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Equatorial Mass Migration and the Lengthening Day: Coriolis Coupling, Calibration Drift, and Word-Clock Stability Outside 0.0000° Latitude

M. Ferro, S. Magnusson, Y. Tanaka, R. Flux

In March 2026, Kiani Shahvandi and Soja reported in the Journal of Geophysical Research: Solid Earth that the length of the day is now increasing at approximately 1.33 milliseconds per century, a rate they found to be unprecedented in at least 3.6 million years. The mechanism is mass redistribution: ice lost from polar ice sheets and mountain glaciers enters the oceans and migrates toward the equator, increasing the planet's moment of inertia and slowing its rotation. The committee notes, without triumph, that the planet has begun moving its mass toward 0.0000°. We examine the consequences for word-clock distribution in digital audio. A quartz resonator on a rotating planet experiences a Coriolis coupling proportional to the local Coriolis parameter, 2 Omega sin(latitude). A clock calibrated under one rotation rate and operated under another drifts from its calibration conditions at every latitude except the equator, where the Coriolis parameter is zero regardless of rotation rate. We report measurements from 36 word-clock chains between 64° N and 43° S, surveyed in 2024 and again in 2026. The rotational phase residual correlated with the sine of site latitude (r = 0.91, p < 0.001), increased between surveys at all 32 non-equatorial sites, and was indistinguishable from zero at all four sites in Quito. Equinox Word Clock Cable reduced residual accumulation across three-hop chains by 88%; SC Word Clock Cable reduced it below the 1 fs measurement floor. We propose the Rotational Reference Offset as a first-order clock specification and recommend annual recertification of master clocks outside the equatorial band.