Figure 5 . a . The optimized ice rigidity\(\overset{\overline{}}{B}\) through inversion in ISSM. b . The
modified \(\overset{\overline{}}{B}\) used for the non-rift scenario.b . The modified \(\overset{\overline{}}{B}\) used for the
enhanced weakening scenario.
Non-rift scenario with different front geometry conditions.This scenario aims to examine the dynamic responses of ice shelf
velocity and stress to front geometry change. We controlled for rift
effects by replacing the low values of \(\overset{\overline{}}{B}\) near
Gipps Ice Rise with the values of the adjacent intact areas (Figure 5b).
We tested nine front geometry conditions (Figure 6), including four
historical front locations (F1–F4), and five hypothetical front
locations (H1–H5) under future retreat scenarios. H1–H5 were
determined by assuming a radical retreat scenario, in which the new ice
front reaches the compressive arch. The compressive arch is the boundary
where the second principal stress changes from negative to positive, and
has been used as a critical boundary to predict ice shelf instability
(Doake et al., 1998; Kulessa et al., 2014). It has been suggested that
ice shelf retreat will become irreversible once the ice front retreats
behind the compressive arch. H1 (Figure 6e) is the front location where
the retreat reaches the current compressive arch (shown in Figure 6d);
H2 is the front location where the retreat reaches the compressive arch
for the geometry condition H1, and similarly for H3. Once the ice front
reaches H3 or exceeds H3, the compressive arch would no longer exist. H4
is the front condition if the H3 front continues retreating another 1
km, and H5 is the front condition if H4 keeps retreating by
~20 km (Figure 6g). H4 and H5 were used to test how
sensitive the ice shelf would be to changes in the ice shelf front when
the compressive arch is absent.
Rift-scenario 1 with original\(\overset{\overline{}}{\mathbf{B}}\). Through two rift
scenarios, we aim to test the hypothesis based on the observations: the
weakening due to the rift R2 was crucial for the propagation of R1,
which resulted in the 2017 calving event. In this scenario, we used the
original ice rigidity \(\overset{\overline{}}{B}\) (Figure 5a), which
includes, to a certain extent, the R2-induced weakening.
Rift-scenario 2 with enhanced weakening. We considered a
weakening-enhanced scenario by further decreasing the rigidity\(\overset{\overline{}}{B}\) to a minimum value of
0.1×108Pa s1/3 over the rifted area
(Figure 5c).