A Southern Ocean Hotspot of Subsurface Warming

• Post by: AntoninoIan Ferola
• July 1, 2026

A recent study investigated how the upper and intermediate layers of the Southern Ocean have changed over the last three decades along a repeated ship transect between New Zealand and Antarctica.

The Southern Ocean is a key component of the climate system. It connects the major ocean basins, absorbs large amounts of heat and carbon, and plays a central role in the formation and transformation of water masses that spread climate signals into the ocean interior. However, long-term observations in this region remain limited, especially in dynamically complex gateways of the Antarctic Circumpolar Current.

In this study, 30 years of summertime temperature profiles collected between 1994 and 2025 were used to reconstruct the thermal structure of the New Zealand-Antarctica sector and to quantify long-term temperature changes across the Antarctic Circumpolar Current. The analysis also identifies the main Southern Ocean water masses crossed by the transect, allowing the observed trends to be interpreted in relation to the regional water-mass structure.

Figure 1. Mean summer temperature, temperature variability and linear temperature trends along the ship transect between New Zealand and Antarctica. The black boxes indicate the climatological cores of the main water masses identified along the section.

The results show that warming is not spatially uniform. Significant subsurface warming emerges along the northern flank of the Antarctic Circumpolar Current, particularly within Subantarctic Mode Water and Antarctic Intermediate Water. These water masses are important pathways for transferring heat from the Southern Ocean into the ocean interior and toward lower latitudes. In contrast, waters located farther south, closer to Antarctica, show little or no long-term warming over the study period.

The strongest warming is concentrated in the last decade and mainly affects the northern water masses. This suggests that the New Zealand–Antarctica sector is an important hotspot of subsurface warming, where heat can be injected below the surface and carried into the ocean interior.

Reference:
Ferola, A. I., Cotroneo, Y., Castagno, P., Fusco, G., Falco, P., Budillon, G., et al. (2026). Emergence of subsurface warming in the Southern Ocean gateway between New Zealand and Antarctica. Geophysical Research Letters, 53, e2025GL121465.

For further details, refer to the full paper: https://doi.org/10.1029/2025GL121465