Have you ever wondered how big the ocean is? For most of us, the vastness of the world and its ocean is hard to grasp. In some ways, we see the huge scope of the universe easier because we can look up into the dark sky and see millions and millions of stars. So when we talk about one ocean, we acknowledge the idea without really understanding it.
Comprehending really large numbers is difficult for almost everyone. Does anyone totally appreciate the national debt? What about a billion gallons of water? How about 5.5 billion gallons of water? That is the average amount of water that flows out of the St. Johns River every day.
And where does it go? How about into an ocean that contains 332,519,000 cubic miles of water (according to the USGS) with each cubic mile containing 1.1 trillion gallons? Talk about a number that is hard to grasp. That is a number with 18 zeros.
In an attempt to answer that age-old question: “Where in the world is water from the St. Johns River?” one of my colleagues at the Marine Science Research Institute had his Physical Oceanography classes launch what we term “drifters.” Drifters are designed to float just beneath the surface and to go with the flow of the water, and to not be so far out of the water that they sail with the wind. While currents and wind often go in the same direction, that is not always the case. The class built three and released them into the Atlantic Ocean at the mouth of the St. Johns River in February 2015. Each had a GPS unit attached that sent a signal to a satellite that allowed it to be tracked as long as the battery lasted.
Regretfully, two of them did not last very long. Both washed ashore, with one looking like it got hit by a ship. Meanwhile, one drifter built with a foam filler volleyball, named “Wilson” after the volleyball in the movie “Castaway,” headed south. Once it reached the Cape Canaveral area, it got caught in an “eddy,” or a circulating current, where it made a loop-to-loop before finally catching the Florida Current.
Water from the Florida Current flows out of the Gulf of Mexico, between Florida and Cuba, then heads north to Cape Hatteras, where it changes names and characteristics to become the Gulf Stream. So “Wilson” rode the current past Jacksonville and continued north, making a few loops as it went, until its battery died in August. “Wilson” was in the north Atlantic, off New England and Canada. Pretty amazing from something launched in February in the St. Johns River.
But “Wilson” was not done. Its batteries restarted and it sent signals that showed it had moved farther northeast to an area south of Greenland. “Wilson” now appears to be done, with the last signal sent right before Labor Day. But it served to demonstrate just how far water can flow when it leaves the St. Johns.
So where does water go when it leaves the St. Johns River? It can go literally anywhere in the world — not only in the oceanic currents, but it can also form clouds and thus rain or snow anywhere in the world. Turns out that the St. Johns River has a pretty far reach into that ocean where the number of gallons has 18 zeros.
ASK RIVER LIFE
How far upstream do we see measurable amounts of salt water in the St. Johns River?
Sea water has flowed farther up the St. Johns River in recent years. Because of dredging the St. Johns River, plus the reduction in flow from the springs that flow into the river as we pumped water from the aquifer, we have seen the salinity gradually increase south of Jacksonville. Historically we thought of the Main Street Bridge as where the river went from marine to fresh. Now, it is closer to the Buckman Bridge. Recognize, too, that the salinity changes with each tidal cycle and can vary drastically with rain and drought conditions.
River Life runs the last Friday of each month in The Florida Times-Union. E-mail A. Quinton White, executive director of Jacksonville University’s Marine Science Research Institute, with questions about our waterways at firstname.lastname@example.org. For more on the MSRI, visit ju.edu/msri.