Reconstruction of past and present methane emission in the Arctic cold seeps using biogeochemical proxies

Global warming is now highly concerned by society as extreme weather is more often than ever, and the Arctic is experiencing warming twice as fast as the global mean. A large amount of carbon is stored in the forms of methane and methane hydrate in the continental margins worldwide. Methane is the most predominant gaseous compound in natural gas hydrate, which is stable under low temperature and high pressure. With the warming Arctic, methane from gas hydrate dissociation may release into the water column and atmosphere in the future and have positive feedback to the warming as methane is one of the most potent greenhouse gases. Therefore, it is crucial to study and understand the state, the drivers, and the fate of methane hydrate in the Arctic marine sediment. In this thesis, I study the methane seepage events in both modern and paleo settings. The methane seepage history was studied using authigenic carbonates, foraminifera, molecular fossils such as lipid biomarkers and sedimentary properties. I focus on two methane seepage sites in the Arctic Ocean, Vestnesa Ridge (1200m water depth), and Storfjordrenna (380 meters water depth). The former is characterized by numerous seafloor pockmarks, subseafloor fluid flow system, and gas flares in the water column whereas the latter is characterized by mound features at the seafloor, and gas flares in the water column. The thesis focused primarily on lipid biomarkers from the anaerobic oxidation of methane (AOM) microbial communities to reconstruct the history of methane seepage. The main research goal is to understand first the cold seep system at the study sites, then the current and paleo drivers of the methane emissions in the Arctic Ocean sediments, whether the discharge was triggered by the warming Arctic or it was a natural process that persists over a long time. Lipid biomarkers is a useful molecular tool to study methane seepage. They are stable over geological time scales and reflect the size as well as the source of the carbon pool based on its concentrations and isotopic signatures. Through these characteristics, they can trace the paleo methane seepage in combination with other methane proxies such as foraminifera and authigenic carbonates. These proxies unravel the history of methane seepage. Lipid biomarkers can also indicate the methane transport modes, diffusion vs. advection when used in combination with other geochemical data in modern settings

Implications of transient methane flux on associated biological communities in high-arctic seep habitats, Storbanken, Norwegian Barents sea

The continental margins of the Arctic Ocean basin contain methane seeps, where transient fluxes of seafloor methane are released due to the thermal dissociation of gas hydrates. An increase in shallow methane seeps identified over the past decade, potentially due to enhanced warming of the Arctic Ocean bottom water and associated destabilization of hydrate structure. Biological communities associated with methane release east of Svalbard in the Barents Sea (Storbanken Crater site, 76° 46.7′N, 35° 43.5′E, depths between 120 m–300 m depths) were investigated using towed camera imagery and ship-based platforms during a 2017 CAGE17-2 cruise on the RV Helmer Hanssen. We analyzed relationships among methane flux data, seafloor habitat characteristics, and biological community structure (i.e., presence and distribution of megafauna and expression of microbial mats) from a total of 14 surveys (6827 images and 40 multicore sediment cores) within the Storbanken Crater area and compared it to 2015 data. Unlike seep expressions at deeper sites (∼1200 m) in the Norwegian margin region, no seep-endemic, chemosynthetic-associated megafaunal species were observed at the shallow surveyed sites and all sites hosted similarly diverse communities of non-seep species, including commercially important fish and crustaceans. Methane concentrations did not markedly differ between the crater and non-crater sites. Rates of methane gas advection through sediments (in the form of flares) were relatively low and concentration of methane was even lower in porewater samples at the crater site. We present the first evidence of methane flare flux and intermittent microbial mat distribution with associated folliculinid ciliates, which suggests a long history of methane emissions and a transient seep environment in spatial and temporal flux. Together, this study presents a critical baseline on the temporal release of arctic methane and benthic biological communities to initiate temporal studies that identify future changes and predict the impact of climate chang

CYP2C19 genotype and platelet aggregation test-guided dual antiplatelet therapy after off-pump coronary artery bypass grafting: A retrospective cohort study

