By Jim Steele
Why did such major coral bleaching occur during the El Niño event?
During an El Niño, warm water stored in the Pacific warm basin of the Coral Triangle sloshes eastward, lowering water temperatures in the western Pacific and raising temperatures in the eastern Pacific, as shown by the temperature anomalies in Figure A.
It also shifts convection centers eastward from the more westerly positions during La Niña and neutral conditions. The resulting changes in air circulation cause downward airflow typical of heat domes and clearer skies over the western Pacific, Atlantic, and Caribbean. This leads to more intense solar radiation and coral light stress in these regions.
Because of the biochemistry that controls photosynthesis, high light stress leads to increased production of dangerous oxidants (also known as ROS: Reactive Oxygen Species). Dangerous oxidants damage living tissue, which is why all organisms naturally produce and absorb antioxidants. So when coral's symbiotic algae produce too many ROS and overwhelm a coral's natural antioxidant systems, the coral sheds its symbiotic algae to prevent further damage, and that leads to coral bleaching.
As peer-reviewed science explains,
“The most likely explanation for the most common form of mass coral bleaching is the production of reactive oxygen species associated with photosystem I of photosynthesis (and to some extent photosystem II): namely superoxide (O2-), hydrogen peroxide (H2O2) and singlet oxygen.”
See “A review: The role of reactive oxygen species in mass coral bleaching Szabó (2020)
Alarmist scientists with a global warming agenda (e.g. Hughes or Hoegh-Guldberg) always tell the clickbait media the same story, namely that global warming is the main cause of coral bleaching. However, increased solar radiation causes both severe light stress and heat stress, and heat stress can reduce the effectiveness of coral antioxidant protection. So both excessive heat and light can increase the accumulation of ROS.
What is the main cause? Unfortunately, studies have rarely satisfactorily separated the two factors. But the studies that have done so suggest that light stress is the main factor. Read for example: Antioxidant responses to heat and light stress differ by habitat in a common reef coral Hawkins (2015). For the species Stylophora pistillata they state:
“Overall, changes in the symbionts' enzymatic antioxidant activity were primarily caused by irradiance rather than temperature, and responses were similar across depth groups. Taken together, our results suggest that in the absence of light stress, warming from 1°C/day to 4°C above ambient temperature is not sufficient to induce significant oxidative stress.”
Thus, regions of reduced cloud cover during El Niño events correlate with the so-called 'global' bleaching events that occurred in 1998, 2010, 2014–2017, and now 2023–24. Accordingly, large El Niño events occurred in the eastern Pacific in 1997–98, 2014–16, and 2023–24, and a Modoki El Niño in 2009–2010. As can be seen from the white circles in Figure B, the bleaching mortality rate during the 2023–24 El Niño is associated with regions in the Caribbean, Gulf of Mexico, and western Pacific, where El Niño caused atmospheric subsidence and reduced cloud cover, increasing light stress.
The alarmists who seek power cannot control solar radiation, but they want to control the population's energy consumption. So they unscientifically blame global warming for coral bleaching as proof that rising CO2 levels are killing corals! Alarmists deny science!
Like this:
Is loading…
