Hydroclimatic relationships and stable isotopic analysis in baldcypress tree rings

Instrumental records of hydroclimatic extremes (e.g., drought, pluvial flooding, tropical cyclones) are temporally and spatially limited, making long-term assessments of the drivers of these events difficult. Paleo-reconstructions of these extreme events are therefore essential in understanding and evaluating future risk, especially within vulnerable coastal communities. In dendrochronology, δ¹⁸O (¹⁸O/¹⁶O) is a known proxy for reconstructing various hydroclimatic parameters (i.e., temperature, atmospheric humidity, streamflow). The tree takes up δ¹⁸O in source water for the development of woody tissue, with the isotopic ratio stored within the α-cellulose of annual tree rings. However, cellulose-derived δ¹⁸O from baldcypress (Taxodium distichum), the longest-lived species in the region, has never been investigated in studies of hydroclimate. In this exploratory study, we evaluate the use of δ¹⁸O-depletion in baldcypress latewood as a proxy for various southeastern hydroclimatic extremes to the comparable instrumental period. Results of baldcypress latewood δ¹⁸O over the Choctawhatchee River Basin were then compared to various climate indices and the instrumental tropical cyclone record, with correlations of varying strength expressed between the produced δ¹⁸O time series and precipitation, streamflow, self-calibrated Palmer Drought Severity Index, and maximum summer temperature. Large decreases in baldcypress δ¹⁸O latewood are determined to be reflective of regional TC precipitation. In direct interspecies comparisons, baldcypress δ¹⁸O is shown to be more sensitive to drought conditions than nearby longleaf pine (Pinus palustris) δ¹⁸O. Results of these comparisons reveal the future potential of the proxy in multivariate climate reconstructions.