Journal Article

Distribution Characteristics and Dynamics of Marine Hydrogen in the Eastern Indian Ocean

Jiang, Yu‐Cheng, Wang, Jian, Xu, Feng, Zhou, Li‐Min, Zhang, Hong‐Hai, Xu, Gao‐Bin, Chen, Zhao‐Hui

2024

Overview

The ocean serves as a significant contributor of atmospheric Hydrogen (H2) with indirect greenhouse effects. However, uncertainties persist regarding internal production and consumption processes of marine H2, as well as controlling factors. Our study examined the spatial distribution and source‐sink dynamics of marine H2 in the Eastern Indian Ocean. H2 concentrations in surface seawater exhibited a range of 2.95–21.96 nmol L−1. High concentrations of H2 were observed in the anoxic water in the Bay of Bengal. Rates of H2 photo‐production and microbial consumption in surface seawater ranged from 1.80 to 17.78 nmol L−1 h−1 and 1.02–9.18 nmol L−1 h−1, respectively. When considering the entire mixed layer, photo‐production contribute to approximately 31%–43% of the total H2 removal, with cyanobacteria potentially serving as another source in the mixed layer. Compared with the sea‐to‐air exchange, microbial consumption was the primary removal pathway of H2 in seawater. Plain Language Summary Atmospheric hydrogen (H2) can influence the environment and climate by consuming hydroxyl radicals (OH·) and indirectly raising greenhouse gas concentrations. Although the ocean serves as a significant source of atmospheric H2, the biogeochemical processes governing its presence in seawater remain poorly understood. The Eastern Indian Ocean, characterized by a substantial inflow of freshwater, exerts a distinct impact on the local ecosystem. We conducted a field investigation in the Eastern Indian Ocean to clarify the sources, sinks, and controlling factors of H2, including the Bay of Bengal with relatively higher primary productivity and the Eastern Equatorial Indian Ocean with low primary productivity, respectively. Our study involved the quantitative assessment of H2 photo‐production, microbial consumption, and sea‐to‐air exchange in seawater, along with the calculation of the H2 budget in the mixed layer. This investigation enhances our understanding of H2 cycling processes in seawater and contributes to the assessment of H2 emissions from the ocean and their impact on the atmospheric budget. Key Points The distribution of H2 was significantly affected by river input in the Eastern Indian Ocean Photo‐production was an important source of H2 in the mixed layer Microbial consumption was the primary sink for H2 in the mixed layer

• Publisher: John Wiley & Sons, Inc,Wiley
• Subject: Air pollution / Anoxia / Budgets / Consumption / Cyanobacteria / Field investigations / Free radicals / Freshwater / Freshwater ecosystems / Greenhouse effect / Greenhouse gases / Hydrogen / Hydroxyl radicals / Inflow / Inland water environment / Marine ecosystems / Microorganisms / Mixed layer / Oceans / Primary production / Productivity / Seawater / Spatial distribution / Water inflow