By 2300, climate change may cause fishery yields to decline by as much as 20% around the globe, and by as much as 60% in the North Atlantic, a new modeling study suggests.
The study primarily attributes this decline to a lack of ocean mixing, such that nutrients sink into the deep ocean instead of staying at the ocean surface; such alterations to ocean mixing would ultimately drive a decline in fish populations near the surface, the authors say. Climate change models consistently estimate that fisheries will decline by the end of this century, yet there have been few efforts to explore what changes might occur beyond 2100. Here, J. Keith Moore and colleagues used modeling to explore the effects of climate change on fisheries under a "business-as-usual" scenario whereby carbon emissions continue apace, at the same level as they are now.
The Southern Ocean currently experiences mixing between the bottom and top oceanic layers, delivering such a substantial amount of nutrients to the surface that an abundance flows into other oceans. However, simulations by Moore et al. suggest that a combination of changing winds and warmer upper oceanic layers, plus a poleward shift of nutrient upwelling in the Antarctic, will cause an increased portion of nutrients to sink into the deeper layer of the ocean and become trapped there (for example, the amount of phosphate being upwelled will be reduced by 41%, the model estimates). This will reduce the delivery of nutrients to other oceanic areas, they note. While ocean warming and stratification will increase globally, deep mixing in the North Atlantic will be particularly reduced, the authors find. They note that the long-term effects of these changes mean that fisheries will be reduced for a thousand years or more.
This is a graphic examining the impacts of seabed mining. Credit: Design Studio, University of Exeter.
Mining on the ocean floor could do irreversible damage to deep-sea ecosystems, says a new study of seabed mining proposals around the world. The deep sea (depths below 200m) covers about half of the Earth's surface and is home to a vast range of species.
Little is known about these environments, and researchers from the University of Exeter and Greenpeace say mining could have "long-lasting and unforeseen consequences"- not just at mining sites but also across much larger areas. The study is the first to give a global overview of all current plans to mine the seabed, in both national and international waters, and looks at the potential impacts including physical destruction of seabed habitats, creation of large underwater plumes of sediment and the effects of chemical, noise and light pollution arising from mining operations.
"Our knowledge of these ecosystems is still limited, but we know they're very sensitive," said Dr David Santillo, a marine biologist and senior Greenpeace scientist based at the University of Exeter. "Recovery from man-made disturbance could take decades, centuries or even millennia, if these ecosystems recover at all."
"As we learn more about deep sea ecosystems and the role of oceans in mitigating climate change, it seems wise to take precautions to avoid damage that could have long-lasting and unforeseen consequences."
Despite the term "mining", much seabed mining would involve extraction of minerals over very wide areas of the sea floor rather than digging down to any great depth, potentially leaving a vast 'footprint' on the deep-sea habitats in which these mineral deposits occur. Rising demand for minerals and metals, including for use in new technology, has sparked renewed interest in seabed mining. Some operations are already taking place, generally at relatively shallow depths near national coastlines. The first commercial enterprise in deeper waters, expected to target mineral-rich sulphides at depths of 1.5-2km off Papua New Guinea, is scheduled to begin early in 2019. Speaking about these plans last year, Sir David Attenborough said it was "tragic that humanity should just plough on with no regard for the consequences".
The Exeter and Greenpeace research team say there are "many questions and uncertainties" around seabed mining, including legal issues and the difficulties of predicting the scale and extent of impacts in advance, and of monitoring and regulating mining activity once it takes place in the deep sea. The paper says that alternatives to seabed mining have already been proposed, including substituting metals in short supply for more abundant minerals with similar properties, as well as more effective collection and recycling of components from disused products and wastes.
