* Arabica stages technical rebound after testing $1/lb
* Colombia October coffee output at six-year high
* Cocoa falls almost 2 percent on options expiration
* Sugar traders add to net longs for 6th straight week
(Adds NEW YORK dateline, byline, comment throughout, updates prices)
NEW YORK/LONDON, Nov 7 (Reuters) - Coffee futures jumped almost 4 percent in a turbulent session on Thursday, triggered by technical buying and bargain hunting after prices plunged to seven-year lows on concern about bumper crops from top producer Brazil.
Cocoa sank, nearly reversing Tuesday's gains as an options expiration led to speculative selling, while sugar edged down.
Relentless selling pushed arabica prices as low as $1.0095 per lb, their weakest since October 2006, pushing them close to the psychologically key $1 mark.
That sparked a flurry of technical buying that put the front month on track for its strongest one-day performance in two months.
"You're seeing a lot of bears take back, not because of any news but because they went for a buck and it got close. That was enough," said Jack Scoville, vice president for Price Futures Group in Chicago.
December arabica coffee futures on ICE rallied almost 4 percent to $1.052 per lb and were up 2.71 percent at $1.0425 per lb at 1:13 p.m. EDT (1813 GMT).
Arabica has been falling for more than two years with large crops in Brazil and a rebound in Colombian production driving prices down from a peak of more than $3 per lb in May 2011 to a low on Thursday of barely more than $1.
It has not breached below $1 since September 2006.
Late Wednesday, data showed Colombia, the world's largest producer of washed arabica, will grow its biggest crop in seven years, increasing output by 43 percent.
An options expiration and a storm headed towards top grower Vietnam lent some support to robusta prices, which recovered from 3-1/2-year lows earlier in the session.
Vietnamese farmers have harvested on average 20 percent of the new 2013/2014 coffee crop in the Central Highlands, traders said, indicating ample bean supply.
Liffe January robusta coffee was up $6 or 0.4 percent at $1,460 a tonne, after hitting a session low of 1431.
Cocoa plunged in its largest daily fall since Aug. 21 as investors continued to book profits, shrugging off the potential impact from a massive typhoon headed towards the Philippines, a major producer.
ICE March cocoa settled down $50, or 1.9 percent, at $2,693 a tonne, as the Ivory Coast harvest accelerates.
Traders eyed $2,630 as the next support level.
"It's long liquidation and profit taking after Tuesday's rally," said Boyd Cruel, analyst at Vision Financial Markets in Chicago.
March cocoa on Liffe settled down 23 pounds or 0.1 percent lower at 1,712 pounds a tonne.
ICE March raw sugar futures lost 0.3 cent or 0.2 percent at 18.06 cents a lb, after hitting a six-week low of 17.81 earlier in the session.
Sugar has been in a steady decline since hitting a two-year high on Oct. 17 after a fire ravaged a major sugar terminal in top grower Brazil.
Concerns about nearby tightness have waned due to ready alternative supplies from India and Thailand. India announced on Thursday it will carry forward stocks of 8.8 million tonnes into the new crop year.
Traders said that U.S. data showing speculators increased their net long position in the week ended Oct. 29 was surprisingly high.
December white sugar on Liffe was off $3.20, or 0.7 percent, at $476.80 a tonne.
(Additional reporting from Sarah McFarlane in London; Editing by James Dalgleish)