1. Deep Migrating Zooplankton in the Gulf of Mexico.
The diel zooplankton motion at 1000 m below the surface .
J Ochoa, A Badan, J Candela, J Sheinbaum
and H. Maske.
CICESE
(M. López, P. Pérez)
Antonio Badan Memorial Symposium
“The Ocean, the Wine and the Valley”
November 16-18, Ensenada, B. C., México.

2. Thanks to Nacho, Joaquin, Miguel O. , Carlos F. , Armando L
Thanks to Nacho, Joaquin, Miguel O., Carlos F., Armando L., Benjamin M, Roberto M., Erik, Domitilo. And all participants; students, land support, ..

3. Thanks to the crew members
of the B/O Justo Sierra, in
particular to Felipe Toto and
Rodolfo Soto

4. CANEKITO
365
1230

5. 75 KHz LR RDI
75 kHz => Therefore we are observing
the motion of scattering features with
spatial extent on the order of 1 cm.
These perturbations include, besides
particles, zooplankton and fishes,
fluctuations due to the stirred
hydrographic fields (Ross, T., and R. Lueck (2003), Sound scattering from oceanic turbulence, GRL, 30(6), 1343)

6. Zooplankton ‘searching’ for food
(at night moves upward)

7. 38 KHz ECHOSOUNDER
Zooplankton ( ‘avoiding’ light(?))
at sunrise migrates downward.

8. -200
-400
--500
From ~400 m to ~200 in ~45 min
~7.4 cm/s

9. Pinot, J.M., Jansa, J., 2001. Time variability of acoustic backscatter from zooplankton in
the Ibiza Channel (western Mediterranean). Deep Sea Research I 48, 1651–1670.
Plueddemann, A., Pinkel, R., Characterization of the patterns of diel migration using
a doppler sonar. Deep-Sea Research 36, 509–530.
Smith, P.E., Ohman, M.D., Eber, L.E., Analysis of the patterns of distribution of
zooplankton aggregations from acoustic Doppler current profiler. California Cooperative
Oceanic Fisheries Investigations 30,
Wilson, C.D., Firing, E., Sunrise swimmers bias acoustic Doppler current profilers.
Deep Sea Res. I 39,
….. ….
(+ hundreds more)

10. MIGRATIONS ALSO OCCUR AT 1000 m DEPTH
van Haren, H Monthly periodicity in acoustic reflections and
vertical motions in the deep ocean. Geophys. Res. Letters., 34, L12603, doi: /2007GL029947
Kaltenberg, Biggs and DiMarco Deep scattering layers of the Northern Gulf of Mexico
observed with a shipboard 38-kHz ADCP. Gulf of Mexico Science 2007(2):

11. All what this study is about:
-Show the mean cycle as a function of depth:
**** Timing of and maximum velocity.
-Show the very high correlation in daily maximum
minus minimum in vertical velocity and echo intensity.
(& speculate on both)

14. Daily vertical velocity cycle as function of year-dayB A

15. Downward motion is delayed at 1000 m relative to 300 m.B A
Downward motion is delayed at 1000 m relative to 300 m.
Upward migration occurs earlier at 1000 m relative to 300 m.

18. Color bar applies to top panels
(lower panels with a factor of 1/3)

19. Hour of peak migration and peak
speeds in mean daily cycle

21. Time series of daily amplitudes:
The amplitude of the vertical daily cycle is defined as the
maximum minus the minimum.
Same for echo intensity (regardless of when it happen during such
cycle. Recall that the maximum of the echo intensity happens
near mid-night at depth, while in the m depth range it
does either at sunrise or sunset. ) . -

22. m m
plot(t,(a-mean(a))/std(a))

23. Mean cycle in echo intensity anomaly

24. All pairs for “w” and “I=echo” are averages over a 150 m thick layer, dots for the layer from 1000 to 1150 m (moorings 2, 3 and 5), and crosses at the 350 to 500 m level (moorings 2, 4 and 5). Solid lines are the ordinary least square fits.

25. The series shown here are running means, of fifteen days length, of the amplitude in vertical velocity (solid trace) and relative backscatter intensity (dashed trace), translated into velocity by the regressions coefficients deduced from the scatter plots. All frames are for averages over layers 150 m thick, the three top frames for layers centered at 425 m and the lower three at 1075 m. The numbers to the left in each frame show the 95% confidence limits for correlation.

26. -The mean diel cycle has a continuous variation with depth
up to 1200 m below the surface of the peak migration timing.
-The cycle is nearly symmetric to solar noon, with upward peak
velocities earlier at depth than closer to surface. Consequently,
at greater depth the nightly shallower stay is longer for the
deeper migrating biota.
The mean deep (~1000 m) cycle (in the Gulf of Mexico) has
peak velocities on the order of 1 cm/s (40 m/h)
(cycles are intensified during summer, with peak velocities
up to 4 cm/s, as intense as near the surface).
-The very high correlation of velocity and echo daily amplitudes suggest the production of sound scattering perturbations due to stirring caused by the swimming activity. -

27. FIN All what this study was about:
-To show the mean cycle as a function of depth:
**** Timing of and the maximum speeds.
-To show the very high correlation in daily maximum
minus minimum in vertical velocity and echo intensity.
(& speculate on both)
FIN

28. Horizontal velocity contamination due to W!!?

29. Yes (due to tilt errors), BUT then W’s are intense!

30. Examples of echo intensity daily cycles

31. The cycle is obvious in velocity and echo intensity
Echo intensity varies depending on zooplankton
swimming intensity (regardless of swimming direction).

32. Mean Vertical Velocity (how long does it takes for
a ‘particle’ to get to the bottom?)
On the order of one month.
Terminal V ~ 1 mm/s
Δρ~0.4 (1 mm) ~0.1 (2 mm).

33. Abstract
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, whereas 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.