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In each of the three main ocean basins, dense water from around Antarctica circulates in the bottom layers, and in the Atlantic ocean, an upper circulation cell that is driven from the north caps the bottom loop.

Credit: © AMS

Averaged along parallels to the equator, the world oceans circulate from pole to pole in two giant vertically stacked loops, finds an inverse modelling study. The upper circulation cell extends to about 2,000 m in depth and connects waters sinking in the northern subpolar regions to water rising in the Southern Ocean. The second loop snuggles up underneath, with water sinking to the bottom around Antarctica and rising on its way north along the basins' rough seafloor.

Rick Lumpkin of the National Oceanic and Atmospheric Administration, Miami, and Kevin Speer of Florida State University used an inverse ocean model — that is, a model that finds the best-fitting circulation pattern given our incomplete knowledge of ocean flows and the exchange between ocean and atmosphere¹. They fed the model with global data on wind as well as heat exchange with the atmosphere, and with the ocean flow data from the World Ocean Circulation Experiment, obtained between 1985 and 1996.

The two-cell global circulation pattern that the model returns differs between the Atlantic and the Indo-Pacific oceans: the upper cell is much more prominent in the Atlantic Ocean.