Short answers, pulled from the story.
The Southern Ocean overturning circulation operates as the southern half of Earth's global thermohaline system. This massive current connects water basins across the entire planet, linking with its better-known northern counterpart known as the Atlantic meridional overturning circulation.
Around 27 ± 7 Sverdrup of deep water wells up to the surface in the Southern Ocean. Observations suggest that approximately 80 percent of global deep water is upwelled in the Southern Ocean.
Harald Sverdrup already wrote about this phenomenon in his 1933 research on vertical circulation in the ocean due to wind action within the Antarctic Circumpolar Current. This pathway allows water to move without the expected turbulent mixing that models previously predicted would occur.
The Southern Ocean plays the greatest role in carbon uptake among all oceans, responsible for around 40% of human-caused emissions absorption. Deep water brings dissolved carbon concentrations much lower than modern surface waters before being transported back to depths.
Since the 1970s, the upper cell has strengthened by 3, 4 sverdrup representing 50, 60% of its flow while the lower cell weakened by a similar amount but represents only 10, 20% weakening due to larger volume. Greater warming increases ice loss from Antarctica generating more fresh meltwater at a rate of 1100, 1500 billion tons per year.