Can we measure the ocean’s ph with Acoustics?
This work is for a proposal for NSF Chemical Oceanography. I showed that there are robust variations in the attenuation of direct water column arrivals in the air-gun shots recorded during the ETOMO experiment, a seismic project designed to image the oceanic crust and upper-most mantle - the ocean was just in the way. In the oceans, the primary control on attenuation is the pH of the water - so one of the seismic techniques I use may help study ocean acidification. Very exciting! Current status is that I’m going to retool this for resubmission spring/summer. Reviews were good, but I probably need to move away from just ocean bottom seismic data to make this a reality.
Example data
This is an example of two arrivals data recorded during the ETOMO experiment on the left, next to an example of the seismic technique I adapted this from. Seismic data is from Byrnes et al., 2019. Attenuation is quantified with t*, with units of seconds (a pseudo-time, not a real travel time. Yes, that’s confusing).
Example measurement
This is the spectral ratio of the two water column arrivals shown above. Note the parabolic curve as opposed to a linear curve. Part of this proposal is showing that while in the Earth, we expect linear ratios, for ocean pH driven attenuation, theory predicts a parabola - that prediction is beautifully fulfilled.
Below is a 3D model of variations in attenuation in the ocean above the Endeavor segment of the Juan de Fuca Ridge (see this paper for details of the ETOMO experiment). Black lines are the ridge axis. This is pretty early - the measurements need to be redo but the station geometry is, of course, set.
