AGU 期刊一周Research Spotlights (June 24~June 30, 2016)

发布时间:2016-7-1 12:42:37 点击次数:710

I. Atmospheric Sciences

1. Climate change causing oceanic boundary currents to intensify and shift poleward

Weather along the eastern coasts of South Africa, Asia, Australasia and South America will get significantly warmer and stormier on average over the next 100 years, a new study finds. The culprit? Climate changes that are causing ocean currents next to these coastal regions, called western boundary currents, to become stronger and extend further toward the poles, according to the new study..

II. Geology & Geophysics

1. Making a Better Magnetic Map

A new version of the World Digital Magnetic Anomaly Map, released last summer, gives greater insight into the structure and history of Earth's crust and upper mantle.

2. Eyjafjallajökull Gave Lava and Ice Researchers an Eyeful

New insights from the 2010 eruption may help volcanologists determine how glaciers shaped ancient lava flows.

III.Hydrology, Cryosphere & Earth Surface

1. A River Network Preserved Beneath the Greenland Ice Sheet

An ancient drainage basin covering one fifth of Greenland predates the ice sheet and strongly influences the modern Jakobshavn Glacier, according to a new analysis of ice-penetrating radar data.

IV. Science Policy

1. Geoscientists React to Brexit Vote

On Thursday, 23 June, voters in the United Kingdom approved a referendum to leave the European Union (EU). As British and European leaders, policy makers, and others debated in recent months the withdrawal’s potential effects on immigration, the stability of the EU, and the global economy, another group of British and EU citizens came forward to express their disappointment with the exit: scientists.

V. Climate Change

1. Capping warming at 2 degrees: New study details pathways beyond Paris

Even if countries adhere to the Paris climate agreement hammered out last fall, capping global warming at 2 degrees Celsius (4 degrees Fahrenheit) would likely require net zero greenhouse gas emissions by 2085 and substantial negative emissions over the long term, according to an in-depth analysis by scientists at the National Center for Atmospheric Research (NCAR) in Boulder, Colorado.

VI. Planetary Sciences

1. Mineral Flaws Clarify How Diamonds Form 

Iron sulfide is one of the most common minerals found in diamonds, but it is rare inside the Earth’s mantle where diamonds form. New findings published Tuesday in Nature Communications explain this paradox—for the first time sulfide has been shown to play an active role in the formation of diamond crystals. The results provide valuable new information about the depth of diamond formation and suggest that sulfide is more than a flaw introduced from the host rock, the study authors said.

VII.Ocean Sciences

1. Stars and Swells Guide a Polynesian Canoe Around the World

Bobbing in the waters off New York City is an unusual sight: a double-hulled Polynesian voyaging canoe, its red sails furled. The Hōkūle‘a is on a mission to sail around the world, navigating by the methods that ancient sailors used. Stars, the Sun, and ocean swells serve as the navigator’s tools when land vanishes over the horizon. As scientists look at how traditional sailors learned to sail, they’re finding that humans can be remarkably good at learning to feel swells and navigate by them. In fact, ancient navigators may have relied on wave patterns that modern scientists are still working to model.

2. Schmidt Ocean dispatch: Big Becomes Great

Ajit Subramaniam defines himself as a Tactile Oceanographer: “I need to throw up in the water before I can understand it,” he jokes. That is why he is very pleased with R/V Falkor and how stable she has been during this expedition, his chronic seasickness has not been an issue and he has been able to concentrate on what he loves. Ajit loves the ocean and he loves rivers. Ajit studies great rivers. As in Amazon great. He has studied the South American giant extensively, so what brought him here? After all, the Amazon is some 13 times larger than the Mekong. “Each river is different.” He says, “Just because you’ve studied one, it would be a big mistake to think you know them all. The Mekong is fascinating because it is in transition. It is changing extremely rapidly, right in front of our eyes.”

VIII.Earth and Space Science

1. Traces of Ancient Buried Subduction Zone Found in China 

A combination of observations and modeling reveals evidence of a late Paleozoic intraoceanic subduction zone in the western Junggar region of northwest China.

2. Research bolsters case for a present-day subsurface ocean on Pluto

When the NASA’s New Horizons spacecraft buzzed by Pluto last year, it revealed tantalizing clues that the dwarf planet might have — or had at one time — a liquid ocean sloshing around under its icy crust. According to a new analysis led by a Brown University Ph.D. student, such an ocean likely still exists today.

3. Schmidt Ocean dispatch: It is what it is – searching for symbiosis

Andreas Novotny thought he would find Hemiaulus here. He has not. “It is what it is, which is fine,” he says. “What we need to do is figure out why.”  Andreas is a PhD. student and his research focuses in the symbiotic relationship between a kind of plankton, a Diatom called Rhizosolenia, and a Nitrogen-fixing Cyanobacteria, called Richelia.

IX. Geophysical Research Letters

1. Does the Caribbean whistle an A-flat, several octaves below the audible range?

We show that an important source of coastal sea level variability around the Caribbean Sea is a resonant basin mode. The mode consists of a baroclinic Rossby wave which propagates westward across the basin and is rapidly returned to the east along the southern boundary as coastal shelf-waves. Almost two wavelengths of the Rossby wave fit across the basin, and it has a period of 120 days. The porous boundary of the Caribbean Sea results in this mode exciting a mass exchange with the wider ocean, leading to a dominant mode of bottom pressure variability which is almost uniform over the Grenada, Venezuela and Colombia basins, and has a sharp spectral peak at 120 day period. As the Rossby waves have been shown to be excited by instability of the Caribbean Current, this resonant mode is dynamically equivalent to the operation of a whistle.

