Marine heat waves across the planet kill many species by heating water from global warming, low oxygen, and toxic algae blooms. In this case, the deaths resulted from increasing temperatures during a hot summer. Tropical pelagic fish fleeing overly heated waters off the coast of South Africa suddenly swam into an upwelling of cold bottom water, killing all but one, a bull shack confirmed by a satellite tag tracking its movements.
Researchers worry that in "some parts of the world, incidents like this appear to be getting more common as currents change (linked directly to climate change) with potentially lethal consequences for marine life.". Limited data measurements and no long-term data on the Southern Ocean make research challenging, if not impossible, so we are flying blind with an enormous gap in Climate understanding. What we know about Agulhas current is that it flows between South Africa's coast and Madagascar, also known as the Screaming Agulhas; it is a Subtropical western boundary current, where its flow is one of the strongest in Earth's oceans: strong, narrow, deep, and warm, moving heat and salt from the tropics to colder water in the Atlantic, where it moderates the planet's climate the ocean and the land.
The Atlantic meridional overturning circulation (AMOC) monitors are in place. Some scientists believe the AMOC is not an immediate threat but is actively tipping nonetheless and likely to break down over the span of a lengthy human lifetime. The most recent study from the Netherlands confirmed that the AMOC is tipping and that the Atlantic S 34th parallel, which includes South Africa, is the critical point of monitoring for the collapse of the N Atlantic's major circulation. This study did not mention the Agulhas.
Agulhas Leakage
The National Science Foundation, in an easy-to-understand article about what paleoclimatology tells us about the AMOC and the Agulhas. This is what the fossil record tells us,
Once in the Atlantic, the salty Agulhas leakage waters eventually flow into the Northern Hemisphere and act to strengthen the Atlantic overturning circulation by enhancing deep-water formation.
Atlantic overturning circulation is technically known as Atlantic meridional overturning circulation (AMOC); it carries warm shallow water into northern latitudes and returns cold deep water southward across the equator.
Recent research points to an increase in Agulhas leakage over the last few decades, caused primarily by human-induced climate change.
The finding is profound, oceanographers say, because it suggests that increased Agulhas leakage could trigger a strengthening in Atlantic overturning circulation--at a time when warming and accelerated meltwater input in the North Atlantic has been predicted to weaken it.
"This could mean that current IPCC model predictions for the next century are wrong, and there will be no cooling in the North Atlantic to partially offset the effects of global climate change over North America and Europe," said Beal.
"Instead, increasing Agulhas leakage could stabilize the oceanic heat transport carried by the Atlantic overturning circulation."
There are also paleoceanographic data to suggest that dramatic peaks in Agulhas leakage over the past 500,000 years may have triggered the end of glacial cycles.
Leakage of the warm and salty inflow of the Indian Ocean into the Atlantic.
The study paper on the mass mortality event titled Climate change-driven cooling, can kill marine megafauna at their distributional limits, published in Nature Climate Change (the pdf release), noted that much research has been conducted on marine life dying from marine heatwaves, particularly those animals that can not adapt or migrate in time. The difference in this study is that tropical pelagic fish, having evolved to live in the warm, open oceans, are forced to migrate from heating waters brought about by burning fossil fuels, increasing significant fish deaths by vortexes of frigid water (30s F). These water temperatures are so extreme that I imagine they would turn human limbs useless in less than a minute.
It's hard to say with certainty that the trend is driven by climate change, in part because these upwellings are so localized that they aren’t well represented in models looking at interactions between the ocean and climate, says David Schoeman, a marine climate change ecologist at the University of the Sunshine Coast who worked on the paper. But the trends are consistent with predictions of how climate change will influence these currents more broadly, and they are sustained over a long enough time that natural fluctuations don’t seem to fully explain it. The researchers also found an increase in cold upwellings at the similar Eastern Australian Current, which borders the eastern edge of Australia though the trend was less strong.
The Cold Bottom Water Crisis
A new analysis by Australian and American researchers, using new and more detailed modeling of the oceans, predicts that the long-feared turn-off of the circulation will likely occur in the Southern Ocean, as billions of tons of ice melt on the land mass of Antarctica. And rather than being more than a century away, as models predict for the North Atlantic, it could happen within the next three decades.
snip
The conveyor is driven by the descent of cold, salty water to the ocean floor in just two places: in the far North Atlantic near Greenland and in the Southern Ocean around Antarctica. In both regions, the mechanism is the same. In cold polar conditions, large volumes of water freeze. The salt in the water is not incorporated into the ice. It remains in the residual liquid water, which grows ever saltier. The saltier water becomes, the denser it becomes. So the residue is heavier than surrounding water and eventually sinks to the ocean floor.
