Spatial and Temporal Changes in Marine-terminating Glaciers on the Antarctic Peninsula since the ...

350 Pages·2015·15.44 MB·English

Spatial and Temporal Changes in Marine-terminating
Glaciers on the Antarctic Peninsula since the 1940s

Alison Joan Cook

Submitted in fulfilment of the requirements for the Degree of Doctor of Philosophy

College of Science
Swansea University

November 2014

The candidate confirms that the work submitted is her own and that appropriate credit
has been given where reference has been made to the work of others.
This copy has been supplied on the understanding that it is copyright material and that no
quotation from the thesis may be published without proper acknowledgement.

DECLARATION

This work has not previously been accepted in substance for any degree and is not being
concurrently submitted in candidature for any degree.

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Date ........................................................................

STATEMENT 1

This thesis is the result of my own investigations, except where otherwise stated. Where
correction services have been used, the extent and nature of the correction is clearly
marked in a footnote(s).

Other sources are acknowledged by footnotes giving explicit references. A bibliography
is appended.

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I hereby give consent for my thesis, if accepted, to be available for photocopying and for
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Abstract
The numerous glaciers on the Antarctic Peninsula are highly sensitive to environmental
changes, with potential to make a significant contribution to sea-level rise, and yet they
have been distinctly under studied. An absence of fundamental details on glacier
characteristics and behaviour is due in part to the inaccessibility of the region. In this
research, the production of a new topographic model and an inventory of 1590 glacier
drainage basins between 63-70° S have enabled detailed analysis of these glaciers for the
first time.
Area change measurements since the 1940s reveal that 90% of the 860 marine-
terminating glaciers have retreated. Greatest glacier area loss has occurred in the north-
east, primarily due to the demise of ice shelves. In the west, an increasing gradient of
overall ice loss from north to south is observed, as well as a distinct region in the north-
west where glaciers have remained stable. There are also clear trends over time, such as
reduction in glacier retreat rates in the late 1980s, and acceleration in retreat since the late
1990s. These statistically significant trends indicate that there are external control factors
currently outweighing local glaciological controls on glacier extent.
Analysis of atmospheric and ocean temperature data reveals that, to the west of the
peninsula, patterns in ocean temperatures have a strong synchroneity with glacier area
change. An increasing ocean temperature gradient from north to south, which strengthens
with depth, is closely correlated with glacier front changes. Furthermore, a warming at
mid ocean depths has occurred since the 1990s. This research suggests that although the
atmosphere is rapidly warming, melt by the ocean is the primary cause of glacier retreat
along the western peninsula. With persistent warm ocean temperatures, glacier retreat
and associated mass loss is set to continue, leading to an increasing contribution to sea-
level rise.

