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Abstract Arid Central Asia represents a key region for understanding climate variability and interactions in the Northern Hemisphere. Patterns and mechanisms of Holocene climate change in arid Central Asia are, however, only partially understood. Multi-proxy data combining diatom, ostracod, sedimentological, geochemical and stable isotope analyses from a ca. 6000-year-old lake sediment core from Son Kol (Central Kyrgyzstan) show distinct and repeated changes in species assemblages. Diatom- and ostracod-inferred conductivity shifts between meso-euhaline and freshwater conditions suggest water balance and regime shifts. Organism-derived data are corroborated by stable isotope, mineralogical and geochemical records, underlining that Son Kol was affected by strong lake level fluctuations of several meters. The δ13Ccarb/δ18Ocarb correlation shows repeated switchovers from a closed to an open lake system. From 6000 to 3800 and 3250 to 1950 cal. yr BP, Son Kol was a closed basin lake with higher conductivities, increased nutrient availability and a water level located below the modern outflow. Son Kol became again a hydrologically open lake at 3800 and 1950 cal. yr BP. Comparisons to other local and regional paleoclimate records indicate that these regime shifts were largely controlled by changing intensity and position of the Westerlies and the Siberian Anticyclone that triggered changes in the amount of winter precipitation. A strong influence of the Westerlies ca. 5000–4400, 3800–3250 and since 1950 cal. yr BP enhanced the amount of precipitation during spring, autumn and winter, whereas cold and dry winters prevailed during phases with a strong Siberian Anticyclone and southward shifted Westerlies at ca. 6000–5000, 4400–3800 and 3250–1950 cal. yr BP. Similarities between variations in winter precipitation at Son Kol and records of the predominant NAO-mode further suggest a teleconnection between wet (dry) winter climate in Central Asia and a positive (negative) NAO-mode. Thus, this study identifies climate fluctuations as the main driver for hydrological regime shifts in Son Kol controlling physicochemical conditions and consequently causing abrupt species assemblage changes. This emphasizes the importance of multi-proxy approaches to identify triggers, thresholds and cascades of aquatic ecosystem transformations.

International audience; Soil warming can increase soil organic carbon (SOC) mineralization, triggering a positive climate-carbon cycle feedback loop. Globally, many soil warming experiments have examined losses of bulk SOC, but few have assessed changes in quality. Accurate knowledge of the latter is required for an in-depth understanding and improved prediction of SOC feedback to climate change. In this study, we used Rock-Eval thermal analysis (RE6) to characterize shifts in SOC thermal stability and bulk chemistry after six years of geothermal warming by 0.6 degrees C, 1.8 degrees C, 3.9 degrees C, 9.9 degrees C, 16.3 degrees C, 40 degrees C, and 80 degrees C in an Icelandic grassland topsoil (0-10 cm). We also used the strong warming-induced depletion of SOC (up to 92% in the 80 degrees C soil) in comparisons of chemical oxidation-resistant and biogeochemically resistant SOC, which are generally assumed to be similar in nature. Sodium hypochlorite (NaOCl) and hydrogen peroxide (H2O2) were used for oxidation. Warming-resistant SOC was strongly depleted in hydrocarbons and enriched in oxygen, confirming that SOC oxidation state, and thus energy content, is an important driver for biogeochemical stability. This was supported by findings that thermal stability, i.e., the amount of energy (temperature) necessary to pyrolyze or oxidize SOC, strongly increased with warming intensity. Of the 31 RE6 parameters tested, the most warming-sensitive were hydrogen index (HI, p = -0.84), oxygen index (OIRE6, rho = 0.83), proportion of total pyrolyzed carbon released as hydrocarbons at 200-650 degrees C (S2/PC, rho = -0.86), and the temperature at which a certain proportion of CO2 evolved during pyrolysis (rho > 0.8). Chemical oxidation of unwarmed soil caused average relative SOC losses of 61% (NaOCl) and 91% (H2O2) and shifts in RE6 properties that differed strongly from warming-induced shifts at comparable SOC losses. Chemical oxidation-resistant SOC was more enriched in oxygen, but slightly enriched in hydrocarbons, and less thermostable than comparable naturally depleted SOC at the same time. A certain overlap, especially for NaOCl-treated soils, is likely, while H2O2-oxidized soils showed very distinct RE6 properties. We concluded that i) soil warming leads to strong shifts in SOC bulk chemistry and thermal stability and ii) H2O2 should be avoided in isolation of a slow SOC kinetic pool.

