A drop of ocean water takes about 1,000 years to circle the entire planet

Earth's oceans are stitched together by one slow global circuit called the thermohaline circulation, driven by differences in water temperature and salinity rather than wind or tides. Cold, salty water sinks near Greenland and Antarctica and crawls along the seafloor for roughly a thousand years before resurfacing in the Pacific and Indian Oceans. Oceanographer Wallace Broecker popularized it as the planet's 'great ocean conveyor belt' and linked it to abrupt past climate swings.

— Wallace S. Broecker, The Great Ocean Conveyor — Oceanography, Vol. 4, No. 2, 1991