Antarctic Sea ice extent proxies from ice core MSA records

1
Antarctic Sea ice extent proxies from ice core
MSA records
ITASE Synthesis Workshop 2-5 Sept 2008, Castine,
Maine

• Mark Curran1 and Nerilie Abram2
• 1ACE CRC and Australian Antarctic Division
• 2British Antarctic Survey

2
Overview

• Review MSA-sea ice relationship
• Discuss support and criticism
• New data and data gaps
• ITASE synthesis product

3
How is MSA production linked to sea ice?
4
Good evidence for a sea ice-MSA link

• Only certain phytoplankton produce MSA (via
  dimethylsulphide (DMS) oxidation)
• These species are associated with sea ice
• Phytoplankton blooms after sea ice decay
• MSA data show highest production in the sea ice
  zone following sea ice decay

5
My previous life Southern Ocean DMSP samples
(1991-95)
Latitude (oS)
LD
(Curran et al, JGR, 1998)
Law Dome (LD)
6
North-South variation of DMSPt with depth
DMSPt (nM)
(Curran et al, JGR, 1998)
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High level of DMSP-DMS-MSA associated with
Antarctic sea ice zone
Turner et al. (1995) Curran (1996) Di Tullio et
al.(1998) Curran et al. (1998) Curran and Jones
(2000) Trevena et al (2000) Minikin et al
(2002)
Andreae et al. (1985) Berresheim (1987) Gibson
et al. (1990) Berresheim et al. (1990)
Fogelqvist (1991) Kirst et al. (1991) Crocker
et al. (1995)
Sea ice could be considered an MSA pump
8
Timing of sea ice coverage and MSA production
Ice spring max
Ice cover ? Sea ice decay ? Algal blooms ? Algal
decay
?
MSA summer max
?
9
MSA some agreement with sea ice area
from Welch et al., 1993
10
Sea ice extent 80-140oE region
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Sea ice extent 1978-1995 (with 3 yr smooth)
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Sea ice extent and MSA 1978-1995 (with 3 yr
smooth)
13
Sea ice extent and MSA 1978-1995 showing
increasing trend
14
Sea ice increase between 1978-1997
from Cavalieri et al., 1997
15
Sea ice extent (incuding early satellite data)
and MSA 1970-1995
16

• Added advantage of using maximum ice edge
• Maximum ice edge is well defined
• Easily picked up by satellite (even the early
  data)
• Good agreement with ship observations

Winter
Summer
from Ackley et al., Polar Research 22, 19 (2003)
17
Sea ice extent (incuding early satellite data)
and MSA 1970-1995
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Early sea ice extent from visible and IR
satellite data
from Zwally et al., Science 220, 1005 (1983)
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Sea ice extent and MSA 1940-1995
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Sea ice extent and MSA 1940-1995 showing decline
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Sea ice extent and MSA 1840-1995 Sector 80-140oE
Curran et al., Science 303, 1203 (2003)
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Sea ice extent and MSA 1840-1995 Sector 0-360oE
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MSA vs sea ice extent at 0-360E (statistically
significant plt0.05)
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Supporting Antarctic sea ice decline

• Fast ice decline (89 years)
• Murphy et al. (1995)
• Longest available satellite records (30 years)
• Cavalieri et al. (2003) Parkinson (2004)
• Whaling records (56 years)
• de la Mare (1997)
• Penguin records (48 years 40 years 39 years)
• Barbraud Weimweskirch(2001) Kato et al(2002)
  Wilson et al(2001)
• Decline in Krill stocks (77 years)
• Atkinson et al. (2004)
• Freshening of ocean surface water (43 years)
• Jacobs et al. (2002)

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Whaling ship locations provide information on the
sea ice edge
From de la Mare (2006)
26
Decline supported by whaling ship records
(1930s-1980s)
from de la Mare, 1997
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Support for decadal variability

• 1903-1992 Fast ice observations, South Orkeny
• Murphy et al., Deep Sea Research I 42, 1045
  (1995)
• 1956-1979 Sea ice observations Syowa Station
• Kusunoki, in Sea level, Ice , Climate Ed I.
  Allison, 171 (1981)
• 1966-1982 Visible, IR and ESMR satellite data
• Zwally et al., Science 220, 1005 (1983)

Only from early data not recent data
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How robust is the MSA proxy?

• What factors influence the suitability of an ice
  core site for an MSA sea ice proxy?
• Can we produce an MSA sea ice proxy at all
  Antarctic ice core sites? Or stack some/all?
• Do we see regional signals?
• Is the relationship always positive?
• What about Arctic ice core sites?
• What about issues of MSA movement and loss?

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What is MSA a proxy for?

