marine science and the coast

Science study links greenhouse gases to African rainfall

CORVALLIS, Ore. – Scientists may have solved a long-standing enigma known as the African Humid Period – an intense increase in cumulative rainfall in parts of Africa that began after a long dry spell following the end of the last ice age and lasting nearly 10,000 years.

In a new study published this week in Science, an international research team linked the increase in rainfall in two regions of Africa thousands of years ago to an increase in greenhouse gas concentrations. The study was funded by the National Science Foundation and the U.S. Department of Energy.

The findings are critical, researchers say, because they provide new evidence that increases in carbon dioxide and other greenhouse gases could have a significant impact on the future climate of Africa.

“This study is important not only because it explains a long-standing puzzle, but it helps to validate model predictions of how rising greenhouse gas concentrations might change rainfall patterns in a highly populated and vulnerable part of the world,” said Peter Clark, an Oregon State University paleoclimatologist and co-author on the study.

The study was led by the National Center for Atmospheric Research (NCAR). It used computer simulations and analysis of geologic records of past climate.

The researchers focused on the era following the last ice age. When ice sheets covering North America and northern Europe began retreating after the last glacial maximum some 21,000 years ago, there was a long dry spell in central Africa that lasted until about 14,700 years ago, when rainfall increased abruptly. Scientists have long been puzzled by the regime shift, which turned deserts into grasslands and earned the African Humid Period moniker.

Rainfall actually increased in two separate regions of Africa – one north of the equator, the other south. Some previous studies had suggested that the shift may have been triggered by changes in the Earth’s orbit, but lead author Bette Otto-Bliesner said orbital patterns alone could not explain increased rainfall of that extent in both regions.

As the Earth emerged from the ice age, atmospheric levels of carbon dioxide and methane increased significantly – almost to pre-industrial levels – by 11,000 years ago. As the planet continued warming, ice sheets melted and the influx of fresh water from North America and northern Europe began weakening the Atlantic Meridional Overturning Circulation, which brings warm water up from the tropics and keeps Europe temperate.

This weakening of the Atlantic ocean current simultaneously moved precipitation southward toward the southernmost part of Africa, and suppressed rainfall in east Africa and northern equatorial Africa during the long dry spell, the researchers say.

When the ice sheets stopped melting, the circulation strengthened and brought precipitation back to the north. This change, coupled with the orbital shift and warming of both the atmosphere and oceans by greenhouse gases, triggered the African Humid Period.

“This study provides yet another demonstration of the sensitivity of the Earth’s climate to small changes in atmospheric greenhouse gases,” said Clark, a professor in OSU’s College of Earth, Ocean, and Atmospheric Sciences.

The science team recreated records of past moisture conditions by examining fossils, former lake levels and other geologic data, and simulated past climate with a power climate model developed by NCAR.

”The future impact of greenhouse gases on rainfall in Africa is a critical socioeconomic issue,” Otto-Bliesner said. “Africa’s climate seems destined to change, with far-reaching implications for water resources and agriculture in ways that may generate new conflicts.”

The study focused on the Sahel region of Africa to the north, including Niger, Chad and northern Nigeria; and the southeastern equatorial region of Africa, including the Democratic Republic of Congo, Rwanda, Burundi, Tanzania and Kenya.

Media Contact: 

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

PNAS study: Ocean biota responds to global warming

CORVALLIS, Ore. – As the Earth warmed coming out of the last ice age, the rate of plankton production off the Pacific Northwest coast decreased, a new study has found, though the amount of organic material making its way to the deep ocean actually increased.

This suggests that during future climate warming, the ocean may be more efficient than previously thought at absorbing carbon dioxide from the atmosphere – at least in some regions – but raises new concerns about impacts on marine life.

Results of the study are being published online today in Proceedings of the National Academy of Sciences.

The ocean absorbs carbon dioxide like a sponge; scientists say that about one-third of all CO2   emitted historically by burning fossil fuels is now in the ocean. “This is a good news/bad news situation,” said Alan Mix, an Oregon State University oceanographer and co-author on the study. “It helps to slow the rise of CO2 in the atmosphere, but it makes the ocean more acidic.”

A major uncertainty has been how life in the ocean will respond to increasing CO2   and global warming. Growth of phytoplankton (microscopic plants such as diatoms) near the sea surface converts carbon dioxide into organic matter. When the plankton die, their organic remains either decompose in the surface ocean, or sink into the abyss.

This sinking of plankton effectively pumps CO2   out of the atmosphere. The so-called “biological pump” stores carbon in the deep sea, which is one way that biology influences global climate.

“It has been assumed that the amount of organic material that sinks to the sea floor would parallel that produced through photosynthesis near the sea surface,” said Mix, who is in OSU’s College of Earth, Ocean, and Atmospheric Sciences. “Surprisingly, our study found that even as plant growth decreased, past warming actually enhanced the biological export of carbon to the deep sea, at least in the northeast Pacific.”

Lead author Cristina Lopes, a visiting scientist at Oregon State who is based at the Instituto Português do Mar e da Atmosfera (IPMA, Portuguese Sea and Atmosphere Institute) in Portugal, and colleague Michal Kucera at the Center for Marine Environmental Sciences at Germany’s University of Bremen, calculated the productivity of marine plankton during the last major global warming event leading to the end of the last ice age. They did so by examining fossil diatoms buried in sediment off the coast of Oregon.

