Seasonal Hydroclimate Recorded in High Resolution δ18O Profiles Across Pinus palustris Growth Rings

Abstract

AbstractRainfall amount and intensity are increasing under anthropogenic climate change, but many instrument records span less than a century. The oxygen isotopic composition of tree‐ring cellulose (δ18Ocell) reflects local source water, climate, and tree physiology. The patterns of δ18Ocell within tree‐rings has the potential to extend pre‐instrument climate records with subannual resolution, but the influences on intra‐ring δ18Ocell profiles are unexplored in many settings. In this study, high‐resolution δ18Ocell profiles were analyzed on three longleaf pine trees growing in a native savanna in Louisiana, United States. The time series covers a wide range of rainfall conditions from 2001 to 2008 C.E. with a total of 421 δ18Ocell analyses. The δ18Ocell values for individual years are well correlated with each other both within and between trees (r = 0.71–0.78). We used principal components analysis and k‐means clustering to differentiate δ18Ocell profiles into two groupings: symmetrical δ18Ocell profiles versus asymmetrical profiles that have depressed latewood δ18Ocell values. The slope of latewood δ18Ocell profiles and mean δ18Ocell values of latewood tissue correlate with total June‐November precipitation. We hypothesize that poorly drained soils in the study area mediate the influence of any individual storm event: in dry years, 18O‐depleted signals from convective storms are moderated by subsequent evaporative enrichment of standing water, whereas in wet years, increased humidity and frequent re‐supply of 18O‐depleted water overrides evaporative enrichment effects, resulting in low δ18Ocell of latewood. These results suggest that δ18Ocell proxies for tropical storm occurrence need to account for soil conditions at the site of tree growth.