Organic matter composition and greenhouse gas production of thawing subsea permafrost in the Laptev Sea

Subsea permafrost represents a large carbon pool that might be or become a significant greenhouse gas source. Scarcity of observational data causes large uncertainties. We here use five 21-56 m long subsea permafrost cores from the Laptev Sea to constrain organic carbon (OC) storage and sources, degradation state and potential greenhouse gas production upon thaw. Grain sizes, optically-stimulated luminescence and biomarkers suggest deposition of aeolian silt and fluvial sand over 160 000 years, with dominant fluvial/alluvial deposition of forest- and tundra-derived organic matter. We estimate an annual thaw rate of 1.3 ± 0.6 kg OC m−2 in subsea permafrost in the area, nine-fold exceeding organic carbon thaw rates for terrestrial permafrost. During 20-month incubations, CH4 and CO2 production averaged 1.7 nmol and 2.4 µmol g−1 OC d−1, providing a baseline to assess the contribution of subsea permafrost to the high CH4 fluxes and strong ocean acidification observed in the region

Fire, vegetation and Holocene climate in the south-eastern Tibetan Plateau: a multi-biomarker reconstruction from Paru Co

The fire history of the Tibetan Plateau over centennial to millennial timescales is still unknown. Recent ice core studies reconstruct fire history over the past few decades but do not extend through the Holocene. Lacustrine sedimentary cores, however, provide continuous records of large-scale and local environmental modifications due to their accumulation of specific organic molecular markers throughout the past millennia. In order to reconstruct Holocene fire events and vegetation changes occurring on the south-eastern Tibetan Plateau and the surrounding areas, we improved and integrated previous analytical methods. The multi-proxy procedure was applied to samples retrieved from Paru Co, a small lake located in the Nyainqentanglha Mountains (29°47'45.6"N; 92°21'07.2"E; 4845m a.s.l.). The investigated biomarkers include n-alkanes as indicators of vegetation, polycyclic aromatic hydrocarbons (PAHs) as combustion proxies, faecal sterols and stanols (FeSts) as indicators of the presence of humans or grazing animals and finally monosaccharide anhydrides (MAs) as specific markers of vegetation burning processes. Relatively high concentrations of both MAs and PAHs demonstrate intense local biomass burning activity during the early Holocene (10.9–10.7calky BP), which correspond to a drier climate following deglaciation. High concentrations of MAs but not PAHs between 10.7–9calky BP suggest a period of regional biomass burning followed by a decreasing fire trend through the mid-late Holocene. This fire history is consistent with local vegetation changes reconstructed from both n-alkanes and regional pollen records, where vegetation types depend on the centennial-scale intensity of monsoon precipitation. FeSts were below detection limits for most of the samples, suggesting limited direct human influences on fire regime and vegetation changes in the lake's catchment. Climate is the main influence on fire activity recorded in Paru Co over millennial timescales, where biomass burning fluctuates in response to alternating warm/humid and cool/dry periods

Rationale, study design, and analysis plan of the Alveolar Recruitment for ARDS Trial (ART): Study protocol for a randomized controlled trial

Background: Acute respiratory distress syndrome (ARDS) is associated with high in-hospital mortality. Alveolar recruitment followed by ventilation at optimal titrated PEEP may reduce ventilator-induced lung injury and improve oxygenation in patients with ARDS, but the effects on mortality and other clinical outcomes remain unknown. This article reports the rationale, study design, and analysis plan of the Alveolar Recruitment for ARDS Trial (ART). Methods/Design: ART is a pragmatic, multicenter, randomized (concealed), controlled trial, which aims to determine if maximum stepwise alveolar recruitment associated with PEEP titration is able to increase 28-day survival in patients with ARDS compared to conventional treatment (ARDSNet strategy). We will enroll adult patients with ARDS of less than 72 h duration. The intervention group will receive an alveolar recruitment maneuver, with stepwise increases of PEEP achieving 45 cmH(2)O and peak pressure of 60 cmH2O, followed by ventilation with optimal PEEP titrated according to the static compliance of the respiratory system. In the control group, mechanical ventilation will follow a conventional protocol (ARDSNet). In both groups, we will use controlled volume mode with low tidal volumes (4 to 6 mL/kg of predicted body weight) and targeting plateau pressure <= 30 cmH2O. The primary outcome is 28-day survival, and the secondary outcomes are: length of ICU stay; length of hospital stay; pneumothorax requiring chest tube during first 7 days; barotrauma during first 7 days; mechanical ventilation-free days from days 1 to 28; ICU, in-hospital, and 6-month survival. ART is an event-guided trial planned to last until 520 events (deaths within 28 days) are observed. These events allow detection of a hazard ratio of 0.75, with 90% power and two-tailed type I error of 5%. All analysis will follow the intention-to-treat principle. Discussion: If the ART strategy with maximum recruitment and PEEP titration improves 28-day survival, this will represent a notable advance to the care of ARDS patients. Conversely, if the ART strategy is similar or inferior to the current evidence-based strategy (ARDSNet), this should also change current practice as many institutions routinely employ recruitment maneuvers and set PEEP levels according to some titration method.Hospital do Coracao (HCor) as part of the Program 'Hospitais de Excelencia a Servico do SUS (PROADI-SUS)'Brazilian Ministry of Healt

