Chen

Report
Melting of the Greenland Ice
Sheet
July 8, 2012
40% surface
melt extent
over ice sheet
July 12, 2012
97% surface
melt extent
over ice sheet
Christine Chen
Overview
1Alley,
Alley et al.1
Sundal et al. 2
Topic approach on a
temporal scale
Historical, Mka and
forward
Recent trends, 1993,
1995-1998
Evidence or Data
Paleoclimate records,
supplemented by
modeling efforts
Remote sensing and
modeling
Topic approach on a
spatial scale
Wide, whole ice sheet
considered
Narrow, 6 glaciers in
southwest Greenland
Nature of argument
Applied, inference of
past climate
conditions based on
paleoclimate records
Applied and
theoretical ,
construction of model
to explain physical
mechanisms behind
movement of imagery
Publication type
Literature Review
Traditional Research
R. B., Andrews, J.T ., Brigham-Grette J., Clarke, G.K.C., Cuffey, K. M., Fitzpatrick, J.J., Funder, S., Marshall, S.J., Miller, G.H.,Mitrovica, J.X., Muhs, D.R.
Otto-Bliesner, B.L., Polyak, L., White, J.W.C. History of the Greenland Ice Sheet: paleoclimatic insights. Quaternary Science Review. 29, 1728-1756 (2010).
2Sundal, A. V., Shepard, A., Nienow, P., Hanna, E. Palmer, S., & Huybrechts, P. Melt-induced speed-up of Greenland ice sheet offset by efficient subglacial
drainage. Nature. 469, 521-524 (2011). Doi: 10.1038/nature09740
Overview
1Alley,
Alley et al.1
Sundal et al. 2
Topic approach on a
temporal scale
Historical, Mka and
forward
Recent trends, 1993,
1995-1998
Evidence or Data
Paleoclimate records,
supplemented by
modeling efforts
Remote sensing and
modeling
Topic approach on a
spatial scale
Wide, whole ice sheet
considered
Narrow, 6 glaciers in
southwest Greenland
Nature of argument
Applied, inference of
past climate
conditions based on
paleoclimate records
Applied and
theoretical ,
construction of model
to explain physical
mechanisms behind
movement of imagery
Publication type
Literature Review
Traditional Research
R. B., Andrews, J.T ., Brigham-Grette J., Clarke, G.K.C., Cuffey, K. M., Fitzpatrick, J.J., Funder, S., Marshall, S.J., Miller, G.H.,Mitrovica, J.X., Muhs, D.R.
Otto-Bliesner, B.L., Polyak, L., White, J.W.C. History of the Greenland Ice Sheet: paleoclimatic insights. Quaternary Science Review. 29, 1728-1756 (2010).
2Sundal, A. V., Shepard, A., Nienow, P., Hanna, E. Palmer, S., & Huybrechts, P. Melt-induced speed-up of Greenland ice sheet offset by efficient subglacial
drainage. Nature. 469, 521-524 (2011). Doi: 10.1038/nature09740
History of the Greenland ice sheet
ice-sheet onset and early fluctuations
CO2
Warm
period
Cool
period
Before 65 Ma
M=Mega=106= 1
million)
Warm to high latitudes
“such warm temperatures
preclude permanent ice
near sea level”
~46 Ma
~46 Ma - ~7.3 Ma
~38-30 Ma
Ocean coring
Ice-rafted debris
~7.3 Ma
History of the Greenland ice sheet
ice-sheet onset and early fluctuations
CO2
Warm
period
Cool
period
Before 65 Ma
M=Mega=106= 1
million)
Warm to high latitudes
“such warm temperatures
preclude permanent ice
near sea level”
~46 Ma
~46 Ma - ~7.3 Ma
~38-30 Ma
Ocean coring
Ice-rafted debris
~7.3 Ma
History of the Greenland ice sheet
ice-sheet onset and early fluctuations
CO2
Warm
period
Before 65 Ma
M=Mega=106= 1
million)
Warm to high latitudes
“such warm temperatures
preclude permanent ice
near sea level”
~46 Ma
~38-30 Ma
~7.3 Ma
“Greenland
seems to have
supported at
least some
glaciation
since at least
38 Ma”
Cool
period
History of the Greenland ice sheet
ice-sheet onset and early fluctuations
~2.4Ma
Boreal
biotic
fossil
Warm
period
Kap Kobenhavn
Formation of North
Greenland
“Funder 2001 postulated
complete
deglaciation of Greenland”
History of the Greenland ice sheet
the most recent million years
[prior to MIS 5e]
