Project Summary

Project Description

Ice sheets are a key component of the Earth system, impacting on global sea level, ocean circulation and bio-geochemical processes. Significant quantities of liquid water are being produced and transported at the ice sheet surface, base, and beneath its floating sections, and this water is in turn interacting with the ice sheet itself.

Surface meltwater drives ice sheet mass imbalance; for example enhanced melt accounts for 60% of ice loss from Greenland, and while in Antarctica the impacts of meltwater are proportionally much lower, its volume is largely unknown and projected to rise. The presence of surface melt water is also a trigger for ice shelf calving and collapse, for example at the Antarctic Peninsula where rising air and ocean temperatures have preceded numerous major collapse events in recent decades.

Meltwater is generated at the ice sheet base primarily by geothermal heating and friction associated with ice flow, and this feeds a vast network of lakes and rivers creating a unique bio-chemical environment. The presence of melt water between the ice sheet and bedrock also impacts on the flow of ice into the sea leading to regions of fast-flowing ice. Meltwater draining out of the subglacial system at the grounding line generates buoyant plumes that bring warm ocean bottom water into contact with the underside of floating ice shelves, causing them to melt.  Meltwater plumes also lead to high nutrient concentrations within the oceans, contributing to vast areas of enhance primary productivity along the Antarctic coast.

Despite the key role that hydrology plays on the ice sheet environment, there is still no global hydrological budget for Antarctica. There is currently a lack of global data on supra- and sub-glacial hydrology, and no systems are in place for continuous monitoring of it or its impact on ice dynamics.

The overall aim of 4DAntarctica is to advance our understanding of the Antarctic Ice Sheet’s supra and sub-glacial hydrology, its evolution, and its role within the broader ice sheet and ocean systems.

The project addresses the following specific objectives:

  • Creating and consolidating an unprecedented dataset composed of ice-sheet wide hydrology and lithospheric products, Earth Observation datasets, and state of the art ice-sheet and hydrology models
  • Improving our understanding of the physical interaction between electromagnetic radiation, the ice sheet, and liquid water
  • Developing techniques and algorithms to detect surface and basal melting from satellite observations in conjunction with numerical modelling
  • Applying these new techniques at local sites and across the continental ice sheet to monitor water dynamics and derive new hydrology datasets
  • Performing a scientific assessment of Antarctic Ice Sheet hydrology and of its role in shaping current changes affecting the ice sheet
  • Proposing a future roadmap for enhanced observation of Antarctica’s hydrological cycle

 

To achieve these objectives, the consortium will make use of a plethora of Earth Observation missions such as CryoSat2, SMOS, Sentinel1&2, ERS1&2, ENVISAT, AMSR-E, TanDEM-X, Landsat, in conjunction with numerical models of ice sheet.

Lithosphere

Partners involved:

  • British Antarctic Survey (BAS)
  • Technical University of Denmark (DTU)

Intended products:

  • Bedrock topography
  • Updated geothermal heat flux

Bedrock topography

Bedrock topography represents an important aspect of ice sheet dynamics. Many of the outlet glaciers overlie deep and narrow trenches cut into the bedrock. It is well known that pronounced topography intensifies the geothermal heat flux in deep valleys and attenuates this flux on mountains. Investigating the magnitude of this effect is an important aspect to better understand ice-sheet processes. This project shall capitalise on recent developments (e.g. GOCE+ Antarctica, Polar Gap, BEDMAP2/3, Bedmachine) and exploit the most advanced bedrock topographic map available to the community.

Geothermal heat flux

Geothermal flux is one of the most dynamically critical ice sheet boundary conditions but is extremely difficult to constrain at the scale required to understand and predict the behaviour of rapidly changing glaciers. In addition, the thermal structure of the Antarctic continent is one of the most unknown parameters, but critical for a variety of applications on different scales, e.g. ice-sheet modelling or glacial-isostatic adjustment. The scope of this project is to better integrate seismological, potential field, magnetic, petrological, thermal modelling and other methodologies to significantly enhance our knowledge of crustal and mantle-derived components within the geothermal heat flux (GHF) budget.

Figure: Geothermall heat flux from (A) satellite magnetic data (Fox Maule et al. 2005), (B) seismological model (An et al. 2015), (C) Heat flux from CryoSMOS. In (D) the difference between the models in (A) and (B) are shown.

