Oxidative stress plays a vital role for the adaptive responses to physical training. However, excessive oxidative stress can precipitate cellular damage, necessitating protective mechanisms to ...mitigate this effect. Glucosinolates, found predominantly in cruciferous vegetables, can be converted into isothiocyanates, known for their antioxidative properties. These compounds activate crucial antioxidant defence pathways and support mitochondrial function and protein integrity under oxidative stress, in both Nrf2-dependent and independent manners. We here administered glucosinolate-rich broccoli sprouts (GRS), in a randomized double-blinded cross-over fashion to 9 healthy subjects in combination with daily intense exercise training for 7 days. We found that exercise in combination with GRS significantly decreased the levels of carbonylated proteins in skeletal muscle and the release of myeloperoxidase into blood. Moreover, it lowered lactate accumulation during submaximal exercise, and attenuated the severe nocturnal hypoglycaemic episodes seen during the placebo condition. Furthermore, GRS in combination with exercise improved physical performance, which was unchanged in the placebo condition.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Fabric (distribution of crystallographic orientations) along the full NEEM ice core, Greenland was measured in the field by an automatic ice texture analyzer every 10 m, from 33 m down to 2461 m ...depth. The fabric evolves from a slightly anisotropic fabric at the top, toward a strong single maximum at about 2300 m, which is typical of a deformation pattern mostly driven by uniaxial compression and simple shearing. A sharp increase in the fabric strengthening rate is observed at the Holocene to Wisconsin (HW) climatic transition. From a simple model we estimate that this depth is located at a transition from a state dominated by vertical compression to a state dominated by vertical shear. Comparisons are made to two others ice cores drilled along the same ridge; the GRIP ice core, drilled at the summit of the ice sheet, and the NGRIP ice core, drilled 325 km to the NNW of the summit along the ridge, and 365 km upstream from NEEM. This comparison tends to demonstrate that the ice viscosity change with the HW climatic transition must be associated with the shear-dominated state to induce the abrupt fabric strengthening observed at NEEM. This comparison therefore reflects the increasing role of shear deformation on the coring site when moving NW along the ridge from GRIP to NGRIP and NEEM. The difference in fabric profiles between NEEM and NGRIP also evidences a stronger lateral extension associated with a sharper ridge at NGRIP. Further along the core, centimeter scale abrupt texture (fabric and microstructure) variations are observed in the bottom part of the core. Their positions are in good agreement with the observed folding layers in Dahl-Jensen et al. (2013).
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Samples from two ice cores drilled at Lomonosovfonna, Svalbard, covering the period 1957–2009, and 1650–1995, respectively, were analyzed for NO3−concentrations, and NO3− stable isotopes (δ15N and ...δ18O). Post‐1950 δ15N has an average of (−6.9 ± 1.9)‰, which is lower than the isotopic signal known for Summit, Greenland but agrees with values observed in recent Svalbard snow and aerosol. Pre‐1900 δ15N has an average of (4.2 ± 1.6)‰ suggesting that natural sources, enriched in the 15 N isotope, dominated before industrialization. The post‐1950 δ18O average of (75.1 ± 4.1)‰ agrees with data from low and polar latitudes, suggesting similar atmospheric NOy (NOy = NO + NO2 + HNO3) processing pathways. The combination of anthropogenic source δ15N and transport isotope effect was estimated as −29.1‰ for the last 60 years. This value is below the usual range of NOx (NOx = NO + NO2) anthropogenic sources which is likely the result of a transport isotope effect of −32‰. We suggest that the δ15N recorded at Lomonosovfonna is influenced mainly by fossil fuel combustion, soil emissions, and forest fires; the first and second being responsible for the marked decrease in δ15N observed in the post‐1950s record with soil emissions being associated to the decreasing trend in δ15N observed up to present time, and the third being responsible for the sharp increase of δ15N around 2000.
