University of Hawaii scientists tracking the ocean debris from the March 11 mega-quake and tsunami in Japan say the widespread flotsam so far has spared Midway, a sensitive wildlife preserve.
But the same currents that are keeping the debris away from Midway are peppering the atoll with junk from the main Hawaiian Islands and the Pacific "garbage patch" between Hawaii and California.
So far, the tsunami debris is passing well north of the Papahanaumokuakea Marine National Monument, which is good news for the monk seals and other endangered species that call Hawaii home.
But its relentless advance will ultimately take it to the West Coast and main Hawaiian Islands as predicted earlier, the oceanographers say.
By one estimate the 9.0-magnitude earthquake off Sendai, Japan, and the resulting tsunami washed 25 million tons of debris into the ocean. Its precise composition is uncertain, but it is a clear hazard to ships, boats, wildlife and coastlines.
Scientists with UH-Manoa, UH-Hilo, the Scripps Institution of Oceanography in La Jolla, Calif., and conservationists with the Ocean Recovery Alliance decided last year to survey the debris field and mark it with buoys that can be tracked by satellite.
Eleven of the buoys, designed to simulate the motion of different types of debris, were deployed late last year in a line between Midway and the leading edge of the debris field.
The data from these satellite-tracked drifters, along with computer models, now allow the movement of the field to be monitored remotely, the scientists say.
An analysis of the ocean currents around Hawaii shows that the general flow has been from the southwest, the UH oceanographers say.
That has kept the debris from Japan north of the islands for now.
The researchers also placed 400 numbered wooden blocks in the debris field. The scientists ask that any boaters, fishermen and beachgoers who find these blocks use the contact information on the blocks to report where they were found.
Those reports will add to the understanding of how the field is moving.
Part of the challenge is telling tsunami debris from "ordinary" debris, much of which winds up in the North Pacific Garbage Patch, formally called the North Pacific Gyre, and on beaches in the Northwestern Hawaiian Islands.
Some of that has been turning up at Midway, said Gisela Speidel, outreach specialist with the International Pacific Research Center.
"My understanding is that this is old marine debris that has been recirculating in the gyre," she said by email.
"Rather than recirculating further south, the debris at present is moving from the main Hawaiian Islands towards Midway. For example, an object recently found on Kure has been tracked to the Big Island."
The research team includes Nikolai Maximenko and Jan Hafner of the International Pacific Research Center, Hank Carson of the University of Hawaii at Hilo, Doug Woodring of the Ocean Recovery Alliance and Luca Centurioni of Scripps.
After reaching the West Coast, the debris is due to reach the main Hawaiian Islands by March 2015, Maximenko has calculated.
The scientists also reported that they found no "significant" radioactivity in the debris field, which had been of concern with the breakdown of the Fukushima Daiichi nuclear plant.
