Stockholm University
34 million years ago the warm ‘greenhouse climate’ of the dinosaur age ended and the colder ‘icehouse climate’ of today commenced. Antarctica glaciated first and geological data imply that the Atlantic meridional overturning circulation, the global ocean conveyor belt of heat and nutrients that today helps keep Europe warm, also started at this time. Why exactly, has remained a mystery.
“We have found a new trigger to explain the start-up of the Atlantic current system during the greenhouse-icehouse climate transition: During the warm climate, buoyant fresh water flooded out of the Arctic and prevented the ocean-sinking that helps power the conveyor. We found that the Arctic-Atlantic gateway closed due to tectonic forces, causing a dramatic increase in North Atlantic salinity. This caused warming of the North Atlantic and Europe, and kickstarted the modern circulation that keeps Europe warm today,” says David Hutchinson, researcher at the Department of Geological Sciences, Stockholm University, and lead author of the article published in Nature Communications.
The team of scientists, from the Bolin Centre for Climate Research, used a combination of geophysical data and climate modelling to show that the freshwater transport through the Arctic-Atlantic gateway plays a critical role in controlling the overturning circulation.
“Not only did deep water start forming in the Atlantic Ocean, it also stopped forming in the North Pacific at the same time, which matches geological evidence. We were surprised to find that our computer simulations can explain both of these changes due to salty ocean currents connecting the Pacific to the Atlantic. Our study is the first to show that these two events are linked, which is very exciting,” says Hutchinson.
The climate at this time was very warm, with atmospheric CO2 levels two to three times the present day levels, and this contributed to extremely fresh Arctic waters. The study begs the question of whether in a future warm world, in which the Arctic may again be very fresh, the sinking in the Atlantic may cease again, which may dramatically alter the climate of Europe. Without the Atlantic conveyor belt, Europe can experience both colder winters and hotter and drier summers, making a more extreme and inhospitable climate.
“Our study helps to bridge the gap between climate modelling and geological observations of the deep past. We hope this will inspire further research from both communities on the deep circulation of the ocean,” says Hutchinson.
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More information
The article “Arctic closure as a trigger for Atlantic overturning at the Eocene-Oligocene Transition” is published in the scientific journal Nature Communications: http://dx.doi.org/10.1038/s41467-019-11828-z
This report from Stockholm University is a meaningless logically dysfunctional non-sequitur.
A. Closure of the Arctic Ocean from tectonics 34 Mya started the AMOC and made it colder.
therefore …
B. Imagine what global warming would be like! 😬
From the article:
The climate at this time was very warm, with atmospheric CO2 levels two to three times the present day levels, and this contributed to extremely fresh Arctic waters.
If there were few if any glaciers to melt in the Arctic (I don’t think Greenland was glaciated yet), why would the Arctic Ocean be any fresher than any other ocean?
All the world’s oceans have clockwise circulation in the Northern Hemisphere and counterclockwise circulation in the Southern Hemisphere, due to the Coriolis acceleration. In the western North Atlantic ocean, the east coast of North America runs SW to NE, so that warm water from the Gulf of Mexico flows NE along the coast to south of Greenland, where it splits, with one branch flowing north between Greenland and Scandinavia, the other flowing east towards Europe. Water from the Arctic returns via Baffin Bay in the cold Labrador Current.
There is a similar circulation in the North Pacific, with warm water flowing NE along the coasts of China, Japan, the Koreas, and the Kamchatka Peninsula, and cold water flowing SE along the west coasts of Canada and the United States. Because of the narrowness of the Bering Strait, there is little exchange of water between the Pacific and Arctic Oceans.
If there was a major warming such that most of Greenland’s and/or Antarctica’s icecap melted, sea levels could rise enough to flood much of Canada’s archipelago north of Hudson Bay, so that Baffin Bay would be much wider, and the cold Labrador current would be stronger, while most of Greenland would remain above sea level. This could push the Gulf Stream farther east, but not eliminate it entirely, since the SW to NE orientation of the east coast of the United States would remain.
But such a flood would inundate most of England, western France, northern Germany, Belgium, Holland, and Denmark, so that a slight change in the Gulf Stream would be the least of their worries.
Not to worry, though–the heat capacity of the Antarctic and Greenland ice caps is so huge that it would take them thousands of years to melt even in a drastically warming climate, and there would be time to adapt.
If you took all of that weight off of Antarctica and Greenland and added it to the sea floor, several isostatic changes would take place.
One could go into all sorts of specifics ideas about the results, but since it is not gonna happen, it seems pointless to spend the time.
For one thing, we would have a lot of new land, and for those places to melt, places too cold now would no longer be too cold.
Nothing last forever, and every thing will need to be replaced at some point.
Many disasters are not hypothetical but certainties and only a matter of time, and many are no less consequential.
We could talk about how much energy would be required to bring all that ice to the melting point and then change the phase to liquid at that same temp.
