There are theories suggesting that the AMO index is in turn driven by fluctuations in the north Atlantic current commonly called the Gulf Stream.

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The author of that work, Glen MacDonald of UCLA, has noted that the only way to get that region so warm is with a massive influx of Gulf Stream water from the Atlantic.

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The cause of this cold lurch was seemingly settled some time ago when Wallace Broecker, a Columbia University geochemist, suggested that a North American ice sheet collapsed, flooding the Atlantic with fresh water, which interrupted the normal circulation of the Gulf Stream.

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