Viscosity structure of Earth's mantle inferred from rotational variations due to GIA process and recent melting events
We examine the geodetically derived rotational variations for the rate of change of degree-two harmonics of Earth's geopotential, J˙2, and true polar wander, combining a recent melting model of glaciers and the Greenland and Antarctic ice sheets taken from the IPCC 2013 Report (AR5) with two re...
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ftanucanberra:oai:openresearch-repository.anu.edu.au:1885/152810 2024-01-14T10:01:44+01:00 Viscosity structure of Earth's mantle inferred from rotational variations due to GIA process and recent melting events Nakada, Masao Okuno, Jun'ichi Lambeck, Kurt Purcell, Anthony application/pdf http://hdl.handle.net/1885/152810 https://doi.org/10.1093/gji/ggv198 https://openresearch-repository.anu.edu.au/bitstream/1885/152810/5/01_Nakada_Viscosity_structure_of_Earth%2527s_2015.pdf.jpg unknown Oxford University Press 0956-540X http://hdl.handle.net/1885/152810 doi:10.1093/gji/ggv198 https://openresearch-repository.anu.edu.au/bitstream/1885/152810/5/01_Nakada_Viscosity_structure_of_Earth%2527s_2015.pdf.jpg Geophysical Journal International Journal article ftanucanberra https://doi.org/10.1093/gji/ggv198 2023-12-15T09:35:45Z We examine the geodetically derived rotational variations for the rate of change of degree-two harmonics of Earth's geopotential, J˙2, and true polar wander, combining a recent melting model of glaciers and the Greenland and Antarctic ice sheets taken from the IPCC 2013 Report (AR5) with two representative GIA ice models describing the last deglaciation, ICE5G and the ANU model developed at the Australian National University. Geodetically derived observations of J˙2 are characterized by temporal changes of −(3.7 ± 0.1) × 10−11 yr−1 for the period 1976–1990 and −(0.3 ± 0.1) × 10−11 yr−1 after ∼2000. The AR5 results make it possible to evaluate the recent melting of the major ice sheets and glaciers for three periods, 1900–1990, 1991–2001 and after 2002. The observed J˙2 and the component of J˙2 due to recent melting for different periods indicate a long-term change in J˙2—attributed to the Earth's response to the last glacial cycle—of −(6.0–6.5) × 10−11 yr−1, significantly different from the values adopted to infer the viscosity structure of the mantle in most previous studies. This is a main conclusion of this study. We next compare this estimate with the values of J˙2 predicted by GIA ice models to infer the viscosity structure of the mantle, and consequently obtain two permissible solutions for the lower mantle viscosity (ηlm), ∼1022 and (5–10) × 1022 Pa s, for both adopted ice models. These two solutions are largely insensitive to the lithospheric thickness and upper mantle viscosity as indicated by previous studies and relatively insensitive to the viscosity structure of the D″ layer. The ESL contributions from the Antarctic ice sheet since the last glacial maximum (LGM) for ICE5G and ANU are about 20 and 30 m, respectively, but glaciological reconstructions of the Antarctic LGM ice sheet have suggested that its ESL contribution may have been less than ∼10 m. The GIA-induced J˙2 for GIA ice models with an Antarctic ESL component of ∼10 m suggests two permissible lower mantle viscosity solutions of ηlm ∼ 2 × ... Article in Journal/Newspaper Antarc* Antarctic Greenland Ice Sheet Australian National University: ANU Digital Collections Antarctic The Antarctic Greenland Geophysical Journal International 202 2 976 992 |
institution |
Open Polar |
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Australian National University: ANU Digital Collections |
op_collection_id |
ftanucanberra |
language |
unknown |
description |
