# Microbial responses to ocean deoxygenation: Revisiting the impacts on organic carbon cycling

## TL;DR

This review examines how microbes affect organic carbon cycling in low-oxygen ocean areas, showing their role in both releasing and storing carbon.

## Contribution

The paper provides a comprehensive analysis of microbial roles in carbon cycling under ocean deoxygenation, integrating multiple biogeochemical cycles.

## Key findings

- Microbes in hypoxic zones significantly influence carbon source-sink dynamics.
- Hypoxic zones act as both transient carbon sources and long-term sinks.
- Interconnected cycling of carbon, nitrogen, sulfur, and phosphorus alters organic matter composition under deoxygenation.

## Abstract

Ocean deoxygenation is impacting and will also in the future impact fundamental biogeochemical cycles. This review explores the ecological functions of microbes under hypoxic and anoxic conditions, emphasizing their critical roles in carbon source-sink dynamics. We examine microbial ecosystems in both open-ocean oxygen minimum zones and China’s coastal hypoxic areas, highlighting the microbial contributions to deoxygenation driven processes. We also explore how organic carbon cycling driven by microbial heterotrophic and autotrophic metabolisms change across oxygen gradients. Furthermore, this review elucidates the interconnected cycling of carbon, nitrogen, sulfur, and phosphorus, which regulate organic matter consumption and/or storage under deoxygenation, and alters the elemental composition of organic matter. Our study highlights the importance of microbial processes in regulating carbon cycle under ocean deoxygenation, emphasizing the dual role of hypoxic zones as transient sources and long-term sinks of organic carbon. Lastly, we highlight current challenges in addressing ocean deoxygenation and provide avenues for future research.

Earth sciences; Geomicrobiology; Biogeochemistry; Oceanography