It's all about the fun-durr-mentals... but, just in case you don't believe that, this morning's angst over copper financing and China credit concerns has sparked notable carry unwinds (USDJPY below 103 and AUDJPY 93) and therefore US equities are tumbling (tick for tick). This morning's volatility in stocks was considerable around the open suggesting a lot of uncertainty and nervousness.
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Charts: Bloomberg