Tree-Ring Analysis of Ancient Bald Cypress Trees and Subfossil Wood
Ancient bald cypress trees found in wetland environments have been used to develop exactly dated annual ring-width chronologies extending from the southeastern United States, across Mexico, and into western Guatemala. These chronologies are sensitive to growing season precipitation and have been used to reconstruct historic moisture levels in the southeastern United States and Mexico. The El Nino/Southern Oscillation (ENSO) is a major influence on these climate reconstructions, especially in Mexico where some of the most extreme droughts occurred during El Nino events. Additionally, most existing bald cypress chronologies made from modern trees have been extended with tree-ring data from “subfossil” wood recovered from surface and submerged river deposits. Well-preserved subfossil logs have also been recovered from buried deposits and may be useful in developing long, continuously dated Holocene chronologies and discontinuous “floating” Pleistocene chronologies. The subfossil bald cypress swamp discovered 6 m below the streets of Washington, D.C. was overrun by the Potomac River, possibly during the previous interglacial period, and provides direct evidence for one potential impact of unmitigated anthropogenic warming and sea level rise.
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