Transcript South Pole Glaciology with the IceCube telescope

South Pole Glaciology
with the IceCube telescope
Kurt Woschnagg
University of California, Berkeley
for the IceCube Collaboration
Open Science Conference, XXX SCAR
St. Petersburg, Russia, July 9, 2008
The IceCube neutrino telescope
IceCube 1 km3 of ice instrumented
surface
1450 m
2450 m
AMANDA
40 strings/2400 optical sensors (2008)
80 strings/4800 optical sensors (2011)
nanosecond
timing
Need to know about ice:
Optical properties
Scattering
Absorption
Depth dependence
Wavelength dependence
Dust, ash, bubbles
Digitized pulse
sent to surface
sensor is hit →
(PMT pulse)
g
Neutrino-induced muon
generates Cherenkov light
Movement
Flow, shear
m
n
Measuring Scattering & Absorption
Monte Carlo model fits to photon timing
scattered
absorbed
photon travel time [ns]
c2 minimum
Optical properties: Scattering and Absorption
Absorption
Scattering
dust peaks correspond to cold periods
during last glacial period
SP ice at 1700 m
SP ice at 850 m
The Dust Logger
laser
baffles
(nylon brushes)
digital
receiver
The Dust Logger
High-resolution log of dust concentration
laser
baffles
(nylon brushes)
digital
receiver
Radar shows sloping isochrons
1 km
~90 m
Subglacial lake
Bingham et al., JGR 112 (2007) F03S26
Distance from South Pole along 150° W (km)
Four seasons of
Dust Logs
in IceCube
21 and 50 :
deployed with string
66 and 52 :
retrievable
(2005)
(2007)
(2006)
(2008)
Dust layer tilt over one kilometer
Hole 52 minus Hole 50
-20 m
+50 m
South Pole ash layers in dust logs
Highly absorbing thin layers give unique
signature in bubbly ice.
New SP fallout layer ~6 kyr B.P.
Also seen in SP ice core
(Palais et al. 1987)
Eight ash layers identified so far.
The darkest ones are likely
tephra from nearby volcanoes .
South Pole Age vs Depth
Volcanic and dust feature tie points
matched to EDML core (dated with Dome C core)
South Pole ice temperature profile
Model:
No strain heating
No horizontal advection
melting
point
South Pole ice temperature profile
Model:
No strain heating
No horizontal advection
melting
point
“old” string (>9 years)
“new” string (<1 year)
Measuring SP deep glacial flow
Ice surface moves
1 inch/day
ice flow model
(based on temperature)
assumed stuck
at bedrock
optical time-of-flight measurements
South Pole deep ice flow
Preliminary
old
new
Expected shear along flow
Found shear across flow
IceCube is installing inclinometers
to further investigate ice shear
/9yr
/9yr
Does impurity content determine where shear occurs?
Smaller grains =
Faster fabric development
(E. Pettit et al.)
Dirty
C-axes
Temperature-only model
too simplistic?
More shear in dirty ice?
Clean
Gow & Meese (2007)