A breakthrough came from applying neural network methods now used by financial and insurance industries. “Inspired by brain research, we adapted these machine learning methods to analyze the fossil record for a new view of how the ocean works,” Kucera said.

The researchers found that during the ice age, the carbon trapped in plankton off Oregon was mostly recycled rather than exported to the deep ocean. As the ice age waned and the ocean warmed, plant growth decreased while carbon export increased.

“This counterintuitive effect was driven by a shift in ecosystems to one dominated by large diatoms,” Lopes said. “Those diatoms bloomed, then sank fast when they died.”

The researchers say their findings don’t necessarily mean that the ocean can continue to absorb increasing amounts of CO2   indefinitely, but that computer models of the ocean’s carbon cycle will need to take into account that plant productivity and carbon export are not always linked.

Evidence that export of carbon to the deep sea increases in some regions during long-term warming may help to slow down global climate change, but it may make some other impacts worse, the researchers point out. For example, as the extra sinking organic matter decomposes, it consumes oxygen dissolved in seawater – and loss of oxygen in the ocean is a growing concern.

Low-oxygen “dead zones” have appeared off the coast of Oregon several times in recent years.

“If these connections between warming and enhanced carbon export that we’ve found in past climate changes are triggered in the future, we can expect those marine dead zones to show up more frequently,” Mix said.

Media Contact: 

Alan Mix, 541-737-5212, amix@coas.oregonstate.edu

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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: 

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: 

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








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.

Study: Could sleeper sharks be preying on protected Steller sea lions?

NEWPORT, Ore. – Pacific sleeper sharks, a large, slow-moving species thought of as primarily a scavenger or predator of fish, may be preying on something a bit larger – protected Steller sea lions in the Gulf of Alaska.

A new study found the first indirect evidence that this cold-blooded shark that can grow to a length of more than 20 feet – longer than a great white shark – may be an opportunistic predator of juvenile Steller sea lions.

Results of the study have just been published in the journal Fishery Bulletin. The findings are important, scientists say, because of management implications for the protected Steller sea lions.

For the past decade, Markus Horning of the Marine Mammal Institute at Oregon State University has led a project in collaboration with Jo-Ann Mellish of the Alaska SeaLife Center to deploy specially designed “life history transmitters” into the abdomens of juvenile Steller sea lions. These buoyant archival tags record data on temperature, light and other properties during the sea lions’ lives and after the animals die the tags float to the surface or fall out ashore and transmit data to researchers via satellite.

From 2005-11, Horning and his colleagues implanted tags into 36 juvenile Steller sea lions and over a period of several years, 17 of the sea lions died. Fifteen transmitters sent data indicating the sea lions had been killed by predation.

“The tags sense light and air to which they are suddenly exposed, and record rapid temperature change,” said Horning, who is in OSU’s Department of Fisheries and Wildlife. “That is an indication that the tag has been ripped out of the body, though we don’t know what the predator is that did this.

“At least three of the deaths were different,” he added. “They recorded abrupt temperature drops, but the tags were still dark and still surrounded by tissue. We surmise that the sea lions were consumed by a cold-blooded predator because the recorded temperatures aligned with the deep waters of the Gulf of Alaska and not the surface waters.

“We know the predator was not a killer whale, for example, because the temperatures would be much higher since they are warm-blooded animals.” Data collected from the transmitters recorded temperatures of 5-8 degrees Celsius.

That leaves a few other suspects, Horning said. However, two known predators of sea lions – great white sharks and salmon sharks – have counter-current heat exchanges in their bodies that make them partially warm-blooded and the tags would have reflected higher temperatures.

By process of elimination, Horning suspects sleeper sharks.

The Oregon State pinniped specialist acknowledges that the evidence for sleeper sharks is indirect and not definitive, thus he is planning to study them more closely beginning in 2015. The number of sleeper sharks killed in Alaska as bycatch ranges from 3,000 to 15,000 annually, indicating there are large numbers of the shark out there. The sleeper sharks caught up in the nets are usually comparatively small; larger sharks are big enough to tear the fishing gear and are rarely landed.

“If sleeper sharks are involved in predation, it creates something of a dilemma,” said Horning, who works out of OSU’s Hatfield Marine Science Center in Newport, Ore. “In recent years, groundfish harvests in the Gulf of Alaska have been limited in some regions to reduce the potential competition for fish that would be preferred food for Steller sea lions.

“By limiting fishing, however, you may be reducing the bycatch that helps keep a possible limit on a potential predator of the sea lions,” he added. “The implication could be profound, and the net effect of such management actions could be the opposite of what was intended.”

Other studies have found remains of Steller sea lions and other marine mammals in the stomachs of sleeper sharks, but those could have been the result of scavenging instead of predation, Horning pointed out.

The western distinct population of Steller sea lions has declined to about 20 percent of the levels they were at prior to 1975.

Media Contact: 

Markus Horning, 541-867-0270, markus.horning@oregonstate.edu

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: 

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

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: 

Sam Chan, 541-737-4828; samuel.chan@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: 

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

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: 

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: 

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