Rapid decline and mortality of a Pleistocene-aged forest now submerged in the northern Gulf of Mexico, USA

The Gulf and Atlantic Coastal Plains of the southern United States are characterized by a wide continental shelf that was subaerially exposed for ca. 80,000 years during glacial-interval marine regressions and transgressions. Given their present submergence, little is known about the vegetation dynamics, particularly at annual time scales, of these formerly terrestrial sites due to erosional processes associated with marine transgressions. Here, we present an annually resolved and well-replicated 489-year tree-ring chronology from macrobotanical specimens—anatomically identified as Taxodium distichum (L.) Rich.—collected in situ from a recently exposed submerged forest in 18 m water depth in the northern Gulf of Mexico. This chronology not only reveals historical vegetation dynamics at annual resolutions during Marine Isotope Stages 3–5a, but it also captures a catastrophic mortality event likely connected to intense storm activity, perhaps driven by freshwater fluxes from Heinrich events. Our findings are supported by coupled climate model simulations from the last glaciation, providing new insights into the environmental history of the southeastern US coastal regions.