Monthly periodicity in acoustic reflections and vertical motions in the deep ocean
Article first published online: 19 JUN 2007
Copyright 2007 by the American Geophysical Union.
Geophysical Research Letters
Volume 34, Issue 12, June 2007
How to Cite
2007), Monthly periodicity in acoustic reflections and vertical motions in the deep ocean, Geophys. Res. Lett., 34, L12603, doi:10.1029/2007GL029947.(
- Issue published online: 19 JUN 2007
- Article first published online: 19 JUN 2007
- Manuscript Accepted: 16 MAY 2007
- Manuscript Revised: 4 MAY 2007
- Manuscript Received: 9 MAR 2007
- monthly periodicity;
- open deep ocean ADCP-data;
- zooplankton migration
 A recent, 1.5 years long record of acoustic Doppler current profiler (ADCP)-data from the Canary Basin (North-Atlantic ocean) likely reflects vertical zooplankton migration between 800 and 1400 m. This record clearly distinguishes 3 major periodicities of down- and upgoing motions to within a precision of ∼1/400: a daily, a seasonal and a monthly cycle. Largest daily excursions occur during full moon. The directly observed hourly mean vertical velocity amplitudes of ∣w∣ = 0.025 ± 0.01 m s−1 are too slow for particles from the observational depths to reach the zone of moon- (and only very weak sun-) light penetration in half a day. It is shown that no physical (internal wave), geochemical or sinking food mechanism can trigger the daily and monthly cycles, which are coupled. It is speculated that an entrained biorhythm running precise internal biochemical clocks controls the vertical migration.