A tip of the hat to Standard & Poor’s?

NYSE Euronext said it experienced huge surges in stock-trading activity on both sides of the Atlantic Ocean during August.

The operator of the New York and Paris stock exchanges said it handled 2.2 million trades a day in Europe, up 70.3 percent from a year ago. This was a record, it said.

In the United States, its average daily volume in stock trades jumped 38.9 percent from a year ago.

This reversed the basic trend in 2011 of significant double-digit drops in average U.S. daily stock trading volume for NYSE Euronext. In July, its daily trading volume in stocks was down 24.0 percent. In June, down 28.9 percent.

The “significantly higher’’ volume in trading occurred across all its venues and in derivative securities, as well as stocks. NYSE Euronext said the activity was “due to heightened market volatility in the U.S. and Europe.’’

The volatility was triggered on August 4 by the first-ever downgrade of U.S. debt, by ratings agency Standard & Poor’s. Four days of highly nervous trading ensued, with the Dow Jones Industrial Average swinging up or down more than 400 points for four days in a row. That was a first.

NYSE Euronext said its average volume of trading in derivatives, worldwide, reached 10.4 million contracts a day in August. That was up 64.6 percent, against a year ago.

In the U.S., options trading hit a new record of 5.8 million contracts a day, up 91.3 percent from a year ago. In Europe, derivatives volume increased 36.5 percent, to 4.5 million contacts a day.

NYSE Euronext’s share of trading in NYSE-listed stocks in August was 36.2 percent. That is down from 38.1 perent in August 2010, but up from 34.3 percent in July 2011 and almost back to the 36.6 percent share of June 2011.