A trader blows a chewing gum bubble as he works on the floor of the New York Stock Exchange shortly after the opening bell, in New York, June 15, 2015. Investors are braced for further reaction on world stock markets after Greece closed its banks and imposed capital controls on Sunday to check the growing strains on its crippled financial system, bringing the prospect of being forced out of the euro into plain sight. After bailout talks between the leftwing government and foreign lenders broke down at the weekend, the European Central Bank froze vital funding support to Greece's banks, leaving Athens with little choice but to shut down the system to keep the banks from collapsing. Across the Atlantic, photos of the hands, faces and expressions of traders at the New York Stock Exchange show the tension of tracking the markets and their reaction to fast-moving stories affecting investor sentiment. REUTERS/Lucas Jackson 

A trader monitors his screen as he works on the floor of the New York Stock Exchange shortly after the opening bell, in New York, June 15, 2015. REUTERS/Lucas Jackson 

A trader works on the floor of the New York Stock Exchange, in New York, June 25, 2015. REUTERS/Lucas Jackson 

A trader shouts as he works on the floor of the New York Stock Exchange shortly after the opening bell in New York, June 24, 2015. REUTERS/Lucas Jackson 

A patch and trader's number is seen sewn to the jacket of a trader working on the floor of the New York Stock Exchange shortly after the opening bell, New York, June 15, 2015. Investors are braced for further reaction on world stock markets after Greece closed its banks and imposed capital controls on Sunday to check the growing strains on its crippled financial system, bringing the prospect of being forced out of the euro into plain sight. After bailout talks between the leftwing government and foreign lenders broke down at the weekend, the European Central Bank froze vital funding support to Greece's banks, leaving Athens with little choice but to shut down the system to keep the banks from collapsing. Across the Atlantic, photos of the hands, faces and expressions of traders at the New York Stock Exchange show the tension of tracking the markets and their reaction to fast-moving stories affecting investor sentiment. REUTERS/Lucas Jackson

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A trader clasps his hands together as he works on the floor of the New York Stock Exchange shortly after the opening bell, New York, June 15, 2015. REUTERS/Lucas Jackson 

A trader works on the floor of the New York Stock Exchange, New York, June 25, 2015. REUTERS/Lucas Jackson 

A trader talks on the telephone while monitoring the movement of the market as he works on the floor of the New York Stock Exchange June 15, 2015. Investors are braced for further reaction on world stock markets after Greece closed its banks and imposed capital controls on Sunday to check the growing strains on its crippled financial system, bringing the prospect of being forced out of the euro into plain sight. After bailout talks between the leftwing government and foreign lenders broke down at the weekend, the European Central Bank froze vital funding support to Greece's banks, leaving Athens with little choice but to shut down the system to keep the banks from collapsing. Across the Atlantic, photos of the hands, faces and expressions of traders at the New York Stock Exchange show the tension of tracking the markets and their reaction to fast-moving stories affecting investor sentiment. REUTERS/Lucas Jackson

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A trader's hand rests on his keyboard next to a cup of coffee on the floor of the New York Stock Exchange shortly after the opening bell, New York, June 15, 2015. REUTERS/Lucas Jackson 

A trader furrows his brow as he works on the floor of the New York Stock Exchange in New York, June 24, 2015. Investors are braced for further reaction on world stock markets after Greece closed its banks and imposed capital controls on Sunday to check the growing strains on its crippled financial system, bringing the prospect of being forced out of the euro into plain sight. After bailout talks between the leftwing government and foreign lenders broke down at the weekend, the European Central Bank froze vital funding support to Greece's banks, leaving Athens with little choice but to shut down the system to keep the banks from collapsing. Across the Atlantic, photos of the hands, faces and expressions of traders at the New York Stock Exchange show the tension of tracking the markets and their reaction to fast-moving stories affecting investor sentiment. REUTERS/Lucas Jackson

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Pins are seen attached to the jacket of a trader working on the floor of the New York Stock Exchange, New York, June 15, 2015. REUTERS/Lucas Jackson 

