1,134 research outputs found
Probing the exchange of CO2 and O2 in the shallow critical zone during weathering of marl and black shale
Chemical weathering of sedimentary rocks can release carbon dioxide (CO2) and consume oxygen (O2) via the oxidation of petrogenic organic carbon and sulfide minerals. These pathways govern Earthâs surface system and climate over geological timescales, but the present-day weathering fluxes and their environmental controls are only partly constrained due to a lack of in situ measurements. Here, we investigate the gaseous exchange of CO2 and O2 during the oxidative weathering of black shales and marls exposed in the French southern Alps. On six fieldtrips over one year, we use drilled headspace chambers to measure the CO2 concentrations in the shallow critical zone, and quantify CO2 fluxes in real-time. Importantly, we develop a new approach to estimate the volume of rock that contributes CO2 to a chamber, and assess effective diffusive gas exchange, by first quantifying the mass of CO2 that is stored in a chamber and connected rock pores. Both rock types are characterized by similar contributing rock volumes and diffusive movement of CO2. However, CO2 emissions differed between the rock types, with yields over rock outcrop surfaces (inferred from the contributing rock volume and the local weathering depths) ranging between 166 tC km-2 yr-1 and 2,416 tC km-2 yr-1 for black shales and between 83 tC km-2 yr-1 and 1,558 tC km-2 yr-1 for marls over the study period. Having quantified diffusive processes, chamber-based O2 concentration measurements are used to calculate O2 fluxes. The rate of O2 consumption increased with production of CO2, and with increased temperature, with an average O2 : CO2 molar ratio of 10 : 1. If O2 consumption occurs by both rock organic carbon oxidation and sulfide oxidation, either an additional O2 sink needs to be identified, or significant export of dissolved inorganic carbon occurs from the weathering zone. Together, our findings refine the tools we have to probe CO2 and O2 exchange in rocks at Earthâs surface and shed new light on CO2 and O2 fluxes, their drivers and the fate of rock-derived carbon
âThat eccentric use of land at the top of the hillâ: Cemeteries and stories of the city
Most contemporary research accounts for conflict within cemetery space, but does not consider the potentially contested and poorly understood role of cemeteries within their broader cityscape. This study draws on stories from cemetery managers across England and Wales to narrate this multifunctionality, as they hold the pivotal role which oversees both the day-to-day running of the cemetery, and its strategic role within a given municipality. The study outlines how cemeteries hold multiple functions in the cities in which they are located, specifically contributing to greenspace or green infrastructure, civic identity and local place attachment. These varying city level roles in turn impact on what is deemed (il)legitimate behaviour within the cemetery. Moreover, they raise important considerations for urban planners and policymakers who currently have little guidance on planning for new or existing cemeteries but are critical in the ongoing successful development of cities
Orbital and SuborbitalâScale Variations of Productivity and Sea Surface Conditions in the Gulf of Alaska During the Past 54,000Â Years: Impact of Iron Fertilization by Icebergs and Meltwater
As a high-nutrient and low-chlorophyll region, the modern Gulf of Alaska (GoA) is strongly impacted by the limitation of iron. Paleostudies along the Alaskan slope have mainly focused on reconstructing environmental conditions over the past 18 ka. Based on micropaleontological, biogeochemical, and sedimentological parameters, we explore a sediment record covering the past 54 ka at Integrated Ocean Drilling Program Site U1419 to understand the impact of orbital- and suborbital-scale climate variability on productivity and sea-surface conditions. Close to the Cordilleran Ice Sheet (CIS), Site U1419 is ideally located to elucidate how the evolution of a large ice mass and glacial processes affected orbital- and suborbital-scale changes in nutrients (e.g., iron) supply. Meltwater discharge from the northern CIS impacted sea surface dynamics of GoA coastal waters. The corresponding increases in bulk biogenic concentrations during Marine Isotope Stage (MIS) 3 and MIS 2 (54â17 ka) suggests a direct impact from iron fertilization. The lack of a consistent relationship between productivity and SST suggests that cooling of surface waters was not the dominant control on primary producers. The inundation of the subaerially exposed continental shelf during the last deglacial (17â10 ka) warming could have served as a major micronutrient source, accounting for a deglacial peak in production. Low productivity after the last deglaciation suggests reduced iron availability, which we link to reduced meltwater inputs from smaller ice masses onshore. Our multiproxy approach reveals a more comprehensive picture of late Quaternary productivity variations compared to earlier studies along the Alaskan margin. The impact of tidewater glaciers and meltwater discharge on past marine productivity and nutrient budget dynamics of high-latitude coastal regions is discussed
Are spherulitic lacustrine carbonates an expression of large-scale mineral carbonation? : A case study from the East Kirkton Limestone, Scotland
BP Exploration Co. is thanked for funding, and particularly the Carbonate Team for supporting this research and for fruitful discussions. West Lothian Council and Scottish Natural Heritage are thanked for allowing access and permission for sampling the site. The Core Store Team at BGS Keyworth is particularly acknowledged for their assistance. Mark Anderson, Tony Sinclair (University of Hull), and Bouk Lacet (VU University Amsterdam) are thanked for technical support. Anne Kelly (SUERC) for carrying out the Strontium Isotope analyses. Mark Tyrer is thanked for his advice on PHREEQC modelling.Peer reviewedPostprin
Effect of site-specific irrigation management on grapevine yield and fruit quality attributes
High-Resolution Magnetic Resonance Imaging of the Regenerating Adult Zebrafish Heart
