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

Rainfall 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 (delta O-18(cell)) reflects local source water, climate, and tree physiology. The patterns of delta O-18(cell) within tree-rings has the potential to extend pre-instrument climate records with subannual resolution, but the influences on intra-ring delta O-18(cell) profiles are unexplored in many settings. In this study, high-resolution delta O-18(cell) 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 delta O-18(cell) analyses. The delta O-18(cell) 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 delta O-18(cell) profiles into two groupings: symmetrical delta O-18(cell) profiles versus asymmetrical profiles that have depressed latewood delta O-18(cell) values. The slope of latewood delta O-18(cell) profiles and mean delta O-18(cell) 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, O-18-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 O-18-depleted water overrides evaporative enrichment effects, resulting in low delta O-18(cell) of latewood. These results suggest that delta O-18(cell) proxies for tropical storm occurrence need to account for soil conditions at the site of tree growth.

Automated summary

This study analyzed high-resolution delta O-18(cell) profiles of three longleaf pine trees in a native savanna in Louisiana, United States, covering a wide range of rainfall conditions from 2001 to 2008. The results showed strong correlations between delta O-18(cell) values within and between trees, and highlighted the influence of specific soil conditions on the expression of latewood delta O-18(cell) values.