I know what you’re thinking. The rel=”nofollow” tag is only used when you link to external websites right? According to Wikipedia, the no follow tag is “ a relation tag (rel=”nofollow”) which can be added to any link and is technically a request from the website to search engines to ignore the link.” Basically, it stops the flow of the link juice, not passing any page rank.
It’s important to keep in mind that although the Googlebot has the ability to crawl as deep as possible, it rarely will go 5, 6 or 7 levels deep. If it does, it’s a rare occasion and those pages likely don’t rank well.
What’s the solution? Slap the rel=”nofollow” tag on all links in your site navigation that don’t need to be crawled as frequently. If you do this, be sure to link somewhere to them without the nofollow, such as from your physical sitemap.
I believe this strategy can work wonders on getting your site’s pages out of the supplemental index. Be sure to leave a comment if you’ve successfully used this method before, or let me know your results after using it.