About 250 trillion tons of salty water sinks in this way around Antarctica each year, subsequently spreading north along the ocean floor into the Indian, Atlantic, and Pacific oceans. Similar volumes spread south from Greenland. The process is known as deep-water formation or ocean overturning, and it has continued largely unchanged for thousands of years.
“The physics at play is pretty simple,” says England. “None of the steps is particularly surprising or complex. But until our study, we did not have the circulation model … to make confident predictions.” The slowdown itself, he says, “didn’t surprise me. But the pace of change — to see a 40 percent slowdown in under three decades — was definitely a surprise.”
And after 2050, their model predicts that things will get even worse. Deep-water formation “looks headed towards collapse this century,” the coordinator of the study, Matthew England of the University of New South Wales, told Yale Environment 360. “And once collapsed, it would most likely stay collapsed until Antarctic melting stopped. At current projections that could be centuries away.”
The groundbreaking modeling study published by Australian and American researchers at the end of March for the first time includes a detailed assessment of the likely impact of melting ice, revealing the importance of this past failure. It predicts a 42 percent decline in deep-water formation in the Southern Ocean by 2050. This is more than twice the 19 percent they predict for an equivalent event in the North Atlantic.
"The physics at play is pretty simple," says England. "None of the steps is particularly surprising or complex. But until our study, we did not have the circulation model … to make confident predictions." The slowdown itself, he says, "didn't surprise me. But the pace of change — to see a 40 percent slowdown in under three decades — was a surprise."
The Pelagic fish die off.
The study focuses on a significant marine die-off in South African waters, specifically the Indian Ocean's Agulhas Current and, to a lesser extent, the Australian Current.
(Agulhas Current enigma: An oceanic gap in our climate understanding=Monga Bay). These currents are where "critical exchanges of heat and salt take place," they are being monitored as they have played a vital role in the planet's changing climate over the past three decades.
Scientists have warned that climate change could alter upwelling zones where ocean currents border continents, in part by strengthening winds that help bring up colder water. In the case of the Agulhas Current, researchers in 2016 reported that since the 1990s its flow had grown broader and was more likely to create potent eddies.“Normally that current brings warmer subtropical water farther south. But as it pushes up against the continental shelf, it can generate eddies, much like the revolving pools of water that form on the downstream sides of boulders in a river. As the eddy’s spin pulls water away from the coast, colder bottom water from as deep as 3 kilometers (1.8 miles) can be pulled toward the coast to replace it. Easterly winds can also push warmer surface water offshore, causing bottom water to rise." The study found that shifts in ocean currents and pressure systems driven by climate breakdown" increased the frequency and intensity of upwellings.”
Jonathan Watts of The Guardian summarizes the Nature Article, writing, Climate crisis increasing frequency of deadly ocean upwells, study finds:
Scientists focused on the mass die-off event in 2021, which they were able to track in unusually precise detail because one of the affected creatures that survived was a bull shark that had been satellite-tagged. They found it had been caught in water that fell more than 10C (50F) below the temperature that such tropical species were used to.
The paper details how the shark changed its behaviour in an attempt to avoid the cold areas. It swam much closer to the surface than normal and moved outside its normal migration pattern.
When we have a million people die from a wet bulb event or something horrific of that nature, you’ll see all the media jump into emergency mode. You need to hold them to account. They’ve enabled this disaster by both siding it,downplaying it, portraying the climate crisis like it’s a natural thing that just happens - rather than the most deadly crime ever committed. Matthew ToddTagged bull sharks appeared to change their behaviour to avoid sudden temperature drops by swimming closer to the surface, sheltering in bays and estuaries and only moving to the extent of their poleward distribution during warm seasons.
The marine biologists worked with oceanographers to map upwelling trends and forecast what could happen in the future as climate disruption becomes ever more pronounced and extreme cold upwellings increase in frequency along with periods of extreme surface heat.
Within individual species, certain groups tend to live on the edge of their population range. Daly said these groups were most vulnerable to the sudden and protracted temperature shifts. “There are bull sharks that run the gauntlet of a cool area to get to thermal refuges. Upwellings could kill off this unique genetic diversity.”
The overwhelming complexity in this diary is not hyperbole, not to be taken with a grain of salt, nor is its content anywhere near complete. It's just the facts that we are aware of so far. A couple of you haven't a clue what is coming. Deal with it or not, but you can bet tomorrow will not be like today.
Whatever we are going to do, we better do it fast.