L3 – Pine Island Glacier
Pine Island Glacier – did we solve it?
Andrew Shepherd
University of Edinburgh
ESA Summer School 2006
L3 – Pine Island Glacier
Cryosphere & climate
IPCC Assessment reports (1990, 1995, 2001)
Global warming
IPCC, 2001
ESA Summer School 2006
Cryosphere & climate
L3 – Pine Island Glacier
IPCC Assessment reports (1990, 1995, 2001)
0.6 °C rise since 1900
Global warming
IPCC, 2001
ESA Summer School 2006
L3 – Pine Island Glacier
Cryosphere & climate
IPCC Assessment reports (1990, 1995, 2001)
Global sea level rise
IPCC, 2001
ESA Summer School 2006
L3 – Pine Island Glacier
Cryosphere & climate
IPCC Assessment reports (1990, 1995, 2001)
15 cm rise since 1900
Global sea level rise
IPCC, 2001
ESA Summer School 2006
Cryosphere & climate
L3 – Pine Island Glacier
IPCC Assessment reports (1990, 1995, 2001)
According to tide gauges,
global sea levels have risen
by 1.5 mm per year during
the 20th century
This rise is ten times
greater than at any other
time during the past 3000
years
ESA Summer School 2006
L3 – Pine Island Glacier
Cryosphere & climate
IPCC Assessment reports (1990, 1995, 2001)
Known sources include:
ESA Summer School 2006
L3 – Pine Island Glacier
Cryosphere & climate
IPCC Assessment reports (1990, 1995, 2001)
Known sources include:
Ocean expansion (0.5 mm)
ESA Summer School 2006
L3 – Pine Island Glacier
Cryosphere & climate
IPCC Assessment reports (1990, 1995, 2001)
Known sources include:
Ocean expansion (0.5 mm)
Glaciers (0.3 mm)
ESA Summer School 2006
L3 – Pine Island Glacier
Cryosphere & climate
IPCC Assessment reports (1990, 1995, 2001)
Known sources include:
Ocean expansion (0.5 mm)
Glaciers (0.3 mm)
Ice sheets (0.2 mm)
ESA Summer School 2006
L3 – Pine Island Glacier
Cryosphere & climate
IPCC Assessment reports (1990, 1995, 2001)
Known sources include:
Ocean expansion (0.5 mm)
Glaciers (0.3 mm)
Ice sheets (0.2 mm)
Rivers (-0.3 mm)
ESA Summer School 2006
Cryosphere & climate
L3 – Pine Island Glacier
IPCC Assessment reports (1990, 1995, 2001)
Known sources include:
Ocean expansion (0.5 mm)
Glaciers (0.3 mm)
Ice sheets (0.2 mm)
Rivers (-0.3 mm)
► In 2001, only 50 % of
measured rise explained by
central estimates
ESA Summer School 2006
Cryosphere & climate
L3 – Pine Island Glacier
IPCC Assessment reports (1990, 1995, 2001)
Known sources include:
Ocean expansion (0.5 mm)
Glaciers (0.3 mm)
Ice sheets (0.2 mm)
Rivers (-0.3 mm)
► In 2001, only 50 % of
measured rise explained by
central estimates
ESA Summer School 2006
Cryosphere & climate
L3 – Pine Island Glacier
IPCC Assessment reports (1990, 1995, 2001)
21st C projection (2 x CO2):
Ocean expansion (× 3)
Glaciers (× 3/4)
Ice sheets (× 1/2)
Rivers (?)
IPCC, 2001
ESA Summer School 2006
Cryosphere & climate
L3 – Pine Island Glacier
IPCC Assessment reports (1990, 1995, 2001)
21st C projection (2 x CO2):
Ocean expansion (× 3)
Glaciers (× 3/4)
Ice sheets (× 1/2)
Rivers (?)
