Melt Ponds and the Prediction of Ice Melt

One of the biggest environmental concerns is that of global climate change. Symptoms of major shifts in the Earth’s climate are everywhere from the melting of glaciers, rising oceans, more severe storms, and warmer temperatures. Of particular worry to scientists and researchers is that of the melting of sea ice. The amount of sea ice has depleted rapidly in the last ten years; so much that the best climate models cannot keep up with the unbelievable rate at which it is melting.

In response, there has been an increased interest in the phenomena of melt ponds and how they can be used to both predict summer ice melting and understand sea dynamics. Melt ponds are vast pools of water that form on ice and ice sheets. These ponds of melted snow form in low areas of sea ice and glaciers and are highly visible both on the ground and from Earth-observing satellites in orbit. Whereas a sheet of white covers most surfaces of Arctic ice in winter, melt ponds are a prominent feature in the summer as the temperatures rise.

Melt ponds are significant because they could help scientists understand sea ice levels, an important factor in global climate change. One of the reasons for this is that sea ice has a key role in the Earth’s climate system. White sea ice reflects a large percentage of sunlight back into space, helping to moderate temperatures. The rate at which sea ice returns energy is called its albedo. However, as sea ice decreases as it does in summertime, dark ocean water absorbs more of that sunlight which could ultimately contribute to global warming.

Mathematics professor from the University of Utah Ken Golden has demonstrated that the formation of melt ponds could help model how sea ice melts and transitions from having a high albedo, or reflection rate, to a low albedo. Golden has used the mathematical concept of fractals and applied them to melt ponds. For instance, as melt ponds grow and become more complex, the total perimeter of those ponds increase much faster than the total area of the ponds, just as in the case of fractals.

Using mathematical patterns like fractals, Golden has proved that the presence or absence of melt ponds on the surface of sea ice drastically changes its albedo. Since water absorbs much more heat than ice or snow, melt ponds can change the heat balance. Warmer waters could then speed the melting of surrounding ice and possibly influence the overall ice extent in the Arctic Ocean. This means that melt ponds could actually predict how much sea ice will melt.

Melt ponds have become such a critical factor for sea ice levels that NASA launched an ER-2 airplane in July of 2014 to collect data and take photographs of them. The ER-2 is a civilian version of the U.S. Air Force’s U2-S reconnaissance plane with one major difference. It is a high-altitude aircraft equipped with the Multiple Altimeter Beam Experimental Lidar (MABEL). MABEL collected information with lasers and photon-detectors. This instrument took measurements of sea ice as well as Alaska’s glaciers, the atmosphere, and the open ocean among other surface features.

One of the main purposes of the mission was to better appreciate the significance of melt ponds and help scientists design algorithms for predicting sea ice coverage from year to year. Scientists still do not understand how melt ponds vary in terms of depth, size, and number and even from region to region. On the other hand, melt ponds can tell researchers much about the sea ice itself. Melt ponds could clue scientists in on the age of sea ice because deeper, small ponds form on bumpy, older ice whereas large, shallow ponds form on newer ice.

NASA is also hoping that their experiments with MABEL will lead to better algorithms for their upcoming Ice, Cloud and land Elevation Satellite-2, or ICESat-2 scheduled to launch in 2017. This satellite will measure the elevation of the Earth by emitting pulses of green laser light and determining how long it takes for the individual photons to bounce off of the surface and come back. The type of ice that these pulses hit can be predicted by measuring the number and pattern of photons that return so scientists can determine whether that ice was smooth, covered with water or snow, or ridged.

In the end, sea ice levels at the end of the season in September are of great concern because of a drastic reduction over the last seven years. In the 1990s, sea ice covered an area of about seven million square kilometers. The number has gone down to less than five square kilometers in five of the last seven years. The summer of 2012 saw one of the lowest levels of sea ice on record at 3.6 million kilometers. Understanding the phenomena of melt ponds more could make a difference in predicting sea ice levels and the Earth’s overall climate patterns.

References:

“Arctic Melt Pond: Image of the Day.” http://earthobservatory.nasa.gov/IOTD/view.php?id=84113

Hohenegger, C., Alali, B., Steffen, K. R., Perovich, D. K., and Golden, K. M.: Transition in the fractal geometry of Arctic melt ponds, The Cryosphere, 6, 1157-1162, doi:10.5194/tc-6-1157-2012, 2012.

“Mathematical Patterns in Sea Ice Reveal Melt Dynamics.” http://blogs.scientificamerican.com/observations/2014/03/13/mathematical-patterns-in-sea-ice-reveal-melt-dynamics/

“More Melt Ponds.” http://earthobservatory.nasa.gov/blogs/earthmatters/2014/08/01/more-melt-ponds/

“NASA’s High-Flying Laser Altimeter to Check Out Summer Sea Ice and More.” http://www.nasa.gov/content/goddard/nasa-s-high-flying-laser-altimeter-to-check-out-summer-sea-ice-and-more/

“Ponds ‘predict Arctic sea-ice melt.’” http://www.bbc.com/news/science-environment-27870459

“September Arctic sea-ice minimum predicted by spring melt-pond fraction.” http://www.nature.com/nclimate/journal/v4/n5/full/nclimate2203.html?WT.ec_id=NCLIMATE-201405