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Subglacial Water Can Accelerate East Antarctic Glacier Flow

Wed, 04/03/2019 - 12:35

Recent projections have identified East Antarctica’s fast-flowing Recovery Glacier, which drains 10% of the continent’s land-based ice, as the region’s largest potential contributor to future global sea level rise. Scientists have hypothesized that water derived from four previously identified subglacial lakes, which are located near the point where Recovery Glacier’s flow accelerates, largely controls the glacier’s discharge.

To better understand the distribution and role of subglacial water within the Recovery system, Diez et al. analyzed two sets of airborne radar data acquired through the IceGrav project in 2013 and the PolarGap project in December of 2015. The combined data set comprises a grid with an overall line spacing of about 10 kilometers across Recovery Lakes A, B, and C, plus a single line across Lake D.

Using several properties, including ice thickness, bed roughness, and radar reflectivity, the researchers classified whether the subice terrain in each grid cell is a lake, a swamp, or dry. Their results suggest that the areas previously classified as Lakes C and D are actually dry and the area comprising the originally proposed Lakes A and B is instead an interconnected, 4,320-square-kilometer swampland, consisting of small lakes surrounded by saturated sediment, which the team renamed Lake AB. These findings are consistent with another recently published article that found no definitive evidence of lakes in these locations.

Using updated charts of bed topography and calculated flow paths, the team also mapped where water is discharging from the lakes. These data indicate that subglacial water seeps from Lake AB’s western shore, lubricating the bed and initiating the rapid ice flow observed in this area.

By contrast, the authors attribute the onset of fast ice flow observed near what was previously interpreted as Lakes C and D to the presence of a substantial topographic step. The resulting 1,300-meter increase in ice thickness—rather than lubrication of the bed—suffices to explain the onset of fast ice flow in this area.

These findings indicate that multiple processes are responsible for speeding up the flow of ice within the Recovery Glacier system. Because not all of these relate to subglacial water, this study demonstrates the importance of characterizing the underlying causes of ice flow acceleration to gain a more nuanced understanding of how this water could affect the glacier’s discharge in a range of future climate change scenarios. (Journal of Geophysical Research: Earth Surface, https://doi.org/10.1029/2018JF004799, 2019)

—Terri Cook, Freelance Writer

Weather-Induced Tsunami Waves Regularly Roll Up on U.S. Shores

Wed, 04/03/2019 - 12:33

Tsunami waves aren’t just caused by earthquakes or landslides—they can be triggered by weather, too.

These meteotsunamis, which are generally smaller and more localized than their seismic brethren, are prevalent along the East Coast of the United States, new research shows. Scientists found that, on average, 25 meteotsunamis rolled up on shorelines each year from 1996 to 2017, according to a recent paper published in the Bulletin of the American Meteorological Society.

Potentially destructive waves—those topping about 60 centimeters in height—occur only about once a year, the data revealed, but such events can cause injuries and significantly contribute to flooding, the researchers concluded.

This storm, off the coast of New Jersey, caused a meteotsunami in 2013. Credit: Buddy Denham Meteorological Waves

“They’re meteorologically driven tsunami waves.”Meteotsunamis, as their name suggests, are similar to seismically induced tsunamis, said Gregory Dusek, a physical oceanographer at the National Oceanographic and Atmospheric Administration’s (NOAA) National Ocean Service in Silver Spring, Md., who led the new study. “They’re meteorologically driven tsunami waves.”

An abrupt change in air pressure or high wind speeds, often associated with storms, can cause meteotsunamis to form in shallow waters. If the waves move at the same speed as the storm system, they receive periodic injections of energy, which cause them to grow in size.

Dusek and his colleagues collected data from 125 tide gauges between Maine and Puerto Rico. These roughly football sized instruments, mounted on piers or bulkheads, measure water height by bouncing microwaves or sound waves off the water’s surface. After subtracting out the signal caused by the tide, researchers looked for signatures of passing meteotsunamis. They flagged energetic waves taller than 20 centimeters that were detected by at least two tide gauges. Dusek and his collaborators also looked for certain meteorological conditions: a wind speed above 10 meters per second or a change in air pressure of at least 0.9 millibar over 6 minutes.

Many Small Ones

The scientists identified 548 meteotsunamis over the 22-year time span, which averages to roughly 25 per year.

“I certainly didn’t expect to see that number,” said Dusek.

However, other recent studies that focused on the Great Lakes and the Gulf of Mexico have corroborated these findings, making the results less surprising, said Dusek.

Most of the meteotsunamis on the East Coast probably didn’t cause damage, researchers found: Over 90% had a peak-to-trough height of less than 40 centimeters. Thirty events had a wave height of more than 60 centimeters, and three were larger than 1 meter. Meter-size waves can injure beachgoers and also contribute to coastal inundation during a storm surge, said Dusek.

New research suggests meteotsunamis are a frequent occurrence along Earth’s coastlines.This study provides insights into the timing and severity of meteotsunamis along a highly populated shoreline, said Eric Anderson, an oceanographer at the NOAA Great Lakes Environmental Research Laboratory in Ann Arbor, Mich., not involved in the research. “[It] supports the notion that meteotsunamis are a frequent occurrence along the Earth’s coastlines.”

A few of the larger meteotsunamis found by Dusek and his colleagues were also detected by Deep-ocean Assessment and Reporting of Tsunamis (DART) buoys. These instruments, designed to measure seismically induced tsunamis, are complementary to tide gauges, said Dusek.

Researchers are planning to combine their tide gauge detections of meteotsunamis with DART data to determine what kinds of events trigger both types of sensors.

—Katherine Kornei (hobbies4kk@gmail.com; @katherinekornei), Freelance Science Journalist

Correction, 4 April 2019: This article has been updated to describe accurately how tide gauges measure water height.