The adult zebrafish is a well-established model for studying heart regeneration, but due to its tissue opaqueness, repair has been primarily assessed using destructive histology, precluding repeated investigations of the same animal. We present a high-resolution, non-invasive in vivo magnetic resonance imaging (MRI) method incorporating a miniature respiratory and anaesthetic perfusion set-up for live adult zebrafish, allowing for visualization of scar formation and heart regeneration in the same animal over time at an isotropic 31âÂľm voxel resolution. To test the method, we compared well and poorly healing cardiac ventricles using a transgenic fish model that exhibits heat-shock (HS) inducible impaired heart regeneration. HS-treated groups revealed persistent scar tissue for 10 weeks, while control groups were healed after 4 weeks. Application of the advanced MRI technique allowed clear discrimination of levels of repair following cryo- and resection injury for several months. It further provides a novel tool for in vivo time-lapse imaging of adult fish for non-cardiac studies, as the method can be readily applied to image wound healing in other injured or diseased tissues, or to monitor tissue changes over time, thus expanding the range of questions that can be addressed in adult zebrafish and other small aquatic species
Late Pliocene Cordilleran Ice Sheet development with warm northeast Pacific sea surface temperatures
The initiation and evolution of the Cordilleran Ice Sheet are relatively poorly constrained. International Ocean Discovery Program (IODP) Expedition 341 recovered marine sediments at Site U1417 in the Gulf of Alaska (GOA). Here we present alkenone-derived sea surface temperature (SST) analyses alongside ice-rafted debris (IRD), terrigenous, and marine organic matter inputs to the GOA through the late Pliocene and early Pleistocene. The first IRD contribution from tidewater glaciers in southwest Alaska is recorded at 2.9 Ma, indicating that the Cordilleran Ice Sheet extent increased in the late Pliocene. A higher occurrence of IRD and higher sedimentation rates in the GOA during the early Pleistocene, at 2.5 Ma, occur in synchrony with SSTs warming on the order of 1 degrees C relative to the Pliocene. All records show a high degree of variability in the early Pleistocene, indicating highly efficient ocean-climate-ice interactions through warm SST-ocean evaporation-orographic precipitation-ice growth mechanisms. A climatic shift towards ocean circulation in the subarctic Pacific similar to the pattern observed during negative Pacific Decadal Oscillation (PDO) conditions today occurs with the development of more extensive Cordilleran glaciation and may have played a role through increased moisture supply to the subarctic Pacific. The drop in atmospheric CO2 concentrations since 2.8 Ma is suggested as one of the main forcing mechanisms driving the Cordilleran glaciation
Chromospheric magnetic field and density structure measurements using hard X-rays in a flaring coronal loop
<p><b>Aims:</b> A novel method of using hard X-rays as a diagnostic for chromospheric density and magnetic structures is developed to infer sub-arcsecond vertical variation of magnetic flux tube size and neutral gas density.</p>
<p><b>Methods:</b> Using Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) X-ray data and the newly developed X-ray visibilities forward fitting technique we find the FWHM and centroid positions of hard X-ray sources with sub-arcsecond resolution (~0.2'') for a solar limb flare. We show that the height variations of the chromospheric density and the magnetic flux densities can be found with an unprecedented vertical resolution of ~150 km by mapping 18-250 keV X-ray emission of energetic electrons propagating in the loop at chromospheric heights of 400-1500 km.</p>
<p><b>Results:</b> Our observations suggest that the density of the neutral gas is in good agreement with hydrostatic models with a scale height of around 140 30 km. FWHM sizes of the X-ray sources decrease with energy suggesting the expansion (fanning out) of magnetic flux tubes in the chromosphere with height. The magnetic scale height B(z)(dB/dz)-1 is found to be of the order of 300 km and a strong horizontal magnetic field is associated with noticeable flux tube expansion at a height of ~900 km.</p>
Antarctic Intermediate Water properties since 400 ka recorded in infaunal (Uvigerina peregrina) and epifaunal (Planulina wuellerstorfi) benthic foraminifera
Reconstruction of intermediate water properties is important for understanding feedbacks within the ocean-climate system, particularly since these water masses are capable of driving highâlow latitude teleconnections. Nevertheless, information about intermediate water mass evolution through the late Pleistocene remains limited. This paper examines changes in Antarctic Intermediate Water (AAIW), the most extensive intermediate water mass in the modern ocean through the last 400 kyr using the stable isotopic composition (δ18O and δ13C) and trace element concentration (Mg/Ca and B/Ca) of two benthic foraminiferal species from the same samples: epifaunal Planulina wuellerstorfi and infaunal Uvigerina peregrina. Our results confirm that the most reasonable estimates of AAIW temperature and Î[CO2â3] are generated by Mg/CaU. peregrina and B/CaP. wuellerstorfi, respectively. We present a 400 kyr record of intermediate water temperature and Î[CO2â3] from a sediment core from the Southwest Pacific (DSDP site 593; 40°30â˛S, 167°41â˛E, 1068 m water depth), which lies within the core of modern AAIW. Our results suggest that a combination of geochemical analyses on both infaunal and epifaunal benthic foraminiferal species yields important information about this critical water mass through the late Pleistocene. When combined with two nearby records of water properties from deeper depths, our data demonstrate that during interglacial stages of the late Pleistocene, AAIW and Circumpolar Deep Water (CPDW) have more similar water mass properties (temperature and δ13C), while glacial stages are typified by dissimilar properties between AAIW and CPDW in the Southwest Pacific. Our new Î[CO2â3] record shows short time-scale variations, but a lack of coherent glacialâinterglacial variability indicating that large quantities of carbon were not stored in intermediate waters during recent glacial periods
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