GSA Data Repository 2019295 D’Arcy, F., et al., 2019, Carbon and sulfur isotopes in tree rings as a proxy for volcanic degassing: Geology, https://doi.org/10.1130/G46323.1

1.1 Appendix I: Ring width, sulfur concentrations, and 1

environmental comparison 2

Ring width 3

The species selected for this study, Alnus Acuminata, is a tall tree of the Alder genus which 4

is locally known as the jaul. This species is native to the area and found in abundance 5

surrounding Turrialba volcano, growing both wild in the national park and as a silviculture crop 6

planted by dairy farmers to maintain the soil and grass quality of their pastures (Russo, 1990). 7

Growing between 1300 to 2500 metres above sea level, A. Acuminata is found as far south as 8

Argentina, where it has been used successfully in subtropical dendrochronology due to its 9

reliable and clearly visible annual rings (e.g., Grau et al., 2003; Morales et al., 2004). These rings 10

are formed as a result of water availability during the growing season (wet season) at high 11

elevation (Morales et al., 2004) in addition to temperature variations, while growth shuts down 12

during the dry season of montane Argentina (Grau et al., 2003). Precipitation is similarly a 13

limiting factor in the dry season of the Costa Rican highlands, which experience a dry season 14

from January to April and a wet season from May to December. Dendrochronological studies 15

have proven successful in tropical environments at high elevation (e.g., Ballantyne et al., 2011; 16

Cook et al., 2010; Stahle, 1999; Worbes, 1995), hence this species is a suitable candidate for this 17

study. 18

One to two 5 mm cores and one 10 mm core were sampled at chest height from each tree 19

using increment borers. To avoid contamination, no lubricant was used, and bark was carefully 20

scraped away with a steel knife to avoid contamination from ash or moss. Cores were handled 21

with nitrile gloves and stored in parafilm in aluminum tubes for transport; the cores were opened 22

in order to dry them and avoid growth of mold before they arrived at the lab. All cores were 23

dried in an oven at 60°C for 24 to 48 hours, then sanded. Ring widths were measured and viable 24

samples were cross-dated. Since no tree ring data exist for this region, the master chronology we 25

created was limited to trees collected during this study. Occasionally, faint and narrow rings 26

were observed which could not be placed with statistical confidence as annual in nature. In 27

general, however, rings were well-developed. The annual nature of the tree rings is supported by 28

the age of LP01. The owner of the tree provided the exact year (1959) when it was planted on 29

their farm, and this date was verified upon cutting the tree and counting the rings. 30

Each tree which underwent isotopic analysis was grouped with trees from the same site, 31

where applicable, and chronologies from each site were averaged and normalized to yield ring 32

width indices (Fig. S1d). In our study, ring size ranged from 0.2 to 2 cm in size. From 33

2010/2011 onwards, rings are narrow in LP01 and TJ05, while in SG08 they are larger. Ring 34

width is highly variable both within single trees or sites and between them. Ring widths of 35

samples TJ05 and LP01 generally are antipathetic to ring widths of SG08 throughout the 36

chronology. 37

Sulfur concentration 38

Sulfur concentrations range from 0.015 % to 0.06 % sulfur (Fig. S1c). These are typical 39

values for wood, which is around 50 % carbon. Sulfur concentrations do not show clear 40

correlations with δ34S (correlation coefficient of 0.12). LP01 and TJ05 have the highest sulfur 41

concentrations after 1999. While LP01 has the lowest δ34S overall, TJ05 has the highest δ34S 42

overall. In 2014/2015, δ34S decreases for both of these samples, while sulfur concentration 43

increases sharply in LP01 but decreases sharply in TJ05. Some studies have reported an inverse 44

trend between δ34S and concentration (Wynn et al., 2014), while others have reported no 45

significant change in sulfur concentration despite large variations in δ34S (Thomas et al., 2013). 46

Although some studies suggest that sulphur will be concentrated in the outermost rings (Fairchild 47

et al., 2009), this may not be the case for A. Acuminata. Our background samples, as well as 48

TJ05, show relatively similar sulfur concentrations (Fig. S1c), increasing confidence that the δ34S 49

trend we see for TJ05 is a result of volcanic emissions affecting the tree environment. 50

Environmental comparison 51

Other than the volcanic pollution-induced 13C enrichment seen for TJ05, year-to-year 52

