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Andrew Wickert

doi:10.5194/gmd-2021-126-ec1

Abstract

Retreat and advance of ice sheets perturb the gravitational field, solid surface and rotation of the Earth, leading to spatially variable sea-level changes over a range of timescales (~O100-6 years), which in turn feed back onto ice sheet dynamics. Coupled ice-sheet – sea-level models have been developed to capture the interactive processes between ice sheets, sea level and the solid Earth, but it is computationally challenging to capture short-term interactions (~O100-2 years) precisely within longer (~O103-6 years) simulations. The classic coupling algorithm assigns a uniform temporal resolution in the sea-level model, causing a quadratic increase in total CPU time with the total number of input ice history steps, which increases with either the length or temporal resolution of the simulation. In this study, we introduce a new “time window” algorithm for sea-level models that enables users to define the temporal resolution at which the ice loading history is captured during different time intervals before the current simulation time. Utilizing the time window, we assign a fine temporal resolution (~O100-2 years) for the period of ongoing and recent history of surface ice and ocean loading changes and a coarser temporal resolution (~O103-6 years) for earlier periods in the simulation. This reduces the total CPU time and memory required per model time step while maintaining the precision of the model results. We explore the sensitivity of sea-level model results to the model's temporal resolution and show how this sensitivity feeds back onto ice sheet dynamics in coupled modelling. We apply the new algorithm to simulate the sea-level changes in response to global ice-sheet evolution over two glacial cycles and the rapid collapse of marine sectors of the West Antarctic Ice Sheet in the coming centuries, providing appropriate time window profiles for each of these applications. The time window algorithm improves the total CPU time by ~50–% in each of these examples, and this improvement would increase with longer simulations than considered here. Our algorithm also allows coupling time intervals of annual temporal scale for coupled ice-sheet – sea-level modelling of regions such as the West Antarctic that are characterized by rapid solid Earth response to ice changes due to the thin lithosphere and low mantle viscosities.

Highlights

It is well established that sea-level changes in response to ice-sheet changes feed back onto the evolution of ice sheets (e.g., Gomez et al, 2012; 2015; de Boer et al, 2014; Konrad et al, 2015; Larour et al, 2019). 35 Changes in grounded ice cover perturb the Earth’s gravitational field, rotation and viscoelastic solid surface, leading to spatially non-uniform changes in the heights of the sea surface geoid and the solid Earth, i.e., sea-level changes (e.g., Peltier, 1974; Farrell and Clark, 1976; Woodward, 1888; Mitrovica and Milne, 2003)
We have developed a new time window algorithm that assigns nonuniform temporal resolution to the 555 inputted ice cover changes in a forward sea-level model
We first tested the sensitivity of sea-level model outputs to the temporal resolution adopted in idealized simulations (Fig. 2)

Summary

Introduction

It is well established that sea-level changes in response to ice-sheet changes feed back onto the evolution of ice sheets (e.g., Gomez et al, 2012; 2015; de Boer et al, 2014; Konrad et al, 2015; Larour et al, 2019). 35 Changes in grounded ice cover perturb the Earth’s gravitational field, rotation and viscoelastic solid surface, leading to spatially non-uniform changes in the heights of the sea surface geoid and the solid Earth, i.e., sea-level changes (e.g., Peltier, 1974; Farrell and Clark, 1976; Woodward, 1888; Mitrovica and Milne, 2003). Sea-level changes occur as an instantaneous response to the surface (ice and water) loading changes associated with elastic deformation of the solid Earth and changes in gravity and rotation, 40 followed by a slower response over tens of thousands of years due to the viscous mantle flowing back towards isostatic equilibrium, once again accompanied by gravitational and rotational effects. Variable changes in the sea surface geoid and the solid Earth (i.e., sea level) have different dominant mechanisms in influencing ice sheets in marine and continental settings. 55 deformation of the bedrock beneath the ice and sea level changes at the grounding line in response to the marine-based ice sheet's growth and retreat affect the ice flux across the grounding line (Gomez et al, 2010, 2012, 2020). This, in turn, influences the ice sheet's surface mass balance (e.g., Crucifix et al, 2001; Han et al, 2021; van den Berg et al, 2008)

Methods

Results

Conclusion