Defining models of glacial isostatic adjustment in West Antarctica and Antarctic Peninsula (UKANET): better constraints on Earth structure and uplift

Lead Research Organisation: Durham University
Department Name: Geography

Abstract

We aim to decrease the uncertainty associated with the measurement of ice mass change in West Antarctica by addressing our lack of knowledge of Earth structure and accuracy of present-day uplift rates. Ice loss from the West Antarctic Ice Sheet (WAIS) currently accounts for around 10% of present-day global sea-level rise. Moreover, this region is undergoing accelerated ice loss. Accurate projections for the evolution of WAIS are currently hindered by uncertainties in measurements of present-day ice mass change. Two key methods for deriving this change are satellite gravimetry, which determines changes in Earth's gravity field due to surface mass redistribution, and altimetry, which measures modifications to the height of the ice surface. Crucially, both of these techniques are susceptible to errors introduced by correcting for the uplift response of the solid Earth to past ice mass loss, a process known as Glacial Isostatic Adjustment (GIA). GIA models require information relating to the regional deglaciation history and the rheological properties of the solid Earth. In most GIA models only 1D global averages of Earth structure are taken in to account; this is a gross oversimplification.
We propose to determine (i) 3D Earth structure in West Antarctica and Antarctic Peninsula through a new passive seismological experiment and (ii) present-day uplift rates through the extension of a NERC-funded GPS network in the Peninsula and new spatially extensive satellite radar interferometry data (InSAR). We will deploy 10 broadband seismometers for 2 years, adjacent to a contemporaneous 2 year POLENET deployment, to estimate 3D variations in Earth rheology by determining S-wave velocity-depth models down to depths of 400 km. Seismic data have never been collected in the southern Antarctic Peninsula region of West Antarctica, and hence very little is known about its Earth structure. The determination of lithospheric structure will also improve our understanding of the tectonic evolution of the region. We propose a 3 year PDRA to carry out the fieldwork and seismological research.
Long time series of surface deformation measurements are important to our understanding of uplift rates due to GIA. A network of 10 GPS sites has been deployed in the southern Antarctic Peninsula since 2009 under a now terminating NERC/AFI grant. At minor additional financial cost, but with significant scientific benefit, we propose to operate this network for a further 2 years. Our Project Partner Matt King (University of Tasmania) will oversee the processing of these data. The seismic structure results will be incorporated into a 3D GIA model as an addition to CI Whitehouse's Fellowship work; a 1.5 year PDRA will combine the GIA and deformation results to more tightly constrain past and present ice mass change in the southern Antarctic Peninsula and West Antarctica.
While the sparse network of GPS will constrain the deformation pattern on a broad scale, we expect smaller wavelength variability in deformation due to present-day ice mass change. Therefore, we plan to apply satellite radar interferometry (InSAR) to the rock outcrops in West Antarctica to increase the spatial sampling of the deformation field by orders of magnitude. Because distances between rock outcrops can be large, the spatial variability of the tropospheric radar propagation delay during interferometric processing has to be estimated from weather models. We propose to test these assumptions with a local field deployment of 6 GPS in the Antarctic Peninsula.
The timing of this grant proposal is critical as 1) BAS logistics are already in place for the funded 2 year iStar programme in the south of the region; 2) US POLENET seismometers will temporarily be positioned to the south and significantly extend our station coverage; 3) the grant supporting the GPS network is ending.

Planned Impact

Who will benefit from our research?
The main beneficiaries of knowledge arising from this project are policy makers, such as the Intergovernmental Panel on Climate Change (IPCC) and the UK Environment Agency (EA), charged with policy and planning related to robust projections of future sea level rise. The Living With Environmental Change (LWEC) initiative, established by the UK government, could use the outputs from this research to improve the capacity of government, business and society to mitigate and adapt to environmental change.

