Gravity maps derived from satellite altimeter measurements provide unprecedented me. Dium-resolution coverage of sparsely surveyed mid-ocean ridges in the southern oceans. A spectral analysis of 76 000 km of coincident shipboard and satellite gravity measurements shows that satellite altimeters can accurately resolve features with half-wavelengths as short as 13 km. The coverage and resolution of these gravity data allow us to determine accurately both the location of poorly charted ridge axes and the variation in axial anomaly character along the ridge axis, although their detailed morphology is not resolved. The results of this study support earlier studies that showed a transition from spreading-rate-dependent axial gravity lows to rate-independent axial highs with increasing spreading rate. Four such transitions are imaged on the Southeast Indian Ridge and Pacific Antarctic Ridge. We expect that these transitions are the result of a temperature-sensitive threshold phenomenon and may be influenced by nearby hot spots.

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