AGU journal highlights -- May 6, 2014

(Press-News.org) The following highlights summarize research papers that have been recently published in Geophysical Research Letters (GRL), Journal of Geophysical Research: Earth Surface (JGR-F), Journal of Geophysical Research: Oceans (JGR-C), and Water Resources Research (WRR).

In this release:

1. Polar hexagon-shaped jet stream could reveal Saturn's rotational period
2. Antarctica's Whillans Ice Plain ice flows are highly variable
3. Climate change, water rights, and agriculture: A case study in Idaho
4. Low impact development boosts groundwater recharge
5. Beaufort Gyre sea ice thins in recent decades, impacts climate
6. New model describes toppling of salt marsh banks

Anyone may read the scientific abstract for any already-published paper by clicking on the link provided at the end of each Highlight. You can also read the abstract by going to http://onlinelibrary.wiley.com/ and inserting into the search engine the full doi (digital object identifier), e.g. doi: 10.1002/2013WR014696. The doi is found at the end of each Highlight below.

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1. Polar hexagon-shaped jet stream could reveal Saturn's rotational period

A hexagon-shaped atmospheric phenomenon first spotted on Saturn by Voyager 1 and 2 has intrigued scientists since the 1980s. More recently, NASA's Cassini mission has periodically observed the hexagon, a strong eastward jet that rotates at 120 meters per second (394 feet per second). Scientists believe that the persistence of the hexagon could put to rest the oft-debated question of the length of Saturn's rotational period.

Sánchez-Lavega et al. present an estimate (in Earth hours) of the length of Saturn's day based on data from Cassini and ground-based images. They tracked the movement of Saturn's hexagon for 5.5 years and find that despite large radiative forcing in Saturn's atmosphere, the rotation of the hexagon remained constant. These findings suggest that the hexagon is deeply rooted within Saturn's atmosphere and that its rotational period could reveal the rotational period of Saturn's internal solid body, which the authors estimate as 10 hours, 39 minutes, and 23.01 seconds, plus or minus 0.01 seconds.

Source: Geophysical Research Letters, doi:10.1002/2013GL059078, 2014 http://onlinelibrary.wiley.com/doi/10.1002/2013GL059078/abstract

Title: The long-term steady motion of Saturn's hexagon and the stability of its enclosed jet stream under seasonal changes

Photo: http://news.agu.org/journal-highlight/2014-05-06/

Authors: A. Sánchez-Lavega, T. del Río-Gaztelurrutia, R. Hueso and S. Pérez-Hoyos: Departamento De Física Aplicada, I, ETS Ingeniería, Universidad del País Vasco, Bilbao, Spain; and Unidad Asociada Grupo Ciencias Planetarias UPV/EHU-IAA (CSIC), Bilbao, Spain;

E. García-Melendo: Departamento De Física Aplicada, I, ETS Ingeniería, Universidad del País Vasco, Bilbao, Spain; and Fundació Observatori Esteve Duran, Seva, Barcelona, Spain;

A. Antuñano and I. Mendikoa: Departamento De Física Aplicada, I, ETS Ingeniería, Universidad del País Vasco, Bilbao, Spain;

J.F. Rojas, Departamento De Física Aplicada, I, ETS Ingeniería, Universidad del País Vasco, Bilbao, Spain; and Unidad Asociada Grupo Ciencias Planetarias UPV/EHU-IAA (CSIC), Bilbao, Spain;

J.Lillo and D. Barrado-Navascués: Departamento de Astrofísica, Centro de Astrobiología (INTA-CSIC), Villanueva de la Cañada, Spain;

J. M. Gomez-Forrellad: Fundació Observatori Esteve Duran, Seva, Barcelona, Spain;

C. Go: Physics Department, University of San Carlos, Cebu City, Philippines, International Outer Planet Watch, Planetary Virtual Observatory Laboratory, Bilbao, Spain;

D. Peach: International Outer Planet Watch, Planetary Virtual Observatory Laboratory, Bilbao, Spain; and British Astronomical Association, London, UK;

T. Barry: International Outer Planet Watch, Planetary Virtual Observatory Laboratory, Bilbao, Spain; and Astronomical Society of South Wales, Sydney, New South Wales, Australia;

D.P. Milika and P. Nicholas: International Outer Planet Watch, Planetary Virtual Observatory Laboratory, Bilbao, Spain;

A. Wesley: International Outer Planet Watch, Planetary Virtual Observatory Laboratory, Bilbao, Spain; and Astronomical Society of Australia, School of Physics, University of Sydney, Sydney, New South Wales, Australia.

