ABSTRACT: Calibration of meteorological conditions with tree ring chemistry: high-resolution stable isotope evidence from robotically micromilled cellulose.

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Abstract

Stable isotope values of tree ring cellulose record variation in humidity, soil moisture and stable isotope values of precipitation. We refine and constrain this hypothesis by examining tree ring cellulose from the northeastern United States. Cottonwood (Populus deltoides) trees from Green Lake State Park (GLSP) in central New York State were robotically micromilled to recover discrete high resolution aliquots of cellulose that represent as little as two weeks growth. d13C, d18O and dD values were compared to meteorological conditions, including temperature, precipitation (amount and isotope value), and humidity to evaluate the integrity with which tree cellulose records atmospheric and soil conditions. Trees from GLSP were selected in part because they are adjacent to our long carbonate-based climate record recovered from Green Lake sediment that has been calibrated with a century of meteorological data. A detailed cellulose-based record can extend our calibration of lake sediment back beyond the century long meteorological record. Thus, by fine-tuning the carbonate record using tree data an accurate climate record dating back millennia can be generated. Correlations between meteorological, carbonate sediment and tree ring records provides a more robust model for interpretation of climate variability using tree ring and carbonate isotope values. Aliquots of cellulose were recovered using a computer-controlled robotic micromilling device at a spatial resolution of ~0.5mm. Ring widths of our cottonwood trees were up to 7mm, permitting high-resolution sampling. Substantial inter- and intra-seasonal variability is apparent in d13C values that vary by up to 2 ‰ seasonally and 5 ‰ over our 63-year tree record. Time-series wavelet analysis of isotope and meteorological data demonstrate a strong solar-climate influence, with d13C lagging behind solar activity by 5-6 years. Lake sediment carbonate d13C values lag behind tree cellulose d13C values which is interpreted to represent the time required for decay of cellulose compounds and incorporation into the lake’s dissolved inorganic carbon reservoir. A significant decrease in d13C beginning in the early-mid 1980’s is attributed to lower SO2 concentrations in the atmosphere (known to interfere with leaf stomata) related to declining steel production. Oxygen values conflate a number of variables, including water sources, temperature and moisture stress resulting in considerable intra-seasonal variability. dD values vary by 50 ‰ and d18O values vary by 6 ‰ over the life of the tree.

Bibliography of Canadian Geomorphology