Borneo stalagmites provide new view of abrupt climate events over 100,000 years

Georgia Tech researchers Stacy Carolin (Ph.D. candidate), Jessica Moerman (Ph.D. candidate), Eleanor Middlemas (undergraduate), Danja Mewes (undergraduate) and two caving guides (Syria Lejau, Jenny Malang) climb out from Cobweb Cave in Gunung Mulu National Park after a day of rock and water sample collection during the Fall 2012 field trip. -  Credit: Kim Cobb
Georgia Tech researchers Stacy Carolin (Ph.D. candidate), Jessica Moerman (Ph.D. candidate), Eleanor Middlemas (undergraduate), Danja Mewes (undergraduate) and two caving guides (Syria Lejau, Jenny Malang) climb out from Cobweb Cave in Gunung Mulu National Park after a day of rock and water sample collection during the Fall 2012 field trip. – Credit: Kim Cobb

A new set of long-term climate records based on cave stalagmites collected from tropical Borneo shows that the western tropical Pacific responded very differently than other regions of the globe to abrupt climate change events. The 100,000-year climate record adds to data on past climate events, and may help scientists assess models designed to predict how the Earth’s climate will respond in the future.

The new record resulted from oxygen isotope analysis of more than 1,700 calcium carbonate samples taken from four stalagmites found in three different northern Borneo caves. The results suggest that climate feedbacks within the tropical regions may amplify and prolong abrupt climate change events that were first discovered in the North Atlantic.

The results were scheduled to be published June 6 in Science Express, the electronic advance online publication of the journal Science, and will appear later in an issue of printed publication. The research was supported by the National Science Foundation.

Today, relatively subtle changes in the tropical Pacific’s ocean and atmosphere have profound effects on global climate. However, there are few records of past climate changes in this key region that have the length, resolution and age controls needed to reveal the area’s response to abrupt climate change events.

“This is a new record from a very important area of the world,” said Kim Cobb, an associate professor in the School of Earth and Atmospheric Sciences at the Georgia Institute of Technology. “This record will provide a new piece of the puzzle from the tropical Pacific showing us how that climate system has responded to forcing events over the past 100,000 years.”

Among the findings were some surprises that show just how complicated the Earth’s climate system can be. While the stalagmite record reflected responses to abrupt changes known as Heinrich events, another major type of event – known as Dansgaard-Oeschger excursions – left no evidence in the Borneo stalagmites. Both types of abrupt climate change events are prominently featured in a previously-published stalagmite climate record from China – which is only slightly north of Borneo.

“To my knowledge, this is the first record that so clearly shows sensitivity to one set of major abrupt climate change events and not another,” said Cobb. “These two types of abrupt change events appear to have different degrees of tropical Pacific involvement, and because the tropical Pacific speaks with such a loud voice when it does speak, we think this is extremely important for understanding the mechanisms underlying these events.”

The researchers were also surprised to discover a very large and abrupt signal in their stalagmite climate records precisely when super-volcano Toba erupted nearby, roughly 74,000 years ago.

The team recovered the stalagmites from caves in Gunung Mulu and Gunung Buda National Parks, in northern Borneo, which is located a few degrees north of the Equator in the western Pacific. Back at their Georgia Tech lab, they analyzed the stalagmites for the ratio of oxygen isotopes contained in samples of calcium carbonate, the material from which the stalagmites were formed. That ratio is set by the oxygen isotopes in rainfall at the site, as the water that seeped into the ground dissolved limestone rock and dripped into the caves to form the stalagmites. The stalagmites accumulate at a rate of roughly one centimeter every thousand years.

“Stalagmites are time capsules of climate signals from thousands of years in the past,” said Stacy Carolin, a Georgia Tech Ph.D. candidate who gathered and analyzed the stalagmites. “We have instrumental records of climate only for the past 100 years or so, and if we want to look deeper into the past, we have to find records like these that locked in climate signals we can extract today.”

In the laboratory, Carolin sawed each stalagmite in half, opening it like a hot dog bun. She then used a tiny drill bit to take samples of the calcium carbonate down the center at one-millimeter steps. Because the stalagmites grew at varying rates, each sample represented as little as 60 years of time, or as much as 200 years. The precise ages of the samples were determined by measuring uranium and thorium isotope ratios, an analysis done with the help of Jess F. Adkins, a professor at the California Institute of Technology and a co-author of the study.

Rainfall oxygen isotopic ratios are good indicators of the amount of rainfall occurring throughout the region, as determined by a modern-day calibration study recently published by another graduate student in Cobb’s lab.

Merging data from the four different stalagmites provided a record of precipitation trends in the western Pacific over the past 100,000 years. That information can be compared to stalagmite and ice core climate records obtained elsewhere in the world.

