Greenland ice sheet

Rapid Sampling of Ice-Sheet Temperatures

Posted by William Colgan on September 10, 2018
Applied Glaciology, New Research / No Comments

We are starting a new two-year project to design, build and deploy a new type of ice-drill to measure temperatures at the ice-bed interface of the Greenland Ice Sheet. Why? Because we are unsure whether the bed is frozen or thawed beneath about one third of the ice sheet. As the rate at which ice flows is dependent on ice temperature – and basal ice temperature in particular – this translates into uncertainty in simulations of how ice sheet form and flow will evolve over time.

We suspect that climate change is likely driving an expansion of the thawed-bedded portion of the ice sheet — eroding the frozen-bedded portion — over time. But in the last sixty years, direct temperature measurements of the ice-bed interface have only been made at six inland ice-sheet locations. These scarce, but tremendously valuable, basal ice temperatures have been measured at the sites of ice core deep-drilling projects. These deep-drilling projects take months or even years to create a 30 cm wide borehole to the ice-sheet bed from which to retrieve delicate ice core.

Figure 1 – Schematic of the HOTROD melt-tip and cross-section of the umbilical cord. The umbilical cord will both power the melt-tip as well as contain embedded ice-temperature sensors.

This project will design, build and deploy a drill for rapid sampling of ice-sheet basal temperatures. HOTROD will use an approximately 5KW electric melt-tip to open 3 cm wide access boreholes to depths of 500 m within days. The HOTROD umbilical cord will not only power the melt-tip, but also have embedded temperature sensors that — with the melt-tip — make a one-way trip to the ice-sheet bed. The heart of the melt-tip will be recently designed heating elements intended for rapid heating of energy-efficient domestic hot water supplies.

In 1971, thermal drilling was used to recover the top 372 m of ice core at Dye-3. The Dye-3 deep ice core was subsequently completed to 2037 m with electro-mechanical drilling in 1981. Thermal drilling technology was last used in Greenland in 1974, to recover a 403 m ice core at Crete, Greenland1. While there’s been numerous hot-water drilling projects since then, the working memory of thermal drilling is fading. The goal of this project is to successfully deploy a melt-tip thermal drill to measure a 500 m deep ice-sheet temperature profile with less than ten days of drilling. Initial field-testing activities will begin in 2019.

Figure 2 – The Dye-3 ice-drilling trench. In comparison to the multi-year logistical footprints of deep ice-coring projects, the HOTROD melt-tip drill will require trace logistics.

We hope that the advent of rapid melt-tip drilling will be a disruptive technology within the sphere of ice-sheet research now dominated by conventional electro-mechanical and hot-water drilling systems. A concerted effort to sample more temperatures at the ice-bed interface may potentially shift our understanding of ice-sheet basal temperatures and even ice-sheet sensitivity to climate change. This project is funded by Villum Experiment, a programme of Villum Foundation that funds science and engineering projects that challenge the norm and have the potential to transform traditional approaches2.

1Langway, C. 2008. The History of Early Polar Ice Cores. Cold Regions Research and Engineering Laboratory. Technical Report 08-1.

2Villum Foundation. 2018. 53 bold ideas receive funding from VILLUM FONDEN.

Tags: , , , , , ,

Greenland ice loss: 8300 tonnes per second

Posted by William Colgan on November 19, 2014
Communicating Science, New Research, Sea Level Rise / No Comments

We have a new study coming out in Earth and Planetary Science Letters that looks into the mass loss of the Greenland ice sheet (Andersen et al., 2015). We used the “input-output” approach, whereby an estimated iceberg production rate is differenced from an estimated snow accumulation rate. The input-output approach we used was slightly different from previous studies (such as Rignot et al., 2008 or Enderlin et al., 2014) because the ice sheet perimeter across which we observed ice flow (or the “flux gate”) was relatively far inland. That meant we had to make a different assumption about the vertical velocity profile at the flux gate, as well as account for changes in ice volume between the flux gate and the tidewater glacier grounding lines. We also used a new combination of satellite-derived ice surface velocity product, airborne radar-derived ice thickness observations, and surface mass balance simulations. Despite all this, our mass loss estimate agrees pretty well with previous studies!

The numbers are pretty striking: We estimate that between 2007 and 2011 the Greenland ice sheet alone, not counting all the peripheral glaciers in Greenland, lost 262 Gt of ice per year. That works out to about 8300 tonnes per second! That means the Greenland ice sheet probably weighs 250,000 tonnes less than when you started reading this blog post. No wonder we can measure its mass loss by gravitational anomalies! The ice sheet is currently losing mass via both surface runoff (the difference between accumulation and melt) and ice dynamics (the production of icebergs). We estimate that runoff comprised about 61 % of the ice sheet’s mass loss, or about 5000 tonnes per second, with iceberg production comprising the remaining 3300 tonnes per second of mass loss. Some big numbers that confirm the Greenland ice sheet is presently raising global mean sea level by about 0.73 mm per year.

Enderlin, E., I. Howat, S. Jeong, M. Noh, J. van Angelen & M. van den Broeke. 2014. An improved mass budget for the Greenland ice sheet. Geophysical Research Letters. 41: doi:10.1002/2013GL059010.

Rignot, E., J. Box, E. Burgess & E. Hanna. 2008. Mass balance of the Greenland ice sheet from 1958 to 2007. Geophysical Research Letters. 35: doi:10.1029/2008GL035417.

Andersen, M., L. Stenseng, H. Skourup, W. Colgan, S. Khan, S. Kristensen, S. Andersen, J. Box, A. Ahlstrøm, X. Fettweis & R. Forsberg. 2015. Basin-scale partitioning of Greenland ice sheet mass balance components (2007–2011). Earth and Planetary Science Letters. 409: 89–95. doi:10.1016/j.epsl.2014.10.015.

Greenland_InputOutput

Diagram showing differences in methodology between our study (TOP) and previous studies (BOTTOM) in converted estimated ice flux (F) into estimated iceberg production (D). We adopt a higher elevation “flux gate”, which necessitates accounting for downstream changes in ice volume (∆S), as well as making a different assumption about the vertical velocity profile at the flux gate. We also use different velocity and ice thickness observations, and a different surface mass balance (SMB) model (from Andersen et al., 2015).

Tags: , , , ,