Marine evidence for episodic Holocene megafloods in North America and the northern Gulf of Mexico

Hemipelagic muds deposited during the past 5.3 cal kyr in the northern Gulf of Mexico (Orca Basin) contain seven intervals punctuated by relatively co arse siliciclastic grain-size peaks, planktonic faunal turnovers, and negat ive delta(13)C excursions. We believe these episodes represent megaflood de posits reflecting historically unprecedented outfall of North American floo dwater and terrigenous mud plumes into the gulf, resulting in collapse of t he open-ocean pelagic ecosystem. The deposits record multidecadal episodes of high continental precipitation and large Mississippi River floods at sim ilar to 4.7, 3.5, 3.0, 2.5, 2.0, 1.2, and 0.3 cal ka (500-1200-year recurre nce interval). Variations in tropical plankton frequencies define submillen ial warming intervals that culminate in these fluvial episodes. Strengthene d tropical currents in the gulf at these times appear to have increased sea surface temperatures and associated flow of moist gulf air to the midwest. Terrestrial paleohydrologic records support the marine evidence for millen nial-scale changes in recurrence of large midwest flood episodes.