Pub Date : 2025-12-01DOI: 10.1016/j.polar.2025.101306
Nilanjana Sorcar , Sankar Bose , J. Amal Dev , Sneha Mukherjee , J.K. Tomson
Pelitic granulites from the Larsemann Hills, Prydz Bay, East Antarctica, preserve a complex polymetamorphic history associated with the supercontinent assembly. This study integrates mineral chemistry, geothermobarometry, phase equilibria modeling, and accessory mineral petrochronology to reconstruct the pressure-temperature-time (P-T-t) evolution of these rocks. Peak metamorphic conditions of ∼950 °C at 8.5 kbar were followed by retrogression along a clockwise P-T path marked by a near-isothermal decompression and a near-isobaric cooling. In situ U-Pb dating of zircon and monazite constrains the timing of peak metamorphism to ∼565 Ma, while apatite U-Pb ages of ∼526 Ma records the subsequent cooling. Older Neoproterozoic ages (∼822–862 Ma) preserved in zircon and monazite indicate an earlier metamorphic episode, reflecting a protracted tectonothermal evolution. Rare earth element partitioning between garnet and zircon supports garnet growth during the Ediacaran-Cambrian high-grade metamorphism. These data collectively document a ∼50 Myr duration of orogenesis and slow cooling rates, consistent with a collisional tectonic setting during the final assembly of East Gondwana, linking Prydz Bay with contemporaneous high-grade terranes in South India, Sri Lanka, and Madagascar.
{"title":"Pressure-Temperature-time (P-T-t) evolution of pelitic granulites from the Larsemann Hills, East Antarctica: Insights from accessory mineral geochronology and phase equilibria modeling","authors":"Nilanjana Sorcar , Sankar Bose , J. Amal Dev , Sneha Mukherjee , J.K. Tomson","doi":"10.1016/j.polar.2025.101306","DOIUrl":"10.1016/j.polar.2025.101306","url":null,"abstract":"<div><div>Pelitic granulites from the Larsemann Hills, Prydz Bay, East Antarctica, preserve a complex polymetamorphic history associated with the supercontinent assembly. This study integrates mineral chemistry, geothermobarometry, phase equilibria modeling, and accessory mineral petrochronology to reconstruct the pressure-temperature-time (P-T-t) evolution of these rocks. Peak metamorphic conditions of ∼950 °C at 8.5 kbar were followed by retrogression along a clockwise P-T path marked by a near-isothermal decompression and a near-isobaric cooling. In situ U-Pb dating of zircon and monazite constrains the timing of peak metamorphism to ∼565 Ma, while apatite U-Pb ages of ∼526 Ma records the subsequent cooling. Older Neoproterozoic ages (∼822–862 Ma) preserved in zircon and monazite indicate an earlier metamorphic episode, reflecting a protracted tectonothermal evolution. Rare earth element partitioning between garnet and zircon supports garnet growth during the Ediacaran-Cambrian high-grade metamorphism. These data collectively document a ∼50 Myr duration of orogenesis and slow cooling rates, consistent with a collisional tectonic setting during the final assembly of East Gondwana, linking Prydz Bay with contemporaneous high-grade terranes in South India, Sri Lanka, and Madagascar.</div></div>","PeriodicalId":20316,"journal":{"name":"Polar Science","volume":"46 ","pages":"Article 101306"},"PeriodicalIF":2.0,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145739150","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The Sør Rondane Mountains (SRM) in eastern Dronning Maud Land, East Antarctica, are situated within the Pan-African suture zone. The timing of the collisional events between West and East Gondwana is regarded as Late Neoproterozoic to Early Cambrian. The geology of the SRM is divided into northeast terrane (NE-terrane) and southwest terrane (SW-terane). These two terranes were collided during the Late Proterozoic. The syenite complex, as post-collisional intrusive rocks, intruding the boundary between the NE- and SW-terranes in the central part of the SRM, consists of a layered syenite and melanosyenite dike. Minettes also occur in the post-collisional mafic intrusive rocks. The U–Pb zircon ages of the layered syenite and the melanosyenite dike are of 559.4 ± 1.6 Ma and 548.8 ± 3.4 Ma, respectively. The recalculated Pb-Pb age of the minette was 557.5 ± 4.8 Ma. According to the dating results, the syenite complex and the minette belongs to the same magmatic stage. The syenite complex and minette have significant characteristics with high-K (K2O/Na2O > 3) and high-light/heavy rare earth element (LREE/HREE) ratios (normalized La/Yb > 10), and SiO2 contents ranging from 44 to 62 wt%. Considering the petrography and geochemistry, the syenite was originated from the minette magma, and the fractionation and accumulation of specific minerals played an important role in the formation of the layered syenite. The minette with a primitive composition bears phenocrysts of Mg- and Cr-rich phlogopite in equilibrium with the mantle peridotite. These features suggest that high-K mafic magma was produced by partial melting of the lithospheric mantle, which was modified by subduction and/or collisional related materials. As the geochemical features of the post-collisional intrusive rocks from central to eastern Dronning Maud Land resembles those of the syenite complex in the SRM, a similar petrogenetic model may be applied to the origin of the high-K mafic magma within the Gondwana suture zone during the Pan-African event.
