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).