Antarctic ice and snow. Photo: Bella Zeldis
The world’s ice sheets are sensitive to environmental change and, as the largest reservoir of freshwater on Earth, melting of the Antarctic Ice Sheet has significant potential to raise sea levels and disrupt global ocean circulation.
To determine ice sheet response to warming, our team of researchers in the Antarctic Ice Dynamics project are looking at environmental records of how the Antarctic ice sheets and surrounding ocean have changed in the past, and comparing those records to signals of change that we can detect today.
Some research highlights from the past year are summarised below:
Viewing beneath the ice at the Kamb Ice Stream (KIS) grounding zone
Partnering with the NASA project RISE UP, ASP researchers published an unprecedented view of the KIS grounding zone using an underwater robot, Icefin. The research team recognized evidence of “ice pumping” – a process of melting, upwelling and refreezing driven by topography in submerged ice that has never before been directly observed in an ice shelf crevasse. Icefin was lowered on a tether through a borehole the KIS research team drilled through the ice shelf with hot water. The team observed diverse ice features that provide valuable information about water mixing and melt rates.
Melting in a basal channel of the KIS
A combination of ground-based observations from over-snow radar surveying and satellite remote sensing were used to identify melting and refreezing in a basal channel of the KIS. The research identified a region of focused melting where a subglacial outlet meets the ocean cavity as well as a downstream region of refreezing. This channel is currently growing at a rate of 35m per year. These new observations of ice flow off the Antarctic continent into the ocean advance our understanding of ice sheet behaviour at this key transition zone.
Seismic surveying at Discovery Deep
In the search for suitable drilling targets, a seismic survey was carried out at Discovery Deep – thought to be the deepest point on the sea floor under the Ross Ice Shelf as a future drilling target. The survey used a well-proven but labour and equipment intensive explosive- and-geophone method, and also trialled a novel approach using a detonating core and an over-ice streamer, on loan from the Alfred Wegener Institute (AWI).
Drill tent at Kamb Ice Stream, 2022. Photo: Theo Calkin
New reconstructions of past ice sheet dynamics
New reconstructions of past Antarctic ice sheet dynamics, based on sedimentological and geochemical analyses, were published. These major contributions contextualize present ice sheet dynamics and aid our ability to predict future changes under emissions scenarios.
Coupled regional atmosphere-ocean model
A new fully coupled regional atmosphere-ocean model (P-SKRIPS) was published and is now available for the Ross Sea region. This model fully conserves heat and mass fluxes transferred between the climate (PWRF) and sea ice-ocean (MITgcm) models. The team examined open water, sea ice cover, and ice sheet interfaces, demonstrating that this conservation of fluxes substantially reduces model error over the Terra Nova Bay and Ross Sea polynyas. This new coupled model is now being used for investigations into polynya influences on sub-ice shelf ocean circulation and melt rates as well as the development and propagation of mesocyclones, and how these processes will change in a warming world.
Ross Ice Shelf sensitivity to changes in climate and glaciological conditions
A new modelling technique investigates Ross Ice Shelf sensitivity to changes in climate and glaciological conditions. The study applies the “automatic differentiation” tool of the Ice Sheet-Sea Level System model to produce spatial maps that identify how sensitive ice volume is to parameter changes. The study findings demonstrate that the ice shelf is most sensitive to changes in basal friction and ice rigidity close to grounding lines and along shear margins of the Siple Coast Ice Streams and Transantarctic Mountains Outlet Glaciers, and ice sheet pinning points and shelf shear margins are highly sensitive to changes in basal melt. The sensitivity maps are now available for prioritizing future field campaigns by determining which locations additional glaciological data will be most useful.
Ice sheet projections for ISMIP6
Extended Antarctic ice sheet projections were contributed to the Ice Sheet Model Intercomparison for CMIP6 (ISMIP6-2300).
Previous ice sheet model studies have highlighted that anthropogenic emissions will influence the Antarctic ice sheet’s contribution to sea level for centuries to come. The international team of ice sheet modellers involved in ISMIP6-2300 have now performed standardized ice sheet projections to the year 2300 to better determine the long-term sea level commitment to emissions scenarios and identify uncertainties in numerical modelling.
Past ASP work quantified the uncertainty related to ice rheology and sliding, and these new projections from the modelling hub advance this uncertainty quantification even further. The ice sheet model is fully coupled to a viscoelastic Earth deformation model to quantify uncertainties related to solid earth rheology as well as two different numerical schemes for the ice sheet grounding line to understand the influence of basal melt in the grounding zone.
Ross Ice Shelf. Photo: Jana Newman