In a world warmed by rising atmospheric greenhouse gas concentrations, precipitation patterns are going to change because of two factors: one, warmer air can hold more water; and two, changing atmospheric circulation patterns will shift where rain falls. According to previous model research, mid- to high-latitude precipitation is expected to increase by as much as 50%. Yet the reasons why models predict this are hard to tease out.
Using a series of highly idealized model runs, Lu et al. found that ocean warming should cause atmospheric precipitation bands to shift toward the poles. The changes in atmospheric circulation brought on by a warming ocean should cause an increase in the intensity and frequency of extreme precipitation events at mid- and high-latitudes, and a reduction in the same near the equator. The changes would mean that, for high-latitude regions, now-rare storms would become much more common.
The authors tested the effect of ocean warming on atmospheric circulation and precipitation using a highly idealized "aquaplanet" model, a representation of the Earth that was just sea and sky, but no land. They ran the model at a range of spatial resolutions and found that the changes in precipitation that stem from changing circulation patterns may possibly outweigh changes that derive from other factors.
University of Oregon-led project that took root in 2008 is now blooming with NSF support.
The experimental research plot near Selma, Ore., is one of three sites in the Pacific Northwest that are being manipulated to grow native prairie plants under conditions projected for climate change at the end of the century. Findings at the Selma site in southwest Oregon, another site in Eugene and a third near Olympia, Wash., are geared to provide conservation groups with information to guide their future decision-making. Credit: University of Oregon.
University of Oregon-led research in prairies of the Pacific Northwest could be a roadmap for the conservation of native plants facing stresses from projected climate changes and invasive species.
To simulate the projections, 12 species of range-limited native grasses and forbs are being grown in 60 plots. The sites are the Siskiyou Field Institute's Deer Creek Center at the headwaters of the Illinois River Valley in southern Oregon, the Nature Conservancy's Willow Creek Preserve in Eugene and the Tenalquot Prairie Preserve in near Olympia, Washington.
Infrared lamps generate warmer temperatures and dry the soils. An irrigation system, which recycles captured rainfall, increases precipitation by 20 percent. The three sites are in a 300-mile-long crosscut of the region that represents a gradient of increasing Mediterranean climate conditions, with warmer temperatures and more severe summer drought from north to south, allowing for an climate-change experiment embedded in a natural climate gradient.
"We are making the Washington prairie site more like what projections are for the end of the century, which are more like southern Oregon is now," Bridgham said. "By then, southern Oregon will be more like much of California."
Also working at the sites are collaborating scientists from Portland State University, the University of Colorado at Boulder and Duke University, who are focusing on regional demographic modeling and long distance dispersal using genetic methods for the various plants under scrutiny. This will allow the plot-level results to apply to the entire Pacific Northwest.
Under a four-year $1.8 million grant awarded in 2008 from the U.S. Department of Energy, Bridgham's team completed 2.5 years of experiments after spending 18 months installing equipment and preparing the plots. Under a new $2.3 million, five-year grant (No. 1340847) from the MacroSystems Biology program of the National Science Foundation, another four years of data will be gathered.
"The previous work and the new work revolve around a fundamental conservation biology question involving the impacts of climate change on native plant species in these imperiled ecosystems," Bridgham said. "While none of our focal species are officially endangered or threatened, they are not common, because less than 5 percent of the prairies are left in the Pacific Northwest. Also, our research is pertinent to plants in other areas that have experienced broad human impacts and are facing impending climate change. "
While the plants placed in each prairie are the same, the genotypes of each species that grow best in each region's soils are used to study local impacts.
The first two years harvested noteworthy trends. Plants in their current ranges struggled to germinate with warming, but species moved beyond their current ranges experienced no negative effects of warming. Increased rainy season precipitation, however, had few effects. The results suggest that native plants may need to move further north or to higher elevations to survive.
Scott Bridgham, a biologist at the University of Oregon, is the principal investigator on a National Science Foundation-funded project to study the impacts of projected climate change on native Northwest prairie plants at three sites, from near Selma, Oregon, to near Olympia, Washington. Credit: University of Oregon.
