Is vulnerability to climate change gendered? And how? Insights from Egypt

Most climate change literature tends to downplay the gendered nature of vulnerability. At best, gender is discussed in terms of the male-female binary, seen as opposing forces rather than in varying relations of interdependency. Such construction can result in the adoption of maladaptive culturally unfit gender-blind policy and interventions. In Egypt, which is highly vulnerable to climate change, gender analysis of vulnerability is almost non-existent. This paper addresses this important research gap by asking and drawing on a rural Egyptian context ‘How do the gendered relational aspects of men’s and women’s livelihoods in the household and community influence vulnerability to climate change?’. To answer this question, I draw on gender analysis of social relations, framed within an understanding of sustainable livelihoods. During 16 months of fieldwork, I used multiple ethnographic methods to collect data from two culturally and ethnically diverse low-income villages in Egypt. My main argument is that experiences of climate change are closely intertwined with gender and wider social relations in the household and community. These are shaped by local gendered ideologies and cultures that are embedded in conjugal relations, kinship and relationship to the environment, as compared across the two villages. In this paper, I strongly argue that vulnerability to climate change is highly gendered and therefore gender analysis should be at the heart of climate change discourses, policy and interventions

Resolving crystallisation ages of Archean mafic-ultramafic rocks using the Re-Os isotope system

Rhenium-Osmium (Re-Os) isotope and elemental data are presented for mafic-ultramafic rocks from the central region of the Lewisian Archean terrain in northwest Scotland. These results give a best estimate for the time of emplacement of the mafic-ultramafic bodies of 2686.7 ± 14.7 Myr (2σ). The initial 187Os/188Os isotope ratio of 0.10940 ± 0.00076 indicates that such material possessed a chondritic Os isotope composition, which suggests that these rocks were formed by direct melting of mantle material, consistent with major and trace element constraints on their formation. Nevertheless, the Re-Os systematics of some of the mafic-ultramafic rocks in the Lewisian have been significantly disturbed, such that the original age information has been lost. These rocks lie on a regression line that defines an age of ~ 3260 Myr, and a negative initial Os isotope composition, suggesting perturbation of the Re-Os system, either through assimilation or post-emplacement elemental exchange. Such a process also appears to have affected the Sm-Nd systematics in the same samples. Crustal assimilation can account for the observed Os and Nd isotope variations but only if the assimilated material possessed 187Os/188Os values of ca. 25 at ~ 2687 Myr. In contrast, the surrounding gneisses and metasediments preserve present-day measured 187Os/188Os values of between 3 and 16. Rather, the spatial variation of initial Os and Nd isotope compositions suggests that isotope perturbation was caused by local sub-solidus element exchange between different lithologies, consistent with major element data and petrographic observations. Taken together, these results highlight the utility of the Re-Os isotope system for obtaining precise ages for Archean mafic-ultramafic rocks, and as a sensitive petrogenetic tracer capable of discriminating between assimilation or elemental exchange. (C) 2000 Elsevier Science B.V. All rights reserved

Sources of unique rhenium enrichment in fumaroles and sulphides at Kudryavy volcano

