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By Root 1224 0

temperature both; normal temperatures for this month averaged -1.2° C, so melted ice actually warmed it. Density was a function of salinity and temperature combined, which was why the movement of seawater was called the thermohaline cycle. Before the fleet of Arctic icebergs had arrived, the surface in the downwelling regions had had an average salinity of 31.0 p.s.u. (practical salinity units; these were measured in various ways, but a p.s.u. was still roughly equivalent to how many grams of salt per kilogram of water). Now the surface salinity was 29.8, the temperature -1.0° C. Following the PI’s red laser dot down the isopycnals on her graph, they could see just how much salinity would have to be bumped to make the cap dense enough to sink down into the water underneath it.

The biggest downwelling region had been north of Iceland and east of Greenland, but the PI explained that all that region was not equally involved. Currents branching from the great current had flowed north and east almost to the coast of Norway, then turned left toward Greenland in very predictable currents, slowing and then swirling down in giant whirlpools that were thirty or fifty kilometers wide, but only three or four centimeters deep. These whirlpools were visible only to satellite laser altimetry, where false-color graphing could make them psychedelically obvious. They had been relatively stable in location, presumably constrained by the sea bottom, the nearest coastline configurations, the force of the currents, and the Coriolis force.

They were small areas compared to the total surface of the ocean, so that the idea of restarting the current did not seem immediately impossible; but as the PI pointed out, one could not restart the circulation merely by increasing density at the old downwelling sites in isolation, separated from the thrust of the Gulf Stream by some hundreds of kilometers of stalled and unusually fresh water. It would be necessary to draw the full momentum of the Gulf Stream back up to the old sites again, by causing surface water to sink just north of the current downwelling sites, then continue the process, in Pied Piper fashion, until they had drawn the Gulf Stream up behind them and could dump as much as needed in the old downwelling locations. This was the only method that the NOAA team could think of to renew the flow; but it added greatly to the amount of water that they had to make sink. To “isopycnalate,” as Edgardo called it.

Extensive computer modeling of various scenarios had led them to believe that in order to create the masses of sinking water necessary, they would have to alter its salinity about two p.s.u., from 29.8 to 31.6—meaning the addition of about two grams of salt for every kilogram of water they had to alter. The necessary volume of water was a much less certain thing, depending as it did on various assumptions plugged into the model, but the minimal volume they had gotten to get good results totaled approximately five thousand cubic kilometers of water. About a thousand kilograms per cubic meter of water, depending on temperature; two grams of salt per kilogram of water . . . thus, about ten billion kilograms of salt.

Five hundred million tons.

Someone whistled.

“Just how much salt is that?” Frank asked.

Edgardo and General Wracke laughed. Diane smiled but said to the NOAA people, “Can you give us a sense of what that means in terms of volumes, availability, shipping capacities and so on?”

“Yes, I’m sure we can. We would have done that already but we just finished the analysis this morning. But I have to say, you know, before we get to that part, that we’re still very uncertain about the wisdom of trying this at all. I mean we don’t really know what effect it will have, and just going by the law of unintended consequences—”

“Please!” Edgardo said, raising a hand. “No more of this law of unintended consequences! There is no such law. You hear this said and then you look for the equation that expresses this law, or even the principle, and there is no equation or principle. There is just the