However, Dr Santillo said demand for seabed mining would also diminish if humanity could cut overproduction and overconsumption of consumer goods. "Rather than using human ingenuity to invent more and more consumer products that we don't actually need, we could deploy it instead to build good that last longer, are easier to repair and make better use of the limited natural resources we have," he said. "With the right approaches, we can avoid the need for seabed mining altogether and stop the 'race to the bottom. As governments prepare to set the rules and the first companies gear up to mine, now is the time to ask whether we just have to accept seabed mining, or should instead decide that the potential damage is just so great that we really need to find less destructive alternatives."
Conservation of shoreline plants and seaweeds could, in turn, help preserve shellfish habitats.
Study authors Nyssa Silbiger, then a UCI postdoctoral researcher, and UCI graduate student Laura Elsberry (standing) survey tide-pool communities at Corona del Mar State Beach. Credit: Cascade Sorte / UCI.
Marine plants and seaweeds in shallow coastal ecosystems can play a key role in alleviating the effects of ocean acidification, and their robust population in shoreline environments could help preserve declining shellfish life, according to a study by University of California, Irvine ecologists.
In a new study on the Pacific Coast, Nyssa Silbiger, former UCI postdoctoral researcher, and Cascade Sorte, assistant professor of ecology & evolutionary biology, determined that marine plants and seaweeds decrease the acidity of their surroundings through photosynthesis. Their findings suggest that maintaining native seawater vegetation could locally lessen the acidifying effects of rising CO2 levels on marine animals who are sensitive to ocean pH, which has declined since preindustrial times.
The study results appear online in the open-access Scientific Reports. "Our findings from sites spanning some 1,000 miles of coastline show that marine life plays a leading role in driving local pH conditions," Sorte said.
About 90 percent of fishery catch comes from coastal ecosystems. Any coastal pH decrease has a major impact on animals such as corals, oysters and mussels, whose shells and skeletons can become more brittle in low-pH environments.
This is a major concern for shellfish fisheries, which contribute over $1 billion annually to the U.S. economy while providing more than 100,000 jobs.
Due to their findings, the authors recommend efforts to conserve marine plants and seaweeds in shoreline habitats, including where commercial seafood is harvested.
"The environmental and economic consequences resulting from ocean acidification are dire," said Silbiger, now an assistant professor of biology at California State University, Northridge. "Decreasing CO2 emissions is still the No. 1 most important way to protect our marine ecosystems, but our research indicates that marine life also has substantial control over coastal pH."
The study received UCI seed funding for single- and multi-investigator research projects and support from the UCI OCEANS Initiative; research travel was sponsored by GoWesty.
Only one-third of the world´s countries, and half of EU Member States, currently meet global targets when it comes to the connectivity of their designated natural protected areas (PAs).
While 14.7% of land around the world is covered by PAs, only 7.5% of the land of the world's countries is covered by PAs that are connected. This currently falls short of meeting the UN target for 2020 of having 17% of the land covered by well-connected PA systems. Considerable efforts are therefore needed to improve PA connectivity globally. These results come from the first global assessment of the connectivity of terrestrial PA systems at country level, conducted by the JRC and published in Biological Conservation. PAs, such as Natura 2000 sites or National Parks, are critical for the conservation of biodiversity and for supporting long-term human wellbeing. However, if PAs are isolated from each other, it is unlikely that they can meet these goals.
The study makes specific recommendations for national authorities worldwide - most of which need to make significant progress by designating new protected areas in strategic locations for connectivity.
Joining the dots: priorities for a well-connected PA system in the EU
When PAs are connected it has a direct and positive impact on wildlife. The endangered brown bears native to the Cantabrian Range in northern Spain are a good example.
By designating PAs in this region, national and regional authorities have supported the recovery in the number of brown bears, and promoted connectivity (gene flow) between two populations that were previously isolated.
The JRC's study finds that an effective and functional network of PAs could be accomplished more widely throughout the EU by following three priority strategies:
First, and most importantly, conserving or restoring pathways for nature (corridors) is vital so that wildlife species can move and other ecological processes can flow through the unprotected lands that separate the PAs. This would require policy planning across a number of areas, from agriculture to transport.