2. Antarctica's Whillans Ice Plain ice flows are highly variable

The Whillans Ice Plain (WIP) is a roughly 20,000-square-kilometer (772-square-mile) region of the West Antarctic Ice Sheet that acts as a massive conveyor, driving glacier ice into the Ross Ice Shelf. As the climate changes, knowing how large bodies of ice like the WIP behave will be important to assessing sea level rise.

Since measurements first began in 1963, researchers have found that the ice flows in the WIP have been slowing down. Based on what were initially decadal observations, researchers calculated that the slowdown was occurring at a constant rate.

Starting in 2007, Beem et al. began collecting annual measurements on the WIP. The authors find that rather than undergoing a steady deceleration, ice flow rates fluctuate on interannual timescales. The ice flow rate is controlled by a range of resistive stresses, such as side drag, basal drag, and other factors, but previous research, combined with the current findings, suggests that changes in basal drag are responsible for the WIP's interannual variability.

What would cause this increase in basal drag? Water loss from the surface beneath the ice—caused by water freezing to the glacier's underside, or by subglacial streams being diverted along a new path, the authors speculate. Both mechanisms are supported by existing research. The authors note that changes to ice flow at WIP are linked to changes in internal glacier dynamics rather than to climate variability.

Source: Journal of Geophysical Research: Earth Surface, doi:10.1002/2013JF002958, 2014 http://onlinelibrary.wiley.com/doi/10.1002/2013JF002958/abstract

Title: Variable deceleration of Whillans Ice Stream, West Antarctica

Authors: L.H. Beem and S.M. Tulaczyk: Department of Earth and Planetary Science, University of California – Santa Cruz, Santa Cruz, California, USA;

M.A. King: School of Geography and Environmental Studies, University of Tasmania, Hobart, Tasmania, Australia; and School of Civil Engineering and Geosciences, University of Newcastle, Newcastle upon Tyne, UK;

M. Bougamont and P. Christoffersen: Scott Polar Research Institute, University of Cambridge – Cambridge, UK;

H.A. Fricker: Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography, University of California – San Diego, La Jolla, California, USA.

3. Climate change, water rights, and agriculture: A case study in Idaho

Water supply is important to agriculture and other consumptive uses in the arid and semiarid climate zones, but it has become increasingly uncertain under a changing climate. More importantly, how agricultural output will be affected may depend on how water resources are allocated based on the dominant sharing rule, according to Xu et al., who conducted a case study in Idaho. In the western United States, climate models predict a large warming trend in climate, which will lead to a reduced amount of snowmelt-driven summer and fall streamflows and increased volatility in irrigation water supply during warm growing seasons. In Idaho, water resources are appropriated according to the Prior Appropriation Doctrine, a first-come, first-served water sharing rule by which local water institutions allocate more water resources to farms with water entitlements that have been in existence longer.

The researchers analyzed how irrigated farmers' land use changed in response to water supply information by using data on farmland use and projections of water supply under a warming climate, including projected seasonal variation. They find that if climate change increases the volatility of the temperature and the water supply, irrigated agriculture in the region could face significant damages. In fact, crop revenue losses could be up to 32 percent, the authors predict. Their analysis also indicates that farmers' priority in water rights affects how they respond to changes in water supply. The authors suggest that both the use of groundwater and a free-market allocation system can help mitigate climate change-induced economic losses. But both these two mitigation methods have environmental and institutional constraints that will potentially limit their ability to reduce the negative effects of climate change.

Source: Water Resources Research, doi:10.1002/2013WR014696, 2014 http://onlinelibrary.wiley.com/doi/10.1002/2013WR014696/abstract

Title: Climate change, water rights, and water supply: The case of irrigated agriculture in Idaho

Authors: Wenchao Xu and Scott E. Lowe: Department of Economics, Boise State University, Boise, Idaho, USA;

Richard M. Adams: Department of Agriculture and Resource Economics, Oregon State University, Corvallis, Oregon, USA.

4. Low impact development boosts groundwater recharge

In San Francisco, as with other places, climate change is threatening to upset the balance the city has struck with the local hydrology. Precipitation in Northern California has already been increasing in winter and decreasing in summer, and projected changes to the behavior of the El Niño–Southern Oscillation hint at more of the same.

While any extra rain may sound like good news for a state currently plagued by drought, the projected increase in extreme winter precipitation events would also cause a host of problems—particularly in urban centers. Pavement and buildings increase overland flow, raising the potential for flash flooding and driving surface pollutants into the water supply. To mitigate against these issues urban planners have turned to "low impact development," a suite of best practices and tools, such as building infiltration trenches and strategically placing vegetation, to capture, filter, and slow the water down.

A suspected side benefit of low impact development is that it could also work to boost groundwater recharge rates. Using experimental plots at San Francisco State University, Newcomer et al. tested how a low impact development-style infiltration trench compared against an irrigated lawn when it came to turning water inputs into groundwater. The authors find that the recharge efficiency of the infiltration trench, at 58 percent to 79 percent, was much higher than that of the lawn, at 8 percent to 33 percent.

