SEASONALLY-RESOLVED TREE-RING ISOTOPE RECORDS OF TROPICAL CYCLONES, DROUGHTS AND MULTI-DECADAL CLIMATE OSCILLATIONS, SOUTHEASTERN US

A recent increase in Atlantic tropical cyclone (TC) activity has been ascribed to both natural and anthropogenic forcings. Geological climate proxies extending beyond the temporal and geographical limits of meteorological records and historical documents are key to characterizing long-term trends and natural variability in TC activity. Tree rings preserve uniquely high resolution and precisely dated records of past environmental conditions. Using detailed meteorological records (1940-1997), O-isotope compositions of a-cellulose in seasonally-resolved components (earlywood and latewood) of tree rings from the SE coastal plain can be demonstrated to preserve an excellent proxy record of TC activity, seasonal droughts, and are superimposed on multi-decadal oscillations interpreted to reflect the dominant climate modes. A seasonally-resolved, 227-year (1770-1997) tree-ring isotope proxy record from felled and remnant pines (Pinus elliottii Engelm.; Pinus palustris Mill.) reveals documented TC and drought events, such as significant TC activity in the 1950 and 1870 decades. Newly recognized TC (e.g., 1857 event) and first evidence for impact of the Great Hurricane of 1780 on the SE USA are also captured. Tree-ring O-isotope series from sub-fossil longleaf pines recovered from Lake Louise (GA) extend the record by many centuries, including portions of the Little Ice Age. TC activity for 1580–1640 was very low, consistent with low N. Atlantic SST and drought records in the African Sahel; activity markedly increased in the 1640s. From 1876-1997, Atlantic Multidecadal Oscillation (AMO) records show a strong negative correlation with tree-ring d¹⁸O values until ~1950s. Breakdown in the correlation with the AMO coincides with a major PDO-ENSO shift from warm to cool conditions (1947–1976) that was followed by two of the strongest La Niña episodes in the last 50 years. Latewood O-isotopes from the 1950s strongly correlate with Niño 3.4 indices. Current and on-going studies of O-isotopes in tree rings may help to develop the extended records necessary to evaluate natural versus anthropogenic impacts on TC frequency.