Precursor of disintegration of Greenland's largest floating ice tongue

Abstract

Abstract. The largest floating tongue of Greenland’s ice sheet, Nioghalvfjerdsbræ, has so far been relatively stable with respect to areal retreat. Curiously, it experienced significant less thinning and ice flow acceleration than its neighbour Zacharias Isbræ. Draining more than 6 % of the ice sheet, Nioghalvfjerdsbræ might become a large contributor to sea level rise in the future. Therefore, the stability of the floating tongue is a focus of this study. We employ a suite of observational methods to detect recent changes. We found that the calving style has changed at the southern part of the eastern calving front from normal tongue-type calving to a crack evolution initiated at frontal ice rises reaching 5–7 km and progressing further upstream compared to 2010. The calving front area is further weakened by a substantial increase of a zone of fragments and open water at the tongue’s southern margin, leading to the formation of a narrow ice bridge. These geometric and mechanical changes are a precursor of instability of the floating tongue. We complement our study by numerical ice flow simulations to estimate the impact of future break-up or disintegration events on the ice discharge. These idealised scenarios reveal that a loss of the south-eastern area would lead to 1 % of increase of ice discharge at the grounding line, while a sudden collapse of the frontal area (46 % of the floating tongue area) will enhance the ice discharge by 8.3 % due to loss in buttressing.

Fractures in glaciers—Crack tips and their stress fields by observation and modeling

“…The true orthophoto processing follows the common photogrammetric approach and with a given surface topography of the glacier, a mosaicing of the individual images is conducted. More details of the MACS‐Polar system can be found in [3]. The resulting mosaic of a crack tip is presented in Figure 2(B).…”

“…A detailed analysis of the crack and the calving front (Figure 2B) was conducted in [3] and has shown that this crack is also a mode I crack. Therefore, it is comparable to the situation of the crevasse field.…”

Extreme melting at Greenland's largest floating ice tongue

“…However, thinning has occurred over the last O. Zeising et al: Extreme melting of 79 • North Glacier 2 decades (Helm et al, 2014;Kjeldsen et al, 2015;Mouginot et al, 2015;Mayer et al, 2018), and cracks have formed at the calving front that might be a precursor to disintegration (Humbert et al, 2023).…”

Extreme melting at Greenland’s largest floating ice tongue

“…The mass loss of the Greenland Ice Sheet over the last decades as a result of a warming atmosphere and ocean has accelerated (Shepherd et al, 2020) and contributed to recent sea-level rise by 1.4 mm a −1 (Khan et al, 2022a). Half of the mass loss is caused by ice-sheet discharge through marine-terminating glaciers (Shepherd et al, 2020), mainly due to the retreat of glacier fronts (King et al, 2020) as the floating ice tongues restrain the outflow of the grounded ice (Fürst et al, 2016).…”

“…Its stability is attributed to pinning points at the calving front (Thomsen et al, 1997), lateral resistance from shear margins (Mayer et al, 2000;Rathmann et al, 2017;Mayer et al, 2018) and confinement of the glacier leading to lateral compression. However, thinning has occurred during the last two decades (Helm et al, 2014;Kjeldsen et al, 2015;Mouginot et al, 2015;Mayer et al, 2018) and cracks have formed at the calving front that might be a precursor of disintegration (Humbert et al, 2022b).…”