Very fresh water in the Arctic ocean means the freezing point is nearer zero c then instead of -2 c. Therefore it would make it easier to freeze especially during winter and these levels of CO2 would not prevent this.
When there is a future major change in the circulation of the Atlantic ocean, whether thousands of years later and natural. The Gulf stream and NAD moves further south and it has never been shown with proxies to fail or shutdown. In the worse case scenario cold polar like ocean water in the North Atlantic ocean and North Sea would hugely cool both winters and summers. There is no mechanism how warmer and drier summers could happen over Europe with Atlantic ocean temperatures many degrees cooler than now. The jet stream would be well to the South of Europe and Atlantic systems would frequently move into Europe causing much wetter and cooler summers, but drier and much colder winters.
The climate of Europe, north Asia and North America/Canada would all be affected because they all surround the Arctic ocean and failure of warmer water moving further North would freeze the Arctic ocean completely even in summer longer term. Although these are based on scientific evidence from proxies not a model guess with no evidence.
In any sort of honest and open climate of scientific discourse, obvious mush like we see being put force by various disciplines that consider themselves to be part of “climate science” would be quickly put to widespread scrutiny and criticism.
Shutting down ocean currents which are wind driven by changing the salinity of surface water in a relatively small area (consider the relative volumes of the ocean and rivers and land ice melting, the turbulence and mixing of surface waters by storms etc, and the small size of this region when one looks AT A GLOBE) is not a well supported notion. Even the terminology of thermohaline circulation has been recommended to be changed to meridional overturning to better describe what is thought to be taking place.
Simplistic ideas with little supporting evidence are a staple of modern climate science (and by extension fields that overlap with it) however, and when they are not challenged, and critical thinking is actively discouraged, dissention from group think is not just frowned upon but punished or not even tolerated, it is predicable the end result will be very far from anything resembling an advancing body of well supported knowledge.
Most of the ocean currents are wind driven and are not shut down by changing salinity of surface water or needed to be shut down. This is because the ocean current often goes the opposite off the winds above 50N for example in the NH especially around Europe. The reason this occurs especially around western Europe is because the AMOC keeps the motion going into the Arctic ocean.
What should happen with ocean currents in the mid-latitude cell is that the prevailing winds are towards North Africa. They then converge in the Hadley cell with the north-easterly trades. Therefore the ocean current should move south down the side of Africa towards the tropical ocean. Instead what happens the AMOC moves more of the current north of here past the UK and into the Artic ocean. That is against the atmospheric winds which would rather push south.(A)
When the wind and ocean currents just follow towards North Africa with what should be the usual westerly flow and converge with the north-easterly trades, that’s when we get an major ice age as proxies have shown in the past.(B)
It’s the energy distribution of the ocean south to North in the mid-latitude cell around North Africa that changes and this is much less wind driven. This is determined by the strength of the AMOC and get a variation between A and B. It is at a point of divergence in winds and not surprising this has become very unstable during ice ages with short dramatic temperature changes.
The notion of a great, coherent oceanic “conveyor belt” as a controlling mechanism in global surface climate is inconsistent both with dynamical theory and with oceanographic observations. At best, thermohaline factors produce a minor adjunct to the wind-driven circulation, with denser parcels of surface water diffusing slowly into lower layers. The practical effect lies primarily in the formation of bottom-water in the polar regions, which is distributed more globally and ventilated in a very sluggish and incoherent overturning cycle. As Carl Wunsch points out, as long the winds continue to blow, the surface currents that indeed affect climate will persist. See, inter alia : https://www.yaleclimateconnections.org/2007/10/common-climate-misconceptions-why-a-gulf-stream-shut-down-and-a-new-european-ice-age-are-unlikely/
“During the warm climate, buoyant fresh water flooded out of the Arctic and prevented the ocean-sinking that helps power the conveyor. We found that the Arctic-Atlantic gateway closed due to tectonic forces, causing a dramatic increase in North Atlantic salinity.”
Pure nonsense. There was no Arctic-Atlantic gateway at all during much of the Eocene. We know this with certainty because there was an extensive exchange of land animals, e g flightless birds and early primates between North America and Europe. On the other hand Europe was separated from Asia by the Turgai strait. That is where the freshwater efflux from the Arctic went.
What happened at the end of the Eocene, the “Grande Coupure”, was that the Turgai strait closed, asian mammals immigrated into Europe and there was no more exchange across the North Atlantic.
Early Oligocene was as a matter of fact when the deep North Atlantic gateway opened not closed:
https://www.nature.com/articles/35073551
“The climate at this time was very warm, with atmospheric CO2 levels two to three times the present day levels, and this contributed to extremely fresh Arctic waters.”
Sure, sure. We all know how fresh the water is in e. g. the very warm Red Sea or Persian Gulf. That the Arctic Ocean freshened during the Paleocene-Eocene was because it was practically isolated and received large quantities of fresh water from rivers, and the climate was cool enough to limit evaporation. In other words it was much like the Baltic or the Black Sea today but on a larger scale.
This would seem to be a severe case of modeling madness.