Voyager: Does water from the California coast ever become water in the Atlantic Ocean?

The simple answer is yes when describing general, large-scale circulation of the oceans.  However, the actual amount of water that might reach the Atlantic Ocean is very small since there are so many possible pathways for water to take along the way.

California coastal water mixes and remixes as it joins near shore circulation. This can then move some water out into the larger-scale coastal currents, eventually joining the southward California Current along the coastline. From there the water would go westward across the North Pacific in the North Equatorial Current. At the Philippines, the water would turn southward into the Mindanao Current.

This flow would continue through the Indonesian Islands, across the Indian Ocean, moving west to Madagascar. The water would continue south and then head west where it would join the Agulhas Current that takes the water around Africa and then northward into the South Atlantic.

The total time for the water to make this trip would probably be about 100 years, which is longer than a direct path because along the route there are lots of eddies, whirlpool-like swirls that can redirect flows of water, to navigate around.

It’s important to note that the water changes as it goes along, mixing with other water types, which affects properties such as temperature and salinity. This example describes California coastal water, which is a warm, shallow part of what’s often called the “global conveyor belt.” At every juncture along the path, however, the water has other directions it can go such as northward into a different current or subsurface where the path would be even longer and less likely to reach the Atlantic Ocean.

— Lynne Talley,  physical oceanographer, Climate, Atmospheric Science, and Physical Oceanography division