1. No category

18O
isotope ratios as Climate Proxy
Fractionation mechanisms
Fractionation ratios and temperature
Ice cores analysis
Minerals and sediments
Corals and trees
http://www.gerhardriessbeck.de
Isotope distribution in
gradually accumulating
arctic snow layers, ice,
ocean sediments, fossils,
rocks and minerals!
Rayleigh processes
A particular important case of isotope fractionation processes is the change of isotopic
composition in a reservoir because of the removal of an increasing fraction of its
content. Two compounds are formed, A and B. This would be the case of partial or
sequential precipitation processes from the initial cloud with B being the rain and A the
remaining cloud system. This process is described by the Rayleigh distillation law in
terms of the fractionation factor  and a factor f, which corresponds to the remaining
fraction of the reservoir.
RB    Rinitial  f  1 RA  Rinitial  f  1
Rcloud  Rinitial f  1
18
O

16
O cloud
18
O
 1

f
16
O initial
R: reservoir
evaporation
E: extract
initial
 cloud


 1000    1  ln f
O
O
18
18
Rrain    Rinitial  f  1
18
18
O
O
 1




f
16
16
O rain
O initial
initial
 rain


 1000  ln   1000    1  ln f
O
O
18
18
precipitation
A cloud migrates over land masses to higher latitudes gradually loosing rain.
The fractionation factor is =1.008! Assuming the initial fractionation to be
0=-8 in the cloud water vapor after the evaporation process from ocean water.
The 18O isotopic abundance
decreases with increasing
distance to coast. 18O
enriched water rains down
first while slowly depleting
the cloud of its 18O isotope
content.
 rain
 initial
 1000  ln   1000    1  ln f
18
18
O
O
 f  0.7   8  1000  ln 1.008  1000  1.008  1  ln 0.7  3 0 00
 rain
18
O
 f  0.25  88  1000  ln 1.008  1000  1.008  1  ln 0.25  11 0 00
 rain
18
O
 cloud
 initial
 1000    1  ln f
18
18
O
O
initial
0
18
O
 f  0.7)   8  1000  (1.008  1)  ln 0.7  11 0 00
 cloud
18
O
 f  0.25  8  1000  (1.008  1)  ln 0.25  19 0 00
 cloud
18
O
The isotope cycle of water
The temperature dependence of fractionation processes can be utilized to
study the water cycle and its impact on the global fractionation distribution.
The global water cycle relies on water exchange between the four reservoirs,
ocean, cryosphere, fresh water, and atmosphere. A volume of ~1/2 million
km3 of water is cycled annually by evaporation and precipitation processes.
Considering a cloud moving northwards gradually changing the 16O/18O
abundance by precipitation. The cloud (and the rain) become enriched in light
16O isotopes with distance according to the Rayleigh distillation process but
by moving north, the cooling of the environment enhances the distillation
because of the temperature dependence of the fractionation factor !
The fractionation factor increases
with decreasing temperature which
enhances the fractionation effect.
C 

 C1  2 
T 

C2
 e
T
for T in Kelvin : C1  0.03 C2  11.63
Fractionation factor 
ln   C1 
1.02
1.018
1.016
1.014
1.012
1.01
1.008
1.006
initial
 cloud


 1000    1  ln f
18
18
O
O
11.63 



 0.03

cloud
initial
T 


 18 O   18 O  1000  e
 1  ln f




initial
 rain


 1000  ln   1000    1  ln f
18
18
O
O
11.63 

initial
 rain



1000

0
.
03



18
18
O
O
T


-40
-20
0
20
40
Temperature oC
60
  0.0311T.63  

 1000   e 
 1  ln f




0
-10
18O
-20
-30
Direct correlation between the
18O fraction and temperature!
cloud T=20C
rain T=20C
-40
cloud T=20C->-20C
rain T=20C->-20C
-50
-60
0
0.5
1-f
1
Correlation 18O to temperature
http://www.gerhardriessbeck.de
Temperature dependence of 18O in snow
and rain is clearly demonstrated by
numerous measurements at different
locations worldwide, as lower the
temperature as lower the 18O content in
snow. This introduces a perfect tool for
determining temperature by the analysis of
accumulated compressed snow layers in
Arctic, Antarctic, or glacier environments.
 O  0.675 T C15
18
0
Ice core drilling
GRIP: European GReenland Ice-core Project
GISP; US Greenland Ice-Sheet Project
Ice Cores
Annual variations of 18O over a
30 year period of relatively
constant global temperatures
(medieval warm period). The
Winter snowfall is consistently
18O depleted (-34‰, T =-38oC)
W
compared to the summer
snowfall (-26‰, TS=-32oC).
-38.5oC
-38.7oC
Temperature record for more than
120,000 years
The observed 18O fluctuations represent the major climate (temperature)
variations earth has experienced beginning with the onset of the last ice
age period through the Holocene period of human evolution.
Corresponding fluctuations were observed in the GISP 2 ice core samples
Going back in time,
ocean sediments, fossils, and rocks
On longer paleoclimate timescales ocean sediment analysis, the analysis of
lithified rocks from former ocean sediments and the analysis of fossils in
terms of elemental and isotope distribution in sediments of fossil molecules
such as CaCO3 or other carbonates, SiO2 or other oxides. For fossil material
biological processes may have changed 18O fractionation during the uptake.
This has to be corrected to determine 18O ratio in former ocean water.
Rock with layers of iron oxide that
was formed in Precambrian more
than 500M years ago.
Mineralized fossil layer in sedimentary
rock. Dating occurs through the analysis
of long-lived radioactivity in the fossil
material.
Paleothermometer CaCO3
Temperature 18O fractionation relation in carbonates is expressed by
a thermometric relation developed by Harold Urey and Brian Epstein:

T0 C  16.5  4.3  
18
O
CO3

18
O
H 2O
 0.13  
18
O
CO3

18
O
H 2O

2
simplified version is : T0C  16.5  4.3   COO3
18
 COO
18
3
  18O 

 18O 
  16 

  16 
  O CO2 ,CO3  O CO2 standard 
 1000  

18


O


 16 


 O CO2 standard


The accuracy of 18O measurements is 0.1‰, that translates into an
uncertainty for the temperature of :
18
T  4.3  
O
CO3
 0.4 C
0
Jurassic belemnite, based on data it
lived for 3.5 years; it was born in fall
and died in spring (Urey 1951)
Paleothermometer SiO2
Measuring 18O for SiO2 requires to correct for systematic variations
with the type of mineral and the type of rock the minerals belong to
since they have formed at different high temperature conditions in
the Pre-Cambrian phase, where the temperature dependence of the
fractionation factor  needs to be considered.
ln   B 
C A
 2
T T
The difference between two minerals M1 and M2 is:
A  106
 M 1,M 2   M 1   M 2 
 B  1000  ln 
2
T
 M 1,M 2   M 1,water   M 2,water
Example
The 18O values for the minerals of a metamorphic rock are for
quartz 18O=+14.8, magnetite 18O=+5. What is the temperature at
which this rock was formed?
A  106
 M 1,M 2   M 1   M 2 
B
T2
5.57  106
 quartz,magnetite  14.8  5  9.8 
T2
5.57  106
T
 7540C
9.8
18
 O
in corals
18O in coral skeletal reflects combination of surface temperature and salinity. In
ocean regions where salinity is constant changes in coral skeletal 18O reflects change
in sea surface temperature. Therefore primarily applicable to tropical ocean regions.
In regions with strong rainfall or river run-off 18O can be used for salinity measures.
Analysis of multiple isotope (or element)
ratios can provide detailed information
about the ocean environment history!
X-ray analysis of
the banding pattern
establishes the chronology scale
of the environment history of the coral.
Analysis of coral growth characteristics gives time line. Bright lines under UV
radiation indicate fresh water inflow and therefore reduced salinity conditions.
Isotope analysis of corals
from the Great Barrier Reef
in Australia indicate a higher
sea surface temperature
and/or higher salinity of the
pacific ocean in the 18th
century than it is today.
Climate history of Pacific and
Indian Ocean environments
Variation of 18O in different coral
reefs over the last 400 years. The
black arrows indicate sudden
changes in temperature or salinity
which is frequently correlated with
the El Nino effect. The cooler time
period after 1800 may be related to
volcano activity (Tambora on the
Sunda Islands in Indonesia)
El Nino reflection in 14C
The 14C enrichment
in ocean surface
water occurred after
nuclear test program
1946-1969 due to
ocean atmosphere
carbon exchange.
Radiocarbon is enriched in Pacific Ocean surface water but reduced by upwelling
of Humboldt current. If upwelling is prevented by ENSO effect, enhanced 14C ratios
are observed. This was used to investigate strength and frequency of past El Nino
events from 14C analysis of skeletal carbonate of corals from the Galapagos Islands.
Dendrochronology
Dendrochronology or
tree-ring dating is the
dating of past events
through study of tree
ring growth.
Trees showing sensitive rings are affected by
slope gradient, poor soils, or too little moisture
and climate conditions.
Trees showing complacent rings have generally
constant climatic conditions such as high water
table, good soil, or protected locations.
Dating back in time
The oldest Trees
drill at
set
Bristlecone pine Dendrochronology
groves are found
elevations up to 11,000 feet (3352m).
"Methuselah" was found
to be 4,723 years old and
remains today the world's
oldest known living tree.
Tree-ring dating ~7000 years backwards
The world map of tree ring recordings
Tree ring analysis can be coupled 18O isotope fractionation analysis for climate
studies and with 14C dating techniques to establish or verify the chronology!
18O in tree rings
5 year study of 18O uptake
Clear correlation of 18O and
climate in tree ring analysis!
Dendrochronology has emerged as a
major tool for calibrating 14C dating
results and plays an increasing role in
climate analysis during the historic
period but also for the entire Holocene!
Climate correlation with human
history and development
The recorded climate history of Earth
The curve records a sequence of cold periods of glaciation and warm
periods of sometimes significantly higher temperatures than observed
during the Holocene period of Human evolution to the present time.