Many dangerous and significant changes are occurring in the southern ocean, which is a key climate regulator. A summary of the findings is below.
The southern ocean is losing its ability to recycle iron due to Chin Strap Penguin population loss.
Rob Yirka writes in Phys.org:
Chinstrap penguins, as their name suggests, have a long line of black feathers along their chins, and they live on the shores of islands in the Southern and Antarctic Oceans. Prior research has shown that due to the large amounts of krill they eat, they are a major recycler of iron in the Southern Ocean. Prior research has also shown that the population of chinstrap penguins has dropped dramatically since the 1980s, primarily due to global temperature increases. In this new effort, the researchers sought to learn more about the impact of iron recycling in the Southern Ocean as the population of chinstrap penguins declines.
Iron is a precious commodity in the world's oceans; phytoplankton need it to grow. And many of the creatures that live in the sea feed on phytoplankton or other creatures that feed on it. Most of the iron that makes its way into the world's oceans gets there via dust carried by the wind. But not much dust makes its way to the Southern Ocean and the iron there needs to be recycled. If it is not, it will drop to the bottom of the seabed where it cannot be accessed. Part of the recycling of iron in the Southern Ocean has traditionally been done by chinstrap penguins. Their diet is most krill, which feed on phytoplankton. The penguins recycle the iron through their feces, which they eject into the water as they swim.
Are we talking about an extinction feedback loop? The article did not say but we do know that icebergs in front of penguin colonies force the birds to swim further than usual to the point of exhaustion that drowns them. Trawling vessels for krill are not helping the situation at all. The biodiversity loss potential is terrifying.
As noted by Yirka above "population of chinstrap penguins has dropped dramatically since the 1980s, primarily due to global temperature increases". The increase in sea ice melt due to heating has exploded over the past two years, seriously impacting the marine system's ability to maintain life.
Sea ice supports many levels of the food web. When sea ice melts it releases iron, which promotes phytoplankton growth. In the spring we see phytoplankton blooms that follow the retreating sea ice edge. If less ice forms, there will be less iron released in the spring, and less phytoplankton growth.The sea ice is critical for the survival of Krill larvae as it feeds on the phytoplankton that grows under the ice. Additionally, the sea ice protects them from grazing by predators. Krill larvae do not fare well in the water column. As a result, species such as whales and penguins depend on this nursery and their poop helps to keep us alive. Any disruption to the ice will impact the finely balanced ecosystem.
The rhythmic expansion and contraction of Antarctic sea ice is like a heartbeat.
But lately, there’s been a skip in the beat. During each of the last two summers, the ice around Antarctica has retreated farther than ever before.
And just as a change in our heartbeat affects our whole body, a change to sea ice around Antarctica affects the whole world.
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One of the largest seasonal cycles on Earth happens in the ocean around Antarctica. During autumn and winter the surface of the ocean freezes as sea ice advances northwards, and then in the spring the ice melts as the sunlight returns.
We’ve been able to measure sea ice from satellites since the late 1970s. In that time we’ve seen a regular cycle of freezing and melting. At the winter maximum, sea ice covers an area more than twice the size of Australia (roughly 20 million square kilometres), and during summer it retreats to cover less than a fifth of that area (about 3 million square km).
In 2022 the summer minimum was less than 2 million square km for the first time since satellite records began. This summer, the minimum was even lower – just 1.7 million square km.
The annual freeze pumps cold salty water down into the deep ocean abyss. The water then flows northwards. About 40% of the global ocean can be traced back to the Antarctic coastline.
By exchanging water between the surface ocean and the abyss, sea ice formation helps to sequester heat and carbon dioxide in the deep ocean. It also helps to bring long-lost nutrients back up to the surface, supporting ocean life around the world.
Not only does sea ice play a crucial role in pumping seawater across the planet, it insulates the ocean underneath. During the long days of the Antarctic summer, sunlight usually hits the bright white surface of the sea ice and is reflected back into space.
This year, there is less sea ice than normal and so the ocean, which is dark by comparison, is absorbing much more solar energy than normal. This will accelerate ocean warming and will likely impede the wintertime growth of sea ice.
As far as the threatened massive marine extensions of West Antarctica's glaciers are concerned, the lack of sea ice threatens to demolish them. When West Antarctica collapses, it will raise sea levels by eleven feet. Two feet of that will be rapid as Thwaites and Pine Island glaciers will be the first to go. Currently, the Bellinghausen Sea is ice-free, and just south are Thwaites and Pine Island which the open ocean has pounded since iceberg B22A moved off its seamount where it had been stuck for twenty years.
