We May Have Gravely Underestimated The Threat of ‘Dead Zones’ in The World’s Oceans

We May Have Gravely Underestimated The Threat of ‘Dead Zones’ in The World’s Oceans

SOURCE: Science Alert DATE: December 14, 2019 SNIP: Scientists call them ‘dead zones’: vast expanses of ocean water that contain little or no oxygen, making it almost impossible for many marine life-forms to survive within them. These giant ecological hazards – which have dramatically expanded in both number and volume in recent decades – are now extending beyond the sea into freshwater sources on land, and according to a new study, we may have underestimated the size of the problem. The conventional view on dead zones (aka oxygen minimum zones [OMZs] and sometimes also called ‘shadow zones’) is that their hypoxic conditions are produced when excess nutrient pollution from human activities flows into coastal waters, encouraging the growth of algae blooms, which in turn decompose into organic material that sinks to the seafloor. As that organic material slowly plummets into the abyss, it attracts and consumes oxygen in a process that deprives marine life of the same vital resource. This overall process is viewed as the primary cause of dead zones, but there could be another important factor behind the problem that we’ve overlooked until now, according to an international team of researchers led by biogeochemist Sabine Lengger from the University of Plymouth, UK. “Our study shows that organic matter that sinks to the seafloor is not just coming from the sea surface, but includes a major contribution from bacteria that live in the dark ocean and can fix carbon as well,” Lengger says. “Existing models could be missing out on a key contribution as a result of which people have underestimated the extent of the oxygen depletion we...
The Ocean Is Losing Its Breath

The Ocean Is Losing Its Breath

SOURCE: Scripps Institution of Oceanography DATE: January 4, 2018 SNIP: In the past 50 years, the amount of water in the open ocean with zero oxygen has gone up more than fourfold. In coastal water bodies, including estuaries and seas, low-oxygen sites have increased more than 10-fold since 1950. Scientists expect oxygen to continue dropping even outside these zones as Earth warms. To halt the decline, the world needs to rein in both climate change and nutrient pollution, an international team of scientists including Lisa Levin, a biological oceanographer at Scripps Institution of Oceanography at the University of California San Diego, asserted in a new paper published Jan. 4 in Science. In areas traditionally called “dead zones,” like those in Chesapeake Bay and the Gulf of Mexico, oxygen plummets to levels so low many animals suffocate and die. As fish avoid these zones, their habitats shrink and they become more vulnerable to predators or fishing. But the problem goes far beyond “dead zones,” the authors point out. Even smaller oxygen declines can stunt growth in animals, hinder reproduction and lead to disease or even death. It also can trigger the release of dangerous chemicals such as nitrous oxide, a greenhouse gas up to 300 times more powerful than carbon dioxide, and toxic hydrogen sulfide. While some animals can thrive in dead zones, overall biodiversity falls. Climate change is the key culprit in the open ocean. Warming surface waters make it harder for oxygen to reach the ocean interior. Furthermore, as the ocean as a whole gets warmer, it holds less oxygen. In coastal waters, excess nutrient pollution from land...
Ocean oxygen decline greater than predicted

Ocean oxygen decline greater than predicted

SOURCE: Climate News Network DATE: May 10, 2017 SNIP: US scientists who have been warning that warmer oceans are more likely to be poorer in dissolved oxygen have now sounded the alarm: ocean oxygen levels are indeed falling, and seemingly falling faster than the corresponding rise in water temperature. That colder water can hold more dissolved gas than warmer water is a commonplace of physics: it is one reason why polar seas are teeming with marine life and tropical oceans are blue, clear and often relatively impoverished. In 2013, an international consortium of marine scientists warned that oxygen levels in the oceans could fall by between 1% and 7% by the century’s end. And this could, other scientists predicted, lead to what they politely called “respiratory stress” “The trend of oxygen falling is about two to three times faster than what we predicted from the decrease of solubility associated with ocean warming,” says Takamitsu Ito, of the School of Earth and Atmospheric Sciences at the Georgia Institute of Technology, who led the...
Carbon pollution is suffocating ocean life and speeding up the next mass extinction

Carbon pollution is suffocating ocean life and speeding up the next mass extinction

SOURCE: Think Progress DATE: May 8, 2017 SNIP: Depletion of dissolved oxygen in our oceans, which can cause dead zones, is occurring much faster than expected, a new study finds. And by combining oxygen loss with ever-worsening ocean warming and acidification, humans are re-creating the conditions that led to the worst-ever extinction, which killed over 90 percent of marine life 252 million years ago. Scientists have long predicted that as carbon pollution warms the globe, the amount of oxygen in our oceans would drop, since warmer water can’t hold as much dissolved gas as colder water. But what is especially worrisome about this new research is how quickly it is happening. “The trend of oxygen falling is about two to three times faster than what we predicted from the decrease of solubility associated with the ocean warming,” said lead researcher Prof. Taka Ito. “This is most likely due to the changes in ocean circulation and mixing associated with the heating of the near-surface waters and melting of polar...