We aim to benefit the general public by furthering their understanding of uncertainty in science using GIA models, ice mass balance and sea level rise as our proxies. We hope to extend this theme out to industry and policy makers in government. We will demonstrate how scientific research can be used to address and reduce uncertainty, but also explain why uncertainty is inherent in the science of sea level rise.

How will they benefit from the research?
This research will help to reduce the uncertainty associated with projections of future sea level rise and the subsequent risk associated with sea-defence planning and coastal adaptation. Our results will evidence and support UK's own sea-level projections, which EA have been developing in conjunction with the Hadley Centre and British Antarctic Survey (BAS) as a response to limitations in the global projections of the IPCC. The IPCC AR5 is currently in draft, and will be published in 2013/14. It will include specific sea-level rise projections to 2100 that will be based almost exclusively on the evidence provided in the peer-reviewed literature. The papers coming out our project will hopefully influence subsequent IPCC drafts.

Publications

10 25 50
 
Description - Through the activities of this grant, a new, high resolution, 3D model of lithosphere and upper mantle structure in the southern Antarctic Peninsula and West Antarctica has been developed for the purposes of glacial isostatic adjustment (GIA) modelling. The model uses a finite element approach.

- Using this model we have shown that accounting for the thinner lithosphere in West Antarctica alters predictions of GIA, and potentially alters our understanding of feedbacks between Earth deformation and ice sheet dynamics. Such spatial variations in Earth structure are not accounted for in the majority of models that seek to quantify the rebound of the solid Earth in response to past ice sheet change.

- We have determined a shear wave model of the West Antarctic crust and upper mantle to ~200 km depth. The model is constructed from the combination of fundamental mode Rayleigh wave phase velocities extracted from ambient noise (periods 8-25s) and earthquake data by two-plane wave analysis (periods 20-143s). The data used to develop the model were derived from our 2016-2018 seismic network, which was deployed across the southern Antarctic Peninsula, and the POLENET seismic network. Key findings are below:

- We interpret the distribution of low seismic velocity anomalies in the uppermost mantle to suggest that recent tectonism in the West Antarctic Rift System (WARS) is mainly concentrated beneath the rift margins and largely confined to the uppermost mantle (<180km).

- We speculate that high velocity zones imaged south of the Marie Byrd Land dome and in the eastern Ross Sea Embayment might reflect the compositional signature of ancient continental fragments, and that a high velocity anomaly located in the southern Weddell Sea Rift System might reflect depleted mantle lithosphere following the extraction of voluminous melt related to Gondwana fragmentation.

- A pronounced low velocity anomaly underlying the southern Transantarctic Mountains is consistent with a published lithospheric foundering hypothesis. Taken together with a magnetotelluric study advocating flexural support of the central TAM by thick, stable lithosphere, this suggests there is along-strike variation in the tectonic history of the TAM.

- Lithospheric thickness estimates extracted from 1D shear wave velocity profiles representative of tectonic domains in West Antarctica indicate an average lithospheric thickness of ~85 km for the WARS, Marie Byrd Land, and Thurston Island block. This increases to ~96 km in the Ellsworth Mountains.

- A surface heat flow of ~60 mW/m2 and attendant geotherm best explains lithospheric mantle shear wave velocities in the central WARS and in the Thurston Island block adjacent to Pine Island Glacier; a ~50 mW/m2 geotherm best explains the velocities in the Ellsworth Mountains, and a ~60 mW/m2 geotherm best explains a less well-constrained velocity profile on the southern Antarctic Peninsula. These are regional average (many hundreds of km) heat flow estimates constrained by seismic data with limited sensitivity to upper crustal composition.
Exploitation Route - GPS rates are published in an open access data repository, so can be used by others to investigate the link between ice mass change, Earth rheology, and solid Earth deformation

- The seismological data collected will be available in an open access data repository in 2020. The models relating to the seismic structure of the upper mantle are being used to quantify spatial variations in mantle rheology, and hence more tightly quantify the solid Earth response to past and present ice sheet change. Once published they will also be made available to other researchers.

