Barack Obama will today (August 25th) nominate Ben Bernanke to serve a second term as chairman of the Federal Reserve.At a speech due to be held later today in Martha's Vineyard, Massachusetts, where the president is vacationing, Obama is expected to praise the helmsmanship displayed by Bernanke as he has steered America through its deepest recession since the 1930s.Widely deemed to have taken swift and decisive action in cutting interest rates and pushing through fiscal stimulus programmes, Bernanke is expected to be at the president's side as he makes the nomination."As an expert on the causes of the Great Depression, I'm sure Ben never imagined that he would be part of a team responsible for preventing another. But ... that's exactly what he has helped to achieve," Obama will say.Bernanke also last week gave support to a rally witnessed in stocks, commodities and high-yield currencies after he expressed his confidence in the prospects for global economic recovery.