Iron and sulphur speciation and cycling in the sediments of marine systems located in the arid environment: Case of the northern Red Sea

High fluxes of iron minerals associated with aeolian dry deposition may result in anomalously high reactive iron content and fast reoxidation of hydrogen sulphide in the sediments that prevents pyrite formation and results in “cryptic” sulphur cycle. In this work, we studied cycling of iron and sulphur in the deep-water (> 800 m water depth) sediments of the Red Sea and its northern extension, Gulf of Aqaba. We found that reactive iron content in the surface sediments of the Gulf of Aqaba and the Red Sea is high, while the content of sulphur-bound iron is very low and decreases with water depth. The presence of pyrite traces and zero-valent sulfur as well as isotopic compositions of sulphate and pyrite, which are consistent with sulphate reduction under substrate-limiting conditions, suggest that cryptic sulfur cycling is likely to be a result of fast reoxidation of hydrogen sulfide rather than microbial sulfate reduction suppression. In the sediments of Shaban Deep, which are overlain with hyper-saline hydrothermal brine, low reactive iron and high organic carbon contents result in a non-cryptic sulphur cycle characterized by preservation of pyrite in the sediments.Thematic collection: This article is part of the Sulfur in the Earth system collection available at: https://www.lyellcollection.org/cc/sulfur-in-the-earth-systemSupplementary material:https://doi.org/10.6084/m9.figshare.c.5508155

Internal microbial zonation assists in the massive growth of marimo, a lake ball of Aegagropila linnaei in Lake Akan

Marimo (lake ball) is an uncommon ball-like aggregation of the green alga, Aegagropila linnaei1. Although A. linnaei is broadly distributed in fresh and brackish waters in the northern hemisphere, marimo colonies are found only in particular habitats. The colonies have been gradually shrinking in recent years. Nevertheless, it is not clear how and why A. linnaei forms such massive spherical aggregations. Here, we report the bacterial microbiomes inside various sizes and aggregating structures of natural marimo collected from Lake Akan, Japan. We observed multi-layers composed of sediment particles only in the sizeable radial-type marimo with a >20 cm diameter, not in the tangled-type marimo. The deeper layers were enriched by Nitrospira, potential novel sulphur-oxidizing bacteria, and sulphate-reducing Desulfobacteraceae bacteria. The sulphur cycle-related bacteria are unique to Lake Akan due to sulphur deposits from the nearby volcanic mountains. Some of them were also recovered from lake sediments. Microorganisms of the multi-layers would form biofilms incorporating nearby sediment, which would function as microbial seals within large radial-type marimo. We propose that the layer structure provides habitats for diverse bacterial communities, promotes airtightness of the marimo, and finally contributes to the massive growth of the aggregation. These findings provide a clue to deciphering the massive growth of endangered marimo aggregates.

Challenging UKESM1 with SO2 and sulphate observational data to evaluate the aerosol sulphur cycle

<div> <p>UKESM1 is the latest generation Earth system model to be developed in the UK. It simulates the core physical and dynamical processes of land, atmosphere, ocean and sea ice systems which are extended to incorporate key marine and terrestrial biogeochemical cycles. These include the carbon and nitrogen cycles and interactive stratosphere-troposphere trace gas chemistry. Feedbacks between these components that have an important amplifying or dampening effect on the physical climate, and/or change themselves in response to changes in the physical climate are also included. One focus for the future development of UKESM1 is improved treatment of sulphur processes, including emission, chemical processing and deposition in the aerosol-chemistry scheme, UKCA-Mode. These processes span land-atmosphere and ocean-atmosphere boundaries and can therefore impact feedbacks between these systems. Emissions of SO2 can be oxidised to form sulphate aerosol, which plays a key role in both acid deposition, atmospheric aerosol loading and cloud properties, thereby directly contributing to the Earth’s radiative balance. Good representation of sulphur processes in UKESM1 is therefore essential for constraining uncertainties associated with the impacts of aerosols on the Earth system and thus understanding the global climate. Here we challenge UKESM1 with observations of SO2 and sulphate from ground-based measurement networks in Europe and the USA, and of SO2 from the Ozone Monitoring Instrument (OMI). We use these to evaluate temporal and spatial biases in the model’s simulation of SO2 and sulphate.  </p> </div><div> <p>We find that UKESM1 captures the historical trend for decreasing concentrations of atmospheric SO2 and sulphate in both Europe and the USA over the period 1987 to 2014. However, in the polluted regions of the Eastern USA and Europe, UKESM1 over-predicts surface SO2 concentrations by an average of 320-340%, while under-predicting surface sulphate concentrations by 25-35%. In the cleaner Western USA, the model over-predicts both surface SO2 and sulphate concentrations by 1200% and 150% respectively. The variability in the direction of UKESM1’s bias according to species and region suggests that the model bias may be driven differently depending on species and region. These drivers likely result from uncertainty in aspects of the sulphur cycle, including SO2 emission, loss processes (oxidation and deposition) or transport. To evaluate UKESM1 at the global scale we use a newly available data product for total column SO2 (TCSO2) from OMI. We find that UKESM1 over-predicts TCSO2 over much of the globe, particularly the large source regions of India, China, the USA and Europe as well as over background regions, including much of the ocean. </p> </div><div> <p>In this study we also assess changes to UKESM1’s SO2 dry deposition parameterization. These changes increase SO2 dry deposition to land and ocean surfaces, thus reducing atmospheric SO2 and sulphate concentrations, and ultimately reducing cold bias in UKESM1's simulation of mid 20th C global mean surface temperatures. In comparison with the ground based and satellite observations, we find that the changes reduce UKESM1's over prediction of surface SO2 concentrations and TCSO2</p> </div>