{"title":"Post-collisional K-rich mafic magmatism in the Sør Rondane Mountains, East Antarctica: Magmatic processes of layered syenite and mantle modification","authors":"Masaaki Owada , Toru Sakiyama , Atsushi Kamei , Toshiaki Shimura , Masaki Yuhara , Kazuhiro Tsukada , Kenji Horie , Tomokazu Hokada , Yasuhito Osanai , Nobuhiko Nakano , Tatsuro Adachi","doi":"10.1016/j.polar.2025.101192","DOIUrl":"10.1016/j.polar.2025.101192","url":null,"abstract":"<div><div>The Sør Rondane Mountains (SRM) in eastern Dronning Maud Land, East Antarctica, are situated within the Pan-African suture zone. The timing of the collisional events between West and East Gondwana is regarded as Late Neoproterozoic to Early Cambrian. The geology of the SRM is divided into northeast terrane (NE-terrane) and southwest terrane (SW-terane). These two terranes were collided during the Late Proterozoic. The syenite complex, as post-collisional intrusive rocks, intruding the boundary between the NE- and SW-terranes in the central part of the SRM, consists of a layered syenite and melanosyenite dike. Minettes also occur in the post-collisional mafic intrusive rocks. The U–Pb zircon ages of the layered syenite and the melanosyenite dike are of 559.4 ± 1.6 Ma and 548.8 ± 3.4 Ma, respectively. The recalculated Pb-Pb age of the minette was 557.5 ± 4.8 Ma. According to the dating results, the syenite complex and the minette belongs to the same magmatic stage. The syenite complex and minette have significant characteristics with high-K (K<sub>2</sub>O/Na<sub>2</sub>O > 3) and high-light/heavy rare earth element (LREE/HREE) ratios (normalized La/Yb > 10), and SiO<sub>2</sub> contents ranging from 44 to 62 wt%. Considering the petrography and geochemistry, the syenite was originated from the minette magma, and the fractionation and accumulation of specific minerals played an important role in the formation of the layered syenite. The minette with a primitive composition bears phenocrysts of Mg- and Cr-rich phlogopite in equilibrium with the mantle peridotite. These features suggest that high-K mafic magma was produced by partial melting of the lithospheric mantle, which was modified by subduction and/or collisional related materials. As the geochemical features of the post-collisional intrusive rocks from central to eastern Dronning Maud Land resembles those of the syenite complex in the SRM, a similar petrogenetic model may be applied to the origin of the high-K mafic magma within the Gondwana suture zone during the Pan-African event.</div></div>","PeriodicalId":20316,"journal":{"name":"Polar Science","volume":"46 ","pages":"Article 101192"},"PeriodicalIF":2.0,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145739080","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-01DOI: 10.1016/j.polar.2025.101234
Igor Popov
Despite the fact that the Arctic region is not typically characterized as arid, it is still susceptible to desertification. In the tundra stretching from the White Sea to the Ob River, patches of sand devoid of vegetation, spanning several hectares, are quite common. A total of 34 clusters of such areas have been identified, covering a combined area of 1,685,750 ha. Among them are three sandy deserts, each spanning several hundred hectares. This phenomenon has been attributed to overgrazing by reindeer. Reindeer, preferring elevated and solid terrain, tend to concentrate in relatively small areas, while wetlands and mires occupy vast expanses around. The resulting overgrazing leads to the loss of vegetation and soil in several hotspots. The formation of these deserts or semi-deserts has been exacerbated by the practices of the local Nenets people. Since remote times they tried to expand their herds even if they cannot consume them, considering them as something like bank account. With the continuous increase in Nenets herders and, consequently, the number of reindeer, the desertification of the tundra is a looming reality. Traditional land use practices, in this case, fail to ensure sustainable development.
