What is the cause of a sharp drop in rankings across Google, Bing and Yahoo?

[ChemistryMarketing]

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[Dave_Schulhof]

Hello, without being able to go into too much detail it could be a number of things:

• Although you removed bad links, if you received a penalisation make sure you get a manual review done by Google. You can access this in webmaster tools. You could still be 'black listed' by google.
• Link profile is small which is not bad but is the content around those links relevant and unique. Are they on high regarded sites?
• Check your robot.txt to make sure you are not blocking pages you shouldnt be and thus not being crawled by search engines
• Is the content on the site definately unique?

[MarieHaynes]

I've only had a quick look, but here is my theory.

If you noticed a sharp drop in Google in October of 2013 then there's a good chance that the Penguin 2.1 update on October 4 affected the site.  I do certainly see links that the Penguin algorithm would look upon unfavorably.  For example:

http://www.westdigitalmarketing.com/blog/funding-solutions-uk-digital-strategy/

http://www.startupoverseas.com/news/invoice-finance-for-an-exporter--cash-flow-and-peace-of-mind.html

http://21stguru.com/index.php?s=A&c=39&p=141

But, as Penguin was only a Google thing, it wouldn't affect your rankings in Bing and Yahoo.  Those unnatural links were probably supporting your rankings in those search engines. So, when you removed bad backlinks in order to clean up for Google's sake, you removed links that were supporting you in Bing and Yahoo and thus those rankings dropped.

There could be other reasons too, but that's my theory.