Jakobshavn's Interrupted Thinning Explained

Jakobshavn Glacier is Greenland's largest and fastest moving glacier. Over the last 20 years, the glacier, known in Greenlandic as Sermeq Kujalleq, has retreated, sped up and thinned. The data shown here reveal that Jakobshavn’s retreat has reversed. Between 2016 and 2018, the glacier advanced and got thicker. Scientists from NASA’s Jet Propulsion Laboratory have linked these changes to cooling of the ocean waters that reach Jakobshavn after traveling around the southern tip of Greenland and reaching into Disko Bay. (See the science paper here) The ocean cooling was likely related to the natural cycles of warming and cooling that happen in the Atlantic as part of the North Atlantic Oscillation. The strong influence of the ocean on the ice loss from Jakboshavn is somewhat surprising because the role of the ocean has been unclear since the glacier’s floating extension, called an ice tongue, disintegrated in 2003. These results mean that future projections of sea level rise will also need to account for the ocean changes in order to accurately predict how fast Greenland’s ice will melt in a warming climate.

This visualization shows a variety of data from the oceans and ice to help explain why Jakobshavn glacier grew thicker and advanced between 2016 and 2017. Initially, the average flow of ice across the Greenland Ice Sheet in these years is shown as colored flow arrows, with blue shades indicating slower movement and red indicating faster. As we draw near we see a large bay named Disko Bay located just to the west of the narrow inlet, or fjord, that is home to Jakobshavn glacier. The water is cut away to reveal the historical temperature of the bay, to a depth of about 400 meters. Around Greenland, water below 150 m depth tends to be warmer than water near the surface. The change in temperature between 1952 and 2017 is shown using blue tones for colder water and red tones for warmer. The deep water warms through most of the 1990s, but cools dramatically after 2015. The ocean temperature changes are shown a second time, with a brief pause on 1979 to see the initial cooler water temperature, 2000 to view the warming and 2017 to view the current cooling trend.

The visualization pulls out to show the entire Greenland Ice Sheet while ocean is drained to reveal the shape and depth of the ocean floor around the ice sheet. Data from the ECCO ocean circulation model shows ocean currents carrying water around the southern tip of Greenland and up the west coast, where it eventually enters Disko Bay and reaches Jakboshavn glacier.

When we zoom in to the Jakobshavn glacier again, we see the glacier is blanketed by more than 40,000 radar observations. These data show the change in elevation between 2016 and 2017 as measured by an aircraft. These elevation changes are colored so that blue colors indicate an rise in the elevation and orange/red colors indicate a fall. The deepest blue color reflects the advance of the glacier from the 2016 front, appearing in the video as a shaded cliff, to its more advanced location in 2017. Farther downstream in the fjord the patches of blue and red show icebergs, which have detached from the front.