BackgroundDual antiplatelet therapy (DAPT) is recommended in patients undergoing off-pump coronary artery bypass graft surgery (OPCAB). Clopidogrel is less effective among patients with loss-of-function (LoF) of CYP2C19 alleles, while ticagrelor has direct effects on P2Y12 receptor. Whether a CYP2C19 genotype plus platelet aggregation test (PAgT)-guided DAPT after CABG could improve clinical outcomes remain uncertain.Materials and methodsFrom August 2019 to December 2020, 1,134 consecutive patients who underwent OPCAB received DAPT for 1 year after surgery in Ruijin Hospital, Shanghai Jiao Tong University School of Medicine. According to the actual treatment they received in real-world, 382 (33.7%) of them received a traditional DAPT: aspirin 100 mg qd + clopidogrel 75 mg qd, no matter the CYP2C19 genotype and response in platelet aggregation test (PAgT). The other 752 (66.3%) patients received an individual DAPT based on CYP2C19 genotype and PAgT: aspirin 100 mg qd + clopidogrel 75 mg qd if CYP2C19 was extensive metabolizer, or moderate metabolizer but normal response in PAgT; aspirin 100 mg qd + ticagrelor 90 mg bid if CYP2C19 was poor metabolizer, or moderate metabolizer but no or low response in PAgT. One-year follow-up was achieved for all patients. The primary outcome was major adverse cardiovascular events (MACE), a composite of cardiovascular death, myocardial infarction, and stroke. The safety outcome was thrombolysis in myocardial infarction (TIMI) criteria major bleeding.ResultsCompared with the traditional DAPT group, the risk of MACE in the individual DAPT group was significantly lower (5.5 vs. 9.2%, HR 0.583; 95% CI, 0.371–0.915; P = 0.019), mainly due to the decreased risk of MI (1.7 vs. 4.2%, HR 0.407; 95% CI, 0.196–0.846; P = 0.016). The risk of TIMI major bleeding events was similar between the two groups (5.3 vs. 6.0%, RR 0.883; 95% CI, 0.537–1.453; P = 0.626).ConclusionFor patients who underwent OPCAB, individual DAPT (CYP2C19 genotype plus PAgT-guided strategy) was associated with a lower risk of MACE and a similar risk of major bleeding

Reconstruction of past and present methane emission in the Arctic cold seeps using biogeochemical proxies

Global warming is now highly concerned by society as extreme weather is more often than ever, and the Arctic is experiencing warming twice as fast as the global mean. A large amount of carbon is stored in the forms of methane and methane hydrate in the continental margins worldwide. Methane is the most predominant gaseous compound in natural gas hydrate, which is stable under low temperature and high pressure. With the warming Arctic, methane from gas hydrate dissociation may release into the water column and atmosphere in the future and have positive feedback to the warming as methane is one of the most potent greenhouse gases. Therefore, it is crucial to study and understand the state, the drivers, and the fate of methane hydrate in the Arctic marine sediment. In this thesis, I study the methane seepage events in both modern and paleo settings. The methane seepage history was studied using authigenic carbonates, foraminifera, molecular fossils such as lipid biomarkers and sedimentary properties. I focus on two methane seepage sites in the Arctic Ocean, Vestnesa Ridge (1200m water depth), and Storfjordrenna (380 meters water depth). The former is characterized by numerous seafloor pockmarks, subseafloor fluid flow system, and gas flares in the water column whereas the latter is characterized by mound features at the seafloor, and gas flares in the water column. The thesis focused primarily on lipid biomarkers from the anaerobic oxidation of methane (AOM) microbial communities to reconstruct the history of methane seepage. The main research goal is to understand first the cold seep system at the study sites, then the current and paleo drivers of the methane emissions in the Arctic Ocean sediments, whether the discharge was triggered by the warming Arctic or it was a natural process that persists over a long time. Lipid biomarkers is a useful molecular tool to study methane seepage. They are stable over geological time scales and reflect the size as well as the source of the carbon pool based on its concentrations and isotopic signatures. Through these characteristics, they can trace the paleo methane seepage in combination with other methane proxies such as foraminifera and authigenic carbonates. These proxies unravel the history of methane seepage. Lipid biomarkers can also indicate the methane transport modes, diffusion vs. advection when used in combination with other geochemical data in modern settings

