Convective circulation of the mantle causes deflections of the Earth's surface that vary as a function of space and time. Accurate measurements of this dynamic topography are complicated by the need to isolate and remove other sources of elevation, arising from flexure and lithospheric isostasy. The complex architecture of continental lithosphere means that measurement of present‐day dynamic topography is more straightforward in the oceanic realm. Here we present an updated methodology for calculating oceanic residual bathymetry, which is a proxy for dynamic topography. Corrections are applied that account for the effects of sedimentary loading and compaction, for anomalous crustal thickness variations, for subsidence of oceanic lithosphere as a function of age and for non‐hydrostatic geoid height variations. Errors are formally propagated to estimate measurement uncertainties. We apply this methodology to a global database of 1936 seismic surveys located on oceanic crust and generate 2297 spot measurements of residual topography, including 1161 with crustal corrections. The resultant anomalies have amplitudes of ±1 km and wavelengths of ∼1000 km. Spectral analysis of our database using cross‐validation demonstrates that spherical harmonics up to and including degree 30 (i.e., wavelengths down to 1300 km) are required to accurately represent these observations. Truncation of the expansion at a lower maximum degree erroneously increases the amplitude of inferred long‐wavelength dynamic topography. There is a strong correlation between our observations and free‐air gravity anomalies, magmatism, ridge seismicity, vertical motions of adjacent rifted margins, and global tomographic models. We infer that shorter wavelength components of the observed pattern of dynamic topography may be attributable to the presence of thermal anomalies within the shallow asthenospheric mantle.

[1] We present a strategy for calculating uplift rates as a function of space and time from large sets of longitudinal river profiles. This strategy assumes that the shape of a river profile is controlled by the history of uplift rate and moderated by the erosional process. We assume that upstream drainage area is invariant. The algorithm was tested on a set of $100 river profiles which were extracted from a digital elevation model of Madagascar. This set of profiles was simultaneously inverted to obtain uplift rate as a smooth function of space and time. The fit between observed and calculated profiles is excellent and suggests that Madagascar was uplifted by 1-2 km at rates of 0.2-0.4 mm/yr during the last $15 Myrs. The location of Madagascar suggests that its topographic elevation is maintained by convective circulation of the sub-lithospheric mantle. Residual depth anomalies of oceanic fragments encompassing the island show that the island straddles a dynamic topographic gradient which generates asymmetric Neogene uplift. Volcanism, warped peneplains and uplifted marine terraces corroborate the existence of youthful uplift. We suggest that sets of longitudinal river profiles contain useful information about the history of regional uplift which can be extracted by inverse modeling and calibrated by independent geologic observations.

[1] Despite its importance, the spatial and temporal pattern of dynamic topography generated by mantle convective circulation is poorly known. We present accurate estimates of dynamic topography from oceanic basins and continental margins surrounding Australia. Our starting point is measurement of residual depth anomalies on the oldest oceanic floor adjacent to the continental shelf. These anomalies were determined from a combined dataset of~200 seismic reflection and wide-angle images of well-sedimented oceanic crust. They have amplitudes of between À1 km and +0.5 km, and their spatial variation is broadly consistent with long-wavelength free-air gravity and shallow seismic tomographic anomalies. Along the Northwest Shelf, a regional depth anomaly of À300 to À700 m intersects the adjacent continental shelf. The temporal evolution of this anomaly was determined by analyzing the stratigraphic architecture of an extensive carbonate platform, which fringes the shelf and records a dramatic switch from progradation to aggradation during Neogene times. Three-dimensional seismic mapping calibrated by boreholes was used to calculate water-loaded subsidence histories at rollover points of clinoforms along the shelf. At 9 AE 3 Ma, the rate of subsidence increases from 5 to up 75 m Myr À1 , generating a subsidence anomaly of À300 to À700 m. The amplitude of this anomaly varies along the shelf and cannot be generated by glacio-eustatic sea-level variation. Instead, we propose that a regional subsidence episode, which affects both the proximal shelf and the distal oceanic basin, was generated by convective drawdown. By combining our results with other published estimates of uplift and subsidence, a map of Australia, which shows the spatial and temporal pattern of dynamic topography is presented. Most, but not all, of Australia's epeirogeny can be attributed to rapid northward motion of the Australian plate over a pre-existing pattern of convective circulation.

In the oceans, our understanding of plate subsidence as a function of age permits residual depth anomalies to be identified and mapped. These anomalies may reflect dynamic topography and could be an important means for constraining convective circulation of the sublithospheric mantle. Here we analyze a global database of seismic reflection and wide‐angle profiles from heavily sedimented oceanic crust, which abuts continental lithosphere. At 449 locations, we calculated water‐loaded subsidence, compared it with a reference age‐depth relationship, and determined residual depth. We then combined these spot measurements of residual depth with observations from mid‐oceanic ridges and from selected ship track bathymetry to construct a global map of residual depth. Our results suggest that the amplitude of residual depth varies by up to ±1 km with wavelengths of order 103 km. We compare our residual depths with free‐air gravity and seismic tomographic anomalies. Our results show that residual depths correlate with long‐wavelength gravity anomalies. In contrast, correlations between residual depths and vertically averaged shear velocity anomalies within the upper and/or the lower mantle are weaker. The largest discrepancies occur at short (∼1000 km) wavelengths. These combined observations suggest that residual depth anomalies could be generate by density variations within a thin (∼102 km) low‐viscosity layer beneath the lithosphere. Our global compilation should play a significant role in helping to refine predictive geodynamical models.

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