Biogeochemical Dynamics in the Arabian Sea

The Arabian Sea’s biogeochemical framework is defined by strong monsoonal forcing and an exceptional oxygen minimum zone (OMZ). Seasonal reversal of winds generates upwelling of cold, nutrient-rich waters along the western shelf, fuelling phytoplankton blooms in the euphotic zone. Beneath this productive layer, intense respiration under stratified conditions consumes dissolved oxygen, sustaining an OMZ between approximately 200 and 1000 metres depth. Within this OMZ, microbial processes such as denitrification and anaerobic ammonium oxidation convert nitrate into gaseous nitrogen species, producing significant nitrogen loss. On the continental margin, dynamic exchanges between sediments and overlying waters further regulate the supply of dissolved inorganic nutrients and trace metals, thereby modulating primary production and carbon export. Iron limitation in high-nutrient, low-chlorophyll regimes, particularly during the late southwest monsoon, underscores the role of trace elements in controlling phytoplankton efficiency. These coupled physical, chemical and biological processes not only shape regional ecology but also influence global biogeochemical cycles, affecting greenhouse-gas fluxes and oceanic nutrient distributions under present and future climate scenarios.

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Biogeochemical Dynamics in the Arabian Sea publication trend

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Technical terms

Oxygen Minimum Zone (OMZ): A mid-water layer with persistently low dissolved oxygen due to high biological respiration and limited ventilation.

Upwelling: The upward movement of deep, nutrient-rich water to the ocean surface driven by wind and Coriolis forces.

Denitrification: The microbial reduction of nitrate to gaseous nitrogen (N₂) under low-oxygen conditions, resulting in nitrogen removal.

Primary Production: The synthesis of organic compounds by phytoplankton from inorganic carbon through photosynthesis in the euphotic zone.

Hypoxia: A state in which dissolved oxygen falls below levels required to sustain most marine life (typically <63 µM).

Anoxia: Near or complete absence of dissolved oxygen (typically <0.05 µM), preventing aerobic respiration.

References

1. Reviews and syntheses: Present, past, and future of the oxygen minimum zone in the northern Indian Ocean. Biogeosciences (2020).
2. The world’s largest coastal deoxygenation zone is not anthropogenically driven. Environmental Research Letters (2021).
3. The Arabian Sea as a high-nutrient, low-chlorophyll region during the late Southwest Monsoon. Biogeosciences (2010).
4. Benthic mineralization and nutrient exchange over the inner continental shelf of western India. Biogeosciences (2014).
5. Oxygen minimum zone of the open Arabian Sea: variability of oxygen and nitrite from daily to decadal timescales. Biogeosciences (2014).
6. Seasonal and interannual variations in the nitrogen cycle in the Arabian Sea. Biogeosciences (2014).