Circulation changes on Antarctic Peninsula from ice cores
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Transcript of Circulation changes on Antarctic Peninsula from ice cores
Circulation changes on Antarctic Peninsula from
ice cores
Liz ThomasLiz Thomas11, Gareth Marshall, Gareth Marshall11
Joe McConnellJoe McConnell22 & Paul Dennis & Paul Dennis33
1.1. British Antarctic SurveyBritish Antarctic Survey2.2. Desert Research InstituteDesert Research Institute3.3. University of East AngliaUniversity of East Anglia
BAS Core locations
• Beethoven– 1991 – 1948
• Berkner– 948 m (completed 2004)
• Dolmen Island– 1982- 1651
• Dyer Plateau– D1 1988-1820
– D2 1989-1506
• James Ross Island– 365 m (completed 2008)
• Gomez– 2006-1850
James Ross IslandFaraday
Rothera
Dolman IslandDyer Plateau (1&2)
Gomez Berkner Island
Beethoven
Drill site
• Medium depth ice core drilled
to a depth of 136 meters with
an electromechanical, 104 mm
diameter drill
• Encompasses the period
between 1855 – 2006 (150
years)
• Ground penetrating radar
(GPR) used to asses
accumulation variability
Gomez ice core (73.59°S, 70.36°W, 1400 m a.s.l)
Site selection
• Strong SAM signal from reanalysis data
• High accumulation site
– High resolution records
• Increased elevation (1992-2003), thought to
be due to greater snowfall
– satellite altimeter data
– [Davis et al., 2005; Wingham et al., 2006].
Correlation between SAM and precipitation from ECMWF 1980-2004
Methods
• Continuous Flow Analysis with Trace
Elements-Dual
• The annual accumulation record was
derived using two methods:
– winter-winter value determined from the
minima of hydrogen peroxide (H2O2)
– summer-summer value based on maxima in
non-sea salt sulphate (nssS)
• Estimated uncertainty in the dating is ±1
year from 1855 to 1875 and <<1 year from
1875 to 2006
Gomez Accumulation
record
• Annual thicknesses converted to
water equivalents
• corrected for thinning assuming a
linear strain rate
• Doubling of accumulation: the mean
for 1855-64 was 0.49 mweq y-1 while
that for 1997-2006 was 1.10 mweq y-1
• Most rapid increase in recent period,
following a slight reduction in the
1970s
Annual snowfall at the Gomez site (dashed) and decadal average (solid)
Elizabeth R. Thomas., G., J, Marshall., Joseph R. McConnell, (2008), A doubling in accumulation in the western Antarctic Peninsula since 1850, Geophysical Research Letters, 35
Atmospheric circulation
Two principal spatial patterns related to known modes of atmospheric circulation variability
1. SAM
– strong negative correlations over the Antarctic continent with ring of positive correlations to the north (exception of the south-east Pacific)
Correlation map of Gomez accumulation vs. 500 hPa geopotential height, 1958-2006
Atmospheric circulation
• Correlation, SAM and the Gomez accumulation record is 0.41
• 28% of the increase in snowfall (1957-2006) due to positive trend in the annual SAM
Correlation map of Gomez accumulation vs. 500 hPa geopotential height, 1958-2006
Relationship with ENSO
• No significant relationship over
the entire 1866-2005 period
• Some periods when significant
(<10% level) positive correlation
with the SOI: El Niño = less
accumulation
• But also periods when negative
correlations exist
Running 21-year correlations between Gomez accumulation and the Southern Oscillation Index
Marine signal
• Large marine input
– Average Na+ (1854- 2006) 39 ppb
• Increase in sea salts since 1950’s
• Changes in sea salt ratio’s
– increased continental input?
• Is changing atmospheric circulation
affecting the marine signal?
Back trajectories
• BADC (www.badc.ac.uk)
• Daily release over 5 days
• Location, height, temperature
• To help identify source of chemical and
isotope signal in ice core
• Combined with satellite data to identify
individual storm events
2 weeks of back trajectory data from Gomez site (Jan 2004)
Isotopes
• Isotope (18O) record
• Compared with 18 months surface
temp from AWS (r2 = 0.89)
• In combination with other chemistry
and a mean seasonal cycle of
precipitation, aim is to derive
seasonal time series
• Back-trajectory analysis to try to
understand intra-annual variability Isotope record from Gomez approx bi-weekly resolution
Conclusions
• The Gomez ice core reveals a doubling of accumulation over the past 150 years
– change is restricted to the central and southern Antarctic Peninsula
• The SAM is a major driver of accumulation variability in the region. – Gomez accumulation provides a good proxy of the SAM – next step to compare with 150 year SAM reconstructions
• No consistent ENSO signal in SW Peninsula accumulation (similar to West Antarctica)
• Gomez core will allow us to derive a temperature record in the southwestern peninsula since 1850 and several other proxy records at a sub-seasonal timescale
• Back trajectories used to identify source of ins in ice core– Help answer questions relating to sea ice effect on temperature