Source: GOCE + Antarctica team

Sub-Glacial Environment

Partners involved:

  • The University of Edinburgh
  • University of Leeds
  • ETH Zürich
  • Institute for Applied Physics “Nello Carrara” (IFAC CNR)
  • Institute of Environmental Geosciences (CNRS Grenoble)
  • Environmental Earth Observation Information Technology (ENVEO)
  • Shepherd Space

Intended products:

  • Ice temperature profiles
  • Ice velocities
  • Grounding line position
  • Time-dependant altimetry
  • Inventory of active sub-glacial lakes
  • Basalt melt generation and sub-glacial hydrology pathways

Basal melting of the Antarctic ice shelves is an important factor in determining the stability of the Antarctic ice sheet. Most of the important processes controlling glacial motion occur in the ice-bed contact. The basal shear stress depends on the geothermal heat flux, bed temperature, roughness, glacier velocity and other factors. In addition, a number of factors can affect bed temperature, which is intimately associated with basal meltwater. The melting point of water decreases under pressure, meaning that water melts at a lower temperature under thicker glaciers. In addition, because thicker glaciers have a lower heat conductance, the basal temperature is also likely to be higher. Also, as friction increases, faster motion will greatly increase frictional heating, resulting in increasing melting – which causes a positive feedback, increasing ice speed. Supraglacial lakes represent another possible supply of liquid water to the base of glaciers, so they can play an important role in accelerating glacial motion. Finally, bed roughness can act to slow glacial motion. The roughness of the bed is a measure of how many boulders and obstacles protrude into the overlying ice.

Figure: Frictional heating in the Smith Glacier region, based on recent investigations with the STREAMICE code (Goldberg et al., 2019). The areas without data represent ice shelf or open ocean.

Figure: Retrieved ice temperature (K) from SMOS observations at (left) 50 m and (right) 2000 m in depth in the framework of the CryoSMOS project.

The combination of EO data and ice flow models to estimates of basal shear stress has been demonstrated to be an efficient tool to estimate basal melt rates. Together with water routing models the complete basal water flow pathways and the corresponding flux can be computed.

Subglacial lake water moves between lakes and rapidly drains, causing catastrophic floods. The exact mechanisms by which subglacial lakes influence ice-sheet dynamics are unknown, and their influence in rapidly flowing ice streams is still a research issue (Bell et al., 2007). It is now well documented that over 400 subglacial lakes exist across the bed of the Antarctic Ice Sheet (Siegert et al., 2015). They comprise a variety of sizes and volumes (from the approx. 250 km long Lake Vostok to bodies of water less than 1 km in length), relate to a number of discrete topographic settings (from those contained within valleys to lakes that reside in broad flat terrain) and exhibit a range of dynamic behaviours (from ‘active’ lakes that periodically outburst some or all of their water to those isolated hydrologically for millions of years). A novel way of using data from ESA’s CryoSat mission has revealed how meltwater from lakes beneath Thwaites Glacier drained into the Amundsen Sea – potentially the largest outflow from subglacial lakes ever reported in this region of West Antarctica (Smith et al., 2017).

Figure: Active sub-glacial lake under the Thwaites glaciers, west-Antarctic ice sheet

Source: University of Edinburgh, Noel Gourmelen

SuPRA-Glacial Environment

Partners involved:

  • Lancaster University
  • Institute for Applied Physics “Nello Carrara” (IFAC CNR)
  • Institute of Environmental Geosciences (CNRS Grenoble)
  • Environmental Earth Observation Information Technology (ENVEO)
  • The University of Edinburgh
  • German Aerospace Center (DLR)

Intended products:

  • Time-dependant and ice-sheet wide characterisation of surface melt (liquid water)
  • Inventory of supra-glacial lakes and streams

Ice sheet surface hydrology is a complex and interconnected system, meltwater runoff forms a network of rivers, lakes and streams which covers vast areas and from which water can be routed 1) to areas where no melt is produced locally (e.g. Kingslake et al., 2017), 2) off the ice completely (e.g. Bell et al., 2017), or 3) into the en-glacial environment through crevasses (cracks) and moulins (e.g. Langley et al., 2016). The presence of water can propagate crevasses and moulins (hydrofracture, e.g. van der Veen, 2007) through the full thickness of a floating ice shelf or grounded ice sheet, providing a conduit for the removal of this water either into the ocean or to the ice bed, respectively. New moulins formed via hydrofracture of supraglacial lakes and their subsequent drainage also provide a conduit for the direct transfer of meltwater to the subglacial environment for the remainder of the melt season (Banwell et al, 2016).

Figure: Continuously acquired Sentinel-1 tracks (6 & 12 days repeat interval) in Antarctica implemented since July 2017.

2017-11-03

2017-11-09

2018-01-02

2018-03-09

Figure: Sentinel-1 brightness image time series covering the Larsen B region in the northern Antarctic Peninsula. The images clearly show the development of melt during the summer season.

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