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AGU Research Spotlight (Aug 10-Aug 16, 2017)

2017-08-18 14:48:53

I.Climate Change

1. Improving Water Resources Management from the Ground Up

The key to sustainable water resources management isn’t satellite technology yet—it’s a new spin on time-tested rain and stream gauges.


2. Greenland Fires Ignite Climate Change Fears

The fires are stoking worries about the vast island’s thawing permafrost.


3. Human-Caused Warming Likely Led to Record Streak of Hot Years

A new study finds it “extremely unlikely” that the consecutive record-breaking global temperatures in 2014, 2015, and 2016 could have occurred without human-caused climate change.


II. Hazards & Disasters

1. A Closer Look at an Undersea Source of Alaskan Earthquakes

A systematic survey offers a striking portrait of movement along a 500-kilometer-long undersea section of the Queen Charlotte–Fairweather fault off the coast of southeastern Alaska.


III. Education

1. Gearing Up for Fall Semester

Geoscience professors explain how they use their summertime to get ready for teaching, researching, and mentoring when the school year begins again.


IV.Atmospheric Sciences

1. Ozone Treaty Taking a Bite Out of U.S. Greenhouse Gas Emissions

Thirty-year-old Montreal Protocol has had a major side benefit of reducing climate-altering greenhouse gas emissions from the U.S.


V. Ocean Sciences

1. Powerful Pacific Forces Disrupt the California Current

Scientists create a 66-year data record to shed light on the role of El Ni?o in the California Current System’s shifting temperatures.


2. New Baseline for Understanding Arctic Oxygen and Nutrient Fluxes

Significant spatial and temporal patterns emerge from the first pan-Arctic comparison of oxygen demand in marine sediments.


VI.Geophysical Research Letters

1. Snow thickness profiling on Antarctic sea ice with GPR—Rapid and accurate measurements with the potential to upscale needles to a haystack

Snow thickness on sea ice is a largely undersampled parameter yet of importance for the sea ice mass balance and for satellite-based sea ice thickness estimates and thus our general understanding of global ice volume change. Traditional direct thickness measurements with meter sticks can provide accurate but only spot information, referred to as “needles” due to their pinpoint focus and information, while airborne and satellite remote sensing snow products, referred to as “the haystack,” have large uncertainties due to their scale. We demonstrate the remarkable accuracy and applicability of ground-penetrating radar (GPR) snow thickness measurements by comparing them with in situ meter stick data from two field campaigns to Antarctica in late winter/early spring. The efficiency and millimeter-to-centimeter accuracy of GPR enables practitioners to acquire extensive, semiregional data with the potential to upscale needles to the haystack and to potentially calibrate satellite remote sensing products that we confirm to derive roughly 30% of the in situ thickness. We find the radar wave propagation velocity in snow to be rather constant (± 6%), encouraging regional snow thickness surveys. Snow thinner than 10 cm is under the detection limit with the off-the-shelf GPR setup utilized in our study.


2. Evidence of minimal carbon sequestration in the productive Amundsen Sea polynya

The Amundsen Sea polynya (ASP) is reportedly the most productive among the coastal polynyas around Antarctica. However, observational constraints limit our understanding of the biological pump and carbon cycle in the ASP. We measured various carbon-related parameters such as primary production, bacterial production, sinking flux of particulate organic carbon (POC), and accumulation of organic carbon in the sediment as well as hydrographic parameters during field observations and by instrument moorings. Over 95% of the photosynthetically produced POC was converted to suspended POC and/or dissolved carbon forms in the upper ~400 m layer. We postulate that most of the carbon transported to the water column by the biological pump in the ASP was flushed out of the shelf without being sequestered for long-term storage in sediments. Lack of bottom water formation due to intrusion of Circumpolar Deep Water in the lower layer reduces carbon sequestration efficiency.


3. Abrupt regime shifts in the North Atlantic atmospheric circulation over the last deglaciation

We analyze modeling results of the North Atlantic atmospheric winter circulation from a transient climate simulation over the last 21,000 years. In agreement with previous studies, we find that the midlatitude jet stream assumes a strong, stable, and zonal disposition so long as the North American ice sheets remain in their continent-wide Last Glacial Maximum (LGM) configuration. However, when the Laurentide ice sheet (LIS) and Cordilleran ice sheet separate (~14,000 years ago), the jet stream abruptly changes to a tilted circulation regime, similar to modern. The proposed explanation is that the dominant stationary wave source in the North Atlantic sector changes from the LIS to the Cordilleran mountain range during the saddle collapse. As long as the LIS dominates, the circulation retains the zonal LGM state characterized by prevalent stationary wave reflection in the subtropical North Atlantic. When the Cordillera takes over, the circulation acquires its modern disposition with a weak and meridionally tilted jet stream and storm track.


4. Dependence of nitrite oxidation on nitrite and oxygen in low-oxygen seawater

Nitrite oxidation is an essential step in transformations of fixed nitrogen. The physiology of nitrite oxidizing bacteria (NOB) implies that the rates of nitrite oxidation should be controlled by concentration of their substrate, nitrite, and the terminal electron acceptor, oxygen. The sensitivities of nitrite oxidation to oxygen and nitrite concentrations were investigated using 15N tracer incubations in the Eastern Tropical North Pacific. Nitrite stimulated nitrite oxidation under low in situ nitrite conditions, following Michaelis-Menten kinetics, indicating that nitrite was the limiting substrate. The nitrite half-saturation constant (Ks = 0.254 ± 0.161 μM) was 1–3 orders of magnitude lower than in cultivated NOB, indicating higher affinity of marine NOB for nitrite. The highest rates of nitrite oxidation were measured in the oxygen depleted zone (ODZ), and were partially inhibited by additions of oxygen. This oxygen sensitivity suggests that ODZ specialist NOB, adapted to low-oxygen conditions, are responsible for apparently anaerobic nitrite oxidation.


VII. AGU Blogs

1. New study details ocean’s role in fourth-largest mass extinction

Extremely low oxygen levels in Earth’s oceans could be responsible for extending the effects of a mass extinction that wiped out millions of species on Earth around 200 million years ago, according to a new study.


2. “Heartbeats” of an underwater volcano’s eruption imaged by ultrasounds (plus VIDEO)

Using acoustic footage of a volcanic eruption and images taken by a remotely operated vehicle (ROV), scientists have documented an underwater volcano’s eruption off the coast of El Hierro, the smallest of the Canary Islands. Though underwater volcanoes are common, footage of their eruptions is rare because of the dangers of getting close enough for observations.



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