An early surprise finding, detailed in a paper under submission by UO doctoral student Lorien Reynolds, is that emissions of carbon dioxide from soil microbes and plant roots in Pacific Northwest prairies will not increase with climatic warming, and may even decrease, in contrast to the predictions of many Earth system models. This is because warmer temperatures dry out the soil. The Pacific Northwest also gets lower amounts of rain during late spring and summer, so warm temperatures are coincidental with drought-like conditions for soil microbes and roots.
"The response of soil respiration to warming depended on the current climate gradient across our sites," he said. "In southern Oregon, we found that warming actually often decreased soil respiration during much of the year because of its drying effect, whereas it tended to have a positive effect in the milder Washington site. This may apply as well to soils in the Great Plains with the increasing summer droughts that are being experienced there. This is a bit of good news."
The project also is studying invasive plant species. At each site, some 30 native species, including the 12 range-limited prairie plants, were planted after treatment with a common herbicide. After a year of light weeding, the invasive species emerging from the seed banks were allowed to grow unimpeded.
Warming and drying Northwest soils, Bridgham said, may make the Northwest more like present-day California grasslands -- dominated by annual invasive plants instead of the current mix of native and invasive perennial species.
Members of the UO team are biologists Bridgham and Barbara "Bitty" Roy, Bart R. Johnson of the Department of Landscape Architecture, and Laurel Pfeifer-Meister, a research associate in the Institute of Ecology and Evolution. Under the NSF grant, the UO team will integrate the research with the training of students from high-school age through postdoctoral associates. Information about the project also will be incorporated into a website for dissemination.
Portland State University's Mitchell B. Cruzan will focus on population genetics of the native prairie plants to determine their abilities to migrate to new locations in today's highly fragmented landscape. William F. Morris of Duke University and Daniel F. Doak of UC-Boulder will combine demographics and population genetics to prepare detailed modeling of the migration capacities of the native species and the invasive perennials and annuals through the end of the century.
"It's known that humans have decreased biodiversity through a number of different mechanisms, with land use being the most important currently," Bridgham said. "Invasive species have also been detrimental to native species biodiversity. However, future climate change may greatly exacerbate the effects of these other factors. We're looking at all of these factors in close collaboration with the Nature Conservancy, the Center for Natural Land Management and the Siskiyou Field Research Institute.
"All are interested in these questions for management practices to enhance and maintain native biodiversity. They need to know what will happen in the future to the native species that they are managing. Will assisted migration of plants northward work to assure they can conserve our native species? We, as scientists, want to provide the data for those who make these decisions. We also have to consider the impact of extinction of our local habitats."
UW graduate student Melinda Webster uses a probe to measure snow depth and verify NASA airborne data. She is walking on sea ice near Barrow, Alaska, in March 2012. Credit: Chris Linder / Univ. of Washington.
From research stations drifting on ice floes to high-tech aircraft radar, scientists have been tracking the depth of snow that accumulates on Arctic sea ice for almost a century. Now that people are more concerned than ever about what is happening at the poles, research led by the University of Washington and NASA confirms that snow has thinned significantly in the Arctic, particularly on sea ice in western waters near Alaska.
A new study, accepted for publication in the Journal of Geophysical Research: Oceans, a publication of the American Geophysical Union, combines data collected by ice buoys and NASA aircraft with historic data from ice floes staffed by Soviet scientists from the late 1950s through the early 1990s to track changes over decades.
Historically, Soviets on drifting sea ice used meter sticks and handwritten logs to record snow depth. Today, researchers on the ground use an automated probe similar to a ski pole to verify the accuracy of airborne measurements.
"When you stab it into the ground, the basket move up, and it records the distance between the magnet and the end of the probe," said first author Melinda Webster, a UW graduate student in oceanography. "You can take a lot of measurements very quickly. It's a pretty big difference from the Soviet field stations."
Webster verified the accuracy of airborne data taken during a March 15, 2012 NASA flight over the sea ice near Barrow, Alaska. The following day Webster followed the same track in minus 30-degree temperatures while stabbing through the snow every two to three steps.