► ~ 0.5 m total sea level rise
IPCC, 2001
► Major contribution is ocean
expansion
ESA Summer School 2006
Cryosphere & climate
L3 – Pine Island Glacier
UK today
ESA Summer School 2006
Cryosphere & climate
L3 – Pine Island Glacier
UK today
No Polar
Ice Sheets
ESA Summer School 2006
L3 – Pine Island Glacier
Antarctica & sea level
Water cycle
ESA Summer School 2006
Antarctica & sea level
L3 – Pine Island Glacier
West Antarctic Ice Sheet
East Antarctic Ice Sheet
ESA Summer School 2006
L3 – Pine Island Glacier
Antarctica & sea level
EAIS
WAIS
ESA Summer School 2006
L3 – Pine Island Glacier
Antarctica & sea level
Continental
Marine
ESA Summer School 2006
L3 – Pine Island Glacier
Antarctica & sea level
ESA Summer School 2006
L3 – Pine Island Glacier
Antarctica & sea level
Continental
Marine
Geometry of marine based
ice sheets are unstable to
advance or retreat – either
event would be accelerating
ESA Summer School 2006
Antarctica & sea level
L3 – Pine Island Glacier
Weddell Sea
West Antarctica is drained
through three sectors
Amundsen
Sea
Ross Sea
ESA Summer School 2006
L3 – Pine Island Glacier
Antarctica & sea level
Amundsen
Only Amundsen Sea sector
Sea
has no ice shelf barrier and is
grounded below sea level
ESA Summer School 2006
L3 – Pine Island Glacier
Antarctic mass balance
1992-2004
35 day repeat
ERS footprint ~ 10 km
Orbit limit ~ 81.5°
Density ∝ latitude
ESA Summer School 2006
L3 – Pine Island Glacier
Antarctic mass balance
1992-2004
35 day repeat
ERS footprint ~ 10 km
Orbit limit ~ 81.5°
Density ∝ latitude
Trends ~ ±20 cm yr-1
ESA Summer School 2006
L3 – Pine Island Glacier
Antarctic mass balance
ESA Summer School 2006
L3 – Pine Island Glacier
Antarctic mass balance
Strong thinning
ESA Summer School 2006
Antarctic mass balance
L3 – Pine Island Glacier
Isostatic
uplift
Elevation
change
Surface
accumulation
Firn
densification
Ice
divergence
Basal
accumulation
ESA Summer School 2006
Antarctic mass balance
L3 – Pine Island Glacier
Isostatic
uplift
Elevation
change
Surface
accumulation
Firn
densification
Ice
divergence
Basal
accumulation
Elevation trends are due to either snowfall or ice flow
ESA Summer School 2006
L3 – Pine Island Glacier
Antarctic mass balance
Snowfall typically fluctuates about a long term mean on
decadal timescales by ~ 25 %
ESA Summer School 2006
L3 – Pine Island Glacier
Antarctic mass balance
On average, Amundsen
Sea sector has deflated by
7 cm yr-1
Snowfall variability is 6
cm yr-1
Although mean deflation
is comparable to snowfall
variability, signal is highly
coherent and peak rate is
50 times greater
ESA Summer School 2006
L3 – Pine Island Glacier
Amundsen Sea
Amundsen Sea Sector is
40 % of WAIS
Drained by the Pine
Island, Thwaites, and
Smith glaciers
Ice volume sufficient to
raise sea levels by 1.1 m
ESA Summer School 2006
Amundsen Sea
L3 – Pine Island Glacier
Deflation is highly correlated with ice flow
Elevation change (m / year)
-3
0
Ice speed (km / year)
0
2.5
ESA Summer School 2006
L3 – Pine Island Glacier
Pine Island Glacier
Deflation peaks at 3 m yr-1 at grounding line, and extends 200 km inland
ESA Summer School 2006
L3 – Pine Island Glacier
Pine Island Glacier
Consistent with InSAR grounding line retreat
Rignot, Science, 1998
ESA Summer School 2006
Pine Island Glacier
L3 – Pine Island Glacier
Consistent with 20 % glacier acceleration
Joughin et al, GRL, 2003
ESA Summer School 2006
Origin of imbalance?