- A preliminary publication associated with this project identified that spatial variations in lithosphere thickness can significantly perturb the predicted pattern of solid Earth deformation in response to ice sheet change. This finding should prompt others to account for spatial variations in Earth rheology when studying glacial isostatic adjustment across west Antarctica
Sectors Environment

 
Description NERC Standard Grant (New Investigator)
Amount £785,489 (GBP)
Funding ID NE/R002029/1 
Organisation Natural Environment Research Council 
Sector Public
Country United Kingdom
Start 01/2018 
End 12/2022
 
Description Visiting Scholar, University of Tasmania
Amount $6,120 (AUD)
Organisation University of Tasmania 
Sector Academic/University
Country Australia
Start 03/2015 
End 04/2015
 
Title British Antarctic Survey GPS Network - BREN-Brennecke Nunataks P.S., UNAVCO, GPS/GNSS Observations Dataset 
Description GPS/GNSS station: Long-term continuous or semi-continuous occupation at a single location 
Type Of Material Database/Collection of data 
Year Produced 2013 
Provided To Others? Yes  
Impact n/a 
URL https://doi.org/10.7283/T52V2D7X
 
Title CAPGIA - West Antarctica Continuous Network, UNAVCO, GPS/GNSS Observations (Aggregation of Multiple Datasets) 
Description GPS/GNSS stations: Long-term continuous or semi-continuous occupations at multiple locations 
Type Of Material Database/Collection of data 
Year Produced 2013 
Provided To Others? Yes  
Impact n/a 
URL https://doi.org/10.7283/T56Q1VN5
 
Description 3D GIA modelling 
Organisation Delft University of Technology (TU Delft)
Country Netherlands 
Sector Academic/University 
PI Contribution Numerical modelling making use of data received from one partner, and delivery of model output to both partners
Collaborator Contribution Sharing of data and model code.
Impact Two publications have so far resulted from this collaboration (van der Wal et al., 2015; Nield et al., 2018).
Start Year 2013
 
Description 3D GIA modelling 
Organisation POLENET
Country Global 
Sector Charity/Non Profit 
PI Contribution Numerical modelling making use of data received from one partner, and delivery of model output to both partners
Collaborator Contribution Sharing of data and model code.
Impact Two publications have so far resulted from this collaboration (van der Wal et al., 2015; Nield et al., 2018).
Start Year 2013
 
Description GPS and GIA 
Organisation Newcastle University
Country United Kingdom 
Sector Academic/University 
PI Contribution Ongoing collaboration with Matt King (University of Tasmania, formerly of Newcastle University, UK), Peter Clarke (Newcastle University, UK), and Terry Wilson (Ohio State University, PI of the NSF-funded POLENET project). My expertise is to produce numerical models of solid Earth deformation in response to changes in surface loading by ice sheets. Such models are tuned or tested using geodetic data.
Collaborator Contribution Matt King's expertise is polar geodesy; including the production and analysis of the polar geodetic data sets that are used to test my numerical models. Peter Clarke's expertise is in linking geodesy and geophysics; including understanding of the solid Earth processes that are represented in my numerical models. Terry Wilson runs the mulit-million dollar NSF-funded POLENET project that is responsible for much of the geodetic infrastructure across West Antarctica.
Impact This collaboration has led to the publication of 13 co-authored, peer-reviewed publications since 2011. I am a project partner on two current projects led by Matt King, which are funded by the Australian Research Council, and one project led by Terry Wilson, which is funded by NSF. I receive no financial input from these projects. I am the PI or Co-I of two NERC-funded projects on which Peter Clarke is a Co-I (reported elsewhere). Though this collaboration I have co-supervised two PhD students.
Start Year 2009
 
