John Guinotte (left), and his brother
Carbon dioxide emissions are causing the oceans to become more acidic, posing a threat to the entire marine ecosystem.
Beachgoers escaping the city's summer heat at this time of year no doubt feel grateful for the ocean. But John Guinotte, a coral specialist at the Marine Conservation Biology Institute in Bellevue, Washington, likes to remind us all how vital the oceans are to life on the planet in ways we don't usually think about. For instance, he notes that the ocean's phytoplankton—the microscopic plant organisms that serve as the base of the aquatic food chain—produce roughly two thirds of the oxygen we breathe. And, by absorbing roughly a third of all the carbon dioxide that humans have been adding to the atmosphere by burning fossil fuels, the oceans have so far managed to slow the buildup of heat-trapping gases in the atmosphere, thereby staving off even more dramatic warming of the planet.
But as Guinotte and his colleagues are discovering, that boon—the oceans' role as a "carbon sink"—comes at a potentially devastating cost: the oceans are becoming more acidic. So far the effects have remained largely out of the public eye. But Guinotte says the changes in ocean chemistry that he sees are great enough to keep him awake at night and may prove to be among the most devastating effects of ever-increasing levels of CO2 in the atmosphere.
Ocean acidification, he explains, spells particular trouble for the coral that he studies closely. And if that process continues on its current trajectory, it poses a dire threat to the whole marine ecosystem. "What I'm really concerned about with ocean acidification," Guinotte says, "is that we are facing the prospect of a crash in marine food webs. There is no question that many of my colleagues in marine science are scared about what is happening. We know we need a more precise understanding of the changes and biological responses now under way— and we need it as quickly as possible, before it is too late to turn things around."
Guinotte has dedicated his life to the study of coral, especially the less well understood deep-sea varieties. He grew up in rural Kansas, so his only early exposure to corals was in the pages of National Geographic. But that changed when he visited his grandfather's winter home in the Florida Keys and learned to scuba dive. That experience, plus his interest in biology and geography, led him to continue his studies in Australia, where he earned a scholarship to pay for his Ph.D. research. He still remembers the thrill of exploring Australia's Great Barrier Reef for the first time. "I was absolutely blown away by the abundance and diversity of coral," he recalls. At that time, back in the late-1990s, scientists were increasingly concerned about coral bleaching caused by environmental stresses such as warming ocean temperatures. Those threats remain, Guinotte says, but ocean acidification may well prove to be an even more serious and intractable problem.
On the macro scale, Guinotte explains, the chemistry of ocean acidification is relatively clear. Scientists know from some 25 years' worth of measurements that the oceans absorb some 22 million tons of carbon dioxide every day via gas exchange between the air and the sea. Even given the vast scale of the oceans, this natural absorption is now occurring at an unprecedented rate and has led the chemistry of the oceans to approach conditions not seen in many millions of years. Many marine species might not be able to adapt quickly enough to survive these changes, Guinotte says.
As carbon dioxide is absorbed by seawater, he explains, the ensuing chemical reaction results in an increase in hydrogen ions, which lowers the ocean's pH, making the water more acidic. Measurements indicate that Earth's oceans are already about 30 percent more acidic than they were before the industrial revolution. As the number of hydrogen ions has risen, the number of carbonate ions available in seawater has also decreased, making it more difficult for the "marine calcifiers," such as coral and shellfish to build their skeletons and protective shells. In essence, "ocean water becomes increasingly corrosive to calcium carbonate. A reduction in carbonate ions not only impedes corals' ability to build their skeletons, but once the calcium carbonate drops below critical levels, the ocean erodes the framework they have built up previously—the reefs upon which corals live." Even if select coral species can survive ocean acidification, Guinotte says, when coral reefs begin to dissolve, the effects on the entire marine ecosystem are likely to be devastating.
One of the worst aspects of this scenario, Guinotte explains, is that scientists know from the fossil record that reefs have been heavily impacted by high carbon dioxide events in the geologic past, and it took them millions of years to recover. "Given that we need to think in human time scales, it means we're playing for keeps here. To me it sometimes seems like a school bus full of children heading for a cliff. Somehow we have to slow it down enough to find some real solutions."
Because of the very clear potential for ocean acidification to have widespread impacts on everything from the tiniest oxygen-providing phytoplankton to the larger fish that feed in the coral reefs—or, as Guinotte has written, "from the shallowest waters to the darkest depths of the deep sea"—the threat to humankind is one of immense proportions.
To figure out precisely how much ocean acidification many varieties of coral will be able to tolerate and what we can do to slow the seemingly inexorable trend enough to preserve the health of the marine ecosystem, Guinotte says we need to make a coordinated effort to research all aspects of the problem, including better monitoring of the carbon in the ocean to track spatial and temporal variations, closer tracking of the abundance of calcifying organisms, more laboratory and field studies of these organisms' physiological responses to increasingly acidic conditions, and more detailed studies modeling the threat to the marine ecosystem. Some of this work is now under way, but Guinotte points out that too much of it has been conducted in piecemeal fashion. Only a more intensive, coordinated effort, he says can provide the information that will allow policymakers to develop strategies to protect critical species, habitats, and ecosystems.
"From the standpoint of the oceans," Guinotte says, "there is no escaping the fact that we are going to need major reductions in our CO2 emissions—something like 80 to 90 percent. When we see governments arguing about reductions of 10 to 15 percent, I think all of us in the marine science community need to say that CO2 reductions of this scale are simply not going to be sufficient. We have to get off fossil fuels."
As he notes, some of his colleagues, such as J. "Charlie" Veron, who has studied coral for decades, have shown from the fossil record that high CO2 concentrations have likely played a big role in mass extinctions of marine life in the past. We know the direction in which we are headed, Guinotte says. "If marine systems start to crash, it may well be too late to stop the train. Governments are likely to panic and make irrational decisions; international tensions could certainly heat up. These are the kinds of things that keep me awake at night. I continue to hope we can get it turned around. But it will take political will, and so far, that has been in short supply. "