Second, coordinated planning of PA connectivity between EU countries is essential. A significant number of PAs are located on or near borders. And if they were to work alone, several EU countries would be too small to ensure connectivity on a scale big enough to match the needs of species movements and other ecological flows.
Third, coordinated management for connectivity of adjacent PAs within countries is needed, to provide effective movement pathways that allow species to reach considerably more land through the concatenation of contiguous PAs than by moving within individual PAs only.
Most of the world's countries need to reinforce their PA systems to reach connectivity targets, particularly by strategically designating new PAs in key locations where they can efficiently function as stepping stones or corridors between other PAs.
The situation and strategic needs in the EU significantly differ from those in other regions or continents. Although half of the EU countries do not yet meet the 17% connectivity target, the PA systems are better designed for connectivity and cover more land in the EU than in the global average.
Currently, when averaging the connectivity levels for all countries across the EU, 18.9% of the land is covered by PAs that are connected (compared to 25.7% of the EU land covered by PAs), which is above the 17% target for 2020. For this reason, less emphasis is necessary in many of the EU countries on designating new PAs for connectivity than on the other priority strategies highlighted above.
Background
The report makes use of the Protected Connected (ProtConn) indicator, which has been developed by JRC scientists to quantify the percentage of a country's land covered by protected and connected areas.
It also differentiates several categories of land through which movement between protected locations may occur, and assesses the part of the connectivity that is actually in the power of a country to influence, factoring out the isolation of terrestrial PAs due to the sea and to foreign lands (both beyond the control of the country).
Researchers at Scripps Institution of Oceanography at the University of California San Diego were part of an international team that for the first time used hydroacoustics as a method for comparing the abundance of fishes within and outside marine protected areas (MPAs).
They found that the abundance of fishes was four times greater in Mexico's protected Cabo Pulmo National Park than in areas outside the park. Study authors said that hydroacoustics points the way toward a new, more cost-effective method of assessing fish populations.
"Managers and authorities in many countries spend a lot of financial resources assessing marine protected areas," said study co-author Octavio Aburto, a marine ecologist at Scripps. "The results of this paper demonstrate that it is possible to use acoustic technologies to generate information about marine resources inside MPAs in a faster and less expensive way, reducing the costs for governments in ocean conservation."
Cabo Pulmo has been the site of several studies by Scripps researchers since 2002. In 1995, local fishermen led the creation of a 71-square-kilometer (27-square-mile) undersea park to protect the waters they fished. The current MPA has been identified as the most successful in the world in terms of maintaining a sustainable fishery in which fleets operate just beyond the boundaries of the MPA. There, as in other parts of the world, surveys of coastal marine life are often performed through underwater visual censuses taken by scuba divers. Results of a 10-year analysis of Cabo Pulmo National Park (CPNP), published in the Public Library of Science (PLoS) ONE journal, revealed that the total amount of fish in the reserve ecosystem (the "biomass") boomed more than 460 percent from 1999 to 2009. Citizens living around Cabo Pulmo, previously depleted by fishing, established the park in 1995 and have strictly enforced its "no take" restrictions.
"We could have never dreamt of such an extraordinary recovery of marine life at Cabo Pulmo," said National Geographic Explorer-in-Residence Enric Sala, who started the study in 1999. "In 1999 there were only medium-sized fishes, but ten years later it's full of large parrotfish, groupers, snappers and even sharks."
The most striking result is that fish communities at a depleted site can recover up to a level comparable to remote, pristine sites that have never been fished by humans. Factors such as the protection of spawning areas for large predators have been key to the reserve's robustness. Most importantly, local enforcement, led by the determined action of a few families, has been a major factor in the park's success. Boat captains, dive masters and other locals work to enforce the park's regulations and share surveillance, fauna protection and ocean cleanliness efforts.