A trader looks at the screens as he works on the floor of the New York Stock Exchange, New York, June 24, 2015. Investors are braced for further reaction on world stock markets after Greece closed its banks and imposed capital controls on Sunday to check the growing strains on its crippled financial system, bringing the prospect of being forced out of the euro into plain sight. After bailout talks between the leftwing government and foreign lenders broke down at the weekend, the European Central Bank froze vital funding support to Greece's banks, leaving Athens with little choice but to shut down the system to keep the banks from collapsing. Across the Atlantic, photos of the hands, faces and expressions of traders at the New York Stock Exchange show the tension of tracking the markets and their reaction to fast-moving stories affecting investor sentiment. REUTERS/Lucas Jackson

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Pins are seen attached to the jacket of a trader working on the floor of the New York Stock Exchange, New York, June 15, 2015. REUTERS/Lucas Jackson 

A trader speaks into a microphone as he works on the floor of the New York Stock Exchange, New York, June 18, 2015. Investors are braced for further reaction on world stock markets after Greece closed its banks and imposed capital controls on Sunday to check the growing strains on its crippled financial system, bringing the prospect of being forced out of the euro into plain sight. After bailout talks between the leftwing government and foreign lenders broke down at the weekend, the European Central Bank froze vital funding support to Greece's banks, leaving Athens with little choice but to shut down the system to keep the banks from collapsing. Across the Atlantic, photos of the hands, faces and expressions of traders at the New York Stock Exchange show the tension of tracking the markets and their reaction to fast-moving stories affecting investor sentiment. REUTERS/Lucas Jackson

PICTURE 14 OF 30 FOR WIDER IMAGE STORY "NYSE - UP CLOSE AND IN DETAIL". SEARCH "LUCAS EXPRESSIONS" FOR ALL IMAGES 

Pins are displayed on a trader's jacket as he works on the floor of the New York Stock Exchange, New York, June 16, 2015. REUTERS/Lucas Jackson 

A trader holds his hand to his lips as he monitors his screen on the floor of the New York Stock Exchange, New York, June 15, 2015. REUTERS/Lucas Jackson 

A fire warden's patch is displayed on the shoulder of a trader while he works on the floor of the New York Stock Exchange, New York, June 16, 2015. REUTERS/Lucas Jackson 

A trader listens out as he works on the floor of the New York Stock Exchange, New York, June 24, 2015. REUTERS/Lucas Jackson 

A trader works on the floor of the New York Stock Exchange, New York, June 25, 2015. REUTERS/Lucas Jackson 

A trader wears a crisply ironed shirt and tie as works on the floor of the New York Stock Exchange, New York, June 25, 2015. REUTERS/Lucas Jackson 

A trader, who has beard stubble on his chin, works on the floor of the New York Stock Exchange, new York, June 24, 2015. REUTERS/Lucas Jackson 

A trader points as he works on the floor of the New York Stock Exchange, New York, June 25, 2015. REUTERS/Lucas Jackson 

A trader works on his personal computer on the floor of the New York Stock Exchange, New York, June 16, 2015. REUTERS/Lucas Jackson 

A trader adjusts his earpiece as he works on the floor of the New York Stock Exchange in New York, June 24, 2015. REUTERS/Lucas Jackson 

Pins are displayed on a trader's jacket as he works on the floor of the New York Stock Exchange, New York, June 16, 2015. REUTERS/Lucas Jackson 

A trader monitors his screen as he works on the floor of the New York Stock Exchange shortly after the opening bell, New York, June 15, 2015. REUTERS/Lucas Jackson 

A watch is seen on the wrist of a trader as he works on the floor of the New York Stock Exchange, New York, June 25, 2015. REUTERS/Lucas Jackson 

A trader touches his face with his fingers as he works on the floor of the New York Stock Exchange, New York, June 18, 2015. REUTERS/Lucas Jackson 

A trader looks up as he works on the floor of the New York Stock Exchange, New York, June 25, 2015. REUTERS/Lucas Jackson 

A trader clasps his hands behind his back as he works on the floor of the New York Stock Exchange shortly after the opening bell in New York, June 24, 2015. REUTERS/Lucas Jackson