L3 – Pine Island Glacier
Geothermal
Shepherd
External
Ocean
Deglaciation
Bindschadler
Surge
Huybrechts
Post
Internal
ESA Summer School 2006
Origin of imbalance?
L3 – Pine Island Glacier
Geothermal
Ocean
Deglaciation
Surge
X
No activity
Shepherd
External
Bindschadler
Huybrechts
Post
Internal
ESA Summer School 2006
Origin of imbalance?
L3 – Pine Island Glacier
Geothermal
Ocean
Deglaciation
X
X
No activity
Shepherd
External
Surge
Too fast
Bindschadler
Huybrechts
Post
Internal
ESA Summer School 2006
Origin of imbalance?
L3 – Pine Island Glacier
Geothermal
Ocean
Deglaciation
X
X
No activity
Shepherd
External
Surge
X
Too fast
Bindschadler
Separate
geometries
Huybrechts
Post
Internal
ESA Summer School 2006
Simulated perturbation of PIG
L3 – Pine Island Glacier
~ 3d model of PIG stress regime (longitudinal, lateral, vertical, gravitational)
Glen’s flow law
Simplify by assuming down-stream component of velocity dominates
Equations solved numerically by finite differences
zero traction
zero velocity
viscous slip law τ = β2u
force balance
ESA Summer School 2006
L3 – Pine Island Glacier
Retreat of
GL by 5 and
10 km,
decrease ice
plain traction
by 50%
Instant
response is
thinning up to
70 km from
GL
Simulated perturbation of PIG
Standard expt.
Observed thinning rate
Insufficient
to explain
observed
rates inland
Payne et al., 2004
ESA Summer School 2006
L3 – Pine Island Glacier
Simulated perturbation of PIG
Introduce timedependence
2d verticallyintegrated model
0 years
Assumes vertical
shear minimal
Dynamic
boundary conditions
at shelf front
Glen’s flow law
Thickness
evolution from ice
flow perturbations
ESA Summer School 2006
L3 – Pine Island Glacier
Simulated perturbation of PIG
Introduce timedependence
2d verticallyintegrated model
2 years
Assumes vertical
shear minimal
Dynamic
boundary conditions
at shelf front
Glen’s flow law
Thickness
evolution from ice
flow perturbations
ESA Summer School 2006
L3 – Pine Island Glacier
Simulated perturbation of PIG
Introduce timedependence
2d verticallyintegrated model
4 years
Assumes vertical
shear minimal
Dynamic
boundary conditions
at shelf front
Glen’s flow law
Thickness
evolution from ice
flow perturbations
ESA Summer School 2006
L3 – Pine Island Glacier
Simulated perturbation of PIG
Introduce timedependence
2d verticallyintegrated model
7 years
Assumes vertical
shear minimal
Dynamic
boundary conditions
at shelf front
Glen’s flow law
Thickness
evolution from ice
flow perturbations
ESA Summer School 2006
L3 – Pine Island Glacier
Simulated perturbation of PIG
Introduce timedependence
2d verticallyintegrated model
10 years
Assumes vertical
shear minimal
Dynamic
boundary conditions
at shelf front
Glen’s flow law
Thickness
evolution from ice
flow perturbations
ESA Summer School 2006
L3 – Pine Island Glacier
Simulated perturbation of PIG
Introduce timedependence
2d verticallyintegrated model
15 years
Assumes vertical
shear minimal
Dynamic
boundary conditions
at shelf front
Glen’s flow law
Thickness
evolution from ice
flow perturbations
ESA Summer School 2006
L3 – Pine Island Glacier
Simulated perturbation of PIG
Introduce timedependence
2d verticallyintegrated model
35 years
Assumes vertical
shear minimal
Dynamic
boundary conditions
at shelf front
Glen’s flow law
Thickness
evolution from ice
flow perturbations
ESA Summer School 2006
L3 – Pine Island Glacier
Simulated perturbation of PIG
Introduce timedependence
2d verticallyintegrated model
50 years
Assumes vertical
shear minimal
Dynamic
boundary conditions
at shelf front
Glen’s flow law
Thickness
evolution from ice
flow perturbations
ESA Summer School 2006
L3 – Pine Island Glacier
