Open Science: Iceberg calving has increased

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New study shows the iceberg calving from the Greenlandic glaciers has increased with almost 20 percent since 1986. The data and code from the research is accessible for anyone interested.

 

 

A new study led by The Geological Survey of Denmark and Greenland (GEUS) and published with Earth Systems Science Data estimate the ice discharge -transfer of land-ice into the ocean, at 276 tidewater glaciers around the Greenland Ice Sheet between 1986 and 2017. This makes it the most dense sampling of the ice sheet’s tidewater glaciers to date.

The ice-sheet-wide discharge or iceberg calving is estimated to have increased from less than 450 Gt/year in the 1980s and 1990s to closer to 500 Gt/year now. That increase of 50 Gt/year is equivalent to an extra 1600 tons per second of icebergs year-round relative to the 1980s and 1990s.

 

Time series of iceberg discharge from the Greenland Ice Sheet. Dots represent when observations occurred. The orange line is the annual average. Coverage denotes the percentage of glaciers from which total discharge is observed at any given time. Total discharge is ‘estimated’, rather than ‘observed’, when coverage is <100 %.

 

Open Science – Data and Code Now Online

“A special thing about this study is, that not only the article and the data, but also the code behind it, is open access. This not only makes the complex results reproducible, but also ensures that other research groups around the world can efficiently build upon this work,” says Kenneth Mankoff, Senior Researcher at GEUS.

For example, the ice-sheet-wide discharge in this study is slightly different from previous studies. It is uncertain how much of this is due to differences in flux gate locations, meaning the virtual lines across the glacier through which the ice discharge is estimated. But now other researchers will be able to use precisely the same flux gates in further studies.

Besides this, the study is based on data from Programme for Monitoring of the Greenland Ice Sheet (PROMICE), which is committed to regularly updating the dataset going forward.

“The study of Greenland mass balance and its contribution to sea level rise will benefit from operational products that are continually updated and derived from reproducible methods, rather than one-off studies that often fail to clearly explain why results are different from other studies,” says Kenneth Mankoff.

Ten-year anniversary of monitoring the Ice sheet in Greenland

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Today is the ten-year anniversary of the monitoring program PROMICE with monitoring of the Greenland ice sheet and thus also free distribution of data from the program to the international research world.
Read more about this event on this newspost from GEUS in danish.

New Cause of Exceptional Greenland Melt Revealed

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A new study by researchers from Denmark and Canada, published inGeophysical Research Letters, has found that the climate models commonly used to simulate melting of the Greenland ice sheet tend to underestimate the impact of exceptionally warm weather episodes on the ice sheet.

The study investigated the causes of ice melt during two exceptional melt episodes in 2012, which occurred on 8-11 July and 27-28 July. During these exceptional melt episodes, which can be regarded as an analogue to future climate, unusually warm and moist air was transported onto the ice sheet. During one episode, the researchers measured the ice sheet melting at more than 28 cm per day, the largest daily melt rate ever documented on the ice sheet. While the two brief melt episodes only lasted six days combined, or 6 % of the melt season, they contributed to 14 % of the total melt.

Using the Programme for monitoring of the Greenland ice sheet (PROMICE) automatic weather station data, the researchers ranked the energy sources contributing to surface melt during 2012 at twelve PROMICE sites around the ice sheet periphery. While ice sheet melt is usually dominated by the radiant energy associated with sunlight, the researchers found that the energy associated with air temperature and moisture content, rather than radiant energy, was responsible for more melt during the 2012 exceptional melt episodes.

Robert Fausto of the Geological Survey of Denmark and Greenland, lead author of the study, explains: “When we were analysing our weather station data, we were quite surprised, that the exceptional melt rates we observed were primarily caused by warm and moist air, because ice sheet wide melt is usually dominated by radiant energy from sunlight. ”

This finding has implications for how the scientific community projects future ice sheet melt using climate models. In the study, the researchers also show that while the models presently used to project ice sheet melt can accurately simulate melt due to radiant energy, models tend to systematically underestimate melt due to the non-radiant energy processes they document.

“It is difficult for the models to fully capture the details of these episodic, but important, non-radiant energy melt events because of the turbulent nature of the atmosphere very near to the ground”, says Peter Langen of the Danish Meteorological Institute, a co-author of the study. “Exceptional melt episodes dominated by non-radiant energy are expected to occur more frequently in the future due to climate change. This makes it critical to better understand the influence of these episodes on ice sheet health,” concludes lead author Robert Fausto.

PROMICE is funded by the Danish Ministry of Energy, Utilities and Climate under Danish Cooperation for Environment in the Arctic (DANCEA) and is operated by the Geological Survey of Denmark and Greenland (GEUS). PROMICE data are freely accessible at http://promice.org. HIRHAM5 climate model simulations were carried out by the Danish Meteorological Institute (DMI) under the Nordforsk project SVALI and the Danish funded Greenland Climate Research Centre project.

Read more on sciencenordic.com

Contacts:
Robert Fausto, Geological Survey of Denmark and Greenland, Denmark ([email protected])
Peter Langen, Danish Meteorological Institute, Denmark ([email protected])
Sandra McLean, York University, Canada ([email protected])

Citation:
Fausto, R. S., D. van As, J. E. Box, W. Colgan, P. L. Langen, and R. H. Mottram (2016), The implication of nonradiative energy fluxes dominating Greenland ice sheet exceptional ablation area surface melt in 2012, Geophys. Res. Lett., 43, doi:10.1002/2016GL067720.