Featured Research

from universities, journals, and other organizations

Climate change: Unstable Atlantic deep ocean circulation may hasten 'tipping point'

Date:
February 20, 2014
Source:
University of Bergen
Summary:
A new study looking at past climate change asks if these changes in the future will be spasmodic and abrupt rather than a more gradual increase in the temperature. Today, deep waters formed in the northern North Atlantic fill approximately half of the deep ocean globally. In the process, this helps moderate the effects of global warming. Changes in this circulation mode are considered a potential tipping point in future climate change that could have widespread and long-lasting impacts. Until now, this pattern of circulation has been considered relatively stable during warm climate states such as those projected for the end of the century. A new study suggests that Atlantic deep water formation may be much more fragile than previously realized.

Ocean wave (stock image). Today, deep waters formed in the northern North Atlantic fill approximately half of the deep ocean globally. In the process, this helps moderate the effects of global warming. Changes in this circulation mode are considered a potential tipping point in future climate change that could have widespread and long-lasting impacts.
Credit: © Irina Belousa / Fotolia

A new study looking at past climate change, asks if these changes in the future will be spasmodic and abrupt rather than a more gradual increase in the temperature.

Today, deep waters formed in the northern North Atlantic fill approximately half of the deep ocean globally. In the process, this impacts the circum-Atlantic climate and regional sea level, and it soak up much of the excess atmospheric carbon dioxide from industrialisation -- helping moderate the effects of global warming. Changes in this circulation mode are considered a potential tipping point in future climate change that could have widespread and long-lasting impacts including on regional sea level, the intensity and pacing of Sahel droughts, and the pattern and rate of ocean acidification and CO2 sequestration.

Until now, this pattern of circulation has been considered relatively stable during warm climate states such as those projected for the end of the century. A new study led by researchers from the Bjerknes Centre of Climate Research at the University of Bergen (UiB) and Uni Research in Norway, suggests that Atlantic deep water formation may be much more fragile than previously realised.

The researchers Eirik Vinje Galaasen (UiB), Ulysses Ninnemann (UiB), Nil Irvali (Uni Research), and Helga (Kikki) Kleiven (UiB) and their colleagues from Rutgers University, USA (Professor Yair Rosenthal), Laboratoire des Sciences du Climat et de l'Environnement, France (Research Scientist Catherine Kissel) and the University of Cambridge, UK (Professor David Hodell) used the shells of tiny single-celled, bottom-dwelling foraminifera found in marine sediment in the North Atlantic Ocean to reconstruct the surface ocean conditions and concomitant deep ocean circulation of about 125,000 years ago. This is the last interglacial period, when the North Atlantic was warmer, fresher and sea level was higher than it is today and looked a lot like what climate models predict it will look by the end of this century.

"At that time, there were a series of sudden and large reductions in the influence of these North Atlantic waters in the deep ocean. These deep water reductions occurred repeatedly, each lasting for some centuries before bouncing back. The unstable circulation operated as if it was near a threshold and flickered back and forth across it," says Eirik Vinje Galaasen, a PhD student and now researcher at UiB's Department of Earth Science, who is the lead author of the paper published in the journal Science.

"These types of changes hadn't been noticed before because they are so short-lived. Geologists hadn't focused on century scale ocean changes because they are difficult to detect," adds Professor Ulysses Ninnemann, from UiB's Department of Earth Science and Galaasen's PhD adviser.

"Our study demonstrates that deep water formation can be disrupted by the freshening of the regional surface water, which might happen due to enhanced precipitation and glacier melting under future climate change scenarios," says Yair Rosenthal, a co-author on the paper.

The international team studied traces of deep ocean properties imprinted in the sediments on the seafloor. Coring into the seafloor mud they could look back in time to reconstruct changes in the abyssal ocean at a location South of Greenland that is sensitive to North Atlantic Deep Water. The mud at this location builds up 10-15 times as fast as normal, recording much shorter changes than at other sites. Although the changes are short from a geological perspective, a few centuries of reduced deep water could be a big deal for societies that would have to grapple with things like draughts and sea level changes that could accompany them.