Ice Drove Past Indo-Pacific Climate Variance

Tue, 04/02/2019 - 12:50

During the Last Glacial Maximum (LGM), about 21,000 years ago, an area encompassing the Indian and westernmost Pacific Oceans experienced big shifts in temperature and rainfall.

In a new study, scientists have melded field data with climate modeling to uncover past drivers of these large climate swings—work that could be useful in predicting what will happen amid future climatic changes.

During the LGM, the prevailing winds in the Indo-Pacific region were reversed compared to what they are today, and there were unusual changes in ocean temperatures. The researchers used both terrestrial and marine proxy data—including microfossils, geochemical indicators of sea surface temperatures, isotopic ratios, and carbon plant typing—from sites in Africa, Asia, and Australia to reconstruct the dramatic and dynamic climatic changes.

“The geologic record tells us that Indonesia and the monsoon regions of the east Indian Ocean became drier and cooler while the west [Indian Ocean] became wetter and remained warmer.”“The geologic record tells us that Indonesia and the monsoon regions of the east Indian Ocean became drier and cooler while the west [Indian Ocean] became wetter and remained warmer,” said study coauthor Jessica Tierney, a paleoclimatologist at the University of Arizona, in a statement.

Well-established dating of the LGM and the large amount of data collected from the time period allowed the team to “infer robust patterns of hydroclimate change and ocean-surface cooling,” they wrote.

To tease out what drove the LGM climatic changes in the region, the team ran a variety of simple and complex climate models, testing different factors—such as greenhouse gas concentrations, ice sheet topography, land cover, and sea levels—to see which best reproduced the climate indicated by the geologic record.

They found that two major factors were likely at play: land exposure and albedo changes.

As ice sheets grew over Canada and Scandinavia, sea levels dropped up to 120 meters, exposing large areas of ocean shelf, including continental land bridges from Thailand to Australia. The increased land cut off ocean throughflow passages and altered tidal mixing, thereby changing regional temperatures, rainfall, and wind patterns.

Increased ice albedo altered monsoon patterns around the world. During the LGM, the changing air masses from albedo weakened the Indian monsoon, cooling the Arabian sea and decreasing moisture supplies to the region.

Fresh Approach to Climate Modeling

The “multipronged approach” and the variety of climate models of different complexity used in this study are strengths of the work, says Katie Dagon, a climate scientist at the National Center for Atmospheric Research in Boulder, Colo., who was not involved in the research. That approach “can be a very effective way of [studying] different mechanisms,” she says.

Dagon notes that it was the uncoupled model, a simpler model that didn’t link the full ocean and atmosphere together, that worked best. She adds that this study is a good example of simple models being effective and that it helps in discussions about approaches to future modeling work.

“The most complicated model is not always the best choice,” Dagon says.

Uncovering the drivers of Indo-Pacific regional climate during the LGM is important for understanding how hydrologic cycles might change in the future.Dagon says the study, by focusing on the LGM and trying to tease apart driving mechanisms during that time period, could help scientists better understand how climate could change in the future.

“The [researchers] talk about the response of greenhouse gases and the fact that it was cooler during that time period,” Dagon says. “It’s interesting to think about how these mechanisms apply to a potentially warmer future climate.”

The study authors noted that uncovering the drivers of Indo-Pacific regional climate during around the LGM is important for understanding how hydrologic cycles might change in the future.

“A big climate shift like this could have a huge impact on water availability over the heavily populated Indian Ocean rim,” said lead author Pedro DiNezio of the University of Texas at Austin in a statement.

—Sarah Derouin (sarah.derouin@gmail.com; @Sarah_Derouin), Science Writer

Spruce Beetle Slows Snow Sublimation in Wyoming’s Mountains

Tue, 04/02/2019 - 12:24

In mid-April 1921, a huge snowstorm hit Silver Lake, Colo. Within 24 hours, the town was buried beneath more than 1.8 meters of snow.

Although Silver Lake’s record-breaking snowfall has yet to be equaled, the Rocky Mountains remain famous for their snowy peaks. A good portion of the snow that falls there sublimates directly from solid snow to water vapor, leaving less snow on the ground to melt. Snow caught on tree branches sublimates fastest, often disappearing within a few days of a snowfall.

But in the mid-2000s, an endemic pest upset the balance. By 2010, a spruce beetle outbreak had killed 75%–85% of mature spruce trees in some areas, opening the canopy. Snow could no longer accumulate there and instead fell between the branches to the slow-sublimating snowpack on the ground.

Frank et al. investigated how canopy loss has affected sublimation rates—a critical factor in the ecosystem’s water dynamics. In a snow-dominated ecosystem, plant and animal life, water chemistry, and water resources are all influenced by sublimation rates. Decreased canopy would decrease the fast-sublimating clumps of snow that gather on branches, but opening up the forest could also increase the amount of wind and sunlight reaching the snowpack on the ground, speeding up its sublimation.

The team used data gathered over 17 years from the Glacier Lakes Ecosystem Experiments Sites in Wyoming’s Snowy Range, a research site managed by the U.S. Department of Agriculture’s Forest Service.

First, the researchers compared sublimation within the canopy with sublimation on the ground and confirmed that canopy snow sublimates more easily than ground snow. Even after the beetle outbreak, half to two thirds of all sublimation came from the diminished canopy. In fact, as more snow falls, a greater percentage of sublimation occurs in the canopy.

The beetle outbreak reduced the amount of snow intercepted by the spruce canopy to a third of its original size. The researchers observed 32% less sublimation from the canopy and only a 3% sublimation increase from snow on the increasingly exposed ground. Altogether, that means that nearly a quarter less sublimation is happening between November and April. The problem extends beyond winter: Another study found that the reduced canopies are releasing about a third less water into the air in the summer.