Marine Isotope
Stages (MIS)
•Dating
technique
based on δ18O
of a marine
indicator,
benthic
foraminifera
History of the Greenland ice sheet
the most recent million years – farfield sea-level indications
dated to MIS 11
21 m above modern sea level
Warm period
marine deposits
Possibly dated
to MIS 11
22 m above modern sea level
Warm period
marine deposits
dated to MIS 11
Warm period
Oxygen-isotope
and faunal data
Higher than present sea level
“These
results,
taken
together, if
accurate,
imply that
all of the
Greenland
Ice sheet, all
of the West
Antarctic ice
sheet, and
part of the
East
Antarctic ice
sheet
disappeared
at this time”
History of the Greenland ice sheet
the most recent million years – farfield sea-level indications
dated to MIS 9
Pleasant point
in Florida Bay
“MIS 9 sea level was close
to but not much above the
present level”
Warm period
Coral from
a fossil reef
~2 m above sea level
dated to MIS 7
Warm period
Coral-bearing
marine deposits
“sea level stood close to its
present level during MIS 7”
“Taken
together,
these data
point to MIS
11 as a time
when sea
level likely
was notably
higher than
now…if so,
melting of
most or all
Greenland’s
ice seems
likely”
History of the Greenland ice sheet
the most recent million years – icesheet indications
dated to MIS 6
Cold period
Support view of most
extensive ice in Greenland
in MIS 6
East
Greenland
Glacial deposits
dated to MIS 11
Central
Greenland
“suggest a major retreat”
Warm period
Ice cores
dated to MIS 11
Warm period
North Atlantic
“point toward MIS 11…as the
most likely time of anomalous
warmth”
Marine sediment records
“data strongly
indicate that
Greenland’s
ice was
notably
reduced
sometime
after
extensive ice
coverage and
large ice ages
began, while
temperatures
surrounding
Greenland
were not
grossly higher
than recently”
History of the Greenland ice sheet
marine isotope stage 5e
Marine Isotope
Stages (MIS)
•Dating
technique
based on δ18O
of a marine
indicator,
benthic
foraminifera
History of the Greenland ice sheet
marine isotope stage 5e – far-field sealevel indications
MIS 5e
Florida Keys
Warm period
Coral reefs
“during MIS 5e local sea
level was at least 6 m
higher than modern-day
sea level”
Conservative estimate
Walking
through an
example…
History of the Greenland ice sheet
marine isotope stage 5e – ice sheet
changes
“The MIS 5e Greenland Ice Sheet covered a smaller area than now, but by
how much is not known with certainty.”
Ice cores
Cuffey and Marshall (2000)
try to determine climate
conditions
-using ice core data as
constraints
-oxygen isotope ratio =
f(elevation of ice-sheet
surface , temperature change
at a constant elevation)
History of the Greenland ice sheet
post-MIS5e cooling to the last glacial
maximum (LGM or MIS2)
Marine Isotope
Stages (MIS)
•Dating
technique
based on δ18O
of a marine
indicator,
benthic
foraminifera
History of the Greenland ice sheet
post-MIS5e cooling to the last glacial
maximum (LGM or MIS2) – climate
forcing
Ice cores
Ocean coring
“A general cooling from MIS
5e (~123 ka) to MIS 2
(coldest temperatures were
at ~24 ka in Greenland)”
History of the Greenland ice sheet
post-MIS5e cooling to the last glacial
maximum (LGM or MIS2) – ice-sheet
changes
Best records of ice-sheet response
Scoresby Sund region
East Greenland
History of the Greenland ice sheet
ice-sheet retreat from the last glacial
maximum (MIS 2)
Marine Isotope
Stages (MIS)
•Dating
technique
based on δ18O
of a marine
indicator,
benthic
foraminifera
History of the Greenland ice sheet
ice-sheet retreat from the last glacial
maximum (MIS 2) – ice-sheet changes
“The Greenland Ice Sheet lost ~40% of its area and notable volume after the last
glacial peak ~24-19 ka.”
