As he plied his loathsome trade in the summer of 1751, the slave-ship captain Henry Ellis paused to engage in a little scientific exploration. En route to Jamaica, in the vicinity of latitude 25 North, Ellis lowered into the ocean a sealed bucket with controllable valves, able to take and hold samples of seawater from multiple depths. To the probe’s designer Ellis reported his success in taking samples from exceptional depths, up to a mile below the surface. His findings surprised him: from a surface temperature of about 25 Celsius, the seawater rapidly chilled with increasing depth, falling to a low of 5-10 C, then rising again below 1300 meters to a maximum of 12 degrees Celsius. The deep, cold water also proved more salty than expected. A practical man - slavers weren’t idealists - Captain Ellis used the chilled water samples to refrigerate his supply of wine.
Slaver Ellis wasn’t conducting oceanographic investigations for a laugh. He considered himself a natural philosopher, having served as de facto science officer on an expedition to the Northwest Passage in 1746-47. After his return Ellis published a book on the voyage, describing the explorers’ reconnaissance of Greenland, trade with the Inuit, and eventual failure to find an ice-free channel beyond Hudson Bay. The voyage and book ingratiated Ellis with a number of scientifically-inclined noblemen, who doubtless helped him raise the capital for his trade in human beings. One high-born friend, Lord Halifax, later appointed Ellis royal governor of Georgia, a colony that had recently legalized slavery. Ellis helped negotiate a stable peace settlement with the neighboring Muskogee Creeks, doubtless thinking himself a humanitarian for doing so. (See Julie Sweet, Negotiating For Georgia (2005), 188 on his governorship.) Illness drove the governor from Savannah after a year, but Ellis eventually returned to American office in Halifax, as lieutenant governor of Nova Scotia.
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| Detail from Ellis’s 1746-47 voyage |
The results of Captain E’s deep-sea experiment remained little-known until the 1790s, when Benjamin Thompson, Count Rumford, theorized that the mass of cold, salty water Ellis discovered was a current of cold seawater, analogous to the Gulf Stream nearer the surface. In the twentieth century, oceanographers concluded that both warm and cold Atlantic currents comprised a great conveyor-belt extending from the Antarctic to the Arctic, powered by heat and the transfer of salts - the Atlantic Meridional Overturning Circulation (AMOC). In our own time, climate scientists have expressed concern that the accelerated melting of the Arctic and Antarctic ice caps, the flow of low-salinity water into the polar zones of the AMOC, and the disruption of thermohaline circulation will shut down the whole circuit. Since the warming Gulf Stream is part of the AMOC, this will spell pretty bad news for Europe. For parts of North America, too: the Gulf Stream deflects a substantial volume of seawater from the East Coast, and its dissipation will cause the relative sea level to rise, contributing to the inundation of low-lying communities.
Careful readers will note that the Atlantic Overturning currents also tie together many of Henry Ellis’s ports of call and places of residence: Greenland, whose melting ice caps now threaten to shut down the Gulf Stream, and the coastal cities of Savannah and Halifax, which are likely to experience considerable flooding if the Atlantic basin sloshes slightly westward. Ellis himself lacked the notional birds-eye view needed to make these connections, or to observe that he had helped make the Atlantic both a web of human-made connections and an avenue of human misery. If he’d made these observations, though, I doubt that they would have changed his behavior. One didn’t rise to high rank in the British Empire on the strength of humane sentiments.