Rhenium (Re) is one of the least abundant elements in Earth, averaging 0.28 ppb in the primitive mantle. The unique occurrence of rheniite ReS2 (74.5 wt% of Re) in Kudryavy volcano precipitates raises questions about recycling of Re-rich reservoirs within the Kurile-Kamchatka volcanic Island arc setting. The sources of this unique Re enrichment have been inferred from studies of Re-Os isotope systematic and trace elements in volcanic gases, sulphide precipitates and host volcanic rocks. The fumarolic gas condensates are enriched in hydrophile trace elements relative to fluid-immobile elements and exhibit high Ba/Nb (133-204), Rb/Y (16-406) and Th/Zr (0.01-0.25) ratios. They are characterised by high Re (7-210 ppb) and Os abundances (0.4-0.9 ppb), with 187Os/188Os ratios in a range 0.122-0.152. This Os isotopic compositional range is similar to that of the peridotite xenoliths from the metasomatised mantle wedge above the subducted Pacific plate, the radiogenic isotopic signature of which is probably due to radiogenic addition from a slab-derived fluid. Re- and Os-rich sulphide and oxide minerals precipitate from volcanic gases within fumarolic fields. Molybdenite (MoS2), powellite (CaMoO4) and cannizzarite (Pb4Bi6S13) contain 1.5-1.7 wt%, 10 ppm, and 65-252 ppb of Re, respectively. Both molybdenite and rheniite contain normal Os concentrations, with total Os abundances in a range from 0.6 to 3.1 ppm for molybdenite, and 2.3-24.3 ppb for the rheniite samples. Repeated analyses of osmium isotope ratios for two rheniite samples form a best-fit line with an initial 187Os/188Os ratio of 0.32 ± 0.15 and an age of 79 ± 11 yr, which is the youngest age ever measured in natural samples. The high Re contents in molybdenite and rheniite led to high radiogenic 187Os values, even in the limited period of time, with 187Os/188Os ratios up to 3.3 for molybdenite and up to 4.4 for rheniite. The Os isotopic compositions of andesite-basaltic rocks from the Kudryavy volcano (187Os/188Os up to 0.326) are more radiogenic than those of residual peridotites and fumarolic gas condensates that are mainly constituted from magmatic vapor. Such radiogenic values can be attributed either to the addition of a radiogenic Os-rich subduction component to the depleted mantle, or to the assimilation of older dacitic caldera walls (187Os/188Os = 0.6) during arc magma ascent and emplacement. The latter hypothesis is supported by the correlation between 187Os/188Os ratio and indicators of fractionation such as MgO or Ni, and by low contents of potentially hydrophile trace elements such as Ba, Rb and Th relative to fluid-immobile elements such as Nb, Zr and Y. The high Re flux in the Kudryavy volcano (estimated at ~46 kg/yr) can be explained by remobilisation of Re by Cl-rich water from an underplated mantle wedge and subducted organic-rich sediments of the Pacific plate. © 2007 Elsevier Ltd. All rights reserved

Mg isotope constraints on soil pore-fluid chemistry: Evidence from Santa Cruz, California

Mg isotope ratios (Mg-26/Mg-24) are reported in soil pore-fluids, rain and seawater, grass and smectite from a 90 kyr old soil, developed on an uplifted marine terrace from Santa Cruz, California. Rain water has an invariant Mg-26/Mg-24 m ratio (expressed as delta Mg-26) at -0.79 +/- 0.05 parts per thousand, identical to seawater delta Mg-26. Detrital smectite (from the base of the soil profile, and therefore unweathered) has a delta Mg-26 value of 0.11 parts per thousand, potentially enriched in Mg-26 by up to 0.3 parts per thousand to the bulk silicate Earth Mg isotope composition (although within the range of all terrestrial silicates). The soil pore-waters show a continuous profile with depth for delta Mg-26, ranging from -0.99 parts per thousand near the surface to -0.43 parts per thousand at the base of the profile. Shallow pore-waters (&lt;1 m) have delta Mg-26 values that are similar to, or slightly lower than the rain waters. This implies that the degree of biological cycling of Mg in the pore-waters is relatively small and is quantified as &lt;32%, calculated using the average Mg isotope enrichment factor between grass and rain (delta Mg-26(grass) - delta Mg-26(rain)) of 0.21 parts per thousand. The deep pore-waters (1-15 m deep) have delta Mg-26 values that are intermediate between the smectite and rain, ranging from -0.76 parts per thousand to -0.43 parts per thousand, and show a similar trend with depth compared to Sr isotope ratios. The similarity between Sr and Mg isotope ratios confirms that the Mg in the pore-waters can be explained by a mixture between rain and smectite derived Mg, despite the fact that Mg and Sr concentrations may be buffered by the exchangeable reservoir. However, whilst Sr isotope ratios in the pore-waters span almost the complete range between mineral and rain inputs, Mg isotopes compositions are much closer to the rain inputs. If Mg and Sr isotope ratios are controlled uniquely by a mixture, the data can be used to estimate the mineral weathering inputs to the pore-waters, by correcting for the rain inputs. This isotopic correction is compared to the commonly used chloride correction for precipitation inputs. A consistent interpretation is only possible if Mg isotope ratios are fractionated either by the precipitation of a secondary Mg bearing phase, not detected by conventional methods, or selective leaching of Mg-24 from smectite. There is therefore dual control on the Mg isotopic composition of the pore-waters, mixing of two inputs with distinct isotopic compositions, modified by fractionation. The data provide (1) further evidence for Mg isotope fractionation at the surface of the Earth and (2) the first field evidence of Mg isotope fractionation during uptake by natural plants. The coherent behaviour of Mg isotope ratios in soil environments is encouraging for the development of Mg isotope ratios as a quantitative tracer of both weathering inputs of Mg to waters, and the physicochemical processes that cycle Mg, a major cation linked to the carbon cycle, during continental weathering. (C) 2010 Elsevier Ltd. All rights reserved.</p

