Thread by @NatGeo

Four oceans or five? It's #WorldOceansDay🌊 and National Geographic is making a change to recognize the Southern Ocean as a fifth official ocean in our atlases and maps! on.natgeo.com/2SmpJb3

I'm Alex Tait (@taitmaps), the Nat Geo Geographer! I work on @InsideNatGeo's mapping projects (including mapping Mount Everest), and I keep our Map Policy up to date

There is of course just one interconnected world ocean, but it has traditionally been divided into four regions: the Pacific, Atlantic, Arctic, and Indian oceans

Scientists have known for many years that the icy waters around Antarctica form a distinct ecological region defined by ocean currents and temperatures

But the international community, through the International Hydrographic Organization (IHO), has not agreed on a name and extent of this fifth ocean region

National Geographic is an important global source for the latest geographic knowledge, so without an official determination from IHO, we are updating our oceans list based on the science and the conventional acceptance of the Southern Ocean

Most scientists and IHO members use the name Southern Ocean, some use Antarctic Ocean, and some use Austral Ocean

The ecological boundary of the Southern Ocean follows a sinuous line around the Antarctic continent called the Antarctic Convergence or polar front

The northern limit of the Southern Ocean varies between about 50 and 62 degrees south latitude. We're using 60 south latitude as proxy for the Southern Ocean's northern ecological limit, this is used by NOAA in the US and by a plurality of members of the IHO

We're excited to bring attention to the Southern Ocean—and with it the richness of this marine ecosystem, which programs like @insidenatgeo's Pristine Seas initiative are working hard to protect on.natgeo.com/3pxuBGq

Our maps are updated. The Southern Ocean is treated the same as the traditional four, and the next quiz question about the number of oceans has an updated official answer from National Geographic—five!