By Jim Steele
Why have major coral bleaching events occurred during EL Nino events?
During an El Nino, warm water stored in the Pacific Warm Pool of the Coral Triangle sloshes eastward. That lowers the ocean temperatures in the western Pacific and raises temperatures in the eastern Pacific as seen in the temperature anomalies of illustration A.
It also shifts the centers of convection from the more westerly positions during La Nina and neutral conditions and moves them eastward. The resulting changes in atmospheric circulation cause downward air flow typical of heat domes and clearer skies over the western Pacific and Atlantic Ocean and Carribean. That causes more intense solar radiation and coral light stress those regions.
Due to the biochemistry governing photosynthesis, high light stress causes the increased production of dangerous oxidants (aka ROS: Reactive Oxygen Species). Dangerous oxidants damage living tissues, which is why all organisms naturally produce and ingest anti-oxidants. So, when corals’ symbiotic algae produce too much ROS and overwhelms a coral’s natural anti-oxidant systems, to prevent further damage, the coral eject their symbiotic algae and that causes bleaching.
As peer reviewed science explains,
“The most likely explanation to the commonest form of mass coral bleaching involves 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 (i.e. Hughes, or Hoegh-Guldberg) always tell click-bait media the same narrative, that global warming is the main cause of bleaching. But increased solar radiation creates both high light stress and heat stress and heat stress can affect the efficiency of the corals’ antioxidant protection. So, both excess heat and light can increase the accumulation of ROS.
Which is the primary cause? Unfortunately rarely have studies satisfactorily separated the two factors. But those that have suggest light stress is the main factor. For example read: Antioxidant responses to heat and light stress differ with habitat in a common reef coral Hawkins (2015). For the species Stylophora pistillata they state,
“Overall, changes in enzymatic antioxidant activity in the symbionts were driven primarily by irradiance rather than temperature, and responses were similar across depth groups. Taken together, our results suggest that in the absence of light stress, heating of 1C/day to 4C above ambient, is not sufficient to induce a substantial oxidative challenge”.
Thus, regions of reduced cloud cover during El Nino events correlate with the so-called “global” bleaching events that happened in 1998, 2010, and 2014-2017 and now 2023-24. Accordingly major eastern-Pacific El Nino events happened in 1997–98, 2014–16, and 2023–24 and a Modoki El Nino 2009-2010. As seen in by the white circles in illustration B, the death rate from bleaching during the 2023–24 El Nino, are associated with regions, Carribean and Gulf of Mexico and the western Pacific, where El Nino induced atmospheric subsidence and reduced cloud cover which increased light stress.
The alarmists seeking power can’t control solar radiation, but they want to control the public’s use of energy. So, they unscientifically blame global warming for coral bleaching as evidence that rising CO2 is killing coral! Alarmists deny the science!
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The 2015/16 Great Barrier Reef bleaching of near surface coral was also coincidental to a drop in average sea level due to the El Nino.
This exposes the surface coral (the ones you see from a low flying plane) to greater direct sunshine.
The coral critters don’t like it, so they take a holiday.
Coral has existed on this planet for many billions of years. The fact that they don’t respond to global warming fears is interesting. They simply do their thing!
Most Coral Reefs are of new creation. With the oceans 120m lower just 15k years ago where we today find the Reefs would have been dry land.
Also, apart from big reductions in sea levels, there were big reductions in sea temps which would have caused corals to move huge distances.
But as Jim says, they have been around through all these changes and if anything, they have thrived with any extra warming.
and as has been indisputably observed after the total obliteration of the Bikini Atoll atom bomb testing in the 1950s, coral reefs grow, proliferate and thrive all by themselves in less than one human lifetime (i.e. < 3 score + 10)
Many millions of years, but yes.
“Corals have been found in fossil reefs as old as 500 million years, but corals similar to the modern colonial varieties have constructed reefs only during the last 60 million years.”
https://www.usgs.gov/centers/pcmsc/coral-reef-facts#:~:text=Corals%20have%20been%20found%20in,the%20last%2060%20million%20years.
Hello evolution.
The reef building coral we see now evolved about 250 million years ago during the age of dinosaurs. The reef building coral from earlier times went extinct by the Permian.
Thanks, bnice2000, that was just what I was going to say.
Those of us that propagate corals in glass boxes know this from practical experience.
Jim,
There was an article not long after the height of the 2015/15 El Nino about some Japanese scientists testing a hypothesis by placing instrumentation at a fair number of places in the western Pacific in an area called “???” Triangle which has one corner in the northern reaches of the Great Barrier Reef. They were measuring water depth and water temperature and followed up the main El Nino water flow by observing the corals at their test locations.
They reported that there was much bleaching in areas where the water level markedly, temporally reduced due to all the water flowing east, but little to none in areas where the local geology prevent the water level from declining so much (some barrier to outward water flow). Essentially this was corals deprived or water cover for some significant number of hours (per day, I believe) vs corals that remained submerged or had little time exposed.
Coral bleaching was not related to water temperature to any significant degree, only to being exposed. Of course the actual damage may be entirely, or mostly, due to the light level that exposed corals were subjected to, i.e. what you described in your article, but indications were strong that it was not so influenced by local weather.