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Acknowledgements
This project was funded by the AXA Research Fund. The AXA global financial
protection group is interested in supporting risk-related climate research and I’m very
grateful to them for the award that facilitated this research.
My supervisors Professor Tavi Murray and Professor Adrian Luckman within the
Glaciology Group at Swansea University, and Professor David Vaughan at the British
Antarctic Survey (BAS), have given me support throughout the project and I’d like to
thank them very much for their valuable expertise and helpful advice.
I’m also extremely grateful to a number of scientists who were happy to contribute their
data to this research. In particular, I’d like to thank Dr Paul Holland (BAS) for providing
the ocean temperature data and for discussion of ideas. Thanks to Dr Nick Barrand
(previously at BAS, now at Birmingham University) for providing temperature records
and melt duration data, as well as DEMs for accuracy tests. Thanks to Dr J. Comiso
(Cryospheric Sciences Laboratory, NASA) for providing his surface temperature gridded
data and Dr J. Lenaerts (Institute for Marine and Atmospheric research, Utrecht
University) for his modelled surface mass balance data. Credit is given to them where
appropriate within the thesis. I’m also grateful to the USGS and BAS for permission to
use the data that I produced during my involvement with the Coastal-Change and
Glaciological Maps of Antarctica programme prior to the PhD.
I have had two fantastic work experience assistants who helped out with the some of the
more laborious tasks in this project. Anna Weissenmayer spent 2 weeks in July 2011
digitising glacier fronts from recent satellite imagery, and Anneka France worked for 6
weeks in July/Aug 2012 editing the GIS database. I’ve also had invaluable emergency
help with IT related issues from Steve Shaw.
Finally, I’d like to say thanks to the Swansea Glaciology Group as well as friends and
colleagues at BAS for support and helpful discussions, and to friends and family who
have spurred me on throughout the past four years!
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Contents
Abstract ............................................................................................................................................ v
Acknowledgements ........................................................................................................................ vii
Contents .......................................................................................................................................... ix
Tables ............................................................................................................................................. xv
Figures ......................................................................................................................................... xvii
Abbreviations ................................................................................................................................ xxi
CHAPTER 1
INTRODUCTION AND AIMS
1.1 Motivation ................................................................................................................... 1
1.2 Aims ............................................................................................................................ 3
1.3 Thesis structure ........................................................................................................... 4
1.4 Published material ....................................................................................................... 5
CHAPTER 2
THE ANTARCTIC PENINSULA ICE SHEET AND CLIMATE CHANGE
2.1 Introduction ................................................................................................................. 7
2.2 Glaciology of the Antarctic Peninsula ........................................................................ 8
2.2.1 History of the AP Cryosphere ............................................................................... 10
2.2.1.1 The Last Glacial Maximum .............................................................................. 10
2.2.1.2 The Cryosphere since the early Holocene ......................................................... 11
2.2.2 Mass balance of the APIS ..................................................................................... 15
2.2.2.1 Mass estimates .................................................................................................. 15
2.2.2.2 Sea-level rise ..................................................................................................... 16
2.2.2.3 Surface mass balance ........................................................................................ 16
2.2.3 Ice Shelves and Glaciers on the AP ...................................................................... 18
2.2.3.1 Ice shelves ......................................................................................................... 18
2.2.3.2 Glaciers ............................................................................................................. 24
2.3 Recent changes in the climate and ocean around the AP .......................................... 32
2.3.1 Climate .................................................................................................................. 32
2.3.1.1 Air Temperature ................................................................................................ 33
2.3.1.2 Surface melt ...................................................................................................... 35
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2.3.1.3 Sea-ice ............................................................................................................... 37
2.3.1.4 Precipitation ....................................................................................................... 38
2.3.2 Ocean ..................................................................................................................... 40
2.3.2.1 West Antarctic Peninsula .................................................................................. 41
2.3.2.2 Weddell Sea Sector............................................................................................ 44
2.3.3 Ocean-Atmosphere Interactions ............................................................................ 45
2.4 Global glacier monitoring and applications to the AP .............................................. 47
2.4.1 Mass balance monitoring ....................................................................................... 48
2.4.2 Glacier-length monitoring ..................................................................................... 49
2.5 Summary ................................................................................................................... 51
CHAPTER 3
A NEW DIGITAL ELEVATION MODEL FOR ANTARCTIC PENINSULA GLACIOLOGY
3.1 Introduction ............................................................................................................... 55
3.2 Digital Elevation Models for glaciological applications ........................................... 56
3.3 High resolution gridded elevation datasets for the Antarctic Peninsula .................... 59
3.4 ASTER GDEM: limitations and potential for use in the AP ..................................... 62
3.5 DEM correction methodology ................................................................................... 65
3.5.1 An alternative approach to ASTER GDEM correction ......................................... 65
3.5.2 ASTER GDEM improvement procedure .............................................................. 67
3.6 Error analysis ............................................................................................................. 71
3.6.1 Vertical accuracy ................................................................................................... 72
3.6.1.1 Absolute vertical accuracy ................................................................................ 72
3.6.1.2 Vertical accuracy for corrected vs. uncorrected regions ................................... 76
3.6.1.3 Vertical accuracy according to slope ................................................................. 77
3.6.2 Horizontal accuracy ............................................................................................... 79
3.6.2.1 Horizontal accuracy based on GPS points and a photogrammetric DEM ......... 80
3.6.2.2 Relative accuracy and consistency tests using SPIRIT DEMs .......................... 81
3.6.2.3 Horizontal differences from the Landsat Image Mosaic of Antarctica ............. 83
3.6.3 Methodology errors ............................................................................................... 84
3.7 Summary ................................................................................................................... 85