Researchers surveyed the waters of the MPA using sound waves produced by hydroacoustic equipment mounted on boats to image schools of fish and other marine life. They performed transects, scanning the water column in rows. They similarly surveyed waters outside the MPA. Fish density, total biomass, and the size of individuals were significantly greater inside the MPA. In comparison with waters outside the MPA, animal abundance in reefs was as much as 50 times higher, "highlighting the importance of both habitat complexity and protection from fishing for fish populations."
"Both hydroacoustics and marine protected areas are well-established but it is novel to use the former to assess the latter," said study lead author Jack Egerton, now a researcher at the University of Texas who performed the work while at Bangor University in Wales, UK. "Through this, we have been able to see how important the Cabo Pulmo National Park is for fish populations in the area."
Although acoustic surveys can be done much faster than underwater visual censuses, the researchers acknowledge that fish sizes can only be approximated and the method doesn't provide species-specific information. However, they concluded that the hydroacoustic method could still be useful in gauging the benefit of MPAs, as conventional survey methods are often prohibitively expensive and can be limited by issues such as diver depth limits and water clarity.
Small no-fishing zones around colonies of African penguins can help this struggling species, new research shows.
Working with the South African government, researchers from the universities of Exeter and Cape Town tested bans on catching "forage fish" such as sardines and anchovies - key prey for the endangered penguins - from 20km around their breeding islands. The body condition and survival of chicks improved when the no-fishing zones were in place. More research is needed, but the scientists say the fishing closures should continue in South Africa and should be considered elsewhere.
"The amount of forage fish caught worldwide is increasing and - although the effects are disputed - the impact on marine ecosystems could be severe," said Dr Richard Sherley, of the Environment and Sustainability Institute on the University of Exeter's Penryn Campus in Cornwall.
"Forage fish are a key link in the food chain as they eat plankton and are preyed on by numerous species including tuna, dolphins, whales and penguins.
"We need to do more to understand the circumstances in which small no-fishing zones will improve the food available to predators, but our research shows this is a promising way to help African penguins."
The test areas were on a small scale compared to some no-fishing zones worldwide, which can cover hundreds of thousands of square kilometres. Researchers examined colonies at Dassen Island, Robben Island, St Croix Island and Bird Island, and compared fishing bans of about three years with similar periods when fishing was allowed. The study says evidence for overall effects was "subtle and inconsistent", with clear benefits for penguin populations at only two of the four islands. Dr Sherley said it was difficult to discover the full effects of the no-fishing zones because many other factors also affect the birds.
"Decades of research may be needed to be absolutely certain of the impact on the penguins' population size," he said.
However, the researchers used a statistical method called Bayesian inference to demonstrate beyond doubt that the zones improved the health and survival rates of penguin chicks.
"There's never going to be a quick answer to problems in complex ecosystems," Dr Sherley said.
"However, without conservation action, there's a good chance African penguins will go extinct in at least some of their current colonies.
"We are calling for a precautionary and adaptive approach - no-fishing zones to protect this species, with an open mind to change as more evidence emerges."
Dr Stephen Votier, senior author of the study, added: "This is an excellent example of how a collaboration between government, fisheries and scientists can lead to positive outcomes for conservation. Statistics have played an important role here - only by using the approach we adopted was it possible to understand fully that these fisheries closures do indeed work."
A new partnership between Global Fishing Watch and NOAA matches night-time imagery with monitoring data from fishing vessels.
Arufura Sea, January, 2018. Vessel Monitoring System (VMS) data from Indonesia is shown in the Global Fishing Watch map as yellowish dots. This image is overlayed with data from NOAA's satellite-based Visible Infrared Imaging Radiometer Suite (VIIRS) which detects many vessels not broadcasting VMS. VIIRS-detected vessels are shown here as blue sailboats. Credit: Global Fishing Watch 2018.
