Featured Research

from universities, journals, and other organizations

Sea temperatures less sensitive to CO2 13 million years ago

Date:
June 6, 2012
Source:
San Francisco State University
Summary:
In the modern global climate, higher levels of carbon dioxide in the atmosphere are associated with rising ocean temperatures. But the seas were not always so sensitive to this CO2 "forcing," according to a new report. Around 5 to 13 million years ago, oceans were warmer than they are today -- even though atmospheric carbon dioxide concentrations were considerably lower.

In the modern global climate, higher levels of carbon dioxide (CO2) in the atmosphere are associated with rising ocean temperatures. But the seas were not always so sensitive to this CO2 "forcing," according to a new report. Around 5 to 13 million years ago, oceans were warmer than they are today -- even though atmospheric carbon dioxide concentrations were considerably lower.

The unusual mismatch between sea temperatures and CO2 levels during this time period hints that the relationship between climate and carbon dioxide hasn't always been the same as it is today, said Petra Dekens, assistant professor of geosciences and a co-author of the new study published in the journal Nature.

"There was a transition, from the Earth's climate system being not as sensitive to changes in atmospheric carbon dioxide to becoming more sensitive to these changes," Dekens said. "What's interesting is that we can see this transition happening within the last 13 million years."

The connection between modern-day ocean warming and increased levels of atmospheric carbon dioxide produced by human activities has been confirmed in numerous studies, many of them collected in the most recent report of the Intergovernmental Panel on Climate Change.

Recent reconstructions of carbon dioxide levels for the late Miocene time period (roughly 5 to 13 million years ago) suggest that CO2 concentrations for the period were only 200-350 parts per million. Modern CO2 concentrations, by contrast, are around 390 parts per million.

The study's lead author, Jonathan P. LaRiviere at the University of California, Santa Cruz, and colleagues including Dekens, sought information on late-Miocene ocean temperatures to analyze alongside the Miocene CO2 reconstructions.

They used an organic compound called unsaturated alkenone as their "fossil thermometers." The compound is produced by tiny phytoplankton and preserved in cores of ocean sediment drawn from the mid-latitude Pacific Ocean basin. Ratios of the compound preserve a record of the water temperature in which the plankton lived.

These data provide the first evidence, Dekens said, that late Miocene sea surface temperatures were significantly warmer than today across a large swath of the North Pacific. The research team found that sea surface temperatures appeared to be highest in the early part of the late Miocene (around 12 to 13 million years ago), and gradually cooled throughout the late Miocene.

The researchers also looked at changes in the late Miocene thermocline, or the ocean layer where warmer, shallow waters meet colder, deeper waters. By comparing oxygen isotope data retrieved from a variety of fossil plankton species that thrive at different ocean depths, they found that the depth of the thermocline has been growing shallow over the past 13 million years.

It is possible, Dekens and colleagues suggest, that changes in the thermocline played some role in creating the warmer waters of the late Miocene -- even as carbon dioxide concentrations stayed relatively low. The depth of the thermocline affects the mixing and circulation of colder and warmer ocean waters, which can in turn affect ocean temperature and atmospheric temperatures in a complex feedback cycle. "We would like to have more records from different regions," Dekens said, "to see if this change in the depth of the thermocline was a global change."

The thermocline might have grown shallow, the researchers say, as massive ocean waterways opened and closed with the shifting of tectonic plates. These changes would have remodeled ocean basins and the major patterns of ocean circulation.

One major waterway that began to close during the period was the Central American Seaway, an ancient body of water separating North and South America. The seaway was later closed by the volcanic creation of the Panama isthmus.

The study published in the June 7 issue of Nature. LaRiviere and Dekens' co-authors include A. Christina Ravelo and Heather L. Ford of the University of California, Santa Cruz; Allison Crimmons of the U.S. Environmental Protection Agency; Mitch Lyle of Texas A&M University; and Michael W. Wara of Stanford Law School.


Story Source:

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


Journal Reference:

  1. Jonathan P. LaRiviere, A. Christina Ravelo, Allison Crimmins, Petra S. Dekens, Heather L. Ford, Mitch Lyle, Michael W. Wara. Late Miocene decoupling of oceanic warmth and atmospheric carbon dioxide forcing. Nature, 2012; 486 (7401): 97 DOI: 10.1038/nature11200

Cite This Page:

San Francisco State University. "Sea temperatures less sensitive to CO2 13 million years ago." ScienceDaily. ScienceDaily, 6 June 2012. <www.sciencedaily.com/releases/2012/06/120606164940.htm>.
San Francisco State University. (2012, June 6). Sea temperatures less sensitive to CO2 13 million years ago. ScienceDaily. Retrieved September 3, 2014 from www.sciencedaily.com/releases/2012/06/120606164940.htm
San Francisco State University. "Sea temperatures less sensitive to CO2 13 million years ago." ScienceDaily. www.sciencedaily.com/releases/2012/06/120606164940.htm (accessed September 3, 2014).

Share This



More Earth & Climate News

Wednesday, September 3, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Raw: Thousands of Fish Dead in Mexico Lake

Raw: Thousands of Fish Dead in Mexico Lake

AP (Sep. 2, 2014) — Over 53 tons of rotting fish have been removed from Lake Cajititlan in western Jalisco state. Authorities say that the thousands of fish did not die of natural causes. (Sep. 2) Video provided by AP
Powered by NewsLook.com
Raw: Iceland Volcano Spewing Smoke

Raw: Iceland Volcano Spewing Smoke

AP (Sep. 2, 2014) — The alert warning for the area surrounding Iceland's Bardarbunga volcano was kept at orange on Tuesday, indicating increased unrest with greater potential for an eruption. Smoke is spewing from the volcano, and lava is spouting nearby. (Sept. 2) Video provided by AP
Powered by NewsLook.com
U.N. Says Ebola Travel Restrictions Will Cause Food Shortage

U.N. Says Ebola Travel Restrictions Will Cause Food Shortage

Newsy (Sep. 2, 2014) — The U.N. says the problem is two-fold — quarantine zones and travel restrictions are limiting the movement of both people and food. Video provided by Newsy
Powered by NewsLook.com
Halliburton Reaches $1B Gulf Spill Settlement

Halliburton Reaches $1B Gulf Spill Settlement

AP (Sep. 2, 2014) — Halliburton's agreement to pay more than $1 billion to settle numerous claims involving the 2010 BP oil spill could be a way to diminish years of costly litigation. A federal judge still has to approve the settlement. (Sept. 2) Video provided by AP
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:

More Coverage


Today's Climate More Sensitive to Carbon Dioxide Than in Past 12 Million Years

June 6, 2012 — Until now, studies of Earth's climate have documented a strong correlation between global climate and atmospheric carbon dioxide; that is, during warm periods, high concentrations of ... read more
from the past week

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