{"title":"Reindeer in a desert (Desertification in the Arctic because of overgrazing)","authors":"Igor Popov","doi":"10.1016/j.polar.2025.101234","DOIUrl":"10.1016/j.polar.2025.101234","url":null,"abstract":"<div><div>Despite the fact that the Arctic region is not typically characterized as arid, it is still susceptible to desertification<span>. In the tundra stretching from the White Sea to the Ob River, patches of sand devoid of vegetation, spanning several hectares, are quite common. A total of 34 clusters of such areas have been identified, covering a combined area of 1,685,750 ha. Among them are three sandy deserts, each spanning several hundred hectares. This phenomenon has been attributed to overgrazing by reindeer. Reindeer, preferring elevated and solid terrain, tend to concentrate in relatively small areas, while wetlands and mires<span> occupy vast expanses around. The resulting overgrazing leads to the loss of vegetation and soil in several hotspots. The formation of these deserts or semi-deserts has been exacerbated by the practices of the local Nenets people. Since remote times they tried to expand their herds even if they cannot consume them, considering them as something like bank account. With the continuous increase in Nenets herders and, consequently, the number of reindeer, the desertification of the tundra is a looming reality. Traditional land use practices, in this case, fail to ensure sustainable development.</span></span></div></div>","PeriodicalId":20316,"journal":{"name":"Polar Science","volume":"46 ","pages":"Article 101234"},"PeriodicalIF":2.0,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145739054","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-01DOI: 10.1016/j.polar.2025.101211
Anna Gebruk , Alexander Kokorin , Maria Mardashova , Yulia Ermilova , Victoria Melnikova , Ilya Fedorov , Alexandra Barymova , Olga Konovalova , Vladimir Rogozhin , Nikolay Shabalin , Svetlana Artemyeva , Viatcheslav V. Rozhnov , Artem Isachenko , Renata Lazareva , Vadim Mokievsky
To address critical gaps in our understanding of benthic ecosystems in the Arctic, this study sampled macrobenthos across the Franz Josef Land archipelago during the 2020–2021 field campaign. In total, 65 benthic grab stations were analysed, and 29 stations assessed for macrofauna with ROV video recordings. The stations, located in shallow waters ranging from 11 to 176 m depth, covered a substantial portion of the archipelago. This data set is by far the largest published on the area's benthic biodiversity since the 1970s. From 143,577 specimens of macrobenthos analysed, a total of 333 taxa (257 species) were identified. Most stations were dominated by three overlapping macrobenthic assemblages: (1) Strongylocentrotus sp. – Ophiura robusta, (2) Hiatella arctica – O. robusta and (3) Astarte spp. Exceptionally high biomass of macrobenthos was noted, reaching 3.9 kg m−2, possibly the highest documented for the Eurasian Arctic shelf. This finding suggests a greater potential for carbon sequestration in this region than previously understood. High spatial heterogeneity and high benthic biomass can be attributed to the complex hydrodynamic regime and abundance of hard substrates in these shallow waters, which also makes the area attractive for benthic predators, in particular the Atlantic walrus (Odobenus rosmarus rosmarus).
