Coke's Muhtar Kent is the latest, but CEO turnover was already on the rise

Muhtar Kent is in good company.

Coca Cola announced Friday morning that its CEO is stepping down, effective May 1 of next year. Kent will remain as chairman of the company; President and CEO James Quincey will take the helm.

As of the end of October 2016, 59 chief executives of S&P 500 companies have either retired, resigned or been terminated, effective by the end of the year, according to corporate data firm Equilar. That figure is higher than in recent years. It indicates that in 2016, more than 10 percent of big-cap companies announced turnover at the top level. Put another way, that's more than one announced departure every week.

The departing CEOs have left for a variety of reasons. In October alone, we had retirement announcements, voluntary resignations and less-than-voluntary resignations. Hershey's chief John Bilbrey stepped down effective next summer to spend more time with his family. He's been with the company since 2011.

Visa head Charlie Scharf stepped down for personal reasons, effective Dec. 1.

Wells Fargo chairman and CEO John Stumpf stepped down following the revelation that the bank's community banking division had opened up to 2 million accounts for customers without their knowledge.

Caterpillar's Doug Oberhelman will retire in January, after the company's big bet on machinery and equipment didn't pay off. Oberhelman was with the firm for a total of 41 years, including the time before he was chief executive.

The average S&P 500 CEO tenure was around 7.4 years as of 2014, according to a previous Equilar study. That's up from 6.6 years in 2005. The next four years will see a reconfiguration of businesses' relationship to politics, and it's anyone's guess how that will affect CEO tenure.

Investors reacted to Coca Cola's pre-market news positively on Friday, sending the stock up about 2.5 percent.