Ultimately, a significant amount of water remains within the forest rather than returning to Wyoming’s dry atmosphere. The reduction in sublimation adds as much water to the ecosystem as a 6% increase in snowfall would. In the western United States’ semiarid climate, this difference in water availability has both ecological and social implications. The hydrologic consequences are unknown, and studies so far have found conflicting or surprising results, but trends will also continue to change as the understory responds and the forest begins to recover from the beetle epidemic. (Water Resources Research, https://doi.org/10.1029/2018WR023054, 2019)

—Elizabeth Thompson, Freelance Writer 

Looking at “Night-Shining” Clouds from the Stratosphere

Tue, 04/02/2019 - 12:19

Night owls and insomniacs who stay up to watch the twilight and night sky in the summer have probably noticed wispy clouds of silvery color that start to appear in the twilight sky. Sometimes they appear as a weak, foggy spot, but other times they are bright, with beautiful wavy surfaces like the surface of the sea. These waves can move in unison in a certain direction, or they can move in different and even in opposite directions. Occasionally, strange waveforms resembling a fish skeleton or small-scale waves suddenly grow above the silvery surfaces of these clouds.

These are noctilucent clouds (NLCs), and they form in the upper atmosphere between 80 and 90 kilometers above Earth’s surface. NLCs are composed of small ice crystals about 50 nanometers in radius. Because they scatter sunlight effectively, these clouds are easily visible against the twilight sky.

On the night of 5–6 July 2018, our research group, a collaboration of scientists from the Swedish Institute of Space Physics, A. M. Obukhov Institute of Atmospheric Physics of the Russian Academy of Sciences, Aerospace Laboratory Stratonautica, and the Moscow Association for Noctilucent Cloud Research, observed NLCs from a vantage point between instruments on the ground and satellite instruments in space. We sent instruments aloft on a meteorological sounding balloon in an experiment we call Stratospheric Observations of Noctilucent Clouds (SONC). We dedicated this stratospheric experiment to studies of NLC dynamics over horizontal distances of more than 100 kilometers.

Noctilucent Clouds from Above and Below

NLCs are regularly observed and studied from the ground using optical imagers and lidars, as well as from space using satellite measurements [Bailey et al., 2009; Dalin et al., 2008; DeLand and Thomas, 2015]. Each of the techniques has its advantages and disadvantages.

Ground-based lidar and optical measurements provide high horizontal and vertical resolutions of approximately 20 and 50–150 meters, respectively [Baumgarten and Fritts, 2014], as well as high temporal resolution, on the order of 10 seconds. However, such measurements are limited by tropospheric weather conditions—the sky must be clear or partly clear—and ground-based instruments can cover only a small region of the globe.

Until now, only a single published noctilucent cloud experiment has been conducted from a stratospheric balloon.Satellite measurements provide a global view of the NLC positions, and they are independent of weather conditions. However, they have a low horizontal resolution (~2 kilometers) and low temporal resolution (~1.5 hours between orbital trajectories). Thus, there is no perfect technique to observe and study spatial-temporal evolutions of NLCs so far.

A stratospheric balloon would seem to be a preferred platform to observe NLCs from a vantage point between ground-based instruments and satellites, but until now, only a single published experiment has been conducted from a stratospheric balloon. The E and B Experiment (EBEX)—named after two modes of the cosmic microwave power spectrum—provided NLC observations over Antarctica between 29 December 2012 and 9 January 2013 [Miller et al., 2015]. While EBEX was gathering data on polarization in the cosmic microwave background, two of its star cameras, having a narrow field of view (~4° by 3°), suddenly captured fine structures of NLCs and their turbulence dynamics on small horizontal scales, from several kilometers down to 10 meters.

The observations from EBEX and the absence of other stratospheric observations of NLCs on large scales motivated us to conduct a new balloon-borne experiment in the summer of 2018. This experiment opens up new horizons (in the literal and figurative senses) for studies of large-scale dynamic processes in the middle atmosphere.

Launching the Experiment The three-axis motorized gimbal stabilized platform of the SONC balloon experiment, designed and built by Aerospace Laboratory Stratonautica. The platform housing the camera is 30 × 20 × 20 centimeters. Credit: Denis Efremov.

We launched the SONC experiment on the night of 5–6 July 2018. We used a meteorological sounding balloon to lift a full-frame, high-resolution, highly sensitive digital camera (Sony Alpha A7S, 35 millimeter, 12 megapixels) into the stratosphere over Moscow, Russia (~56°N, 41°E). The camera was equipped with a wide-angle lens that captured an image over an area spanning approximately 110° by 82° (14 millimeters, f-number f/2.8).

Since a payload gondola constantly rotates and shakes during a flight, the NLC camera was placed onto a specially designed three-axis motorized gimbal stabilized platform built by Aerospace Laboratory Stratonautica. The NLC camera took images every 6 seconds during the whole flight and collected several thousands of images. A flight with a long duration would require a thermostabilization system, but the SONC experiment did not require it. A camera can readily survive the low stratospheric temperatures (about –50°C) for the 2 hours allotted to this experiment.

We launched the SONC balloon at 21:34 Universal Time (UT), and it landed at 23:19 UT on 5 July 2018, with a total flight duration of about 1.7 hours. We chose a launch time on the basis of the long-term statistics of NLC observations in the Moscow region from 1962 to the present time, which demonstrated that the highest probability (~80%) of observing NLCs on a clear night is at the beginning of July.

The balloon, which was designed to reach an altitude of 30 kilometers, reached its maximum altitude at 20.4 kilometers, where it burst for unknown reasons. The NLC camera descended with a parachute and was successfully recovered. A GPS receiver installed in the gondola provided information on the balloon’s trajectory (Figure 1). Ground support was provided by three automated NLC cameras in the Moscow region. These cameras photographed the NLCs at the same time as the photos captured from the SONC balloon. This overlap allows us to estimate the altitude of NLCs and their dynamics in 3-D space using a triangulation technique.

