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The spatial distribution of marine di-nitrogen (N2) fixation informs our understanding of the sensitivities of this process as well as the potential for this new nitrogen (N) source to drive export production, influencing the global carbon (C) cycle and climate. Using geochemically-derived δ15N budgets, we quantified rates of N2fixation and its importance for supporting export production at stations sampled near the southwest Pacific Tonga-Kermadec Arc. Recent observations indicate that shallow (<300 m) hydrothermal vents located along the arc provide significant dissolved iron to the euphotic zone, stimulating N2fixation. Here we compare measurements of water column δ15NNO3+NO2with sinking particulate δ15N collected by short-term sediment traps deployed at 170 m and 270 m at stations in close proximity to subsurface hydrothermal activity, and the δ15N of N2fixation. Results from the δ15N budgets yield high geochemically-based N2fixation rates (282 to 638 µmol N m-2d-1) at stations impacted by hydrothermal activity, supporting 64 to 92% of export production in late spring. These results are consistent with contemporaneous15N2uptake rate estimates and molecular work describing highTrichodesmiumspp. and other diazotroph abundances associated with elevated N2fixation rates. Further, the δ15N of sinking particulate N collected at 1000 m over an annual cycle revealed sinking fluxes peaked in the summer and coincided with the lowest δ15N, while lower winter sinking fluxes had the highest δ15N, indicating isotopically distinct N sources supporting export seasonally, and aligning with observations from most other δ15N budgets in oligotrophic regions. Consequently, the significant regional N2fixation input to the late spring/summer Western Tropical South Pacific results in the accumulation of low-δ15NNO3+NO2in the upper thermocline that works to lower the elevated δ15NNO3+NO2generated in the oxygen deficient zones in the Eastern Tropical South Pacific.
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This content will become publicly available on August 1, 2026
Between a Rock and a Soft Place: Biomass δ 15 N Values of Yellowstone Hot Spring Microbial Communities and Their Potential for Preservation in the Rock Record
Abstract Nitrogen isotope (δ15N) values in ancient rocks have been used to interpret the presence of nitrogen metabolisms and fixed N availability across the Archean and Paleoproterozoic eons. However, how δ15N signals produced by nitrogen metabolisms of microbial communities, the impact of the geochemical environments they live in on those signals, and the fidelity of those signals through preservation in the rock record have not been fully constrained and validated. Thus, it is imperative to study modern microbial systems to test the validity of using δ15N signals produced by microbial communities to interpret what geochemical environments and nitrogen metabolisms influenced the production of those signals. Hydrothermal systems are an ideal place to examine the biotic and abiotic factors that impact δ15N signals—physical processes generate geochemical environments with wide ranges of fixed N availability and the physicochemical environments exclude multicellular eukaryotic organisms. Previous work has demonstrated the presence of nitrogen fixation genes in microbial communities across a range of temperature (16–89°C) and pH (1.9–9.8) gradients. Here, we test the validity and fidelity of using microbial community δ15N signals as indicators of geochemical environment and nitrogen metabolisms (specifically, biological nitrogen fixation) present in eight hydrothermal systems across Yellowstone National Park. Our results suggest that δ15N values measured in the ancient rock record can provide information about the N cycling and prevailing environmental conditions during deposition, but only if viewed within appropriate context.
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- Award ID(s):
- 1939303
- PAR ID:
- 10636416
- Publisher / Repository:
- AGU
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Biogeosciences
- Volume:
- 130
- Issue:
- 8
- ISSN:
- 2169-8953
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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