UW graduate student Melinda Webster uses a probe to measure snow depth and verify NASA airborne data. She is walking on sea ice near Barrow, Alaska, in March 2012. Her backpack holds electronics that power the probe and record the data. Credit: Chris Linder / Univ. of Washington.
The authors compared data from NASA airborne surveys, collected between 2009 and 2013, with U.S. Army Corps of Engineers buoys frozen into the sea ice, and earlier data from Soviet drifting ice stations in 1937 and from 1954 through 1991. Results showed that snowpack has thinned from 14 inches to 9 inches (35 cm to 22 cm) in the western Arctic, and from 13 inches to 6 inches (33 cm to 14.5 cm) in the Beaufort and Chukchi seas, west and north of Alaska.
That's a decline in the western Arctic of about a third, and snowpack in the Beaufort and Chukchi seas less than half as thick in spring in recent years compared to the average Soviet-era records for that time of year.
"Knowing exactly the error between the airborne and the ground measurements, we're able to say with confidence, Yes, the snow is decreasing in the Beaufort and Chukchi seas," said co-author Ignatius Rigor, an oceanographer at the UW's Applied Physics Laboratory.
The authors speculate the reason for the thinner snow, especially in the Beaufort and Chukchi seas, may be that the surface freeze-up is happening later in the fall so the year's heaviest snowfalls, in September and October, mostly fall into the open ocean.
Snow depth. Change in springtime Arctic snow depth compared to the average. The data come from Soviet drifting ice stations (1950-1987), US Ice Mass Balance buoys (1993-2013), and the NASA IceBridge airborne project (2009-2013). For measurements in the western Arctic only, the trend was a decline of 0.27 cm per year (about 1 inch less per decade) with 99 percent significance. Credit: M. Webster / Univ. of Washington.
What thinner snow will mean for the ice is not certain. Deeper snow actually shields ice from cold air, so a thinner blanket may allow the ice to grow thicker during the winter. On the other hand, thinner snow cover may allow the ice to melt earlier in the springtime.
Thinner snow has other effects, Webster said, for animals that use the snow to make dens, and for low-light microscopic plants that grow underneath the sea ice and form the base of the Arctic food web.
The new results support a 15-year-old UW-led study in which Russian and American scientists first analyzed the historic Arctic Ocean snow measurements. That paper detected a slight decline in spring snow depth that the authors believed, even then, was due to a shorter ice-covered season.
"This confirms and extends the results of that earlier work, showing that we continue to see thinning snow on the Arctic sea ice," said Rigor, who was also a co-author on the earlier paper.
The recent fieldwork was part of NASA's Operation IceBridge program, which is using aircraft to track changes while NASA prepares to launch a new ice-monitoring satellite in 2017. The team conducted research flights in spring 2012 as part of a larger program to monitor changes in the Arctic.
Declines in ocean productivity, increases in ocean acidification, and the cumulative effects of multiple stressors on ocean health are among the most pressing issues facing coastal and maritime countries, according to a survey of scientists by a University of York researcher.
All three issues were ranked in the top five ocean research priorities by oceanographers and marine ecologists from around the globe, in a survey led by Dr Murray Rudd, from York's Environment Department, and reported in Frontiers in Marine Science.
The survey asked 2,197 scientists from 94 countries – who ranged in background from marine geologists to anthropologists - their opinions on what research was needed most to help sustain ocean health.
Dr Rudd said: "The large survey allowed us to bring tremendous expertise to bear on identifying the really important things we need to know to sustain healthy oceans. The survey respondents represented some 36,000 person-years of experience in ocean research.
"I hope that the results of this survey can be used to help target ocean research on questions that, if answered, would be central to achieving ocean sustainability."
Dr Rudd identified 657 research questions potentially important for informing decisions regarding ocean governance and sustainability. These were distilled to a short list of 67 distinctive research questions that were ranked in an internet survey by scientists.
Other questions ranked as of high importance by respondents included those on methods for measuring greenhouse gas exchange between oceans and the atmosphere, the role of the ocean in storing energy from global warming, and the effects of declines in ocean biodiversity.