Fig. 1. The SONC balloon reached a maximum altitude of a little more than 20 kilometers about 75 minutes into its 1.7-hour flight. Balloon-Borne Observation of Noctilucent Clouds

The balloon-borne camera captured a large-scale NLC field with a number of interesting features, which we are currently analyzing. Here we report the following general characteristics of the NLC display. NLCs were observed between 20:30 and 23:15 UT on 5 July 2018, and they were located between 82.6 and 85.1 kilometers altitude. The NLC field extended along the horizon from the northwest to northeast at a low elevation, as seen from the balloon, and the NLCs traveled from the south to the north at an observed mean speed of approximately 43 meters/second.

The horizontal extent of the NLC field from its western to eastern observable border was about 1,400 kilometers, and it extended about 800 kilometers from the northern to southern border. Such large distances are impossible to observe from the ground because of Earth’s curvature and the limited area of the twilight sky illuminated by the Sun. An observer on the ground watched only the central part of the NLC field (about 1,000 by 500 kilometers) because its far eastern and western wings were located below the ground observer’s local horizon.

Thus, a balloon-borne NLC observation provides an obvious great advantage over a ground-based observation, yielding much larger spatial coverage. This coverage is comparable to observations made from space, but it comes at a much lower cost. At the same time, we are able to resolve NLC details as small as 100 meters, a resolution that is unachievable by current space observations of NLCs.

New Horizons and Next Steps

Stratospheric balloon-borne observations offer a combination of large spatial coverage and high-resolution images currently impossible to achieve from either the ground or space.The combination of large spatial coverage (1,400 kilometers or more) and high-resolution images (~100 meters) is a unique characteristic inherent to stratospheric balloon-borne observations of noctilucent clouds. Such a combination of resolutions is currently impossible to achieve from either the ground or space. In general, a balloon-borne observation provides us with several new opportunities:

For long-duration flights spanning several days, we can observe NLCs for 24 hours a day. This duration is possible because the sky is always almost black above 20 kilometers altitude (there is very little Rayleigh atmospheric scattering). This vantage point lets us detect noctilucent clouds with very low brightness levels (see below). We can measure neutral wind velocity at the mesopause and the large-scale trajectory of NLC fields (over 1,400 kilometers). We can obtain quantitative information on a wide range of atmospheric waves (gravity and planetary waves, solar tides) propagating through the summer mesopause. A camera equipped with a narrow field of view lens (~10°) can provide quantitative information on small-scale turbulent dynamics (down to 1 meter). Thin parallel bands of atmospheric gravity waves mark the final stage of evolution of this bank of noctilucent clouds, seen from the stratosphere at 19.5 kilometers altitude at 22:45 UT on 5 July 2018. Credit: Aerospace Laboratory Stratonautica

For the next phase of our project, we will build a new NLC imager, which we plan to launch for several days. This imager will have four cameras equipped with wide- and narrow-angle lenses to resolve large-scale atmospheric gravity waves and small-scale dynamics like wave instabilities and turbulent processes in NLCs. We may be making a circumpolar flight around the North Pole for 15–20 days using a big scientific balloon whose volume is kept approximately constant, enabling it to keep a constant altitude for a long time.

North Atlantic Circulation Patterns Reveal Seas of Change

Tue, 04/02/2019 - 12:18

Atlantic Meridional Overturning Circulation (AMOC), involving the deep-ocean mixing of warm, salty waters with colder, fresher waters in the North Atlantic, is a major influencer of Earth’s climate. As warm tropical currents journey north, pushed by prevailing winds, they cool, become denser, and sink in a process known as overturning.

Historically, most models have shown that the bulk of this overturning occurs in the Labrador Sea, west of Greenland. But a new study indicates that the eastern North Atlantic between Greenland and Scotland may actually be the dominant overturning venue.“As climate is warming and surface waters are warming and sea ice melts and more fresh water is being added to the system, we are trying to figure out how we can expect the AMOC to change in the years and decades ahead.”

The new study is the first report from the initial phase of the Overturning in the Subpolar North Atlantic Program (OSNAP), in which moored instruments and subsurface floats are being used to monitor the rates and patterns of overturning circulation in the North Atlantic.

“As climate is warming and surface waters are warming and sea ice melts and more fresh water is being added to the system, we are trying to figure out how we can expect the AMOC to change in the years and decades ahead,” says Susan Lozier, a physical oceanographer at Duke University and lead author of the new study published in Science.

OSNAP is not the only program monitoring AMOC. Efforts to begin systematically monitoring variables such as sea surface temperature, salinity, and currents gave rise to the Rapid Climate Change–Meridional Overturning Circulation and Heat-flux Array (RAPID-MOCHA), deployed in 2004. RAPID-MOCHA takes ongoing measurements at a latitude of 26.5°N, across the Atlantic between Florida and Morocco.

The Overturning in the Subpolar North Atlantic Program (OSNAP) includes an array of moored instruments and subsurface floats used to monitor the rates and patterns of overturning circulation in the North Atlantic. The related RAPID-MOCHA program takes ongoing measurements at 26.5°N latitude between Florida and Morocco. Credit: Lozier et al., 2019, http://doi.org/10.1126/science.aau6592

Installed in 2014, OSNAP’s array links several existing data collection nodes, including the German Labrador Sea exit array and the recently installed U.S. Ocean Observatories Initiative array in the southwest Irminger Sea, to cover the vast region of ocean that stretches between Newfoundland and Scotland.

“Taking measurements at one latitude [as RAPID-MOCHA does] tells you a lot but not everything,” says Meric Srokosz, a physical oceanographer at the National Oceanography Centre in Southampton, England, who helps run the RAPID program but was not involved in the new study. “OSNAP’s measurements at different latitudes are giving us a more complete picture of what the overall overturning circulation in the Arctic is doing.”

Data Reveal New Patterns

The most unexpected finding of the new OSNAP study is that the overturning cycle is dominated not by conditions in the Labrador Sea, as oceanographic models had long indicated, but by changes in OSNAP East—the waters east of Greenland in the Irminger and Iceland Basins.The most unexpected finding of the new OSNAP study is that the overturning cycle is dominated not by conditions in the Labrador Sea, as oceanographic models had long indicated, but by changes in OSNAP East—the waters east of Greenland in the Irminger and Iceland Basins.

