About
284
Publications
52,819
Reads
How we measure 'reads'
A 'read' is counted each time someone views a publication summary (such as the title, abstract, and list of authors), clicks on a figure, or views or downloads the full-text. Learn more
12,621
Citations
Introduction
I am Professor of Polar Geodesy, University of Tasmania. My field of expertise is geodetic observation of the global water cycle, including ice sheet mass balance and sea level change and particularly using the Global Positioning System (GPS) and the Gravity Recovery and Climate Experiment (GRACE). I also work on reduction of systematic and random errors in these techniques in order to maximise the information content in the data and improve the reliability of the interpretations.
Additional affiliations
September 2012 - present
August 2001 - December 2013
Education
February 1998 - August 2002
Publications
Publications (284)
Antarctica's contribution to global sea-level rise (SLR) is deeply uncertain, with subglacial water suspected to play a critical role, yet its impact remains unclear. We demonstrate that water at the base of ice sheets influences sliding behavior and that its exclusion from models can underestimate SLR projections and delay the predicted onset of t...
Plain Language Summary
Previous research linked the recent salinity increase in the western Ross Sea to weakened easterly winds from the Amundsen Sea. However, insufficient observations limit the further investigation of the linkage and underlying mechanisms between atmospheric forcing and shelf water salinity changes. In this study, we use a globa...
We explore the links between elevation variability of the Antarctic Ice Sheet (AIS) and large-scale climate modes. Using multiple linear regression, we quantify the time-cumulative effects of El Niño Southern Oscillation (ENSO) and the Southern Annular Mode (SAM) on gridded AIS elevations. Cumulative ENSO and SAM explain a median of 29% of the part...
Plain Language Summary
This study investigates how variations in the height of the Antarctic Ice Sheet (AIS) are connected to large‐scale climate patterns. We used a statistical method to measure the effects of two climate phenomena: El Niño Southern Oscillation (ENSO) and the Southern Annular Mode (SAM). We found that the cumulative effects of the...
We developed an enhanced Kalman‐based approach to quantify abrupt changes and significant non‐linearity in vertical land motion (VLM) along the coast of Chile and the Antarctic Peninsula using a combination of multi‐mission satellite altimetry (ALT), tide gauge (TG), and GPS data starting from the early 1990s. The data reveal the spatial variabilit...
We explore the links between elevation variability of the Antarctic Ice Sheet (AIS) and large-scale climate modes. Using multiple linear regression, we quantify the cumulative effects of El Nino Southern Oscillation (ENSO) and the Southern Annular Mode (SAM) on gridded AIS elevations. Cumulative ENSO and SAM explain a median of 29% of the partial v...
In recent sea level studies, discrepancies have arisen in ocean mass observations obtained from the Gravity Recovery and Climate Experiment and its successor, GRACE Follow-On, with GRACE estimates consistently appearing lower than density-corrected ocean volume observations since 2015. These disparities have raised concerns about potential systemat...
Multiple datasets show the Antarctic Ice Sheet has lost mass over recent decades and therefore contributed to sea-level rise. Short-term variability in ice mass has been associated partly with El Niño/Southern Oscillation (ENSO), for both the grounded ice sheet and its bounding ice shelves, but a connection with the Southern Annular Mode—the domina...
Large earthquakes in the vicinity of Antarctica have the potential to cause postseismic viscoelastic deformation affecting measurements of displacement that are used to constrain models of glacial isostatic adjustment (GIA). In November 2013, a Mw 7.7 strike‐slip earthquake occurred in the Scotia Sea, 650 km from the Antarctic Peninsula. GPS time s...
Intense atmosphere-ocean-ice interactions in the Ross Sea play a vital role in global overturning circulation by supplying saline and dense shelf waters. Since the 1960s, freshening of the Ross Sea shelf water has led to a decline in Antarctic Bottom Water formation. Since the early 2010s, however, the salinity of the western Ross Sea has rebounded...
While satellite altimeters have revolutionized ocean science, validation measurements in high wave environments are rare. Using geodetic Global Navigation Satellite System (GNSS) data collected from the Southern Ocean Flux Station (SOFS, −47°S, 142°E) since 2019, as part of the Southern Ocean Time Series (SOTS), we present a validation of satellite...