Dr Rudd said: "Climate change can affect plankton growth, which forms the basis of the ocean food chain, and increase acidity levels, which make life increasingly difficult for shellfish. When combined with the variety of other ocean stressors, ranging from increasing levels of contaminants to oxygen-depleted dead zones, the potential effects of changes in the ocean loom large for society."
Social scientists who participated in the survey thought that work on how to better communicate science to policy-makers and the public was the most important research priority.
Dr Rudd said: "Despite significant differences between physical and ecological scientists' priorities regarding specific research questions, they shared seven common priorities among their top 10. Social scientists' priorities were, however, much different, highlighting their research focus on managerial solutions to ocean challenges and questions regarding the role of human behaviour and values in attaining ocean sustainability. Therefore, while the results from this survey provide a comprehensive and timely assessment of current ocean research priorities among research active scientists, they also highlight potential challenges in stimulating cross-disciplinary research."
The results reproduce Antarctica's recent contribution to sea level rise as observed by satellites in the last two decades and show that the ice continent could become the largest contributor to sea level rise much sooner than previously thought.
"If greenhouse gases continue to rise as before, ice discharge from Antarctica could raise the global ocean by an additional 1 to 37 centimeters in this century already," says lead author Anders Levermann. "Now this is a big range – which is exactly why we call it a risk: Science needs to be clear about the uncertainty, so that decision makers at the coast and in coastal megacities like Shanghai or New York can consider the potential implications in their planning processes," says Levermann.
Antarctica Currently Contributes Less Than 10 Percent to Global Sea Level Rise
The scientists analyzed how rising global mean temperatures resulted in a warming of the ocean around Antarctica, thus influencing the melting of the Antarctic ice shelves. While Antarctica currently contributes less than 10 percent to global sea level rise and is a minor contributor compared to the thermal expansion of the warming oceans and melting mountain glaciers, it is Greenland and especially the Antarctic ice sheets with their huge volume of ice that are expected to be the major contributors to future long-term sea level rise. The marine ice sheets in West Antarctica alone have the potential to elevate sea level by several meters - over several centuries.
According to the study, the computed projections for this century's sea level contribution are significantly higher than the latest IPCC projections on the upper end. Even in a scenario of strict climate policies limiting global warming in line with the 2°C target, the contribution of Antarctica to global sea level rise covers a range of 0 to 23 centimeters.
A Critical Input to Future Projections
"Rising sea level is widely regarded as a current and ongoing result of climate change that directly affects hundreds of millions of coastal dwellers around the world and indirectly affects billions more that share its financial costs," says co-author Robert Bindschadler from the NASA Goddard Space Flight Center. "This paper is a critical input to projections of possible future contributions of diminishing ice sheets to sea level by a rigorous consideration of uncertainty of not only the results of ice sheet models themselves but also the climate and ocean forcing driving the ice sheet models. Billions of Dollars, Euros, Yuan etc. are at stake and wise and cost-effective decision makers require this type of useful information from the scientific experts."
While the study signifies an important step towards a better understanding of Antarctica in a changing climate and its influence on sea level change within the 21st century, major modeling challenges still remain: Datasets of Antarctic bedrock topography, for instance, are still inadequate and some physical processes of interaction between ice and ocean cannot be sufficiently simulated yet.
Notably, the study's results are limited to this century only, while all 19 of the used comprehensive climate models indicate that the impacts of atmospheric warming on Antarctic ice shelf cavities will hit with a time delay of several decades. "Earlier research indicated that Antarctica would become important in the long term," says Levermann. "But pulling together all the evidence it seems that Antarctica could become the dominant cause of sea level rise much sooner."
Finding the deepest iceberg scours to date provides new insights into the Arctic's glacial past
A rare blue iceberg in Antarctic waters. Photo: J. Wassmuth, Alfred-Wegener-Institut.