Location matters, Lozier says. “As we’re trying to understand the sensitivities of this system to changes, we need to know, where is the water getting warmer? Where is the fresh water coming in from the Arctic? All those factors make a big difference in predicting how the overturning will change over time.”

OSNAP data also revealed new variability patterns for AMOC. For decades, scientists assumed that overturning was consistent over timescales of hundreds to thousands of years or longer, Lozier says.

“But in the 1990s we became concerned that variation could occur on much shorter timescales—on the order of decades to centuries—and that a decline in overturning could perhaps trigger rapid climate change,” she explains.

As it turns out, scientists’ suspicions about short-term variation were indeed correct: RAPID’s data indicate that variability in the rate of overturning is occurring on interannual timescales.

“The AMOC is more variable on much shorter timescales than anybody expected,” says Srokosz. “In 2009 and 2010 there was a big dip when the AMOC dropped by 30% and then rapidly recovered, which was a big surprise. Computer models didn’t indicate that such variability was possible.”

Overall, since monitoring began in 2004, RAPID has recorded an overall decline in the overturning rate of the AMOC.

Monitoring North Atlantic Carbon Sinks

As the overturning of seawater in the North Atlantic changes, so does the ocean’s ability to absorb and store atmospheric carbon, Lozier says.

“Since the Industrial Revolution, the oceans have taken up about a third of the anthropogenic carbon dioxide humans have produced.”“If the overturning slows down, the ocean will take up less anthropogenic carbon, which would leave more anthropogenic carbon in the atmosphere, which could trigger rapid warming.”

Half of that carbon dioxide is now sequestered in the deep ocean, including the North Atlantic.

“If the overturning slows down, the ocean will take up less anthropogenic carbon, which would leave more anthropogenic carbon in the atmosphere, which could trigger rapid warming,” she says.

To better understand the role of the North Atlantic in carbon storage, the Argo ocean observing program will soon add biogeochemical carbon sensors to their network of data-collecting floats in the North Atlantic. The Argo floats collect data at depths of 1,000 meters, periodically rising to the surface as well as diving to depths of 2,000 meters.

“Adding the carbon monitoring component will be the biggest expansion to the OSNAP project to date,” Lozier says.

The OSNAP team also plans to continue collecting data for the duration of the 5-year initial project phase and to seek funding for continued monitoring.

“As of now, we have a 21-month record, and we can’t yet say anything about whether the AMOC is slowing down, but our observations will provide some important ground truthing for modeling studies that are working to anticipate future changes.”

Srokosz looks forward to when data from RAPID-MOCHA and OSNAP can be overlapped.

“It will be interesting to get 10 years of overlap between the two data sets to help link what’s happening at different latitudes in the North Atlantic,” he says. “The major obstacle will be to keep both programs funded.”

—Mary Caperton Morton (caperton27@gmail.com; @theblondecoyote), Science Writer

This article is part of a series made possible through the generous collaboration of the writers and editors of Earth magazine, formerly published by the American Geosciences Institute.

Compiling a Census for SEAFLEAs

Tue, 04/02/2019 - 12:13

Methane emission sites, found everywhere on the world’s seafloors, are interesting to a wide variety of geoscientists and are a source of greenhouse gas. Currently, no global open-source database of these sites exists, but the U.S. Naval Research Laboratory has begun compiling a database of global seafloor anomalies associated with methane emission sites. At a town hall meeting held during AGU’s Fall Meeting 2018, collaborators came together to offer guidance on forming this open-source database of seafloor fluid expulsion anomalies (SEAFLEAs).

Despite increasing numbers of SEAFLEA discoveries, many SEAFLEA locations remain unpublished, and data mining from literature can be tedious and time-consuming. Much about SEAFLEA formation and morphology is still to be discovered—specifically, their distribution on the seafloor. A comprehensive open-source global database of SEAFLEA locations could address these issues.

December’s town hall addressed several questions on how best to establish a collaborative data set:

What data are of particular interest: site locations, plume height, hardgrounds, pockmarks, mounds, or other features and phenomena? What form should data be stored in: spreadsheets or shape files? What, if any, data standards should be implemented? Hunting for SEAFLEAs

SEAFLEAs have been reported for decades in numerous locations, some extensively, using both remote sensing and observational data. These fluid expulsion sites can take on a variety of forms: authigenic carbonate deposits (formed in situ), mounds, bubble plumes, and seafloor methane hydrates, among others. These sites are typically colder than 50°C, earning the name “cold seeps.” They are rich in methane and are likely the result of tectonic stresses or sediment dewatering. Cold seeps are distinctly different from hot (hydrothermal) vents associated with seafloor spreading, which exhibit temperatures over 100°C.

Recently, multibeam sonar systems, which usually identify solid objects, have been modified to show returns (sound reflections) from the water column, where bubble plumes associated with some expulsion sites create strong signals. Increasing use of multibeam sonar promises to be a significant source of SEAFLEA locations. Sonar can pick up not only water column anomalies but also high-backscatter hardgrounds (rocklike formations like authigenic carbonates) commonly associated with cold seeps.

Setting Up the Database

By establishing a collaborative database, we intend to create a central information source and to distribute the administrative burdens. Contributors will add to the database simultaneously with their own research efforts. We intend for the database to be impactful and enduring, creating a foundation for global, regional, and site-specific research into seafloor seepage and serving as a starting point for prediction of regional and global trends, hazards, and other seafloor phenomena.

Most attendees at the town hall were interested in a general data set with no specific features required. They considered phenomena such as areally extensive hardgrounds, mounds, and pockmarks and point source data, such as seep locations, to be equally important. Thus, attendees preferred a data set consisting of geographic information system (GIS)-compatible shape files, which can store both point and shape data with associated features in attribute tables.

