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Working in the Twilight Zone

Particles sinking from sunlit surface waters through the ocean’s dimly lit twilight zone are often swept sideways by currents. Conventional moored or tethered traps designed to catch the particles for study are like “rain gauges in hurricanes,” said WHOI biogeochemist Ken Buesseler. So Buesseler and engineer Jim Valdes have been designing a neutrally buoyant, untethered vehicle called the Twilight Zone Explorer, which will be swept along with the currents. It will surface periodically to relay data via satellite. (Illustration by Jack Cook, Woods Hole Oceanographic Institution)