Description GPS and GIA 
Organisation POLENET
Country Global 
Sector Charity/Non Profit 
PI Contribution Ongoing collaboration with Matt King (University of Tasmania, formerly of Newcastle University, UK), Peter Clarke (Newcastle University, UK), and Terry Wilson (Ohio State University, PI of the NSF-funded POLENET project). My expertise is to produce numerical models of solid Earth deformation in response to changes in surface loading by ice sheets. Such models are tuned or tested using geodetic data.
Collaborator Contribution Matt King's expertise is polar geodesy; including the production and analysis of the polar geodetic data sets that are used to test my numerical models. Peter Clarke's expertise is in linking geodesy and geophysics; including understanding of the solid Earth processes that are represented in my numerical models. Terry Wilson runs the mulit-million dollar NSF-funded POLENET project that is responsible for much of the geodetic infrastructure across West Antarctica.
Impact This collaboration has led to the publication of 13 co-authored, peer-reviewed publications since 2011. I am a project partner on two current projects led by Matt King, which are funded by the Australian Research Council, and one project led by Terry Wilson, which is funded by NSF. I receive no financial input from these projects. I am the PI or Co-I of two NERC-funded projects on which Peter Clarke is a Co-I (reported elsewhere). Though this collaboration I have co-supervised two PhD students.
Start Year 2009
 
Description GPS and GIA 
Organisation University of Tasmania
Country Australia 
Sector Academic/University 
PI Contribution Ongoing collaboration with Matt King (University of Tasmania, formerly of Newcastle University, UK), Peter Clarke (Newcastle University, UK), and Terry Wilson (Ohio State University, PI of the NSF-funded POLENET project). My expertise is to produce numerical models of solid Earth deformation in response to changes in surface loading by ice sheets. Such models are tuned or tested using geodetic data.
Collaborator Contribution Matt King's expertise is polar geodesy; including the production and analysis of the polar geodetic data sets that are used to test my numerical models. Peter Clarke's expertise is in linking geodesy and geophysics; including understanding of the solid Earth processes that are represented in my numerical models. Terry Wilson runs the mulit-million dollar NSF-funded POLENET project that is responsible for much of the geodetic infrastructure across West Antarctica.
Impact This collaboration has led to the publication of 13 co-authored, peer-reviewed publications since 2011. I am a project partner on two current projects led by Matt King, which are funded by the Australian Research Council, and one project led by Terry Wilson, which is funded by NSF. I receive no financial input from these projects. I am the PI or Co-I of two NERC-funded projects on which Peter Clarke is a Co-I (reported elsewhere). Though this collaboration I have co-supervised two PhD students.
Start Year 2009
 
Description SERCE 
Organisation Scientific Committee on Antarctic Research
Country United Kingdom 
Sector Charity/Non Profit 
PI Contribution I am the co-director of a Scientific Research Program (SRP) titled: Solid Earth Response and influence on Cryosphere Evolution (SERCE), hosted by the Scientific Committee on Antarctic Research (SCAR). This program aims to facilitate collaborative research in the field of Glacial Isostatic Adjustment. We have an annual budget of US$20,000, which is spent on running workshops and training activities associated with ice sheet - solid Earth feedbacks, and facilitating Early Career Researcher (ECR) attendance at these activities. Tasks associated with my role include: completing annual reports on program activities, sitting on the UK National Committee for Antarctic Research, co-organizing workshops and training schools, allocating ECR travel funds, and planning for future activities.
Collaborator Contribution My co-director (Matt King, University of Tasmania) makes an equal contribution to this activity.
Impact Co-sponsorship of training school on Glacial Seismology (2017). Co-sponsorship of workshop on Glacial Isostatic Adjustment and Elastic Deformation (2017). Co-sponsorship of workshop on Antarctic Heat Flux (2018) and Polar Geodesy (2018). Beneficiaries of SERCE support are encouraged to acknowledge this in publications where the author has benefited from attending SERCE-organised activities. High profile article published in 2019 describing the research aims and outstanding research questions associated with SERCE activities.
Start Year 2016
 
