Oceans: An Essential Global Resource
June 8 is World Oceans Day, a day to celebrate our world’s shared ocean and our personal connection to the sea, as well as to raise awareness about the crucial role the ocean plays in our lives and the important ways people can help protect it.
The world’s oceans – their temperature, chemistry, currents and life – drive global systems that make the Earth habitable for humankind.
Our rainwater, drinking water, weather, climate, coastlines, much of our food, and even the oxygen in the air we breathe, are all ultimately provided and regulated by the sea. Throughout history, oceans and seas have been vital conduits for trade and transportation.
Careful management of this essential global resource is a key feature of a sustainable future. The challenge of caring for our oceans is being taken up by people around the world.
Facts and Figures
Oceans cover three quarters of the Earth’s surface, contain 97 percent of the Earth’s water, and represent 99 percent of the living space on the planet by volume.
Over three billion people depend on marine and coastal biodiversity for their livelihoods.
Globally, the market value of marine and coastal resources and industries is estimated at $3 trillion per year or about five percent of global GDP.
Oceans contain nearly 200,000 identified species, but actual numbers may lie in the millions.
Oceans absorb about 30 percent of carbon dioxide produced by humans, buffering the impacts of global warming.
Oceans serve as the world’s largest source of protein, with more than 2.6 billion people depending on the oceans as their primary source of protein.
Marine fisheries directly or indirectly employ over 200 million people.
Subsidies for fishing are contributing to the rapid depletion of many fish species and are preventing efforts to save and restore global fisheries and related jobs, causing ocean fisheries to generate $50 billion less per year than they could.
As much as 40 percent of the world oceans are heavily affected by human activities including pollution, depleted fisheries and loss of coastal habitats.
Case Study: U.S. Coast Guard Rescues Sea Turtles
Last week, a law enforcement team from the U.S. Coast Guard Cutter Stratton sped to the scene of a suspicious object floating in a known drug transit zone in the Eastern Pacific Ocean. When the crew arrived at the scene, they found two sea turtles entangled in fishing line and make shift buoys.
“There was no question what we had to do. And no one spoke a word. We immediately moved in to rescue mode,” said Petty Officer 2nd Class Hylan Rousseau. The Coast Guardsmen on board the vessel removed green fishing line. One of the turtles had line wrapped around its neck, which restricted its airway causing apparent respiratory distress.
“We cut the first turtle free without much incident. While we were freeing him, we could see the second, and much larger turtle, was quite literally choking to death,” said Chief Petty Officer Brian Milcetich, a member of the law enforcement team. “He had been trying so hard to free himself from the fishing line that he had cinched the line around his own neck.”
After lifting the approximately 70-pound turtle on board, the delicate process began. A specialized pair of sheers normally used by emergency medical technicians was used to sever the line. Following the rescue, the crew stowed their gear and continued patrolling the area.
Case Study: Australia’s Humpback Whales
On ScienceNetworkWK Michelle Wheeler reports that humpback whales are facing pressure from both reduced food availability because of climate change and from being disturbed by mining and boats as they make their annual migration along Western Australia’s (WA) coast.
The impacts have recently been documented in two studies. In the first study, researchers used historical whaling data from Albany, Carnarvon and Point Cloates to examine the body condition of humpback’s caught in WA waters from 1947-1963.
They used oil yields as a proxy for whale body condition and found the whale’s fat content, or energy reserves, was highest when there was a lot of krill available. This in turn was associated with high sea ice cover in Antarctica the previous winter.
Whale researcher Janelle Braithwaite says the research is important in trying to assess climate change impact in the Southern Ocean in the future. “If there’s less sea ice then there’s going to be less food for whales,” she says.
“If there’s less food for whales, then our results indicate that the whales aren’t going to be as fat, and this is going to cause problems when it comes to trying to complete migration on their limited energy reserves as well as also reproducing.”
A second study led by Braithwaite used theoretical models to determine the optimal speed whales would travel and the ideal amount of rest they would have if they wanted to conserve energy.
The results closely mirrored what happens naturally in the wild, suggesting whale migration has evolved to conserve energy on the long journey, Braithwaite says. She says mining off the coast and boats in places like Exmouth Gulf and Shark Bay can disrupt these natural migration patterns.
“Human activities do have the potential to disrupt this energy conservation by disturbing [the whales] when they’re resting so they can’t rest for long enough, making them swim faster so they’re using more energy,” Braithwaite says.
Braithwaite says the two papers show humpbacks are facing new challenges, just as their numbers have begun to recover from whaling. “If you have a low krill year…and then they’re migrating and they encounter a lot of human activity, mining off the coast, lots of boats…they’re vulnerable to being exhausted and not being able to complete their migration and successfully reproduce.”
Case Study: Nitrous Oxide
Nitrous oxide is a potent greenhouse gas that can contribute to climate change and damage the ozone layer, but its cycling in and out of ocean waters has remained poorly understood.
New research by MIT postdoc Andrew Babbin and three others has provided a way to quantify its ocean cycling. The findings, based on computer analysis and sampling of ocean waters from different depths, show that this source of atmospheric nitrous oxide has been drastically underestimated. There have been a lot of estimates on what the sources and sinks are, both on land and in the ocean, Babbin says. But the new measurements show that in parts of the ocean, those estimates were off by at least a factor of 10.
A particular zone of the ocean — a boundary between oxygen-rich surface waters and oxygen-free, or anoxic, deep waters — plays a key role in nitrogen cycling. This suboxic zone experiences an imbalance between bacterial processes that create nitrous oxide and those that break it down — and the excess of nitrous oxide created by this imbalance is given off to the atmosphere.
Ocean nitrification begins with nitrogen entering the sea as runoff from agricultural fertilizers and other sources. Marine microbes take in nitrogen compounds, such as ammonia, and chemically modify them, releasing nitrous oxide as a byproduct. Other bacteria carry out denitrification, a process that breaks down nitrogen compounds through steps that ultimately lead to nitrogen gas — but which can also release some nitrous oxide.
Most of the time these processes balance out. “The denitrifying bacteria that produce nitrous oxide also consume it, and it was thought that these two processes are pretty tightly coupled,” Babbin says. But that’s not the case in the suboxic layer, resulting in leftover nitrous oxide that leaks away to the surface.
The research involved taking water samples from various depths at three different locations in the eastern tropical North Pacific, and then measuring these samples in the lab to determine their denitrification rates. The sampling region is one of three known to have extensive suboxic zones, Babbin says, along with the eastern tropical South Pacific and the Arabian Sea.
Babbin’s measurements demonstrate that production of nitrous oxide in just these three small regions could equal the total worldwide marine production that had been estimated in climate models, including the most recent International Panel on Climate Change report: some four million metric tons of nitrous per year. While that amount is dwarfed by carbon dioxide production, nitrous oxide is 300 times more potent as a greenhouse gas.
Anoxic regions of the ocean are expected to increase significantly in size, thus also expanding suboxic zones and their nitrous oxide production — which could amplify climate change. “These findings are highly significant,” says James Galloway, a professor of environmental sciences at the University of Virginia who was not involved in this research, “as they indicate that now the oceans can be expected to increase their nitrous oxide emissions, just as continents are expected to, due to agriculture.”