Abstract. Long viewed as a mostly noble, atmospheric species, recent work demonstrates that nitrogen in fact cycles throughout the Earth system, including the atmosphere, biosphere, oceans, and solid Earth. Despite this new-found behaviour, more thorough investigation of N in geologic materials is limited due to its low concentration (one to tens of parts per million) and difficulty in analysis. In addition, N can exist in multiple species (NO3−, NH4+, N2, organic N), and determining which species is actually quantified can be difficult. In rocks and minerals, NH4+ is the most stable form of N over geologic timescales. As such, techniques designed to measure NH4+ can be particularly useful.We measured a number of geochemical rock standards using three different techniques: elemental analyzer (EA) mass spectrometry, colorimetry, and fluorometry. The fluorometry approach is a novel adaptation of a technique commonly used in biologic science, applied herein to geologic NH4+. Briefly, NH4+ can be quantified by HF dissolution, neutralization, addition of a fluorescing reagent, and analysis on a standard fluorometer. We reproduce published values for several rock standards (BCR-2, BHVO-2, and G-2), especially if an additional distillation step is performed. While it is difficult to assess the quality of each method, due to lack of international geologic N standards, fluorometry appears better suited to analyzing mineral-bound NH4+ than EA mass spectrometry and is a simpler, quicker alternative to colorimetry.To demonstrate a potential application of fluorometry, we calculated a continental crust N budget based on new measurements. We used glacial tills as a proxy for upper crust and analyzed several poorly constrained rock types (volcanics, mid-crustal xenoliths) to determine that the continental crust contains  ∼  2  ×  1018 kg N. This estimate is consistent with recent budget estimates and shows that fluorometry is appropriate for large-scale questions where high sample throughput is helpful.Lastly, we report the first δ15N values of six rock standards: BCR-2 (1. 05  ±  0. 4 ‰), BHVO-2 (−0. 3  ±  0. 2 ‰), G-2 (1. 23  ±  1. 32 ‰), LKSD-4 (3. 59  ±  0. 1 ‰), Till-4 (6. 33  ±  0. 1 ‰), and SY-4 (2. 13  ±  0. 5 ‰). The need for international geologic N standards is crucial for further investigation of the Earth system N cycle, and we suggest that existing rock standards may be suited to this need.

With the accelerating development of direct and indirect anthropogenic threats, including climate change and pollution as well as extractive industries such as deep-sea mining, there is an urgent need for simple but effective solutions to identify conservation priorities for deep-sea species. The International Union for Conservation of Nature (IUCN) Red List of Threatened Species is an effective and well-recognized tool to promote the protection of species and presents an opportunity to communicate conservation threats to industry, policy makers, and the general public. Here, we present the Vent Red List for molluscs: a complete global assessment of the extinction risk of all described molluscs endemic to hydrothermal vents, a habitat under imminent threat from deep-sea mining. Of the 184 species assessed, 62% are listed as threatened: 39 are Critically Endangered, 32 are Endangered, and 43 are Vulnerable. In contrast, the 25 species that are fully protected from deep-sea mining by local conservation measures are assessed as Least Concern, and a further 45 species are listed as Near Threatened, where some subpopulations face mining threats while others lie within protected areas. We further examined the risk to faunas at specific vent sites and biogeographic regions using a relative threat index, which highlights the imperiled status of vent fields in the Indian Ocean while other vent sites within established marine protected areas have a high proportion of species assessed as Least Concern. The Vent Red List exemplifies how taxonomy-driven tools can be utilized to support deep-sea conservation and provides a precedent for the application of Red List assessment criteria to diverse taxa from deep-sea habitats.

Evolution of two novel feeding strategies among caenogastropod molluscs, suspension feeding in calyptraeids such as Crepidula fornicata and predatory feeding with a pleurembolic proboscis among neogastropods, may have both involved elongation of the anterior esophagus. Emergence of predatory feeding with a proboscis is particularly significant because it correlates with the rapid adaptive radiation of buccinoidean and muricoidean neogastropods during the Cretaceous. However, the notion that this important evolutionary transition involved elongation of the anterior esophagus to extend down a long proboscis has been disputed by evidence that it may have been the wall of the buccal cavity that elongated. We undertook a comparative study on foregut morphogenesis during larval and metamorphic development in C. fornicata and in three species of neogastropods with a pleurembolic proboscis to examine the hypothesis that the same region of foregut has elongated in all. We approached this by identifying a conserved marker for the boundary between buccal cavity and anterior esophagus, which was recognizable before the developing foregut showed regional differences in length. A survey of four species of littorinimorph caenogastropods suggested that the site of neurogenic placodes for the buccal ganglia could serve as this marker. Results showed that foregut lengthening in C. fornicata involved elongation posterior to neurogenic placodes for buccal ganglia, an area that corresponded to the anterior esophagus in the other littorinimorphs. However, foregut elongation occurred anterior to neurogenic placodes for buccal ganglia in two buccinoidean and one muricoidean neogastropod. The elongated foregut within the pleurembolic proboscis of these neogastropods qualifies as anterior esophagus only if the definition of the anterior esophagus is expanded to include the dorsal folds that run down the roof of the buccal cavity. Regardless of how the anterior esophagus is defined, comparative developmental data do not support the hypothesis of homology between the elongated adult foregut regions in C. fornicata and in neogastropods with a pleurembolic proboscis.

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Abstract. Long viewed as a mostly noble, atmospheric species, recent work demonstrates that nitrogen in fact cycles throughout the Earth system, including the atmosphere, biosphere, oceans, and solid Earth. Despite this new-found behaviour, more thorough investigation of N in geologic materials is limited due to its low concentration (1 to 10 s ppm) and difficulty in analysis. In addition, N can exist in multiple species (NO3−, NH4+, N2, organic-N), and determining which species is actually quantified can be difficult. In rocks and minerals, NH4+ is the most stable form of N over geologic time scales. As such, techniques designed to measure NH4+ can be particularly useful. We measured a number of geochemical rock standards using three different techniques: mass spectrometry, colourimetry, and fluorometry. The fluorometry approach is a novel adaptation of a technique commonly used in biologic science, applied herein to geologic NH4+. Briefly, NH4+ can be quantified by HF-dissolution, neutralization, addition of a fluorescing reagent, and analysis on a standard fluorometer. We reproduce published values for several rock standards (BCR-2, BHVO-2, and G-2), especially if an additional distillation step is performed. While it is difficult to assess quality of each method, due to lack of international geologic N standards, fluorometry appears better suited to analyzing mineral-bound NH4+ than mass spectrometry, and is a simpler, quicker alternative to colourimetry. To demonstrate a potential application of fluorometry, we calculated a continental crust N budget based on new measurements. We used glacial tills as a proxy for upper crust and analyzed several poorly constrained rock types (volcanics, mid-crustal xenoliths) to determine that the continental crust contains ∼ 2 × 1018 kg N. This estimate is consistent with recent budget estimates, and shows that fluorometry is appropriate for large-scale questions where high sample throughput is helpful. Lastly, we report the first δ15N values of six rock standards: BCR-2 (1.05 ± 0.4 ‰), BHVO-2 (−0.3 ± 0.2 ‰), G-2 (1.23 ± 1.32 ‰), LKSD-4 (3.59 ± 0.1 ‰), Till-4 (6.33 ± 0.1 ‰), and SY-4 (2.13 ± 0.5 ‰). The need for international geologic N standards is crucial for further investigation of the Earth system N cycle, and we suggest that existing rock standards may be suited to this need.