• Sea ice extent?
• (how do we interpret changes in sea ice extent
  thermodynamics or dynamics or both?)
• Sea ice concentration?
• Source is open ocean within the sea ice zone
• Biological activity within the sea ice zone?
• Complex biological pump only 5 gets into the
  atmosphere as DMS
• Sulpur chemistry in atmosphere

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Why we should NOT expect agreement

• sea ice formation (ocean and atmosphere
  circulation, ENSO)
• sea ice decay (rates, timing, percentage decay)
• biological activity (seeding, nutrients, light,
  iron etc)
• phytoplankton speciation (succession and
  distribution)
• DMS production (from phytoplankton, directly from
  sea ice)
• air-sea transfer of DMS (wind speeds)
• atmospheric oxidation of DMS (and pathways to
  MSA)
• aerosol transport and pathways
• snow precipitation (frequency, duration and
  seasonal timing)
• wet versus dry deposition
• post-depositional effects (e.g. movement and
  losses)
• snow accumulation rate
• ice core dating

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But remember at Law Dome ..
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Possible reasons why a strong positive MSA-sea
ice link IS seen at Law Dome .

• Low SIE variability in the surrounding region
• Narrow band of sea ice in this region
• Regular cyclonic transport over sea ice to Law
  Dome
• Sensitive to Southern Ocean signals as it is the
  most northerly coast of Antarctica (apart from
  the tip of the Peninsula) and is close to the
  coast
• Regular snow accumulation at Law Dome
• High snow accumulation at Law Dome
• Excellent preservation of the ice core record
• Accurate ice core dating
• References Morgan et al. (1997) Palmer et al.
  (2001) McMorrow et al. (2002) Zwally et
  al. (2002)

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A very simplified approach ..
Sea ice extent
Seasonal progression
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A very simplified approach ..
Sea ice extent
Seasonal progression
35
A very simplified approach ..
Sea ice extent
Seasonal progression
36
A very simplified approach ..
Sea ice extent
Seasonal progression
37
A very simplified approach ..
max
Sea ice extent
Seasonal progression
38
A very simplified approach ..
max
Sea ice extent
Seasonal progression
39
A very simplified approach ..
max
MSA concentration
Sea ice extent
Seasonal progression
40
A very simplified approach ..
max
MSA concentration
Sea ice extent
Seasonal progression
41
A very simplified approach ..
max
MSA concentration
Sea ice extent
Seasonal progression
42
A very simplified approach ..
max
MSA concentration
Sea ice extent
Seasonal progression
43
A very simplified approach ..
max
MSA concentration
Sea ice extent
Seasonal progression
44
A very simplified approach ..
max
MSA concentration
Sea ice extent
Seasonal progression
45
A very simplified approach ..
max
total
MSA concentration
Sea ice extent
Seasonal progression
46

• BIG sea ice year BIG MSA year
• Ice cores can record annual MSA data
• Need to compare annual MSA data (centred around
  the summer) i.e. summer production with
• Maximum extent of sea ice preceding the summer
  (satellite instrumental calibration)
• (Recent support for this approach found summer
  Krill densities correlate with previous winter
  sea ice extent see Atkinson et al., Nature 432,
  100, 2004)

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MSA sea ice Wilhelm II Land
Foster et al, (2006)
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MSA sea ice correlations

• Positive correlation
• Newall Glacier (Antarctic) - Welch et al. (1993)
• Greenland (Arctic) - Legrand et al.(1997)
• Law Dome (Antarctic) - Curran et al. (2003)
• A-B Seas (Antarctic) - Abram et al. (2006)
• Whilem II Land (Antarctica) Foster et al (2006)
• Coastal DML (Antarctica)- Isaksson (unpublished)
• ITASE WAIS (Antarctica) McConnell (unpublished)
• Negative correlation
• Dolleman Island (Antarctica) Pasteur et al.
  (1995)
• Svalbard (Arctic) - ODwyer et al. (2000)
• Siple Dome (Antarctica) Kreutz (2000)
• Lambert Glacier (Antarctica) Sun et al (2002)
• Weddell Sea region (Antarctic) - Abram et al.
  (2006)

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How do we explain negative correlations?