为了解决我们对北极底栖生物生态系统理解的关键空白，本研究在2020-2021年实地考察期间对弗朗茨约瑟夫群岛的大型底栖动物进行了采样。总共分析了65个底栖生物抓取站，并通过ROV视频记录对29个站的大型动物进行了评估。这些监测站位于水深11米至176米的浅水区，覆盖了群岛的大部分地区。该数据集是自20世纪70年代以来该地区底栖生物多样性公布的最大数据集。在143577份大型底栖动物标本中，共鉴定出333个分类群（257种）。3种大型底栖动物组合(1)strongylocentrrotus sp. - Ophiura robusta, （2) Hiatella arctica - O. robusta和(3)Astarte spp）占据了大部分站点的优势。大型底栖动物的生物量特别高，达到3.9 kg m - 2，可能是有记录以来最高的。这一发现表明，该地区的碳封存潜力比以前所了解的要大。高空间异质性和高底栖生物生物量可归因于这些浅水复杂的水动力制度和丰富的硬底物，这也使该地区对底栖动物捕食者具有吸引力，特别是大西洋海象（Odobenus rosmarus rosmarus）。
{"title":"Franz Josef Land's macrobenthos: Record-high wet biomass values on the Eurasian Arctic shelf","authors":"Anna Gebruk , Alexander Kokorin , Maria Mardashova , Yulia Ermilova , Victoria Melnikova , Ilya Fedorov , Alexandra Barymova , Olga Konovalova , Vladimir Rogozhin , Nikolay Shabalin , Svetlana Artemyeva , Viatcheslav V. Rozhnov , Artem Isachenko , Renata Lazareva , Vadim Mokievsky","doi":"10.1016/j.polar.2025.101211","DOIUrl":"10.1016/j.polar.2025.101211","url":null,"abstract":"<div><div>To address critical gaps in our understanding of benthic ecosystems in the Arctic, this study sampled macrobenthos across the Franz Josef Land archipelago during the 2020–2021 field campaign. In total, 65 benthic grab stations were analysed, and 29 stations assessed for macrofauna with ROV video recordings. The stations, located in shallow waters ranging from 11 to 176 m depth, covered a substantial portion of the archipelago. This data set is by far the largest published on the area's benthic biodiversity since the 1970s. From 143,577 specimens of macrobenthos analysed, a total of 333 taxa (257 species) were identified. Most stations were dominated by three overlapping macrobenthic assemblages: (1) S<em>trongylocentrotus</em> sp. <em>– Ophiura robusta</em>, (2) <em>Hiatella arctica – O. robusta</em> and (3) <em>Astarte</em> spp. Exceptionally high biomass of macrobenthos was noted, reaching 3.9 kg m<sup>−2</sup>, possibly the highest documented for the Eurasian Arctic shelf. This finding suggests a greater potential for carbon sequestration in this region than previously understood. High spatial heterogeneity and high benthic biomass can be attributed to the complex hydrodynamic regime and abundance of hard substrates in these shallow waters, which also makes the area attractive for benthic predators, in particular the Atlantic walrus (<em>Odobenus rosmarus rosmarus</em>).</div></div>","PeriodicalId":20316,"journal":{"name":"Polar Science","volume":"46 ","pages":"Article 101211"},"PeriodicalIF":2.0,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145739075","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This research marks the first comprehensive structural analysis of the Instekleppane outcrop, located in the western part of the Lützow-Holm Complex (LHC), a Neoproterozoic-Cambrian high-grade metamorphic terrane, East Antarctica. The ∼1 km2 outcrop, situated southwest of Syowa Station and east of Shirase Glacier, was investigated as part of the 65th Japanese Antarctic Research Expedition (JARE-65). The lithological assemblage includes felsic orthopyroxene-biotite gneiss, garnet-bearing felsic granulite, Mg-Al-rich gneiss, mafic hornblende-orthopyroxene-clinopyroxene granulite, ultramafic rocks, and minor granitic intrusions. Six stages of deformation (D0–D5) were identified, of which four (D0 to D3) are considered as major events. D0 corresponds to the development of primary sedimentary or magmatic layering and D1 corresponds to initial foliation development. While D2 is characterized by earlier layer parallel stretching and the formation of B21 mafic boudins followed by two folding phases: F21 (recumbent, isoclinal, intrafolial folds) and F22 (overturned folds), both with E–W trending axial planes. D3 is marked by upright to plunging open folds (F3) with NW–SE axial planes. D4 corresponds to reverse shear zones, and D5 involves strike-slip shear zones. The deformation history at the Instekleppane shares similarities with nearby high-grade terranes such as Rundvågshetta and Langhovde, suggest a regionally consistent ductile deformation history within the LHC during its tectonic evolution.