Description AGU Fall Meeting 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other audiences
Results and Impact Conference presentation by postdoc Grace Nield on "The sensitivity of Glacial Isostatic Adjustment in West Antarctica to Lateral Variations in Earth Structure" at the 2017 American Geophysical Union Fall Meeting. Received questions from audience and ongoing discussion afterwards.
Year(s) Of Engagement Activity 2008,2017
 
Description Blog on Antarctic Research 
Form Of Engagement Activity Engagement focused website, blog or social media channel
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact I write an occasional blog about my research on Antarctica. The reason for writing the blog is to provide insight to the general public on why the research is important, and how we go about carrying out science in such a hostile environment. I receive very positive, informal feedback on the posts, either in person or via social media (Twitter). In particular, it has been a delight to be able to highlight the number of women working in Antarctica, or on Antarctic Science; people have expressed surprise at this, and hopefully my writing has made people think twice about what an 'Antarctic Scientist' might look like!
Year(s) Of Engagement Activity 2016,2017
URL http://antarcticpippa.blogspot.co.uk/
 
Description EGU2018 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other audiences
Results and Impact Conference presentation by postdoc Grace Nield on "The influence of high resolution 3D Earth structure in West Antarctica on Glacial Isostatic Adjustment" at the 2018 European Geosciences Meeting. Received questions from audience and ongoing discussion afterwards.
Year(s) Of Engagement Activity 2018
 
Description ESA2017 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other audiences
Results and Impact Two members of the UKANET project invited to attend a workshop hosted ESA (European Space Agency) at the British Antarctic Survey. Short presentations by all attendees and discussion of different approaches to modelling 3D Earth structure when seeking to understand glacial isostatic adjustment across Antarctica.
Year(s) Of Engagement Activity 2017
 
Description GIA Workshop, Iceland 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other audiences
Results and Impact Conference presentation by postdoc Grace Nield on "The sensitivity of Glacial Isostatic Adjustment in the Antarctic Peninsula to variations in lithospheric thickness" at international workshop on Glacial Isostatic Adjustment and Elastic Deformation. Received questions from audience and ongoing discussion afterwards.
Year(s) Of Engagement Activity 2017
 
Description POLAR18 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other audiences
Results and Impact Presentation on the research of post-doc Grace Nield at the POLAR18 conference in Davos, June 2018. Talk title: The sensitivity of GIA in West Antarctica to laterally varying Earth structure. Questions and ongoing discussion with other scientists in the field after the talk.
Year(s) Of Engagement Activity 2018
 
Description SERCE/POLENET GIA Summer School 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Postgraduate students
Results and Impact Invited Lecturer at summer school on Glacial Isostatic Adjustment. Delivered lectures and one-to-one tutorials to PhD students, postdocs, and permanent academic staff from around the world, including online participants.
Year(s) Of Engagement Activity 2015
URL http://polenet.org/gia-training-school-application
 
Description School Visit (Durham) 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Schools
Results and Impact Delivered school assembly for ~200 primary school children (including ~30 deaf children) on Antarctica Day, 2017. Talked about living and working in Antarctica, held follow-up Q&A session with the whole school, and separately for Year 2 pupils. Also assisted with a science experiment for Year 4 in which they investigated the insulating properties of of different materials: activity involved measuring the rate at which beakers of hot water gradually cooled.

Separate school visit to county Durham primary school in spring 2018 - similar activities and similar size audience.
Year(s) Of Engagement Activity 2017,2018
 
Description Science talk at Rothera Field Station (Antarctica) 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other audiences
Results and Impact Whilst carrying out fieldwork in Antarctica I delivered a science talk on my research to other scientists and support staff working on the base. The audience comprised the widest mix of people you could think of - chefs, pilots, doctors, plumbers, mountaineers, engineers, divers, biologists, mechanics, as well as a few scientists from my field. These are the people who help deliver Antarctic Science, so I wanted them to understand the importance and the implications of this work. I aimed to pitch the talk at a level that everyone could relate to; it was clear that this aim was achieved as questions extended for over 20 minutes and continued informally for the rest of the evening.
Year(s) Of Engagement Activity 2016