Multiple sulfur isotopes in methane seep carbonates track unsteady sulfur cycling during anaerobic methane oxidation

The anaerobic oxidation of methane coupled with sulfate reduction (AOM-SR) is a major microbially-mediated methane consuming process in marine sediments including methane seeps. The AOM-SR can lead to the formation of methane-derived authigenic carbonates which entrap sulfide minerals (pyrite) and carbonate-associated sulfate (CAS). We studied the sulfur isotope compositions of the pyrite and CAS in seafloor methane-derived authigenic carbonate crust samples from the North Sea and Barents Sea which reflect the time-integrated metabolic activity of the AOM-SR community as well as the physical conditions under which those carbonates are formed. In these samples, pyrite exhibits δ³⁴S values ranging from -23.4‰ to 14.8‰ and Δ³³S values between −0.06‰ and 0.16‰, whereas CAS is characterized by δ³⁴S values ranging from 26.2‰ to 61.6‰ and Δ³³S mostly between −0.05‰ and 0.07‰. Such CAS sulfur isotope compositions are distinctly lower in δ³⁴S-Δ³³ space from published porewater sulfate values from environments where the reduction of sulfate is mostly coupled to sedimentary organic matter oxidation. Mass-balance modelling suggests that (1) AOM-SR appears to cause rapid carbonate precipitation under high methane flux near or at the sediment-water interface and (2) that the precipitation of pyrite and carbonates are not necessarily synchronous. The sulfur isotopic composition of pyrite is interpreted to reflect more variable precipitating conditions of evolving sulfide with porewater connectivity, fluctuating methane fluxes and oxidative sulfur cycle. Taken together, the multiple isotopic compositions of pyrite and sulfate in methane-derived authigenic carbonates indicate protracted precipitation under conditions of non-steady state methane seepage activity

Multiple sulfur isotopes in methane seep carbonates track unsteady sulfur cycling during anaerobic methane oxidation

The anaerobic oxidation of methane coupled with sulfate reduction (AOM-SR) is a major microbially-mediated methane consuming process in marine sediments including methane seeps. The AOM-SR can lead to the formation of methane-derived authigenic carbonates which entrap sulfide minerals (pyrite) and carbonate-associated sulfate (CAS). We studied the sulfur isotope compositions of the pyrite and CAS in seafloor methane-derived authigenic carbonate crust samples from the North Sea and Barents Sea which reflect the time-integrated metabolic activity of the AOM-SR community as well as the physical conditions under which those carbonates are formed. In these samples, pyrite exhibits δ³⁴S values ranging from -23.4‰ to 14.8‰ and Δ³³S values between −0.06‰ and 0.16‰, whereas CAS is characterized by δ³⁴S values ranging from 26.2‰ to 61.6‰ and Δ³³S mostly between −0.05‰ and 0.07‰. Such CAS sulfur isotope compositions are distinctly lower in δ³⁴S-Δ³³ space from published porewater sulfate values from environments where the reduction of sulfate is mostly coupled to sedimentary organic matter oxidation. Mass-balance modelling suggests that (1) AOM-SR appears to cause rapid carbonate precipitation under high methane flux near or at the sediment-water interface and (2) that the precipitation of pyrite and carbonates are not necessarily synchronous. The sulfur isotopic composition of pyrite is interpreted to reflect more variable precipitating conditions of evolving sulfide with porewater connectivity, fluctuating methane fluxes and oxidative sulfur cycle. Taken together, the multiple isotopic compositions of pyrite and sulfate in methane-derived authigenic carbonates indicate protracted precipitation under conditions of non-steady state methane seepage activity