Global Fishing Watch has entered into a new data-sharing partnership with the U.S. National Oceanic and Atmospheric Administration (NOAA) to improve understanding of the activity of fishing vessels in Indonesian waters. Through the partnership, Global Fishing Watch and NOAA are matching Vessel Monitoring System (VMS) data from the Indonesian government with NOAA's satellite based Visible Infrared Imaging Radiometer Suite (VIIRS), which reveals the locations of brightly lit vessels at night. The idea is to identify fishing vessels that are not picked up by other monitoring systems and to test and refine the use of VIIRS for identifying and distinguishing different types of fishing vessels.
By cross matching VMS from Indonesia with VIIRS, the team found that roughly 80 percent of VIIRS detections could not be correlated to a vessel broadcasting VMS. The vast majority of these vessels are likely to be fishing vessels using bright lights to attract fish. While a small number may be other types of vessels, most ships do not use lights bright enough for detection. This work indicates that the addition of VIIRS data can greatly enhance transparency in commercial fishing in Indonesia.
The team believes most of the VIIRS detections are from fishing vessels not required to carry VMS because they are under the 30 gross ton (GT) threshold established by the government of Indonesia. It is also possible that some vessels detected only by VIIRS meet the size requirement but have switched off their VMS or have a faulty device. Another possibility is that VIIRS is detecting foreign boats that are not carrying VMS because they are poaching from Indonesian waters.
On the left, blue boats represent vessels detected by NOAA's satellite-based Visible Infrared Imaging Radiometer Suite (VIIRS) over the Arufura Sea on January, 2018. On the right, yellow dots represent active fishing vessels using Indonesia's Vessel Monitoring System plotted on the Global Fishing Watch map. About 80 percent of VIIRS-detected vessels do not broadcast VMS, and so combining the two data sources provides a more complete picture of fishing activity in Indonesia. Credit: Global Fishing Watch 2018.
"I'm excited for this opportunity to see the dark fleet," said David Kroodsma, Global Fishing Watch Research Program Director. The dark fleet being a common term used to describe vessels that don't show up in vessel monitoring systems and therefore are said to operate in the dark. "NOAA's VIIRS data shows us vessels we can't see by any other means and helps us to gain a more complete picture of fishing activity."
Global Fishing Watch detects nearly all large fishing vessels in Indonesian waters by combining Indonesia's VMS data and publicly broadcast AIS data which is required on vessels exceeding 300 GT. Global Fishing Watch can even tell when vessels turn off their monitoring devices. But the system is unable to see vessels when they are not broadcasting either AIS or VMS. Incorporating VIIRS, which represents a completely new source of data, into the Global Fishing Watch database and, eventually, the public mapping platform, will reveal the activity of even more of the world's commercial fishing fleet.
To cross match VMS and VIIRS, NOAA's Earth Observation Group developed an orbital model that predicts the probable location of each VMS-broadcasting vessel at the time of the VIIRS data collection. The model checks the predicted location against the actual VIIRS detections to define matches. Prior to the partnership with Global Fishing Watch, NOAA had access to two months of Indonesia VMS data, which they used to develop their cross-matching algorithm.
The partnership with Global Fishing Watch has provided three years-worth of Indonesian VMS data, which NOAA has now matched to its VIIRS vessel detections. In addition, the partnership has provided NOAA with valuable information on vessel gear types and identification numbers in the VMS records.
Arufura Sea, January, 2018. Comparing Vessel Monitoring System (VMS) data from Indonesia with satellite-based Visible Infrared Imaging Radiometer Suite (VIIRS) data reveals a more complete picture of fishing activity in Indonesia. Credit: Global Fishing Watch 2018.
This new data is enabling NOAA to calculate the frequency of VIIRS boat detections for the different fishing gear types and to work towards a calibration for estimating wattage from the VIIRS detected radiance. "When I saw what Global Fishing Watch could provide in the data, I said, Wow, that could really help us a lot, because we don't have access to this information in any other way," said Chris Elvidge, NOAA's Earth Observation Group Lead. His team is creating an atlas of fishing grounds for Indonesia using the three years of VMS provided by Global Fishing Watch and multiple years of VIIRS data.