Highlights: • MPA is the most widely employed marine management tools. • Five potential habitats selected for MPA declaration in Bangladesh. • These habitats cover 7% of total maritime area of Bangladesh. • Local community involvement is required for a successful implementation of MPA. Abstract: Marine protected areas (MPAs) have become one of the most widely employed marine management tools worldwide for conserving species and habitats, maintaining ecosystem functioning, and ensuring sustainable use of marine resources. In this study, we adopted a science-based, stakeholder-driven and ecosystem based approach to identify coastal and marine habitats for potential MPA declaration towards achieving Aichi target 11. In addition, we also proposed an integrated management approach for MPA management in Bangladesh. Primary data were collected through stakeholder consultations from the three coastal zones of Bangladesh and secondary data were collected from an extensive literature review. We developed a priority index to select the most important habitats for MPA declaration. Our analysis suggests five potential habitats within the maritime boundary of Bangladesh for MPA declaration. These habitats cover an area of 8838 km2 which is about 7.5% of the total maritime area of Bangladesh. Declaration of the MPAs will contribute to conserve the nursing and breeding habitats of fishes, crabs and seabirds, and thus will protect the marine biodiversity. To achieve this goal, local community involvement is required. This study will serve as a baseline for declaring MPAs in a solid scientific way through community engagement.

AbstractSouthern smelts (Retropinna spp.) in coastal rivers of Australia are facultatively diadromous, with populations potentially containing individuals with diadromous or wholly freshwater life histories. The presence of diadromous individuals is expected to reduce genetic structuring between river basins due to larval dispersal via the sea. We use otolith chemistry to distinguish between diadromous and nondiadromous life histories and population genetics to examine interbasin connectivity resulting from diadromy. Otolith strontium isotope (87Sr:86Sr) transects identified three main life history patterns: amphidromy, freshwater residency and estuarine/marine residency. Despite the potential for interbasin connectivity via larval mixing in the marine environment, we found unprecedented levels of genetic structure for an amphidromous species. Strong hierarchical structure along putative taxonomic boundaries was detected, along with highly structured populations within groups using microsatellites (FST = 0.046–0.181), and mtDNA (ΦST = 0.498–0.816). The presence of strong genetic subdivision, despite the fact that many individuals reside in saline water during their early life history, appears incongruous. However, analysis of multielemental signatures in the otolith cores of diadromous fish revealed strong discrimination between river basins, suggesting that diadromous fish spend their early lives within chemically distinct estuaries rather than the more homogenous marine environment, thus avoiding dispersal and maintaining genetic structure.

AbstractKnowledge of the reproductive cycle in exploited species is important for a sustainable management of fisheries. Standardized scales to assess maturity stages are a fundamental tool to understand the demographic composition of exploited populations. Staging scales for female Norway lobster, Nephrops norvegicus, have been subject to a series of changes, and multiple inconsistent scales are in use in different fisheries regions. A unified, evidence‐based scale has not previously been established. We reviewed previous staging scales for the female ovary maturation and propose a revised scale based on the correlation between macroscopic and microscopic ovary characteristics. To provide better‐informed tools for future stock assessment, female stages were characterized through external observation on ovary color and size, and the progress of vitellogenesis. This study clarifies several biological phases that were conflated in previous scales. First, we demonstrate how to distinguish between immature ovaries in juvenile females versus the earliest ovary maturation stage in adults. Second, the new scale differentiates between “mottled” ovaries seen in two separate biological stages: the spent ovaries that undergo partial resorption in berried females, versus ovaries of females which failed to spawn and undergo full resorption. To ensure consistent application, colors are assessed relative to international standards (RAL/Pantone). This new, practical staging scheme clarifies the correlation between microscopic characteristics and macroscopically observable details in ovary maturation. Adoption of this unified staging scale will improve maturity analyses, help to identify stocks with potentially reduced reproductive capacity, and facilitate broad‐scale comparisons.