Tibetan Plateau lacustrine sediments as paleofire archives

Biomass burning as a natural process producing greenhouse gases may influence both regional and global climate, and it has become of planetary concern due to anthropogenic activities (Simoneit, 2000; Hopmans et al., 2012; Zennaro et al., 2014). The present work gives information about past fire events in the Tibetan Plateau and helps to increase the understanding of the interaction between Holocene's climate and fire activity. Tibetan Plateau is located in Asia, which is known to be the Earth's largest and most populated continent, and its extension is approximately 1,000 km north to south and 2,500 km east to west, with an average elevation exceeding 4,500 m. We reconstructed biomass burning events of the last 10,500 years recorded in sediments collected from lake Paru Co (4,845 m above sea level), a small moraine dammed lake located on the South-Eastern Tibetan Plateau. Sediment samples were extracted using accelerate solvent extraction and different organic molecular proxies were analysed by GC-MS and IC-MS. We used monosaccharide anhydrides, levoglucosan and its isomers and polycyclic aromatic hydrocarbons as proxies for biomass burning. These are specific molecular markers originated from the pyrolysis of cellulose showing significant fire events and indicating changes in burned fuel. The relationship between this multi-proxy approach and climatic, meteorological and charcoal data allows the reconstruction and contextualization of past fire events and suggests a correspondence between dry climate period and presence of more intense fire events, especially in the Early Holocene

Tibetan Plateau lacustrine sediments as paleofire archives

Biomass burning as a natural process producing greenhouse gases may influence both regional and global climate, and it has become of planetary concern due to anthropogenic activities (Simoneit, 2000; Hopmans et al., 2012; Zennaro et al., 2014). The present work gives information about past fire events in the Tibetan Plateau and helps to increase the understanding of the interaction between Holocene's climate and fire activity. Tibetan Plateau is located in Asia, which is known to be the Earth's largest and most populated continent, and its extension is approximately 1,000 km north to south and 2,500 km east to west, with an average elevation exceeding 4,500 m. We reconstructed biomass burning events of the last 10,500 years recorded in sediments collected from lake Paru Co (4,845 m above sea level), a small moraine dammed lake located on the South-Eastern Tibetan Plateau. Sediment samples were extracted using accelerate solvent extraction and different organic molecular proxies were analysed by GC-MS and IC-MS. We used monosaccharide anhydrides, levoglucosan and its isomers and polycyclic aromatic hydrocarbons as proxies for biomass burning. These are specific molecular markers originated from the pyrolysis of cellulose showing significant fire events and indicating changes in burned fuel. The relationship between this multi-proxy approach and climatic, meteorological and charcoal data allows the reconstruction and contextualization of past fire events and suggests a correspondence between dry climate period and presence of more intense fire events, especially in the Early Holocene

Tibetan Plateau lacustrine sediments as paleofire archives

Biomass burning as a natural process producing greenhouse gases may influence both regional and global climate, and it has become of planetary concern due to anthropogenic activities (Simoneit, 2000; Hopmans et al., 2012; Zennaro et al., 2014). The present work gives information about past fire events in the Tibetan Plateau and helps to increase the understanding of the interaction between Holocene's climate and fire activity. Tibetan Plateau is located in Asia, which is known to be the Earth's largest and most populated continent, and its extension is approximately 1,000 km north to south and 2,500 km east to west, with an average elevation exceeding 4,500 m. We reconstructed biomass burning events of the last 10,500 years recorded in sediments collected from lake Paru Co (4,845 m above sea level), a small moraine dammed lake located on the South-Eastern Tibetan Plateau. Sediment samples were extracted using accelerate solvent extraction and different organic molecular proxies were analysed by GC-MS and IC-MS. We used monosaccharide anhydrides, levoglucosan and its isomers and polycyclic aromatic hydrocarbons as proxies for biomass burning. These are specific molecular markers originated from the pyrolysis of cellulose showing significant fire events and indicating changes in burned fuel. The relationship between this multi-proxy approach and climatic, meteorological and charcoal data allows the reconstruction and contextualization of past fire events and suggests a correspondence between dry climate period and presence of more intense fire events, especially in the Early Holocene

Molecular-Multiproxy Assessment of Land-Derived Organic Matter Degradation Over Extensive Scales of the East Siberian Arctic Shelf Seas

Global warming triggers permafrost thaw, which increases the release of terrigenous organic matter (terr-OM) to the Arctic Ocean by coastal erosion and rivers. Terrigenous OM degradation in the Arctic Ocean contributes to greenhouse gas emissions and severe ocean acidification, yet the vulnerability of different terr-OM components is poorly resolved. Here, terr-OM degradation dynamics are studied with unprecedented spatial coverage over the World's largest shelf sea system—the East Siberian Arctic Shelf (ESAS), using a multi-proxy molecular biomarker approach. Mineral-surface-area-normalized concentrations of terr-OM compounds in surface sediments decreases offshore. Differences between terr-OM compound classes (lignin phenols, high-molecular weight [HMW] n-alkanes, n-alkanoic acids and n-alkanols, sterols, 3,5-dihydroxybenzoic acids, cutin acids) reflect contrasting influence of sources, propensity to microbial degradation and association with sedimenting particles, with lignin phenols disappearing 3-times faster than total terr-OM, and twice faster than other biomarkers. Molecular degradation proxies support substantial terr-OM degradation across the ESAS, with clearest trends shown by: 3,5-dihydroxybenzoic acid/vanillyl phenol ratios, acid-to-aldehyde ratios of syringyl and vanillyl phenols, Carbon Preference Indices of HMW n-alkyl compounds and sitostanol/β-sitosterol. The combination of terr-OM biomarker data with δ13C/Δ14C-based source apportionment indicates that the more degraded state of lignin is influenced by the relative contribution of river-transported terr-OM from surface soils, while HMW n-alkanoic acids and stigmasterol are influenced by erosion-derived terr-OM from Ice Complex deposits. Our findings demonstrate differences in vulnerability to degradation between contrasting terr-OM pools, and underscore the need to consider molecular properties for understanding and modeling of large-scale biogeochemical processes of the permafrost carbon-climate feedback.ISSN:0886-6236ISSN:1944-922