Post #4692

Climate Models Missed Something Big About the Southern Ocean. The Truth Is More Worrying Climate projections have long indicated that global warming might weaken the Southern Ocean’s capacity to absorb carbon dioxide (CO2). Yet, long-term measurements reveal that this crucial ability has remained largely unchanged in recent decades. A new study by scientists at the Alfred Wegener Institute (AWI) offers insight into why this might be the case. For many years, low-salinity water near the ocean’s surface has helped trap carbon in the deep sea, preventing it from escaping back into the atmosphere. However, climate change is now disrupting this balance and altering how effectively the Southern Ocean functions as a carbon sink. The findings are detailed in the journal Nature Climate Change. Oceans collectively take up about one quarter of the CO2 produced by human activity. Of that amount, the Southern Ocean alone accounts for roughly 40 percent, making it one of the planet’s most important regions for slowing global warming. Its powerful influence stems from the region’s unique circulation patterns. Deep waters rise to the surface, exchange gases with the atmosphere, and then sink again, carrying newly absorbed CO2 into the depths. “Previous studies suggested that global climate change would strengthen the westerly winds over the Southern Ocean, and with that, the overturning circulation too,” says Léa Olivier. “However, that would transport more carbon-rich water from the deep ocean to the surface, which would consequently reduce the Southern Ocean’s ability to store CO₂.” Although strengthening winds have already been observed and attributed to human-made change in recent modeling and observational studies, there is no evidence pointing to the Southern Ocean absorbing less CO₂ – at least at this point. Long-term observations by the AWI and other international research institutes suggest that climate change may be affecting the properties of surface and deep water masses. The Southern Ocean’s surface water salinity has reduced as a result of increased input of freshwater caused by precipitation and melting glaciers and sea ice. This “freshening” reinforces the density stratification between the two water masses, which in turn keeps the CO₂-rich deep water trapped in the lower layer and prevents it from breaking through the barrier between the two layers. Source:SciTechDaily @EverythingScience