Recent articles and social media posts inaccurately summarized findings from a June 2025 PNAS paper by claiming that a ‘major current in the Southern Ocean has reversed’. In reality, the PNAS paper does not mention any ‘ocean current reversal’. Instead, the paper mentions a ‘reversal’ of a decades-long trend: the Southern Ocean’s surface is now becoming saltier, instead of ‘fresher’. A saltier ocean surface can speed up the melting of Antarctic sea ice – floating ice which surrounds Antarctica – by drawing heat in the ocean upward toward the ice. This trend surprised scientists in the study, given that prior observations show the Southern Ocean’s surface becoming fresher (less salty) since the 1980s.

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Figure 1 – Plot showing that sea ice began retreating around 2015 when the Southern Ocean’s surface became saltier, as shown by the red line representing sea surface salinity (SSS) anomalies obtained via satellite. Source: Silvano et al. (2025)^[1]

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