Investigating the influence of sea ice on Antarctic outlet glacier dynamics

Overview

The Antarctic Ice Sheet’s contribution to global mean sea level rise has accelerated over recent decades (The IMBIE Team, 2018). This has largely been caused by a dynamic imbalance from major outlet glaciers in West Antarctica, driven by warm ocean currents (modified Circumpolar Deep Water: mCDW) melting the underside of their floating portions, causing ice marginal thinning, grounding line retreat and increased ice discharge (e.g. Pritchard et al., 2012). Similar processes have also been invoked to explain mass loss in Wilkes Land, East Antarctica (Rignot et al., 2019).

The link between intrusions of mCDW and basal melting beneath ice shelves is undisputed and this process is likely to play a key role in the future sea-level contribution from Antarctica (DeConto et al., 2021). This is because basal melting beneath ice shelves has the potential to reduce their buttressing effect and increase ice discharge from inland (Gudmundsson et al., 2019). However, recent work has also shown that buttressing forces can be provided by sea-ice and/or a mixture of calved icebergs bound together with sea-ice (known as mélange) (e.g. Joughin et al., 2008; Amundson et al., 2010; Robel, 2017). This work has mostly been focussed on outlet glaciers in Greenland, where the presence/absence of sea-ice and mélange have been shown to influence the timing and sequence of calving events, seasonal changes in ice velocity, and longer term patterns of glacier advance/retreat (see review in Carr et al., 2013).

Although likely to be an important control on glacier dynamics, much less work has investigated the buttressing effect of sea-ice/mélange around Antarctica. Here, sea-ice occurs in much larger concentrations than Greenland, and preliminary work suggests that multi-year land-fast sea ice is an important control on major calving events, and the disaggregation/disintegration of floating ice tongues/shelves (e.g. Miles et al., 2017; Arthur et al., 2021; see Figure 1). Moreover, the calving of large icebergs can also feedback and impact on the distribution of sea ice and polynyas (e.g. Massom, 2003). There are also important feedbacks between sea ice and ocean stratification/temperatures, whereby reduced sea ice concentrations can lead to increased intrusions of mCDW (e.g. Miles et al., 2016).

The overall aim of this project is to use remote sensing observations to explore the sensitivity of Antarctic outlet glaciers to variations in sea ice conditions.

The primary research questions are:
• To what extent are outlet glaciers sensitive to variability in sea ice conditions at their termini?
• How do sea ice conditions control the magnitude and periodicity of calving events?
• To what extent do sea ice conditions influence both short-term (seasonal) and longer-term (decadal) variations in velocity?
• Where in Antarctica are glaciers most sensitive to changes in sea ice conditions (both at present and in the future)?

Methodology

The project will initially target a sample of geographically-spread marine-terminating outlet glaciers across Antarctica that are influenced by different sea ice regimes. A variety of remote sensing data (ideally both optical imagery and altimeter data) and secondary datasets will be used to determine changes in frontal position, ice velocity and ice surface elevation over the last few decades (depending on data availability), with annual to sub-annual resolution available from the 2000s, and with even higher temporal resolution for the last few years (e.g. to explore seasonal variations in velocity and frontal position). Temporal trends will then be compared to data on sea-ice conditions derived from both primary and secondary data sources e.g. sea ice concentrations from the Nimbus-7 satellite and Defense Meteorological Satellite Program (DMSP) (Comiso et al., 2014) or the ARTIST Sea ice (ASI) algorithm from Advanced Microwave Scanning Radiometer – EOS (AMSR-E) data (Spreen et al., 2008). Analyses are likely to focus on various aspects of sea ice, such as its presence/absence/concentration and, where available, inferences/measurements of its thickness and rheology/strength. The project will also explore sea surface and sub-surface ocean temperatures from reanalysis products (e.g. the Met Office Haldley Centre EN4 analyses) and, where available, meteorological and ship-based measurements. Evaluation and statistical analysis of these empirical datasets will be used to test hypotheses that seek to explain outlet glacier behaviour in the different regions.

Optionally, and depending on student interests and skills, there is scope to incorporate a numerical modelling element to further explore the buttressing effect of sea ice/mélange and to test/isolate hypothesised controls on outlet glacier dynamics.

