On August 15, 2001, the Scripps Institution of Oceanography's 170-foot Research Vessel New Horizon left port in San Diego laden with equipment and researchers from Berkeley Lab and other organizations, its primary mission to calibrate and test new instruments for measuring the carbon dynamics of the ocean. But within days one important device, a new SOLO float, had gone missing.
SOLO stands for Sounding Oceanographic Lagrangian Observer, a float programmed to rise and sink to measure ocean water temperature and salinity. Jim Bishop of the Earth Sciences Division, co-director of DOE's Center for Research on Ocean Carbon Sequestration, worked with colleagues to augment the basic SOLO design with instruments to monitor concentrations and sizes of particulate matter and equip SOLOs for satellite telemetry.
The worst place I knew
"I torture-test this stuff," says Bishop, chief scientist on the voyage, "and for the trial of the SOLO, I picked the worst place I knew."
Point Conception, west and north of Santa Barbara, is a good place to test a depth-diving carbon sensor because of the rich biology of its coastal waters. But the swift California Current that flows down the coast has been infamous since the days of Sir Francis Drake, and the Point's high winds frequently turn the sea surface to chop.
The newly launched SOLO sent plenty of information as the New Horizon continued north to Monterey Bay. Mornings and afternoons the float dove to 300 meters and at night to 1,000 meters, resurfacing, as programmed, to send its accumulated data to ORBCOMM satellites overhead.
But it wasn't sending its positions, which it should have been able to determine using an onboard global position system (GPS). Perhaps rough seas prevented a good satellite fix.
The forensic science of the sea
One, the Multiple Unit Large Volume Filtration System (MULVFS), collects particulate matter in sizes from micrometers to millimeters. The other, the CTD for conductivity, temperature, and depth makes measurements similar to the SOLO carbon observers. By operating the two instruments side by side, says Bishop, "we could look at the signals we were getting from the CTD, then look at what the MULVFS brought up and say, 'My gosh, here's what we saw.'"
Everybody in the 13-member scientific crew worked long and hard. Berkeley Lab photographer Roy Kaltschmidt did double duty, helping deploy and retrieve the massive instruments and analyze the results.
All the while the mystery of the hide-and-seek SOLO was deepening. The float wasn't hiding intentionally, but because it was submerged for all but a couple of hours a day, it might as well have been a submarine with orders to run silent, run deep.
Next page: After the Float