I hit the thermocline at 0930, two hundred kilometers off the shelf break. The temperature dropped eleven degrees in forty meters, and with it, everything I thought I knew about underwater acoustics went silent. The sonar array — twelve hydrophones spaced across the ridge — had picked up a signal I could not explain: rhythmic, low-frequency, and moving against the current.
Signal Loss at 400 Meters
Below four hundred meters, the water column does something strange to digital transmissions. Our relay buoys — standard issue, rated for six-hundred-meter operation — began dropping packets at 380. By 420, we had lost sixty percent of the telemetry feed. The logs revealed a pattern: interference spikes synchronized with vertical migration cycles. Krill clouds, refracting the signal path. Biology, not engineering.
Every organism in the mesopelagic zone is a transmitter. You just have to learn their frequency.