We seek to quantify and understand the residual signal in GPS and GLONASS estimates of ocean tide loading displacements (OTLDs) after removing state-of-the-art model estimates. To consider contributions over a broad spatial scale, we estimate OTLD over the Australian continent using $$\sim $$ ∼ 5.5 years of continuous GPS and GLONASS data from 360...
In preparation for validation of the swath-based altimetry mission (Surface Water Oceanography Topography, SWOT), we developed a buoy array, equipped with Global Navigation Satellite System/Inertial Navigation System, capable of accurately observing sea surface height (SSH), wave information and tropospheric delay. Here we present results from an 8...
GNSS equipped buoys remain an important tool in altimetry validation. Progressive advances in altimetry missions require associated development in such validation tools. In this paper, we enhanced an existing buoy approach and gained further understanding of the buoy dynamics based on in situ observations. First, we implemented the capability to se...
We further developed a space–time Kalman approach to investigate time-fixed and time-variable signals in vertical land motion (VLM) and residual altimeter systematic errors around the Australian coast, through combining multi-mission absolute sea-level (ASL), relative sea-level from tide gauges (TGs) and Global Positioning System (GPS) height time...
We know that systematic errors can affect performance (so-called bias drift)…➢ Studies estimating bias drift assume VLM@ TGs is known (via GIA or GPS)…➢ Studies estimating VLM from altimetry assume bias drift is zero (or use global values)…➢ Studies estimating bias drift or VLM, apply a linear regression to derive the unknown quantities…
The East Antarctic Ice Sheet contains the vast majority of Earth’s glacier ice (about 52 metres sea-level equivalent), but is often viewed as less vulnerable to global warming than the West Antarctic or Greenland ice sheets. However, some regions of the East Antarctic Ice Sheet have lost mass over recent decades, prompting the need to re-evaluate i...
Tides influence basal melting of individual Antarctic ice shelves, but their net impact on Antarctic-wide ice–ocean interaction has yet to be constrained. Here we quantify the impact of tides on ice shelf melting and the continental shelf seas using a 4 km resolution circum-Antarctic ocean model. Activating tides in the model increases the total ba...
We present a finite-element model of post-seismic solid Earth deformation built in the software package Abaqus (version 2018). The model is global and spherical, includes self-gravitation and is built for the purpose of calculating post-seismic deformation in the far field (>∼300 km) of major earthquakes. An earthquake is simulated by prescribing s...
Plain Language Summary
The bedrock around the Antarctic Ice Sheet is moving in response to past and present changes in the weight of the ice sheet. Identifying the response to past ice‐sheet changes (since ∼20,000 years ago) is important since it is an important correction to satellite measurements used to obtain present‐day changes of the ice shee...
In Antarctica, Global Positioning System (GPS) vertical time series exhibit non‐linear signals over a wide range of temporal scales. To explain these non‐linearities, a number of hypotheses have been proposed, among them the short‐term rapid solid Earth response to contemporaneous ice mass change. Here we use GPS vertical time series to reveal the...
We constrain viscoelastic Earth rheology and recent ice‐mass change in the northern Marguerite Bay region of the Antarctic Peninsula. Global Positioning System (GPS) time series from Rothera and San Martin stations show bedrock uplift range of ∼−0.8–1.8 mm/year over 1999–2005 and 2016–2020 but ∼3.5–6.0 mm/year over ∼2005–2016. Digital elevation mod...
We further developed a space-time Kalman approach to estimate time-variable signals in residual altimeter systematic errors and vertical land motion (VLM) around the Australian coast since the 1990s, through combining multi-mission absolute sea-level (ASL), relative sea-level (RSL) from tide gauges (TGs) and GPS heights records. Our results confirm...
Accurate measurement of the local component of geodetic motion at GPS stations presents a challenge due to the need to separate this signal from the tectonic plate rotation. A pressing example is the observation of glacial isostatic adjustment (GIA) which constrains the Earth's response to ice unloading, and hence, contributions of ice-covered regi...
Physical processes within geoscientific models are sometimes described by simplified schemes known as parameterisations. The values of the parameters within these schemes can be poorly constrained by theory or observation. Uncertainty in the parameter values translates into uncertainty in the outputs of the models. Proper quantification of the unce...
Vertical land motion (VLM) is the connection between absolute sea‐level (ASL) from a satellite altimeter (ALT) and relative sea‐level from a tide gauge (TG). VLM is often sparsely observed yet is required for understanding sea‐level rise. Many studies have sought to exploit ALT and TG data to infer VLM, yet regionally correlated systematic errors i...