Global Fishing Watch is able to provide the VMS data because of its partnership with Indonesia, which began publicly sharing their VMS through the Global Fishing Watch platform in June 2017. They are the first nation to take such bold steps toward transparency, and Peru has recently signed an MOU to do the same.
Now that Global Fishing Watch has access to the VIIRS boat detection data they can vastly expand the number of fishing boat records reported in the public database. In addition, it would be possible to cross match VMS or AIS data with VIIRS boat detections to identify "dark vessels" which may be fishing illegally. The combined data sources could also be analyzed to detect clusters of fishing boats straddling international boundaries, or fishing in Marine Protected Areas.
In a new commentary in the journal Nature Climate Change, IIASA researchers argue that a broader range of scenarios is needed to support international policymakers in the target of limiting climate change to under 2°C above pre-industrial levels, and to avoid potential negative environmental and social consequences of carbon dioxide removal on a massive scale.
"Many currently used emissions pathways assume that we can slowly decrease fossil fuel emissions today and make up for it later with heavy implementation of negative emissions technologies," says IIASA Ecosystems Services and Management Program Director Michael Obersteiner, lead author of the article. "This is a problem because it assumes we can put the burden on future generations--which is neither a realistic assumption nor is it morally acceptable from an intergenerational equity point of view."
The researchers point out that 87% of the scenarios in the IPCC 5th Assessment Report that limit climate change to less than 2°C rely heavily on negative emissions in the second half of the century, with most of the carbon dioxide removal coming from a suite of technologies known as Bioenergy with Carbon Capture and Storage (BECCS). Assuming that it's even possible to deploy BECCS on the scale required (a big question for a technology that has not yet been widely tested or implemented), massive implementation of land-based carbon dioxide removal strategies would have impacts on both the environment and the food system, with previous research showing trade-offs for food security and environmental conservation.
At the same time, reliance on future negative emissions to achieve climate goals may also fail to account for feedbacks in the climate system such as methane release from thawing permafrost, which are not yet fully understood.
"Many of our scenarios do not account for the uncertainties related to the climate mitigation process. Are our carbon budget estimates reasonable? Are the technologies going to develop the way we need them to be? Are natural carbon sinks reliable, or might they turn around?" says IIASA researcher Johannes Bednar, a coauthor.
In the article, the researchers present four archetype scenarios that incorporate a broader range of potential mitigation options. These include:
Major reliance on carbon dioxide removal in the future, the current archetype of many existing scenarios for achieving the 2°C or more stringent 1.5°C target.
Rapid decarbonization starting immediately, and halving every decade as proposed in a recent Science commentary coauthored by IIASA researchers.
Earlier implementation of carbon dioxide removal technologies, and phasing out by the end of the century
Consistent implementation of carbon dioxide removal from now until the end of the century.
Under all these scenarios, current country commitments under the Paris Agreement would not be sufficient to achieve the required cuts, the researchers say.
The article adds to a large body of significant IIASA research on pathways and scenarios for climate mitigation, as well as integrated research on climate and other sustainable development goals. It also provides a critical look at the current outlook for reaching climate targets.
IIASA researcher Fabian Wagner, another study coauthor adds, "In this paper we have shown that negative emission technologies may not only be an asset but also an economic burden if not deployed with care. We as scientists need to be careful when we communicate to policymakers about how realistic different scenarios might be. When we present scenarios that require the world to convert an amount of land equivalent to all today's cropland to energy plantations, alarm bells should go off."
Increased fluctuations in the path of the North Atlantic jet stream since the 1960s coincide with more extreme weather events in Europe such as heat waves, droughts, wildfires and flooding, reports a University of Arizona-led team. The research is the first reconstruction of historical changes in the North Atlantic jet stream prior to the 20th century. By studying tree rings from trees in the British Isles and the northeastern Mediterranean, the team teased out those regions' late summer weather going back almost 300 years -- to 1725.
