Recent Changes in Dissolved Oxygen Concentrations in the Arabian Sea using BGC-Argo Data

Dissolved oxygen (DO) is an important passive tracer of the ocean that plays an essential role in structuring marine ecosystems. The thickest and most intense oxygen minimum zone (OMZ) at intermediate depths is found in the Arabian Sea, which is located in the northwestern part of the tropical Indian Ocean. In this work, changes in DO concentration in the water column of the Arabian Sea are extensively examined over the recent decade utilizing BGC-Argo profile records. Here, the upper layer experiences deoxygenation, which is attributed to improved stratification. In contrast, below the top ocean, the DO concentration shows significant increasing trend throughout the depths. The oxygenation at intermediate levels of this region is caused by enhanced isopycnal mixings in the presence of salt finger instabilities. This research reveals the role of salinity in regulating DO variations in the water column. This investigation also demonstrates that the OMZ in this region has shrunk over the period by roughly 200 m from the bottom. Furthermore, DO concentrations in the OMZ have increased by around 140%, which is associated with the North Indian Intermediate Water masses over the study region.