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AGU Research Spotlight (Nov 09-Nov 15, 2017)

2017-11-17 13:07:37

I.Climate Change

1.Human Activity Increasing Rate of Record-Breaking Hot Years

A new study finds human-caused global warming is significantly increasing the rate at which hot temperature records are being broken around the world.


2.Future Looks Drier as Drylands Continue to Expand

A recent article in Reviews of Geophysics examined the areas of land globally that are classified as drylands and the impact of their growth on human communities.


II. Ocean Sciences

1. Sounding the Black Smoker Plumes

Imaging sonar, an emerging technique for monitoring heat from seafloor hydrothermal vents, gives scientists a new look at interacting systems off the coast of Canada.


2.Run-Ups of Unusual Size

Not all waves are created equal when it comes to eroding sandy shorelines. Here’s a look at the physics that drives the big ones.


III. Planetary Sciences

1. Comparing Craters

An analysis suggests that craters degrade faster on Mercury than the Moon, raising questions about landscape evolution on different planetary bodies.


IV.Geology & Geophysics

1. The Gravity of Geophysics

A recent article in Reviews of Geophysics examined terrestrial techniques for measuring changes in gravity over time and their application to the geosciences.


2.Hunting Rare Fossils of the Ediacaran

The search for fossil imprints and casts of squishy organisms takes time, perseverance, and sometimes a sprinkle of luck.


3.Tracing Water’s Path Through the Santa Clara Valley Aquifer

In an increasingly drought prone climate, scientists study the impacts of drought on aquifer systems.


4.Analog Modeling Recreates Millions of Years in a Few Hours

Second Workshop on Analog Modeling of Tectonic Processes; Austin, Texas, 17–19 May 2017



1. Improved Simulation of Gross Primary Productivity

A new model better explains seasonal variations in biomass.


VI.Geophysical Research Letters

1. The Prevalence of Oceanic Surface Modes

Satellite observations have revolutionized oceanography, capturing diverse phenomena over much of the globe. However, it remains to understand how surface fields, like sea surface height, reflect the motion occurring at depth. The vertical structure of ocean eddies is often expressed in terms of “baroclinic modes,” which are basis functions derived assuming a flat ocean bottom. Bathymetry alters the modes though, weakening the bottom velocities. Using analytical solutions, we demonstrate that with realistic bathymetry and/or bottom friction, the bottom velocities are nearly zero. The resulting “surface modes” should be ubiquitous in the ocean. This would explain the dominant mode of variability obtained from globally distributed current meter data and is consistent with energy spectra derived from sea surface height data. The results yield a simple way to infer subsurface velocities from satellite data and suggest that ocean analyses should be made in terms of surface modes and topographic waves.


2. Stratospheric Ozone Depletion: An Unlikely Driver of the Regional Trends in Antarctic Sea Ice in Austral Fall in the Late Twentieth Century

It has been suggested that recent regional trends in Antarctic sea ice might have been caused by the formation of the ozone hole in the late twentieth century. Here we explore this by examining two ensembles of a climate model over the ozone hole formation period (1955–2005). One ensemble includes all known historical forcings; the other is identical except for ozone levels, which are fixed at 1955 levels. We demonstrate that the model is able to capture, on interannual and decadal timescales, the observed statistical relationship between summer Amundsen Sea Low strength (when ozone loss causes a robust deepening) and fall sea ice concentrations (when observed trends are largest). In spite of this, the modeled regional trends caused by ozone depletion are found to be almost exactly opposite to the observed ones. We deduce that the regional character of observed sea ice trends is likely not caused by ozone depletion.


3. Mesoscale Eddies Control the Timing of Spring Phytoplankton Blooms: A Case Study in the Japan Sea

Satellite Chlorophyll a (CHL) data were used to investigate the influence of mesoscale anticyclonic eddies (AEs) and cyclonic eddies (CEs) on the timing of spring phytoplankton bloom initiation around the Yamato Basin (133–139°E and 35–39.5°N) in the Japan Sea, for the period 2002–2011. The results showed significant differences between AEs and CEs in the timing and initiation mechanism of the spring phytoplankton bloom. Blooms were initiated earlier in CEs which were characterized by shallow mixed-layer depths (< 100 m). the early blooming preceded the end of winter cooling (i.e., while net heat flux (q0) is still negative) and is initiated by the increased average light within the shallow mixed-layer depth. conversely, blooms appeared in the aes despite deeper mixed-layer depth (> 100 m) but close to the commencement of positive Q0. This suggests that the relaxation of turbulent mixing is crucial for the bloom initiation in AEs.


