7731 20260107135318.0 10.1007/s10712-024-09874-4 DOI SCART-2026-0017 Cazenave, A. Why is the Earth System oscillating at a 6-year period? 2025 3EU_GRACEFUL/ 3EU_GRACEFUL/ 3EU_GRACEFUL NO Pfeffer, J. Mandea, M. Dehant, V. Gillet, N. Surveys in Geophysics 2025 26 veronique.dehant@ksb-orb.be published in REFERD