U.S. stocks see-sawed around the unchanged mark in early trade on Monday after the S&P 500 suffered its worst weekly drop since May 2012 and the Dow moved into negative territory for the year on global growth concerns.

The benchmark S&P index slumped 3.1 percent last week to sit just above its support level, the 200-day moving average of around 1,905. The declines were sparked by a cut in the global growth forecast by the International Monetary Fund and disappointing economic data in Europe.

A serious slowdown in the global economy could lead the U.S. Federal Reserve to delay an increase in interest rates if deemed serious enough, Fed officials said over the weekend.

Earnings season will pick up this week, with results expected from Dow components Intel (INTC.O), Johnson & Johnson (JNJ.N), UnitedHealth (UNH.N), American Express (AXP.N) and General Electric (GE.N), as well as financials Morgan Stanley (MS.N), Citigroup (C.N), Bank of America (BAC.N) and Wells Fargo (WFC.N).

"Some of it is going to be a knee-jerk reaction bounce but I think you are going to get a better idea once the earnings start," said Ken Polcari, Director of the NYSE floor division at O’Neil Securities in New York.

"I think you are going to be surprised, earnings are going to be solid and the guidance forward is going to be OK, so I don’t think this nervousness is justified."

Volume may be muted on Monday in light of the U.S. Columbus Day holiday, which could create more volatility.

Canadian Pacific Railway Ltd (CP.TO) has approached CSX Corp (CSX.N) about merging the two North American railroad operators to create a transcontinental carrier worth more than $60 billion, according to the Wall Street Journal.

CSX shares jumped 11.6 percent to $33.42, lifting the Dow Jones transportation average .DJT, while U.S.-listed shares of Canadian Pacific rose 3.5 percent.

At 9:44AM the Dow Jones industrial average .DJI rose 38.34 points, or 0.23 percent, to 16,582.44, the S&P 500 .SPX gained 3 points, or 0.16 percent, to 1,909.13 and the Nasdaq Composite .IXIC added 0.97 points, or 0.02 percent, to 4,277.20.

The largest percentage gainer on the S&P 500 was, while the largest percentage decliner was AutoNation (AN.N), down 6.1 percent.

The largest percentage gainer on the Nasdaq 100 was Vertex Pharmaceuticals (VRTX.O), up 3.5 percent, while the largest percentage decliner was Seagate Tech (STX.O), down 2.2 percent.

Among the most active stocks on the NYSE were Bank of America (BAC.N), up 0.24 percent to $16.52, and Petrobras (PBR.N), up 8.13 percent to $16.89.

On the Nasdaq, GT Advanced Tech (GTAT.O), down 29.0 percent to $0.58 and APPLE (AAPL.O), up 0.7 percent to $101.41, were among the most actively traded.

Advancing issues were outnumbering declining ones on the NYSE by 1,806 to 897, for a 2.01-to-1 ratio on the upside; on the Nasdaq, 1,217 issues were rising and 1,009 falling for a 1.21-to-1 ratio favoring advancers.

The benchmark S&P 500 index was posting 2 new 52-week highs and 13 new lows; the Nasdaq Composite was recording 6 new highs and 100 new lows.