was implemented to assess current exposure and associated risk due to reduced aragonite saturation state (Ωar) and pH conditions with respect to the magnitude, duration and severity of exposure below the biological thresholds in the Salish Sea and compare it to the pre-industrial time. We further investigated individual effects of atmospheric CO2 uptake and nutrient-driven eutrophication on the changes in the chemical exposure since the pre-industrial time. Our model predicts an average decrease in Ωar of about 0.11 and average decrease in pH of about 0.06 in the top 100 m of the water column of the Salish Sea since the pre-industrial times that predispose pelagic calcifiers to increased magnitude, duration and severity of exposure. Accordingly, we demonstrate that present-day exposure is below the thresholds for pteropod sublethal effects across the entire Salish Sea basin, while mortality threshold exposure occurs on a spatially limited basis. The greatest risk for the larval Dungeness crabs is associated with the spatially limited exposures to low calcite saturation state in the South Sound in the springtime, where an increase in internal dissolution could induce additional energetic costs. The main anthropogenic driver behind the predicted impacts is atmospheric CO2 uptake, while nutrient-driven eutrophication plays only a marginal role over spatially and temporally limited scales. Reduction of CO2 emissions can help sustain biological species vital for ecosystem functions and society.

Phosphorites, glass ramps and carbonate factories: The evolution of an epicontinental sea and a late Palaeozoic upwelling system (Phosphoria Rock Complex)

AbstractThe Permian Phosphoria Rock Complex of the western USA contains an enigmatic assemblage of bioelemental rocks (i.e. phosphorites and cherts) that accumulated in a depositional system with no modern analogue. This study utilizes detailed sedimentological, stratigraphic and petrographic examination to evaluate the genetic relations of phosphorites, spiculitic chert and carbonates of the Ervay cycle (depositional sequence) and propose a unified oceanographic model for their deposition. The Ervay cycle contains three marine and one terrestrial facies association, each of which composes the bulk of a single lithostratigraphic unit. The marine facies associations include: (i) granular phosphorites (Retort Member); (ii) spiculitic cherty dolostones (Tosi Member); and (iii) marine to peritidal carbonates (Ervay Member). Red beds and intercalated gypsum (Goose Egg Formation) accumulated in the vast desert adjacent to the sea. The three marine members are chronostratigraphically distinct, successive and conformably stacked. They are not coeval facies belts. They reflect the progressive evolution of the epicontinental sea from the location of: (i) authigenic phosphogenesis (lowstand to transgression); to (ii) a glass ramp with biosiliceous (sponge) deposition (transgression); to (iii) a carbonate ramp (regression). This succession of switching biochemical sediment factories records the evolution of sea‐level, nutrient supply, upwelling, oxygenation and dissolved Si. Intense upwelling, potentially coupled with aeolian input, led to sedimentary condensation and phosphogenesis. Decreased upwelling intensity during transgression increased oxygenation sufficiently for a siliceous sponge benthos. Sponges were favoured over biocalcifiers due to elevated dissolved silica and a low carbonate saturation state. The cessation of sponge dominance and transition to a carbonate ramp occurred due to decreasing upwelling intensity, Si drawdown and an increased carbonate saturation state. These results provide insight into the role of Si loading in faunal turnover on glass ramps and highlight how differences in dissolved Si utilizers in pre‐Cretaceous versus post‐Cretaceous upwelling systems influence the resultant deposits.

Lack of synsedimentary chemical alteration in polar carbonates (Ross Sea, Antarctica): Resolution of a conundrum

ABSTRACTAlthough rare in space and time, skeletal carbonates deposited on polar shelves hold great potential for improving understanding of the oceanography of the high latitudes. Low temperatures, low carbonate saturation states, and strong seasonality govern not only the nature of carbonate communities, but also how their deposits translate into the rock record. To understand the effects of early seafloor processes on preservation, we investigated late Quaternary carbonates recovered in piston cores from the Ross Sea, Antarctica. Sediments are unconsolidated skeletal gravels and sands that mantle areas of the outer shelf swept by strong bottom currents. Deposits are dominated locally by either stylasterine hydrocorals, barnacles, or bryozoans, which comprise assemblages with strong similarities to modern benthic communities. Radiocarbon ages indicate that carbonate factories were most prolific during the lead-up to the Last Glacial Maximum (Tartanian), when sediment input was minimized, and have been mostly dormant since. Results show that synsedimentary alteration is not substantially different in the temperate and polar realms with the significant exception of chemical diagenesis. As is common in temperate deposits, skeletal grains undergo disarticulation, fracturing, abrasion, and intense bioerosion. By contrast, cementation is absent and rare aragonite grains are preserved, indicating that taphonomic loss is not as prevalent as in temperate deposits. Primary skeletal microstructures and stable-isotope compositions are preserved, indicating that chemical alteration of grains is negligible. The preservation of aragonite in polar settings is herein attributed to low rates of organic-matter burial and very low temperatures, which strongly limit microbial activity. These factors allow interstitial waters to remain weakly supersaturated with respect to aragonite. Comparison with Permian analogs indicates that lithification is delayed until deposits reach burial depths at which chemical compaction proceeds. The ultimate end product is limestone with prominent compaction features and a tightly packed fabric. Calcitic skeletal material can retain primary geochemical compositions through the lithification process, although growth of burial cement in intraparticle porosity complicates selective sampling of unaltered material. In providing a cold-water end member for the spectrum of synsedimentary diagenetic processes, results highlight specific differences that should be accounted for when interpreting the deposits of polar, cold-water carbonate systems.