Though groundwater will certainly be beneficial during San Francisco's increasingly dry summers, sustaining groundwater stores in coastal cities is particularly important long term. As the sea level rises, salt water threatens to infiltrate coastal aquifers. Only by maintaining sufficient groundwater stores can this important freshwater source be maintained.

Photo: http://news.agu.org/journal-highlight/2014-05-06/

Source: Water Resources Research, doi:10.1002/2013WR014282, 2013 http://onlinelibrary.wiley.com/doi/10.1002/2013WR014282/abstract

Title: Urban recharge beneath low impact development and effects of climate variability and change

Authors: Michelle E. Newcomer: Department of Earth and Climate Sciences, San Francisco State University, San Francisco, California, USA; and Department of Civil and Environmental Engineering , University of California, Berkeley, Berkeley, California, USA;

Jason J. Gurdak, Leonard S. Sklar, and Leora Nanus: Department of Earth and Climate Sciences, San Francisco State University, San Francisco, California, USA.

5. Beaufort Gyre sea ice thins in recent decades, impacts climate

The accumulation and melting of sea ice in the Arctic has an enormous impact on the local climate, which in turn can affect the global climate. As the climate warms and Arctic sea ice retreats, it has become crucial to understand the complex ice-atmosphere-ocean dynamics within the Arctic. One major component in this dynamic is the Beaufort Gyre (BG), a wind-driven sea ice circulation and freshwater reservoir in the Arctic's Beaufort Sea.

The BG is a notoriously dangerous area to observe because of its hostile conditions. Working around this, Krishfield et al. set out to investigate recent rapid sea ice decline in the BG, using data already collected between 2003 and 2012. The authors used data from moorings, ship-based surveys, and satellite radiometers to estimate ice thickness, which, when combined with satellite estimates of ice extent, can give an estimate of sea ice volume.

The authors find a net sea ice decline over the 9 years studied, with record minima of ice volume in 2007 and 2012. Freshwater export from this region during the last 3 years was also observed. These data indicate that an anticyclonic climate regime that has been persistent in the BG since the late 1990s may be weakening, which may lead to a relatively warmer and wetter climate locally, but could produce cooling in the North Atlantic.

Source: Journal of Geophysical Research: Oceans, doi:10.1002/2013JC008999, 2014 http://onlinelibrary.wiley.com/doi/10.1002/2013JC008999/abstract

Title: Deterioration of perennial sea ice in the Beaufort Gyre from 2003 to 2012 and its impact on the oceanic freshwater cycle

Authors: R. A. Krishfield and A. Proshutinsky: Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, USA;

K. Tateyama: Department of Civil and Environmental Engineering, Kitami Institute of Technology, Kitami, Hokkaido, Japan;

W. J. Williams, E. C. Carmack and F. A. McLaughlin: Fisheries and Oceans Canada, Institute of Ocean Sciences, Sidney, British Columbia, Canada;

M.-L. Timmermans: Yale University, New Haven, Connecticut, USA.

6. New model describes toppling of salt marsh banks

Salt marshes are coastal habitats that store important nutrients and serve as shelter for many estuarial species. These habitats are threatened by rising seas and human expansion, so it has become increasingly important to improve models of how these habitats degrade.

There are many ways that salt marshes retreat naturally, including surface erosion or widespread slumping into the sea, via processes such as sliding or toppling. Studying the way the edge of a salt marsh erodes is important for determining morphological changes in the marsh, but, so far, no mechanical models exist that describe how toppling occurs.

Bendoni et al. present the first model for toppling induced by wind waves—waves of water pushed by the wind. The authors conducted laboratory experiments to investigate the effects of wind waves on salt marsh edges and find that failure occurs when water fills tension cracks, putting stress on the soil that causes it to fail. The authors then created a model based on their findings that replicates lab results well. These models may help improve salt marsh management strategies.

Source: Journal of Geophysical Research: Earth Surface, doi:10.1002/2013JF002967, 2014 http://onlinelibrary.wiley.com/doi/10.1002/2013JF002967/abstract

Title: On salt marshes retreat: Experiments and modeling toppling failures induced by wind waves

Authors: M. Bendoni, L. Cappietti and L. Solari: Department of Civil and Environmental Engineering, University of Florence, Florence, Italy;

S. Francalanci, CERAFRAI—Center of Research and Advanced Education for Hydrogeological Risk Prevention, Retignano di Stazzema, Lu, Italy.

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Mary Catherine Adams Phone (direct): +1 202 777 7530
E-mail: mcadams@agu.org

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