Elastic deformation due to present-day mass change at GNSS measurements sites in East Antarctica

The Tenth Symposium on Polar Science/Ordinary sessions: [OG] Polar Geosciences, Wed. 4 Dec. / 3F Seminar room, National Institute of Polar Researc

Marine Isotope Stage 3 and Holocene relative sea level variations in East Antarctica derived from glacial isostatic adjustment modelling

第3回極域科学シンポジウム　横断セッション「海・陸・氷床から探る後期新生代の南極寒冷圏環境変動」11月26日（月）、27日（火） ２階ラウン

Spatial distribution and volume of Antarctic Ice Sheet at Last Glacial Maximum

第2回極域科学シンポジウム/第31回極域地学シンポジウム 11月16日（水） 国立国語研究

Links between global magmatism and GIA -Future plan-

The Tenth Symposium on Polar Science/Special session: [S] Future plan of Antarctic research: Towards phase X of the Japanese Antarctic Research Project (2022-2028) and beyond, Tue. 3 Dec. / Entrance Hall (1st floor) at National Institute of Polar Research (NIPR

Some remarks on the depth of the continental shelf around the Antarctic continental margin

第6回極域科学シンポジウム[OG] 地圏11月16日（月）　国立極地研究所１階交流アトリウ

A Geophysical Interpretation of the Secular Displacement and Gravity Rates Observed at Ny-Ålesund, Svalbard in the Arctic— Effects of Post-Glacial Rebound and Present-Day Ice Melting

We have analysed the Ny-Ålesund very long baseline interferometry (VLBI) data over the period 1994 August to 2004 May, and we obtain secular displacement rates relative to a NNR-NUVEL-1A reference frame of and for the north, east and vertical directions, respectively. The corresponding global positioning system (GPS) station displacement rates relative to the same reference frame for the north, east, and vertical directions are at NYA1 and at NALL, where these GPS rates were derived from the ITRF2000 velocity solution of Heflin. From the comparison at 25 globally distributed collocated sites, we found that the difference in uplift rate between VLBI and GPS at Ny-Ålesund is mainly due to a GPS reference frame scale rate error corresponding to 1.6 mm yr−1 in the GPS vertical rates. The uplift rate was estimated to be 5.2 ± 0.3 mm yr−1 from the analysis of the tide gauge data at Ny-Ålesund. Hence the uplift rates obtained from three different kinds of data are very consistent each other. The absolute gravity (AG) measurements at Ny-Ålesund, which were carried out four times (period: 1998–2002) by three different FG5 absolute gravimeters, lead to a decreasing secular rate of . In this analysis, the actual data obtained from a superconducting gravimeter at Ny-Ålesund were used in the corrections for the gravity tide (including the ocean tide effect) and for the air pressure effect. We have estimated three geophysical contributions to examine the observed rates: (1) the effect of the sea-level (SL) change on a timescale of a few decades, (2) the effect of the present-day ice melting (PDIM) in Svalbard and (3) the sensitivity of the computed post-glacial rebound (PGR) effects to different choices of the models of past ice history and Earth\u27s viscosity parameters. Our analysis indicates that the effect of SL change can be neglected as the main source of the discrepancy. On the other hand, the effect of PDIM cannot be ignored in explaining the mutual relation between the observed horizontal and vertical rates and the predicted ones. A large melting rate of the order of −75 cm yr11 (i.e. roughly 1.6 times larger than the mean rate derived from glaciology over Svalbard) would explain the observed uplift but only half of the gravity changes. Our comparison results clearly point out the importance of both the estimation accuracy of the elastic deformations and better observation accuracy to constrain the size of PGR effects in the northwestern Svalbard more tightly

ヒョウメン ショウシャ ネンダイホウ ニオケル ケイタイガタ デンドウ カッター ヲ モチイタ アラタナ シリョウ サイシュ ホウホウ

宇宙線生成核種を用いた表面露出年代測定法は,地球表層における様々な現象を理解するために非常に重要な年代測定法である.この年代測定法には,年代決定精度が試料形状に依存するという特徴があり,試料採取の際に試料の厚さと形を高精度で測定することが必要となる.しかし,ハンマーやタガネを用いた従来の手法では,このような要求を満たす試料採取は時として困難であった.そこで本研究では,新たに携帯型電動カッターを用いた試料採取手法を提案する.この手法は,迅速かつ精密な試料採取および形状測定を可能とすることから,結果として年代測定精度の向上につながるものである.簡単な理論計算に基づき不完全な試料形状に起因する年代差を求めたところ,試料の採取深度が大きくなるにしたがって年代差が大きくなることが分かり,表面露出年代測定法における精密な試料形状測定の重要性が示された.Surface exposure dating using in situ cosmogenic nuclides has contributed to our understanding of Earth-surface processes. The precision of the ages estimated by this method is affected by the sample geometry; therefore, high accuracy measurements of the thickness and shape of the rock sample (thickness and shape) is crucial. However, it is sometimes diffi cult to meet these requirements by conventional sampling methods with a hammer and chisel. Here, we propose a new sampling technique using a portable electric rock cutter. This sampling technique is faster, produces more precisely shaped samples, and allows for a more precise age interpretation. A simple theoretical modeldemonstrates that the age error due to defective sample geometry increases as the total sample thickness increases, indicating the importance of precise sampling for surface exposure dating

Nonmonotonic Postdeglacial Relative Sea Level Changes at the Aftermath of Marinoan (635 Ma) Snowball Earth Meltdown

© 2019. American Geophysical Union. All Rights Reserved. Marinoan snowball Earth offers us a set of sedimentary and geochemical records for exploring glacial isostatic adjustment (GIA) associated with one of the most severe glaciations in Earth history. An accurate prediction of GIA-based relative sea level (RSL) change associated with a snowball Earth meltdown will help to explore sedimentary records for RSL changes and to place independent constraints on mantle viscosity and on the durations of syndeglaciation (Td) and cap carbonate deposition. Here we mainly examine postdeglacial RSL change characterized by an RSL drop and a resumed transgression inferred from the cap dolostones on the continental shelf in south China. Such a nonmonotonic RSL behavior may be a diagnostic GIA signal for the Marinoan deglaciation resulting from a significantly longer postdeglacial GIA response than that for the last deglaciation. A postdeglacial RSL drop followed by transgression in south China, which is significantly affected by Earth\u27s rotation, is predicted over the continental shelf for models with Td ≤ 20 kyr and a deep mantle viscosity of ~5 × 1022 Pa s regardless of the upper mantle viscosity. The inferred GIA model also explains the postdeglacial RSL changes such as sedimentary-inferred RSL drops on the continental shelf in northwestern Canada and California at low-latitude regions insignificantly affected by Earth\u27s rotation. Furthermore, the good match between the predicted and observed RSL changes in south China suggests an approximate duration of ~50 kyr for the Marinoan 17O depletion event, an atmospheric event linked to the post-Marinoan drawdown of CO2 and the concurrent rise of O2