Biomarkers of Alzheimer's disease in severe obstructive sleep apnea-hypopnea syndrome in the Chinese population.

Patients with severe obstructive sleep apnea-hypopnea syndrome are often accompanied by symptoms such as decreased cognitive function and daytime sleepiness, while cognitive function is often associated with biomarkers of Alzheimer's disease. Therefore, this study aims to explore the level of Alzheimer's disease biomarkers in the plasma of obstructive sleep apnea-hypopnea syndrome patients as well as the relationship between cognitive function and daytime sleepiness. Between May and July 2019, 35 patients requiring hospitalization for severe obstructive sleep apnea-hypopnea syndrome and 16 normal control patients were selected from West China Hospital. Alzheimer's disease biomarkers (Aβ40, Aβ42, t-tau, p-tau) in plasma were detected by ELISA in all 51 subjects. The differences in Alzheimer's disease biomarkers between the two groups were compared. In addition, a correlation analysis of disease-related indicators and univariate analysis of the risk factors of obstructive sleep apnea-hypopnea syndrome was conducted using the logistic regression model. The plasma levels of Alzheimer's disease biomarkers (Aβ40, t-tau, p-tau) in patients with severe obstructive sleep apnea-hypopnea syndrome were significantly higher than those in the control group (29.24 ± 32.52, 13.18 ± 10.78, p = 0.049; 11.88 ± 7.05, 7.64 ± 4.17, p = 0.037; 26.31 ± 14.41, 17.34 ± 9.12, p = 0.027). Aβ42, Aβ40, t-tau, and p-tau were significantly negatively correlated with mean oxygen saturation, low oxygen saturation and Mini-Mental State examination scale scores, and positively correlated with oxygen desaturation index and Epworth Sleepiness Scale scores. T-tau and p-tau can be used as new risk factors for obstructive sleep apnea-hypopnea syndrome. Alzheimer's disease biomarkers in the plasma of obstructive sleep apnea-hypopnea syndrome patients are higher than those in the control group, and the mechanism of action may be related to sleep disorders and night hypoxia. The Alzheimer's disease biomarkers deposited in plasma may also cause the decline of patients' cognitive function, increased daytime sleepiness and accelerate the progression of obstructive sleep apnea-hypopnea syndrome.

Dense Mytilus Beds Along Freshwater-Influenced Greenland Shores: Resistance to Corrosive Waters Under High Food Supply

Arctic calcifiers are believed to be particularly vulnerable to ocean acidification as the Arctic already experiences low carbonate saturations states due to low temperature and high inputs of freshwater. Here, we report the finding of dense beds of Mytilus growing in tidal lagoons and river mouths, where the availability of carbonate ions is remarkably low Ωarag < 0.5. Although these Mytilus grow in the intertidal zone, and therefore are covered by seawater during high tide, δ18O isotopes of shell carbonate were low − 2.48 ± 0.05‰, confirming that their shells were deposited under low salinity conditions, i.e., reflecting a contribution from 18O-depleted freshwater. δ18O isotopes of shell carbonate became heavier with increasing salinity, with mean values of − 0.74 ± 0.96‰ for Mytilus growing in tidal pools. We calculated, based on δ18O isotopic composition standardized to a common temperature, that freshwater accounted for 7% of the carbonate oxygen in the shells of Mytilus at the habitats with near full-strength seawater salinity compared with 25% in shells collected at sites temporarily exposed to freshwater. The composition of the periostracum revealed a trend for shells from river mouths and brackish tidal lagoons to be more depleted in polysaccharides than shells exposed to higher salinity. We conclude that the high food supply associated with riverine discharge allows Mytilus to cope with the low saturation states by using energy to calcify and modify their periostracum to protect the shells from dissolution. These findings suggest that Arctic Mytilus are highly resistant to low saturation states of carbon minerals if supplied with sufficient food.