{"title":"Structural evolution of the Instekleppane, Lützow-Holm Complex: Deformation patterns in high-grade zones of east Antarctica","authors":"Lakshmanan Sreehari , Tatsuro Adachi , Yuki Mori , Tomokazu Hokada","doi":"10.1016/j.polar.2025.101249","DOIUrl":"10.1016/j.polar.2025.101249","url":null,"abstract":"<div><div><span><span>This research marks the first comprehensive structural analysis of the Instekleppane outcrop, located in the western part of the Lützow-Holm Complex (LHC), a Neoproterozoic-Cambrian high-grade metamorphic terrane, East </span>Antarctica. The ∼1 km</span><sup>2</sup><span><span><span> outcrop, situated southwest of Syowa Station and east of Shirase Glacier, was investigated as part of the 65th Japanese Antarctic Research Expedition (JARE-65). The lithological assemblage includes felsic orthopyroxene-biotite gneiss, garnet-bearing felsic </span>granulite, Mg-Al-rich gneiss, mafic hornblende-orthopyroxene-clinopyroxene granulite, </span>ultramafic rocks, and minor granitic intrusions. Six stages of deformation (D</span><sub>0</sub>–D<sub>5</sub>) were identified, of which four (D<sub>0</sub> to D<sub>3</sub>) are considered as major events. D<sub>0</sub> corresponds to the development of primary sedimentary or magmatic layering and D<sub>1</sub> corresponds to initial foliation development. While D<sub>2</sub> is characterized by earlier layer parallel stretching and the formation of B<sub>21</sub> mafic boudins followed by two folding phases: F<sub>21</sub> (recumbent, isoclinal, intrafolial folds) and F<sub>22</sub> (overturned folds), both with E–W trending axial planes. D<sub>3</sub> is marked by upright to plunging open folds (F<sub>3</sub>) with NW–SE axial planes. D<sub>4</sub> corresponds to reverse shear zones, and D<sub>5</sub><span> involves strike-slip shear zones. The deformation history<span><span> at the Instekleppane shares similarities with nearby high-grade terranes such as Rundvågshetta and Langhovde, suggest a regionally consistent ductile deformation history within the LHC during its </span>tectonic evolution.</span></span></div></div>","PeriodicalId":20316,"journal":{"name":"Polar Science","volume":"46 ","pages":"Article 101249"},"PeriodicalIF":2.0,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145739148","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-01DOI: 10.1016/j.polar.2025.101259
Aswathy Shaji , Anu Gopinath , Midhun Shah Hussain , Sabu Prabhakaran , K. Anoop Krishnan
This study focuses on the speciation of metals (Cr, Mn, Fe, Ni, Cu, Zn) in the surface sediments collected from Arctic fjords and lakes as part of the India Expedition to Arctic during the years 2018 and 2019. The speciation studies were performed focusing on five fractions, namely, exchangeable, bound to carbonates, bound to Fe-Mn oxides, bound to organic matter and residual metal. The sedimentary characteristics like pH, TOC and elemental concentrations were also studied to understand the role of these parameters in affecting the metal distribution in different fraction within the sediments. Different risk indices like, Risk Assessment Code (RAC), modified RAC, Individual Contamination Factor (ICF) and Global Contamination Factor (GCF) were also evaluated to find out the threats posed by these contaminates in this pristine environment. The various risk assessment of the metals under study reveals the presence of a low to moderate contamination prevailing in the system.
{"title":"Metal speciation in the surface sediments of an Arctic fjord and nearby lakes","authors":"Aswathy Shaji , Anu Gopinath , Midhun Shah Hussain , Sabu Prabhakaran , K. Anoop Krishnan","doi":"10.1016/j.polar.2025.101259","DOIUrl":"10.1016/j.polar.2025.101259","url":null,"abstract":"<div><div>This study focuses on the speciation of metals (Cr, Mn, Fe, Ni, Cu, Zn) in the surface sediments collected from Arctic fjords and lakes as part of the India Expedition to Arctic during the years 2018 and 2019. The speciation studies were performed focusing on five fractions, namely, exchangeable, bound to carbonates, bound to Fe-Mn oxides, bound to organic matter and residual metal. The sedimentary characteristics like pH, TOC and elemental concentrations were also studied to understand the role of these parameters in affecting the metal distribution in different fraction within the sediments. Different risk indices like, Risk Assessment Code (RAC), modified RAC, Individual Contamination Factor (ICF) and Global Contamination Factor (GCF) were also evaluated to find out the threats posed by these contaminates in this pristine environment. The various risk assessment of the metals under study reveals the presence of a low to moderate contamination prevailing in the system.</div></div>","PeriodicalId":20316,"journal":{"name":"Polar Science","volume":"46 ","pages":"Article 101259"},"PeriodicalIF":2.0,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145739194","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The first comprehensive multi-day geological survey was conducted at Instekleppane in the southern part of the Lützow-Holm Complex, East Antarctica, by the 65th Japanese Antarctic Research Expedition (JARE65). This exposure is predominantly composed of felsic orthopyroxene-biotite gneiss, leucocratic garnet-biotite gneiss, granitic biotite gneiss, and felsic garnet-orthopyroxene-biotite gneiss with intercalations of mafic granulites, meta-ultramafic rocks, and Mg–Al-rich rocks. Several Mg–Al-rich rocks, such as sapphirine-cordierite-biotite gneiss and garnet-sapphirine-orthopyroxene-cordierite gneiss, have reaction textures indicating decompression under ultrahigh-temperature (UHT) conditions. Similar lithological relations and metamorphic signatures have been reported from Rundvågshetta, suggesting a possible geological linkage between these exposures.
