Long-term nitrogen burial exceeds denitrification in global fjords

Area of Science:

• Marine science
• Biogeochemistry
• Oceanography

Background:

• Nitrogen availability is a key regulator of oceanic primary productivity and carbon sequestration.
• Fjords represent a significant portion of marine carbon burial but their nitrogen loss pathways are poorly understood.

Purpose of the Study:

• To quantify nitrogen loss via sediment burial in global fjords.
• To compare the significance of burial versus microbial nitrogen loss in fjords.
• To assess the impact of climate warming on nitrogen cycling in fjords.

Main Methods:

• Analysis of nitrogen burial rates in global fjords.
• Comparison of nitrogen burial with microbial nitrogen loss (denitrification, anammox).
• Assessment of environmental factors influencing nitrogen loss.

Main Results:

• Global fjords are hotspots for nitrogen burial, accounting for up to 18% of oceanic nitrogen burial.
• Sediment burial is the dominant nitrogen loss mechanism in fjords, exceeding microbial processes.
• Microbial nitrogen loss is influenced by temperature and nutrient availability, particularly in anoxic fjords.

Conclusions:

• Fjords efficiently sequester excess nitrogen in sediments over long timescales.
• Accelerated warming is predicted to increase both nitrogen burial and microbial nitrogen loss in fjords.
• These changes will significantly impact nitrogen budgets in fjords and the wider ocean.