Simulated perturbation of PIG
Introduce timedependence
2d verticallyintegrated model
150 years
Assumes vertical
shear minimal
Dynamic
boundary conditions
at shelf front
Glen’s flow law
Thickness
evolution from ice
flow perturbations
ESA Summer School 2006
Simulated perturbation of PIG
L3 – Pine Island Glacier
Accumulated thinning matches observed changes inland
Conclude that a reduction in ice thickness at the grounding line is
sufficient to trigger inland thinning
Cumulative thinning (m)
20
15
10
5
after 1 year
after 80 years
after 20 years
after 100 years
after 40 years
after 150 years
after 60 years
0
−5
−10
−15
−50
0
50
100
150
Distance from grounding line (km)
200
250
Payne et al., 2004
ESA Summer School 2006
L3 – Pine Island Glacier
Origin of perturbation
Amundsen Sea glaciers terminate in short
floating ice shelves
● Abbot
● Cosgrove
● Pine Island
● Thwaites
● Crosson
● Dotson
● Getz
ESA Summer School 2006
L3 – Pine Island Glacier
Origin of perturbation
Bathymetry shows deep troughs channel
water to glacier grounding lines
ESA Summer School 2006
L3 – Pine Island Glacier
Origin of perturbation
Pine Island Bay gyre draws water from
continental shelf
ESA Summer School 2006
L3 – Pine Island Glacier
Origin of perturbation
Circumpolar Deep water is 4 C above
freezing point
ESA Summer School 2006
L3 – Pine Island Glacier
Origin of perturbation
Warm CDW infiltrates Pine Island Bay and
reaches glacier grounding lines
● Abbot
● Cosgrove
● Pine Island
● Thwaites
● Crosson
● Dotson
● Getz
ESA Summer School 2006
L3 – Pine Island Glacier
Origin of perturbation
Ice shelf thinning mirrors that of tributary
glaciers
● Abbot
● Cosgrove
● Pine Island
● Thwaites
● Crosson
● Dotson
● Getz
ESA Summer School 2006
L3 – Pine Island Glacier
Origin of perturbation
Thinning is correlated with melt potential of
ocean current (10 m yr-1 C-1)
● Abbot
● Cosgrove
● Pine Island
● Thwaites
● Crosson
● Dotson
● Getz
ESA Summer School 2006
Origin of perturbation
L3 – Pine Island Glacier
2d plume model of ice-ocean interaction
beneath PIG reproduces observed pattern of
steady-state ice melting
10
0
melt rate (m yr-1)
-1 0
-2 0
-3 0
-4 0
-5 0
-6 0
0
20
40
60
D is ta n c e fro m g ro u n d in g lin e (k m )
80
● Abbot
● Cosgrove
● Pine Island
● Thwaites
● Crosson
● Dotson
● Getz
Payne et al, JGR (2006)
ESA Summer School 2006
Origin of perturbation
L3 – Pine Island Glacier
Perturbation experiment shows a 0.5 °C
warming of ocean temperature is sufficient to
cause observed ice shelf thinning
18
17
-1
melt rate (m yr )
17.5
16.5
16
15.5
15
14.5
-0.3
-0.2
-0.1
0
salin ity ch an g e (p p t)
standard
0
0.1
0.2
0.3
tem p . ch an g e (d eg . C )
● Abbot
● Cosgrove
● Pine Island
● Thwaites
● Crosson
● Dotson
● Getz
ESA Summer School 2006
The future
L3 – Pine Island Glacier
PIG
Totten
Thwaites
Cook
Dynamic thinning ongoing
in all submarine sectors
of Antarctica
ESA Summer School 2006
L3 – Pine Island Glacier
The future
Retreat of submarine
glaciers is supposed to be
an accelerating process
ESA Summer School 2006
L3 – Pine Island Glacier
The future
PIG deflation is accelerating
Joughin et al., GRL, 2003
ESA Summer School 2006
L3 – Pine Island Glacier
The future
Ocean temperatures are set to
rise by 1.0 C around Antarctica
ESA Summer School 2006
Summary
L3 – Pine Island Glacier
Amundsen Sea glaciers are losing 30 Gt of ice each year
Equivalent to a sea level contribution of 0.1 mm yr-1
Triggered by ocean currents 0.5°C above freezing
Consistent with rate of global warming during 20th century
All coastal, submarine glaciers in Antarctica are in retreat
PIG retreat has accelerated over last decade
