Abstract

Abstract. Glacial isostatic adjustment is largely governed by the rheological properties of the Earth's mantle. Large mass redistributions in the ocean–cryosphere system and the subsequent response of the viscoelastic Earth have led to dramatic sea level changes in the past. This process is ongoing, and in order to understand and predict current and future sea level changes, the knowledge of mantle properties such as viscosity is essential. In this study, we present a method to obtain estimates of mantle viscosities by the assimilation of relative sea level rates of change into a viscoelastic model of the lithosphere and mantle. We set up a particle filter with probabilistic resampling. In an identical twin experiment, we show that mantle viscosities can be recovered in a glacial isostatic adjustment model of a simple three-layer Earth structure consisting of an elastic lithosphere and two mantle layers of different viscosity. We investigate the ensemble behaviour on different parameters in the following three set-ups: (1) global observations data set since last glacial maximum with different ensemble initialisations and observation uncertainties, (2) regional observations from Fennoscandia or Laurentide/Greenland only, and (3) limiting the observation period to 10 ka until the present. We show that the recovery is successful in all cases if the target parameter values are properly sampled by the initial ensemble probability distribution. This even includes cases in which the target viscosity values are located far in the tail of the initial ensemble probability distribution. Experiments show that the method is successful if enough near-field observations are available. This makes it work best for a period after substantial deglaciation until the present when the number of sea level indicators is relatively high.

Highlights

  • Glacial isostatic adjustment (GIA) describes the continual response of the Earth to mass redistribution between continental glaciers, ice sheets, and the ocean during glacial cycles (e.g. Lambeck et al, 2003)

  • In set-up 1, we studied the convergence of the weighted mean to the target values of the reference model when all available observations from the time interval 25.5 ka until the present day are considered

  • We have shown that our algorithm is able to recover a synthetic mantle viscosity structure through assimilation of palaeo sea level rates of change

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Summary

Introduction

Glacial isostatic adjustment (GIA) describes the continual response of the Earth to mass redistribution between continental glaciers, ice sheets, and the ocean during glacial cycles (e.g. Lambeck et al, 2003). Glacial isostatic adjustment (GIA) describes the continual response of the Earth to mass redistribution between continental glaciers, ice sheets, and the ocean during glacial cycles Deformation of the Earth’s surface due to those mass redistributions has led to rising and falling sea levels, with local amplitudes exceeding a 100 m The behaviour of sea level during glaciation and deglaciation is very complex and differs in the near-, intermediate, and far field (Khan et al, 2015). The rheology of the Earth’s mantle plays a significant role in surface deformation in the near-field of ice sheets (Lambeck et al, 1998). The Earth’s response after deglaciation is one important process that allows it to infer mantle viscosities (Steffen and Wu, 2011; Peltier, 1996). Obtaining reliable values for mantle viscosity is the basis for a precise determination of Earth’s deformation history, mass re-

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