Pelagic Methane Cycling in the Arabian Sea Oxygen Minimum Zone

Abstract The Arabian Sea experiences an intense perennial Oxygen Minimum Zone (OMZ) (150–1,200 m) in its northern and central regions. Earlier measurements during the 1990s (Joint Global Ocean Flux Study, India) revealed methane (CH 4 ) oversaturation in the upper 300–400 m in this region. The basin is reported to have experienced warming and OMZ intensification in recent years, while the particle flux is expected to remain moderately steady. In response to the above phenomena, we aimed to examine the change in CH 4 distribution in comparison to the 1990s by studying the depth profiles of CH 4 along 8–21°N over 68°E meridian from February 2017 to October 2024. The present study showed CH 4 oversaturation in the upper 135–350 m in the OMZ region and 100–150 m in the non‐OMZ region. The upper OMZ CH 4 maxima exhibits moderate spatial variability with higher concentrations toward the north. However, there was no significant change in the CH 4 maxima in the OMZ in comparison to those during the 1990s. The waters in the OMZ core and below were undersaturated with CH 4 as observed in the 1990s. We hypothesize that the CH 4 build‐up in the OMZ waters was possibly related to its in situ production from the anoxic micro‐niches in sinking detrital particulate matter. The CH 4 undersaturation in the core of OMZ was possibly due to reduced particle fluxes, which led to low CH 4 production potential. However, the potential role of oxidants such as nitrite and oxygen on the CH 4 cycling in the Arabian Sea OMZ needs further research.