Observations and models of dynamic topography: Current status and future directions.

Abstract

The slow creeping motion of Earth’s mantle drives transient changes in surface topography across a variety of spatial and temporal scales. Recent decades have seen substantial progress in understanding this so-called `dynamic topography’, with a growing number of studies highlighting its fundamental role in shaping the surface of our planet. In this review, we outline the current frontiers of geodynamical research into dynamic topography. It begins with a summary of ongoing observational, theoretical and computational efforts that aim to quantify the present-day expression of dynamic topography, including its geographical distribution and sensitivity to different components of the mantle's flow regime. Next, observational constraints that shed light on how dynamic topography has changed over time are summarised, and compared with predictions from a range of geodynamical modelling studies, to highlight our current understanding of its evolution through the geological past. Although many model predictions can be reconciled with the available observational constraints, these comparisons demonstrate that there remain inconsistencies, particularly at shorter spatial and temporal scales. These discrepancies allow us to isolate the shortcomings of existing modelling approaches and identify pathways towards improving future reconstructions of dynamic topography through space and time. Such reconstructions are vital if we are to robustly connect the evolution of Earth's surface environments to the processes that are occurring deep within its interior.

Geodynamically corrected Pliocene shoreline elevations in Australia consistent with mid-range projections of Antarctic ice loss

“…The latter parameter applies to models in which the basal layers of LLVPs contain compositional anomalies (C = 1), since recent studies find that these regions likely contain smaller proportions of low-viscosity post-perovskite and larger volumes of high-viscosity silicic phases (e.g., stishovite and seifertite) compared to background mantle material 32 . This inference is further supported by recent work demonstrating that geoid observations are better matched by model predictions when LLVP material is assigned a similar viscosity to its surroundings, indicating that thermal and compositional controls on viscosity may counterbalance one another in the lowermost mantle 70 .…”

“…Having smoothed and corrected the V S lookup table, velocities from five different seismic tomographic models-LLNL-G3D-JPS 30 ; S40RTS 39 ; SAVANI 40 ; SEMUCB-WM1 41 ; TX2011 42 -are converted into temperature, with values adjusted by a constant offset to ensure mean temperatures are consistent with the mantle geotherm 68 . Note that, following Richards et al 32 and Davies et al 70 , we high-pass filter the seismic velocity models within the 1000-2000 km depth range in order to correct for vertical smearing of long-wavelength structure and obtain an acceptable fit to the observed long-wavelength geoid-to-topography ratio. This filtering is accomplished by multiplying the spherical harmonic coefficients, c lm , of the seismic velocity fields with a monotonic truncation function, f (l) that increases smoothly from 0 to 1 with spherical harmonic degree according to…”

The Topographic Signature of Mantle Pressure Build‐Up Beneath Subducting Plates: Insights From Spherical Subduction Models

“…Davies et al. (2022) is their case with both upper mantle structure and temperature/pressure‐dependent viscosity. In the “filtered” version of Holdt et al.…”

“…I propose this mismatch is evidence for an upwards tilt of SPs that, despite large RT scatter (due to the dominance of other topographic sources), is not reflected in flow models without decoupled and/or high resolution slabs. The negative tilt in mantle flow models is due to the dynamic drawdown driven by dense slab anomalies, in (Davies et al, 2022;Steinberger et al, 2019). Topography gradient (Δ x topo) is extracted 400 km outboard of the trench, and positive values represent upwards tilt toward the trench.…”

“…The Steinberger (2016) topographies are expanded up to spherical harmonic degree 31 (and is their case without lateral viscosity variations) and Holdt et al (2022) up to degree 41. Davies et al (2022) is their case with both upper mantle structure and temperature/pressure-dependent viscosity. In the "filtered" version of Holdt et al (2022), subduction segments are counted only if they are within 150 km distance of 5 or more residual depth measurements.…”