Using a GIS program, preferably open source, would also allow multiple users to access and maintain the data set. Remaining hurdles to setting up the database include data verification, a means of collaborating between institutions, details on storage and dissemination, and implementing data standards (e.g., via the Open Geospatial Consortium or the International Hydrographic Organization).

The town hall brought together academic, government, and private sector researchers and scientists at all career levels, each contributing to the initialization of this new database. Although hurdles remain, establishing the community of users, developers, and contributors represents the first step toward an open, collaborative database of seafloor fluid expulsion anomalies.

—Benjamin Phrampus (benjamin.phrampus.ctr@nrlssc.navy.mil), American Society for Engineering Education Postdoctoral Research Program, U.S. Naval Research Laboratory, Stennis Space Center, Miss.; and Taylor Lee and Warren Wood, U.S. Naval Research Laboratory, Stennis Space Center, Miss.

Sea-Surface Carbon Patterns Linked to Large-scale Climate Modes

Tue, 04/02/2019 - 11:30

Understanding the dominant spatial and temporal modes of variability in global sea surface partial pressure of carbon dioxide (pCO2) is necessary for teasing out the main mechanisms responsible for driving the marine carbon cycle. However, the existing global network of observation-based estimates of this important measure of air-sea carbon dioxide exchange are hampered by data gaps in both space and time.

Landschützer et al. [2019] have developed a new 34-year time series of observationally based global surface ocean pCO2 that uses a sophisticated neural network based-clustering technique along with the application of physical drivers known to influence the sea surface carbonate system. The global multi-decadal pCO2 record is compared to representative indices of the large-scale climate variability, such as the El Nino-Southern Oscillation (ENSO), Southern Annular Mode (SAM), the Atlantic Meridional Oscillation and the Pacific Decadal Oscillation.

Thermal changes driven by ocean circulation and the biological response to the large-scale climate modes drive most regional variability in the global ocean pCO2, although in the North Atlantic the variability is mostly thermally driven, possibly due to solubility changes. The most dominant oscillation periods of the global pCO2 are somewhat patchy but still show large-scale coherent patterns (see figure above). Nonetheless, the authors recognize the shortcomings of resolving 10-year and longer cycles from a 34-year time series and emphasize the need for the ongoing coordination in the collection of surface pCO2 data in the global oceans.

Citation: Landschützer, P., Ilyina, T., & Lovenduski, N. S. [2019]. Detecting regional modes of variability in observation‐based surface ocean pCO2. Geophysical Research Letters, 46. https://doi.org/10.1029/2018GL081756

—Janet Sprintall, Editor, Geophysical Research Letters

Youth Call Climate Change a Generational Justice Issue

Mon, 04/01/2019 - 20:48

“Climate change is a generational justice and equity issue,” Jonah Gottlieb, a high school junior in Rohnert Park, Calif., told youth and adults in a jam-packed room in the U.S. Capitol Building. It was filled with earnest middle schoolers and high schoolers as well as adult climate change activists and some members of Congress.

Climate change “disproportionately affects students and young people in future generations.”Climate change, Gottlieb said, “disproportionately affects students and young people in future generations.”

As the codirector of Schools for Climate Action, Gottlieb was at the Capitol for the Youth and Educator Climate Advocacy Summit on 28 March to encourage Congress to support climate change policies. He and other advocates also hand delivered sample climate action resolutions to every member of Congress. Similar resolutions, calling for action on the issue, have already been adopted by more than 60 education-related organizations. Among those organizations are school boards, unions, and student councils.

The summit was one of a string of youth actions against climate change, which also included protests around the world on 15 March.

Gottlieb said that there are two reasons why so many youths believe in the need for climate action. “One is because we know what the consequences are,” he said. “And number two is we’re taking science classes right now.”

Calling on Congress

“The history of climate neglect does not have to be our enduring legacy. The 116th Congress can break the pattern of climate neglect.”Schools for Climate Action cofounder Park Guthrie told the crowd that Congress has known about the harm from climate change for decades but has chosen not to act. “The history of climate neglect does not have to be our enduring legacy. The 116th Congress can break the pattern of climate neglect,” he said.

Guthrie, who is a sixth grade science teacher in Occidental, Calif., later told Eos that “the education sector is a natural” for taking a lead on climate action.

“We’re the ones focused on the next generation. We see the harm. We believe the science. Our hearts are broken,” he said, adding that he thinks the resolutions are making a difference.

Schools for Climate Action helps school boards, student councils, and others pass nonpartisan climate action resolutions to help push Congress to act on climate change.

“We have laid the groundwork for trying to educate the public and Congress about climate change, but these kids are going to be the tipping point in demanding to stop harm and neglect and to take action on climate change,” Lynne Cherry, founder and director of Young Voices for the Planet, told Eos. The nonprofit, which has produced a series of films about kids working on climate change issues, cosponsored the Capitol Hill event along with Schools for Climate Action.

Having the Most at Stake

At the event, several members of Congress also spoke out for climate change action.

“You do have the most at stake, you’re going to inherit whatever mess we’ve created, and you’re going to have to figure that out and live with it,” Rep. Mike Thompson (D-Calif.) told the youth in the audience. “The fact that you are plugged in now is incredibly important. It’s impressive the resolutions that you have had different bodies pass, bringing this [issue] to their attention.”

Thompson said that he has cosponsored the nonbinding Green New Deal resolution in Congress because of the need to make a bold and aspirational statement about dealing with climate change. The resolution “has been heralded by some as the answer to all of our woes and by others as the beginning of the end,” he said. “The truth of the matter is the Green New Deal is a resolution. It’s not a law that we would pass. It’s a resolution that states certain principles” about reducing the threat of climate change.

“It’s going to be you and your generation that forces everyone else to do the right thing.”Rep. Ben Ray Luján (D-N.M.) also roused the crowd. “It’s going to be you and your generation that forces everyone else to do the right thing,” he told the youth. “We can do something real about [climate change], and it starts with you.”

