I think they, the BaRkers, are the only reliable source around. Some of the articles published recently are completely insane, the conclusion contradicts the results of the experiment.

http://www.vpi.com/sites/default/fil...ce_Jan2012.pdf
the counter spin...

http://www.usgs.gov/newsroom/article.asp?ID=3066

the article...

http://www.sciencedirect.com/science...2209811100520X