Project Timeline

Year 1

Training in Remote Sensing and GIS; review of relevant literature and datasets; collection and analysis of remote sensing datasets and identification of target Antarctic outlet glaciers; attendance at relevant training workshops and summer schools; national conference attendance

Year 2

Collection and analysis of glaciological, atmospheric and oceanic datasets; preparation of manuscript(s); set-up optional numerical modelling and perform idealised experiments to explore sea ice/mélange buttressing

Year 3

Further data collection; preparation of additional manuscript(s); conduct optional modelling experiments of past and future glacier behaviour using numerical modelling; prepare research papers; conference attendance

Year 3.5

Submission of further research papers; further modelling (if required); international conference attendance; compilation and submission of thesis

Training
& Skills

The student will receive both generic and bespoke training in Remote Sensing and GIS, including software such as QGIS and ArcGIS (where required). Numerical modelling skills will be provided via ‘hands-on’ training from the supervisory team, and specific training in Matlab and statistical software (e.g. Stata), supplemented with an internationally-recognised summer school in Karthaus and numerical modelling training workshops (e.g. Úa). Broader transferable skills (e.g. communicating science, media engagement, thesis writing, writing for publication, presentation skills) will be developed through various training events at Durham University offered by IAPETUS2. We anticipate this project will be completed as a series of publications/papers led by the student, under the guidance and supervision of the supervisors.

References & further reading

Arthur, J.F. et al. (2021) The triggers of the disaggregation of Voyeykov Ice Shelf (2007), Wilkes Land, East Antarctica, and its subsequent evolution. Journal of Glaciology 67(265), 933–951.
Carr, J.R., Stokes, C.R. & Vieli, A. (2013) Recent progress in understanding marine-terminating Arctic outlet glacier response to climatic and oceanic forcing: twenty years of rapid change. Progress in Physical Geography 37, 436-467.
Comiso, J.C. (2014) “Bootstrap Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I-SSMIS, Version 2.” NASA National Snow and Ice Data Center Distributed Active Archive Center, Boulder, CO.
Massom, R.A. (2003) Recent iceberg calving events in the Ninnis Glacier region, East Antarctica. Antarctic Science, 15, 303-313.
DeConto, R.M. et al. (2021) The Paris Climate Agreement and future sea-level rise from Antarctica. Nature 593, 83-89.
Gudmundsson, G.H., Paolo, F.S., Adusumilli, S. & Fricker, H.A. (2019) Instantaneous Antarctic ice sheet mass loss driven by thinning ice shelves. Geophys. Res. Lett. 46, 13,903-13,909.
Joughin, I. et al. (2008) Continued evolution of Jakobshavn Isbrae following its rapid speedup. Journal of Geophysical Research 113: F04006.
Miles, A.W.J., Stokes, C.R. & Jamieson, S.S.R. (2016) Pan-ice sheet glacier terminus change in East Antarctica reveals sensitivity of Wilkes Land to sea-ice changes. Sci. Adv., 2 (5), e1501350.
Miles A.W.J., Stokes, C.R. & Jamieson S.S.R. (2017) Simultaneous disintegration of outlet glaciers in Porpoise Bay (Wilkes Land), East Antarctica, driven by sea ice break-up. Cryosphere 11(1), 427–442.
Pritchard, H.D. et al. (2012) Antarctic ice-sheet loss driven by basal melting of ice shelves. Nature 484, 502-505.
Rignot et al. (2019) Four decades of Antarctic Ice Sheet mass balance from 1979-2017. Proceedings of the National Academy of Sciences, 116 (4), 1095-1103.
Robel, A. (2017) Thinning sea ice weakens buttressing force of iceberg mélange and promotes calving. Nature Communications, 8: 14596.
Spreen, G., Kaleschke, L. & Heygster, G. (2008) Sea ice remote sensing using AMSR-E 89-GHz channels. Journal of Geophysical Research: Oceans 13(2), 1–14.
The IMBIE Team (2018) Mass balance of the Antarctic Ice Sheet from 1992 to 2017. Nature 558, 219-222.

Further Information

Professor Chris R. Stokes
Durham University
E-mail: c.r.stokes@durham.ac.uk
Tel. 0191 334 1955

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