New Ag3PO4 comparison material for stable oxygen isotope analysis

Rationale A silver phosphate reference material (Ag3PO4) for the measurement of stable oxygen isotope compositions is much needed; however, it is not available from the authorities distributing reference materials. This study aims to fill this gap by calibrating a new Ag3PO4 stable isotope comparison material produced by the University of Natural Resources and Life Sciences (BOKU). Methods Aliquots of Ag3PO4 were distributed to four laboratories who frequently measure the delta O-18 value in Ag3PO4; the University of Natural Resources and Life Sciences (BOKU), the University of Western Australia (UWA), the University of Helsinki (UH), and the Helmholtz Centre for Environmental Research (UFZ). The instruments used to perform the measurements were high-temperature conversion elemental analysers coupled with continuous flow isotope ratio mass spectrometers. The working gas delta O-18 value was set to 0 parts per thousand and the normalization was done by a three-point linear regression using the reference materials IAEA-601, IAEA-602, and NBS127. Results The mean delta O-18 value of the new BOKU Ag3PO4 comparison material on the VSMOW-SLAP scale is 13.71 parts per thousand and the combined uncertainty is estimated as +/- 0.34 parts per thousand. This estimated uncertainty is within the range typical for comparison materials of phosphates and sulphates. Consistent results from the different laboratories probably derived from similar instrumentation, and use of the same reference materials and normalization procedure. The matrix effect of the different reference materials used in this study was deemed negligible. Conclusions The BOKU Ag3PO4 can be used as an alternative comparison material for stable oxygen isotope analysis and is available for stable isotope research laboratories to facilitate calibration.Peer reviewe

Silica Storage, Fluxes, and Nutrient Stoichiometry in Different Benthic Primary Producer Communities in the Littoral Zone of a Deep Subalpine Lake (Lake Iseo, Italy)

Benthic vegetation at the land-water interface is recognized as a filter for silica fluxes, which represents an important but under-investigated subject. This paper aims to analyze stocks and fluxes of biogenic (BSi) and dissolved (DSi) silica in relation to nitrogen (N) and phosphorus (P) in the littoral zone of a deep lake. Specifically, we evaluated how different primary producers can influence BSi retention and DSi release. The study was performed from April to October in 2017, in three different benthic communities: submerged aquatic vegetation (SAV) and microphytobenthos (MPB), both occurring in soft bottom sediments, and epilithic macro- and microalgae (EA) on rocky substrates. The main result was that SAV and MPB were a DSi source and a N and P sink with the DSi efflux from SAV nearly three times as much as in MPB patches. These findings corroborate the hypothesis that SAV mediates the DSi transport from pore water to the water column. Conversely, EA communities were a DSi sink and a N and P source. Overall, these results highlight the fact that the littoral zone of lakes plays a key role in regulating aquatic Si cycling, which is likely to depend on the health status of SAV communitie

Arctic coastal benthos long-term responses to perturbations under climate warming

Climate warming influences structure and function of Arctic benthic ecosystems. Assessing the response of these systems to perturbations requires long-term studies addressing key ecological processes related to recolonization and succession of species. Based on unique time-series (1980-2017), this study addresses successional patterns of hard-bottom benthos in two fjords in NW Svalbard after a pulse perturbation in 1980 and during a period of rapid climate warming. Analysis of seafloor photographs revealed different return rates of taxa, and variability in species densities, through time. It took 13 and 24 years for the community compositions of cleared and control transects to converge in the two fjords. Nearly two decades after the study initiation, an increase in filamentous and foliose macroalgae was observed with a subsequent reorganization in the invertebrate community. Trait analyses showed a decrease in body size and longevity of taxa in response to the pulse perturbation and a shift towards small/medium size and intermediate longevity following the macroalgae takeover. The observed slow recovery rates and abrupt shifts in community structure document the vulnerability of Arctic coastal ecosystems to perturbations and continued effects of climate warming. This article is part of the theme issue 'The changing Arctic Ocean: consequences for biological communities, biogeochemical processes and ecosystem functioning'.publishe