"We find that the position of the North Atlantic Jet in summer has been a strong driver of climate extremes in Europe for the last 300 years," said Valerie Trouet, an associate professor of dendrochronology at the University of Arizona Laboratory of Tree-Ring Research.
Having a 290-year record of the position of the jet stream let Trouet and her colleagues determine that swings between northern and southern positions of the jet became more frequent in the second half of the 20th century, she said.
"Since 1960 we get more years when the jet is in an extreme position." Trouet said, adding that the increase is unprecedented.
When the North Atlantic Jet is in the extreme northern position, the British Isles and western Europe have a summer heat wave while southeastern Europe has heavy rains and flooding, she said. When the jet is in the extreme southern position, the situation flips: Western Europe has heavy rains and flooding while southeastern Europe has extreme high temperatures, drought and wildfires.
"Heat waves, droughts and floods affect people," Trouet said. "The heat waves and drought that are related to such jet stream extremes happen on top of already increasing temperatures and global warming -- it's a double whammy."
Extreme summer weather events in the American Midwest are also associated with extreme northward or southward movements of the jet stream, the authors write.
"We studied the summer position of the North Atlantic jet. What we're experiencing now in North America is part of the same jet stream system," Trouet said.
This winter's extreme cold and snow in the North American Northeast and extreme warmth and dryness in California and the American Southwest are related to the winter position of the North Pacific Jet, she said.
The paper, "Recent enhanced high-summer North Atlantic Jet variability emerges from three-century context," by Trouet and her co-authors Flurin Babst of the Swiss Federal Research Institute WSL in Birmensdorf and Matthew Meko of the UA is scheduled for publication in Nature Communications on Jan. 12. The U.S. National Science Foundation and the Swiss National Science Foundation funded the research.
"I remember quite vividly when I got the idea," Trouet said. "I was sitting in my mom's house in Belgium."
While visiting her family in Belgium during the very rainy summer of 2012, Trouet looked at the newspaper weather map that showed heavy rain in northwestern Europe and extreme heat and drought in the northeastern Mediterranean.
"I had seen the exact same map in my tree-ring data," she said. The tree rings showed that hot temperatures in the Mediterranean occurred the same years that it was cool in the British Isles -- and vice versa.
The part of an annual tree ring that forms in the latter part of the growing season is called latewood. The density of the latewood in a particular tree ring reflects the August temperature that year. Other investigators had measured the annual latewood density for trees from the British Isles and the northeastern Mediterranean for rings formed from 1978 back to 1725. Because August temperatures in those two regions reflect the summer position of the North Atlantic jet stream, Trouet and her colleagues used those tree-ring readings to determine the historical position of the jet stream from 1725 to 1978. For the position of the jet stream from 1979 to 2015, the researchers relied on data from meteorological observations.
"There's a debate about whether the increased variability of the jet stream is linked to man-made global warming and the faster warming of the Arctic compared to the tropics," Trouet said.
"Part of the reason for the debate is that the data sets used to study this are quite short -- 1979 to present. If you want to see if this variability is unprecedented, you need to go farther back in time -- and that's where our study comes in."
With the discovery of much older trees in the Balkans and in the British Isles, Trouet hopes to reconstruct the path of the North Atlantic jet stream as much as 1,000 years into the past. She is also interested in reconstructing the path of the North Pacific jet stream, which influences the climate and weather over North America.
Oscillations of water temperature in the tropical Pacific Ocean can induce rapid melting of Antarctic ice shelves.
Front of the Getz Ice Shelf. Credit: Jeremy Harbeck/NASA.
A new study published Jan. 8 in the journal Nature Geoscience reveals that strong El Nino events can cause significant ice loss in some Antarctic ice shelves while the opposite may occur during strong La Nina events.
El Niño and La Niña are two distinct phases of the El Niño/Southern Oscillation (ENSO), a naturally occurring phenomenon characterized by how water temperatures in the tropical Pacific periodically oscillate between warmer than average during El Niños and cooler during La Niñas.