Key Points
First Svalbard δ15N and δ18O ice core records
Ice core δ15N reflects fossil fuel combustion, soil emissions, and forest fires
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
This paper presents and discusses the texture, fabric, water stable isotopes (δ18O, δD) and gas properties (total gas content, O2, N2, Ar, CO2, and CH4 mixing ratios) of two climatically contrasted ...(Holocene vs. Pleistocene) ice wedges (IW-26 and IW-28) from Cape Mamontov Klyk, Laptev Sea, in northern Siberia. The two ice wedges display contrasting structures: one being of relatively "clean" ice and the other showing clean ice at its centre as well as debris-rich ice on both sides (referred to as "ice-sand wedge"). Our multiparametric approach allows discrimination between three different ice facies with specific signatures, suggesting different climatic and environmental conditions of formation and various intensities and nature of biological activity. More specifically, crystallography, total gas content and gas composition reveal variable levels of meltwater infiltration and contrasting contributions from anaerobic and aerobic conditions to the biological signatures. Stable isotope data are drawn on to discuss changes in paleoenvironmental conditions and in the temporal variation of the different moisture sources for the snow feeding into the ice wedges infillings. Our data set also supports the previous assumption that the ice wedge IW-28 was formed in Pleistocene and the ice wedge IW-26 in Holocene times. This study sheds more light on the conditions of ice wedge growth under changing environmental conditions.
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An important share of paleoclimatic information is buried within the lowermost layers of deep ice cores. Because improving our records further back in time is one of the main challenges in the near ...future, it is essential to judge how deep these records remain unaltered, since the proximity of the bedrock is likely to interfere both with the recorded temporal sequence and the ice properties. In this paper, we present a multiparametric study (δD-δ18Oice, δ18Oatm, total air content, CO2, CH4, N2O, dust, high-resolution chemistry, ice texture) of the bottom 60 m of the EPICA (European Project for Ice Coring in Antarctica) Dome C ice core from central Antarctica. These bottom layers were subdivided into two distinct facies: the lower 12 m showing visible solid inclusions (basal dispersed ice facies) and the upper 48 m, which we will refer to as the "basal clean ice facies". Some of the data are consistent with a pristine paleoclimatic signal, others show clear anomalies. It is demonstrated that neither large-scale bottom refreezing of subglacial water, nor mixing (be it internal or with a local basal end term from a previous/initial ice sheet configuration) can explain the observed bottom-ice properties. We focus on the high-resolution chemical profiles and on the available remote sensing data on the subglacial topography of the site to propose a mechanism by which relative stretching of the bottom-ice sheet layers is made possible, due to the progressively confining effect of subglacial valley sides. This stress field change, combined with bottom-ice temperature close to the pressure melting point, induces accelerated migration recrystallization, which results in spatial chemical sorting of the impurities, depending on their state (dissolved vs. solid) and if they are involved or not in salt formation. This chemical sorting effect is responsible for the progressive build-up of the visible solid aggregates that therefore mainly originate "from within", and not from incorporation processes of debris from the ice sheet's substrate. We further discuss how the proposed mechanism is compatible with the other ice properties described. We conclude that the paleoclimatic signal is only marginally affected in terms of global ice properties at the bottom of EPICA Dome C, but that the timescale was considerably distorted by mechanical stretching of MIS20 due to the increasing influence of the subglacial topography, a process that might have started well above the bottom ice. A clear paleoclimatic signal can therefore not be inferred from the deeper part of the EPICA Dome C ice core. Our work suggests that the existence of a flat monotonic ice–bedrock interface, extending for several times the ice thickness, would be a crucial factor in choosing a future "oldest ice" drilling location in Antarctica.
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Crystallographic investigations have been conducted of cold (−17°C) debris‐bearing ice from the base of an Antarctic outlet glacier (Taylor Glacier). The 4‐m‐thick sequence studied has been retrieved ...from a 20‐m‐long tunnel dug from the glacier snout and has been analyzed with an automatic ice fabric analyzer (AIFA). The top and bottom of the sequence consists of clean meteoric ice (englacial facies), whereas alternating debris‐rich and clean bubbly ice layers are found in the middle part (stratified facies). Ice from the englacial facies displays a polygonal texture and a strong c‐axis clustering toward the vertical, denoting recrystallization through “subgrain rotation” (SGR). In contrast, clean ice from the stratified facies shows SGR fabrics which are delimited at the contact with debris‐rich layers by large, interlocking grains organized in ribbons. These two distinct textures within the stratified facies are associated with looser c‐axis patterns at the scale of single thin sections, which is interpreted as resulting from “migration recrystallization” (MR). The change from SGR to MR trends marks a clear increase in grain boundary and nucleation kinetics (hence the term “discontinuous recrystallization”) and may be associated with strain localization at rheological interfaces during basal ice genesis. Analogies with bottom ice from deep polar ice sheets, where temperature is commonly higher than at the studied site, are highlighted. Two recrystallization scenarios are proposed, accounting for the development of both types of fabrics. It is shown that by controlling the repartition of stress and strain energy within basal ice, the rheology of debris‐bearing ice layers plays a decisive role in recrystallization dynamics at structural interfaces. We also demonstrate how the same recrystallization regimes may occur in cold glaciers and temperate ice sheets, provided that strain accumulation has been high enough in the former. This challenges the common belief that migration fabrics observed in bottom ice from deep ice sheets are exclusive to warm, stagnant, annealed ice.