We examine the geodetically derived rotational variations for the rate of change of degree-two harmonics of Earth's geopotential, J˙2, and true polar wander, combining a recent melting model of glaciers and the Greenland and Antarctic ice sheets taken from the IPCC 2013 Report (AR5) with two representative GIA ice models describing the last deglaciation, ICE5G and the ANU model developed at the Australian National University. Geodetically derived observations of J˙2 are characterized by temporal changes of −(3.7 ± 0.1) × 10−11 yr−1 for the period 1976–1990 and −(0.3 ± 0.1) × 10−11 yr−1 after ∼2000. The AR5 results make it possible to evaluate the recent melting of the major ice sheets and glaciers for three periods, 1900–1990, 1991–2001 and after 2002. The observed J˙2 and the component of J˙2 due to recent melting for different periods indicate a long-term change in J˙2—attributed to the Earth's response to the last glacial cycle—of −(6.0–6.5) × 10−11 yr−1, significantly different from the values adopted to infer the viscosity structure of the mantle in most previous studies. This is a main conclusion of this study. We next compare this estimate with the values of J˙2 predicted by GIA ice models to infer the viscosity structure of the mantle, and consequently obtain two permissible solutions for the lower mantle viscosity (ηlm), ∼1022 and (5–10) × 1022 Pa s, for both adopted ice models. These two solutions are largely insensitive to the lithospheric thickness and upper mantle viscosity as indicated by previous studies and relatively insensitive to the viscosity structure of the D″ layer. The ESL contributions from the Antarctic ice sheet since the last glacial maximum (LGM) for ICE5G and ANU are about 20 and 30 m, respectively, but glaciological reconstructions of the Antarctic LGM ice sheet have suggested that its ESL contribution may have been less than ∼10 m. The GIA-induced J˙2 for GIA ice models with an Antarctic ESL component of ∼10 m suggests two permissible lower mantle viscosity solutions of ηlm ∼ 2 × ... |
format |
Article in Journal/Newspaper |
author |
Nakada, Masao Okuno, Jun'ichi Lambeck, Kurt Purcell, Anthony |
spellingShingle |
Nakada, Masao Okuno, Jun'ichi Lambeck, Kurt Purcell, Anthony Viscosity structure of Earth's mantle inferred from rotational variations due to GIA process and recent melting events |
author_facet |
Nakada, Masao Okuno, Jun'ichi Lambeck, Kurt Purcell, Anthony |
author_sort |
Nakada, Masao |
title |
Viscosity structure of Earth's mantle inferred from rotational variations due to GIA process and recent melting events |
title_short |
Viscosity structure of Earth's mantle inferred from rotational variations due to GIA process and recent melting events |
title_full |
Viscosity structure of Earth's mantle inferred from rotational variations due to GIA process and recent melting events |
title_fullStr |
Viscosity structure of Earth's mantle inferred from rotational variations due to GIA process and recent melting events |
title_full_unstemmed |
Viscosity structure of Earth's mantle inferred from rotational variations due to GIA process and recent melting events |
title_sort |
viscosity structure of earth's mantle inferred from rotational variations due to gia process and recent melting events |
publisher |
Oxford University Press |
url |
http://hdl.handle.net/1885/152810 https://doi.org/10.1093/gji/ggv198 https://openresearch-repository.anu.edu.au/bitstream/1885/152810/5/01_Nakada_Viscosity_structure_of_Earth%2527s_2015.pdf.jpg |
geographic |
Antarctic The Antarctic Greenland |
geographic_facet |
Antarctic The Antarctic Greenland |
genre |
Antarc* Antarctic Greenland Ice Sheet |
genre_facet |
Antarc* Antarctic Greenland Ice Sheet |
op_source |
Geophysical Journal International |
op_relation |
0956-540X http://hdl.handle.net/1885/152810 doi:10.1093/gji/ggv198 https://openresearch-repository.anu.edu.au/bitstream/1885/152810/5/01_Nakada_Viscosity_structure_of_Earth%2527s_2015.pdf.jpg |
op_doi |
https://doi.org/10.1093/gji/ggv198 |
container_title |
Geophysical Journal International |
container_volume |
202 |
container_issue |
2 |
container_start_page |
976 |
op_container_end_page |
992 |
_version_ |
1788067506659786752 |