Improved models of West Antarctic glacial isostatic adjustment through new crustal motion data
Lead Research Organisation:
British Antarctic Survey
Department Name: Science Programmes
Abstract
This project addresses the current uncertainty in the present-day contribution of the West Antarctic Ice Sheet to global sea level rise. These estimates are primarily derived from space geodetic (altimetry or time-variable gravity) measurements, with time-variable gravity data from the GRACE satellite mission the only technique capable of determining ice mass balance for the entire ice sheet. Accurate correction of total mass change (measured by GRACE) to obtain ice mass change is, however, complicated by a lack of confidence in accurately correcting for glacial isostatic adjustment (GIA). Indeed, recent published estimates of ice mass change for West Antarctica are swamped by the present uncertainty in GIA models. Global Positioning System (GPS) time series offer important constraints on GIA and, indeed, have been installed in many of the critical locations. However, the current network of GPS sites, whilst allowing separation of wildly different GIA models, is too sparse to provide the tight constraints required for producing improved models / for that a high spatial resolution of GPS sites is required. In particular, the southern Antarctic Peninsula/Ronne Ice Shelf contains a very large GRACE signal, but the current station density there is too sparse to unambiguously determine the origin of the gravity change. Further suitable rock outcrops are available in this region for additional data collection and situating there new, more densely spaced, continuous sites would provide the required constraints. Here, we propose to place improved constraints on an Antarctic GIA model through newly collected GPS-data, thereby allowing us to compute new accurate and precise estimates of ice mass contributions to sea level rise from West Antarctica.
Publications
Bertler N
(2018)
The Ross Sea Dipole - temperature, snow accumulation and sea ice variability in the Ross Sea region, Antarctica, over the past 2700 years
in Climate of the Past
Bradley S
(2015)
Low post-glacial rebound rates in the Weddell Sea due to Late Holocene ice-sheet readvance
in Earth and Planetary Science Letters
Hindmarsh R
(2018)
Past Glacial Environments
Lee JE
(2020)
An 83,000 year old ice core from Roosevelt Island, Ross Sea, Antarctica
in Climate of the Past
Matsuoka K
(2015)
Antarctic ice rises and rumples: Their properties and significance for ice-sheet dynamics and evolution
in Earth-Science Reviews
Ritz C
(2015)
Potential sea-level rise from Antarctic ice-sheet instability constrained by observations.
in Nature
Thomas I
(2011)
Widespread low rates of Antarctic glacial isostatic adjustment revealed by GPS observations ANTARCTIC GLACIAL ISOSTATIC ADJUSTMENT
in Geophysical Research Letters
Wearing M
(2017)
Assessment of ice flow dynamics in the zone close to the calving front of Antarctic ice shelves
in Journal of Glaciology
Description | Using year-round continuous GPS, we measured the vertical movement of the land at nunataks in Antarctica accessible from Rothera. This motion is a response to changes in ice-loading since the last glacial maximum. The land should be moving up, because the ice load has decreased over several thousand years. The upwards vertical motion rates were much smaller than expected, meaning that we have had to revise our views on the timing of the deglaciation of Antarctica. In several locations we identified recent unstable advance of the Antarctic ice-sheet as the most likely cause of the unexpectedly low uplift rates. This ice-sheet advance was a likely explanation of results from one particular GPS station, which showed the land-surface moving downwards. |
Exploitation Route | Further research into Antarctic deglaciation |
Sectors | Environment |
Title | Effect of glacio-isostatic movement on depth of ice at the grounding-line |
Description | The grounding-line (GL) of a marine ice-sheet is the location where the ice has thinned with flow to reach the flotation thickness. Therefore, the GL indicates where an ice-shelf commences. Ice flux across the GL increases with the thickness of the ice, and recent theoretical work indicates that flux is proportional to the thickness to a power between four and five. These considerations led to the idea that a GL on a reverse slope (sloping inwards) is dynamically unstable, i.e. sensitive to the operation of feedbacks, since a retreat of the GL would lead to greater ice flux and further retreat. In contrast, an advance would lead to lower ice flux and further advance. An early discovery in glacial geology was the association of uplift of the earth surface with the retreat of large ice-sheets, owing to the unloading. For marine ice-sheets, such uplift means a further source of change in the ice-thickness at the grounding-line. Our discovery was that such shallowing can turn the unstable retreat of a marine ice-sheet into an unstable advance. This was used to explain some anomalous measurements of uplift from Antarctica, undertaken by recently installed continuous GPS stations. The anomalous results are either very slow rates of uplift, or in one case, downwards motion. The cause of these was attributed to reloading by ice, due to plausibly unstable GL readvance in the Weddell Sea sector of the the West Antarctic ice-sheet over the past 4000 years. |
Type Of Material | Improvements to research infrastructure |
Provided To Others? | No |
Impact | Publication of two papers (i)"Thomas, I.D., M.A. King, M.J. Bentley, P.L. Whitehouse, N.T. Penna, S.D.P. Williams, R.E.M. Riva, D.A. Lavallee, P.J. Clarke, E.C. King, R.C.A. Hindmarsh, H. Koivula, (2011), "Widespread low rates of Antarctic glacial isostatic adjustment revealed by GPS observations", Geophys. Res. Lett.,38, L22302, doi:10.1029/2011GL049277" (ii) "Bradley, S.L., R.C.A. Hindmarsh, P.L. Whitehouse, M.J. Bentley and M.A. King, (2015), Low post-glacial rebound rates in the Weddell Sea due to Late Holocene ice-sheet readvance, Earth Planet. Sci. Lett., 413, 79-89, doi:10.1016/j.epsl.2014.12.039" |
