Working Group on the delineation of glaciers, ice sheets and ice sheet basins (2024-2028)
- Ken Mankoff, USA
- Fabien Maussion, UK
Glaciers vs Ice sheet
The group of researchers focusing on glaciers work with a widely adopted standard: the Randolph Glacier Inventory (RGI), available since 2012 and regularly updated since then. Almost all large-scale studies use the RGI as reference, and deviations from this standard in the peer-reviewed literature – even if they intended to represent an improvement to the RGI – have often led to confusion. The RGI, however, is not always used as a standard in the ice sheet community, and existing ice sheet products (volume or mass change estimates) often overlap with the RGI, especially in Antarctica where only a few studies have tried to clearly delineate analysis domains across research communities. Ice bodies inventoried in the RGI are categorized as part of the ice sheet in various other products, leading to double counting.
Preliminary attempts to address this problem have been made in Greenland, with the introduction of the concept of “connectivity level”, describing the strength of the dynamical connection of peripheral glaciers to the ice sheet. Still, challenges and inconsistencies remain. Even recent community efforts to produce consensus estimates of mass changes of the Greenland ice sheet cannot unambiguously define over which domain these estimates are valid. Finally, there are additional challenges in maintaining such a dataset in the face of rapid change, where the connectivity between peripheral glaciers and the ice sheet may be different after decades of retreat.
Basins within the ice sheets
Within the ice sheet community, similar issues exist with internal basin boundaries as with external boundaries. A few common products define large-scale regions (e.g., NW Greenland, East Antarctica), but these products do not necessarily reflect the complete extent of the ice sheets (i.e., the edges of the ice sheet are not always included in the reference geospatial data set). These products also use different areas to define labeled regions, making it challenging to compare results that use different products. For example the “Zwally” region 7.1 covering Sermeq Kujalleq (Jakobshavn Isbræ) is 95,458 km2, while the “Mouginot” basin covering the same glacier is 78,155 km2, or nearly 20 % smaller. This area discrepancy does not impact ice discharge, but significantly impacts the accumulation area, and therefore estimates of Jakobshavn Isbræ mass balance.
The issues are compounded when working with individual basins, where the signal-to-noise ratio increases due to smaller areas and the relatively larger impact of changing basin boundaries. There is a growing interest and need in basin-scale mass balance estimates. However, basin-scale mass-balance estimates are highly sensitive to the basin area, making individual results challenging to interpret, and multiple results using different basin definitions impossible to compare.
The proposed WG will have the following general objectives:
- Make a community standard agreement on which ice masses in and around Greenland and Antarctica fall into the “glacier” category and which are part of the main ice sheets
- Make a community standard agreement on internal ice sheet basins, subregions and boundaries
- Develop methods and tools to support mass change estimates that avoid under- or over-counting
- Engage a sustainable community
- Review report outlining the current situation, extracting the relevant information and suspected double counting in previous studies and IPCC report and proposed solutions to improve the situation
- Publication of a GIS standard data set defining the ice sheet and glacier domain in vector format, and at various resolutions in raster format along with a rule-set to create them
- Publication of algorithms used to accomplish D2, if there is an algorithmic definition
- Publication of rule-sets, data sets and algorithms for ice sheet ice drainage basins boundaries
Contributors and Participants
Status of the activities
Publications that have resulted from the WG