Le Mouël, J.-L.; Lopes, F., and Courtillot, V., . Sea-level change at the Brest (France) tide gauge and the Markowitz component of Earth's rotation.
This paper centers on singular spectrum analysis (SSA) of variations in sea level in Brest (France) and in Earth's axis of rotation. Brest tide gauge data (recording the Brest sea level [BSL]) are available from 1807 onward. The main features of the BSL curve are common to most stations in the Northern Hemisphere; hence, the Brest curve has recorded a gross Earth datum. Pole positions (coordinate m2), another gross Earth datum, are from the International Earth Rotation and Reference System Service (1845–2019). The first SSA components of both series, i.e. the trends, are similar, with a major acceleration event near 1900 and sea level lagging pole motion by ∼5 to 10 years. SSA components with periods of 1, 5.4, and ∼11 years are common to the two series. An important feature is a 0.5-year component that is present in sea level but absent from pole motion. The remarkable similarity of the two trends and their phase lag suggests a causal relationship opposite the one that is generally accepted.