The research, funded by NASA and the NASA Earth and Space Science Fellowship, provides new insights into how Antarctic ice shelves respond to variability in global ocean and atmospheric conditions.
The study was led by Fernando Paolo while a PhD graduate student and postdoc at Scripps Institution of Oceanography at the University of California San Diego. Paolo is now a postdoctoral scholar at NASA's Jet Propulsion Laboratory. Paolo and his colleagues, including Scripps glaciologist Helen Fricker, discovered that a strong El Niño event causes ice shelves in the Amundsen Sea sector of West Antarctica to gain mass at the surface and melt from below at the same time, losing up to five times more ice from basal melting than they gain from increased snowfall. The study used satellite observations of the height of the ice shelves from 1994 to 2017.
"We've described for the first time the effect of El Niño/Southern Oscillation on the West Antarctic ice shelves," Paolo said. "There have been some idealized studies using models, and even some indirect observations off the ice shelves, suggesting that El Niño might significantly affect some of these shelves, but we had no actual ice-shelf observations. Now we have presented a record of 23 years of satellite data on the West Antarctic ice shelves, confirming not only that ENSO affects them at a yearly basis, but also showing how."
The opposing effects of El Niño on ice shelves - adding mass from snowfall but taking it away through basal melt - were at first difficult to untangle from the satellite data. "The satellites measure the height of the ice shelves, not the mass, and what we saw at first is that during strong El Niños the height of the ice shelves actually increased," Paolo said. "I was expecting to see an overall reduction in height as a consequence of mass loss, but it turns out that height increases."
After further analysis of the data, the scientists found that although a strong El Niño changes wind patterns in West Antarctica in a way that promotes flow of warm ocean waters towards the ice shelves to increase melting from below, it also increases snowfall particularly along the Amundsen Sea sector. The team then needed to determine the contribution of the two effects. Is the atmosphere adding more mass than the ocean is taking away or is it the other way around?
"We found out that the ocean ends up winning in terms of mass. Changes in mass, rather than height, control how the ice shelves and associated glaciers flow into the ocean," Paolo said. While mass loss by basal melting exceeds mass gain from snowfall during strong El Niño events, the opposite appears to be true during La Niña events.
Over the entire 23-year observation period, the ice shelves in the Amundsen Sea sector of Antarctica had their height reduced by 20 centimeters (8 inches) a year, for a total of 5 meters (16 feet), mostly due to ocean melting. The intense 1997-98 El Nino increased the height of these ice shelves by more than 25 centimeters (10 inches). However, the much lighter snow contains far less water than solid ice does. When the researchers took density of snow into account, they found that ice shelves lost about five times more ice by submarine melting than they gained from new surface snowpack.
"Many people look at this ice-shelf data and will fit a straight line to the data, but we're looking at all the wiggles that go into that linear fit, and trying to understand the processes causing them," said Fricker, who was Paolo's PhD adviser at the time the study was conceived. "These longer satellite records are allowing us to study processes that are driving changes in the ice shelves, improving our understanding on how the grounded ice will change," Fricker said.
"The ice shelf response to ENSO climate variability can be used as a guide to how longer-term changes in global climate might affect ice shelves around Antarctica," said co-author Laurie Padman, an oceanographer with Earth & Space Research, a nonprofit research company based in Seattle. "The new data set will allow us to check if our ocean models can correctly represent changes in the flow of warm water under ice shelves," he added.
Melting of the ice shelves doesn't directly affect sea level rise, because they're already floating. What matters for sea-level rise is the addition of ice from land into the ocean, however it's the ice shelves that hold off the flow of grounded ice toward the ocean.
Understanding what's causing the changes in the ice shelves "puts us a little bit closer to knowing what's going to happen to the grounded ice, which is what will ultimately affect sea-level rise," Fricker said. "The holy grail of all of this work is improving sea-level rise projections," she added.
