| Summary: | We analyze recordings of four geomagnetic observatories located in the French sub-antarctic and antarctic territories: Amsterdam Island (AMS), Crozet (CZT), Kerguelen (PAF), Durmont d'Urville (DRV). These recordings cover several decades of the geomagnetic field variation sampled every minute. We report results of a classical spectral analysis, where we estimate the spectral content of these series. Unlike previous studies, we attempt to identify the inter-annual variability of magnetic signals generated by Ocean tides, therefore we analyze monthly sets of the magnetic field recordings. We identify different tidal constituents, i.e. diurnal, semi-diurnal and short-periodic shallow water tides. Almost all show a long-term variability (seasonality) in their strength, particularly the shallow-water MK3 tide at Amsterdam Island (AMS), but also diurnal and semi-diurnal tides such as O1, K1 and M2. Causes of the long-term variability of shallow water tides and the diurnal and semi-diurnal tides might be different and may depend on different driving mechanisms i.e. wind forcing and the strength and shape of the Antarctic Circumpolar Current (ACC). We attempt to quantify these forcings and their variability throughout time.
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