I have read, without the authors pointing to evidence, that coral bleaching is more common when waters become colder than normal than when waters become warmer than normal. I presume “normal” refers to the particular location. Do you know the truth of that claim?
A new Ice Age would kill all of the known reefs just because of sea level getting lower. The reefs we know today are young less than 15k years old.
I think you mean a new Glacial Period. The Earth is still in a 2+ million-year ice age named the Quaternary Glaciation with ice caps and 200,000 glaciers. The current ice age won’t end until all of the natural ice melts
The 2015 and 2023/24 bleaching events occurred during both high TSI and an El Niño. Oddly many of the bleaching alert zones from the article graphic are in areas with little to no coral reef bases according to NOAA’s reef base map. I covered this issue in my 2020 symposium poster.
Good article
I remember a coral are dying article from the 1960s. I guess there are always some coral dying somewhere that will make a good scare the readers article.
Sometimes the coral actually die, no doubt. But coral bleaching is not equivalent to coral dying.
It’s like when we get sick from food poisoning. We vomit, we rest, we recover, we eat again. Sure, we could have such a severe case as to die, but that’s not the common case.
I’ve been asked how did a La Nina cause bleaching.
The La Nina bleaching on the Great Barrier Reef is the exception that proves the point about changing cloud cover & light stress. Indeed, La Nina normally brings more cloud cover to the GBR, can raise sea leve and minimizes bleaching. But synoptic meteorology can override that generality and reduce the cloud cover.
Please read:
Atypical weather patterns cause coral bleaching on the Great Barrier Reef, Australia during the 2021–2022 La Niña Hamish McGowan & Alison Theobald (2023) Univ. of Queensland.
I’ve included their map of Total Cloud Cover and High Cloud Cover showing the region of reduced cloud cover correlates to the GBR region of bleaching. Some excerpts:
“Analysis of the synoptic meteorology of GBR coral bleaching during El Nino events (1983–2016) between 23 degrees 26′ 24″ S to 14 degrees 40′ 12″ S found reduced high cloud cover was pivotal in inducing thermal stress and bleaching at individual coral reef scale and not background oceanic warming trends.”
“Cloud controls the amount of solar radiation received at the water surface and is the primary energy input to the surface energy balance of coral reefs.”
Due to a weak Australian Monsoon Season and transport of dry air from the southwest that reduced clooud cover, they concluded “The resulting increase in solar radiation over the GBR and lower wind speeds, while humidity at the surface remained near average likely caused the increase in recorded water temperatures and DHW that exceeded levels only previously observed during El Nino events.”
Jim thanks for bringing this to our attention, it helps to flesh out the idea of solar super-sensitivity, where the sun’s activity sets up the atmospheric conditions necessary for subsequent warming.
The GBR La Niña coral bleaching began again in December 2021, after over a year of the TEMIS UV Index for Australia being about 2 standard deviations above average, ie, relative cloudlessness.
According to my work the 2020-on La Niña resulted from an accumulated TSI deficit below the decadal threshold during the solar minimum, driving clearer skies that induced higher surface insolation.
In the La Niña cases from the Nature article figure 2, DHW peaked in March as the SH summer ends.
The information from the Nature paper indirectly helps to establish this ocean warming effect where/when the seasonal sun passes over during reduced cloud cover, and its detrimental effect on corals, at the time of rising TSI above the decadal ocean warming threshold (the red line in TSI plots below).
It is often claimed the La Niña warms the ocean, when actually, warming didn’t start during these post solar minima type La Niñas until TSI reached the decadal warming threshold – a fine distinction, ocean warming that damages corals under clearer La Niña skies.
Coral bleaching occurs after the coral expels its colorful symbiotic algae before they replace it with a different strain that matches their needs better. They need the algae to provide it with nutrients so if the bleaching lasts a long time it will kill them but most of the time they just get a new strain of algae.
Corals in the Great Barrier Reef are constantly mutating. During the coordinated ejection of gametes into the environment, close species can form new species.
Why are reef building corals found only in warm ocean climates if warming is bad for corals?
Actually, there are reef building corals found in colder waters mostly at substantial depths. Google will be happy to tell you more than you probably want to know about them. The largest known cold water coral reef is the Rost reef off the coast of Norway. There’s a Wikipedia article, https://en.wikipedia.org/wiki/Deep-water_coral
What ocean locations are too hot for corals? Why is the Great Barrier Reef only found north of Brisbane? Why doesn’t the reef extend southward to Sydney, Melbourne, or Hobart?
Why do tropical islands routinely have coral reefs, while those outside the tropics have none?
it was the clouds again
How dare Jim Steele contradict the CO2 Coalition!
Releasing the Gas of Life by burning fossil fuels promotes a Greening Earth by raising CO2 levels that have fallen dangerously close to the Red Line Of Death,
That greening obviously includes the algae in corals, which require plentiful sunlight to grow and produce the oxygen vital to animal life including corl polyps-
Does Steele wants to turn the Great Barrier Reef into and anoxic Dead Zone ?
EAST POLE You are a scumbag troll. Nothing in this article contradicts the CO2 Coaltion. and all you have shown is how incredibly stupid you are using such retarded arguments.