The midwinter cruise was a continuation of the PASTA (Po and Apennine Sediment Transport and Accumulation) study. PASTA is a component of EuroSTRATAFORM, a research program using selected areas of the European continental margin to explore the fate of sediment particles from their sources in rivers to their deposition on shallow deltas, on the continental shelf, and in deep-sea basins. This article summarizes successes and problems encountered during the recent voyage.
USGS instruments deployed last fall have produced a spectacular record at our two sites off the Chienti River in Italy. Virtually complete records of waves, currents, temperature, salinity, and suspended-sediment concentrations between late November and mid-February were recovered from our instruments during the recent PASTA voyage on the Harbor Branch Oceanographic Institution's research vessel Seaward Johnson II.
These records document the persistent coastal current responsible for transporting sediment, nutrients, and contaminants southward along the Italian coast. Even two new instruments that had never been in saltwater before provided valuable records for the first part of the deployment. Dave Rubin and Hank Chezar's sediment microphotography device yielded intriguing photos of bottom sediment at the 9-m-depth site. The high-resolution scanning sonar, built by Chris Sherwood and Marinna Martini (USGS) with help from Jim Irish and Robin Singer at the Woods Hole Oceanographic Institution (WHOI), revealed bottom conditions that shifted between small ripples and upper plane-bed conditions.
The tripods were recovered by WHOI divers, with backup from USGS divers Chuck Worley and Dann Blackwood. Chuck and Dann dove to clear a line (not ours!) from the ship's propeller and ran sidescan-sonar surveys of the instrument sites.
Fishing pressure from small trawlers presents a major danger to oceanographic instruments off the Italian coast, and all three of our tripods had been hit at some point. One tripod was toppled on St. Valentine's Day (3 days before we recovered it!), the second was rotated 180 degrees early in the deployment and left slightly bent but fully operational, and the third was lifted briefly off the bottom but left in place. Despite these bumps and bangs, we got complete data sets (minus 3 days at one site). Other EuroSTRATAFORM investigators had worse luck: two other tripods were toppled earlier in the experiment, and four buoys were damaged or moved. Overall, the instrumentation array fared quite well, with nearly complete records from eight bottom-mounted sites, partial records from two more sites, and complete loss of data at only one site.
We owe much of our success in this turnaround to folks at the Marine Operations Facility in Woods Hole, MA (Dave [Twig] Nichols, Jonathan Borden, and Rick Rendigs), and their counterparts at the Marine Facility in Redwood City, CA (Dave Hogg, Dave Gonzales, Kevin O'Toole, and Hal Williams). These guys built and shipped the instruments (and critical spare parts and batteries) on a tight schedule.
The WHOI divers (Jay Sisson and Glenn MacDonald) were heroic, diving in cold water with strong currents and zero visibility to recover the tripods. Luckily, Stefano Miserocchi (one of our Italian coinvestigators) navigated to the sites with even better precision than his differential global-positioning system (DGPS) is theoretically capable of.
The captain and crew of the research vessel Seward Johnson II were outstanding, and Chuck Nittrouer (University of Washington) was responsible for coordinating the whole project and the difficult logistics of an overseas cruise involving 21 principal investigators from 11 institutions.
The study is funded by the Office of Naval Research and the USGS Coastal and Marine Geology Program's Community Sediment-Transport Modeling project.
in this issue: Adriatic Sea Instrument Redeployment