Small sinking particles control anammox rates in the Peruvian oxygen minimum zone

Area of Science:

• Marine microbial ecology
• Biogeochemical cycles
• Oceanography

Background:

• Anaerobic oxidation of ammonium (anammox) is a key process for oceanic nitrogen loss, primarily occurring in oxygen minimum zones (OMZs).
• Ammonium released from sinking particles is hypothesized to fuel anammox processes.
• The specific role of particle size and remineralization in supporting anammox remains under investigation.

Purpose of the Study:

• To investigate the relationship between small sinking particles and anammox rates in the Peruvian OMZ.
• To quantify ammonium release from particles and its availability to free-living anammox bacteria.
• To assess the contribution of small particles to oceanic nitrogen loss.

Main Methods:

• In situ measurements of anammox rates during cruises in the Peruvian OMZ (April-June 2017).
• Modeling of ammonium release from sinking particles.
• Calculation of theoretical encounters between free-living anammox bacteria and ammonium near particles.

Main Results:

• Anammox rates showed a strong correlation with the volume of small particles (128-512 µm).
• Modeled ammonium release indicated small particles contribute approximately 75% of ammonium in anoxic waters.
• Free-living anammox bacteria frequently encounter ammonium in the vicinity of small particles.

Conclusions:

• Abundant, slow-sinking small particles play a significant, underestimated role in oceanic nutrient budgets.
• The volume of small particles can be utilized to estimate nitrogen loss across extensive oceanic regions.
• This study highlights the importance of particle dynamics in regulating marine biogeochemical cycles.