Scientists from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) have found between Greenland and Spitsbergen the scours left behind on the sea bed by gigantic icebergs. The five lineaments, at a depth of 1,200 metres, are the lowest-lying iceberg scours yet to be found on the Arctic sea floor. This finding provides new understanding of the dynamics of the Ice Age and the extent of the Arctic ice sheet thousands of years ago. In addition, the researchers could draw conclusions about the export of fresh water from the Arctic into the North Atlantic. The AWI scientists have published their findings in the online portal of the scientific journal Geophysical Research Letters.
"Whenever icebergs run aground, they leave scours on the seabed. Depending on their depth and location, those markings may continue to exist over long periods of time," explained Jan Erik Arndt, AWI bathymetrician and lead author for this paper.
It is traces exactly like this that he, together with three colleagues at AWI, discovered on the Hovgaard Ridge. The Hovgaard Ridge is a plateau in the deep Arctic Sea, located a good 400 kilometres off of Greenland's eastern coast. Found at a depth of 1,200 metres the five lineaments are the deepest iceberg scours found to date in the Arctic. The scours are as much as four kilometres long and 15 metres in depth. "Such scours are a window into the past. Thanks to these iceberg scours we now know that a few very large, but also many smaller icebergs, passed across the Hovgaard Ridge," the scientist said.
The discovery of the scours on Hovgaard Ridge was fortuitous and by no means the result of a defined search. Jan Erik Arndt and his colleagues discovered the lineaments when examining bathymetric data from the year 1990. The data were collected by the research ship Polarstern while preparing cartography for the Fram Strait. "When we examined the data once again and in greater detail, we became aware of the scours. Given their depth, it quickly became clear that we had found something very interesting," says Jan Erik Arndt.
The scientists today work with better hardware and software than what was available in the 1990s. This new technology allows closer scrutiny of the old data. That is why the scours have surfaced on the scientists' monitors only now, 24 years after the data were collected.
The scientists can, however, only roughly bracket the period within which the icebergs scoured the ridge crest. It is clear, however, that it must have taken place within the past 800,000 years. Since sea level during the glacial period was a good 120 metres lower than today, the icebergs reached to a depth of at least 1,080 metres below sea level. Since about a tenth of an iceberg will, as a rule, be exposed, AWI scientists estimate the height of the iceberg to be roughly 1,200 metres – about three times the height of the Empire State Building. "To calve such megascale icebergs, the edge of the ice sheet covering the Arctic Ocean must have been at least 1,200 metres thick," Jan Erik Arndt notes.
Today scientists search in vain for such megascale icebergs. "We currently find the largest icebergs in the Antarctic. The very biggest reach only 700 metres below the water's surface," noted the bathymetrician. One remaining riddle is the birthplace of the massive icebergs that scraped Hovgaard Ridge. The AWI scientists suggest that two areas off the northern coast of Russia are the most likely sites.
The researchers are interested in these scours not only because of the size of the icebergs. The traces have caused a flare up in the old discussion about how fresh water was transported from the Arctic and into the Atlantic Ocean. In the past, some scientists assumed that thick sea ice was primarily responsible for fresh water export from the Arctic. The newly discovered scours, however, support another hypothesis: Large icebergs drifted southward through the Fram Strait, carrying large volumes of frozen fresh water into the North Atlantic.
Numerous studies make the increased imports of fresh water responsible for the end of North Atlantic deep water formation at the close of the last ice age. As a consequence, the Gulf Stream ebbed, making for drastic cooling in Europe. Since the currents in the Atlantic are an important engine, driving the global system of circulation, the effects were perceived around the world. "The fact that icebergs of this order of magnitude were driven from the Arctic is clear evidence that icebergs played a more serious role in freshwater imports than what we had previously assumed," Jan Erik Arndt concludes.
Mother sea otter with rare twin pups, Morro Bay, California. Photo by Mike Baird (CC).
Predators play important roles in maintaining diverse and stable ecosystems. Climate change can push species to move in order to stay in their climatic comfort zones, potentially altering where species live and how they interact, which could fundamentally transform current ecosystems.
