Scientists have suspected that the phenomena of the longtime pattern of fluctuating freezing temperatures and warm seasons that suddenly changed a million years ago and the ice ages appeared to last longer and be more dramatic. Somehow this event was related to a shutdown of a key of Atlantic Ocean current system that is repeatedly slowing.

A direct link between the events has been made because of a new study of sediments from the ocean’s bottom connects this slowdown with an enormous buildup of carbon transported from the air into the abyss. This carbon would have dripped back into the air pretty quickly with the system working at full speed but during this period it somehow stalled in the depths. This phenomenon implies that the carbon drawdown chilled the planet – the exact opposite of the greenhouse aftermath we see now, as the humans keep sending carbon into the air.

Experts say that if the current keeps lessening, we should probably expect this to hinder upon us because it won’t store our emissions. The study appears in the journal Nature Geoscience ​this week, and it was led by researchers at Colombia University’s Lamont-Doherty Earth Observatory.

The system of currents named the Atlantic Meridional Overturning Circulation (AMOC) was purposely aimed by the researchers. This system is streaming northward near the surface, and it transfers within warm, salty water into the latitudes near Greenland and north of Europe, from near the equator. Here, absorbing vast amounts of carbon from the atmosphere, it reaches colder water from the Arctic Ocean, which makes it more compressed and then falls into the abyss.

To release carbon back in the atmosphere the water travels back south where most of it re-emerges in the Southern Ocean. This cycle takes place over decades to centuries.

When it all began?

Steven Goldstein, a Lamont-Doherty geochemist and his then student Leopoldo Pena conducted a study back in 2014 – both are also coauthors of a new study – showed that it was approximately 950,000 years ago when this current dramatically began to cripple.

This slowdown interacted straightly with an enormous build-up of carbon in the depths of the Atlantic ocean, and correlating decline of carbon in the air, the new study showed. This occurrence was the probable trigger for a succession of ice ages that came every 100,000 years, which build up less ice than the later ones, versus the previous ones that appeared approximately every 40,000 years.

This turning point is called the Mid-Pleistocene Transition by scientists. The new order of design has persevered through the last ice age, which they say it ended approximately 15,000 years ago. No one knows why this arrangement persisted, but the study conducted by Goldstein and Pena shows without a doubt that the carbon had a substantial effect on climate as it winded up in the ocean.

Jesse Farmer, a student at Lamont-Doherty who did the work as a Ph.D. said that it was like flipping a switch, or a “one-to-one relationship.” He also said that the event is clearly showing that between the climate and the carbon that ended up in the ocean is a close relationship.

The parallel between then and now

Analyses of studies that the researches conducted by closely examining cores of deep-sea sediments from the north and south Atlantic, where ancient waters crossed by and deposited chemical indications about their insides in the shells of microscopic beings were finally confirmed in 2014.

They showed clearly that the Atlantic Ocean current lessened to a point never seen before, for an awfully long period, about 950,000 years ago. Because of the AMOC weakening, approximately 50 billion tons more carbon than during former glaciations was accumulated by the deep water, which is proportionate with nearly one-third of the human diffusions that all the world’s oceans have thus far accumulated in the present. Given the background, the oceans collect about one-fourth of what the humans emit, vegetation and land take up approximately one-third, and the rest remains in the atmosphere.

The air had held up nearly 280 parts per million carbon in the warm course conducting to this event. As calculated by ice cores, the airborne carbon dioxide went down to 180 ppm with the slowdown. During the former glaciations, the atmospheric carbon had declined as well, but from 280 ppm down to barely about 210 ppm. This usual repeating 280 ppm warm-era figure has become outdated because of the human emissions throughout the last two centuries. At this point, the atmospheric carbon is up about 410 parts per million.

The Atlantic Ocean current arose again at a given point, and the things warmed for some time before falling back to another very much alike ice age, after 100,000 years.

Bärbel Hönisch, Farmer’s advisor and coauthor of the study​ said that it is difficult to say what the trigger was although there are lots of theories about what caused the events to happen. The researcher stated that there are lots of different twists that one could imagine turning.

Goldstein’s group and others embraced the idea that in the north, everything is removed on land down to bedrock by repeated build-ups of glaciers. Before dumping icebergs into the oceans, consecutive glaciers can affix fast to the bedrock and expand even more.

That enters more freshwater to combine with the AMOC, making it lighter and ultimately not able to sink. On the other end, ice would also grow in Antarctica and release more icebergs, which would support the growth of more sea ice by making the ocean waters less salty and colder. In theory, this would keep the water from the depths of the ocean to rise and discharge their carbon and would cap the surface. If this is the actual way it works, it’s a chicken-and-egg sort of question because it is still not apparent what starts or ends any of the processes.

It appears that the strength of the AMOC had minimized by a bizarre 15 percent since the mid-20th century although it was believed that it oscillated naturally. What is behind the unusual event, no one knows, and not even what kind of effects it might generate if the slowdown persists.

A slowdown approximately 13,000 years ago, at the backside of the last ice age, was succeeded by an extreme cold snap about 400 years later, which lasted centuries. Farmer, now a postdoctoral researcher at Princeton University stated that when comparing the weakening that is happening today with that of the past one should be careful. He continues saying that the ocean circulation is not going to save the planet from warming climate because of the way the different climate system parts communicate with each other.

What will happen if the Atlantic Ocean current continues weakening

If the AMOC persists in its weakening, it is safe to presume that less carbon-laden water will disappear in the north, and any carbon already appearing in the deep sea will most expectedly keep fizzing up without a problem in the Southern Ocean. The conclusion is that carbon will keep on building up in the atmosphere and not in the ocean.

Atlantic Ocean current is only a part of a broader system of global circulation that links all the oceans, a system called Great Ocean Conveyor, a term created by the late Lamont-Doherty scientist Wallace Broecker. The scientist laid the groundwork for plenty of today’s research. There are a lot of missing pieces to the puzzle for not much is known about the carbon dynamics of the Indian and Pacific oceans, which together minimize the Atlantic.

The ongoing research at Lamont-Doherty is directed at building carbon chronologies of those other oceans in the following years.

Laura Haynes, Heather Ford, Maureen Raymo, Maria Jaume-Seguí, Steven Goldstein, Maayan Yehudai and Joohee Kim​ also coauthored the study, all of them from Lamont-Doherty. Among them were also Dirk Kroon, Simon Jung and Dave Bell of the University of Edinburgh and Leopoldo Pena of the University of Barcelona.