New Research Quantifies Drivers of North Indian Ocean Sea Level Rise

The North Indian Ocean is rising at 4.55 mm per year, significantly outstripping many global averages. This early-stage research, currently awaiting peer review, indicates that heat—not just melting ice—is the primary engine behind the **North Indian Ocean sea level rise**.

Mechanisms of North Indian Ocean sea level rise

Researchers analysed satellite altimetry and GRACE gravimetry from 2003 to 2021. They separated the rise into three distinct components:

• Thermosteric: Expansion caused by rising water temperatures.
• Halosteric: Changes in volume due to salinity shifts.
• Mass: Physical addition of water from melting glaciers or crustal shifts.

While global sea levels are increasingly mass-driven, this preprint suggests the NIO remains dominated by thermosteric expansion. The data reveals a complex regional mosaic. The Bay of Bengal sees additional rise from freshwater runoff, while the Arabian Sea's trend is tempered by high-salinity inflows from the Red Sea and Persian Gulf.

Regional Heterogeneity and Climate Modes

The study identifies six sub-basins with varying rates. The Eastern Bay of Bengal leads with a 5.15 mm/yr increase, whereas the Western Arabian Sea shows a lower 4.10 mm/yr rate. In the Eastern Equatorial Indian Ocean, a significant mass component suggests the 2004 Sumatra-Andaman earthquake caused lasting crustal adjustments. These fluctuations appear tightly linked to climate modes like the Indian Ocean Dipole and ENSO, which dictate year-to-year variability. The findings imply that coastal protection strategies must look beyond global ice-melt models to account for regional heat absorption. However, the study does not solve the uncertainty regarding how local coastal subsidence or vertical land movement might exacerbate these satellite-measured trends. As a preliminary report, these conclusions remain subject to rigorous validation.