Global marine gravity from retracked Geosat and ERS‐1 altimetry: Ridge segmentation versus spreading rate

TLDR

The study speculates that a single mechanism, possibly lithospheric or asthenospheric, controls both ridge segmentation and spreading‑rate transitions. The authors reduced marine gravity anomaly errors by retracking raw waveforms, using the EGM2008 model for seamless land‑ocean transition, and applying biharmonic spline interpolation to generate residual vertical deflection grids. Retracked data improved range precision by 40 % (ERS‑1) and 27 % (Geosat), yielding global gravity grids with 2–4 mGal errors, while resolving spreading ridges that vary from 50–80 km segments at <60 mm/a to 100–1000 km at higher rates, marking a transition from axial valley to axial high.

Abstract

Three approaches are used to reduce the error in the satellite‐derived marine gravity anomalies. First, we have retracked the raw waveforms from the ERS‐1 and Geosat/GM missions resulting in improvements in range precision of 40% and 27%, respectively. Second, we have used the recently published EGM2008 global gravity model as a reference field to provide a seamless gravity transition from land to ocean. Third, we have used a biharmonic spline interpolation method to construct residual vertical deflection grids. Comparisons between shipboard gravity and the global gravity grid show errors ranging from 2.0 mGal in the Gulf of Mexico to 4.0 mGal in areas with rugged seafloor topography. The largest errors of up to 20 mGal occur on the crests of narrow large seamounts. The global spreading ridges are well resolved and show variations in ridge axis morphology and segmentation with spreading rate. For rates less than about 60 mm/a the typical ridge segment is 50–80 km long while it increases dramatically at higher rates (100–1000 km). This transition spreading rate of 60 mm/a also marks the transition from axial valley to axial high. We speculate that a single mechanism controls both transitions; candidates include both lithospheric and asthenospheric processes.