Mg isotope constraints on soil pore-fluid chemistry: Evidence from Santa Cruz, California

Mg isotope ratios (26Mg/24Mg) are reported in soil pore-fluids, rain and seawater, grass and smectite from a 90 kyr old soil, developed on an uplifted marine terrace from Santa Cruz, California. Rain water has an invariant 26Mg/24Mg ratio (expressed as δ 26 Mg ) at -0.79 ± 0.05‰, identical to seawater δ 26 Mg . Detrital smectite (from the base of the soil profile, and therefore unweathered) has a δ 26 Mg value of 0.11‰, potentially enriched in 26Mg by up to 0.3‰ compared to the bulk silicate Earth Mg isotope composition (although within the range of all terrestrial silicates). The soil pore-waters show a continuous profile with depth for δ 26 Mg , ranging from -0.99‰ near the surface to -0.43‰ at the base of the profile. Shallow pore-waters (&lt;1 m) have δ 26 Mg values that are similar to, or slightly lower than the rain waters. This implies that the degree of biological cycling of Mg in the pore-waters is relatively small and is quantified as &lt;32%, calculated using the average Mg isotope enrichment factor between grass and rain ( δ 26 Mg grass - δ 26 Mg rain ) of 0.21‰. The deep pore-waters (1–15 m deep) have δ 26 Mg values that are intermediate between the smectite and rain, ranging from -0.76‰ to -0.43‰, and show a similar trend with depth compared to Sr isotope ratios. The similarity between Sr and Mg isotope ratios confirms that the Mg in the pore-waters can be explained by a mixture between rain and smectite derived Mg, despite the fact that Mg and Sr concentrations may be buffered by the exchangeable reservoir. However, whilst Sr isotope ratios in the pore-waters span almost the complete range between mineral and rain inputs, Mg isotopes compositions are much closer to the rain inputs. If Mg and Sr isotope ratios are controlled uniquely by a mixture, the data can be used to estimate the mineral weathering inputs to the pore-waters, by correcting for the rain inputs. This isotopic correction is compared to the commonly used chloride correction for precipitation inputs. A consistent interpretation is only possible if Mg isotope ratios are fractionated either by the precipitation of a secondary Mg bearing phase, not detected by conventional methods, or selective leaching of 24Mg from smectite. There is therefore dual control on the Mg isotopic composition of the pore-waters, mixing of two inputs with distinct isotopic compositions, modified by fractionation. The data provide (1) further evidence for Mg isotope fractionation at the surface of the Earth and (2) the first field evidence of Mg isotope fractionation during uptake by natural plants. The coherent behaviour of Mg isotope ratios in soil environments is encouraging for the development of Mg isotope ratios as a quantitative tracer of both weathering inputs of Mg to waters, and the physicochemical processes that cycle Mg, a major cation linked to the carbon cycle, during continental weathering

Mg isotope constraints on soil pore-fluid chemistry: Evidence from Santa Cruz, California

