The meridional streamfunction in the Southern Ocean is dominated by the Deacon Cell, a large overturning cell of the magnitude 20 Sverdrups. We explain the nature of this cell by analysing particle trajectories calculated using the time-averaged velocity field produced by the global ocean model OCCAM. The respective contributions to the meridional streamfunction from three groups of trajectories are calculated: those that start at the northern boundary of the selected domain (28S) and end in the Drake Passage, those that start in the Drake Passage and end at the northern boundary, and those that start in the Drake Passage and return to the Drake Passage after encircling the Antarctica. Taken together, these three groups make up most of the Deacon cell.

When taken separately, the first two groups (starting or ending at the northern boundary) do not give any overturning cell in the meridional streamfunction. However, the superposition of these two contributions to the streamfunction give an overturning cell of about 10 Sverdrups, i.e. roughly half of the Deacon cell.

The remaining half is due to the third group, i.e. trajectories that both start and end in the Drake Passage. Much of their contribution to the meridional streamfunction is caused by the fact that the Antarctic Circumpolar Current (ACC) is particularly shallow in the northward stretch just after the Drake Passage. This results in an apparent overturning cell when projecting on the meridional plane. However, there is also at least 3.5 Sverdrups of real Lagrangian overturning. It is caused by the trajectories spiraling downward on the northern side of the ACC and upward on the southern side. This can be seen on a Poincare section, where consecutive intersections of trajectories with a vertical plane in the Drake Passage are plotted.