Australia: The Land Where Time Began

A biography of the Australian continent 

Mantle Flow on a Large Scale Revealed by Global Dynamic Topography Observations to Have a Limited Influence

A fraction of the topography of the surface of the Earth that varies with space and time is maintained by convective circulation of the mantle. It is shown by most predictive models that this dynamic topography has peak amplitudes of about ± 2 km, dominated by wavelengths of 10⁴ km. In this study Haggard, White & Al-Attar tested these models against their comprehensive observational database of 2,120 spot measurements of dynamic topography that had been determined by analysing oceanic seismic surveys. These accurate measurements, the robustness of which has been carefully tested and benchmarked, have typical peak amplitudes of ± 1 km and wavelengths of approximately 10³ km, and generate a global spherical harmonic model when combined with limited continental constraints.  It was revealed by their power spectral analysis that there were significant discrepancies between observed and predicted topography. Observed dynamic topography has peak amplitudes of about ± 500 m at longer wavelengths, such as 10⁴ km. Significant dynamic topography is still observed at shorter wavelengths, such as 10³ km. In this study it was shown that these discrepancies can be explained if short-wavelength dynamic topography is generated by density anomalies, which are temperature driven, within a sub-plate asthenospheric channel. It is shown by stratigraphic observations from adjacent continental margins that these dynamic topographic signals evolve quickly over time. On the surface of the Earth more rapid temporal and spatial changes in vertical displacement have direct consequences for fields as diverse as mantle flow, oceanic circulation and climate changes over the long term.

Sources & Further reading

1. Haggard, M. J., N. White and D. Al-Attar (2016). "Global dynamic topography observations reveal limited influence of large-scale mantle flow." Nature Geosci 9(6): 456-463.