What was done
The authors studied siliciclastic sediment grain size, planktonic foraminiferal and pteropod relative frequencies, and the carbon and oxygen isotopic compositions of two species of planktonic foraminifera in cored sequences of hemipelagic muds deposited over the past 5300 years in the northern Gulf of Mexico for evidence of variations in Mississippi River outflow characteristics over this time period.

What was learned
The data indicated the occurrence of large megafloods - "almost certainly larger than historical floods in the Mississippi watershed" - at 4700, 3500, 3000, 2500, 2000, 1200 and 300 years before present.  These fluvial events were likely "episodes of multidecadal duration," spawned by the export of extremely moist gulf air to midcontinental North America that was driven by natural same-time-scale oscillations in Gulf of Mexico ocean currents.

What it means
Think what would happen if, in the words of the authors, the United States were soon to experience a multidecadal episode of "historically unprecedented precipitation and flooding in the Mississippi watershed."  Before it was even in full-swing, the IPCC-inspired media would probably have driven the U.S. Senate to unanimous ratification of a dozen Kyoto protocols.  But would they have been right?  Such an occurrence of "historically unprecedented" extreme weather sure sounds like what the climate models are predicting to occur as a consequence of the ongoing rise in the air's CO2 content; but it is clear that these particular hydrologic events were in no way related to variations in atmospheric CO2 concentration, as they occurred over a period of near-constancy in this atmospheric property.  How easy it would be to make a monumental mistake in our stewardship of the planet!  We must be ever so careful not to rush to judgment in matters of such import.