Low oxygen conditions on coral reefs could intensify by up to 287% by 2100: Study – Times of India

NEW DELHI: Using climate models, scientists have predicted a substantial increase in cases of hypoxia, or lack of oxygen, on coral reefs by 2100 under all warming conditions. According to them, the increase ranges from 13 to 42 percent under one scenario, and from 97 to 287 percent under the more extreme scenario.
Researchers say hypoxia is likely to become more common as global temperatures continue to rise and ocean heat waves become more frequent and intense.
An international team of researchers led by the Scripps Institution of Oceanography at the University of California San Diego, US, captured the current state of hypoxia at 32 different locations around the world and revealed that hypoxia has already spread to many reefs. Is.
Although oceanic deoxygenation, the overall reduction of oxygen content in the world’s oceans and coastal waters, has been well documented, hypoxia on coral reefs has been relatively little explored.
Loss of oxygen in the ocean is predicted to threaten marine ecosystems globally, although more research is needed to better understand the biological effects on tropical corals and coral reefs.
The study claims to provide an unprecedented examination of oxygen loss on coral reefs worldwide under ocean warming. It was published in the journal Nature Climate Change.
The authors found that hypoxia is already occurring in some reef habitats, and is expected to worsen if ocean temperatures continue to warm due to climate change.
They also used models of four different climate change scenarios to project that ocean warming and deoxygenation would substantially increase the duration, intensity, and severity of hypoxia on coral reefs by the year 2100.
The analysis was led by a marine scientist Ariel Pizner When she was a Ph.D. Scripps Oceanography..
Pizner and colleagues used independent sensor data to explore oxygen variability and exposure to hypoxia at 32 diverse reef sites in 12 locations in Japan, Hawaii, Panama, Palmyra, Taiwan, and elsewhere. These sensors measured temperature, salinity, pH and oxygen levels every 30 minutes.
Historically, hypoxia has been defined by a very specific oxygen concentration cutoff in water – less than two milligrams per liter (mg/L) – a limit set in the 1950s.
The researchers noted that a universal threshold may not apply to all environments or all reefs or all ecosystems, and therefore, they explored the possibility of four different hypoxia thresholds: weak (5 mg/L), mild ( 4 mg/L), moderate (3 mg/L), and severe hypoxia (2 mg/L).
Based on these thresholds, they found that more than 84 percent of the reefs in the study experienced “weak to moderate” hypoxia and 13 percent experienced “severe” hypoxia at some point during the data collection period.
As the researchers expected, oxygen was lowest in the morning and highest in the mid-afternoon at all sites, as a result of nighttime respiration and daytime photosynthesis, respectively.
During the day when the primary producers on the reef have sunlight, they photosynthesize and produce oxygen, Pizner said.
But at night, when there is no sunlight, there is no oxygen production and everything on the rock is respiring, breathing in oxygen and exhaling carbon dioxide. This results in an oxygen-poor atmosphere, and sometimes sinks into hypoxia.
“This is a normal process, but as ocean temperatures rise, seawater holds less oxygen while the biological demand for oxygen increases, which exacerbates this hypoxia at night,” said the study’s senior author, BioGeo. said the chemist. Andreas AndersonScripps Oceanography.
“Imagine you’re a person who’s used to sea level conditions, and then every night you have to sleep somewhere in the Rocky Mountains, where the oxygen in the air is low.
“It’s similar to what these corals do at night and early in the morning when they’re exposed to hypoxia,” Anderson said.
“And in the future, if these hypoxic events increase in duration and intensity, it could be like sleeping on Mount Everest every night,” Anderson said.
Establishing baseline conditions will be “must” through continuous and additional oxygen measurements on coral reefs over different seasons and long time scales, as a single definition of ‘hypoxia’ may not fit all environments.

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