There will be "winners" and "losers" as species adapt to a changing climate. Ecologists are just beginning to understand why different competitors may be favored by climate change and how consumer-resource interactions are modified. Impacts on one species can affect many organisms in an ecosystem. Because predator species are animals that survive by preying on other organisms, they send ripples throughout the food web, regulating the effects other animals have on that ecosystem. This cause and effect process is called a "trophic cascade," or the progression of direct and indirect effects predators have across lower levels in a food chain.
Sea otter populations provide a historical example of this phenomenon. The fur trade spanning the late 1700s to early 1900s decimated their numbers across their range, from Alaska to Baja California, Mexico. Populations went from an estimated several hundred-thousand to more than a million down to 1,000. Today, there are estimated to be just over 106,000 worldwide, with just under 3,000 in California. Now sea otters and other important predator species face the challenges of a changing climate.
"The near extinction of sea otters is one of the most dramatic examples of human-induced impacts to the structure and functioning of temperate nearshore marine ecosystems," said Rebecca G. Martone, of the Center for Ocean Solutions at Stanford University.
In the U.S., there are two distinct sea otter subspecies, the Northern sea otter (Enhydra lutris kenyoni) and the Southern sea otter (Enhydra lutris nereis). Northern sea otters are found in the Aleutian Islands, Southern Alaska, British Columbia, and Washington. Southern sea otters, also known as California sea otters, live in the waters along the California coastline and range from San Mateo County in the north to Santa Barbara County in the south.
Sea otters live offshore in forests of kelp—huge, yellow-brown, rubbery seaweed reaching from the sea floor to the surface, like tall trees. In coastal North America, sea otters help maintain healthy kelp forests, which benefits other marine species dependent on this habitat.
Sea otters must eat about 25% of their body weight daily to maintain their body temperature since unlike other marine mammals they rely solely on their fur rather than an extra layer of blubber to stay warm—it's like a 120-pound human eating 30 pounds of food per day. Some of otters' favorites are abalone, clams, crabs, mussels, shrimp, and sea urchins. Few predators can crack the globe-shaped spiny urchins, which in unchecked hordes will chew through the holdfasts of the kelp, leaving vast barrens in place of the vibrant forests. The otter is a "keystone predator" whose presence has an outsized effect on its kelp forest habitat.
Without sea otters, the undersea sea urchins they prey on would devour the kelp forests, resulting in dense areas called sea urchin barrens that have lower biodiversity due to the loss of kelp that provide 3-dimensional habitat and a food source for many species. Researchers found that when sea otters arrive in an area from which they have been absent, they begin feasting on urchins. As a result, the kelp forest begins to grow back, changing the structure of kelp forest communities.
Many fish, marine mammals and birds are also found in kelp forest communities, including rockfish, seals, sea lions, whales, gulls, terns, snowy egrets as well as some shore birds. Otters might also offer a defense against climate change because healthy kelp forests can grow rapidly and store large amounts of carbon.
Dr. Martone's analyses of the effects of sea otters on kelp forest ecosystems can help shape predictions of how climate change and trophic cascades, in concert with other drivers, affect coastal ecosystems. The ecological impacts of a changing climate are evident, from terrestrial polar regions to tropical marine environments. Ecologists' research into the tropic cascading effects of predators will assist decision makers by providing important scientific findings to prepare for the impacts of climate change occurring now and into the future. Speakers for the symposia include marine, freshwater and terrestrial experimental ecologists who will present their research and offer insights from different approaches used to studying consumer-resource interactions.
Global warming might increase, not decrease, ocean's dissolved oxygen where it is least plentiful
A commonly held belief that global warming will diminish oxygen concentrations in the ocean looks like it may not be entirely true. According to new research published in Science magazine, just the opposite is likely the case in the eastern tropical northern Pacific, with its anoxic zone expected to shrink in coming decades because of climate change.
An international team of scientists came to that surprising conclusion after completing a detailed assessment of changes since 1850 in the eastern tropical northern Pacific Ocean's oxygen minimum zone (OMZ). An ocean layer beginning typically a few hundred to a thousand meters below the surface, an OMZ is by definition the zone with the lowest oxygen saturation in the water column. OMZs are a consequence of microbial respiration and can be hostile environments for marine life.
