What was done
The authors identified conspicuous gray clay-rich flood deposits in the predominantly olive varved sediments of the Santa Barbara Basin off the coast of California, USA, which they accurately dated by varve-counting.  They then compared their findings with those of others from throughout Mesoamerica and South America and speculated as to what might have caused the floods.

What was learned
Six prominent flood events were determined to have occurred at approximately AD 212, 440, 603, 1029, 1418 and 1605, "suggesting," in the words of the authors, "a quasi-periodicity of ~200 years," with "skipped" flooding just after AD 800, 1200 and 1800.  They further note that "the floods of ~AD 1029 and 1605 seem to have been associated with brief cold spells," that "the flood of ~AD 440 dates to the onset of the most unstable marine climatic interval of the Holocene (Kennett and Kennett, 2000)," and that "the flood of ~AD 1418 occurred at a time when the global atmospheric circulation pattern underwent fundamental reorganization at the beginning of the 'Little Ice Age' (Kreutz et al., 1997; Meeker and Mayewski, 2002)."  Last of all, they report that "the quasi-periodicity of ~200 years for southern California floods matches the ~200-year periodicities found in a variety of high-resolution palaeoclimate archives and, more importantly, a c.208-year cycle of solar activity and inferred changes in atmospheric circulation."

What it means
The authors "hypothesize that solar-modulated climatic background conditions are opening a ~40-year window of opportunity for flooding every ~200 years," and that "during each window, the danger of flooding is exacerbated by additional climatic and environmental cofactors."  They also note that "extrapolation of the ~200-year spacing of floods into the future raises the uncomfortable possibility for historically unprecedented flooding in southern California during the first half of this century."  Hence, if and when such flooding occurs, there will be no need to suppose it came as a consequence of what climate alarmists call the unprecedented warming of the past century.

References
Kennett, D.J. and Kennett, J.P.  2000.  Competitive and cooperative responses to climatic instability in coastal southern California.  American Antiquity 65: 379-395.

Kreutz, K.J., Mayewski, P.A., Meeker, L.D., Twickler, M.S., Whitlow, S.I. and Pittalwala, I.I.  1997.  Bipolar changes in atmospheric circulation during the Little Ice Age.  Science 277: 1294-1296.

Meeker, L.D. and Mayewski, P.A.  2002.  A 1400-year high-resolution record of atmospheric circulation over the North Atlantic and Asia.  The Holocene 12: 257-266.