δ13C shifts of +0.5 ‰ to +0.8 ‰ are observed in each sample at varying times (1994/1995 to 53

1996/1997 for TJ05, 2002/2003 to 2004/2005 for SG08, and 2008/2009 to 2010/2011 for LP01). 54

These shifts are not persistent, however, and may be attributed either to analytical uncertainty or 55

to short-term variability caused by natural fluctuations as seen in other studies (e.g., Savard et al., 56

2002). These minor enrichments may be caused by precipitation or temperature fluctuations, as 57

they appear to correspond to years of unusually high rainfall (Fig. S1e). In 2004/2005, SG08 58

produced narrow rings, which correspond with a plateau in δ13C and may support the hypothesis 59

that these minor effects are rainfall induced. 60

Soil acidification caused by anthropogenic SO2 pollution has been shown to increase 61

sulfur concentration in tree rings (Tendel and Wolf, 1988), and soil acidification also occurs at 62

nitrogen-fertilized pastures (Noble et al., 1998). The tree from which came sample LP01 was 63

located on a well-established dairy pasture in a fertile valley directly on the southern flank of the 64

volcano. This acidity may explain the elevated sulfur concentration in the rings of LP01, but 65

reducing conditions are expected to cause an enrichment in residual sulfate (Chambers and 66

Trudinger, 1979). Since LP01 was located in a relatively flat area where soil depth is greater and 67

the tree was relatively old (59 years, as compared to ~30 year age of the other trees), the uptake 68

and mobility of sulfur may be affected by these conditions (Pearson et al., 2005). If the roots 69

have grown sufficiently, they may reach the saturated zone in deeper soils, tapping a source of 70

sulfate dissolved in deeper groundwater (Yang et al., 1996). 71

72

Figure S1: (a) Biannual δ13C values relative to VPDB with analytical error of ± 0.1 ‰. 73

These values are not corrected for the Suess effect of global atmospheric 13C depletion due 74

to fossil fuel consumption. (b) Biannual δ34S values relative to VCDT with analytical error 75

of ± 1 ‰. (c) Percent sulfur as calculated from Elemental Analyser results for wood 76

powder analysis. (d) Ring width index normalized for comparison between different tree 77

sites. (e) Total precipitation for Costa Rica (gray), Turrialba volcano weather station 78

(orange) and Talamanca Mountains Cerro Buenavista weather station (green), where the 79

translucent colour represents total precipitation in the rainy season (May to December) 80

and the solid colour represents total precipitation in the dry season (January to April) 81

(data provided by the Instituto Meteorológico Nacional). 82

83

1.2 Appendix II: Tree sample locations 84

85

86

Table S1: List of tree samples chosen for dendrochemical analysis. Four samples were 87

chosen at varying distances around the volcano and at background in order to assess the 88

effect of the volcanic plume. Duplicate trees could not be assessed due to sampling 89

constraints in this first study, but an error analysis between and within trees (Appendix 90

III) was performed to better understand the variations. Soil ph was determined using 91

litmus paper in the field when soil humidity was sufficient. Trade winds are northeasterlies, 92

and the mean plume direction heading is 247° ± 19° (Conde et al., 2014). Locations are in 93

decimal degrees using the WGS84 datum. 94

95

Tree

name

Latitude Longitude

(decimal degrees

relative to WGS84)

Elevation

(m)

Distance

to crater

(km)

Heading

from

crater

Type Soil pH

TJ05 10.00610° -83.77373° 2772 1.5 215° Forested

slope

4-5

LP01 09.99791° -83.77053° 2598 2.5 192° Dairy

pasture

4-5

TJ13 09.99697° -83.74500° 2251 3.5 153° Grassy

slope

7

SG08 09.57669° -83.80103° 2442 50 184° Rocky Too dry to

slope measure

96

97

98

99

1.3 Appendix III: Mass spectrometry details and error 100

analysis 101

102

Table S2: Error assessment of replications, intra-tree, inter-tree, and cellulose samples 103

Sample δ34S Mean

Deviation

from

mean Sample δ13C Mean

Deviation

from

mean

Whole wood analytical error (Sulfur quadruplicate, carbon duplicates)

