If the plumes did exist, much of the wisdom about combating oil spills might need to be reconsidered. The plumes would suggest that any future oil leak in deep water could be expected to do much of its damage in the sea, not on shore.

But where were the plumes?

After a slow start, American science is finally beginning to tackle the oil disaster in earnest. The National Oceanic and Atmospheric Administration, the federal agency charged with monitoring the health of the oceans, is sending multiple boats into the gulf. The National Science Foundation, another arm of the government, is issuing rapid grants to finance academic teams, including the one aboard the Walton Smith. BP, the oil company responsible for the spill, has pledged $500 million for research. And scientists like those aboard the Walton Smith are getting emergency financing from the government for their studies.

This stepped-up effort is starting to bear fruit. This week, another research vessel confirmed the existence of a huge undersea plume. And on Thursday, a team of scientists appointed by the Obama administration offered a more credible estimate of the flow rate at the broken well, putting it at two to four times the previous calculation.

That higher estimate only added to the sense among academic scientists that much of the oil must be hovering in the deep sea, instead of surfacing. The goal of the researchers aboard the Walton Smith was to nail the existence of such deep-sea plumes beyond any doubt.

They sailed early this week from Gulfport, Miss., and went back to the spot where they had originally discovered a large plume. It was no longer there.