Although they didn't have a position, "we knew where we put it, we knew the currents in the region, and we had the data on temperature and salinity it was sending back," Bishop says.

Temperatures were useful because, for example, upwelling waters near shore are colder than offshore waters. At Bishop's instigation the New Horizon had been equipped to measure temperature and salinity; this data could be compared with what SOLO was reporting as the ship closed on the float.

Currents were trickier. Although the California Current moves southward on the surface, at mid-depths there is a "poleward countercurrent." With SOLO spending so much time below, the float might well be drifting in different directions at different times of day.

An unexpected clue came on a 1,000-meter dive when SOLO reported reaching a depth of only 706 meters: it had hit the bottom.

BERKELEY LAB'S CHRIS GUAY MONITORS DATA FROM A NEW OPTICAL SENSOR HE PIONEERED AT THE LAB TO MEASURE INORGANIC FORMS OF PARTICULATE CARBON IN THE OCEAN.

On August 27, an exhausted Jim Bishop wrote up his weekly Chief Scientist report as a debate among a group of fictional puzzle-solvers: playing himself, the Chief Scientist claims "I can find SOLO with a thermometer," while a Dynamicist claims "I can find SOLO with a basic understanding of the dynamics of the California Current," and another researcher claims "I can find SOLO with a bathymetric map" (that is, a depth chart). The sailors in the galley got into the act and began practicing to retrieve the float with rod and reel; any albacore snagged during this exercise were purely fortuitous.

Bishop's fiction imagined the "shore-based SOLOists" simply waiting for the SOLO to "tell us where it is," and on August 23 it did just that. Apparently carried poleward by mid-depth currents, SOLO reported a position north-northeast of where it had been launched. Then the GPS "clammed up" again.

When the float hit bottom a second time, Bishop claimed that this event was welcomed by one of the researchers who was out to get core samples.

A dark and stormy night

Captain Murray Stein of the New Horizon laid out a search plan that brought the ship ever closer to its quarry, employing his own knowledge of the area. The ship arrived near Point Conception on Saturday, August 25, in 12-foot seas and 35-knot winds, with only three hours of daylight remaining.

While researchers aboard plotted temperature gradients and depth soundings, scientists onshore had ordered SOLO to abort its dive program and stay on the surface. The first signal to abort was not received. Did the second get through? Unless they found the float, the searchers would never know.

At last SOLO sent one more position report. Remarkably, the captain's search plan already had the ship heading straight for it, but another anxious hour went by before the searchlight caught the gleam of reflective tape on SOLO's antenna, bobbing in the rough seas. The captain eased the ship alongside, and at 11:30 p.m. Berkeley Lab's Todd Wood made the critical snatch. The SOLO was lifted aboard without a scratch.

Bishop concluded his log entry by noting that, despite the wayward SOLO, the mission's science was "a 200 percent success" —but oddly, he remarked, "the rod and reel club" from the galley was still angling off the stern days after the float had been recovered.

Lessons learned from the SOLO's "torture test" will be put to good use, Bishop says, when four more floats are launched in the raging waters of the Antarctic this coming January.

Additional Information:

• Return to part 1 of this article
• For more about the DOE's Center for Research on Ocean Carbon Sequestration, visit http://www-esd.lbl.gov/DOCS/index2.html.