{"title":"High-grade metamorphic rocks in Instekleppane, Lützow-Holm Complex, east Antarctica: A potential new locality of ultrahigh-temperature (UHT) metamorphic rocks","authors":"Tatsuro Adachi , Lakshmanan Sreehari , Yuki Mori , Tomokazu Hokada","doi":"10.1016/j.polar.2025.101263","DOIUrl":"10.1016/j.polar.2025.101263","url":null,"abstract":"<div><div>The first comprehensive multi-day geological survey was conducted at Instekleppane in the southern part of the Lützow-Holm Complex, East Antarctica, by the 65th Japanese Antarctic Research Expedition (JARE65). This exposure is predominantly composed of felsic orthopyroxene-biotite gneiss, leucocratic garnet-biotite gneiss, granitic biotite gneiss, and felsic garnet-orthopyroxene-biotite gneiss with intercalations of mafic granulites, meta-ultramafic rocks, and Mg–Al-rich rocks. Several Mg–Al-rich rocks, such as sapphirine-cordierite-biotite gneiss and garnet-sapphirine-orthopyroxene-cordierite gneiss, have reaction textures indicating decompression under ultrahigh-temperature (UHT) conditions. Similar lithological relations and metamorphic signatures have been reported from Rundvågshetta, suggesting a possible geological linkage between these exposures.</div></div>","PeriodicalId":20316,"journal":{"name":"Polar Science","volume":"46 ","pages":"Article 101263"},"PeriodicalIF":2.0,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145739149","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-01DOI: 10.1016/j.polar.2025.101255
Kohei Sumiya , Dai Sumiyoshi , Kazutoshi Sato , Akihiko Murata , Shigeto Nishino , Kohei Matsuno
Sea ice in the Pacific Arctic Ocean has been rapidly decreasing over recent decades. However, knowledge of its effects on microplankton is limited. To elucidate the effect of sea ice reduction on the microplankton community of the Pacific Arctic Ocean, we examined the differences in the microplankton community and hydrography between 2019 and 2020. Based on the cluster analysis, the microplankton community was divided into six groups. In the southern Chukchi Sea, high cell densities were observed with high variability in group occurrence owing to the inflow of nutrient-rich Pacific water. In the northern Chukchi Sea, a 1-month inter-annual difference in sea ice melting timing induced changes in the microplankton community through hydrographical changes. Early sea ice melting stimulates the growth of phytoplankton species (Proboscia alata), which can utilize organic nitrogen compounds. In the marginal ice zone, a 10-day inter-annual difference in sea ice melting was observed, resulting in variations in hydrographic conditions; however, these changes did not affect the microplankton community. Our findings indicate that microplankton production and diversity respond differently to sea ice melting in varies by region in the Pacific Arctic Ocean.
