Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Corals show ocean temperature boundary rising with climate change

12.10.2010
Researchers looking at corals in the western tropical Pacific Ocean have found signs of a profound shift in the depth where warm surface water and colder deeper water meet--a shift predicted by computer models of global warming.

The finding is the first physical evidence supporting what climate modelers have been predicting as the effects of global climate change on the subsurface ocean circulation.

The new study has been accepted for publication in Geophysical Research Letters, a journal of the American Geophysical Union.

"We're trying to find a way to understand how the warm water in the tropical Pacific has changed in the last century, but more importantly during the last several decades," says Branwen Williams, who conducted this research while a doctoral student at Ohio State University in Columbus, Ohio. She is now a postdoctoral fellow at the University of Toronto in Ontario, Canada.

"The Pacific is really important since it serves as a strong driver and changes in this ocean can have a very strong impact on global climate and oceanography."

What plagues modelers and researchers alike is the limited amount of information available about the ocean when studying climate change. Satellite data and physical measurements are mainly restricted to the ocean's surface waters. What happens deeper in the waters is often an unknown.

Williams and Andrea Grottoli, an associate professor of earth sciences at Ohio State and Williams' former advisor, turned to a prolific form of soft, flexible coral, the Gorgonians, growing on a reef off the island nation of Palau.

"These corals 'sway' with the current underwater," Grottoli explains, "like trees in the wind. Since they aren't restricted to shallow and warmer surface waters like other tropical corals, they provide an opportunity to reconstruct a picture of subsurface ocean circulation in a region."

Specifically, the researchers were interested in how the boundary layer between the warmer, shallow water and the colder deeper water -- the thermocline -- has changed. But directly measuring that over time and across a broad area is impossible.

Instead, they used the soft corals as a substitute, a proxy, for determining how the thermocline rose and fell over time. Working with samples taken from corals at five meters (16.4 feet), 85 meters (279 feet) and 105 meters (345 feet), they analyzed the chemical structure of the coral skeleton that had built up over time.

Slices cut through the base "trunk" of the coral revealed concentric circles resembling tree rings which showed the growth of the "trunk" over time. By analyzing material from the rings from the outer surface inward to the center, they assembled a growth record covering the last century or so.

They were looking for the ratio between two isotopes of nitrogen in the material as a clue to how the thermocline rose or fell over time. Warmer waters above the thermocline contained lower levels of nutrients resulting in organic matter with a high ratio of nitrogen-15 to nitrogen-14 isotopes. Waters below the thermocline held higher levels of nutrients resulting in organic matter with a low ratio of nitrogen-15 to nitrogen-14 isotopes.

As the polyps in the coral consumed the organic matter over the years, the nitrogen isotopes were chemically recorded in the coral. By comparing the nitrogen-15 to nitrogen-14 ratios in samples from the three depths, Williams and Grottoli were able to draw a picture of how the thermocline moved.

"Over several decades, specifically since the mid- to late-1970s, the records show that the mean depth of the thermocline has been getting shallower," Williams says.

The researchers did a similar analysis of the ratio of two carbon isotopes in the coral samples as well. "I think it's fair to say that the carbon isotope record supports this interpretation," Grottoli says. "It's another piece of evidence backing our conclusions."

The researchers were also looking at how the coral record meshed with the Pacific Decadal Oscillation (PDO), a long-lived pattern of climate variability similar to the El Niño phenomenon.

While El Niño changes over a period of years, the PDO changes over decades.

"Climate modelers looking at how the Pacific might respond to global warming have predicted that the atmospheric patterns in the tropical Pacific would weaken, and if that happened, you would expect the thermocline to get shallower in the western tropical Pacific," Williams says.

"Our data are some of the first proxy data to support what the modelers have been predicting."

Grottoli saysthat the thermocline shift in the 1970s is important because it coincides with changes in the PDO from a negative phase to a positive phase.

"We think the thermocline rose when the PDO shifted," she says, "that it was a cumulative effect of both the natural variability of the PDO plus the warming global temperatures." Grottoli says that their coral record covered two other known times when the PDO shifted - in the 1920s and 1940s when average ocean termperatures were a bit lower than today - but neither caused a rise in the thermocline, based on their study.

The researchers want to repeat their study using coral samples from other locations, moving eastward across the Pacific, to test their findings that the thermocline shift wasn't a regional phenomenon, that it is occurring all across the ocean basin, Williams says.

Along with Williams and Grottoli, Patrick Colin, director of the Coral Reef Research Foundation, assisted in the project. Support for the research came from the National Science Foundation, the PADI Foundation, the Andrew Mellon Foundation and the National Ocean Sciences Accelerator Mass Spectrometry Facility at the Woods Hole Oceanographic Institution.

Notes for Journalists
As of the date of this press release, the paper by Williams et al. is still "in press" (i.e. not yet published). Journalists and public information officers (PIOs) of educational and scientific institutions who have registered with AGU can download a PDF copy of this paper by clicking on this link:

http://www.agu.org/journals/pip/gl/2010GL044867-pip.pdf

Or, you may order a copy of the paper by emailing your request to Maria-Jose Vinas at mjvinas@agu.org. Please provide your name, the name of your publication, and your phone number.

Images:
Available for download at:
http://researchnews.osu.edu/archive/thermoclinepix.htm
Title:
"Recent shoaling of the nutricline and thermocline in the western tropical Pacific"

Contact information for the authors:

Branwen Williams, Tel. +1 (905) 828-5419; Mail branwen.williams@utoronto.ca Andrea Grottoli, Tel +1 (614) 292-5782; Mail grottoli.1@osu.edu

Maria-Jose Vinas | American Geophysical Union
Further information:
http://www.agu.org

More articles from Earth Sciences:

nachricht NASA examines newly formed Tropical Depression 3W in 3-D
26.04.2017 | NASA/Goddard Space Flight Center

nachricht Early organic carbon got deep burial in mantle
25.04.2017 | Rice University

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Making lightweight construction suitable for series production

More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.

Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...

Im Focus: Wonder material? Novel nanotube structure strengthens thin films for flexible electronics

Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.

"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...

Im Focus: Deep inside Galaxy M87

The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.

Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...

Im Focus: A Quantum Low Pass for Photons

Physicists in Garching observe novel quantum effect that limits the number of emitted photons.

The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...

Im Focus: Microprocessors based on a layer of just three atoms

Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.

Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Expert meeting “Health Business Connect” will connect international medical technology companies

20.04.2017 | Event News

Wenn der Computer das Gehirn austrickst

18.04.2017 | Event News

7th International Conference on Crystalline Silicon Photovoltaics in Freiburg on April 3-5, 2017

03.04.2017 | Event News

 
Latest News

Scientist invents way to trigger artificial photosynthesis to clean air

26.04.2017 | Materials Sciences

Ammonium nitrogen input increases the synthesis of anticarcinogenic compounds in broccoli

26.04.2017 | Agricultural and Forestry Science

SwRI-led team discovers lull in Mars' giant impact history

26.04.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>