How does rising atmospheric CO2 affect marine organisms?

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A Brief (One Millennium) History of the Gulf Stream
Lund, D.C., Lynch-Stieglitz, J. and Curry, W.B. 2006. Gulf Stream density structure and transport during the past millennium. Nature 444: 601-604.

Many people fear -- or at least claim they do -- that global warming will lead to enhanced precipitation and melting of ice in high northern latitudes, which will lead to augmented freshwater runoff to the North Atlantic Ocean, which will lead to a precipitous decline in North Atlantic Deep Water formation, which will produce a swift reduction in the global ocean's thermohaline circulation, which could shut down the Gulf Stream and bring cold times to Europe.

What was done
In a study that comes to bear upon this climate-alarmist scenario, Lund et al. used the δ18O of foraminifera obtained from sediment cores retrieved near the Dry Tortugas and Great Bahama Bank to reconstruct density profiles of the Florida Current (the portion of the Gulf Stream that flows through the Straits of Florida) over the past millennium.

What was learned
In the words of the three researchers, "the cross-current density gradient and vertical current shear of the Gulf Stream were systematically lower during the Little Ice Age (AD ~1200 to 1850)," and they estimate that the "Little Ice Age volume transport was ten percent weaker than today's," stating additionally that "the intervals 0-100 yr BP [years before present] and 1,000-1,100 yr BP are characterized by higher transport."

What it means
In contrast to climate-alarmist contentions that the Gulf Stream could weaken in response to global warming, real-world data indicate that during portions of both the Medieval and Current Warm Periods the strength of the Gulf Stream was actually enhanced relative to what it was during the cooler Little Ice Age, which finding runs exactly counter to what Al Gore and many of his followers have long suggested should be the case.

Reviewed 12 November 2008