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NEW YORK (MarketWatch) — U.S. stocks wrapped up a good year on a down note, as morning gains turned into sizeable losses on Wednesday.

The Dow Jones Industrial Average failed to close out 2014 above 18,000 after topping that big round number for the first time last week. Even so, it recorded its sixth straight year of gains, dating back to the end of the 2008-2009 bear market.

The S&P 500 SPX, -0.98% slid 21.45 points, or 1%, to end at 2,058.90, leaving the benchmark with a still-impressive yearly advance of 11.4%. It has now climbed for three straight years, giving investors gains of nearly 64% in that span.

The Dow Jones Industrial Average DJIA, -1.20%  dropped by 160 points, or 0.9%, to 17,823.07. The blue-chip gauge, up 7.5% for the year, clambered above 18,000 at the open and was up by as much as 60 points for the day before tumbling into the red. Wednesday’s loss, the biggest since Dec. 12, nudged it into a loss for December as well, its first monthly loss in three.

The tech-heavy Nasdaq Composite COMP, -0.91%  shed 41.39 points, or 0.9%, to end at 4,736.05, achieving a 2014 gain of 13.4%. It, too, has notched annual gains for three straight years.

The Russell 2000 RUT, -1.27%  lost 8.36 points, or 0.7%, to close at 1,204.70, leaving the small-cap index with a yearly advance of 3.5%.

Some market watchers said there was no single factor behind the stock market’s choppiness on Wednesday, and investors shouldn’t read that much into its moves on relatively light, pre-holiday volume. Others suggested typical end-of-quarter action occurred, where portfolio managers bid up stocks in the morning, then ran out of money and walked away, leaving equities vulnerable for an afternoon fade.

“It’s thin trading, and there’s not much news out there,” Joseph Quinlan, chief market strategist at U.S. Trust, told MarketWatch. Composite volumes for the New York Stock Exchange and Nasdaq were below their 30-day moving averages, according to FactSet data.

On the economic front Wednesday, investors took in worse-than-anticipated readings for weekly jobless claims and Chicago-area business conditions. On the upside, a gauge of pending home sales rose 0.8% in November, topping expectations.

The advance during 2014 was driven largely by improving corporate earnings, steady gains by the U.S. economy and a still-accommodative Federal Reserve, even as the central bank is widely expected to begin raising interest rates in mid-2015. The S&P has averaged a yearly rise of 9.7% over the past two decades, so 2014’s advance ranks as above average, albeit well below 2013’s jump of 29.6%.

Southwestern Airlines Co. LUV, -0.99%   was the best-performing S&P component of 2014, surging 125%. Transocean Ltd. RIG, -4.09%  was the biggest laggard, plunging 63%. Among individual sectors, utilities led the pack, rising more than 28%, while the energy sector slid 10% to bring up the rear.

Both the New York Stock Exchange and Nasdaq will be closed Thursday for New Year’s Day. Markets will reopen on Friday.

Movers and shakers: Diamond Offshore Drilling Inc. DO, -4.90%   closed down 3.6% for the S&P 500’s worst performance on Wednesday. Energy stocks have been hit by plunging oil prices, and crude was down again.

NephroGenex Inc. NRX, +2.86%  finished up 187% after the small biotech late Tuesday announced positive safety study results for a diabetic nephropathy treatment.

Meadowbrook Insurance Group Inc. MIG, -0.71%  also gained, rising 18.7%, after news that China’s Fosun International Ltd. 0656, +1.10%  will buy the U.S. insurer for $433 million.

Other markets: In Asia, most markets ended higher. although Australia and New Zealand finished in the red. The stock markets in Japan, South Korea, Indonesia, Thailand and the Philippines were closed for New Year’s Eve.

Trading was upbeat but thin in Europe. German and Italian stock markets were closed.