“This record, which spans the entire last glacial period, adds significantly to the understanding of how various climate forcings are felt by the western tropical Pacific,” Carolin added.

Climate scientists are interested in learning more about abrupt climate changes because they indicate that the climate system may have “tipping points.” So far, the climate system has responded to rising carbon dioxide levels at a fairly steady rate, but many scientists worry about possible nonlinear effects.

“As a society, we haven’t really thought enough about the fact that we are moving Earth’s climate system toward a new state very quickly,” said Cobb. “It’s important to remember that the climate system has important nonlinearities that are most evident in these abrupt climate events. Ultimately, we’d like to be able to reproduce the global signatures of these abrupt climate events with numerical models of the climate system, and investigate the physics that drive such events.”

For Carolin, studying the half-meter-long stalagmites brought an awareness that the Earth has not always been as we know it today.

“You have to be impressed with the scope of what you are studying, and recognize that the state our climate is in today is incredibly different from Earth’s climate during the last Ice Age,” she said. “As we consider how humans may be affecting climate, dissecting what was going on tens of thousands of years ago in all regions of the globe can help scientists better predict how the Earth will respond to modern climate forcings.”

Volcanoes cause climate gas concentrations to vary

MIPAS data confirm the correlation between high sulfur dioxide concentrations (yellow-red) and high-reaching volcano eruptions (triangles). -  (Figure: KIT/M. Höpfner)
MIPAS data confirm the correlation between high sulfur dioxide concentrations (yellow-red) and high-reaching volcano eruptions (triangles). – (Figure: KIT/M. Höpfner)

Trace gases and aerosols are major factors influencing the climate. With the help of highly complex installations, such as MIPAS on board of the ENVISAT satellite, researchers try to better understand the processes in the upper atmosphere. Now, Karlsruhe Institute of Technology presents the most comprehensive overview of sulfur dioxide measurements in the journal of Atmospheric Chemistry and Physics (doi:10.5194/acpd-13-12389-2013).

“Sulfur compounds up to 30 km altitude may have a cooling effect,” Michael Höpfner, the KIT scientist responsible for the study, says. For example, sulfur dioxide (SO2) and water vapor react to sulfuric acid that forms small droplets, called aerosols, that reflect solar radiation back into universe. “To estimate such effects with computer models, however, the required measurement data have been lacking so far.” MIPAS infrared spectrometer measurements, however, produced a rather comprehensive set of data on the distribution and development of sulfur dioxide over a period of ten years.

Based on these results, major contributions of the sulfur budget in the stratosphere can be analyzed directly. Among others, carbonyl sulfide (COS) gas produced by organisms ascends from the oceans, disintegrates at altitudes higher than 25 km, and provides for a basic concentration of sulfur dioxide. The increase in the stratospheric aerosol concentration observed in the past years is caused mainly by sulfur dioxide from a number of volcano eruptions. “Variation of the concentration is mainly due to volcanoes,” Höpfner explains. Devastating volcano eruptions, such as those of the Pinatubo in 1991 and Tambora in 1815, had big a big effect on the climate. The present study also shows that smaller eruptions in the past ten years produced a measurable effect on sulfur dioxide concentration at altitudes between 20 and 30 km. “We can now exclude that anthropogenic sources, e.g. power plants in Asia, make a relevant contribution at this height,” Höpfner says.

“The new measurement data help improve consideration of sulfur-containing substances in atmosphere models,” Höpfner explains. “This is also important for discussing the risks and opportunities of climate engineering in a scientifically serious manner.”

MIPAS (Michelson Interferometer for Passive Atmospheric Sounding) was one of the main instruments on board of the European environmental satellite ENVISAT that supplied data from 2002 to 2012. MIPAS was designed by the KIT Institute of Meteorology and Climate Research. All around the clock, the instrument measured temperature and more than 30 atmospheric trace gases. It recorded more than 75 million infrared spectra. KIT researchers, together with colleagues from Forschungszentrum Jülich, have now developed the MIPAS successor GLORIA that may be the basis of a future satellite instrument for climate research.

Slow earthquakes: It’s all in the rock mechanics

Earthquakes that last minutes rather than seconds are a relatively recent discovery, according to an international team of seismologists. Researchers have been aware of these slow earthquakes, only for the past five to 10 years because of new tools and new observations, but these tools may explain the triggering of some normal earthquakes and could help in earthquake prediction.

“New technology has shown us that faults do not just fail in a sudden earthquake or by stable creep,” said Demian M. Saffer, professor of geoscience, Penn State. “We now know that earthquakes with anomalous low frequencies — slow earthquakes — and slow slip events that take weeks to occur exist.”