No "The Day After Tomorrow" scenario

A popularised notion is that if the ocean circulation declines it could cause large cooling or, as in the case of the Hollywood movie The Day After Tomorrow, a new ice age. Although some cooling did occur locally south of Greenland when the circulation slowed, there was no evidence for really large cooling associated with these changes. It could be that human beings haven't been able to find it yet, but equally reasonable is that humankind simply don't get really big cooling as the ocean slows down because when it is really warm, sea ice cannot form, and this supercharges the cooling effect of ocean circulation changes. In any event, the super cooling or slide into the next ice age as popularised in a Hollywood blockbuster did not occur.

Will this happen to the future Earth?

Many models have actually predicted a slow and gradual decline in North Atlantic circulation over the next century. However, different models offer widely different scenarios for what will happen in the future. While the climate of the last interglacial is not exactly what will be the case in a future greenhouse world, it does share some features, including being fresher and warmer by a few degrees Celsius in the northern Atlantic.

Training models, if models can capture the types of changes we see in the past, may also be doing a good job at predicting the future. The seafloor evidence suggests that there were large and fast changes in circulation the last time the ocean looked the way it may look by the end of this century.


Story Source:

The above story is based on materials provided by University of Bergen. Note: Materials may be edited for content and length.


Journal Reference:

  1. Eirik Vinje Galaasen, Ulysses S. Ninnemann, Nil Irvalı, Helga (Kikki) F. Kleiven, Yair Rosenthal, Catherine Kissel, and David A. Hodell. Rapid Reductions in North Atlantic Deep Water During the Peak of the Last Interglacial Period. Science, 20 February 2014 DOI: 10.1126/science.1248667

Cite This Page:

University of Bergen. "Climate change: Unstable Atlantic deep ocean circulation may hasten 'tipping point'." ScienceDaily. ScienceDaily, 20 February 2014. <www.sciencedaily.com/releases/2014/02/140220141625.htm>.
University of Bergen. (2014, February 20). Climate change: Unstable Atlantic deep ocean circulation may hasten 'tipping point'. ScienceDaily. Retrieved October 23, 2014 from www.sciencedaily.com/releases/2014/02/140220141625.htm
University of Bergen. "Climate change: Unstable Atlantic deep ocean circulation may hasten 'tipping point'." ScienceDaily. www.sciencedaily.com/releases/2014/02/140220141625.htm (accessed October 23, 2014).

Share This



More Earth & Climate News

Thursday, October 23, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

San Diego Zoo's White Rhinos Provide Hope for the Critically Endangered Species

San Diego Zoo's White Rhinos Provide Hope for the Critically Endangered Species

Reuters - Light News Video Online (Oct. 22, 2014) — The pair of rare white northern rhinos bring hope for their species as only six remain in the world. Elly Park reports. Video provided by Reuters
Powered by NewsLook.com
Trick-or-Treating Banned Because of Polar Bears

Trick-or-Treating Banned Because of Polar Bears

Buzz60 (Oct. 21, 2014) — Mother Nature is pulling a trick on the kids of Arviat, Canada. As Mara Montalbano (@maramontalbano) tells us, the effects of global warming caused the town to ban trick-or-treating this Halloween. Video provided by Buzz60
Powered by NewsLook.com
Traditional Farming Methods Gaining Ground in Mali

Traditional Farming Methods Gaining Ground in Mali

AFP (Oct. 20, 2014) — He is leading a one man agricultural revolution in Mali - Oumar Diatabe uses traditional farming methods to get the most out of his land and is teaching others across the country how to do the same. Duration: 01:44 Video provided by AFP
Powered by NewsLook.com
How Detroit's Money Woes Led To U.N.-Condemned Water Cutoffs

How Detroit's Money Woes Led To U.N.-Condemned Water Cutoffs

Newsy (Oct. 20, 2014) — The United Nations says water is a human right, but should it be free? Detroit has cut off water to residents who can't pay, and the U.N. isn't happy. Video provided by Newsy
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:

Strange & Offbeat Stories

 

Plants & Animals

Earth & Climate

Fossils & Ruins

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins