OREGON STATE UNIVERSITY

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PNAS Commentary: Study sheds new light on sea level rise at last ice age

CORVALLIS, Ore. – A new study published last week in Proceedings of the National Academy of Sciences calculated global sea level changes over the past 35,000 years, concluding that in order to account for the amount of sea level lowering at the peak of the last ice age, much more ice would have had to have been tied up on land than previously thought.

The researchers further concluded that most of this “excess ice” – or an amount greater than today – was likely added to the present Antarctic ice sheets. Lead researcher Kurt Lambeck from Australian National University and colleagues estimated that during the last glacial maximum, these ice sheets had enough excess ice to increase global sea levels some 25 meters, much more than the 10-meter excess scientists previously estimated.

These new findings are critical to understanding the sources of sea level rise that is taking place today in response to a warming climate, according to Peter Clark, an Oregon State University paleoclimatologist, who co-authored a commentary piece on the research in the latest edition of PNAS, which will be published this week.

“Essentially, this new study implies that the Antarctic ice sheets are losing less mass today than had previously been estimated through satellite measurements,” said Clark, a professor in OSU’s College of Earth, Ocean, and Atmospheric Sciences. “During the last ice age, the ice sheets were so large and heavy they pushed the entire land mass down and displaced the viscous mantle below.

“As the ice sheets began to retreat, the land mass beneath began to rise due to the area below being refilled by the mantle as it slowly flows back,” Clark added. “This process is continuing today and needs to be accounted for when estimating from satellites current mass loss from the Antarctic ice sheets. If the effect of this process is bigger than previously thought, then current mass loss is less than we thought.

“If this is the case, then at least some of the rising sea level today that is being attributed to loss of the Antarctic ice sheets must have some other source.”

The other main sources of sea level rise today are from the loss of the Greenland ice sheets, receding glaciers on a global basis, and the expansion of the ocean itself through warming.

Studies show that sea level today is rising globally at a rate of about 3.0 millimeters a year, and about 1/10th of that (0.3 mm) was thought to be from Antarctica.

“If this new study holds up, that means that the rate of contribution from Antarctica to today’s rise is less than 0.3 millimeters,” Clark said. “Learning the source of the increase will help us better understand how sea level rise may play out in the future.”

Prior to Lambeck’s study, the prevailing theory among many scientists was that Antarctic ice sheets contained enough ice to raise global sea levels about 70 meters if it had melted all at once some 21,000 years ago. These ice sheets today hold enough water to raise sea levels 60 meters – about 10 meters less than during the last glacial maximum.

But the study by Lambeck and colleagues, which was based on a comprehensive analysis of nearly 1,000 paleo-sea level markers, suggests instead that the Antarctic had enough mass during the last ice age to raise global sea levels some 85 meters if melted.

In contrast, the entire Greenland ice sheet today contains enough ice to raise global sea levels about seven meters, if melted at once.

Clark, who was a coordinating lead author on sea level rise for the 2013 Intergovernmental Panel on Climate Change (IPCC) report, cautioned that there may be other explanations for the “excess ice” thought to account for the lower sea levels during the last ice age. These might include a greater influence from the lateral viscosity of the Earth’s mantle fluid, the possibility of a large, grounded East Siberian ice sheet, and the influence of physical factors on organisms used as proxies to determine sea level rises.

Lev Tarasov of Memorial University of Newfoundland, co-authored the commentary with Clark.

Media Contact: 
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Peter Clark, 541-737-1247; clarkp@geo.oregonstate.edu

New study shows three abrupt pulse of CO2 during last deglaciation

CORVALLIS, Ore. – A new study shows that the rise of atmospheric carbon dioxide that contributed to the end of the last ice age more than 10,000 years ago did not occur gradually, but was characterized by three “pulses” in which C02 rose abruptly.

Scientists are not sure what caused these abrupt increases, during which C02 levels rose about 10-15 parts per million – or about 5 percent per episode – over a period of 1-2 centuries. It likely was a combination of factors, they say, including ocean circulation, changing wind patterns, and terrestrial processes.

The finding is important, however, because it casts new light on the mechanisms that take the Earth in and out of ice age regimes. Results of the study, which was funded by the National Science Foundation, appear this week in the journal Nature.

“We used to think that naturally occurring changes in carbon dioxide took place relatively slowly over the 10,000 years it took to move out of the last ice age,” said Shaun Marcott, lead author on the article who conducted his study as a post-doctoral researcher at Oregon State University. “This abrupt, centennial-scale variability of CO2 appears to be a fundamental part of the global carbon cycle.”

Some previous research has hinted at the possibility that spikes in atmospheric carbon dioxide may have accelerated the last deglaciation, but that hypothesis had not been resolved, the researchers say. The key to the new finding is the analysis of an ice core from the West Antarctic that provided the scientists with an unprecedented glimpse into the past.

Scientists studying past climate have been hampered by the limitations of previous ice cores. Cores from Greenland, for example, provide unique records of rapid climate events going back 120,000 years – but high concentrations of impurities don’t allow researchers to accurately determine atmospheric carbon dioxide records. Antarctic ice cores have fewer impurities, but generally have had lower “temporal resolution,” providing less detailed information about atmospheric CO2.

However, a new core from West Antarctica, drilled to a depth of 3,405 meters in 2011 and spanning the last 68,000 years, has “extraordinary detail,” said Oregon State paleoclimatologist Edward Brook, a co-author on the Nature study and an internationally recognized ice core expert. Because the area where the core was taken gets high annual snowfall, he said, the new ice core provides one of the most detailed records of atmospheric CO2.

“It is a remarkable ice core and it clearly shows distinct pulses of carbon dioxide increase that can be very reliably dated,” Brook said. “These are some of the fastest natural changes in CO2 we have observed, and were probably big enough on their own to impact the Earth’s climate.

“The abrupt events did not end the ice age by themselves,” Brook added. “That might be jumping the gun a bit. But it is fair to say that the natural carbon cycle can change a lot faster than was previously thought – and we don’t know all of the mechanisms that caused that rapid change.”

The researchers say that the increase in atmospheric CO2 from the peak of the last ice age to complete deglaciation was about 80 parts per million, taking place over 10,000 years. Thus, the finding that 30-45 ppm of the increase happened in just a few centuries was significant.

The overall rise of atmospheric carbon dioxide during the last deglaciation was thought to have been triggered by the release of CO2 from the deep ocean – especially the Southern Ocean. However, the researchers say that no obvious ocean mechanism is known that would trigger rises of 10-15 ppm over a time span as short as one to two centuries.

“The oceans are simply not thought to respond that fast,” Brook said. “Either the cause of these pulses is at least part terrestrial, or there is some mechanism in the ocean system we don’t yet know about.”

One reason the researchers are reluctant to pin the end of the last ice age solely on CO2 increases is that other processes were taking place, according to Marcott, who recently joined the faculty of the University of Wisconsin-Madison.

“At the same time CO2 was increasing, the rate of methane in the atmosphere was also increasing at the same or a slightly higher rate,” Marcott said. “We also know that during at least two of these pulses, the Atlantic Meridional Overturning Circulation changed as well. Changes in the ocean circulation would have affected CO2 – and indirectly methane, by impacting global rainfall patterns.”

“The Earth is a big coupled system,” he added, “and there are many pieces to the puzzle. The discovery of these strong, rapid pulses of CO2 is an important piece.”

Media Contact: 
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Shaun Marcott, smarcott@wisc.edu;

Ed Brook, 541-737-8197, brooke@geo.oregonstate.edu

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(Feature photo at left) - Donald Voigt from Penn State looks at an ice core in January 2012 during the WAIS Divide project. Photo courtesy of Gifford Wong, Dartmouth

 

 

 

 

 

 

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OSU scientists have examined air bubbles trapped in a new ice core that are providing them with some of the clearest indications of atmospheric conditions during the last ice age.

Scientists discover carbonate rocks are unrecognized methane sink

CORVALLIS, Ore. – Since the first undersea methane seep was discovered 30 years ago, scientists have meticulously analyzed and measured how microbes in the seafloor sediments consume the greenhouse gas methane as part of understanding how the Earth works.

The sediment-based microbes form an important methane “sink,” preventing much of the chemical from reaching the atmosphere and contributing to greenhouse gas accumulation. As a byproduct of this process, the microbes create a type of rock known as authigenic carbonate, which while interesting to scientists was not thought to be involved in the processing of methane.

That is no longer the case. A team of scientists has discovered that these authigenic carbonate rocks also contain vast amounts of active microbes that take up methane. The results of their study, which was funded by the National Science Foundation, were reported today in the journal Nature Communications.

“No one had really examined these rocks as living habitats before,” noted Andrew Thurber, an Oregon State University marine ecologist and co-author on the paper. “It was just assumed that they were inactive. In previous studies, we had seen remnants of microbes in the rocks – DNA and lipids – but we thought they were relics of past activity. We didn’t know they were active.

“This goes to show how the global methane process is still rather poorly understood,” Thurber added.

Lead author Jeffrey Marlow of the California Institute of Technology and his colleagues studied samples from authigenic compounds off the coasts of the Pacific Northwest (Hydrate Ridge), northern California (Eel River Basin) and central America (the Costa Rica margin). The rocks range in size and distribution from small pebbles to carbonate “pavement” stretching dozens of square miles.

“Methane-derived carbonates represent a large volume within many seep systems and finding active methane-consuming archaea and bacteria in the interior of these carbonate rocks extends the known habitat for methane-consuming microorganisms beyond the relatively thin layer of sediment that may overlay a carbonate mound,” said Marlow, a geobiology graduate student in the lab of Victoria Orphan of Caltech.

These assemblages are also found in the Gulf of Mexico as well as off Chile, New Zealand, Africa, Europe – “and pretty much every ocean basin in the world,” noted Thurber, an assistant professor (senior research) in Oregon State’s College of Earth, Ocean, and Atmospheric Sciences.

The study is important, scientists say, because the rock-based microbes potentially may consume a huge amount of methane. The microbes were less active than those found in the sediment, but were more abundant – and the areas they inhabit are extensive, making their importance potential enormous. Studies have found that approximately 3-6 percent of the methane in the atmosphere is from marine sources – and this number is so low due to microbes in the ocean sediments consuming some 60-90 percent of the methane that would otherwise escape.

Now those ratios will have to be re-examined to determine how much of the methane sink can be attributed to microbes in rocks versus those in sediments. The distinction is important, the researchers say, because it is an unrecognized sink for a potentially very important greenhouse gas.

“We found that these carbonate rocks located in areas of active methane seeps are themselves more active,” Thurber said. “Rocks located in comparatively inactive regions had little microbial activity. However, they can quickly activate when methane becomes available.

“In some ways, these rocks are like armies waiting in the wings to be called upon when needed to absorb methane.”

The ocean contains vast amounts of methane, which has long been a concern to scientists. Marine reservoirs of methane are estimated to total more than 455 gigatons and may be as much as 10,000 gigatons carbon in methane. A gigaton is approximate 1.1 billion tons.

By contrast, all of the planet’s gas and oil deposits are thought to total about 200-300 gigatons of carbon.

Media Contact: 
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Andrew Thurber, 541-737-4500, athurber@coas.oregonstate.edu

Study finds air temperature models poor at predicting stream temps

CORVALLIS, Ore. – Stream temperatures are expected to rise in the future as a result of climate change, but a new study has found that the correlation between air temperature and stream temperature is surprisingly tenuous.

The findings cast doubt on many statistical models using air temperatures to predict future stream temperatures.

Lead author Ivan Arismendi, a stream ecologist at Oregon State University, examined historic stream temperature data over a period of one to four decades from 25 sites in the western United States to see if increases in air temperature during this period could have predicted – through the use of statistical models – the observed stream temperatures.

He discovered that many streams were cooler than the models predicted, while others were warmer. The difference in temperature between the models and actual measurements, however, was staggering – as much as 12 degrees Celsius different in some rivers.

Results of the study have recently been published in the journal Environmental Research Letters. The study involved scientists from Oregon State, the U.S. Forest Service and the U.S. Geological Survey, and was supported by all three organizations, as well as by the National Science Foundation.

“These air-stream temperature models originated as a tool for looking at short-term relationships,” said Arismendi, a researcher in the OSU Department of Fisheries and Wildlife. “The problem is that people are starting to use them for long-term extrapolation. It is unreliable to apply uniform temperature impacts on a regional scale because there are so many micro-climate factors influencing streams on a local basis.”

Sherri Johnson, a U.S. Forest Service research ecologist and co-author on the study, said the findings are important because decisions based on these models may not be accurate. Some states, for example, have projected a major loss of suitable habitat for trout and other species because the models suggest increases in stream temperature commensurate with projected increases in air temperature.

“It just isn’t that simple,” Arismendi said. “Stream temperatures are influenced by riparian shading and in-stream habitat, like side channels. Dams can have an enormous influence, as can groundwater. It is a messy, complex challenge to project stream temperatures into the future.”

What made this study work, the authors say, was evaluating more than two dozen sites that had historic stream temperature data, which can be hard to find. The development about a dozen years ago of data loggers that can be deployed in streams is contributing enormous amounts of new data, but accurate historic records of stream temperatures are sparse.

Researchers at USGS and at sites like the H.J. Andrews Experimental Forest in Oregon, part of the National Science Foundation’s Long-Term Ecological Research program, have compiled stream data for up to 44 years, giving Arismendi and his colleagues enough historical data to conduct the comparative study.

In many of the 25 sites examined in the study, the researchers found that the difference between model-projected stream temperatures and actual stream temperatures was as great as the actual amount of warming projected – 3.0 degrees Celsius, or 5.5 degrees Fahrenheit. And in some cases, the projections were even farther off target.

“The models predictions were poor in summer and winter, and when there are extreme situations,” Arismendi noted. “They were developed to look at Midwest streams and don’t account for the complexity of western streams that are influenced by topography, extensive riparian areas and other factors.”

Increases in air temperatures in the future are still likely to influence stream temperatures, but climate sensitivity of streams “is more complex than what is being realized by using air temperature-based models,” said Mohammad Safeeq, an Oregon State University researcher and co-author on the study.

“The good news is that some of the draconian projections of future stream temperatures may be overstated,” noted Safeeq, who is in OSU’s College of Earth, Ocean, and Atmospheric Sciences. “On the other hand, some may actually be warmer than what air temperature-based models project.”

Not all streams will be affected equally, Johnson said.

“The one constant is that a healthy watershed will be more resilient to climate change than one that isn’t healthy – and that should continue to be the focus of restoration and management efforts,” she noted.

Jason Dunham, an aquatic ecologist with the USGS and co-author on the study, said the study highlights the value of long-term stream temperature records in the Northwest and globally.

“Without a long-term commitment to collecting this kind of data, we won’t have the ability to evaluate existing models as we did in this work,” Dunham said. “Long-term datasets provide vital material for developing better methods for quantifying the effects of climate on our water resources.”

Media Contact: 
Source: 

Ivan Arismendi, 541-750-7443;

Sherri Johnson, 541-758-7771

Anglers, beachcombers asked to watch for transponders from Japan

CORVALLIS, Ore. – Northwest anglers venturing out into the Pacific Ocean in pursuit of salmon and other fish this fall may scoop up something unusual into their nets – instruments released from Japan called “transponders.”

These floating instruments are about the size of a 2-liter soda bottle and were set in the ocean from different ports off Japan in 2011-12 after the massive Tohoku earthquake and tsunami. Researchers from Tattori University for Environmental Studies in Japan have been collaborating with Oregon State University, Oregon Sea Grant, and the NOAA Marine Debris Program on the project.

The researchers’ goal is to track the movement of debris via ocean currents and help determine the path and timing of the debris from the 2011 disaster. An estimated 1.5 million tons of debris was washed out to sea and it is expected to continue drifting ashore along the West Coast of the United States for several years, according to Sam Chan, a watershed health specialist with Oregon State University Extension and Oregon Sea Grant.

“These transponders only have a battery life of about 30 months and then they no longer communicate their location,” Chan said. “So the only way to find out where they end up is to physically find them and report their location. That’s why we need the help of fishermen, beachcombers and other coastal visitors.

“These bottles contain transmitters and they are not a hazardous device,” Chan added. “If you find something that looks like an orange soda bottle with a short antenna, we’d certainly like your help in turning it in.”

Persons who find a transponder are asked to photograph it if possible, and report the location of their find to Chan at Samuel.Chan@oregonstate.edu; or to the NOAA Marine Debris Program regional coordinator in their area at http://marinedebris.noaa.gov/contact-us. They will provide shipping instructions to persons who find the transponders so that the instruments can be returned to the research team.

One of the first transponders discovered in the Northwest washed ashore near Arch Cape, Oregon, in March 2013, about 19 months after it was set adrift. The persons who found it reported it to Chan, who began collaborating with researchers in Japan.

Another transponder was found near the Haida Heritage Site, formerly the Queen Charlotte Islands – the same location where a Harley-Davidson motorcycle floated up on a beach in a shipping container long after being swept out to sea in Japan by the tsunami.

“These transponders have recorded a lot of important data that will help us better understand the movement of tsunami and marine debris throughout the Pacific Ocean,” Chan said. “Everyone’s help in recovering these instruments is greatly appreciated.”

Media Contact: 
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Sam Chan, 541-737-4828; samuel.chan@oregonstate.edu

Concern grows over pet pills and products, as well as those of owners

CORVALLIS, Ore. – Scientists have long been aware of the potential environment impacts that stem from the use and disposal of the array of products people use to keep themselves healthy, clean and smelling nice.

Now a new concern is emerging – improper disposal of pet care products and pills.

Dog shampoos, heartworm medicine, flea and tick sprays, and a plethora of prescription and over-the-counter medicines increasingly are finding their way into landfills and waterways, where they can threaten the health of local watersheds. An estimated 68 percent of American households have at least one pet, illustrating the potential scope of the problem.

How bad is that problem? No one really knows, according to Sam Chan, a watershed health expert with the Oregon Sea Grant program at Oregon State University.

But Chan and his colleagues aim to find out. They are launching a national survey (online at: http://tinyurl.com/PetWellbeingandEnvironment)  of both pet owners and veterinary care professionals to determine how aware that educated pet owners are of the issue, what is being communicated, and how they dispose of  “pharmaceutical and personal care products” (PPCPs) for both themselves and their pets. Pet owners are encouraged to participate in the survey.

“You can count on one hand the number of studies that have been done on what people actively do with the disposal of these products,” Chan said. “PPCPs are used by almost everyone and most wastewater treatment plants are not able to completely deactivate many of the compounds they include.”

Increasingly, Chan said, a suite of PPCPs used by pets and people are being detected at low levels in surface water and groundwater. Examples include anti-inflammatory medicines such as ibuprofen, antidepressants, antibiotics, estrogens, the insect repellent DEET, and ultraviolet (UV) sunblock compounds.

Some of the impacts from exposure to these products are becoming apparent. Fish exposed to levels of antidepressants at concentrations lower than sewage effluence, for example, have been shown to become more active and bold – making them more susceptible to predation, noted Chan, an OSU Extension Sea Grant specialist.

“Triclosan is another concern; it is a common anti-microbial ingredient in soaps, toothpaste, cosmetics, clothing, cookware, furniture and toys to prevent or reduce bacterial contamination for humans and pets,” Chan said. “It is being linked to antibiotic resistance in riparian zones, as well as to alterations in mammal hormone regulation – endocrine disruptor – and impacts on immune systems.”

Another common endocrine disruptor, the researchers say, is coal tar, a common ingredient in dandruff shampoo for humans, and pet medicines for skin treatment.

Jennifer Lam conducted a preliminary survey of veterinary practitioners as part of her master’s thesis at Oregon State University and found awareness by veterinary professionals of the environmental issues caused by improper disposal of PPCPs was high. Yet many did not share that information with their clients.

In fact, veterinarians only discussed best practices for disposal with their clients 18 percent of the time, her survey found.

“The awareness is there, but so are barriers,” Lam said. “Communicating about these issues in addition to care instructions takes time. There may be a lack of educational resources – or a lack of awareness on their availability. And some may not think of it during the consultation process.”

The National Sea Grant program recently partnered with the American Veterinary Medicine Association to promote the reduction of improper PPCP disposal. The national survey is a first step in that process.

“Most people tend to throw extra pills or personal care products into the garbage and in fewer instances, flush them down the drain,” Chan said. “It seems like the right thing to do, but is not the most environmentally friendly method for disposing unused or expired PPCPs. Waste in landfills produce leachates and these contaminates may not be fully deactivated by current wastewater treatments. They can get into groundwater and streams, where they can cause a variety of environmental problems and create a health risk as well.”

When disposing of expired or unneeded medications, the researchers say, don’t flush them. Instead, take to them to a drug take-back event or depository. New rules to be implemented by the U.S. Drug Enforcement Agency (DEA) later this fall will make drug take-back options more available.

Chan and Lam suggest that in areas where take-back options are not available, people should mix unused or unwanted drugs with coffee grounds or kitty litter – something that will be unpalatable to pets. Then put the mixture in a sealed container and deposit it in the trash.

Results from the national survey led by Oregon Sea Grant will provide much-needed information to guide education, watershed monitoring and improvements on ways to reduce PPCP contamination and their environmental impacts.

The survey will continue until Nov. 1.

Media Contact: 
Source: 

Sam Chan, 503-679-4828, sam.chan@oregonstate.edu;

Jennifer Lam, lamj@onid.oregonstate.edu

OSU part of major grant to study Southern Ocean carbon cycle

CORVALLIS, Ore. – A new six-year, $21 million initiative funded by the National Science Foundation will explore the role of carbon and heat exchanges in the vast Southern Ocean – and their potential impacts on climate change.

The Southern Ocean Carbon and Climate Observations and Modeling program will be headquartered at Princeton University, and include researchers at several institutions, including Oregon State University. It is funded by NSF’s Division of Polar Programs, with additional support from the National Oceanic and Atmospheric Administration and NASA.

The Southern Ocean acts as a carbon “sink” by absorbing as much as half of the human-derived carbon in the atmosphere and much of the planet’s excess heat. Yet little is known of this huge body of water that accounts for 30 percent of the world’s ocean area.

Under this new program known by the acronym SOCCOM, Princeton and 10 partner institutions will create a physical and biogeochemical portrait of the ocean using hundreds of robotic floats deployed around Antarctica. The floats, which will be deployed over the next five years, will collect seawater profiles using sophisticated sensors to measure pH, oxygen and nitrate levels, temperature and salinity – from the ocean surface to a depth of 1,000 meters, according to Laurie Juranek, an Oregon State University oceanographer and project scientist.

“This will be the first combined large-scale observational and modeling program of the entire Southern Ocean,” said Juranek, who is in OSU’s College of Earth, Ocean, and Atmospheric Sciences. “It is a very important region, but difficult to access – hence the use of robotic floats to collect data. However, not everything that we need to know can be measured by sensors, so we’ll need to get creative.”

Juranek's role in this project is to develop relationships between the measured variables and those that can't be measured directly by a sensor but are needed for understanding Southern Ocean carbon dioxide exchanges. These relationships can be applied to the float data as well as to high-resolution models. To do this work she is partnering with colleagues at NOAA's Pacific Marine Environmental Laboratory.

In addition to its role in absorbing carbon and heat, the Southern Ocean delivers nutrients to lower-latitude surface waters that are critical to ocean ecosystems around the world, said program director Jorge Sarmiento, Princeton's George J. Magee Professor of Geoscience and Geological Engineering and director of the Program in Atmospheric and Oceanic Sciences. And as levels of carbon dioxide increase in the atmosphere, models suggest that the impacts of ocean acidification are projected to be most severe in the Southern Ocean, he added.

"The scarcity of observations in the Southern Ocean and inadequacy of earlier models, combined with its importance to the Earth's carbon and climate systems, means there is tremendous potential for groundbreaking research in this region," Sarmiento said.

Media Contact: 
Source: 

Laurie Juranek, 541-737-2368; ljuranek@coas.oregonstate.edu

Study resolves discrepancy in Greenland temperatures during end of last ice age

CORVALLIS, Ore. – A new study of three ice cores from Greenland documents the warming of the large ice sheet at the end of the last ice age – resolving a long-standing paradox over when that warming occurred.

Large ice sheets covered North America and northern Europe some 20,000 years ago during the coldest part of the ice age, when global average temperatures were about four degrees Celsius (or seven degrees Fahrenheit) colder than during pre-industrial times. And then changes in the Earth’s orbit around the sun increased the solar energy reaching Greenland. Beginning some 18,000 years ago, release of carbon from the deep ocean led to a graduate rise in atmospheric carbon dioxide (CO2).

Yet past analysis of ice cores from Greenland did not show any warming response as would be expected from an increase in CO2 and solar energy flux, the researchers note.

In this new study, funded by the National Science Foundation and published this week in the journal Science, scientists reconstructed air temperatures by examining ratios of nitrogen isotopes in air trapped within the ice instead of isotopes in the ice itself, which had been used in past studies.

Not only did the new analysis detect significant warming in response to increasing atmospheric CO2, it documents a warming trend at a rate closely matching what climate change models predict should have happened as the Earth shifted out of its ice age, according to lead author Christo Buizert, a postdoctoral researcher at Oregon State University and lead author on the Science article.

“The Greenland isotope records from the ice itself suggest that temperatures 12,000 years ago during the so-called Younger Dryas period near the end of the ice age were virtually the same in Greenland as they were 18,000 years ago when much of the northern hemisphere was still covered in ice,” Buizert said. “That never made much sense because between 18,000 and 12,000 years ago atmospheric CO2 levels rose quite a bit.”

“But when you reconstruct the temperature history using nitrogen isotope ratios as a proxy for temperature, you get a much different picture,” Buizert pointed out. “The nitrogen-based temperature record shows that by 12,000 years ago, Greenland temperatures had already warmed by about five degrees (Celsius), very close to what climate models predict should have happened, given the conditions.”

Reconstructing temperatures by using water isotopes provides useful information about when temperatures shift but can be difficult to calibrate because of changes in the water cycle, according to Edward Brook, an Oregon State paleoclimatologist and co-author on the Science study.

“The water isotopes are delivered in Greenland through snowfall and during an ice age, snowfall patterns change,” Brook noted. “It may be that the presence of the giant ice sheet made snow more likely to fall in the summer instead of winter, which can account for the warmer-than-expected temperatures because the snow records the temperature at the time it fell.”

In addition to the gradual warming of five degrees (C) over a 6,000-year period beginning 18,000 years ago the study investigated two periods of abrupt warming and one period of abrupt cooling documented in the new ice cores. The researchers say their leading hypothesis is that all three episodes are tied to changes in the Atlantic meridional overturning circulation (AMOC), which brings warm water from the tropics into the high northern latitudes.

The first episode caused a jump in Greenland’s air temperatures of 10-15 degrees (C) in just a few decades beginning about 14,700 years ago. An apparent shutdown of the AMOC about 12,800 years ago caused an abrupt cooling of some 5-9 degrees (C), also over a matter of decades.

When the AMOC was reinvigorated again about 11,600 years ago, it caused a jump in temperatures of 8-, 11 degrees (C), which heralded the end of the ice age and the beginning of the climatically warm and stable Holocene period, which allowed human civilization to develop.

“For these extremely abrupt transitions, our data show a clear fingerprint of AMOC variations, which had not yet been established in the ice core studies,” noted Buizert, who is in OSU’s College of Earth, Ocean, and Atmospheric Sciences.  “Other evidence for AMOC changes exists in the marine sediment record and our work confirms those findings.”

In their study, the scientists examined three ice cores from Greenland and looked at the gases trapped inside the ice for changes in the isotopic ration of nitrogen, which is very sensitive to temperature change. They found that temperatures in northwest Greenland did not change nearly as much as those in southeastern Greenland – closest to the North Atlantic – clearly suggesting the influence of the AMOC.

“The last deglaciation is a natural example of global warming and climate change,” Buizert said. “It is very important to study this period because it can help us better understand the climate system and how sensitive the surface temperature is to atmospheric CO2.”

“The warming that we observed in Greenland at the end of the ice age had already been predicted correctly by climate models several years ago,” Buizert added. “This gives us more confidence that these models also predict future temperatures correctly.”

Media Contact: 
Source: 

Christo Buizert, 541-737-1209

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Study: Pacific Northwest shows warming trend over past century-plus

CORVALLIS, Ore. – The annual mean temperature in the Pacific Northwest has warmed by about 1.3 degrees Fahrenheit since the early 20th century – a gradual warming trend that has been accelerating over the past 3-4 decades and is attributed to anthropogenic, or human, causes.

The study is one of the first to isolate the role of greenhouse gases associated with regional warming, the authors say. It was published in a recent issue of the Journal of Climate, a publication of the American Meteorological Society.

“The amount of warming may not sound like a lot to the casual observer, but we already are starting to see some of the impacts and what is particularly significant is that the rate of warming is increasing,” said Philip Mote, director of the Oregon Climate Change Research Institute at Oregon State University and a co-author on the study.

“Just a 1.3-degree increase has lengthened the ‘freeze-free’ season by 2-3 weeks and is equivalent to moving the snowline 600 feet up the mountain,” Mote added. “At the rate the temperature is increasing, the next 1.3-degree bump will happen much more quickly.”

In their study, the researchers looked at temperatures and precipitation from 1901 to 2012 in the Northwest, which includes Washington, Oregon, Idaho, western Montana, and the northwestern tip of Wyoming. They examined four different factors to determine the influence of human activities, including greenhouse gases and aerosols; solar cycles; volcanic eruptions; and naturally occurring phenomena including El Niño events and the Pacific Decadal Oscillation.

Using what is called a “multilinear regression” approach, they were able to tease out the influences of the different factors. Volcanic activity, for example, led to cooler temperatures in 1961, 1982 and 1991. Likewise, El Niño events led to warming in numerous years.

“Natural variation can explain much of the change from year to year, but it cannot account for this long-term warming trend,” noted David Rupp, a research associate with the Oregon Climate Change Research Institute and co-author on the report. “Anthropogenic forcing was the most significant predictor of, and leading contributor to, the warming.”

Among the study’s findings:

  • The Northwest experienced relatively cool periods from 1910-25 and from 1945-60, and a warm period around 1940 and from the mid-1980s until the present.
  • The warmest 10-year period has been from 1998 to 2007, and very few years since 1980 have had below average annual mean temperatures.
  • The most apparent warming trend is in the coldest night of the year, which has warmed significantly in recent decades.
  • The only cooling trend the study documented was for spring temperatures the last three decades and is tied to climate variability and increasing precipitation during those spring months.

“The spring has been robustly wetter,” Mote said, “and that has brought some cooler temperatures for a couple of months. But it has been drier in the fall and winter, and the warming in fall and winter has been steepest since the 1970s.”

Lead author John Abatzoglou of the University of Idaho said that the study ties the warming trend to human activities.

“Climate is a bit like a symphony where different factors like El Niño, solar variability, volcanic eruptions and manmade greenhouse emissions all represent different instruments,” Abatzoglou said. “At regional scales like in the Northwest, years or decades can be dominated by natural climate variability, thereby muffling or compounding the tones of human-induced warming.

“Once you silence the influence of natural factors,” he said, “the signal of warming due to human causes is clear – and it is only getting louder.”

The researchers also explored but were unable to find any link between warming in the Northwest over the past century and solar variability.

A major concern, the authors say, is that the warming seems to be increasing.

“Climate is complex and you can get significant variations from year to year,” Mote said. “You have to step back and look at the big picture of what is happening over time. Clearly the Northwest, like much of the world, is experiencing a warming pattern that isn’t likely to change and, in fact, is accelerating.

“At this rate, the chance of the temperature only going up 1.3 degrees in the next century is close to zero.”

The study was funded by the U.S. Department of Agriculture and the National Oceanic and Atmospheric Administration.

Media Contact: 
Source: 

Phil Mote, 541-913-2274, philip.mote@coas.oregonstate.edu

David Rupp, 541-737-5222, David.Rupp@oregonstate.edu

John Abatzoglou, jabatzoglous@uidaho.edu, 208-885-6239

Study provides new look at ancient coastline, pathway for early Americans

CORVALLIS, Ore. – The first humans who ventured into North America crossed a land bridge from Asia that is now submerged beneath the Bering Sea, and then may have traveled down the West Coast to occupy sites in Oregon and elsewhere as long as 14,000 to 15,000 years ago.

Now a new study has found that the West Coast of North America may have looked vastly different than scientists previously thought, which has implications for understanding how these early Americans made this trek.

The key to this new look at the West Coast landscape is a fresh approach to the region’s sea level history over the last several thousand years. Following the peak of the last ice age about 21,000 years ago, the large continental ice sheets began to retreat, causing sea levels to rise by an average of about 430 feet. When the ice was prominent and sea levels were lower, large expanses of the continental shelf that today are submerged were then exposed.

As the melting progressed and sea levels rose, likely archaeological sites along the coast were submerged.

Most past models have assumed that as the massive North American ice sheets melted, global sea levels rose in concert – a phenomenon known as “the bathtub model.” But the authors of this new study, which was just published in the Journal of Archaeological Science, say sea level rise does not happen uniformly.

“During the last deglaciation, sea level rise was significantly influenced by the weight of the large ice sheets, which depressed the land under and near the ice sheets,” said Jorie Clark, a courtesy professor at Oregon State University and lead author on the study. “As the ice sheets melted, this land began to rise. At the same time, the weight of the water melting from the ice sheets and returning to the oceans also depressed the ocean basins.

“This exchange of mass between ice sheets and oceans led to significant differences in sea level at any given location from the assumption of a uniform change,” she added.

The implications of this new approach are significant. The researchers ran models of what the sea level may have looked like over the last 20,000 years – based on knowledge of ice sheet dimensions and the topography of the ocean floor – and concluded that parts of the West Coast looked radically different than previous reconstructions based on a model of uniform sea level rise.

The central Oregon shelf, for example, was thought to be characterized by a series of small islands some 14,000 years ago. However, the models run by Clark and her colleagues suggest that much of the continental shelf was exposed as a solid land mass, creating an extensive coastline. In some areas, the change in estimated sea level may have been as much as 100 feet.

 “There has been new evidence that the peopling of the Americas happened earlier than was long thought to be the case, which has put a lot of focus on coastal paleogeography,” said Clark, who is in OSU’s College of Earth, Ocean, and Atmospheric Sciences. “This new look at sea level changes helps explain how that earlier introduction into the Americas could be possible.”

 “It is also important for predicting where coastal villages that are now submerged on the continental shelf may be located.”

 Other authors on the study were Jerry Mitrovica of Harvard University, and Jay Alder of the U.S. Geological Survey.

Media Contact: 
Source: 

Jorie Clark, 541-737-1575; clarkjc@geo.oregonstate.edu