The Southern Ocean is a stormy place; the epithets “Roaring Forties” and “Furious Fifties” are well deserved. When there is less ice, the coastline is more exposed to storms. Waves pound on coastlines and ice shelves that are normally sheltered behind a broad expanse of sea ice. This battering can lead to the collapse of ice shelves and an increase in the rate of sea level rise as ice sheets slide off the land into the ocean more rapidly.
A separate article from The Conversation creative commons.
Antarctic alarm bells: observations reveal deep ocean currents are slowing earlier than predicted
Antarctica sets the stage for the world’s greatest waterfall. The action takes place beneath the surface of the ocean. Here, trillions of tonnes of cold, dense, oxygen-rich water cascade off the continental shelf and sink to great depths. This Antarctic “bottom water” then spreads north along the sea floor in deep ocean currents, before slowly rising, thousands of kilometres away.
In this way, Antarctica drives a global network of ocean currents called the “overturning circulation” that redistributes heat, carbon and nutrients around the globe. The overturning is crucial to keeping Earth’s climate stable. It’s also the main way oxygen reaches the deep ocean.
But there are signs this circulation is slowing down and it’s happening decades earlier than predicted. This slowdown has the potential to disrupt the connection between the Antarctic coasts and the deep ocean, with profound consequences for Earth’s climate, sea level and marine life.
We found melting of Antarctic ice is disrupting the formation of Antarctic bottom water. The meltwater makes Antarctic surface waters fresher, less dense, and therefore less likely to sink. This puts the brakes on the overturning circulation.
Why it Matters:
As the flow of bottom water slows, the supply of oxygen to the deep ocean declines. The shrinking oxygen-rich bottom water layer is then replaced by warmer waters that are lower in oxygen, further reducing oxygen levels.
Ocean animals, large and small, respond to even small changes in oxygen. Deep-ocean animals are adapted to low oxygen conditions but still have to breathe. Losses of oxygen may cause them to seek refuge in other regions or adapt their behaviour. Models suggest we are locked in to a contraction of the “viable” environment available to these animals with an expected decline of up to 25%.
Slowdown of the overturning may also intensify global warming. The overturning circulation carries carbon dioxide and heat to the deep ocean, where it is stored and hidden from the atmosphere. As the ocean storage capacity is reduced, more carbon dioxide and heat are left in the atmosphere. This feedback accelerates global warming.
Reductions in the amount of Antarctic bottom water reaching the ocean floor also increases sea levels because the warmer water that replaces it takes up more space (thermal expansion).
The Findings:
The findings are striking. Over three decades, between 1992 and 2017, the overturning circulation of this region slowed by almost a third (30%) causing less oxygen to reach the deep. This slowing was caused by freshening close to Antarctica.
We found this freshening reduces the density and volume of Antarctic bottom water formed, as well as the speed at which it flows.
The observed slowdown would have been even greater if not for a short-lived climate event that drove a partial and temporary recovery of bottom water formation. The recovery, driven by increased salinity, further illustrates the sensitivity of bottom water formation to salinity changes on the Antarctic continental shelf.
Worryingly, these observations show that changes predicted to occur by 2050 are already underway.
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If we don't go extinct first, we have Tsunamis to worry about. Climate change could unleash gigantic tsunamis in the Southern Ocean by triggering underwater landslides in Antarctica, a new study warns.
By drilling into sediment cores hundreds of feet beneath the seafloor in Antarctica, scientists discovered that during previous periods of global warming — 3 million and 15 million years ago — loose sediment layers formed and slipped to send massive tsunami waves racing to the shores of South America, New Zealand and Southeast Asia.
And as climate change heats the oceans, the researchers think there's a possibility these tsunamis could be unleashed once more. Their findings were published May 18 in the journal Nature Communications.
"Submarine landslides are a major geohazard with the potential to trigger tsunamis that can lead to huge loss of life," Jenny Gales, a lecturer in hydrography and ocean exploration at the University of Plymouth in the U.K., said in a statement. "Our findings highlight how we urgently need to enhance our understanding of how global climate change might influence the stability of these regions and potential for future tsunamis."
SST=Sea Surface Temperatures for reference