2. Predicting Atlantic seasonal hurricane activity using outgoing longwave radiation over Africa

Seasonal hurricane activity is a function of the amount of initial disturbances (e.g., easterly waves) and the background environment in which they develop into tropical storms (i.e., the main development region). Focusing on the former, a set of indices based solely upon the meridional structure of satellite-derived outgoing longwave radiation (OLR) over the African continent are shown to be capable of predicting Atlantic seasonal hurricane activity with very high rates of success. Predictions of named storms based on the July OLR field and trained only on the time period prior to the year being predicted yields a success rate of 87%, compared to the success rate of NOAA's August outlooks of 53% over the same period and with the same average uncertainty range (±2). The resulting OLR indices are statistically robust, highly detectable, physically linked to the predictand, and may account for longer-term observed trends.

3. Long-term pCO2 trends in Adirondack Lakes

Lakes are globally significant sources of CO2 to the atmosphere. However, there are few temporally resolved records of lake CO2 concentrations and long-term patterns are poorly characterized. We evaluated annual trends in the partial pressure of CO2 (pCO2) based on chemical measurements from 31 Adirondack Lakes taken monthly over an 18 year period. All lakes were supersaturated with CO2 and were sources of CO2 to the atmosphere. There were significant pCO2 trends in 29% of lakes. The median magnitude of significant positive trends was 32.1 μatm yr−1. Overall, 52% of lakes had pCO2 trends greater than those reported for the atmosphere and ocean. Significant trends in lake pCO2 were attributable to regional recovery from acid deposition and changing patterns of ice cover. These results illustrate that lake pCO2can respond rapidly to environmental change, but the lack of significant trend in 71% of lakes indicates substantial lake-to-lake variation in magnitude of response.

4. Surrogate gas prediction model as a proxy for Δ14C-based measurements of fossil fuel CO2

The measured 14C:12C isotopic ratio of atmospheric CO2 (and its associated derived Δ14C value) is an ideal tracer for determination of the fossil fuel derived CO2 enhancement contributing to any atmospheric CO2 measurement (Cff). Given enough such measurements, independent top-down estimation of U.S. fossil fuel CO2 emissions should be possible. However, the number of Δ14C measurements is presently constrained by cost, available sample volume, and availability of mass spectrometer measurement facilities. Δ14C is therefore measured in just a small fraction of samples obtained by flask air sampling networks around the world. Here we develop a projection pursuit regression (PPR) model to predict Cffas a function of multiple surrogate gases acquired within the NOAA/Earth System Research Laboratory (ESRL) Global Greenhouse Gas Reference Network (GGGRN). The surrogates consist of measured enhancements of various anthropogenic trace gases, including CO, SF6, and halocarbon and hydrocarbon acquired in vertical airborne sampling profiles near Cape May, NJ and Portsmouth, NH from 2005 to 2010. Model performance for these sites is quantified based on predicted values corresponding to test data excluded from the model building process. Chi-square hypothesis test analysis indicates that these predictions and corresponding observations are consistent given our uncertainty budget which accounts for random effects and one particular systematic effect. However, quantification of the combined uncertainty of the prediction due to all relevant systematic effects is difficult because of the limited range of the observations and their relatively high fractional uncertainties at the sampling sites considered here. To account for the possibility of additional systematic effects, we incorporate another component of uncertainty into our budget. Expanding the number of Δ14C measurements in the NOAA GGGRN and building new PPR models at additional sites would improve our understanding of uncertainties and potentially increase the number of Cffestimates by approximately a factor of 3. Provided that these estimates are of comparable quality to Δ14C-based estimates, we expect an improved determination of fossil fuel CO2emissions.

5. Deep-time evidence for climate sensitivity increase with warming

Future global warming from anthropogenic greenhouse gas emissions will depend on climate feedbacks, the effect of which is expressed by climate sensitivity, the warming for a doubling of atmospheric CO2 content. It is not clear how feedbacks, sensitivity, and temperature will evolve in our warming world, but past warming events may provide insight. Here we employ paleoreconstructions and new climate-carbon model simulations in a novel framework to explore a wide scenario range for the Paleocene-Eocene Thermal Maximum (PETM) carbon release and global warming event 55.8 Ma ago, a possible future warming analogue. We obtain constrained estimates of CO2 and climate sensitivity before and during the PETM and of the PETM carbon input amount and nature. Sensitivity increased from 3.3–5.6 to 3.7–6.5 K (Kelvin) into the PETM. When taken together with Last Glacial Maximum and modern estimates, this result indicates climate sensitivity increase with global warming.

 

X. AGU News Home

1. Study: As Alaska warms, methane emissions appear stable

WASHINGTON, DC — Analysis of nearly three decades of air samples from Alaska’s North Slope shows little change in long-term methane emissions despite significant Arctic warming over that time period, according to new research published in Geophysical Research Letters, a journal of the American Geophysical Union.

2. NEW FINDINGS HINT AT OXYGEN-RICH PAST ON MARS

WASHINGTON, DC — The discovery of manganese oxides in Martian rocks might tell us that the Red Planet was once more Earth-like than previously believed. A new paper inGeophysical Research Letters, a journal of the American Geophysical Union, reveals NASA’s Curiosity rover observed high levels of manganese oxides in Martian rocks, which could indicate higher levels of atmospheric oxygen once existed on our neighboring planet. This hint of more oxygen in Mars’ early atmosphere adds to other Curiosity findings—such as evidence of ancient lakes—revealing how Earth-like our neighboring planet once was.