Figure 4 . Flow velocity maps (a–f ) of six selected
periods with ice front changes, and along-flow velocity profiles for C4
(g ) and C6 (h ). The locations of the C4 and C6
centerlines are shown in panel a .
5 Modeling experiments
The observational data have indicated a clear but also complex linkage
between ice shelf retreat, flow acceleration, and rift development. Both
front geometry change and rift development modulate the stress
conditions across the ice shelf, which in turn change flow velocities
and strain rates, further affecting rifting and calving. We conducted
diagnostic modeling experiments to investigate how varying front
geometry and rift-induced weakening control the dynamic responses of ice
shelf flow velocities and stress fields.
5.1 Ice rigidity inversion and modeling scenarios
Before the diagnostic experiments, we first solved for the ice rigidity\(\overset{\overline{}}{B}\) using the inversion procedure in ISSM. We
used the 450-m resolution MEaSUREs phase-based Antarctica ice velocity
data product (Mouginot et al., 2019) to solve for\(\overset{\overline{}}{B}\). We used this velocity product to avoid
uncertainties induced by velocity interpolation errors. This velocity
product agrees best with the derived 2008–2010 flow velocities, with an
average difference of 10±25 m/year. Figure 5a shows the optimized ice
rigidity \(\overset{\overline{}}{B}\). This paramater defines the
relationship between strain rate and stress, and is affected by ice
temperature, fabric, water content, impurities and presence of cracks.
Low values of \(\overset{\overline{}}{B}\) indicate “soft” ice and
high values indicate “stiff” ice. The spatial pattern of\(\overset{\overline{}}{B}\) (Figure 5a) shows a good agreement with the
suture zones and the zones of rapid shearing where outlet glaciers are
flowing past promontories near the upglacier end of the ice shelf. The
low values of \(\overset{\overline{}}{B}\) near Gipps Ice Rise
(highlighted area in Figure 5a) are due to the observed rift that
mechanically weakened the ice shelf, thus making the ice appear
“softer” than the surrounding ice. This results from the objective of
parameter inversion, which is to minimize the difference between modeled
and observed flow velocities under the continuum-mechanical modeling
framework. When simulating for the years without rifting, these low
values of \(\overset{\overline{}}{B}\) derived from the rifted condition
could artificially influence the model simulations. We modified the\(\overset{\overline{}}{B}\) values in this rifted area (Figures 5b and
c) for different modeling scenarios. We considered three scenarios as
follows.