Figure 1 : (a) Greenland's Peripheral Glaciers and (b) Flade Isblink Ice Cap. The data used to draw these maps are based on the RGI v6.0 (https://www.glims.org/RGI/).

The fate of freshwater runoff from Greenland Peripheral Glaciers into the ocean

To start the new year off on the right foot, let's take a look into the future....projections of peripheral glacier ice melt!

Peripheral glaciers in Greenland are ice masses that are not dynamically coupled to the ice sheet, as they are either entirely detached or separated from the ice sheet by well-defined glacial divides.

Muhammad Shafeeque and Ben Marzeion tell us this week what their initial results suggest about the fate of peripheral glacier runoff.

January 31, 2022

What is the scientific background?

Projections of freshwater contributions from peripheral glaciers into the sea are essential for understanding how the interactions between glaciers and ocean will evolve in a warming climate. Increased meltwater will eventually end up in the ocean, altering the density distribution within the fjord, and thereby fjord circulation and submarine melt rates. Precise projections of freshwater input from Greenland glaciers will help quantify its effects on regional hydrography and understand the feedback between melting glaciers and ocean circulation.

How to project freshwater contributions?

The predictions are only possible using advanced glacier models atmospheric conditions from climate models . We have set up the Open Global Glacier Model (OGGM) using CMIP6 climate data for projecting the glacier processes and freshwater contributions for Greenland’s peripheral glaciers. OGGM is an open-source modeling framework that simulates past and future mass-balance, runoff, volume, and geometry of (almost) any glacier in the world in a fully automated and extensible workflow. In our work, we use OGGM with a frontal ablation module that parameterizes the annual ice mass losses of calving fronts due to ice thinning caused by the combination of surface and submarine ablation.

Figure 2: Seasonal distribution of freshwater runoff components, average for (a) 2001-2010 (b) 2091-2100. (c) Projected fraction of glacier volume with respect to the volume in 2019 under future climate change (GCMs = 12). (d) Annual freshwater runoff projected under future climate change; colored vertical lines show the peak water timing for respective SSPs.

The components of the total annual runoff

We compute the total annual runoff from the glacier in the simulation. This consists of the following components:

  • melt off-glacier: snowmelt on areas that used to be covered by glacier, but are glacier free at the considered time;
  • melt on-glacier: ice + seasonal snowmelt on the glacier;
  • liquid precipitation on-glacier;
  • liquid precipitation off-glacier. 

The runoff is approx. zero in the winter months and is high in summer, but the annual cycle of runoff changes as the glacier retreats. Model projections indicate that by the decade 2091-2100,  melt-on-glacier will reduce by 30 %. On the other hand, melt-off-glacier and liquid-precipitation-off-glacier will increase by 21 % and 9 %, respectively (Fig. 2a&b).

When will total annual runoff reach its maximum?

A typical use case for simulating and analyzing the hydrological outputs of glaciers is for “peak water” estimations. “Peak water” is the point in time when total annual runoff from a glacier reaches its maximum under a given climate scenario. For meltwater dominated-runoff, for example at the Flade Isblink in Northeast Greenland (Fig. 1b), the peak water coincides with the peak in meltwater release. As this glacier shrinks, meltwater is released from storage within the glacier, until an annual maximum is reached.

The projected glacier volume will continue to decrease under future climate change in the 21st century (Fig. 2c). All climate scenarios show that, after losing 20 % of glacier volume, the freshwater contribution from Flade Isblink decreases sharply after  roughly 2080 (Fig. 2d). For Flade Isblink, the future projections under CMIP6 climate forcing indicate that the annual runoff will increase in all the scenarios for the first half of the 21st century. The higher emission scenarios (SSP370 and SSP585) can reach peak water later in the century since the excess melt can continue to increase. For the lower emission scenarios (SSP126 and SSP245), the glacier would approach a new equilibrium, which reduces the runoff earlier in the century. After peak water is reached (SSP126: ~2059, SSP585: ~2075 in these projections), the annual runoff begins to decrease.