Using core samples of the seabed in three locations, the scientists measured the isotopic ratio of nitrogen-15 to nitrogen-14 in the organic matter therein; the ratio can be used to estimate the extent of anoxia in these OMZs. The core depth correlates with age, giving the team a picture of how the oxygen content varied over the time period.
From 1990 to 2010, the nitrogen isotope record indicates that oxygen content steadily decreased in the area, as expected. But before that, and particularly clearly from about 1950 to 1990, oceanic oxygen steadily increased, which, according to co-author Robert Thunell, a marine scientist at the University of South Carolina, runs counter to conventional wisdom.
"The prevailing thinking has been that as the oceans warm due to increasing atmospheric greenhouse gases, the oxygen content of the oceans should decline," Thunell says. "That's due to two very simple processes.
"One, as water becomes warmer, the solubility of oxygen decreases in it, so it can hold less oxygen. And two, as the surface of the ocean warms, its density decreases and the oceans become more stratified. When that happens, the surface waters that do have oxygen don't mix down into the deeper waters of the ocean."
But that just covers the supply side of oxygen in the ocean, Thunell says. Just as important is the oxygen demand, particularly for the degradation of sinking organic matter.
Phytoplankton grow in surface waters, and they are the primary producers of this organic matter. After they die, their detritus slowly sinks from the surface to the sea floor, and there is a layer in the water column, the OMZ, where microbes consume much of the detritus, a process that depletes oxygen through bacterial respiration.
The extent of oxygen deprivation in the OMZ largely reflects how much phytoplankton is being produced on the surface, Thunell says. Plenty of phytoplankton production at the surface means less oxygen underneath.
And that, the team thinks, is why the oxygen concentrations in the Pacific Ocean so clearly increased from 1950 to 1990. Phytoplankton production is enhanced by strong winds (because they cause upwelling of nutrients from deeper waters) and diminished by weaker winds, and the scientists found evidence that trade winds were weaker then.
Looking at two different measures of wind intensity (the East-West difference in sea level pressure and the depth of the thermocline) over the time periods involved, they conclude that trade winds were diminishing over the course of 1950 to 1990, but then picked up from 1990 to 2010.
They're not sure why wind strength increased around 1990, but think it may be related to the Pacific Decadal Oscillation. "A lot of people are familiar with ENSO, or El Nino, which is a kind of interannual climate variability," Thunell says. "The Pacific Decadal Oscillation is analogous to a super-ENSO, but one that's varying on decadal time scales."
Over the course of coming decades, though, trade wind speed is expected to decrease from global warming, Thunell says, and the result will be less phytoplankton production at the surface and less oxygen utilization at depth, causing a concomitant increase in the ocean's oxygen content.
"That has some important implications for fisheries," he says. "One of the issues over the past 20 to 30 years is that oxygen has been declining and these oxygen minimum zones have been expanding, which could have a negative impact on fisheries.
"But if the last 20 to 30 years are not the norm because of these unusually strong trade winds, then there won't necessarily be that impact on the fisheries. If the trend reverses, and we go back to weaker trade winds — as people predict will happen because of the warming oceans — then the decrease in oxygen in the oceans that we've been seeing may be reversed."
Waves crashing over a roadway in Temwaiku, on the low-lying Pacific island nation of Kiribati. Image: Annika Dean.
An Australian–US team of climate researchers has solved a puzzle that has challenged scientists for over a decade. Climate models predict that the equatorial Pacific trades should weaken with increasing greenhouse gases. Yet, since the early 1990s, satellites and climate stations reveal a rapid and unprecedented strengthening of the Pacific trade winds, accelerating sea level rise in the western Pacific and impacting both Pacific and global climate.
"The answer to the puzzle is that recent rapid Atlantic Ocean warming has affected climate in the Pacific," say the scientists. Their findings from observations and modeling experiments are published in the August 3, 2014, online issue of Nature Climate Change.
