The Southern Ocean’s carbon sink gets stronger

Since 1750 Earth’s oceans have absorbed nearly 30% of anthropogenic carbon dioxide emissions. Although the Southern Ocean—the circumpolar waters surrounding Antarctica—occupies just a quarter of the total ocean area, it’s thought to be responsible for up to half of that uptake (see the article by Adele Morrison, Thomas Frölicher, and Jorge Sarmiento, Physics Today, January 2015, page 27). Air–sea fluxes of CO₂ are proportional to the difference Δp in partial pressure of the gas in the atmosphere and in the ocean. In 2007 flux estimates indicated that the Southern Ocean’s carbon sink had weakened in recent decades—a trend attributable to an intensification and southward shift of the westerly winds: The stronger the winds, the greater the upwelling of deep, carbon-rich waters. According to two new studies, the slowdown ended in 2002, and by 2012 the Southern Ocean had regained its expected strength, absorbing about 1.2 petagrams...