Global oceans set to warm 1°C next century
21st century response not in current sea level projections
ESA Summer School 2006
Summary
L3 – Pine Island Glacier
Amundsen Sea glaciers are losing 30 Gt of ice each year
Equivalent to a sea level contribution of 0.1 mm yr-1
Triggered by ocean currents 0.5°C above freezing
Consistent with rate of global warming during 20th century
All coastal, submarine glaciers in Antarctica are in retreat
PIG retreat has accelerated over last decade
Global oceans set to warm 1°C next century
21st century response not in current sea level projections
ESA Summer School 2006
Summary
L3 – Pine Island Glacier
Amundsen Sea glaciers are losing 30 Gt of ice each year
Equivalent to a sea level contribution of 0.1 mm yr-1
Triggered by ocean currents 0.5°C above freezing
Consistent with rate of global warming during 20th century
All coastal, submarine glaciers in Antarctica are in retreat
PIG retreat has accelerated over last decade
Global oceans set to warm 1°C next century
21st century response not in current sea level projections
ESA Summer School 2006
Summary
L3 – Pine Island Glacier
Amundsen Sea glaciers are losing 30 Gt of ice each year
Equivalent to a sea level contribution of 0.1 mm yr-1
Triggered by ocean currents 0.5°C above freezing
Consistent with rate of global warming during 20th century
All coastal, submarine glaciers in Antarctica are in retreat
PIG retreat has accelerated over last decade
Global oceans set to warm 1°C next century
21st century response not in current sea level projections
ESA Summer School 2006
Summary
L3 – Pine Island Glacier
Amundsen Sea glaciers are losing 30 Gt of ice each year
Equivalent to a sea level contribution of 0.1 mm yr-1
Triggered by ocean currents 0.5°C above freezing
Consistent with rate of global warming during 20th century
All coastal, submarine glaciers in Antarctica are in retreat
PIG retreat has accelerated over last decade
Global oceans set to warm 1°C next century
21st century response not in current sea level projections
ESA Summer School 2006
Summary
L3 – Pine Island Glacier
Amundsen Sea glaciers are losing 30 Gt of ice each year
Equivalent to a sea level contribution of 0.1 mm yr-1
Triggered by ocean currents 0.5°C above freezing
Consistent with rate of global warming during 20th century
All coastal, submarine glaciers in Antarctica are in retreat
PIG retreat has accelerated over last decade
Global oceans set to warm 1°C next century
21st century response not in current sea level projections
ESA Summer School 2006
Summary
L3 – Pine Island Glacier
Amundsen Sea glaciers are losing 30 Gt of ice each year
Equivalent to a sea level contribution of 0.1 mm yr-1
Triggered by ocean currents 0.5°C above freezing
Consistent with rate of global warming during 20th century
All coastal, submarine glaciers in Antarctica are in retreat
PIG retreat has accelerated over last decade
Global oceans set to warm 1°C next century
21st century response not in current sea level projections
ESA Summer School 2006
Summary
L3 – Pine Island Glacier
Amundsen Sea glaciers are losing 30 Gt of ice each year
Equivalent to a sea level contribution of 0.1 mm yr-1
Triggered by ocean currents 0.5°C above freezing
Consistent with rate of global warming during 20th century
All coastal, submarine glaciers in Antarctica are in retreat
PIG retreat has accelerated over last decade
Global oceans set to warm 1°C next century
21st century response not in current sea level projections
ESA Summer School 2006
L3 – Pine Island Glacier
50 % of Antarctic thinning is within 148 km of coast
89 % of coastal 100 km remains unsurveyed
ESA Summer School 2006