Tracking circulation of abyssal circulation pathways in the Indian Ocean

Abyssal circulation pathways and deep upwelling hotspots, ventilating the Indian Ocean abyss as reflected in dissolved oxygen concentrations (Image: Kaushik Mishra and Bishakhdatta Gayen)

The abyssal water occupies a significant volume of the world’s oceans. The movement of abyssal water is slow, occurring on timescales of a century, but it plays an important role in transporting water masses, nutrients, and ventilating heat and gases. The Indian Ocean (IO) houses the largest fraction of the global abyssal water volume compared to its size. In addition to insufficient measurements, there have been relatively few modeling efforts to study the abyssal transports.

In a new study, researchers at the Centre for Atmospheric and Oceanic Sciences (CAOS), IISc and collaborators sought to quantify previously unknown circulation and ventilation pathways of deep and abyssal waters in the Indian Ocean.

The team used a high-resolution regional ocean model, re-analyses, and observation datasets to assess the circulation of abyssal waters. They found that abyssal waters enter through the southern boundary of the IO, adjoining the Southern Ocean, along three unique pathways that flood the IO.

The team also quantified the vertical transport along specific sub-regions within the IO domain. These sub-regions act as “hot spots” for the abyssal water upwelling, where a large fraction of the upwelled waters are transformed into deep waters and return southward as part of the basin-scale overturning circulation. In a warming climate scenario, when the abyssal water volume is projected to contract at an alarming rate, these pathways could play an important role in modulating the future ocean state.

From left to right: Kaushik Mishra, Bishakhdatta Gayen, Kathryn L Gunn, PN Vinayachandran, Nihar Paul

REFERENCE:

Mishra K, Gayen B, Gunn KL, Vinayachandran PN, Paul N, Tracing the abyssal water pathways in the Indian Ocean, Geophysical Research Letters (2026).

https://doi.org/10.1029/2026GL124017

WEBSITE:

https://bishakhdatta.com/research-group/