Plain Language Summary
The solid Earth changes shape due to the changing weight of the ocean as the ocean tides rise and fall. Measuring this change and comparing it to predictions can yield insights into the interior properties of the Earth, tens to hundreds of kilometers below the surface. We used GPS to measure the changing shape of New Zealand...
Simple fault models predict earthquake nucleation near the eventual hypocenter (self-nucleation). However, some earthquakes have migratory foreshocks and possibly slow slip that travel large distances toward the eventual mainshock hypocenter (migratory nucleation). Scarce observations of migratory nucleation may result from real differences between...
Within the past 125,000 years, variations in Earth’s climate have resulted in global sea levels fluctuating from 130 to 140 m lower than present day to 6 to 9 m higher. Presently, global mean sea level is rising at its fastest rate in the past 6000 years (at ~ 3.6 mm/year for 2006–2015) and is accelerating. In this chapter, we discuss both the caus...
Physical processes within geoscientific models are sometimes described by simplified schemes known as parameterisations. The values of the parameters within these schemes can be poorly constrained by theory or observation. Uncertainty in the parameter values translates into uncertainty in the outputs of the models. Proper quantification of the unce...
The Antarctic Ice Sheet (AIS) is out of equilibrium with the current anthropogenic‐enhanced climate forcing. Paleoenvironmental records and ice sheet models reveal that the AIS has been tightly coupled to the climate system during the past and indicate the potential for accelerated and sustained Antarctic ice mass loss into the future. Modern obser...
Ground displacements due to ocean tide loading have previously been successfully observed using Global Positioning System (GPS) data, and such estimates for the principal lunar M2 constituent have been used to infer the rheology and structure of the asthenosphere. The GPS orbital repeat period is close to that of several other major tidal constitue...
Global Navigation Satellite System (GNSS)-equipped buoys have a fundamental role in the validation of satellite altimetry. Requirements to validate next generation altimeter missions are demanding and call for a greater understanding of the systematic errors associated with the buoy approach. In this paper, we assess the present-day buoy precision...
Accurate measurement of the local component of geodetic motion at GPS stations presents a challenge due to the need to separate this signal from the tectonic plate rotation. A pressing example is the observation of glacial isostatic adjustment (GIA) which constrains the Earth’s response to ice unloading, and hence, contributions of ice-covered regi...
We consider the viscoelastic rheology of the solid Earth under the Antarctic Peninsula due to ice mass loss that commenced after the breakup of the Larsen-B ice shelf. We extend the previous analysis of nearby continuous GPS time-series to include five additional years and the additional consideration of the horizontal components of deformation. Th...
Tides influence basal melting of individual Antarctic ice shelves, but their net impact on Antarctic-wide ice-ocean interaction has yet to be constrained. Here we quantify the impact of tides on ice shelf melting and the continental shelf seas by means of a 4 km resolution circum-Antarctic ocean model. Activating tides in the model increases the to...
Tides influence basal melting of individual Antarctic ice shelves, but their net impact on Antarctic-wide ice-ocean interaction has yet to be constrained. Here we quantify the impact of tides on ice shelf melting and the continental shelf seas by means of a 4 km resolution circum-Antarctic ocean model. Activating tides in the model increases the to...
We present a finite-element model of postseismic solid Earth deformation built in the software package ABAQUS (version 2018). The model is global and spherical, and includes self-gravitation and is built for the purpose of calculating postseismic deformation in the far-field (> ~ 300 km) of major earthquakes. An earthquake is simulated by prescribi...
Plain Language Summary
The rate of snowfall in Antarctica varies over months to millennia. Snowfall is expected to increase over coming decades as the climate warms and evaporates more water from the Southern Ocean and then falls as snow. The question we focus on is “when can we be sure a new trend has emerged?”. To help answer this question we exa...
Understanding the processes involved in basal melting of Antarctic ice shelves is important to quantify the rate at which Antarctica will lose mass. Current research of of ice shelf-ocean interaction is almost exclusively guided by satellite derived estimates of Antarctic-wide ice shelf melting, which highlight deep warm water intrusions and meltin...