Methane seepage at Vestnesa Ridge (NW Svalbard) since the Last Glacial Maximum

Multiple proxies in the geological record offshore NW Svalbard track shallow subseafloor diagenesis and seafloor methane seepage during the Last Glacial Maximum (LGM) extent and the disintegration of the Svalbard Barents Sea Ice Sheet (SBIS). Vestnesa Ridge, located at 79°N and in 1200 m water depth, is one of the northernmost known active methane seep sites and is characterised by a subseafloor fluid flow system, numerous seafloor pockmarks and gas flares in the water column. In this study, we develop a Late Pleistocene and Holocene stratigraphic framework, use stable oxygen and carbon isotope signatures (δ^(18)O, δ^(13)C) of benthic and planktic foraminifera, the mineralogical and carbon isotope composition of methane-derived authigenic carbonate (MDAC) and sediment geochemical data of ten sediment cores to assess methane seepage variability on Vestnesa Ridge. The studied cores cover the age range between 31.9 and 10 cal ka BP and record 32 negative δ^(13)C excursions in benthic and planktic foraminifera with amplitudes down to −29 ‰ VPDB. These δ^(13)C excursions are often associated with elevated Ca/Ti and Sr/Ti elemental ratios in sediments and MDAC nodules. The precipitation of MDAC overgrowth on foraminiferal tests explains most of the negative δ^(13)C excursions. In this dataset, the oldest recorded methane emission episodes on Vestnesa Ridge occurred between the LGM (24–23.5 cal ka BP) and Heinrich Event 1 (HE 1; 17.7–16.8 cal ka BP). Geological indicators for past subseafloor methane cycling and seafloor methane seepage, such as negative foraminiferal δ13C excursions, MDAC nodules, and elevated Sr/Ti elemental ratios recorded in post-LGM sediments, possibly represent vertical migration of the sulphate-methane transition zone (SMTZ) and post-date sedimentation by up to 13.4 ka. However, it is important to note that indications of post-LGM seafloor methane seepage at Vestnesa Ridge also correspond to the established methane efflux chronology for the adjacent Barents Sea shelf, implying that glacio-isostatic adjustments and associated re-activation of pre-existing deep-seated faults after disintegration of the SBIS are likely important controlling factors on fluid migration towards the seafloor

Diagenetic Mg-calcite overgrowths on foraminiferal tests in the vicinity of methane seeps

Methane is a potent greenhouse gas and some episodes of past global warming appear to coincide with its massive release from seafloor sediments as suggested by carbon isotope records of foraminifera. Here, we present structural, geochemical, and stable carbon isotope data from single foraminiferal calcite tests and authigenic Mg-calcite overgrowths in a sediment core recovered from an area of active methane seepage in western Svalbard at ca. 340 m water depth. The foraminifera are from intervals in the core where conventional bulk foraminiferal δ13C values are as low as -11.3 ‰. Mg/Ca analyses of the foraminiferal tests reveal that even tests for which there is no morphological evidence for secondary authigenic carbonate can contain Mg-rich interlayers with Mg/Ca up to 220 mmol/mol. Transmission electron microscopy (TEM) of the contact point between the biogenic calcite and authigenic Mg-calcite layers shows that the two phases are structurally indistinguishable and they have the same crystallographic orientation. Secondary ion mass spectrometry (SIMS) analyses reveal that the Mg-rich layers are strongly depleted in 13C (δ13C as low as -34.1 ‰). These very low δ13C values indicate that the authigenic Mg-calcite precipitated from pore waters containing methane-derived dissolved inorganic carbon at the depth of the sulfate–methane transition zone (SMTZ). As the depth of the SMTZ can be located several meters below the sediment-seawater interface, interpretation of low foraminiferal δ13C values in ancient sediments in terms of the history of methane seepage at the seafloor must be undertaken with care

COMPORTAMIENTO SEXUAL, DESCRIPCIÓN MORFOLÓGICA DE LA GLÁNDULA METATORÁCICA E IDENTIFICACIÓN DE LOS SÉNSULOS ANTENALES DE Leptoglossus zonatus DALLAS (HETEROPTERA: COREIDAE)

Leptoglossus zonatus es un insecto polífago que causa pérdidas económicas en diferentes cultivos como el maíz, sorgo, frutales y algunos cultivos industriales. En este trabajo se determinó la edad y la hora de mayor actividad sexual colocando parejas de adultos de dos días de edad. Las observaciones se realizaron cada dos horas en un periodo de 24 horas continuas cada tercer día, durante un periodo de tiempo total de 60 días. También se describió el comportamiento sexual de este insecto en condiciones de laboratorio, mediante la construcción de un etograma; utilizando 3 grupos de insectos formando 30 parejas (2 machos, 1 hembra; 2 hembras, 1 macho y 2 hembras, 2 machos) cada uno. También se caracterizó morfológicamente la glándula metatorácica (MTG) en ambos sexos, la cual se encuentra en la fosa coxal metatorácica y está formada por un reservorio bien diferenciado, dos conductos y dos glándulas accesorias. Además se estudiaron los sénsulos antenales de ambos sexos, por medio de microscopía electrónica de barrido. Se identificaron seis tipos de estructuras sensoriales: tricoideos, placoideos, basicónicos, celocónicos, campaniformes, y microtrichias. En ambos sexos no se encontró una diferencia sexual en estos sénsulos. Se realizaron mediciones de la antena y tamaño del cuerpo de ambos sexos (n=10). La longitud de la antena de machos fue 12.35 ± 0.20 mm y de hembras 12.33 ± 0.26 mm, el ancho de la antena de machos fue 0.23 ± 0.01mm y de hembras 0.23 ± 0.011 mm, el ancho del flagelo de machos fue 0.31 ± 0.01mm y hembras 0.33 ± 0.01 mm, el largo del flagelo en machos fue de 9.83 ± 0.16 mm y hembras 10.07 ± 0.16 mm y longitud del cuerpo en machos fue de 15.51 ± 0.27 mm y para hembras fue de 16.88 ± 0.44 mm (media ± EE). En esta última medición se encontró que la hembra fue significativamente más grande que el macho. El tiempo promedio de maduración sexual fue de 25 ± 8.20 días (media ± DE). Dos picos máximos de actividad fueron registrados, en la fotofase fue a las 14:00 h y en la escotofase a las 22:00 h. Los patrones de comportamiento establecidos fueron: acicalamiento, movimiento del abdomen, movimiento de antenas, tocado de antenas por ambos sexos, monta y la cópula. En la descripción morfológica de la glándula metatorácica no se encontró un dimorfismo sexual en este insecto

