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...
Scientists Urge Immediate, Decisive Action to Tackle Deoxygenation in Oceans

Scientists Urge Immediate, Decisive Action to Tackle Deoxygenation in Oceans

SOURCE: IISD DATE: September 13, 2018 SNIP: According to UNESCO-IOC, oxygen has decreased by two percent in the world’s oceans over the past 50 years, and the volume of oxygen-depleted water has grown fourfold. The reasons for this deoxygenation include increasing global warming and over-fertilization of the oceans, which leads to algae blooms and increased depletion of oxygen through biomass degradation. These changes are further expected to change feedbacks in the atmosphere as greenhouse gases (GHGs), including methane and nitrous oxide, form in the oxygen-free water. Over 300 scientists from 33 countries issued a declaration calling for more marine and climate protection in order to urgently tackle the decline of oxygen in the world’s oceans. The scientists urge increased international efforts to enhance global awareness of oxygen depletion, immediate and decisive action to limit marine pollution and decisive climate change mitigation actions to limit global warming. The ‘Kiel Declaration’ states that oxygen in the ocean “supports the largest ecosystems on the planet,” and expresses alarm that the ocean is losing oxygen, primarily as a result of GHG emissions and pollution by nutrients and organic waste. The Declaration recognizes that both the Paris Agreement on climate change and the 2030 Agenda for Sustainable Development “demand conservation and sustainable use of the ocean, seas and marine resources,” but stresses that these aims are “severely threatened by ocean...
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...