"We were surprised to find that the main cause of the Pacific wind, temperature, and sea level trends over the past 20 years lies in the Atlantic Ocean," says Shayne McGregor at the University of New South Wales and lead author of the study. "We saw that the rapid Atlantic surface warming observed since the early 1990s, induced partly by greenhouse gasses, has generated unusually low sea level pressure over the tropical Atlantic. This, in turn, produces an upward motion of the overlying air parcels. These parcels move westward aloft and then sink again in the eastern equatorial Pacific, where their sinking creates a high pressure system. The resulting Atlantic–Pacific pressure difference strengthens the Pacific trade winds."
"Stronger trade winds in the equatorial Pacific also increase the upwelling of cold waters to the surface. The resulting near-surface cooling in the eastern Pacific amplifies the Atlantic–Pacific pressure seesaw, thus further intensifying the trade winds," says Axel Timmermann, corresponding author of the study at the University of Hawaii International Pacific Research Center. He comments further, "It turns out that the current generation of climate models underestimates the extent of the Atlantic–Pacific coupling, which means that they cannot properly capture the observed eastern Pacific cooling, which has contributed significantly to the leveling off, or the hiatus, in global warming."
In contrast to previous studies that explain the eastern Pacific cooling as resulting solely from natural climate variability, the international climate research team points to a climate feedback that has been overlooked, namely, that the recent Atlantic warming affects the atmospheric circulation over the Pacific, leading to an increased persistence of cold ocean conditions there.
"It will be difficult to predict when the Pacific cooling trend and its contribution to the global warming hiatus will come to an end. The natural variability of the Pacific, associated for instance with the El Niño-Southern Oscillation, is one candidate that could drive the system back to a more even Atlantic–Pacific warming situation," says co-author Matthew England from the University of New South Wales.
"Our study documents that some of the largest tropical and subtropical climate trends of the past 20 years are all linked: Strengthening of the Pacific trade winds, acceleration of sea level rise in the western Pacific, eastern Pacific surface cooling, the global warming hiatus, and even the massive droughts in California," explains co-author Malte Stuecker from the University of Hawaii Meteorology Department.
"We are just starting to grasp the scope of the impacts of this global atmospheric reorganization and of the out-of phase temperature trends in the Atlantic and Pacific regions," adds Fei-Fei Jin, climate scientist also at the University of Hawaii Meteorology Department.
Wildlife Conservation Society, University of Queensland, and others urge more focus on more imminent threats
Walruses. Photo by: Magnus Elander (CC).
Scientists studying the potential effects of climate change on the world's animal and plant species are focusing on the wrong factors, according to a new paper by a research team from the Wildlife Conservation Society, University of Queensland, and other organizations. The authors claim that most of the conservation science is missing the point when it comes to climate change.
While the majority of climate change scientists focus on the "direct" threats of changing temperatures and precipitation after 2031, far fewer researchers are studying how short-term human adaptation responses to seasonal changes and extreme weather events may threaten the survival of wildlife and ecosystems much sooner. These indirect effects are far more likely to cause extinctions, especially in the near term.
"A review of the literature exploring the effects of climate change on biodiversity has revealed a gap in what may be the main challenge to the world's fauna and flora," said the senior author Dr. James Watson, Climate Change Program Director and a Principle Research Fellow at the University of Queensland.
The research team conducted a review of all available literature published over the past twelve years on the impacts of climate change on species and ecosystems. In their review, the authors classified studies examining the projected changes in temperature and precipitation as "direct threat" research. Direct threats also included changes such as coral bleaching, shifting animal and plant life cycles and distributions, and habitat loss from sea level rise. Human responses to climate change—including everything from shifting agriculture patterns, the construction of sea walls to protect cities from sea level rise, changes in human fishing intensity, diversion of water, and other factors—were classified as "indirect threats."
The authors found that the vast majority of studies (approximately 89 percent of the research included in the review) focused exclusively on the direct impacts of climate change. Only 11 percent included both direct and indirect threats, and the authors found no studies focusing only on indirect threats.
"The reactions of human communities to these changes should be treated as a top priority by the research community," said Dr. Watson. "The short-term, indirect threats are not merely 'bumps in the road'—they are serious problems that require a greater analysis of social, economic, and political issues stemming from changes already occurring."