Title | Modelling ice-sheet grounding-line migration |
Description | In the 1970s several papers were published pointing out that if ice-flux across the grounding-line (the origin of the floating ice-shelf) increased with ice thickness, then grounding-lines situated on locations where the bed deepened up-glacier (has a 'reverse slope'), the situation was potentially unstable. For example, a small retreat of the grounding line would increase ice-flux, causing the ice-sheet to lose volume and induce further retreat of the grounding line. In contrast, a small advance would reduce ice-flux, allowing the ice-sheet to gain volume and result in more advance. These ideas had to wait until 2007 before they were given a rigorous mathematical footing by Schoof. Schoof gave a formula for flux as a function of thickness, which allowed the testing of numerical models. Two model intercomparisons have been carried out, both lead-authored by Frank Pattyn, with DOI's 10.5194/tc-6-573-2012 and 10.3189/2013JoG12J129. Richard Hindmarsh participated in these intercomparisons. We now have greatly increased confidence in the ability of numerical models to accurately compute grounding-line migration. |
Type Of Material | Improvements to research infrastructure |
Year Produced | 2012 |
Provided To Others? | Yes |
Impact | Greatly increased confidence in the numerical simulations of grounding line motion. |
Title | Questions about ice dynamics formulated on the basis of newly acquired data |
Description | The large group of earth scientists involved in investigating the palaeo-Antarctic Ice-Sheet (p-AIS) and palaeo-British-Irish Ice-Sheet (p-BIIS) has quite naturally led them to think about ice dynamical explanations for their observations. Nearly all of their conjectures and questions are well thought-through, which ultimately create questions for ice dynamicists and modellers to answer. We are improving and amending models to focus on these questions. |
Type Of Material | Computer model/algorithm |
Year Produced | 2015 |
Provided To Others? | Yes |
Impact | There are several different groups working on the p-AIS and p-BIIS, all aiming to make use of the new data. These groups talk with each other, but are all interested in different aspects of the behaviour of the ice-sheet. |
Description | Durham LGM Antarctica |
Organisation | Durham University |
Department | Department of Geography |
Country | United Kingdom |
Sector | Academic/University |
PI Contribution | BAS have organised the data gathering, geophysical surveying of ice-rises by radar-techniques. We can use these data to date the retreat of the main Antarctic grounding line. These ice-rises are located within the Ronne Ice Shelf. |
Collaborator Contribution | The project is ongoing - Durham have committed to using the data to model the behaviour of the Antarctic ice-sheet since the Last Glacial Maximum. |
Impact | BAS have completed the geophysical surveys. The data are due to be shared; once this occurs, Durham will use the data, in conjunction with other data they have acquired and models, to constrain the behaviour of the West Antarctic ice-sheet in the Weddell Sea area. BAS will contribute by collaborating on the organisation of the modelling studies. |
Start Year | 2013 |
Description | Newcastle GIA |
Organisation | University of Newcastle |
Country | Australia |
Sector | Academic/University |
PI Contribution | (i) BAS provided the solar and wind-driven power stations to support year-round continuous rock-based GPS measurements of isostatic uplift. (ii) BAS used the data in models to illuminate the complexity of the retreat history. |
Collaborator Contribution | Newcastle and Durham gathered and analysed the GPS data, using them to estimate uplift rates. |
Impact | (i) A data paper by Thomas et al, published in Geophysical Research Letters in 2011 - it's DOI number is 10.1029/2011GL049277. The paper was multi-disciplinary, involving (a) the construction and installation by BAS teams of continuous GPS stations in Antarctica; and (b) the analysis of these data by Newcastle and Durham using dedicated software to produce uplift rates. (ii) The use of these data to show that low uplift rates in the Weddell Sea area could be explained by readvance of part of the West Antarctic ice-sheet over the past 4000 years. The work was published in Earth and Planetary Science Letters in 2015, with DOI 10.1016/j.epsl.2014.12.039. The work was multi-disciplinary, involving mathematical modelling, solid-earth geophysics and glaciology. This work was a collaboration between BAS, Durham and Newcastle - a Newcastle collaborator Matt King has now moved to Tasmania. |
Start Year | 2011 |
Title | BASISM - the BAS Ice Sheet Model |
Description | BASISM has been developed over the past fifteen years, and has achieved successes in formal model intercomparison projects (MIPs), as well as being used to settle some long-standing problems. |
Type Of Technology | Software |
Year Produced | 2013 |
Impact | This software (and its brethren) have been used in MIPs to validate theoretical advances in grounding-line motion/stability and ice-stream formation. |
Description | Workshop on "Ice-Rises"; Tromsö 2014 |
Form Of Engagement Activity | A formal working group, expert panel or dialogue |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Professional Practitioners |
Results and Impact | The workshop was on the subject of "Ice Rises" - these are islands of grounded ice, surrounded by open sea or ice shelves, situated on the continental shelf ringing the main Antarctic ice-sheets. Ice-rises can be used for and in many applications. The workshop was 'networking' for interested workers from many disciplines. The organisers of the workshop were Kenichi Matsuoka (NPI Tromsö) and Richard Hindmarsh (BAS). A review paper Matsuoka et al. 2015 appeared - its DOI number is 10.1016/j.earscirev.2015.09.004 |
Year(s) Of Engagement Activity | 2014 |