A tree-ring oxygen isotope record of tropical cyclone activity, moisture stress, and long-term climate oscillations for the southeastern United States.

摘要

Geological proxies extending beyond temporal and geographical limits of climate records are key to understanding climate variability. Tree rings preserve uniquely high resolution and precisely dated records of past environmental conditions. Oxygen isotopic compositions of alpha-cellulose in seasonally resolved components (earlywood (EW) and latewood (LW)) of tree rings of southeastern coastal plain pines predominantly reflect precipitation source and/or temperature providing a snapshot of climate activity for the region.; A 227-year record of EW and LW oxygen isotope compositions of alpha-cellulose in slash and longleaf pine (Pinus palustris Mill. and Pinus elliottii Engelm.) tree rings record evidence of past tropical cyclone activity, seasonal moisture stress, and multidecadal climate oscillations. Topical cyclones produce large amounts of precipitation with distinctly lower oxygen isotope ratios than typical low-latitude thunderstorms and can persist in soil waters for several weeks becoming incorporated into the cellulose during tree growth. The proxy record compares well with the most reliable instrumental record (1940--1997) and the continuous proxy is supported by instrumental and historical documents back to 1770.; Long-term variations in the oxygen isotope compositions of tree-ring alpha-cellulose are governed by the influence of long-term climate oscillations, such as the Atlantic Multidecadal Oscillation (AMO), Pacific Decadal Oscillation (PDO), and El Nino Southern Oscillation (ENSO). AMO shows a strong negative correlation until ∼1950s which coincides with a major PDO-ENSO shift (1947--1976) that was followed by two strong La Nina episodes. Spectral analysis of LW tree-ring oxygen isotopes reveals significant periodicities that may reflect solar activity [i.e., Gleissberg Period (82.7); Bruckner Cycle (33.7)] and ENSO (7.9 and 5.1) influences on climate of the southeastern U.S. as well as tropical-only (5--6) and baroclinically enhanced (7--9) Atlantic hurricanes periodicities.; Oxygen isotopes of alpha-cellulose from sub-fossil longleaf pines record southeastern U.S. climate conditions during a portion of the Little Ice Age (1580--1650). These results support previous studies that suggest this area did not experience dramatic climate effects of the Little Ice Age. The results suggest that tropical cyclone activity was low to moderate for 1580--1640, but increased noticeably in the last decade of the study (1640s).