A stationary tropospheric sulphur cycle for Earth system models of intermediate complexit

<p>A stationary, computationally efficient  scheme, ChAP-1.0 (Chemistry and Aerosol Processes, version 1.0) for the sulphur cycle in the troposphereis developed. This scheme is envisaged to be implemented into Earth system models of intermediate complexity (EMICs). The scheme accounts for sulphur dioxide emissions into the atmosphere, its deposition to the surface, oxidation to sulphates, and dry and wet deposition of sulphates on the surface.<br>The calculations with the scheme were performed with the anthropogenic emissions of sulphur compounds into the atmosphere for 1850-2000 according to the CMIP5 (Coupled Models Intercomparison Project, phase 5) 'historical' protocol, with the ERA-Interim meteorology, and assuming that natural sources of sulphur into the atmosphere remain unchanged during this period. The model reasonably reproduces characteristics of the tropospheric sulphur cycle known from observations and other simulations (e.g., in the Atmospheric Chemistry and Climate Model Intercomparison Project phase II (ACCMIP) simulations, Copernicus Atmosphere Monitoring Service (CAMS) reanalysis, and the Meteorological Synthesizing Centre–West of the European Monitoring and Evaluation Programme (EMEP MSC-W) data). In particular, in 1980's and 1990's, , when the global anthropogenic emission of sulphur, global atmospheric burdens of SO<sub>2</sub> and SO<sub>4</sub> account, correspondingly, 0.2 TgS and 0.4 TgS. In our scheme, about half of the emitted sulphur dioxide is deposited to the surface and the rest in oxidised into sulphates. The latter mostly removed from the atmosphere by wet deposition. The lifetime of the SO<sub>2</sub> and SO<sub>4</sub> in the atmosphere is, respectively, 1.0±0.1 days and 4.1±0.3 days.<br>Despite its simplicity, our scheme may be successfully used to simulate sulphur/sulphates pollution in the atmosphere at coarse spatial and time scales and an impact of this pollution to direct radiative effect of sulphates on climate, their respective indirect (cloud- and precipitation-related) effects, as well as an impact of sulphur compounds on the terrestrial carbon cycle.</p>

A southern African perspective on the co-evolution of early life and environments

The Kaapvaal and Zimbabwe cratons host some of the earliest evidence for life. When compared to the contemporaneous East Pilbara craton, cherts and other metasedimentary horizons in southern Africa preserve traces of life with far greater morphological and geochemical fidelity. In spite of this, most fossiliferous horizons of southern Africa have received relatively limited attention. This review summarises current knowledge regarding the nature of early life and its distribution with respect to environments and ecosystems in the Archaean (>2.5 Ga) of the region, correlating stratigraphic, sedimentological, geochemical and palaeontological understanding. There is abundant and compelling evidence for both anoxygenic photosynthetic and chemosynthetic biomes dominating Palaeoarchaean-Mesoarchaean strata dating back to around 3.5 Ga, and the prevalence of each is tied to palaeoenvironmental parameters deducible from the rock record. Well-developed, large stromatolites characteristic of younger Mesoarchaean-Neoarchaean sequences were probably constructed by oxygenic photosynthesisers. Isotopic evidence from the Belingwe greenstone belt and the Transvaal Supergroup indicates that both a full sulphur cycle and complex nitrogen cycling were in operation by the Mesoarchaean-Neoarchaean. The Archaean geological record of southern Africa is thus a rich repository of information regarding the co-evolving geosphere and biosphere in deep time.

ChAP 1.0: A stationary tropospheric sulphur cycle for Earth system models of intermediate complexity

A stationary, computationally efficient scheme ChAP-1.0 (Chemical and Aerosol Processes, version 1.0) for the sulphur cycle in the troposphere is developed. This scheme is designed for Earth system models of intermediate complexity (EMICs). The scheme accounts for sulphur dioxide emissions into the atmosphere, its deposition to the surface, oxidation to sulphates, and dry and wet deposition of sulphates on the surface. The calculations with the scheme are performed forced by anthropogenic emissions of sulphur dioxide into the atmosphere for 1850–2000 adopted from the CMIP5 dataset and by the ERA-Interim meteorology assuming that natural sources of sulphur into the atmosphere remain unchanged during this period. The ChAP output is compared to changes of the tropospheric sulphur cycle simulations: with the CMIP5 data, with the IPCC TAR ensemble, and with the ACCMIP phase II simulations. In addition, in regions of strong anthropogenic sulphur pollution, ChAP results are compared to other data, such as the CAMS reanalysis, EMEP MSC-W, and with individual model simulations. Our model reasonably reproduces characteristics of the tropospheric sulphur cycle known from these information sources. In our scheme, about half of the emitted sulphur dioxide is deposited to the surface and the rest in oxidised into sulphates. In turn, sulphates are mostly removed from the atmosphere by wet deposition. The lifetime of the sulphur dioxide and sulphates in the atmosphere is close to 1 day and 5 days, respectively. The limitation of the scheme are acknowledged and the prospects for future development are figured out. Despite its simplicity, ChAP may be successfully used to simulate anthropogenic sulphur pollution in the atmosphere at coarse spatial and time scales.