Physiological potential and evolutionary trajectories of syntrophic sulfate-reducing bacterial partners of anaerobic methanotrophic archaea

Sulfate-coupled anaerobic oxidation of methane (AOM) is performed by multicellular consortia of anaerobic methanotrophic archaea (ANME) in obligate syntrophic partnership with sulfate-reducing bacteria (SRB). Diverse ANME and SRB clades co-associate but the physiological basis for their adaptation and diversification is not well understood. In this work, we used comparative metagenomics and phylogenetics to investigate the metabolic adaptation among the 4 main syntrophic SRB clades (HotSeep-1, Seep-SRB2, Seep-SRB1a, and Seep-SRB1g) and identified features associated with their syntrophic lifestyle that distinguish them from their non-syntrophic evolutionary neighbors in the phylum Desulfobacterota. We show that the protein complexes involved in direct interspecies electron transfer (DIET) from ANME to the SRB outer membrane are conserved between the syntrophic lineages. In contrast, the proteins involved in electron transfer within the SRB inner membrane differ between clades, indicative of convergent evolution in the adaptation to a syntrophic lifestyle. Our analysis suggests that in most cases, this adaptation likely occurred after the acquisition of the DIET complexes in an ancestral clade and involve horizontal gene transfers within pathways for electron transfer (CbcBA) and biofilm formation (Pel). We also provide evidence for unique adaptations within syntrophic SRB clades, which vary depending on the archaeal partner. Among the most widespread syntrophic SRB, Seep-SRB1a, subclades that specifically partner ANME-2a are missing the cobalamin synthesis pathway, suggestive of nutritional dependency on its partner, while closely related Seep-SRB1a partners of ANME-2c lack nutritional auxotrophies. Our work provides insight into the features associated with DIET-based syntrophy and the adaptation of SRB towards it

Stable Isotope Analysis of Intact Oxyanions Using Electrospray Quadrupole-Orbitrap Mass Spectrometry

The stable isotopes of sulfate, nitrate, and phosphate are frequently used to study geobiological processes of the atmosphere, ocean, as well as land. Conventionally, the isotopes of these and other oxyanions are measured by isotope-ratio sector mass spectrometers after conversion into gases. Such methods are prone to various limitations on sensitivity, sample throughput, or precision. In addition, there is no general tool that can analyze several oxyanions or all the chemical elements they contain. Here, we describe a new approach that can potentially overcome some of these limitations based on electrospray hyphenated with Quadrupole Orbitrap mass spectrometry. This technique yields an average accuracy of 1–2‰ for sulfate δ34S and δ18O and nitrate δ15N and δ18O, based on in-house and international standards. Less abundant variants such as δ17O, δ33S, and δ36S, and the 34S–18O “clumped” sulfate can be quantified simultaneously. The observed precision of isotope ratios is limited by the number of ions counted. The counting of rare ions can be accelerated by removing abundant ions with the quadrupole mass filter. Electrospray mass spectrometry (ESMS) exhibits high-throughput and sufficient sensitivity. For example, less than 1 nmol sulfate is required to determine 18O/34S ratios with 0.2‰ precision within minutes. A purification step is recommended for environmental samples as our proposed technique is susceptible to matrix effects. Building upon these initial provisions, new features of the isotopic anatomy of mineral ions can now be explored with ESMS instruments that are increasingly available to bioanalytical laboratories