HR: 17:35h
AN: OS54A-06    [Abstracts]
TI: The diel zooplankton motion at 1000 and 300 m depth
AU: * Ochoa, J
EM: jochoa@cicese.mx
AF: Department of Physical Oceanography/CICESE, Km 107 Carretera Ensenada-Tijuana, Ensenada, BC 22800, Mexico
AU: Badan, A
EM: abadan@cicese.mx
AF: Department of Physical Oceanography/CICESE, Km 107 Carretera Ensenada-Tijuana, Ensenada, BC 22800, Mexico
AU: Candela, J
EM: jcandela@cicese.mx
AF: Department of Physical Oceanography/CICESE, Km 107 Carretera Ensenada-Tijuana, Ensenada, BC 22800, Mexico
AU: Sheinbaum, J
EM: julios@cicese.mx
AF: Department of Physical Oceanography/CICESE, Km 107 Carretera Ensenada-Tijuana, Ensenada, BC 22800, Mexico
AB: A well known feature of a large fraction of the zooplankton in the 300 m near-surface layer is the daily vertical migration cycle, which is phase locked with the light cycle. Less documented is the similar cycle in deeper layers away from significant light. Here we show, based on direct measurements, the mean vertical velocity cycle for layers 170 m thick, one centered at 1000 m and another, for reference, at 300 m depth, in the central Gulf of Mexico. Averages over 473 days are computed timing each cycle with the sunrise and sunset. Both cycles are highly symmetrical odd functions where, in the deeper layer, the downward/upward migration is delayed/advanced relative to the upper layer by about 1 h 40 min. In the upper layer, the peak speeds are close to 40 mm/s, with corresponding vertical displacements about 250 m, and in the deeper layer the peak speeds are 10 mm/s with vertical displacements of approximately 120 m. In the upper layer, the peak downward motion occurs minutes before sunrise, wheras in the lower layer, the peak downward velocity occurs 1.5 hours after the sunrise. The peak upward velocities are found 1.5 hours before sunset in the deeper layer and just minutes after sunset in the upper layer. Therefore, the nightly permanence towards shallower water lasts longer, for about 3.5 hours, in the deeper layers than closer to surface.
DE: 4227 Diurnal, seasonal, and annual cycles (0438)
DE: 4273 Physical and biogeochemical interactions
SC: Ocean Sciences [OS]
MN: 2007 Joint Assembly