A Generational Betrayal

Also at the event, Sen. Sheldon Whitehouse (D-R.I.) said that “the fossil fuel industry has developed an enormously powerful and often secret army to apply pressure to Congress” to prevent any action on climate change. Whitehouse said bipartisan discussions about climate change in Congress “stopped dead” following the U.S. Supreme Court’s 2010 Citizens United decision, which led to unprecedented political spending. He said that bipartisan conversation “now is just beginning to reemerge.”

“We are enjoying a carbon polluting economy, whose costs are going to come for you and going to come for your children and going to come for their children.”“We are enjoying a carbon polluting economy, whose costs are going to come for you and going to come for your children and going to come for their children,” he said. Whitehouse added that there are a lot of ways to reduce the threats of climate change and that putting a price on carbon pollution needs to be part of the solution. “A big bill that does a lot of things but doesn’t have a carbon price can’t work,” he said.

Climate change “is a generational betrayal,” and the youth “are on the losing end of the betrayal,” Whitehouse told Eos.

He said the summit could help make a difference. “When kids are doing something sincere about which they feel passionately, I think it’s extra incumbent on adults to come and listen and engage with them. And I think that their voices are really, really important, as we have seen with the students in Europe,” Whitehouse said, referring to the big student climate change protests in Europe.

“If you’re a kid, you’re always struggling to be taken seriously,” he said. “I think for members of Congress to show up resolves that struggle. They were taken seriously and should be.”

—Randy Showstack (@RandyShowstack), Staff Writer

Largest Delta Plain in Earth’s History Discovered in Arctic

Mon, 04/01/2019 - 20:45

A river delta plain nearly 2 million square kilometers in size once dominated the northern shores of ancient Pangaea, according to a recent study. The Triassic Boreal Ocean delta plain, whose deposits are currently located in the Barents Sea, is around 230 million years old and is the largest delta plain, modern or past, known to exist.

“We always knew it was large. There was little doubt about that,” Tore Klausen, lead researcher on the discovery, told Eos. When Klausen and his team began connecting their observations to those from collaborators, “then we started to realize just how large it was.” Klausen is a senior explorationist at Petrolia NOCO AS in Bergen, Norway.

Learning from the Past

Deltas can support large-scale agriculture and have sustained some of the largest ancient civilizations. The Nile delta in Egypt, the Yangtze delta in China, and the Ganges-Brahmaputra delta in India and Bangladesh are a few examples. Many countries today continue to rely on lush and sediment-rich deltas to support agriculture.

“You can use ancient deltas to understand how modern river systems should be behaving.”But this same propensity for humans to congregate around deltas makes it more difficult for scientists to study how they naturally grow and change.

“Modern river deltas are very controlled and regulated, and this hampers the natural evolution of these delta plains,” said coauthor Björn Nyberg, a sedimentologist at the University of Bergen in Norway. “Over 90% of the world’s population lives within 10 kilometers of a river source.”

But “you can use ancient deltas to understand how modern river systems should be behaving,” he said.

A Delta the Size of Alaska

How does one team map out a delta more than a thousand kilometers across? “We used seismic reflectors, which is essentially like sonar, to look at the different rock layers in the subsurface,” Nyberg explained. The delta’s channels and meanders left behind ribbon-like deposits of sediment with a distinctive seismic signature in the rock record.

The footprint of the Triassic Boreal Ocean (TBO) river delta compared to the footprints of some of the largest modern deltas. Distance is measured in kilometers (km). Credit: Klausen et al., 2019, https://doi.org/10.1130/G45507.1, Figure 4A, CC-BY 4.0

The team combined the seismic data with measurements from boreholes as well as from where the delta deposits lie exposed in rocky outcrops in Svalbard, Norway. Ages from zircons sampled across the region ensured that the deposits were the same age despite being separated by a great distance.The delta “is essentially 10 times bigger than the modern Amazon delta or the Ganges in India. It absolutely out scales any other example that we know of.”

All told, the Triassic Boreal Ocean delta plain spanned at least 1.65 million square kilometers in northern Pangaea. That’s about 1% of the total land area of Earth right now.

“It’s basically the size of Alaska,” Nyberg said. “That is essentially 10 times bigger than the modern Amazon delta or the Ganges in India. It absolutely out scales any other example that we know of.”

Incomplete Puzzle

The team measured past seafloor depths—paleobathymetry—and found that the delta emptied into a very large basin only about 400 meters deep. Most modern deltas exist near the edges of continental shelves that quickly drop to thousands of meters deep, which cuts off delta growth.

A large supply of sediment, monsoon-like rainfalls, and steady sea levels all contributed to the delta’s growth, the researchers said, but the shallow basin was the key to its gargantuan size. The shallow gradient let the delta plain grow uninterrupted for more than a million years.

And the delta plain might have been even larger than Klausen’s team could measure. “We don’t see the end of the delta plain,” Klausen said. “There are time-equivalent deposits in eastern Greenland and Canada, for instance, which are possibly linked to the delta plain.”

“There are likely pieces of the puzzle that still need to be added this story,” he added.

The team published this discovery in Geology on 22 March.

“The Triassic delta plain system built across this shelf region is truly vast,” Elizabeth Miller, a structural geologist at Stanford University in Stanford, Calif., told Eos. This study’s detailed seismic reflection data “allow unprecedented documentation of large-scale depositional systems from Paleozoic to modern times,” according to Miller, who was not involved with this research.

Exciting and Familiar

Beyond its size, one aspect of the Triassic Boreal Ocean delta plain that excited the scientists was its timing.

“Right before this, we were coming out of the Permian extinction, the mass extinction which wiped out the majority of life on Earth,” Nyberg said. “Then right after, in the Triassic, you get this perfect set of conditions that’s creating this vast delta plain on the northern coast of Pangea, and it’s one of the only areas that’s very hospitable to life after this mass extinction.”“The channels split and evolve and are dancing around on the delta plain much like we see today.”

