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...
Oceans losing oxygen at unprecedented rate, experts warn

Oceans losing oxygen at unprecedented rate, experts warn

SOURCE: The Guardian DATE: December 7, 2019 SNIP: Oxygen in the oceans is being lost at an unprecedented rate, with “dead zones” proliferating and hundreds more areas showing oxygen dangerously depleted, as a result of the climate emergency and intensive farming, experts have warned. Sharks, tuna, marlin and other large fish species were at particular risk, scientists said, with many vital ecosystems in danger of collapse. Dead zones – where oxygen is effectively absent – have quadrupled in extent in the last half-century, and there are also at least 700 areas where oxygen is at dangerously low levels, up from 45 when research was undertaken in the 1960s. All fish need dissolved oxygen, but the biggest species are particularly vulnerable to depleted oxygen levels because they need much more to survive. Evidence shows that depleted levels are forcing them to move towards the surface and to shallow areas of sea, where they are more vulnerable to fishing. Some ocean areas are naturally lower in oxygen than others, but these are even more susceptible to damage when their oxygen levels are depleted further, the report’s authors said. Species that can more easily tolerate low oxygen levels, such as jellyfish, some squid and marine microbes, can flourish at the expense of fish, upsetting the balance of ecosystems. The natural oceanic cycles of phosphorus and nitrogen are also at risk. The world’s oceans are already being overfished, and assailed by a rising tide of plastic waste, as well as other pollutants. Seas are about 26% more acidic than in pre-industrial times because of absorbing the excess carbon dioxide in the atmosphere, according...
Atlantic Ocean ‘running out of breath’

Atlantic Ocean ‘running out of breath’

SOURCE: BBC DATE: June 18, 2019 SNIP: A huge international research programme has been launched to assess the health of the Atlantic Ocean. The iAtlantic project is the biggest ever mounted in the planet’s second largest ocean.It involves more than 30 partners, funded by the EU, and is being co-ordinated by Edinburgh University. The scientists will use an array of hi-tech devices, including robot submarines, to scan the deep ocean from the Arctic to South America. They want to assess the effects of climate change on plants and animals. “What will happen to these animals in the future as the Atlantic changes?” Prof Roberts says. “As it gets warmer, as it gets more acidic and also – in some areas – as it runs out of breath. “Because the Atlantic, like many ocean basins in the world, is being deoxygenated – it’s losing the oxygen that is vital to life.” The cause is climate change, 90% of the world’s global warming has been absorbed by the...