AN EXTREME TURN-OF-THE-CENTURY HYDROLOGIC
EVENT RECORDED IN δ 18 O FROM BRISTLECONE
PINE TREE-RING CELLULOSE
Max B. Berkelhammer and Lowell D. Stott
Department of Earth Sciences
University of Southern California
Pacific Climate Conference
May 14, 2007

• Ring-width (Hughes, LaMarche, Fritts etc…): temperature, volcanism, precipitation.
• δ 13 C (Leavitt, Epstein): drought, soil moisture, atmospheric CO
2
• δ 14 C (Stuvier, Suess, Ferguson): radiocarbon calibration, solar variability
• D/H (Feng and Epstein): Temperature
• δ 18 O: ????

En route to
Cellulose:
1) Precipitation
4) Evapotranspiration
5) Photosynthesis
6) Translocation
2) Infiltration
3) Uptake
7) Cellulose
Synthesis

Source Water/Precipitation:
• Temperature
• Trajectory/source region
• “Amount effect”
Leaf-atmosphere Response
• Humidity
• Stomatal conductance
• Temperature/wind

R leaf
= α * [ α k
R source
( e i
− e s e i
Inter-leaf Diffusion
) + α kb
R source
( e s
− e a e i
Movement across leaf boundary
) + R a
( e a e i
)]
Exchange with atmosphere
• leaf =Leaf Water
• source =Source Water
• R =isotopic ratio
• e = Vapor Pressure term
• s =Leaf Surface
• i =Interleaf
• a =Atmosphere
• α *= water-vapor fractionation factor
(temperature-dependent)
• α k
=kinetic fractionation factor
(inter-leaf diffusion)
• α kb
=kinetic fractionation factor
(leaf-atmosphere boundary diffusion)
SEM image of open stomata
From: Roden et al. 2000

δ 18 O cellulose
= f
0
• ( δ 18 O source
+ ε
0
) + ( 1 − f
0
) • ( δ 18 O leaf
+ ε
0
)
Enriched
Sugars
+
Depleted
Source
Water
=
C
E
L
L
U
L
O
S
E
•Source water is substrate for synthesis of cellulose
•“F” term (0.42) describes amount of exchange between enriched photosynthates and source water
• “ ε ” is a biochemical fractionation factor (27‰) associated with the synthesis cellulose
From: Roden et al. 2000

San Gabriel Mountains:
Precipitation samples
White Mountains:
Cellulose Samples

• Trees of similar age were cored with 5 mm increment borer
• Dated using Methusela Walk Chronology (ITRDB)
• Cores without missing rings were selected for analysis
• Sliced into annual samples under microscope with scalpel
• Extract cellulose from wood using a modified version of the “Brendel method” (Brendel, 2000)
• Pyrolysis at 1054° to produce CO
• Analysis on continuous flow IRMS, reported relative to
VSMOW
• Intermittent standards confirm 0.3‰ analytical uncertainty

• Funnel collector with mineral oil to prevent evaporation
• Water collected following each precipitation event and collectors redeployed
• Water samples were equilibrated with CO known isotopic composition
2 of
• CO
2 was analyzed on a dual-inlet IRMS
• Isotopic composition of water was backcalculated

18
BcP4-1
BcP2-4

18
•Relatively stable
•Strong bidecadal
Red line is mean value

Palmer Drought Severity Index
(Cook et al. NCDC Database )
Bristlecone Pine δ 18 O

Bristlecone Pine δ 18 O
Santa Barbara Basin Benthic δ 13 C
Interpreted as upwelling proxy
(Holsten et al. 2004)
Walker Lake δ 18 O
Interpreted as lake level proxy
(Yuan et al. 2006)

•The major isotopic excursions correlate with climatic events as evidenced from instrumental and proxy records…
•Literature suggests this would be due to: a)Changes in Humidity b)Changes in Source Water c)A combination of the two

• Instrumental humidity record
• Modeling results to test humidity-cellulose sensitivity
Relative Humidity (%)

• Instrumental humidity record
Modeling suggests:
• Humidity could only account for a fraction of the isotopic variability (~1.5‰)
• Modeling results
• A change in isotopic composition of source water is more likely candidate to explain major transition
Relative Humidity (%)

Scenario 1:
Changes in utilization
• Long residence time
• Subdued climate signature
• Generally enriched values
Deep Water
• Short Residence time
• Responsive to climate
• Generally depleted values
Shallow
Water

Scenario 1 (cont.):
Changes in utilization
Major earthquakes

1. Magnitude of isotopic shift exceeds shallow/deep water isotopic gradient (Tang and Feng, 2001)
2. Earthquakes were likely too distal to generate a major hydrologic change
3. These trees have a characteristically shallow root system

Isoto pically deple ted
Isot opic ally enri che d d he ric en ly al ic op ot
Is

• Friedman et al. 1992 showed isotopic composition of precipitation in the region has high seasonal and interannual variability.
• Data from individual storms during a winter season shows difference between North Pacific storms (~-11‰ ) and “Pineapple Express” storm (~-2.5‰ ) can be close to 9‰.

*
Modified From: Dettinger, 2005
* Ralph et al. 2004

• Storms currently occur a few times a year*
• Storms occur in December and January when the Jet Stream is at its southern most latitude*
• Seem to have a positive correlation with positive phase of PDO*
• Could subtropical storms have been the dominant winter storm type prior to 1850?
*(Dettinger, 2005)

• Cellulose has similar spectrum as drought patterns in the area during the instrumental period
• Major mid-19 th century transition is documented in many other proxy records (regionally and globally)
• Geochemical modeling suggests that a change in source water is likely candidate to explain major transition
• Water utilization is possible but unlikely explanation
• Change in storm trajectories bringing sub-tropical storms
(enriched isotopic values) to the region could produce observed variability

Period of major climatic change
Bristlecone Pine δ 18 O
Interpreted as change in storm trajectories
Santa Barbara Basin Benthic δ 13 C
Interpreted as upwelling proxy
(Holsten et al. 2004)
Walker Lake δ 18 O
Interpreted as lake level proxy
(Yuan et al. 2006)

• Lowell Stott and Miguel Rincon (USC)
• Thomas Harlan (LTRR)
• John Louth (National Forest Service)
• Pat Chapman (Chapman Ranch)
• GSA and USC for funding
• Thanks for listening