ALBERT

Description: Culture studies of microorganisms have shown that the hydrogen isotopic composition of fatty acids depends on their metabolism, but there are only few environmental studies available to confirm this observation. Here we studied the seasonal variability of the deuterium-to-hydrogen (D / H) ratio of fatty acids in the coastal Dutch North Sea and compared this with the diversity of the phyto- and bacterioplankton. Over the year, the stable hydrogen isotopic fractionation factor epsilon between fatty acids and water (epsilon lipid/water) ranged between -172 and -237 per mil, the algal-derived polyunsaturated fatty acid nC20:5 generally being the most D-depleted (-177 to -235 per mil) and nC18:0 the least D-depleted fatty acid (-172 to -210 per mil). The in general highly D-depleted nC20:5 is in agreement with culture studies, which indicates that photoautotrophic microorganisms produce fatty acids which are significantly depleted in D relative to water. The epsilon lipid/water of all fatty acids showed a transient shift towards increased fractionation during the spring phytoplankton bloom, indicated by increasing chlorophyll a concentrations and relative abundance of the nC20:5 polyunsaturated fatty acids, suggesting increased contributions of photoautotrophy. Time periods with decreased fractionation (less negative epsilon lipid/water values) can potentially be explained by an increased contribution of heterotrophy to the fatty acid pool. Our results show that the hydrogen isotopic composition of fatty acids is a promising tool to assess the community metabolism of coastal plankton potentially in combination with the isotopic analysis of more specific biomarker lipids.

Description: Aim To quantify the influence of a suite of landscape, abiotic, biotic, and host-level variables on ranavirus disease dynamics in amphibian assemblages at two biological levels (site and host-level). Location Wetlands within the East Bay region of California, USA. Methods We used competing models, multimodel inference, and variance partitioning to examine the influence of 16 landscape and environmental factors on patterns in site-level ranavirus presence and host-level ranavirus infection in 76 wetlands and 1,377 amphibian hosts representing five species. Results The landscape factor explained more variation than any other factors in site-level ranavirus presence, but biotic and host-level factors explained more variation in host-level ranavirus infection. At both the site- and host-level, the probability of ranavirus presence correlated negatively with distance to nearest ranavirus-positive wetland. At the site-level, ranavirus presence was associated positively with taxonomic richness. However, infection prevalence within the amphibian population correlated negatively with vertebrate richness. Finally, amphibian host species differed in their likelihood of ranavirus infection: American Bullfrogs had the weakest association with infection while Western Toads had the strongest. After accounting for host species effects, hosts with greater snout-vent length had a lower probability of infection. Main conclusions Strong spatial influences at both biological levels suggest that mobile taxa (e.g., adult amphibians, birds, reptiles) may facilitate the movement of ranavirus among hosts and across the landscape. Higher taxonomic richness at sites may provide more opportunities for colonization or the presence of reservoir hosts that may influence ranavirus presence. Higher host richness correlating with higher ranavirus infection is suggestive of a dilution effect that has been observed for other amphibian disease systems and warrants further investigation. Our study demonstrates that an array of landscape, environmental, and host-level factors were associated with ranavirus epidemiology and illustrates that their importance varies with biological level.

Description: Down core marine sediment samples from ODP Site 1240 have been used for the analysis of the C28 and C30 1,14-diols, the C37:2 and C37:3 long chain ketones (alkenones) and the 24-methylcholesta-5,22-dien-3β-ol (brassicasterol) as proxies of primary productivity. Alkenones were also used to infer past sea surface temperatures through the unsaturation index UK'37. The C29 n-alkane was measured to obtain information on continental material inputs. δD of C37-alkenones and δ¹⁸O-seawater of Globigerinoides ruber were used as indicators of relative salinity changes. This data has been used for the study of the period between 150 and 110 ka (sediment depth from ca. 13 to 17 m), according to the age model from Rippert et al. (2017).

Description: Sea surface salinity is an essential environmental parameter necessary to understand past changes in global climate. However, reconstructing absolute salinity of the surface ocean with high enough accuracy and precision remains a complicated task. Hydrogen isotope ratios of long-chain alkenones (δ2HC37) have been shown to reflect salinity in culture studies and have been proposed as a tool to reconstruct sea surface salinity in the geological record. The correlation between δ2HC37 - salinity in culture is prominently caused by the relationship between δ2HH2O and salinity, as well as the increase in fractionation factor α with increasing salinity. The δ2HC37 - salinity relationship in the natural environment is poorly understood. Here, surface sediments from a variety of environments that cover a wide range of salinities were analyzed to constrain the environmental relationship between salinity and hydrogen isotopes of alkenones. δ2HC37 correlates significantly (R2 =0.55, p 〈 0.0001, n = 95) with annual mean salinity, but interestingly, the biological hydrogen isotope fractionation (αC37) seems independent of salinity. These findings are different from what has previously been observed in culture experiments, but align with other environmental datasets and suggest that the salinity effect on biological hydrogen isotope fractionation observed in culture is not apparent in sediments. The absence of a correlation between αC37 and salinity for marine surface sediments might be best explained by a mixing of multiple alkenone-producing species that fractionate in distinct ways contributing to the sedimentary alkenone signal. Nevertheless, sedimentary δ2HC37 ratios still correlate with salinity and δ2HH2O, suggesting that δ2HC37 ratios are useful for paleosalinity reconstructions. Our surface sediment calibration presented here can be used when different species contribute to the sedimentary alkenone pool and substantial changes in salinity are expected.