Isotopes and Tree Rings

Isotopes in Tree Rings

• Environmental processes captured in tree rings can be embodied either physically or chemically.

• Chemical properties involve (1) individual elements, (2) chemical compounds, and (3) stable isotopes.

• Individual elements and chemical compounds often indicate pollution events, i.e. exogenous disturbance pulses and trends.

• Examples• lead from gasoline• nickel contamination in groundwater• titanium from natural sources

• Isotopes indicate past changes in environmental processes that cause differences in the relative proportions of an element’s isotopes.

• Isotopes: Atoms with the same number of protons, but differing numbers of neutrons. Isotopes are different forms of a single element.

• Isotopes: Atoms with the same number of protons, but differing numbers of neutrons. Isotopes are different forms of a single element.

• Isotopes indicate past changes in environmental processes that cause differences in the relative proportions of an element’s isotopes.

• Example: Carbon 12 and Carbon 13 are both isotopes of carbon, one with 6 neutrons and one with 7 neutrons (both with 6 protons).

• Example: Oxygen 16, Oxygen 17, and Oxygen 18 are all isotopes of oxygen, one with 8 neutrons, one with 9 neutrons (rare), and one with 10 neutrons (all with 8 protons).

• Reference = Vienna Standard Mean Ocean water (VSMOW) for oxygen and Vienna PeeDee (River) Belemnite (VPDB) for carbon.

Isotopes and Climate Change

Hurricane Convection and Precipitation

Lawrence, J.R. 1998: Isotopic spikes from tropical cyclones in surface waters: Opportunities in hydrology and palaeoclimatology. Chemical Geology 144: 153-160.

18O (SMOW) ‰

P (

mb

)

-30 -15 -10 -5

200

-20-25

600

400

800

H. Olivia

TX hurricanes

“normal” precipitation Lawrence and Gedzelman 2002

18 O

(S

MO

W)

‰

5

0

-15

-5

-10

2/1 4/17 7/2 9/15 12/1DATE

CHANTAL

ALLISON

GROUND WATER

Lawrence and Gedzelman 2001

Unusual 18O in hurricanesUnusual 18O in hurricanes

Unusual 18O in soil waterUnusual 18O in soil water

Hypothesis: Because hurricane precipitation results in 18 O-depleted latewood cellulose, hurricane events can be identified by values of δ18O in the tree-ring record.

Eglin AFB

Sandy Isle

Valdosta

Francis Marion NF

Distribution of Pinus palustris

Big Thicket

Wormsloe

Fredericksburg

Hope Mills

St. Augustine

Hurricanes do not happen hereHurricanes do not happen here

Hurricanes happen hereHurricanes happen here

Methods

1. Measure/crossdate tree rings using skeleton plots and COFECHA.

2. Seasonally-resolved sampling (earlywood, latewood for each year) using razor or microtome

Grissino-Mayer,2004

Lake Louise, Georgia

18 living trees43 remnants, stumps, snags

61 total trees/94 measured radii

Interseries correlation: 0.58

Average mean sensitivity: 0.35

Lake Louise, Georgia

18 living trees43 remnants, stumps, snags

61 total trees/94 measured radii

Interseries correlation: 0.58

Average mean sensitivity: 0.35

3. Remove pine resins and other extractives (Loader et al., 1997; sonification) to yield α-cellulose.

4. Run ~80 ug through mass spec

α-cellulose

28

29

30

31

32

33

34

35

36

37

38

39

1770 1790 1810 1830 1850 1870 1890 1910 1930 1950 1970 1990

Year

18 O

-c

ellu

lose

(V

-SM

OW

)

LWLWEWEW

To remove trends To remove trends that might mask that might mask the hurricane the hurricane signal, perform signal, perform AR-1 modelingAR-1 modeling

Residuals < –1 Residuals < –1 are associated are associated with hurricane with hurricane activityactivity

Many residualsMany residuals> –1 and < –> –1 and < – 0.5 0.5 are also associated are also associated with hurricane with hurricane activityactivity

Most residuals > Most residuals > +1 are associated +1 are associated with known with known droughtsdroughts

Hurricane Florence 1953

Hurricane #314-23 August

Hurricane #417-30 August

Hurricane #730 Sep-7 Oct

Hurricanes of 1871

PROXY RECORD OF HURRICANES Between 1770 and 1997, we found no

hurricane event where residual is > –0.5.

1950s was the busiest decade since 1870s.

Little activity between 1881 and 1930.

Significant activity from 1840 until 1880 (especially 1870s).

Unrecognized events in 1847, 1857, and elsewhere. New historical evidence since found for 1857 event.

Only two decades with no hurricane activity, 1830s and 1890s.

First U.S. record of “Great Hurricanes of 1780” that affected Caribbean region.