Recent development of carbon electrode materials for electrochemical supercapacitors

Supercapacitors have gained much attention due to their remarkable merits such as stable cycle performance, high power density and excellent charge and discharge performance at high rate. From this perspective, carbon-based materials are widely explored as the active electrode materials for supercapacitors by taking advantages of hierarchical porous structure, excellent chemical stability, multistage pore structure, high surface area, and excellent conductivity. Various studies have explored many methods to utilize carbon-based electrodes. The large amount of defects inside carbon materials including functional groups, heteroatoms, name as foreign-doping, can provide pseudocapacitance. Meanwhile, self-doping (voids, vacancies, defects, etc.) may also enhance the electric double-layer capacitance. In this context, a brief overview of carbon materials for supercapacitor is expounded, including their characteristics, development process and the future challenges, providing a referential guide to those new to this field

Multi-proxy approach to unravel methane emission history of an Arctic cold seep

Arctic Ocean sediments contain large amounts of methane in the form of free gas and gas hydrate. This highly dynamic methane reservoir is susceptible to be modified by bottom water warming. The warming may lead to gas hydrate destabilization releasing elevated methane fluxes to the seafloor and seawater. Reconstructing past methane dynamics can be achieved by using specific proxies left in the geological record. In this study, we apply a multi-proxy approach for paleo seepage reconstruction from sediment records at gas hydrate mounds (GHMs) in Storfjordrenna (south of the Svalbard archipelago). These shallow water (∼380 m water depth) systems are potentially vulnerable to global warming related temperature changes. 14C dating of foraminifera shells indicated an onset of deglaciation in the Storfjordrenna region at ∼20 kyr BP and allowed us to establish a stratigraphic context based on sediment Zr/Rb and Fe/Ca ratios. Several major (between 15 and 17 kyr BP) and minor methane venting phases were identified and interpreted to be related to gas hydrate instability triggered by isostatic adjustment right after the onset of the deglaciation. The detection of all major methane releases was only possible by combining data sets of stable carbon isotope compositions of foraminifera, mineralogy and δ13C values of authigenic carbonates, and abundance and stable carbon isotope signatures of lipid biomarkers. The most robust single proxy in this study was provided by the δ13C values of archaeal biomarkers. In contrast, the sediment Ba/Ti ratios recorded only the major events. Our results highlight the complexity and heterogeneity of methane dynamics in a small area of some hundred meters across

Study on the Influence of Window Type on Natural Ventilation Effect Based on CFD Simulation

Good natural ventilation is one of the basic conditions for people to be able to work and live indoors. In this paper, wind velocity, wind velocity non-uniformity coefficient and air age are taken as the evaluation indexes of indoor ventilation condition. A simulation software Airpak is used to build room models with three window types (with the same ventilation area), namely, top-hung window, casement window and sliding window. The wind incidence angle was adjusted between 0°- 90°, and the indoor wind velocity and air age of the room were simulated when the casement window was opened at 90°, the sliding window was fully opened and the top-hung window was opened at 30°. The average wind velocity, wind velocity non-uniformity coefficient and air age of the room under each working condition were calculated and analyzed to evaluate the freshness and comfort of the indoor air, so as to provide guidance for the reasonable design of indoor layout

A Review of Solar Energy Use in Biogas Digester Heating

Abstract: Several factors affect biogas fermentation, among which the temperature fluctuation is crucial. Domestic and foreign biogas fermentation heating systems are also diverse. Among various exist methods of heating biogas fermentation, solar biogas fermentation heating systems are also diverse. The current study reviewed various solar-heating biogas fermentation systems at home and abroad, describing the principle of the solar-heating system, the collector, the heat storage material and the research and application progress. It briefly discussed its characteristics, summarising the critical technology of solar biogas heating systems