International audienceMg isotope ratios ( 26Mg/ 24Mg) are reported in soil pore-fluids, rain and seawater, grass and smectite from a 90 kyr old soil, developed on an uplifted marine terrace from Santa Cruz, California. Rain water has an invariant 26Mg/ 24Mg ratio (expressed as δ26Mg) at -0.79 ± 0.05‰, identical to seawater δ26Mg. Detrital smectite (from the base of the soil profile, and therefore unweathered) has a δ26Mg value of 0.11‰, potentially enriched in 26Mg by up to 0.3‰ compared to the bulk silicate Earth Mg isotope composition (although within the range of all terrestrial silicates). The soil pore-waters show a continuous profile with depth for δ26Mg, ranging from -0.99‰ near the surface to -0.43‰ at the base of the profile. Shallow pore-waters (24Mg from smectite. There is therefore dual control on the Mg isotopic composition of the pore-waters, mixing of two inputs with distinct isotopic compositions, modified by fractionation. The data provide (1) further evidence for Mg isotope fractionation at the surface of the Earth and (2) the first field evidence of Mg isotope fractionation during uptake by natural plants. The coherent behaviour of Mg isotope ratios in soil environments is encouraging for the development of Mg isotope ratios as a quantitative tracer of both weathering inputs of Mg to waters, and the physicochemical processes that cycle Mg, a major cation linked to the carbon cycle, during continental weathering

Positive correlation between Li and Mg isotope ratios in the river waters of the Mackenzie Basin challenges the interpretation of apparent isotopic fractionation during weathering

During chemical weathering, magnesium (Mg) is released by the dissolution of both carbonate and silicate sources. The degree to which solute concentrations and isotopic compositions of rivers reflect the relative proportions of these two inputs, or cycling by a series of processes associated with weathering is poorly constrained. In the river waters of the Mackenzie Basin (Canada), the Mg content is high and Mg isotope ratios (26Mg/24Mg expressed as ) show in excess of one per mil variability. Part of this variability is attributed to the 3‰ range in the carbonate and silicate rocks drained. Despite this inherent lithological control on river water values, there is also evidence for a fractionation control. A linear positive covariation between lithium (7Li/6Li, expressed as ) and Mg isotope ratios in the river waters of the Mackenzie Basin is reported. This covariation is not expected because previously reported fractionation related to physicochemical processes associated with clays or oxides should induce a negative covariation with Mg isotope ratios.This continental-scale covariation can be resolved by either process-related fractionation or mixing. Evidence for fractionation associated with clays is provided firstly by comparing Mg and Li isotopes in both the waters and sediments carried in suspension. Secondly a linear covariation between the sediment concentrations of large ion lithophile elements caesium and rubidium (a proxy for clay content of the sediment) and values of the water suggests that processes linked to clay, such as neoformation of clay, cation exchange or adsorption may be important. Simple models illustrate that if the covariation is induced by fractionation, there is either more than one process acting, or a single process is kinetically limited. Alternatively, the data can be reconciled by mixtures between at least three different water bodies, two of which have similar isotopic compositions but differing Li/Mg ratios. This intriguing data set highlights the challenges associated with distinguishing mixing from process with stable isotope data. Despite the complexity, the data question to what extent and by what mechanism clays mediate river water chemistry, at least in terms of the stable isotope compositions of Mg and Li. These questions are fundamental to the quantification of carbon dioxide consumption by silicate weathering and its role in climatic feedback

Accuracy of stable Mg and Ca isotope data obtained by MC-ICP-MS using the standard addition method