“One of the things that we’re really excited to look at in the future is what role this massive delta had in evolution and the resurgence of both terrestrial and marine life,” he said.

Despite this ancient delta plain’s oversized footprint, many aspects of it are familiar.

“As you move down the delta plain and start affecting it with tides and standing water, the channels split and evolve and are dancing around on the delta plain much like we see today,” Klausen said. “There is much we can take from the modern to understand the ancient.”

“Apart from the actual size,” he said, “they are not too different.”

—Kimberly M. S. Cartier (@AstroKimCartier), Staff Writer

Ocean Warming Resumes in the Tropical Pacific

Mon, 04/01/2019 - 13:18

Following a significant increase in globally averaged surface temperatures during the last quarter of the 20th century, this warming trend decelerated between 1998 and 2013. Because the slowdown did not match the sustained increase in anthropogenic greenhouse gas emissions, this so-called global warming hiatus triggered intense scientific and public debate. Numerous scientists have argued the hiatus resulted from a redistribution of heat from the upper to the deep oceans that is associated with natural variations in Earth’s climate system such as the El Niño–Southern Oscillation and the Pacific Decadal Oscillation.

Now Cha et al. present evidence that since 2011, the tropical Pacific Ocean has been shifting toward more El Niño–like conditions that coincide with a resumption of global warming. Using hindcast simulations from the Regional Oceanic Modeling System combined with ensemble empirical mode decomposition statistical analyses, the team determined that the tropical Pacific is experiencing a slow, decadal-scale shift that is distinct from interannual, El Niño–like variability.

The results indicate the observed changes are strongly correlated with a shift in trade wind patterns related to an alteration in the phase of the Pacific Decadal Oscillation. Because these winds help control the speed of the Equatorial Undercurrent, the new pattern has altered the tropical Pacific’s upper ocean circulation and contributed to the regional redistribution of heat, resulting in sea surface warming in the central eastern tropical Pacific. The authors argue these changes have contributed to substantial increases in sea level in the central eastern tropical Pacific, as well as subsurface cooling and corresponding decreases in sea level in the western tropical Pacific.

By linking changes in trade wind patterns to ocean circulation and surface warming trends, the researchers offer convincing support that the Pacific Decadal Oscillation and other natural, longer-term variations in climate may contribute substantially to ocean warming. Because this proposed mechanism has important implications for predicting sea level and ocean warming on decadal timescales, the authors argue that ocean-atmosphere interactions—which were not included in this study—should be incorporated into future research to better understand climate-related processes in the tropical Pacific. (Geophysical Research Letters, https://doi.org/10.1029/2018GL080651, 2018)

—Terri Cook, Freelance Writer

How Did We Get Here?

Mon, 04/01/2019 - 13:17

The shells of tiny ancient sea organisms hold the evidence that underpins one of the newest fields in the Earth sciences. In the 1950s, Cesare Emiliani at the University of Chicago was learning how to measure stable isotopes in invertebrates and use those data as a proxy to make conclusions about environmental factors. One day he turned that study to ancient foraminifera taken from sediments in the ocean floor. The oxygen isotopes he found in their shells told him that the ocean was once much warmer—that, in fact, the ocean changed over time. Paleoceanography was born.

“In our present time of environmental change, it is, more than ever, important to use proxy data on Earth’s past in order to evaluate Earth’s future, thus making our past a key guide to our future.”In April, as AGU continues its Centennial celebrations, we’re looking at this nascent but critical field, which has already proved so prolific it’s expanded into two major components. AGU launched its Paleoceanography journal in 1986 and, as it embraced the growth and evolution in the field, changed its name to Paleoceanography and Paleoclimatology last year. “We now use, in addition to fossils, a broad and growing range of stable isotope compositions, trace element concentrations and organic biomarkers in fossils and sediments as quantitative proxies for a growing number of environmental properties,” wrote journal editor in chief Ellen Thomas when she announced the change in Eos. “In our present time of environmental change, it is, more than ever, important to use proxy data on Earth’s past in order to evaluate Earth’s future, thus making our past a key guide to our future.”

Paleoclimatologists know better than anybody that understanding Earth’s past is necessary for understanding what’s happening to the climate today—and why the recent warming can’t simply be explained by natural cycles. As a result, this young field has been uniquely shaped by the challenge and urgency in communicating its findings to the public. It’s no surprise that a recent workshop for scientists to learn lessons in persuasive communication from lawyers was funded by the National Science Foundation (NSF) Paleoclimate Program.

This direct evidence of the ocean’s “long memory” means that the effects from modern warming will be seen throughout the planet for a long, long time.We know that however our society reacts to that information in the coming decades, the consequences will be reflected in our environment for a very long time. For this reason, one important topic of study right now is determining how much heat is stored in the oceans. A recent study used data collected by the HMS Challenger expedition that launched in 1872, beginning the modern era of the study of oceanography. Comparing the temperature observations with those taken today shows that the Pacific Ocean is still cooling in response to the Little Ice Age during the 14th to 19th centuries. This direct evidence of the ocean’s “long memory” means that modern climate models—most of which only use data from the beginning of the Industrial Revolution—need to incorporate ancient signals and that the effects from modern warming will be seen throughout the planet for a long, long time.

Cesare Emiliani’s revolutionary work continues today through programs such as the core drilling conducted aboard the JOIDES Resolution vessel and that of NSF’s Paleo Perspectives on Climate Change, which is currently soliciting proposals that will provide data on Earth’s past climate sensitivity to specific variables.

At AGU and Eos, we continue to support the work of and listen carefully to the information learned by paleoceanographers and paleoclimatologists because every time we learn more about our past, we learn a little bit more about our future.

—Heather Goss (@heathermg), Editor in Chief, Eos

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