In this article published in Nature Climate Change, Zhetao Tan reveals that changes in the ocean are occurring even faster than we thought and that vast regions of the global ocean are now undergoing simultaneous transformations—warming, changes in salinity, oxygen depletion, and acidification. These combined changes, observed at depths of up to 1,000 meters, indicate that the ocean is entering a new climate state.

Between 30% and 40% of the upper layers already show significant changes in at least two key properties. Some areas are reaching alarming levels, with a quarter of the ocean affected by multiple changes at the same time.

The most affected regions include the tropical and subtropical Atlantic, the North Pacific, the Arabian Sea, and the Mediterranean. These changes threaten ecosystems, fisheries, food security, and the ocean’s ability to absorb heat and carbon.

Zhetao Tan’s work develops a new analytical tool that can now detect these critical zones and help policymakers guide ocean protection policies.

Reference: Tan, Z., K. von Schuckmann, S. Speich, L. Bopp, J. Zhu, and L. Cheng. Observed large-scale and deep-reaching compound ocean state changes over the past 60 years. Nature Climate Change, 2025. https://doi.org/10.1038/s41558-025-02484-x