4. Accelerating Thermokarst Transforms Ice-Cored Terrain Triggering a Downstream Cascade to the Ocean

Recent climate warming has activated the melt-out of relict massive ice in permafrost-preserved moraines throughout the western Canadian Arctic. This ice that has persisted since the last glaciation, buried beneath as little as 1 m of overburden, is now undergoing accelerated permafrost degradation and thermokarst. Here we document recent and intensifying thermokarst activity on eastern Banks Island that has increased the fluvial transport of sediments and solutes to the ocean. Isotopic evidence demonstrates that a major contribution to discharge is melt of relict ground ice, resulting in a significant hydrological input from thermokarst augmenting summer runoff. Accelerated thermokarst is transforming the landscape and the summer hydrological regime and altering the timing of terrestrial to marine and lacustrine transfers over significant areas of the western Canadian Arctic. The intensity of the landscape changes demonstrates that regions of cold, continuous permafrost are undergoing irreversible alteration, unprecedented since deglaciation (~13 cal kyr B.P.).


5. Modeling the Response of Nioghalvfjerdsfjorden and Zachariae Isstr?m Glaciers, Greenland, to Ocean Forcing Over the Next Century

Recent studies have shown that the Northeast Greenland Ice Sheet region has been undergoing significant acceleration and dynamic thinning since 2010, and these changes are closely related to regional atmospheric and oceanic warming. Here we model the response of Nioghalvfjerdsfjorden (79North) and Zachariae Isstr?m (ZI) to ocean forcing to investigate their evolution over the coming decades. Our model suggests that 79North will retreat slowly over the next century, whereas ZI will lose its floating ice tongue completely and retreat rapidly for 70 years. After 70 years, ZI will stabilize 30 km upstream of its current position on a topographic ridge. Frontal melt rates need to reach 6 m/d in the summer to dislodge the glacier from this ridge. ZI will then continue a fast and unstoppable retreat, contributing more than 16.2 mm to global sea level rise by 2100.


6. Teleconnection Between Atlantic Multidecadal Variability and European Temperature: Diversity and Evaluation of the Coupled Model Intercomparison Project Phase 5 Models

A realistic simulation of the Atlantic Multidecadal Variability (AMV) and related teleconnections is essential to resolve and understand the potential predictability over Europe at decadal timescale. Based on a large ensemble of state-of-the-art climate models, we show that a considerable intermodel spread exists in the spatiotemporal properties of the simulated AMV and teleconnections with European summer temperature. The greater the persistence, variance, and basin-scale spatial coherence, the stronger the teleconnection. We demonstrate that only a few members of a few models produce a teleconnection that is consistent with observational estimates over the instrumental period. This highlights the possible extreme nature of the last century teleconnection and/or a detrimental underestimation of ocean-land teleconnectivity in many climate models. Yet we emphasize the considerable uncertainties due to methods used to disentangle internal and externally forced variations in observations, and to sampling, which must be correctly accounted when analyses are performed on short temporal records.



VII. AGU Blogs

1. New Antarctic heat map reveals sub-ice hotspots

An international team of scientists, led by British Antarctic Survey (BAS), has produced a new map showing how much heat from the Earth’s interior is reaching the base of the Antarctic Ice Sheet. The map is part of a new paper accepted for publication in Geophysical Research Letters, a journal of the American Geophysical Union.


2.Rising sea levels could weaken coral reefs’ protective influence on Brazil’s coast

Rising sea levels could diminish the ability of Brazil’s coral reef systems to weaken incoming ocean waves, resulting in stronger waves hitting populated areas on the Brazilian coastline, according to new research published in Earth’s Future, a journal of the American Geophysical Union.


3.Friday fold: soft sediment deformation in California’s Castaic Formation

The Friday fold comes to us today from Bret Leslie of the Nuclear Regulatory Commission, a friend through the Geological Society of Washington. It shows soft sediment deformation in the Late Miocene Castaic Formation, a unit deposited in the Ridge Basin, a wrench basin that opened in a releasing bend along the San Andreas Fault:


4.Salmon complete 1,000-mile journey, and life

In early November, a time when shadows lengthen and deep cold hardens the landscape, chum salmon have returned to spawn in the lower Delta River. In spots, the water is so shallow that dorsal fins wiggle in the frigid air. Some fish get frostbite on really cold days.


5.Storbreen, Svalbard Major Retreat Opens New Fjord

Storbreen Glacier (ST) terminates on the north side of Hornsund in southern Svalbard.  From 1990 to 2017 Storbreen has experienced a substantial retreat opening a new fjord and separating from Hornbreen (H).  Svalbard is host to 163 tidewater glaciers with a collective calving front of 860 km B?aszczyk et al, 2009). 



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