The standard addition method is evaluated to verify the accuracy and precision of Mg and Ca isotope data with complex matrices, using the standard-sample bracketing technique and analysis by MC-ICP-MS. The 44Ca/42Ca ratio of seawater (expressed as δ44 42Ca relative to SRM915a) was determined as 0.93±0.03‰ (95% confidence), in agreement with estimates obtained by the double spike method. Using standard addition, the seawater 26Mg/24Mg ratio (expressed as δ26Mg relative to the DSM3 standard) was determined as −0.80±0.06‰ (95% confidence) in agreement with previous estimates. Four terrestrial silicate rocks (MORB, flood basalt, glacial flour, and granodiorite) and olivine mineral separates from an island basalt are shown to exhibit no scatter within the error of the method, averaging a δ26Mg of −0.20±0.05‰ (95% confidence). Although a number of silicate rock data for Mg isotope ratios have already been reported, this is the first detailed effort to validate the accuracy of such data and test for residual analytical artifact after chemical purification of samples. Data regressions were evaluated statistically using the mean square weighted deviate (MSWD), demonstrating that the uncertainty on individual data points are generally over estimated. The external two standard deviation uncertainty on individual data points is estimated by Monte Carlo simulation as b0.075‰ (about a factor of two improvement on early publications of Mg isotope data). The consistency of the standard addition estimates of δ26Mg in silicate rocks imply that if any residual matrix effects are present, then they must be less than the spread of the data (0.11‰) given the diverse range of matrices in each of the samples. The δ26Mg values of the silicate rocks suggest that Mg isotope ratios in silicate material may only have a very restricted range. The δ26Mg values of silicate material in the present study falls between the average values reported by Teng et al. [Teng, F.Z., Wadhwa, M., Helz, R.T., 2007. Investigation of magnesium isotope fractionation during basalt differentiation: implications for a chondritic composition of the terrestrial mantle. Earth and Planetary Science Letters 261, 84–92. doi:10.1016/j. epsl.2007.06.004] and Wiechert and Halliday [Wiechert, U., Halliday, A.N., 2006. Non-chondritic magnesium and the origins of the inner terrestrial planets. Earth and Planetary Science Letters 256, 360–371. doi:10.1016/ j.epsl.2007.01.007] and given the spread of published δ26Mg values for chondritic material, a chondritic composition for terrestrial Mg cannot be ruled out.We suggest that some of the small discrepancies between our data and analysis of the same samples in earlier studies, may have arisen because the chemical purification of Mg prior to analysis can easily induce analytical artifact. This method could be expanded to the isotope ratios of other elements, which also rely on correcting for mass bias using the standard-sample bracketing method, where similar analytical discrepancies may also exist

High-pressure behaviour of KMF₃ perovskites

The structural stability of cubic KMF3 (M: Mg, Zn, Co, Ni) perovskites has been studied by powder X-ray diffraction under pressure. Neither superlattice reflections nor peak splitting associated to a phase transition were detected in the 0-10 GPa pressure range. Furthermore, KMgF3 showed no structural changes up to 50 GPa. The results were compared with previous reports on isostructural KMnF3. Tolerance factor and site parameters ratio have been analysed as high-pressure stability indexes for this family of perovskites

Calcium isotope ratios in the world's largest rivers: A constraint on the maximum imbalance of oceanic calcium fluxes

International audienceThe oceanic mass balance of calcium (Ca) is defined by a balance between the inputs (rivers and hydrothermal) and outputs (bulk carbonate) of Ca. Large rivers were analyzed for Ca isotope ratios (44Ca/42Ca, expressed as ? Ca) to investigate the source and cycling of riverine Ca, and to add an isotopic mass balance constraint to the oceanic budget of Ca. The new data account for approximately one-third of the total Ca supplied to the oceans by rivers. Inter-sample and seasonal variability was assessed by analyzing more than one sample for many rivers. The range in the ? Ca of large rivers at high water stand is extremely narrow at 0.27‰. Variations in ? Ca do not correlate with proxies for carbonate, silicate or evaporite derived Ca, and are more likely related either to inherent variability in the lithological sources of Ca or to process related fractionation. The spread in riverine ? Ca overlaps with the spread in marine limestone ? Ca consistent with most riverine Ca coming from the recycling of limestones. The Ca isotope composition of continental runoff has an average ? Ca value of 0.38 ± 0.04‰, identical to recent (5 M.yr) bulk carbonate ooze (0.33 ± 0.13‰, 2S.D.). Isotopic mass balance constrains that the input and output fluxes of Ca to and from the oceans, are balanced to within 15% over time-scales similar to the residence time of Ca in the oceans (1 M.yr). A greater imbalance between the fluxes would result in a detectable difference between the ? Ca value of bulk carbonate and the riverine input at the current level of uncertainty. The input and output fluxes could be imbalanced over much shorter time-scales (such as glacial-interglacial cycles), in which case the ocean-carbonate system will not yet have responded, because of the long residence time of Ca. The maximum current flux imbalance of 15% would be sufficient to account for the total variations in Ca concentration over the Tertiary. Such an interpretation is not unique, but is the simplest interpretation given the similarity between the input and output isotopic compositions, and rules out hypotheses of extreme imbalance in the recent global biogeochemical cycle of Ca