An international team of scientists, leveraging pioneering satellite data processing algorithms developed by ICM-CSIC, has detected an unprecedented reversal in the Southern Ocean's deep circulation (SMOC) since 2016. This shift, marked by a sustained increase in surface salinity, causes deep, warmer, CO₂-rich waters to rise to the surface instead of sinking. The reversal is linked to accelerated sea ice melt and, as stated by the researchers, could potentially double atmospheric CO₂ concentrations by releasing centuries-trapped carbon, leading to severe global climate impacts and cascading effects on other circulation systems like the AMOC. However, the accompanying discussion highlights significant debate, with critics arguing the claim of "doubling atmospheric CO₂" is a severe exaggeration not supported by the original scientific paper, which does not mention CO₂. The discussion also raises questions about the definition of "unprecedented" given the novelty of the observational data.
Summary of the Transcript and Discussion:
Major Ocean Circulation Reversal: An international team has detected a reversal in the Southern Ocean's deep circulation (SMOC) since 2016, a phenomenon described as unprecedented.
Key Indicator: The reversal is identified by a sustained increase in surface salinity in the region between the polar and subpolar gyres of the Antarctic Ocean.
Mechanism: Instead of sinking, surface water is being replaced by deep water masses rising to the surface, bringing heat and carbon dioxide (CO₂) that had been trapped for centuries.
Stated Consequences (from news article): This upwelling is believed to drive accelerated melting of sea ice in the Southern Ocean and could potentially double current atmospheric CO₂ concentrations, with catastrophic global climate consequences and cascading effects on other circulation systems like the AMOC.
Technological Breakthrough: The discovery was made possible by new data processing algorithms for the European SMOS satellite, developed by the Barcelona Expert Center (BEC), an ICM-CSIC laboratory, which enabled unprecedented quality surface salinity data in the previously inaccessible Southern Ocean.
Importance of SMOC: The SMOC plays a crucial role in regulating the planet’s heat and carbon, and its disruption could impact global climate, including Europe.
Future Research: BEC has launched two new ESA-funded projects for 2025: ARCTIC-FLOW (Arctic Ocean freshwater/density fluxes) and CCI OSHF (Ocean Surface Heat Flux), to further monitor and understand these changes.
Controversy over CO2 Claims (Discussion): Several commentators dispute the claim that the reversal "could double current atmospheric CO₂ concentrations," calling it a significant exaggeration. They note the original PNAS paper does not mention CO₂ or carbon, focusing instead on upwelling, and that estimated carbon flux from deep-ocean outgassing is orders of magnitude smaller.
Nature of Deep Water: Discussion clarifies that the deep water is "warmer" and "saltier" relative to the surface water, not necessarily hot in an absolute sense, and the rising CO2 is from dissolved gas due to high pressure at depth, not "deep-ocean vents."
Novelty vs. Periodicity: Given that this is the first time such observations could be made in this region, some question whether the reversal is truly "unprecedented" or a natural, periodic phenomenon not previously observable.
Critique of Journalism: Concerns were raised about the news article's interpretation and potential for misleading information, contrasting it with the more conservative language of the scientific paper.
Broader Climate Implications (Discussion): The reversal is expected to expose ice shelves to warmer water (accelerating sea-level rise from land-based ice), reduce the Southern Ocean's role as a carbon sink, and potentially perturb atmospheric circulation patterns, with unknown downstream implications for other ocean currents. The discussion also touches on the likelihood of pessimistic climate estimates coming to pass and the societal implications of climate change.