A bottled message dated 1969 has washed up on an Australian beach, Sky News reported. Its author, a Briton named Paul Gilmore, has also been located, after the message was posted on Facebook and went viral. Oceanic currents perform many natural wonders.
Paul Gilmore’s family moved from England to Australia via a ship when he was 13 years old, according to the Sky News article. He wrote a half-dozen messages along the way and sealed them in bottles, casting them into the ocean, complete with a return address. Now, after a half-century, one of them has been found by a man named Paul Elliott and his son, Jyah, after it washed up on Talia Beach in South Australia. Oceanic currents are responsible for some of the greatest features of our world. But how?
Surface Currents and Gyres
There are two kinds of water currents that cause water circulation around the globe—surface currents and deep currents. “The currents that most of us are familiar with on a day-to-day basis are what we would call ‘wind-driven’ or ‘surface’ currents—that is, the act of the wind, driving along the surface of the water, pulls some of the water with it in a shearing action,” said Dr. Sean K. Todd, the Steven K. Katona Chair in Marine Sciences at the College of the Atlantic in Bar Harbor, Maine. “Surface water is dragged by these surface winds in directions that are more or less parallel to the wind.”
Dr. Todd explained that as different parts of our planet are barraged with heat and radiation from the Sun, they deflect it to varying levels of success. The equator has solar winds shot directly at it, while areas to the north and south more effectively experience solar winds drifting along them. When combined with the rotation of the Earth, they create global wind currents that collide in places like the north Atlantic Ocean and churn the water into enormous surface currents that flow clockwise. These gentle, ocean-sized surface currents are called gyres. The familiarly named “Gulf Stream” that flows north along the East Coast of the United States is merely one side of the massive North Atlantic gyre.
Deep Currents and Thermohaline Circulation
Another immeasurable impact oceanic currents have on our lives is that of thermohaline circulation, which regulates heat levels around the globe—although it happens in such deep currents that most of us will never see it. “Water has a high specific heat capacity, meaning it can absorb heat without changing too much in temperature,” Dr. Todd said. “As we’ve noted, heating of the Earth’s surface is uneven, with far more radiation received at the equator than at the poles. This heat is redistributed partly through air movement, but also through the movement of water cycling through the ocean depths.”
Dr. Todd explained that at both the North and South Poles, the ever-cooling waters become dense and sink to lower depths. There, it finds its way closer to the equator. At the same time, the denser, colder water is replaced at the poles by warmer water that has been carried along the surface from the equator with the aid of the previously mentioned wind currents. In this way, it redistributes heat throughout the ocean. “The name we give to this process is thermohaline circulation, but one of the circuits that’s created also has a more common name—that of the ‘global ocean conveyor,” he said.
Surface currents and gyres caused by solar winds played a clear role in delivering Paul Gilmore’s 50-year message to Paul and Jyah Elliott, but they only tell part of the story of oceanic currents. Thermohaline circulation and the global ocean conveyor are the other side of that coin. Only time will tell if Gilmore’s remaining messages will wash ashore.
Dr. Sean K. Todd contributed to this article. Dr. Todd holds the Steven K. Katona Chair in Marine Sciences at the College of the Atlantic in Bar Harbor, Maine. He received a Joint Honours undergraduate degree in Marine Biology and Oceanography from Bangor University in the United Kingdom and his master’s and doctoral degrees in Biopsychology at Memorial University of Newfoundland in St. John’s, Canada.