Inorganic ions such as phosphate and sulfate are essential macronutrients required for a broad spectrum of cellular functions and their regulation. In a constantly fluctuating environment ...microorganisms have for their survival developed specific nutrient sensing and transport systems ensuring that the cellular nutrient needs are met. This chapter focuses on the S. cerevisiae plasma membrane localized transporters, of which some are strongly induced under conditions of nutrient scarcity and facilitate the active uptake of inorganic phosphate and sulfate. Recent advances in studying the properties of the high-affinity phosphate and sulfate transporters by means of site-directed mutagenesis have provided further insight into the molecular mechanisms contributing to substrate selectivity and transporter functionality of this important class of membrane transporters.
Ice‐penetrating radar profiles across the grounding line of a small ice‐rise promontory located within the Roi Baudouin Ice Shelf in the Dronning Maud Land sector of East Antarctica show downward ...dipping englacial radar‐detected reflectors. Model results indicate that this reflector pattern is best fit by including basal melting of at least 15 cm a−1. This rate of melting is low compared with rates observed on larger ice shelves in both West and East Antarctica. Ice cores extracted from a rift system close to the ice‐rise promontory show several meters of marine ice accreted beneath the shelf. These observations of low rates of basal melting, and limited distribution of accreted marine ice suggest that either Antarctic surface water may reach the ice shelf base or that circulation beneath the shelf is likely dominated by the production of high salinity shelf water rather than the incursion of circumpolar deep water, implying a weak sub‐shelf circulation system here. Many of the ice shelves located along the coast of Dronning Maud Land are, like Roi Baudouin Ice Shelf, characterized by frequent ice rises and promontories. Therefore, it is highly likely that these are also of shallow bathymetry and are subject to similarly weak side‐shelf basal melting and refreezing.
Key Points
Multisciplinary approach to understanding ice/ocean interaction
Evidence for sub‐shelf melting at the grounding line
Evidence of marine ice accretion in adjacent areas
The orientations of individual crystals within a polycrystalline aggregate subjected to stress have a strong influence on its bulk strain rate and flow behavior. The ability to include the effect of ...crystal fabric and recrystallization processes in an ice flow law, especially at the bottom of glaciers and ice sheets where temperature is close to the pressure-melting point, is important because the stratigraphy of the ice body may be affected and the paleoclimate reconstruction hampered. We present herein three newly developed deformation apparatuses offering the possibility, from single experiments, of investigating different finite strain stages and their corresponding c-axis fabric and grain texture patterns in various confined, shear flow configurations (simple shear, pure shear and compression/extension bending). The technical set-ups and major advantages compared to classical methods are explained, and results from experiments are discussed in order to illustrate the functioning and purposes of the methods. In all experiments, significant variations in the microstructural development have been observed that reflect the varying orientations of the anisotropy and its relationship to the stress pattern. In monocrystalline ice-bending experiments, the pre-existing c-axis fabric is shown to have a profound influence on the response to stress and possibly to the type of slip system activated.
We propose a new method to investigate the relationships between neighbouring crystals and apply it to the textures measured along the upper 900 m of the
NorthGRIP ice core. This method shows ...unexpected correlations between neighbours in the so-called
normal grain growth regime, questioning the classical view on the onset of
rotation recrystallization in ice-sheets. Moreover, the fractionation rate associated to the
rotation recrystallization appears constant through time. Finally, grains with low-angle boundaries do not present a special distribution pattern of their
c-axes. This suggests that
rotation recrystallization is an isotropic process not affected by the direction of the macroscopic strain.
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