Marine primary production is dominated by diatoms and these are dependent upon the riverine delivery of silicon (Si) to the ocean. In paleoreconstruction of silicic acid utilisation by diatoms, it is assumed that the isotopic composition of the Si that is delivered from the continent to the oceans remains constant. In this study it is shown that glacier-fed Icelandic rivers differ from those directly draining basaltic catchments in their dissolved Si isotope compositions. Lighter values (d30Si=+0.17±0.18‰) are associated with the high physical erosion rates in glacial rivers, and heavier values (d30Si=+0.97±0.31‰) are associated with lower physical erosion rates and enhanced formation of secondary minerals in direct runoff rivers. The Si isotopic compositions correlate with those of Li and provide evidence of a climatic dependence that is likely to have led to glacial–interglacial differences. Based on existing d30Si measurements from diatoms in a sediment record from the Southern Ocean, the interpretation of changes in Si utilisation between the Last Glacial Maximum (LGM) and the early Holocene is revisited taking into account changing isotopic compositions of the river water delivered to the ocean over glacial–interglacial intervals. During the LGM, Si utilisation values are higher when allowing for changing Si isotope input to the ocean (59±5%), than when a constant Si isotope input is assumed (42–47±5%). This reduces but does not eliminate the difference relative to the Holocene (88±5%). Therefore, changes in Si isotope delivery to the ocean need to be taken into account in the precise reconstruction of ocean Si utilisation and primary productivity over glacial–interglacial timescales.

The quantification of volatile emissions from volcanoes is an integral part of understanding magmatic systems, with the exsolution and extent of volcanic degassing having a large impact on the nature of an eruption. Measurements of volatiles have traditionally focused on gas emissions into the atmosphere, but volatiles can also become dissolved in proximal water bodies en route to the surface. Thus the monitoring of rivers draining active volcanic areas can provide insights to identifying changes in activity. This process is particularly important for sub-glacial volcanoes in Iceland, where much of the volatile release is transported within glacial outbreak floods, termed jokulhlaups. Monitoring and characterising these phenomena is hampered by the dependence on spot sampling of stochastic events under challenging field conditions, which often leads to bias in the collected data. A recent technological advance is the osmotic sampler, an electricity-free pump that continuously collects water that can subsequently be divided into time-averaged samples. This technique allows for continued and unsupervised deployment of a sampler for weeks to months, representing a cost-efficient form of chemical monitoring. In this study we deployed osmotic samplers in two rivers in southern Iceland. Skalm is a proglacial river from Mýrdalsjokull glacier and Katla volcano, while Skafta is a larger drainage system from the western part of Vatnajokull glacier. Both rivers are prone to jokulhlaups from geothermal and volcanic sources, and a small jokulhlaup of geothermal origin occurred during the second deployment in Skafta in January 2014. The two deployments show that osmotic samplers are capable of delivering accurate chemical data in turbulent conditions for several key elements. Total dissolved fluxes for the deployment at Skafta are calculated to be Na = 9.9 tonnes/day, Mg = 10.5 t/d, Si = 34.7 t/d, Cl = 11.0 t/d, Ca = 31.6 t/d, DIC = 50.8 t/d, and SO4 = 28.3 t/d, with significant elevations of element concentrations during the jokulhlaup. Dissolved fluxes vary considerably on temporal scales from days to seasons, so that spot sampling may miss pulses in concentrations. This is particularly important for elements such as Mn. The continuous geochemical records from the osmotic samplers make it possible to identify pulses of fluxes attributed to sea spray, groundwater, and subglacial sources. The samplers can also be combined with existing methods of river monitoring, such as conductivity and discharge, to accurately assess changes to fluvial chemistry due to volcanic inputs. Moreover, there is the potential to deploy osmotic samplers in a range of other affected water bodies (e.g. wells, springs, lakes) to gain further insights into volcanic processes.