Figure 2. Acoustic data, measured by EK60 over the course of
the experiment, at ETNP Station P2. Shown are data from the 18000 Hz
frequency band, which have highest depth penetration, but which appear
to co-occur with data from other frequency bands (see Figure S3). Values
are in return signal intensity and have not been normalized to observed
biomass. Horizontal blue lines
indicate the top and bottom of the ODZ, while the horizontal green line
indicates the base of the photic zone.
Times are local Mexico General
Standard time, which is the local time for the nearest port of call in
Manzanillo and is equivalent to United States Central Standard Time. The
black and white bar at the top indicates day and night periods, with day
defined as times when the center of the sun is above the horizon, per
the OCE R package. Diamonds indicate the depths and times of UVP casts,
with casts deeper than 1000 m shown as diamonds on the 1000 m line.
Several patterns are evident A. Two bands of organisms can be
seen leaving the surface at dawn, spending the day between 250 m and
500 m and returning to the surface at dusk. B. Another group of
nocturnally migrating organisms can be seen leaving the surface at dusk,
spending the night near 250 m and returning at dawn. C. Some
organisms appear at the base of the photic zone, during some, but not
all mid days, and then disappear in the evening. D. A group of
very deep migrating organisms appears to leave the surface with the diel
migrators and pass all the way through the ODZ and out of the EK60’s
field of view. It returns at dusk. E. Swarms of organisms
appear between 500 m and 1000 m disappearing later in the day. Swarms
appear in the deepest layers at night and appear progressively shallower
as the day progresses.
Flux data from traps
Flux measurements at Station P2 were consistent between the different
particle trap types, showing a profile that broadly followed a power law
with respect to depth, with the exception that flux appeared to increase
in one trap at 500 m (Figure 3).