LP01-96-97 6.1

7.14

1.03 TJ 6a93x -27.28 -27.25 0.04

LP01-96-97_1 8.0 0.85 TJ 6a93y -27.22

LP01-96-97_2 6.3 0.81 TJ 6b93x -27.32 -27.34 0.03

LP01-96-97_3 8.1 1.00 TJ 6b93y -27.36

Std. Dev. 1.07 TJ 5c93x -25.82 -25.95 0.19

TJ 5c93y -26.08

TJ 5d93x -25.75 -25.84 0.13

TJ 5d93y -25.93

TJ 6a01x -26.87 -26.90 0.04

TJ 6a01y -26.92

TJ 6b01x -26.63 -26.66 0.03

TJ 6b01y -26.68

TJ 5c01x -26.38 -26.34 0.05

TJ 5c01y -26.30

TJ 5d01x -26.21 -26.25 0.06

TJ 5d01y -26.29

Pooled Std. Dev. 0.06

Whole wood intra-tree variation between cores

TJ5d 01x 6.47 6.55 0.08 TJ5d 01x -26.21 -26.29 0.08

TJ5c 01x 6.63 TJ5c 01x -26.38

TJ5c 93x 6.23 6.10 0.13 TJ5c 93x -25.82 -25.79 0.03

TJ5d 93x 5.97 TJ5d 93x -25.75

TJ6b 01x 9.16 8.05 1.11 TJ6b 01x -26.63 -26.75 0.12

TJ6a 01x 6.93 TJ6a 01x -26.87

TJ6a 93x 4.87 TJ6a 93x -27.28

TJ6b 93x nd TJ6b 93x nd

Pooled Std. Dev. 0.65 Pooled Std. Dev. 0.08

Whole wood inter-tree variation

TJ5 2001-2013 average 6.55 0.75 TJ5 2001-2013 average -26.29 0.23

TJ6 2001-2013 average 8.05 TJ6 2001-2013 average -26.75

Std. Dev. 1.06 Std. Dev. 0.32

TJ5 1993-2000 average 6.10 0.61 TJ5 1993-2000 average -25.79 0.75

TJ6a 93x 4.87 TJ6a 93x -27.28

Std. Dev. 0.87 Std. Dev. 1.05

Whole wood (x) and holocellulose (s)

TJ6a 93x 4.9 5.65 0.78 TJ6a 93x -27.28 -27.18 0.09

TJ6a 93s 6.4 TJ6a 93s 27.09

TJ5c 93x 6.2 5.01 1.22 TJ5c 93x -25.82 -25.71 0.10

TJ5c 93s 3.8 TJ5c 93s -25.61

TJ5c 01x 6.6 5.72 0.91 TJ5c 01x -26.38 -26.22 0.16

TJ5c 01s 4.8 TJ5c 01s -26.07

TJ6a 01x 6.9 7.29 0.35 TJ6a 01x -26.87 -26.73 0.14

TJ6a 01s 7.6 TJ6a 01s -26.59

TJ5d 01x 6.5 6.10 0.37 TJ5d 01x -26.21 -26.15 0.06

TJ5d 01s 5.7 TJ5d 01s -26.09

TJ6b 01x 9.2 7.95 1.21 TJ6b 01x -26.63 -26.58 0.06

TJ6b 01s 6.7 TJ6b 01s -26.52

Pooled Std. Dev. 0.88 Pooled Std. Dev. 0.11

104

Mass spectrometry 105

For carbon, 1.1-1.5 mg of wood powder were combusted in tin capsules with an 106

Elementar Vario Microcube and the δ13C in the resulting CO2 gas measured by an Isoprime 100 107

mass spectrometer. Two internal standards were used for calibration (-42.16 ‰ and -17.14 ‰) 108

and cross-checked with a third internal standard (-28.75 ‰). Stable carbon isotopic ratios were 109

calculated as 110

δ C 𝐶/ 𝐶

𝐶/ 𝐶1

and normalized on the VPDB scale (NBS19-LSVEC). 111

For sulfur, 25-40 mg of wood powder were weighed into tin boats and combusted in the 112

Elementar Pyrocube, releasing N2, CO2 and SO2. Due to the large sample mass, a carbo-sorb trap 113

was added to immobilize excess CO2 not trapped by the Pyrocube’s own purge and trap system, 114

so that δ34S in the SO2 could be analysed by the Isoprime 100. Peak heights varied between 0.2-115

