Trends and connections across the Antarctic cryosphere

Satellite observations have transformed our understanding of the Antarctic cryosphere. The continent holds the vast majority of Earth’s fresh water, and blankets swathes of the Southern Hemisphere in ice. Reductions in the thickness and extent of floating ice shelves have disturbed inland ice, triggering retreat, acceleration and drawdown of marine-terminating glaciers. The waxing and waning of Antarctic sea ice is one of Earth’s greatest seasonal habitat changes, and although the maximum extent of the sea ice has increased modestly since the 1970s, inter-annual variability is high, and there is evidence of longer-term decline in its extent

Observations of Radar Penetration into Snow on Sea Ice

Sea ice is an important indicator of climate change. The ability to measure sea ice thickness is essential for monitoring trends in the volume of Arctic and Antarctic sea ice. Several methods of determining sea ice thickness are presented and it is concluded that the most appropriate for studying sea ice thickness trends on long time- and length-scales is satellite radar altimetry. One key uncertainty associated with determining sea ice thickness using satellite radar altimetry is the penetration of the radar into the snow cover. We discuss the dielectric theory related to penetration into snow. The bandwidth of satellite radar altimeters is not sufficient to resolve the air/snow and snow/ice interfaces, or layers within the snow pack. For these reasons we investigate the radar penetration into snow on sea ice using sled- and air-borne radars with wide bandwidths so that the interfaces are resolved. Coincident field measurements of the physical snow characteristics were also gathered. Data from three studies are presented. The first study is an analysis of data from the UCL Ground Penetrating Radar (GPR) deployed from an icebreaker ship off the coast of Antarctica. The radar dominant scattering surface was the snow/ice interface for 30% of the snow pits. The second is an analysis of data from the Airborne Synthetic aperture and Interferometric Altimeter System (ASIRAS) off the coast of Arctic Canada. In 2006 the radar dominant scattering surface was closer to the snow/ice than air/snow interface for 25% of the echoes; in 2008, this was 60%. The third is an analysis of coincident GPR and ASIRAS data over Arctic sea ice. We found average radar penetration (P) of 0.29 for GPR and ASIRAS data at the South site. Retrieved sea ice thickness would increase by a factor of two with P=0.29 compared with P=1

Increased Arctic sea ice volume after anomalously low melting in 2013

Changes in Arctic sea ice volume impact on regional heat and freshwater budgets, on patterns of atmospheric circulation at lower latitudes and, potentially, on global climate. Despite a well-documented ~40% decline in summer Arctic sea ice extent since the late 1970’s, it has been difficult to quantify trends in sea ice volume because detailed thickness observations have been lacking. Here, we assess changes in northern hemisphere sea ice thickness and volume using five years of CryoSat-2 measurements. Between autumn 2010 and 2012, there was a 14% reduction in Arctic sea ice volume, in keeping with the long-term decline in extent. However, we observe 33% and 25% more ice in autumn 2013 and 2014, respectively, relative to the 2010-2012 seasonal mean, offsetting earlier losses. The increase was driven by the retention of thick sea ice northwest of Greenland during 2013 which, in turn, was associated with a 5% drop in the number of days on which melting occurred – conditions more typical of the late 1990’s. In contrast, springtime Arctic sea ice volume has remained stable. The sharp increase in sea ice volume after just one cool summer indicates that Arctic sea ice may be more resilient than has been previously considered

How vegetation reinforces soil on slopes

International audienceOnce the instability process e.g. erosion or landslides has been identified on a slope, the type of vegetation to best reinforce the soil can then be determined. Plants improve slope stability through changes in mechanical and hydrological properties of the root-soil matrix. The architecture of a plants root system will influence strongly these reinforcing properties. We explain how root morphology and biomechanics changes between species. An overview of vegetation effects on slope hydrology is given, along with an update on the use of models to predict the influence of vegetation on mechanical and hydrological properties of soil on slopes. In conclusion, the optimal root system types for improving slope stability are suggeste