{"title":"Influence of early sea ice melting on the autumn microplankton community of the Pacific Arctic Ocean","authors":"Kohei Sumiya , Dai Sumiyoshi , Kazutoshi Sato , Akihiko Murata , Shigeto Nishino , Kohei Matsuno","doi":"10.1016/j.polar.2025.101255","DOIUrl":"10.1016/j.polar.2025.101255","url":null,"abstract":"<div><div>Sea ice in the Pacific Arctic Ocean has been rapidly decreasing over recent decades. However, knowledge of its effects on microplankton is limited. To elucidate the effect of sea ice reduction on the microplankton community of the Pacific Arctic Ocean, we examined the differences in the microplankton community and hydrography between 2019 and 2020. Based on the cluster analysis, the microplankton community was divided into six groups. In the southern Chukchi Sea, high cell densities were observed with high variability in group occurrence owing to the inflow of nutrient-rich Pacific water. In the northern Chukchi Sea, a 1-month inter-annual difference in sea ice melting timing induced changes in the microplankton community through hydrographical changes. Early sea ice melting stimulates the growth of phytoplankton species (<em>Proboscia alata</em>), which can utilize organic nitrogen compounds. In the marginal ice zone, a 10-day inter-annual difference in sea ice melting was observed, resulting in variations in hydrographic conditions; however, these changes did not affect the microplankton community. Our findings indicate that microplankton production and diversity respond differently to sea ice melting in varies by region in the Pacific Arctic Ocean.</div></div>","PeriodicalId":20316,"journal":{"name":"Polar Science","volume":"46 ","pages":"Article 101255"},"PeriodicalIF":2.0,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145739073","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-01DOI: 10.1016/j.polar.2025.101302
Y. Hiroi , T. Hokada , N. Furukawa , T. Adachi , B. Prame , L.R.K. Perera , M. Satish-Kumar , Y. Motoyoshi
The garnetiferous granulite in central Sri Lanka contains more than 27 minerals with various textures and compositions. The garnet + orthopyroxene + biotite + plagioclase + quartz + ilmenite + rutile + pyrrhotite + melt assemblage may have been stable at the metamorphic peak. The estimated peak P–T conditions are >0.6 GPa and >800 °C. Garnet occurs as anhedral porphyroblasts up to 1 cm in diameter. Some grains contain numerous inclusions, including melt inclusions (felsite–nanogranite inclusions, or FNIs), while others are free of inclusion except for fine–grained ilmenite and rutile. They commonly exhibit compositional zoning, with Mg decreasing and Ca increasing towards the margin. Some grains exhibit P zoning and are divided into P–poor core, P–rich mantle and P–poor rim. In the P–rich mantle, the FNIs are surrounded by areas of P depletion, indicating FNIs’ strong effect on the behavior of P in garnet. Grandidierite exclusively occurs in FNIs. Cathodoluminescence imaging revealed "hidden" dendritic high–quartz within anhedral quartz grains in FNIs. Dynamic crystallization experiments reproduced the characteristic texture. Plagioclase and biotite exhibit extremely wide compositional variations depending on their occurrence mode. Zoned carbonate and moganite–containing chalcedony occur as inclusions in garnet in places. These features all resulted from high–temperature metamorphism followed by the complex cooling history experienced by the rocks in a crustal–scale suture zone.
{"title":"Hidden dendritic high quartz, grandidierite, euhedrally zoned Mg–Fe carbonate and chalcedony in garnet; documentation and significance of multi–stage recrystallization of garnetiferous granulite from central Sri Lanka during rapid cooling","authors":"Y. Hiroi , T. Hokada , N. Furukawa , T. Adachi , B. Prame , L.R.K. Perera , M. Satish-Kumar , Y. Motoyoshi","doi":"10.1016/j.polar.2025.101302","DOIUrl":"10.1016/j.polar.2025.101302","url":null,"abstract":"<div><div>The garnetiferous granulite in central Sri Lanka contains more than 27 minerals with various textures and compositions. The garnet + orthopyroxene + biotite + plagioclase + quartz + ilmenite + rutile + pyrrhotite + melt assemblage may have been stable at the metamorphic peak. The estimated peak <em>P–T</em> conditions are >0.6 GPa and >800 °C. Garnet occurs as anhedral porphyroblasts up to 1 cm in diameter. Some grains contain numerous inclusions, including melt inclusions (felsite–nanogranite inclusions, or FNIs), while others are free of inclusion except for fine–grained ilmenite and rutile. They commonly exhibit compositional zoning, with Mg decreasing and Ca increasing towards the margin. Some grains exhibit P zoning and are divided into P–poor core, P–rich mantle and P–poor