Fig. 3: Median ocean sound levels sampled at Axial Seamount.

a Median ocean sound levels in the one-third octave bands centered at 63 and 125 Hz during 2018–2021 sampled at Axial Seamount. Two-week running average sound levels for each calendar year are visualized as smoothed solid colored lines overlaid on semi-transparent points that represent daily median sound levels. Breaks in the solid colored lines indicate data gaps. The solid blue arrow points to spring–summer 2020, when low ambient sound levels were observed. Increase in 2021 levels is likely due to a change in hydrophone depth. b Received sound levels from an airgun survey at Axial Seamount during July–August of 2019 in comparison to received levels during years with no surveys. Low received levels observed during the survey were due to a pause in airgun activity²¹.