Figure 12
Ice rafted debris
(IRD)
Summary of Fig 12:
Early debris inputs
Mid-Holecene -> very little debris
Late Holecene -> steady delivery of debris
Figure 8
Summary for
Question: What causes melting over the Greenland
ice sheet?
Conclusion: “…in the suite of observations as a
whole, the behavior of the Greenland Ice Sheet has
been more closely tied to temperature than to
anything else…However the data do not preclude the
possibility that local or regional events may at times
have been controlled by precipitation”
Evidence: Paleoclimatic indicators, both marine and
terrestrial
Break for Discussion
Overview
1Alley,
Alley et al.1
Sundal et al. 2
Topic approach on a
temporal scale
Historical, Mka and
forward
Recent trends, 1993,
1995-1998
Evidence or Data
Paleoclimate records,
supplemented by
modeling efforts
Remote sensing and
modeling
Topic approach on a
spatial scale
Wide, whole ice sheet
considered
Narrow, 6 glaciers in
southwest Greenland
Nature of argument
Applied, inference of
past climate
conditions based on
paleoclimate records
Applied and
theoretical ,
construction of model
to explain physical
mechanisms behind
movement of imagery
Publication type
Literature Review
Traditional Research
R. B., Andrews, J.T ., Brigham-Grette J., Clarke, G.K.C., Cuffey, K. M., Fitzpatrick, J.J., Funder, S., Marshall, S.J., Miller, G.H.,Mitrovica, J.X., Muhs, D.R.
Otto-Bliesner, B.L., Polyak, L., White, J.W.C. History of the Greenland Ice Sheet: paleoclimatic insights. Quaternary Science Review. 29, 1728-1756 (2010).
2Sundal, A. V., Shepard, A., Nienow, P., Hanna, E. Palmer, S., & Huybrechts, P. Melt-induced speed-up of Greenland ice sheet offset by efficient subglacial
drainage. Nature. 469, 521-524 (2011). Doi: 10.1038/nature09740
How does
surface melt
relate to ice
flow?
Background:
Previous research led to
contradictory statements
melt increases  flow increases
“basal lubrication”
melt decreases flow increases
Revelation:
“melt induced acceleration of flow
ceases during years of high melting
once subglacial drainage becomes
efficient”
Timeframe:
1993, 1995-1998
Synthetic Aperture
Radar (SAR)
-sends radio wave pulses
-many echo waveforms
received successively at
different antenna positions
Sundal et al.
-”significant flow increase in
summer relative to winter at
all six glaciers”
-”marked decrease in the
variance of ice speed in winter
compared to summer”
Sundal et al.
-Run-off data extracted from a model
-high run-off and melt-extent = “highmelt year”
1995,1998 = “high melt year”
1993,1996,1997=“low melt year”
Summer
Early Late
High melt
year
“seasonal velocity
fluctuations are
broadly coincident
with fluctuations in
the degree of
surface melting”
Low melt
year
Late summer speed up is markedly low in
high melt (warm) years
“Switch from
inefficient (cavity)
to efficient
(channelized)
mode of drainage”
Summary for
Question: How to improve simulations of the
Greenland ice-sheet flow under climate warming
scenarios?
Conclusion: “…should account for the dynamic
evolution of subglacial drainage; a simple model of
basal lubrication alone misses key aspects of the ice
sheet’s response to climate warming.”
Evidence: SAR imagery and modeling
Break for Discussion – End
Thoughts from this seminar…
What makes studying climate problems so difficult?
•
Dealing with a Complex System
– Acts on many different spatial scales
• earth-sun system
• atmosphere-ocean interactions
—Acts on many different temporal scales
– Many components interacting with each other at the same time
• Tool limitations
— assumptions and simplification in modeling
— assumptions in classifying in remote sensing
— weather conditions for in situ data
• Data limitations
— Incomplete data sets
• Funding
— Different data types
• Challenges in combining them
Break for Discussion – End

similar documents