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SUMMARY Mass loss from polar ice sheets is becoming the dominant contributor to current sea level changes, as well as one of the largest sources of uncertainty in sea level projections. The spatial pattern of sea level change is sensitive to the geometry of ice sheet mass changes, and local sea level changes can deviate from the global mean sea level change due to gravitational, Earth rotational and deformational (GRD) effects. The pattern of GRD sea level change associated with the melting of an ice sheet is often considered to remain relatively constant in time outside the vicinity of the ice sheet. For example, in the sea level projections from the most recent IPCC sixth assessment report (AR6), the geometry of ice sheet mass loss was treated as constant during the 21st century. However, ice sheet simulations predict that the geometry of ice mass changes across a given ice sheet and the relative mass loss from each ice sheet will vary during the coming century, producing patters of global sea level changes that are spatiotemporally variable. We adopt a sea level model that includes GRD effects and shoreline migration to calculate time-varying sea level patterns associated with projections of the Greenland and Antarctic Ice Sheets during the coming century. We find that in some cases, sea level changes can be substantially amplified above the global mean early in the century, with this amplification diminishing by 2100. We explain these differences by calculating the contributions of Earth rotation as well as gravitational and deformational effects to the projected sea level changes separately. We find in one case, for example, that ice gain on the Antarctic Peninsula can cause an amplification of up to 2.9 times the global mean sea level equivalent along South American coastlines due to positive interference of GRD effects. To explore the uncertainty introduced by differences in predicted ice mass geometry, we predict the sea level changes following end-member mass loss scenarios for various regions of the Antarctic Ice Sheet from the ISMIP6 model ensemblely, and find that sea level amplification above the global mean sea level equivalent differ by up to 1.9 times between different ice mass projections along global coastlines outside of Greenland and Antarctica. This work suggests that assessments of future sea level hazard should consider not only the integrated mass changes of ice sheets, but also temporal variations in the geometry of the ice mass changes across the ice sheets. As well, this study highlights the importance of constraining the relative timing of ice mass changes between the Greenland and Antarctic Ice Sheets.
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Capturing the interactions between ice sheets, sea level and the solid Earth on a range of timescales: a new “time window” algorithm
Abstract. Retreat and advance of ice sheets perturb the gravitational field, solidsurface and rotation of the Earth, leading to spatially variable sea-levelchanges over a range of timescales O(100−6 years), which in turn feedback onto ice-sheet dynamics. Coupled ice-sheet–sea-level models havebeen developed to capture the interactive processes between ice sheets, sealevel and the solid Earth, but it is computationally challenging to captureshort-term interactions O(100−2 years) precisely within longer O(103−6 years) simulations. The standard forward sea-level modelling algorithmassigns a uniform temporal resolution in the sea-level model, causing aquadratic increase in total CPU time with the total number of input icehistory steps, which increases with either the length or temporal resolutionof the simulation. In this study, we introduce a new “time window”algorithm for 1D pseudo-spectral sea-level models based on the normal modemethod that enables users to define the temporal resolution at which the iceloading history is captured during different time intervals before thecurrent simulation time. Utilizing the time window, we assign a finetemporal resolution O(100−2 years) for the period of ongoing andrecent history of surface ice and ocean loading changes and a coarsertemporal resolution O(103−6 years) for earlier periods in thesimulation. This reduces the total CPU time and memory required per modeltime step while maintaining the precision of the model results. We explorethe sensitivity of sea-level model results to the model temporal resolutionand show how this sensitivity feeds back onto ice-sheet dynamics in coupledmodelling. We apply the new algorithm to simulate sea-level changes inresponse to global ice-sheet evolution over two glacial cycles and the rapidcollapse of marine sectors of the West Antarctic Ice Sheet in the comingcenturies and provide appropriate time window profiles for each application.The time window algorithm reduces the total CPU time by ∼ 50 % in each of these examples and changes the trend of the total CPU timeincrease from quadratic to linear. This improvement would increase withlonger simulations than those considered here. Our algorithm also allows for couplingtime intervals of annual temporal scale for coupled ice-sheet–sea-levelmodelling of regions such as West Antarctica that are characterized byrapid solid Earth response to ice changes due to the thin lithosphere andlow mantle viscosities.
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- Award ID(s):
- 1745074
- PAR ID:
- 10351122
- Date Published:
- Journal Name:
- Geoscientific Model Development
- Volume:
- 15
- Issue:
- 3
- ISSN:
- 1991-9603
- Page Range / eLocation ID:
- 1355 to 1373
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.5194/gmd-15-1355-2022
