A persistently weak dollar is confounding currency traders and roiling global financial markets.

Investors across asset classes are feeling the effects of the buck’s rocky start to the year, with the ICE U.S. Dollar Index DXY, -0.06% a measure of the currency against six major rivals, dropping 3.5% in the year to date, adding on from its 10% loss last year. Last week alone, the buck dropped 1.7%