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1. Vertical trophic structure and niche partitioning of gelatinous predators in a pelagic food web: Insights from stable isotopes of siphonophores

   https://doi.org/10.1002/lno.12536  

   Hetherington, Elizabeth D; Close, Hilary G; Haddock, Steven_H D; Damian‐Serrano, Alejandro; Dunn, Casey W; Wallsgrove, Natalie J; Doherty, Shannon C; Choy, C Anela (April 2024, Limnology and Oceanography)

   Abstract Gelatinous zooplankton are increasingly recognized as key components of pelagic ecosystems, and there have been many recent insights into their ecology and roles in food webs. To examine the trophic ecology of siphonophores (Cnidaria, Hydrozoa), we used bulk (carbon and nitrogen) and compound‐specific (nitrogen) isotope analysis of individual amino acids (CSIA‐AA). We collected samples of 15 siphonophore genera using blue‐water diving, midwater trawls, and remotely operated vehicles in the California Current Ecosystem, from 0 to 3000 m. We examined the basal resources supporting siphonophore nutrition by comparing their isotope values to those of contemporaneously collected sinking and suspended particles (0–500 m). Stable isotope values provided novel insights into siphonophore trophic ecology, indicating considerable niche overlap between calycophoran and physonect siphonophores. However, there were clear relationships between siphonophore trophic positions and phylogeny, and the highest siphonophore trophic positions were restricted to physonects. Bulk and source amino acid nitrogen isotope (δ¹⁵N) values of siphonophores and suspended particles all increased significantly with increasing collection depth. In contrast, siphonophore trophic positions did not increase with increasing collection depth. This suggests that microbially reworked, deep, suspended particles with higher δ¹⁵N values than surface particles, likely indirectly support deep‐pelagic siphonophores. Siphonophores feed upon a range of prey, from small crustaceans to fishes, and we show that their measured trophic positions reflect this trophic diversity, spanning 1.5 trophic levels (range 2.4–4.0). Further, we demonstrate that CSIA‐AA can elucidate the feeding ecology of gelatinous zooplankton and distinguish between nutritional resources across vertical habitats. These findings improve our understanding of the functional roles of gelatinous zooplankton and energy flow through pelagic food webs. 

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2. Isotope effect suggests site‐specific nonadiabaticity on Ge(111) c (2×8)

   https://doi.org/10.1002/ntls.20230019  

   Krüger, Kerstin; Wang, Yingqi; Zhu, Lingjun; Jiang, Bin; Guo, Hua; Wodtke, Alec M.; Bünermann, Oliver (November 2023, Natural Sciences)

   Abstract Energy transferred in atom‐surface collisions typically depends strongly on projectile mass, an effect that can be experimentally detected by isotopic substitution. In this work, we present measurements of inelastic H and D atom scattering from a semiconducting Ge(111)c(2×8) surface exhibiting two scattering channels. The first channel shows the expected isotope effect and is quantitatively reproduced by electronically adiabatic molecular dynamics simulations. The second channel involves electronic excitations of the solid and, surprisingly, exhibits almost no isotope effect. We attribute these observations to scattering dynamics, wherein the likelihood of electronic excitation varies with the impact site engaged in the interaction. Key PointsPrevious work revealed that H atoms with sufficient translational energy can excite electrons over the band gap of a semiconductor in a surface collision.We studied the isotope effect of the energy transfer by H/D substitution and performed band structure calculations to elucidate the underlying excitation mechanism.Our results suggest a site‐specific mechanism that requires the atom to hit a specific surface site to excite an electron‐hole pair. 

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3. Meridional Central Pacific Ocean Depth Section for Pb and Pb Isotopes (GEOTRACES GP15, 152°W, 56°N to 20°S) Including Shipboard Aerosols

   https://doi.org/10.1029/2024JC021674  

   Jiang, Shuo; Lanning, Nathan; Boyle, Edward; Fitzsimmons, Jessica; Ramezani, Jahandar; Wang, Avery G; Zhang, Jing (January 2025, Journal of Geophysical Research: Oceans)

   Goodkin, Nathalie (Ed.)

