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.

Unusual d18O in hurricanes 200 Lawrence and Gedzelman 2002 “normal” precipitation Unusual d18O in hurricanes 400 P (mb) 600 H. Olivia 800 Lawrence and Gedzelman 2001 5 TX hurricanes GROUND WATER -30 -25 -20 -15 -10 -5 d18O (SMOW) ‰ d18O (SMOW) ‰ Lawrence flew through Olivia and Puerto vallarta thunderstorm on same day. The orange line is Rayleigh curve and PV l thunderstorm was right on line. Note how much more depleted Olivia is. At surface, values are less negative because T is higher. Bottom signal shows low 18O pulses due to hurricanes. Time along bottom shows: up to 6 weeks to grow cellulose with low 18O before evap ameliorates signal. -5 ALLISON -10 Unusual d18O in soil water CHANTAL -15 2/1 4/17 7/2 9/15 12/1 DATE

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.

Fredericksburg Hope Mills Distribution of Pinus palustris Sandy Isle Francis Marion NF Wormsloe Valdosta Big Thicket Eglin AFB St. Augustine

Hurricanes do not happen here Hurricanes happen here Hurricanes do not happen here Close up of LLC 004. Note variability in ring widths = sensitivity to climate.

Methods 1. Measure/crossdate tree rings using skeleton plots and COFECHA. 2. Seasonally-resolved sampling (earlywood, latewood for each year) using razor or microtome Lake Louise, Georgia 18 living trees 43 remnants, stumps, snags 61 total trees/94 measured radii Interseries correlation: 0.58 Average mean sensitivity: 0.35 Lake Louise, Georgia 18 living trees 43 remnants, stumps, snags 61 total trees/94 measured radii Interseries correlation: 0.58 Average mean sensitivity: 0.35 Grissino-Mayer,2004

4. Run ~80 ug through mass spec 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

EW LW

Residuals < –1 are associated with hurricane activity To remove trends that might mask the hurricane signal, perform AR- 1 modeling Residuals < –1 are associated with hurricane activity Many residuals > –1 and < – 0.5 are also associated with hurricane activity Most residuals > +1 are associated with known droughts

Hurricanes of 1871 Hurricane #4 17-30 August Hurricane #3 14-23 August Hurricane #7 30 Sep-7 Oct

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. Four hurricanes occurred in October 1780. Over 25,000 people died in these hurricanes, the most deaths recorded for any Atlantic hurricane in history. Each hurricane killed at least 1,000 people. A powerful hurricane in the eastern Gulf of Mexico from October 17-21 killed 2,000 people, mostly in western Cuba.