CARBON ISOTOPES OF MAPLE SYRUP: A RECORD OF ATMOSPHERIC AND ENVIRONMENTAL CHANGE

Carbon isotope analysis of maple syrup has primarily been used to detect adulteration of maple syrup through the addition of relatively inexpensive cane and corn sugar. This detection method makes use of the difference in carbon fractionation of C3 vs. C4 plants, but overlooks the dynamic controls on plant δ¹³C. Carbon isotopes of atmospheric CO₂ have increasingly been pulled toward that of fossil fuels since industrialization, and plant physiology may be affected by a variety of environmental factors. Syrup δ¹³C is naturally scattered; this study found that syrup from one sugarbush in Vermont spanned 1.0‰ in a single season (1993, n=51). Even so, New York and Vermont maple syrups spanning 1970 to 2006 generally reflect the atmospheric trend in δ¹³C, dropping by ~1.3‰. Syrup grade and time in season, however, show no correlation with δ¹³C. 95% of literature analyses of maple syrup are in the range -22.8 to -25.0‰ (n=231). Most syrups from this study (n=101) are within this range, and some from central NY cluster at the high end of this range. Two authentic Hamilton, NY syrups have δ¹³C = -22.3‰ (1996) and -23.0‰ (1997), higher than the authentication cut-off of -23.2‰ proposed by Morselli and Baggett (1984). This study suggests that syrup carbon isotope ratios are comparable only in view of changing atmospheric CO₂ compositions, and authentication methods should incorporate a full understanding of the factors affecting maple syrup δ¹³C.