1.2 nA, so an amplitude correction was calculated to detrend the raw δ34S signal in relation to 116

peak size. The instrument was calibrated with three international standards: IAEA S1 (-0.3 ‰), 117

IAEA S2 (22.63 ‰), and IAEA S3 (-32.49 ‰). Standards and blanks were included throughout 118

the run to account for any drift and baseline changes, although sulfur contents of blanks were 119

negligible. Stable sulfur isotopic ratios, defined as 120

δ S 𝑆/ 𝑆

𝑆/ 𝑆1

were normalized on the V-CDT scale. Sulfur concentrations were measured concurrently from 121

the Elementar pyrocube using a Thermal Conductivity Detector (TCD). 122

Errors and reproducibility 123

A test for δ13C analytical error was performed on eight whole wood powders. Each was 124

analysed twice, and yielded a pooled standard deviation of 0.06 ‰ between duplicates. The 125

analytical error for carbon was rounded to 0.1 % for error bars. A separate test was performed to 126

assess δ34S analytical error, in which one whole wood powder was split ad weighed into four 127

capsules which were each analyzed. The standard deviation for the quadruplicate δ34S run was 128

0.93 ‰, which was rounded to 1 ‰ for error bars. In addition to errors from the mass 129

spectrometry and processing, a fundamental step in any dendrochemical study requires an 130

assessment of error between trees and within trees. To address these concerns, a series of 131

duplication tests were performed on homogenized wood from two trees located 5 km apart. 132

Two trees were selected for error analysis, and two cores from each tree were cut and 133

ground into two time increments: pre-2000 and post-2000 bulk wood. By comparing the results 134

of the same sets of years from each tree, a temporal comparison can be made between trees. 135

Then, by comparing the results from two cores taken from different sides of the same tree, we 136

can assess the variations in the dendrochemistry within the tree. The pooled standard deviation 137

between duplicate cores for δ34S whole wood was 0.65 ‰, with only the duplicate analysis from 138

tree 1 (TJ6) possessing a deviation from the mean exceeding 0.2 ‰. The pooled standard 139

deviation between cores for δ13C was 0.08 ‰. The largest variability is observed between trees, 140

with a standard deviation of 1.1 ‰ for carbon and 0.87 ‰ for sulfur from the 1993-2000 bulk 141

wood. The standard deviation of the 2000-2013 bulk wood is 0.3 ‰ for carbon, and 1.06 ‰ for 142

sulfur. 143

Although either whole wood, lignin, or cellulose may be used in carbon isotopic analysis, 144

softwoods are sometimes processed through a cellulose extraction step in order to remove any 145

resins (McCarroll and Loader, 2004). In cedar trees, it was also shown that water soluble sulfur, 146

presumably in resins, is much less abundant than organically bound sulfur, but the two 147

components differ in δ34S caused due to either fractionation or translocation effects (Kawamura 148

et al., 2006). Even though alder trees are not softwoods, in order to assess the effect of intra-tree 149

fluid extraction on isotopic results for A. Acuminata in this environment, a subset of the bulk 150

wood powders underwent a Soxhlet chemical extraction to isolate holocellulose. The samples 151

which underwent a Soxhlet extraction experienced a systematic δ13C shift of +0.1 to +0.3 ‰, but 152

a random δ34S shift of +1.5 to -2.5 ‰. Results of the intra-tree, inter-tree, and cellulose tests are 153

presented in Table S2, and plotted in Figure S2. 154

155

156

Figure S2: Stable isotopic ratios of bulk wood samples. δ13C values are calculated relative 157

to VPDB with analytical error of ± 0.1 ‰. δ34S values are calculated relative to VCDT with 158

analytical error of ± 1 ‰.159

160

161

1.4 Appendix IV: Isotopic data 162

163

Table S3: Biannual δ13C values in per mil are relative to VPDB with analytical error of ± 164

0.1 ‰, and values are also shown with correction for the Suess effect of global atmospheric 165

13C depletion due to fossil fuel consumption. Percent sulfur as calculated from Elemental 166

Analyser results and accompanying biannual δ34S values in per mil relative to VCDT, with 167

analytical error of ± 1 ‰. 168

Sample Year Measured

δ13C (‰)

