Post on 17-Oct-2020
EGU Vienna5 May 2010
Ilka Weikusat - Characterization of subgrain boundary types inpolar ice (EPICA-DML ice core)
TS3.1 - Deformationprocesses
Introduction
subGB inice
Frequency
Types
type I
type II
type III
Statistics
Summary
Characterization of subgrainboundary types in polar ice (EPICA-
DML ice core)
Foto
: RAD
ARSA
TAn
tarc
tic M
appi
ngM
issi
on
Ilka Weikusat1,Atsushi Miyamoto2, Martyn R. Drury3,
Sepp Kipfstuhl1, Sérgio H. Faria4,Gill M. Pennock3, and Nobuhiko Azuma5
1Alfred-Wegener-Institut für Polar- undMeeresforschung (Bremerhaven, Germany)
2Institute of Low Temperature Science (Sapporo, Japan)3Utrecht University (The Netherlands)
4University of Göttingen (Germany)5Nagaoka University of Technology (Japan)
EGU Vienna5 May 2010
Ilka Weikusat - Characterization of subgrain boundary types inpolar ice (EPICA-DML ice core)
TS3.1 - Deformationprocesses
Introduction
subGB inice
Frequency
Types
type I
type II
type III
Statistics
Summary
MotivationSchematic Cross section through an ice sheet
EGU Vienna5 May 2010
Ilka Weikusat - Characterization of subgrain boundary types inpolar ice (EPICA-DML ice core)
TS3.1 - Deformationprocesses
Introduction
subGB inice
Frequency
Types
type I
type II
type III
Statistics
Summary
Relevance
(from Hondoh 2000)
Glide systems in ice
Glide on non-basal planes≈60x harder!
But needed for deformationcompatibility
EGU Vienna5 May 2010
Ilka Weikusat - Characterization of subgrain boundary types inpolar ice (EPICA-DML ice core)
TS3.1 - Deformationprocesses
Introduction
subGB inice
Frequency
Types
type I
type II
type III
Statistics
Summary
subGB
EDML 2095.1m
Grain boundary
Air hydrate
Subgrain boundary
Slipband
MicrostructureMapping (µSM)
Glass plate
Grain boundary
Sublimation
Samplefigure: Kipfstuhl
EGU Vienna5 May 2010
Ilka Weikusat - Characterization of subgrain boundary types inpolar ice (EPICA-DML ice core)
TS3.1 - Deformationprocesses
Introduction
subGB inice
Frequency
Types
type I
type II
type III
Statistics
Summary
State
modified after: De La Chapelle et al. 1998
upperfew X00m
deeperfewX00m
Literature - recrystallization regimes in ice sheets
normal graingrowth(NGG)
polygonization / rotationrecrystallization
GB migrationrecrystallization
(T>-10°C)
- with nucleation
Regular straight GB, “foam texture”
subGB
irregular GB
Expected in µSM
EGU Vienna5 May 2010
Ilka Weikusat - Characterization of subgrain boundary types inpolar ice (EPICA-DML ice core)
TS3.1 - Deformationprocesses
Introduction
subGB inice
Frequency
Types
type I
type II
type III
Statistics
Summary
subGB density:
Weikusat et al. 2009, J. Glaciol.
!
"subGB
=LsubGB
A
L : total subGB lengthA : area
frequencybut, ice core data (EDML) do not show a
“subGB depth range”
... (and neither do other parameterssupport the three recrystallizationregimes)
EGU Vienna5 May 2010
Ilka Weikusat - Characterization of subgrain boundary types inpolar ice (EPICA-DML ice core)
TS3.1 - Deformationprocesses
Introduction
subGB inice
Frequency
Types
type I
type II
type III
Statistics
Summary
Weikusat et al. 2009, J. Glac.
subGB types (morphologic)
EGU Vienna5 May 2010
Ilka Weikusat - Characterization of subgrain boundary types inpolar ice (EPICA-DML ice core)
TS3.1 - Deformationprocesses
Introduction
subGB inice
Frequency
Types
type I
type II
type III
Statistics
Summary
Relevance
(from Hondoh 2000)
Glide systems in ice
Glide on non-basal planes≈60x harder!
But needed for deformationcompatibility
(after Montagnat and Duval, 2004)
creep test σ-range:Ice sheet σ-range:
!
