Global Migration Mapped with Lidar
During World War II, naval oceanographers discovered a reflective layer that rose and fell across their sonar screens once each day. Further research revealed that it comprised a global ocean migration of swarms of fish and tiny sea creatures called zooplankton migrating toward the ocean surface as the sun set to feed under cover of darkness, then swimming back to the inky depths at dawn to escape their own predators during daylight hours.
From an article in WYDaily by David Malmquist.
Initially valued as a way for submarines to hide their movements, this daily vertical migration is now known to play a major role in the global carbon cycle, as the consumption of surface algae by migrating zooplankton carries carbon to the deep sea, thereby reducing carbon-dioxide levels in the surface ocean and atmosphere. But the exact amount of carbon exported to the deep sea via this “biological pump” has remained difficult to quantify on a global basis, based as it is on intermittent measurements from single ships atop a vast ocean.
A study published in the December 12 issue of Nature reports on the use of satellite-borne lidar to map the daily vertical migration of zooplankton across the world’s seas over the course of a decade. Lidar is the laser equivalent of sonar, using pulses of light rather than sound to image objects in the air and water.
Lead author Michael Behrenfeld of Oregon State University says, “What the lidar allowed us to do is sample these migrating animals on a global scale every 16 days for 10 years. We’ve never had anywhere near that kind of global coverage to allow us to look at the[ir] behavior, distribution, and abundance.”
VIMS professor and co-author Deborah Steinberg contributed to the study by “ground-truthing” the satellite-based measurements with data obtained from ships by deploying fine-mesh nets to collect, then count and identify the many species of migrating zooplankton. She has been conducting field studies of zooplankton vertical migration for the last three decades, most recently near Antarctica, Bermuda, and in the northeast Pacific as part of the EXPORTS project.
“Combining data from ships and satellites allows us to greatly expand our research footprint,” says Steinberg. “It helps to increase our quantitative understanding of the role of zooplankton in the global carbon cycle, particularly in terms of its variability in time and space. That knowledge is critically important for refining global climate models.”
Joining Behrenfeld and Steinberg on the study were researchers from 11 other marine and space science institutes around the world, including NASA Langley Research Center in Hampton and NASA Headquarters in Washington, D.C. Other collaborators hailed from the European Institute for Marine Studies in France, the University of Alaska Fairbanks, University of British Columbia, University of California Santa Barbara, University of Maine, University of Virginia and University of Washington.
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