• Local sea ice conditions geography of
  embayments etc
• Lack of open water in summer for biological
  activity and therefore MSA production
• Distance to the source circulation strength
• Atmospheric mixing and transport pathways

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The simple approach ..
max
MSA concentration
Sea ice extent
total
Seasonal progression
Big ice year
Low MSA year
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The simple approach ..
MSA concentration
Sea ice extent
max
total
Seasonal progression
Low ice year
High MSA year
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Bellingshausen region ice cores
James Ross Island
Dyer Plateau
Beethoven Peninsula
ITASE01_5
Winter sea ice extent
Summer sea ice extent
From Abram et al, 2008
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MSA-sea ice correlation results
Annual ice core MSA vs winter sea ice
extent (JIC/Jacka 10º sea ice compilation
post-1973)
Correlation coefficient (r)
Significance
Greater than 90

Greater than 95

Greater than 99

From Abram et al, 2008
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MSA-sea ice correlation results
0o
Bellingshausen stacked MSA vs winter sea ice
extent (1973-1990)



90oW
90oE



Correlation coefficient (r)
Significance
180o
Greater than 90

Greater than 95

Greater than 99

From Abram et al, 2008
55
MSA-NCEP/NCAR correlation results
Surface air temperature
Sea ice extent






Correlation coefficient (r)
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20th century sea ice reconstructions
Bellingshausen stacked MSA record
3s
2s
1s
Normalised MSA concentration
-1s
-2s
4
Number of cores
2
0
1880
1900
1920
1940
1960
1980
2000
From Abram et al, 2008
57
20th century sea ice reconstructions
Bellingshausen stacked MSA record
Mean trend -0.14s / decade
3s
2s
1s
Normalised MSA concentration
-1s
-2s
Air temperature anomaly (ºC)
1900
1920
1940
1960
1980
Jones (1990) J Clim.
From Abram et al, 2008
58
r2 0.65
(72 days)
1o
South Orkney sea ice duration
Change in winter sea ice extent
0o
-1o
(-72 days)
r2 0.48
1o
Bellingshausen stacked MSA
Change in winter sea ice extent
0o
-1o
r2 0.36
1o
Law Dome MSA
Change in winter sea ice extent
0o
-1o
1880
1900
1920
1940
1960
1980
2000
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20th century sea ice reconstructions
Weddell Sea Mean change 0.35 retreat Greatest
decline 1930-1960
Bellingshausen Sea Mean change 0.45
retreat Gradual decline through 1900s
Law Dome region Mean change 0.47
retreat Greatest decline 1950-1990
From Abram et al, 2008
60
Good coverage but still big gaps for future work
Coastal Dronning Maud Land Unpublished data
(Isaksson)
Lambert Glacier
Sun et al., (2002) Ann. Glac.
Weddell Sea region Pasteur et al., (1995) Ann.
Glac. Abram et al., (2007) JGR
Bellingshausen Sea This study
ITASE00_1 (WAIS divide) Unpublished data
(McConnell)
Mt Brown
Forster et al., (2006) Ann. Glac.
Siple Dome
Kreutz et al., (2000) JGR
Law Dome
GD17
Newell Glacier
Curran et al., (2003)Science
Talos Dome
Welch et al., (1993) GRL
From Abram et al, 2008
61
Summary MSA as a sea ice proxy

• MSA in coastal ice cores is generally positively
  correlated with winter sea ice extent
• But exceptions do occur (Weddell Sea, Eastern
  Ross Sea, Lambert Glacier)
• Correlations are on a local to regional scale
  (40-60 degrees longitude)
• Reconstructions can be improved by regional
  stacking of MSA records

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Summary sea ice reconstructions

• Reconstructions suggest that winter sea ice
  around Antarctica has retreated during the 20th
  century
• Mean 20th century retreat of 0.35o - 0.47o
  latitude, but with strong interannual/decadal
  variability
• Regional differences in timing of sea ice retreat
  are evident
• Weddell Sea greatest decline 1930-1960
• A-B Sea gradual decline through 20th century
• Law Dome region greatest decline 1950-1990

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Where to from here?

• Data quality issues
• MSA in situ movement and loss (firn vs ice)
• MSA loss during storage
• Melter effects on MSA analysis
• Differences between the Arctic and Antarctic?
• Is this due to the large decadal variability in
  the Antarctic?
• Antarctic wide spatial study understand why the
  relationships vary?
• AAD/BAS ice cores
• ITASE network

64
What is the dominant source of sea salt to
Antarctica ocean or sea ice?
Long range transport (oceanic)
?100?
Storms
??
0
5
Mt Brown
15
GD17
GC41
83
EPICA
DSS
1My
Sea ice
Antarctica
Ocean
65
Antarctic Ice Thickness
Vostok
Dome C
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ITASE synthesis product?

• Antarctic wide (or regional) sea ice
  reconstruction over the last 200-1000 years
• Sea salt budget across Antarctica with respect to
  sea ice and open ocean sources
• These products are very important to a lot of
  research users, particularly outside ice core
  community and the ITASE network of ice cores are
  a key to achieving these goals

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Thank you
Acknowledge assistance of many, including funding
agencies, students, colleagues, field assistants
and logistic support.