Nitrogen Isotope Geochemistry in Subduction Zones

Nitrogen isotope geochemistry in subduction zones investigates how nitrogen, a critical volatile for life and climate, is cycled between Earth’s surface and its deep interior. As oceanic plates descend, they carry sedimentary and crustal nitrogen—often hosted as ammonium (NH4+) in minerals such as phengite—into high-pressure, high-temperature regimes. During prograde metamorphism, nitrogen partitions between solid phases and fluids, with pressure, temperature and redox state governing whether it is retained in the slab or released into the mantle wedge and ultimately outgassed at volcanic arcs. Stable isotope ratios (δ¹⁵N) record this transfer, preserving signatures of surface sources, fluid–rock interaction and deep-mantle processes. The net balance between nitrogen ingassing (delivery into the mantle) and outgassing (return to the atmosphere) shapes long-term atmospheric evolution, influences mantle fertility and contributes to global nitrogen budgets. Recent experimental and analytical advances—from high-pressure solubility measurements in lower-mantle minerals to in situ isotope analyses of fluid inclusions—have refined our understanding of slab nitrogen retention, highlighted key carrier phases and clarified the fate of subducted nitrogen in both cold and warm geotherms. A comprehensive picture of these processes is essential for decoding Earth’s volatile history and its implications for surface habitability.

Research from Nature Portfolio

Recent studies have quantified nitrogen partitioning during the phengite to K-hollandite transition under pressures of 10–12 GPa and temperatures of 800–1100 °C, demonstrating that only a fraction of slab-hosted nitrogen survives to lower-mantle depths. The phengite–fluid and K-hollandite–fluid partition coefficients indicate that up to 43 % of sedimentary nitrogen may be transported beyond arc-forming depths along cold slabs, but less under warmer conditions. Complementary high-pressure experiments on bridgmanite have revealed that its nitrogen solubility increases with temperature between 1400 and 1700 °C at 28 GPa, implying a hidden deep reservoir capable of storing several times the present atmospheric nitrogen mass. Together, these findings revise estimates of nitrogen transport efficiency into the lower mantle and underscore the importance of mineral solubility controls on deep nitrogen storage.

Nitrogen Isotope Geochemistry in Subduction Zones publication trend

The graph below shows the total number of articles in nitrogen isotope geochemistry in subduction zones across all publications each year (not limited to Nature Index journals).

Technical terms

δ¹⁵N: The ratio of ¹⁵N to ¹⁴N in a sample relative to a standard, expressed in per mil (‰), used to trace nitrogen sources and processes.

Fluid–mineral partition coefficient: The ratio of nitrogen concentration in a mineral phase to that in an associated fluid at equilibrium, reflecting how nitrogen is distributed during metamorphism.

Ingassing: Net transfer of nitrogen from Earth’s surface into the mantle via subduction.

Outgassing: Release of nitrogen from the mantle to the atmosphere, primarily through volcanic emissions.

Phengite: A high-pressure mica that hosts ammonium in subducting sedimentary rocks and influences nitrogen retention during slab metamorphism.

References

1. Inefficient nitrogen transport to the lower mantle by sediment subduction. Nature Communications (2024).
2. Temperature dependence of nitrogen solubility in bridgmanite and evolution of nitrogen storage capacity in the lower mantle. Scientific Reports (2023).
3. The origin and evolution of Earth's nitrogen. National Science Review (2024).
4. Deep Nitrogen Fluxes and Sources Constrained by Arc Lava Phenocrysts. Geophysical Research Letters (2024).