˙ " = B # exp($Q /RT) #% n
T = absolute temperatureR = gas constantB, n, Q = constants
Flow law used in icesheet modelling
EGU Vienna5 May 2010
Ilka Weikusat - Characterization of subgrain boundary types inpolar ice (EPICA-DML ice core)
TS3.1 - Deformationprocesses
Introduction
subGB inice
Frequency
Types
type I
type II
type III
Statistics
Summary subGB types(morphologic)
EDML 655.9m
µSM
EGU Vienna5 May 2010
Ilka Weikusat - Characterization of subgrain boundary types inpolar ice (EPICA-DML ice core)
TS3.1 - Deformationprocesses
Introduction
subGB inice
Frequency
Types
type I
type II
type III
Statistics
Summary
EBSD example
EDML 655.9m
subGB types(structural) >10°
>2°>1°>0,75°>0,5°
ice core axis incrystal reference
EBSD data
EGU Vienna5 May 2010
Ilka Weikusat - Characterization of subgrain boundary types inpolar ice (EPICA-DML ice core)
TS3.1 - Deformationprocesses
Introduction
subGB inice
Frequency
Types
type I
type II
type III
Statistics
Summary
Basal twist
EDML 655.9m
subGB types(structural) >10°
>2°>1°>0,75°>0,5°
ice core axis incrystal reference
subGB parallel to basal plane
subGB || basal plane+
Rot. Axis basal plane=
Twist boundary with setsof screw dislocations
on basal (b=a)
T
Rotation Axis is c-axis
EBSD data
EGU Vienna5 May 2010
Ilka Weikusat - Characterization of subgrain boundary types inpolar ice (EPICA-DML ice core)
TS3.1 - Deformationprocesses
Introduction
subGB inice
Frequency
Types
type I
type II
type III
Statistics
Summary
Basal tilt
EDML 655.9m
subGB types(structural) >10°
>2°>1°>0,75°>0,5°
ice core axis incrystal reference
subGB normal to basal plane
Rotation Axis is close to prism plane normal
sGB basal plane+
Rot. Axis || basal plane =
Tilt boundary withedge dislocations
on basal (b=a)
T
EBSD data
EGU Vienna5 May 2010
Ilka Weikusat - Characterization of subgrain boundary types inpolar ice (EPICA-DML ice core)
TS3.1 - Deformationprocesses
Introduction
subGB inice
Frequency
Types
type I
type II
type III
Statistics
Summary
Non-basal tiltsubGB types(structural) >10°
>2°>1°>0,75°>0,5°
ice core axis incrystal reference
subGB parallel to basal plane
Rotation Axis is close to prism plane normal
sGB || basal plane+
Rot. Axis || basal plane=
Tilt boundary with edge dislocations on non-basal (b=c or b=c+a)
a
EBSD data
EGU Vienna5 May 2010
Ilka Weikusat - Characterization of subgrain boundary types inpolar ice (EPICA-DML ice core)
TS3.1 - Deformationprocesses
Introduction
subGB inice
Frequency
Types
type I
type II
type III
Statistics
Summary
subGB types statistics
NsGB = 165 ; [%]
basa
l pla
ne:
Non-basal tilt boundaryBurgers vector = c or c+a
X-ray Laue diffraction DataWeikusat et al. 2010, submitted to J. Glac.
Basal tilt boundaryBurgers vector = a
Basal twist boundaryBurgers vectors = a
EGU Vienna5 May 2010
Ilka Weikusat - Characterization of subgrain boundary types inpolar ice (EPICA-DML ice core)
TS3.1 - Deformationprocesses
Introduction
subGB inice
Frequency
Types
type I
type II
type III
Statistics
Summary
Summery• Three recrystallization regimes have to be reconsidered
• Subgrain boundaries identified as– Tilt boundary comprised of
edge dislocations in basal plane (b=a)
– Twist boundary comprised of sets ofscrew dislocations in basal plane (b=a)
– Tilt boundary comprised ofedge dislocations in NON-basal plane (b=c or b=c+a)
• Surprising: Non-basal tilt boundaries are quite common
EGU Vienna5 May 2010
Ilka Weikusat - Characterization of subgrain boundary types inpolar ice (EPICA-DML ice core)
TS3.1 - Deformationprocesses
Introduction
subGB inice
Frequency
Types
type I
type II
type III
Statistics
Summary Thank you.
ilka.weikusat@awi.de
EGU Vienna5 May 2010
Ilka Weikusat - Characterization of subgrain boundary types inpolar ice (EPICA-DML ice core)
TS3.1 - Deformationprocesses
Introduction
subGB inice
Frequency
Types
type I
type II
type III
Statistics
Summary
References
• Hondoh, T. Hondoh, T. (ed.) Nature and behaviour ofdislocations in ice Physics of Ice Core Records, HokkaidoUniversity Press, 2000, 3-24
• Weikusat, I.; Kipfstuhl, S.; Faria, S. H.; Azuma, N. & Miyamoto,A. Subgrain boundaries and related microstructural features inEPICA-Dronning Maud Land (EDML) deep ice core J. Glaciol.,2009, 55, 461-472
• Montagnat, M. & Duval, P. Dislocations in ice and deformationmechanisms: from single crystals to polar ice Deffect andDiffusion Forum, Scitec Pub., 2004, 229, 43-54
• De La Chapelle, S.; Castelnau, O.; Lipenkov, V. & Duval, P.Dynamic recrystallization and texture development in ice asrevealed by the study of deep ice cores in Antarctica andGreenland J. Geophys. Res., 1998, 103, 5.091-5,106
• Weikusat, I., Miyamoto, A., Faria, S. H., Kipfstuhl, S., Azuma,N., Hondoh, T.(2010).Subgrain boundaries in Antarctic icequantified by X-ray Laue diffraction, J. Glaciol. [SUBMITTED]