Mass loss from the Antarctic ice sheet is sensitive to conditions in ice shelf grounding zones, the transition between grounded and floating ice. To observe tidal dynamics in the grounding zone, we moored an ocean pressure sensor to Ross Ice Shelf, recording data for 54 days. In this region the ice shelf is brought out of hydrostatic equilibrium by...
We present a new, open-source viscoelastic solid earth deformation model, Elmer/Earth. Using the multi-physics finite-element package Elmer, a model to compute viscoelastic material deformation has been implemented into the existing linear elasticity solver routine. Unlike approaches often implemented in engineering codes, our solver accounts for t...
Ground displacements due to ocean tide loading have previously been successfully observed using GPS data, and such estimates for the principal lunar M2 constituent have been used to infer the rheology and structure of the asthenosphere. The GPS orbital repeat period is close to several other major tidal constituents (K1, K2, S2) thus GPS-estimates...
The secular rate of Australia's vertical surface deformation due to past ice‐ocean loading changes is not consistent with present vertical velocities observed by a previously sparse network of Global Positioning System (GPS) sites. Current understanding of the Earth's rheology suggests that the expected vertical motion of the crust should be close...
We show the results from the analysis of 2 MultiGNSS datasets: UK (21 stations) and NZ (77 stations). We assessed the possible PPP processing strategies: GPS-only, GLONASS-only and GPS+GLONASS for recovery of eight major OTL constituents.
Our results suggest that no single strategy provides consistently better constituent estimates across all coor...
Recent studies suggest that Antarctica has the potential to contribute up to ~15 m of sea-level rise over the next few centuries. The evolution of the Antarctic Ice Sheet is driven by a combination of climate forcing and non-climatic feedbacks. In this review we focus on feedbacks between the Antarctic Ice Sheet and the solid Earth, and the role of...
Abstract. We present a new, open source visco-elastic Earth-deformation model, Elmer/Earth. Using the multi-physics Finite Element package Elmer, a model to compute visco-elastic material deformation has been implemented into the existing linear elasticity solver routine. Unlike approaches often implemented in engineering codes, our solver accounts...
Satellite altimetry provides the ongoing sea level climate data record that provides evidence for one of the most significant manifestations of climate change on Earth. External and independent validation of satellite altimetry is a core component of mission design, providing confidence in such a seminal climate record. The global tide gauge networ...
The Antarctic Ice Sheet (AIS) holds the largest potential source of sea-level rise in a warming world. Remote sensing observations of the change in AIS mass reveals that it is only just beginning to respond to anthropogenic climate warming. Estimates of AIS contribution to sea-level rise to the year 2100 have continued to evolve since the Intergove...
Developing a hybrid approach for Ocean Tide Loading constituents extraction with GPS and GLONASS. We focus on 8 major constituents showing that extraction of K1 and K2 from GLONASS-only with the rest of constituents from GPS+GLONASS returns minimized OTL residuals. Also, we assessed the impact of integer ambiguity resolution and the effect from inc...
Antarctica is often associated with images of masculine figures battling against the blizzard. The pervasiveness of heroic white masculine leadership and exploration in Antarctica and, more broadly, in Science, Technology, Engineering, Mathematics, and Medicine (STEMM) research cultures, has meant women have had lesser access to Antarctic research...
Spatially correlated common mode error (CME) always exists in regional, or-larger, global positioning system (GPS) networks. We applied independent component analysis (ICA) to GPS vertical coordinate time-series in Antarctica from 2010 to 2014 and made a comparison with the principal component analysis (PCA). Using PCA/ICA, the time-series can be d...
Many glaciers in the Antarctic Peninsula are now rapidly losing mass. Understanding of the dynamics of these fast-flowing glaciers, and their potential future behaviour, can be improved through ice sheet modelling studies. Inverse methods are commonly used in ice sheet models to infer the spatial distribution of a basal friction coefficient, which...
The Wordie Ice Shelf–Fleming Glacier system in the southern Antarctic Peninsula has experienced a long-term retreat and disintegration of its ice shelf in the past 50 years. Increases in the glacier velocity and dynamic thinning have been observed over the past two decades, especially after 2008 when only a small ice shelf remained at the Fleming G...
Marine-terminating ice sheets are of interest due to their potential instability, making them vulnerable to rapid retreat. Modelling the evolution of glaciers and ice streams in such regions is key to understanding their possible contribution to sea level rise. The friction caused by the sliding of ice over bedrock and the resultant shear stress ar...