Our Changing Oceans

The relationship between people and Earth’s oceans is long and deep; we depend on them for a stable climate, oxygen, food, travel, recreation, and resources. But that relationship is getting more complicated. Human activity increasingly threatens ocean ecosystems and marine life, while human-induced climate change is causing the oceans to encroach on land, threatening coastal communities.

At the Linda N. Cabot Science Symposium at the Radcliffe Institute, “From Sea to Changing Sea,” held at the Knafel Center, scientists from a wide range of disciplines drew a portrait of oceans in flux. They discussed the history of the oceans and the diverse life they hold, the role they play in the global climate system, and the sobering science of how climate change will impact life in the sea and on land.

The Evolution of Oceans

Life on Earth depends on the oceans that blanket three-quarters of its surface.

They began forming nearly four billion years ago, as the hot, churning planet cooled. “What was this ancient ocean like?” asked David Emerson, a senior research scientist at the Bigelow Laboratory for Ocean Sciences, in Maine. He has found clues in ancient sea floors, such as layers of iron-rich rock that may have been laid down by primitive microbes that used iron and light for energy.

Eventually, microbes called cyanobacteria developed the ability to perform photosynthesis with water, sunlight, and carbon dioxide, producing oxygen. This process created our current atmosphere and was “the most important evolutionary adaptation that we know of,” Emerson said.

Over time, complex organisms emerged. “Our ocean isn’t one homogenous bucket of soup; it’s an environment that has many habitats within it,” said Peter Girguis, a professor of organismic and evolutionary biology at Harvard. Near the ocean’s surface, organisms must cope with variable light and temperature. In the deep ocean, the environment is more stable, but it’s one that we would hardly recognize: dark, still, and under intense pressure, giving rise to diverse sponges, squids, fish, and soft-bodied seafloor organisms.

Can this great diversity continue to evolve and to thrive in oceans altered by human activity? Unfortunately, Girguis said, evolution is usually very slow, and “most organisms today are not really poised to respond to the rapid change in our environment.”

Climate Control

Ocean water and ice help stabilize our climate, and this system is being altered by an unprecedented increase in carbon dioxide levels and global temperatures, largely from the burning of fossil fuels. The polar ice sheets in Greenland and Antarctica have waxed and waned over Earth’s history, explained Maureen Raymo, the director of the Lamont-Doherty Core Repository at Columbia University. But human activity is changing the system beyond this natural variability. While the ultimate impact will depend on the actions of governments and citizens, seas may rise by four feet or more by the end of this century. “Five million people live within four feet of sea level in the US today,” she said. “There’s a huge amount of real estate that is in this zone of risk.”

Warming has already dramatically changed the Arctic, explained Rebecca Woodgate, the senior principal oceanographer at the University of Washington. Ocean passages that were once dangerous or impossible for ships are now open to luxury cruises. “We are left with only 30 percent of the ice we used to have in the summer decades ago,” she said, and the ice has thinned.

Our oceans have also been serving as a buffer against rapid climate change. “The ocean is really helping us out,” said Lynne Talley, a distinguished professor at Scripps Institution of Oceanography at the University of California, San Diego. It has absorbed about 30 percent of the carbon dioxide that humans have emitted, and about 90 percent of the excess heat added to the planet.

Impacts of Change

These changes will be felt in New England. As Radcliffe Institute Dean Lizabeth Cohen noted at the start of the day, “The coastline is literally right at our doorstep, so concerns about rising sea levels hit very close to home.”

Sea-level rise is not uniform; because of gravitational effects and subsiding land, it will be more acute here than in other parts of the world, said Ellen Douglas, an associate professor of hydrology at the University of Massachusetts Boston. Meanwhile, storms are expected to become more common, and rising seas will exacerbate flooding. Simple flood maps fail to account for real-life storm patterns, so Douglas’s team has modeled the effects of future floods on Boston’s infrastructure to give government agencies a better idea of the city’s vulnerabilities.

Over the past decade or so, the Gulf of Maine “warmed faster than 99 percent of the global ocean,” said Andrew Pershing, the chief scientific officer at the Gulf of Maine Research Institute. One of the major casualties of that change is New England’s cod fishery. Overfishing played a role in plummeting fish stocks, but warmer waters have made recovery challenging.

“We’re not only warming the atmosphere and the oceans, but we’re also changing the chemistry of the oceans in specific and measurable ways,” said Anne L. Cohen, an associate scientist at Woods Hole Oceanographic Institution. High levels of carbon dioxide make the ocean more acidic, which reduces the amount of calcium carbonate available to marine organisms to construct skeletons and shells. Coral bleaching is a well-known effect of ocean acidification, but economically important creatures such as mussels and sea scallops are also at risk.

Greenhouse gases are not the only means by which humans impact ocean life, however; the very sounds we make can be disruptive underwater. Christopher Clark, the founding director of the Bioacoustics Research Program at Cornell University, recounted his discovery decades ago of the hidden world of long-distance communication by Southern right whales. These and other marine animals depend on sound to maintain relationships. “Acoustics is their world,” he said. Humans, too, use underwater sound for communication, navigation, and defense, and we’re creating a dangerous din through shipping and oil and gas exploration.

These findings highlight the need for policies that can balance human interests with environmental protection. Rear Admiral Steven D. Poulin, commander of the First Coast Guard District, finished the day with a look at the complexities of policing and protecting the oceans. “We must ensure that we are good stewards of our oceans and that we do all we can to ensure sustainability. That stewardship will require collaboration between countries and across domains of science and government.”

Courtney Humphries is a freelance science writer.