δ13C Suess

corrected*

(‰)

% Sulfur

Amplitude-

corrected

δ34S (‰)

SG_08_94_5 1994/1995 -24.7 -23.3 0.036 9.6 SG_08_97_6 1996/1997 -25.4 -23.9 0.030 9.9 SG_08_98_99 1998/1999 -26.0 -24.5 0.028 10.4 SG_08_00_01 2000/2001 -25.9 -24.3 0.026 8.9 SG_08_02_3 2002/2003 -26.4 -24.8 0.023 10.5 SG_08_04_5 2004/2005 -25.7 -24.0 0.024 10.2 SG_08_06_7 2006/2007 -25.8 -24.0 0.025 7.6 SG_08_08_9 2008/2009 -25.9 -24.0 0.026 8.3 SG_08_10_11 2010/2011 -26.6 -24.8 0.027 9.4 SG_08_12_13 2012/2013 -26.0 -24.1 0.028 7.9 SG_08_14_15 2014/2015 -25.9 -24.0 0.041 9.1 LP_01_94_5 1994/1995 -25.0 -23.6 0.029 6.9 LP_01_96_7 1996/1997 -25.3 -23.8 0.025 8.1 LP_01_98_99 1998/1999 -25.6 -24.1 0.043 7.6 LP_01_00_01 2000/2001 -25.6 -24.0 0.042 6.7 LP_01_02_3 2002/2003 -25.6 -24.0 0.045 6.7 LP_01_04_5 2004/2005 -25.9 -24.2 0.047 6.3 LP_01_06_7 2006/2007 -25.9 -24.2 0.039 6.1 LP_01_08_9 2008/2009 -26.4 -24.6 0.043 6.5 LP_01_10_11 2010/2011 -25.7 -23.8 0.038 6.4 LP_01_12_13 2012/2013 -26.2 -24.2 0.045 6.5 LP_01_14_15 2014/2015 -26.2 -24.2 0.058 5.9 TJ_05_94_5 1994/1995 -26.3 -24.9 nd nd TJ_05_96_7 1996/1997 -25.8 -24.3 nd nd TJ_05_98_99 1998/1999 -26.0 -24.5 0.043 11.9 TJ_05_00_01 2000/2001 -26.3 -24.7 0.054 11.9 TJ_05_02_03 2002/2003 -26.3 -24.6 0.042 11.8 TJ_05_04_5 2004/2005 -26.5 -24.8 0.035 9.5 TJ_05_06_7 2006/2007 -26.3 -24.5 0.036 9.2 TJ_05_08_9 2008/2009 -26.1 -24.3 0.033 10.7

TJ_05_10_11 2010/2011 -26.1 -24.2 0.028 11.5 TJ_05_12_13 2012/2013 -25.9 -23.9 0.036 8.0 TJ_05_14_15 2014/2015 -24.9 -22.9 0.020 6.3 TJ13_94_95 1994/1995 nd nd 0.030 10.2 TJ13_96 97 1996/1997 -26.6 -25.1 nd nd TJ13_98 99 1998/1999 -26.1 -24.6 0.022 8.7 TJ13_00 01 2000/2001 -26.1 -24.5 0.026 9.7 TJ13_02 03 2002/2003 -26.5 -24.8 0.029 8.7 TJ13_04 05 2004/2005 -26.6 -24.9 0.025 8.7 TJ13_06 07 2006/2007 -26.4 -24.6 0.030 8.8 TJ13_08 09 2008/2009 -26.3 -24.5 0.024 8.5 TJ13_10 11 2010/2011 -26.4 -24.6 0.028 7.6 TJ13_12 13 2012/2013 -26.3 -24.4 0.017 9.1 TJ13_14 15 2014/2015 -26.8 -24.9 nd nd

169 *The Suess correction involves subtracting the difference between the pre-industrial and 170

global atmospheric δ13C for each set of years: δ13Ccorrected = δ13Cplant – (δ13Catm + 6.4) 171 (McCarroll and Loader, 2004). Average global atmospheric δ13C for each set of years was 172 obtained from the Mauna Loa observatory (http://cdiac.ess-dive.lbl.gov/d13_flask_mauna_loa.html). 173 174

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228

Appendix DR2 (all raw and processed data)

2019295 Appendix DR2.xlsx