   Abstract Most oceanic lead (Pb) is from anthropogenic emissions into the atmosphere deposited into surface waters, mostly during the past two centuries. The space‐ and time‐dependent emission patterns of anthropogenic Pb (and its isotope ratios) constitute a global geochemical experiment providing information on advective, mixing, chemical, and particle flux processes redistributing Pb within the ocean. Pb shares aspects of its behavior with other elements, for example, atmospheric input, dust solubilization, biological uptake, and reversible exchange between dissolved and adsorbed Pb on sinking particles. The evolving distributions allow us to see signals hidden in steady‐state tracer distributions. The global anthropogenic Pb emission experiment serves as a tool to understand oceanic trace element dynamics. We obtained a high‐resolution (5° station spacing) depth transect of dissolved Pb concentrations and Pb isotopes from Alaska (55°N) to just north of Tahiti (20°S) near 152°W longitude. The sections reveal distinct sources of Pb (American, Australian, and Chinese), transport of Australian style Pb to the water mass formation region of Sub‐Antarctic Mode Water which is advected northward, columnar Pb isotope contours due to reversible particle exchange on sinking particles from high‐productivity particle veils, and a gradient of high northern deep water [Pb] to low southern deep water [Pb] that is created by reversible exchange release of Pb from sinking particles carrying predominantly northern hemisphere Pb.²⁰⁸Pb/²⁰⁶Pb versus²⁰⁶Pb/²⁰⁷Pb isotope relationships show that most oceanic Pb in the North Pacific is from Chinese and American sources, whereas Pb in the South Pacific is from Australian and American sources. 

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4. To eat or not to eat: novel stable isotope models reveal a shift in carnivory with nutrient availability for aquatic Utricularia spp.

   https://doi.org/10.1093/aob/mcae119  

   Kurosawa, Emmi; Wells, Naomi_S; Gibson, Robert; Lyons, Zachary; Kesseli, Richard; Oakes, Joanne_M (August 2024, Annals of Botany)

   Abstract Background and AimsFreshwater nitrogen inputs are increasing globally, altering the structure and function of wetland ecosystems adapted to low nutrient conditions. Carnivorous wetland plants of the genus Utricularia are hypothesized to reduce their reliance on carnivory and increase their assimilation of environmental nutrients when the supply of ambient nutrients increases. Despite success in using stable isotope approaches to quantify carnivory of terrestrial carnivorous plants, quantifying carnivory of aquatic Utricularia requires improvement. MethodsWe developed stable isotope mixing models to quantify aquatic plant carnivory and used these models to measure dietary changes of three Utricularia species, Utricularia australis, U. gibba and U. uliginosa, in 11 wetlands across a 794-km gradient in eastern Australia. Diet was assessed using multiple models that compared variations in the natural-abundance nitrogen isotope composition (δ15N) of Utricularia spp. with that of non-carnivorous plants, and environmental and carnivorous nitrogen sources. Key ResultsCarnivory supplied 40–100 % of plant nitrogen. The lowest carnivory rates coincided with the highest availability of ammonium and dissolved organic carbon. ConclusionsOur findings suggest that Utricularia populations may adapt to high nutrient environments by shifting away from energetically costly carnivory. This has implications for species conservation as anthropogenic impacts continue to affect global wetland ecosystems. 

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5. W-band S – Z relationships for rimed snow particles: observational evidence from combined airborne and ground-based observations

   https://doi.org/10.5194/amt-16-6123-2023  

   Fuller, Shelby; Marlow, Samuel A.; Haimov, Samuel; Burkhart, Matthew; Shaffer, Kevin; Morgan, Austin; Snider, Jefferson R. (December 2023, Atmospheric Measurement Techniques)

   Abstract. Values of undercatch-corrected liquid-equivalent snowfall rate (S) at a ground site and microwave reflectivity (Z) retrieved using an airborne W-band radar were acquired during overflights. The temperature at the ground site was between −6 and −15 ∘C. At flight level, within clouds containing ice and supercooled liquid water, the temperature was approximately 7 ∘C colder. Additionally, airborne measurements of snow particle imagery were acquired. The images demonstrate that most of the snow particles were rimed, at least at flight level. A relatively small set of S–Z pairs (four) is available from the overflights. Important distinctions between these measurements and those of Pokharel and Vali (2011), who reported S–Z pairs and an S–Z relationship for rimed snow particles, are (1) the fewer S–Z pairs, (2) the method used to acquire S, and (3) the altitude, relative to ground, of the W-band Z retrievals. This analysis corroborates the fact that the S–Z relationship reported in Pokharel and Vali (2011) yields an S – in scenarios with snowfall produced by riming – substantially larger than that derived using an S–Z relationship developed for unrimed snow particles. 

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