Image credit: NASA

Melt Water In Antarctica Could Stall Major Ocean Currents

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The world’s ocean may seem fairly uniform when viewed from the deck of a ship or from an airplane, but there is a lot going on beneath the surface. Huge rivers of water conduct the heat of the tropics to the Arctic and Antarctica, where the water is cooled before it starts traveling toward the equator once again. Those who live along the east coast of North America and in Europe are familiar with the Gulf Stream. Without it, those places would not be uninhabitable but they would be a lot colder than they are today.

Antarctica ocean currents
This animation shows the path of the global conveyor belt. The blue arrows indicate the path of deep, cold, dense water currents. The red arrows indicate the path of warmer, less dense surface waters. It is estimated that it can take 1,000 years for a “parcel” of water to complete the journey along the global conveyor belt. Credit: NOAA

Suffice it to say that ocean currents are like the cooling system of an automobile. If something happens to disrupt the proper flow of coolant, bad things can happen to the engine. The same can be said for the Earth if those ocean currents are disrupted. Not only do they help regulate the temperature of the Earth’s land masses, they also bring vital nutrients with them that are essential to marine life. Above is a graphic from NOAA that explains how ocean currents work. What follows is a verbal explanation from NOAA.

“Thermohaline circulation drives a global-scale system of currents called the “global conveyor belt.” The conveyor belt begins on the surface of the ocean near the pole in the North Atlantic. Here, the water is chilled by arctic temperatures. It also gets saltier because when sea ice forms, the salt does not freeze and is left behind in the surrounding water. The cold water is now more dense, due to the added salts, and sinks toward the ocean bottom. Surface water moves in to replace the sinking water, thus creating a current.

“This deep water moves south, between the continents, past the equator, and down to the ends of Africa and South America. The current travels around the edge of Antarctica, where the water cools and sinks again, as it does in the North Atlantic. Thus, the conveyor belt gets “recharged.” As it moves around Antarctica, two sections split off the conveyor and turn northward. One section moves into the Indian Ocean, the other into the Pacific Ocean.

“These two sections that split off, warm up, and become less dense as they travel northward toward the equator, so that they rise to the surface. They then loop back southward and westward to the South Atlantic, eventually returning to the North Atlantic, where the cycle begins again.

“The conveyor belt moves at much slower speeds — a few centimeters per second — than wind driven or tidal currents (tens to hundreds of centimeters per second). It is estimated that any given cubic meter of water takes about 1,000 years to complete the journey along the global conveyor belt. In addition, the conveyor moves an immense volume of water — more than 100 times the flow of the Amazon River.

“The conveyor belt is also a vital component of the global ocean nutrient and carbon dioxide cycles. Warm surface waters are depleted of nutrients and carbon dioxide, but they are enriched again as they travel through the conveyor belt as deep or bottom layers. The base of the world’s food chain depends on the cool, nutrient rich waters that support the growth of algae and seaweed.”

Antarctica Is Melting

New research published in the journal Nature on March 29 finds that as Antarctica warms, melt water from its glaciers could slow those massive ocean currents by 40% as soon as 2050. The result would be substantial changes to the Earth’s climate in ways that are not fully understood but likely involve an acceleration of droughts, flooding, and rising sea levels. The research suggests that such a slowdown in ocean current could alter the world’s climate for centuries. That in turn could generate a cascade of impacts including faster sea level rise, alterations in weather patterns, and possible starvation for marine life denied access to vital sources of nutrients.

Professor Matt England, of the Climate Change Research Center at the University of New South Wales and a co-author of the research published in Nature, said the whole deep ocean current was heading for collapse on its current trajectory. “In the past, these circulations have taken more than 1,000 years or so to change, but this is happening over just a few decades. It’s way faster than we thought these circulations could slow down. We are talking about the possible long term extinction of an iconic water mass.”

The slowdown in the deep ocean current relates to the amount of water that sinks to the bottom and then flows north. Dr. Qian Li, formerly of the University of New South Wales and now at the Massachusetts Institute of Technology, was the lead author of the research, which was coordinated by England. The authors wrote the slowdown would “profoundly alter the ocean overturning of heat, fresh water, oxygen, carbon and nutrients, with impacts felt throughout the global ocean for centuries to come.” One of the consequences could be a radical shift in rainfall — too much in some places and too little in others.

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Knock-On Effects

“We don’t want to set off a self-reinforcing mechanism in those places,” Li said, and added that the slowdown effectively stagnates the deep ocean, starving it of oxygen. When ocean organisms die, they add nutrients to the ocean water that sinks to the bottom and circulates around the world’s ocean. Those nutrients get returned in upwells that feed phytoplankton. which are a foundation for the marine food chain.

Dr. Steve Rintoul, an oceanographer and expert on the Southern Ocean at the Australian government’s Commonwealth Scientific and Industrial Research Organisation, said as the deep ocean circulation slows, fewer nutrients would be returned to upper layers of the ocean — affecting the production of phytoplankton over centuries.

“Once that overturning circulation slows down, we can only get it back again by no longer releasing melt water around Antarctica, which means we need a cooler climate and then have to wait for it to restart. The longer we go on with higher rates of greenhouse gas emissions, the more changes we commit ourselves to. Going back 20 years, we thought the deep ocean wasn’t changing that much. It was too far away to be responsive. But the observations and the models have shown that’s not the case.”

Professor Stefan Rahmstorf, an oceanographer and head of earth system analysis at the Potsdam Institute for Climate Impact Research, said the new study showed “a dramatic further weakening is likely around Antarctica in the coming decades.” He suggested the models used in major UN climate reports had a “longstanding and major shortcoming” because they didn’t capture how melt water influenced the deep ocean. “The melt water dilutes the salt content of these ocean regions, thereby making the ocean waters less dense and thus not heavy enough to sink down and push away the waters already there.”

The Takeaway

There is a connection here between slowing ocean currents and the potential need for geoengineering to cool the Earth as average global temperatures continue to rise. Both will have wildly unpredictable results that could prove devastating to human life in many parts of the world.

The antidote, of course, is to produce much less carbon dioxide and methane emissions, but world leaders have been slow to address those issues vigorously because doing so will result in significant pushback from fossil fuel vendors as well as anger among consumers who rely on fossil fuels to power their cars, heat their homes, and keep the internet functioning.

If the US was serious about making consumers pay for the damage done by burning fossil fuels, the cost of electricity from thermal generating stations would double or triple and the price of gasoline will be well over $10 a gallon. The vast majority of the electorate would scream if either of those things happen and vote for candidates who promised to bring back the good old days. In other words, we are likely to keep slouching our way into an uncertain future where our grandchildren will be left with the fallout from our failure to act in any meaningful way.

Another troubling aspect of the slowdown in ocean currents as a result of an increase in melt water in Antarctica is that a slowdown in the deep ocean current could also affect the amount of carbon dioxide the deep oceans can store, Professor Rahmstorf said. We could help alleviate the situation by slashing carbon and methane emissions, but there is little evidence the political will to do so exists.


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Steve Hanley

Steve writes about the interface between technology and sustainability from his home in Florida or anywhere else The Force may lead him. He is proud to be "woke" and doesn't really give a damn why the glass broke. He believes passionately in what Socrates said 3000 years ago: "The secret to change is to focus all of your energy not on fighting the old but on building the new." You can follow him on Substack and LinkedIn but not on Fakebook or any social media platforms controlled by narcissistic yahoos.

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