rim. In the P–rich mantle, the FNIs are surrounded by areas of P depletion, indicating FNIs’ strong effect on the behavior of P in garnet. Grandidierite exclusively occurs in FNIs. Cathodoluminescence imaging revealed \"hidden\" dendritic high–quartz within anhedral quartz grains in FNIs. Dynamic crystallization experiments reproduced the characteristic texture. Plagioclase and biotite exhibit extremely wide compositional variations depending on their occurrence mode. Zoned carbonate and moganite–containing chalcedony occur as inclusions in garnet in places. These features all resulted from high–temperature metamorphism followed by the complex cooling history experienced by the rocks in a crustal–scale suture zone.</div></div>","PeriodicalId":20316,"journal":{"name":"Polar Science","volume":"46 ","pages":"Article 101302"},"PeriodicalIF":2.0,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145739092","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-01DOI: 10.1016/j.polar.2025.101250
E.O. Dubinina , Ju.N. Chizhova
The isotope (δ18O and δ2H) variations in river waters are averaged in the river plume zones during their residence at the Arctic shelf. We demonstrate that the residence time (τ) of river waters on the Arctic shelf can be estimated using the sinusoidal modelling of stable isotope (δ18О, δ2H) composition of the freshwater component (FC) in river plumes. The plume zones of six Siberian rivers the Ob, Yenisei, Khatanga, Lena, Indigirka and Kolyma were sampled during the summer period in 2015–2017. The τ value of waters of the Ob, Yenisei, Lena, and Kolyma rivers were calculated using sinusoidal model and seasonal δ18О and δ2Н data for these rivers extracted from the Arctic GRO dataset. The calculated τ-values for the Yenisei and Ob plumes are maximal (τ = 4.3–5.5 months), while for the Lena and Kolyma plumes, the τ value is almost twice as low (2–3 months). These estimations show that spring continental waters are present within the river plumes at the end of ice-free season. Based on the FC isotope composition and τ values obtained for river plumes, the general geographic pattern of isotope signatures of summer continental runoff entering the Arctic shelf can be considered as a result of the continental effect of winter precipitation. The δ18О(FC) and δ2H(FC) relationship of averaged data obtained for summer runoff for studied Siberian rivers show absence of the evaporation effect and close to the Global Meteoric Waters line: δ2Н = 8.12(±0.42) × δ18О + 8.6(±7.9).
{"title":"Isotope (δ18O, δ2H) signature of river and plume waters: Residence time of summer Siberian river runoff on the East Arctic shelf","authors":"E.O. Dubinina , Ju.N. Chizhova","doi":"10.1016/j.polar.2025.101250","DOIUrl":"10.1016/j.polar.2025.101250","url":null,"abstract":"<div><div>The isotope (δ<sup>18</sup>O and δ<sup>2</sup><span><span>H) variations in river waters are averaged in the </span>river plume<span> zones during their residence at the Arctic shelf. We demonstrate that the residence time (τ) of river waters on the Arctic shelf can be estimated using the sinusoidal modelling of stable isotope (δ</span></span><sup>18</sup>О, δ<sup>2</sup>H) composition of the freshwater component (FC) in river plumes. The plume zones of six Siberian rivers the Ob, Yenisei, Khatanga, Lena, Indigirka and Kolyma were sampled during the summer period in 2015–2017. The τ value of waters of the Ob, Yenisei, Lena, and Kolyma rivers were calculated using sinusoidal model and seasonal δ<sup>18</sup>О and δ<sup>2</sup>Н data for these rivers extracted from the Arctic GRO dataset. The calculated τ-values for the Yenisei and Ob plumes are maximal (τ = 4.3–5.5 months), while for the Lena and Kolyma plumes, the τ value is almost twice as low (2–3 months). These estimations show that spring continental waters are present within the river plumes at the end of ice-free season. Based on the FC isotope composition and τ values obtained for river plumes, the general geographic pattern of isotope signatures of summer continental runoff entering the Arctic shelf can be considered as a result of the continental effect of winter precipitation. The δ<sup>18</sup>О(FC) and δ<sup>2</sup><span>H(FC) relationship of averaged data obtained for summer runoff for studied Siberian rivers show absence of the evaporation effect and close to the Global Meteoric Waters line: δ</span><sup>2</sup>Н = 8.12(±0.42) × δ<sup>18</sup>О + 8.6(±7.9).</div></div>","PeriodicalId":20316,"journal":{"name":"Polar Science","volume":"46 ","pages":"Article 101250"},"PeriodicalIF":2.0,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145739195","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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