These new observations have put a big wrinkle into our thinking about how faults work, according to the researchers who also include Chris Marone, professor of geosciences, Penn State; Matt J. Ikari, recent Ph.D. recipient, and Achim J. Kopf, former Penn State postdoctural fellow, both now at the University of Bremen, Germany. So far, no one has explained the processes that cause slow earthquakes.

The researchers thought that the behavior had to be related to the type of rock in the fault, believing that clay minerals are important in this slip behavior to see how the rocks reacted. Ikari performed laboratory experiments using natural samples from drilling done offshore of Japan in a place where slow earthquakes occur. The samples came from the Integrated Ocean Drilling Program, an international collaborative. The researchers reported their results recently in Nature Geoscience.

These samples are made up of ocean sediment that is mostly clay with a little quartz.

“Usually, when you shear clay-rich fault rocks in the laboratory in the way rocks are sheared in a fault, as the speed increases, the rocks become stronger and self arrests the movement,” said Saffer. “Matt noticed another behavior. Initially the rocks reacted as expected, but these clays got weaker as they slid further. They initially became slightly stronger as the slip rate increased, but then, over the long run, they became weaker.

The laboratory experiments that produced the largest effect closely matched the velocity at which slow earthquakes occur in nature. The researchers also found that water content in the clays influenced how the shear occurred.

“From the physics of earthquake nucleation based on the laboratory experiments we would predict the size of the patch of fault that breaks at tens of meters,” said Saffer. “The consistent result for the rates of slip and the velocity of slip in the lab are interesting. Lots of things point in the direction for this to be the solution.”

The researchers worry about slow earthquakes because there is evidence that swarms of low frequency events can trigger large earthquake events. In Japan, a combination of broadband seismometers and global positioning system devices can monitor slow earthquakes.

For the Japanese and others in earthquake prone areas, a few days of foreknowledge of a potential earthquake hazard could be valuable and save lives.

For slow slip events, collecting natural samples for laboratory experiments is more difficult because the faults where these take place are very deep. Only off the north shore of New Zealand is there a fault that can be sampled. Saffer is currently working to arrange a drilling expedition to that fault.

Technology in the extreme

Radio transmitters that can withstand temperatures of up to 900 oC could soon be dropped into the depths of the earth to provide early warning of a volcanic eruption.

The state-of-the-art technology being pioneered by experts at Newcastle University uses Silicon Carbide electronics that can withstand temperatures equal to the inside of a jet engine.

Measuring subtle changes in the levels of key volcanic gases such as carbon dioxide and sulphur dioxide, the wireless sensor would feed back real-time data to the surface, providing vital information about volcanic activity and any impending eruption.

And because of its unique molecular structure – which is more stable than silicon – Silicon Carbide also has a high radiation tolerance opening up possibilities for its use in the nuclear industry.

The team has developed the necessary components and are now working to integrate them into a device about the size of an iPhone that could be used in a variety of locations such as power plants, aircraft engines and even volcanoes.

The device, featured today in The Engineer, is one of a number of technologies which has been developed by experts at the university’s Centre for Extreme Environment Technology, which was set up to ‘go where no technology has gone before’ and unlock the secrets of some of the world’s harshest environments.

Building reliable components that will continue to work under these conditions has been an on-going challenge for electronic engineers and the team at Newcastle University is recognised as a world leader in the field.

Dr Alton Horsfall, who leads the Silicon Carbide work alongside Professor Nick Wright, explains: “At the moment we have no way of accurately monitoring the situation inside a volcano and in fact most data collection actually goes on post-eruption. With an estimated 500 million people living in the shadow of a volcano this is clearly not ideal.

“We still have some way to go but using silicon carbide technology we hope to develop a wireless communication system that could accurately collect and transmit chemical data from the very depths of a volcano.”

And the device has other uses. “If someone sets off a bomb on the underground, for example, this will still sit on the wall and tell you what’s going on,” says Dr Horsfall.

Volcanic monitoring is just one of the strands of research being carried out at the Centre for Extreme Environment Technology.

With expertise in underwater communications, Professor Bayan Sharif, Jeff Neasham and Dr Charalampos Tsimenidis have developed a micro Remotely-Operated Vehicle that can be used to feed back environmental data about our coastlines. The team is also working on through metal communications which involves transmitting a signal through almost 10cm of steel and wireless sensor networks.

Professor Nick Wright, pro-vice chancellor for innovation and research at Newcastle University, added: “The situations we are planning to use our technology in means it’s not enough for the electronics to simply withstand extremes of temperature, pressure or radiation – they have to continue operating absolutely accurately and reliably.

“Increasingly mankind is spreading out into harsher and more extreme environments as our population grows and we explore new areas for possible sources of energy and food in order to sustain it.

“But with this comes new challenges and this is why research into extreme technologies is becoming ever more important.”