A research group led by Assistant Professor Jun'ichi Okuno, Assistant Professor Akihisa Hattori, Associate Professor Koichiro Doi, and Associate Professor Yuichi Aoyama from the National Institute of Polar Research/SOKENDAI (The Graduate University for Advanced Studies) and Professor Emeritus Yoichi Fukuda of Kyoto University announced their clarification that the ice sheet around Lützow-Holm Bay in East Antarctica underwent complex fluctuations approximately 9,000 to 6,000 years ago (mid-Holocene). It experienced a rapid thinning of about 400 meters followed by re-thickening of 65 to 100 meters. This was revealed through integrated analysis involving three different methods: numerical modeling of glacial isostatic adjustment (GIA), surface exposure dating of rocks through topographic surveys, and GNSS observations by satellite. From these findings, further contributions may lead to improved accuracy in future sea level rise predictions. The results were published in Scientific Reports on November 17.
(b-d) Vertical displacement time series at the three GNSS sites analyzed by Hattori et al.
(2021). The vertical displacement represents the difference from the average height during the observation period at each site (upward is positive), and error bars indicate the estimated errors of the PPP analysis. The analysis periods are 2007-2018 for SYOG (Syowa Station) and 2010-2018 for the other sites. The solid red lines show the linear trends of the regressions.
Maps created using GMT version 6.5.0 (https://www.generic-mapping-tools.org/). Background imagery from Landsat Image Mosaic of Antarctica (LIMA), courtesy of the U.S. Geological Survey.
Source: Okuno et al., Sci Rep 15, 40207 (2025).
The Antarctic ice sheet is the largest ice mass on Earth, and its fluctuations are directly linked to global sea level changes. However, the conditions, amounts and rates of change within the Antarctic ice sheet are not well understood.
GIA modeling, which uses geophysical phenomena, is a method for estimating historic ice sheet fluctuations. However, previous GIA modeling has approximated the ice sheet fluctuation history of the entire Antarctic using data from limited observation points. As such, region-specific complex fluctuation patterns could not be determined.
In conventional research, there were observational constraints in Antarctica and so ice sheets were thought to change relatively simply, but in recent years, more attention has been brought to the possibility of more complex fluctuation patterns.
Therefore, the research group examined detailed reconstructions of ice sheet fluctuations from approximately 10,000 years ago to the present by combining three methods.
First, they integrated numerical modeling of GIA and surface exposure dating of rocks through topographic surveys, which had previously been conducted separately. Surface exposure dating estimates the exposure time of the ground surface from the accumulation of nuclides. These form in rocks when the surface is exposed to cosmic rays.
As a result, in utilizing observation data spanning more than 10 years, they succeeded in reading traces of ice sheet fluctuations from approximately 9,000 years ago using present-day crustal movements. The GNSS observation point at Syowa Station began continuous observations in 1995 and was registered in the International GNSS Service network in 1999; observations continue to this day. In addition, GNSS observations in exposed rock areas have been conducted since 2000 and are currently ongoing as unmanned observations.
The most groundbreaking discovery was that the Antarctic ice sheet exhibitied a complex pattern of rapid thinning followed by re-thickening. In conventional global models, it was estimated that after beginning to thin, the ice sheet gradually continued to thin until the present day.
The study revealed that Antarctic ice sheet fluctuations display region-specific patterns that cannot be captured by conventional global models, and that stabilization and partial re-thickening can occur following periods of rapid thinning.
Furthermore, the researchers succeeded in precisely estimating the internal structure of the Earth beneath East Antarctica.
The integrated method established can be applied to ice sheet research in other regions of Antarctica and the Arctic. It has the potential to become a new standard method for global ice sheet fluctuation research.
Okuno commented: "The key was the fusion of different fields: topography, geodesy, and modeling. We were able to clarify ice sheet fluctuations from 9,000 years ago from crustal movements of several millimeters per year by virtue of the steady accumulation of data through Japan's Antarctic observations over more than 20 years. The response of ice sheets to climate change is more complex than initially imagined, and we aim to expand this method to other regions in the future to elucidate the complete picture."
Journal Information
Publication: Scientific Reports
Title: Mid Holocene rapid thinning and rethickening of the East Antarctic ice sheet suggested by glacial isostatic adjustment
DOI: 10.1038/s41598-025-24176-4
This article has been translated by JST with permission from The Science News Ltd. (https://sci-news.co.jp/). Unauthorized reproduction of the article and photographs is prohibited.