Recycling versus loss in the marine nitrogen cycle: controls, feedbacks, and the impact of expanding low oxygen regions

RECLESS will predict how ongoing ocean deoxygenation impacts microbial nitrogen transformations and thereby the future availability of nitrogen to support oceanic primary production and carbon sequestration.

Microbial conversions of bioavailable nitrogen to dinitrogen in oxygen-depleted waters currently account for ~30% of the marine nitrogen loss, despite oxygen-depleted waters making up just 0.1% of the ocean volume.

Models predict accelerating expansion of oxygen depletion, which entails increased nitrogen loss with negative impacts on ecosystem function and oceanic carbon sequestration, as well as an associated production of greenhouse-forcing nitrous oxide.

However, biogeochemical ocean models currently fail to reproduce fundamental aspects of the microbial nitrogen transformations observed experimentally, including how nitrogen is either recycled or lost in oxygen-depleted waters.

This reflects fundamental knowledge gaps concerning the environmental controls on growth, mortality, and activity of microbial populations, which preclude robust model predictions.

RECLESS breaks new ground by synergistically integrating innovative oceanographic, biogeochemical, ecophysiological, and model-based investigations to close these gaps.

With unprecedented in situ ecophysiological experiments using novel custom-made instrumentation as a cornerstone, RECLESS will identify key organisms, quantify their response to environmental controls, and construct the first comprehensive global microbial ecosystem model for oxygen-depleted marine systems.

This model will enable robust predictions of how ocean deoxygenation affects nitrogen cycling and loss, greenhouse gas production, and interactions with the carbon cycle.

Thus, RECLESS will transform our understanding of the present and future marine nitrogen cycle and its climate interactions, and set new standards for the integration of microbial processes in global biogeochemical analyses.