Holocene deglaciation of the northern Fildes Peninsula, King George Island, Antarctica

The timing and magnitude of Holocene glacial oscillations in most currently ice-free areas of Antarctica remain unknown. This work focuses on the recent deglaciation in the northern sector of the Fildes Peninsula, King George Island, northern Antarctic Peninsula. The ice cap covering ca. 90% of the island has receded since the Last Glacial Maximum and exposed ca. 29 km2 of ice-free land. We reconstruct its glacial history based on a dataset of 12 36Cl exposure ages obtained through cosmic-ray exposure (CRE) dating of moraine boulders, polished surfaces and erratic boulders surrounding the peninsula's northern plateau. Results reveal that the deglaciation of the northern Fildes Peninsula took place during the Holocene Thermal Maximum at 7–6 ka, when warm conditions promoted a massive glacial retreat. The present arrangement of ice-free areas was in place by 6 ka. Small cirque moraines suggest the subsequent occurrence of favourable climate conditions for glacial expansion fed by intense snow deflation at 4.6 and 1 ka at the foot of the northern plateau. The deglaciation pattern of the Fildes Peninsula resulted from the combined shrinkage of different ice masses, rather than of the long-term retreat of the King George Ice Cap. No evidence of glacier expansion during more recent cold periods (i.e. the Little Ice Age) was found. These results fit well with regional deglacial histories inferred from lacustrine sediments and raised beaches and complement the existing chronological framework to help better understand the peninsula's Holocene geoecological dynamics.info:eu-repo/semantics/acceptedVersio

Local habitat filtering shapes microbial community structure in four closely spaced lakes in the High Arctic

Arctic lakes are experiencing increasingly shorter periods of ice cover due to accelerated warming at northern high latitudes. Given the control of ice cover thickness and duration over many limnological processes, these changes will have pervasive effects. However, due to their remote and extreme locations even first-order data on lake ecology is lacking for many ecosystems. The aim of this study was to characterize and compare the microbial communities of four closely spaced lakes in Stuckberry Valley (northern Ellesmere Island, Canadian Arctic Archipelago), in the coastal margin zone of the Last Ice Area, that differed in their physicochemical, morphological and catchment characteristics. We performed high-throughput amplicon sequencing of the V4 16S rRNA gene to provide inter- and intra-lake comparisons. Two deep (>25 m) and mostly oxygenated lakes showed highly similar community assemblages that were distinct from those of two shallower lakes (<10 m) with anoxic bottom waters. Proteobacteria, Verrucomicrobia, and Planctomycetes were the major phyla present in the four water bodies. One deep lake contained elevated proportions of Cyanobacteria and Thaumarchaeota that distinguished it from the others, while the shallow lakes had abundant communities of predatory bacteria, as well as microbes in their bottom waters that contribute to sulfur and methane cycles. Despite their proximity, our data suggest that local habitat filtering is the primary determinant of microbial diversity in these systems. This study provides the first detailed examination of the microbial assemblages of the Stuckberry lakes system, resulting in new insights into the microbial ecology of the High Arctic

The timing and widespread effects of the largest Holocene volcanic eruption in Antarctica.

The caldera collapse of Deception Island Volcano, Antarctica, was comparable in scale to some of the largest eruptions on Earth over the last several millennia. Despite its magnitude and potential for far-reaching environmental effects, the age of this event has never been established, with estimates ranging from the late Pleistocene to 3370 years before present. Here we analyse nearby lake sediments in which we identify a singular event produced by Deception Island's caldera collapse that occurred 3980 ± 125 calibrated years before present. The erupted tephra record the distinct geochemical composition of ejecta from the caldera-forming eruption, whilst an extreme seismic episode is recorded by lake sediments immediately overlying the collapse tephra. The newly constrained caldera collapse is now the largest volcanic eruption confirmed in Antarctica during the Holocene. An examination of palaeorecords reveals evidence in marine and lacustrine sediments for contemporaneous seismicity around the Antarctic Peninsula; synchronous glaciochemical volcanic signatures also record the eruption in ice cores spread around Antarctica, reaching >4600 km from source. The widespread footprint suggests that this eruption would have had significant climatic and ecological effects across a vast area of the south polar region

La deglaciación de las áreas libres de hielo de las islas Shetland del Sur (Antártida): ejemplos de Byers (Livingston) y Barton (King George)

El proceso de deglaciación de las actuales áreas libres de hielo existentes en la zona de la Antártida marítima tiene notables repercusiones geomorfológicas y ecológicas. No obstante, la cronología del retroceso glaciar es aún poco conocida. Éste es el caso de las áreas deglaciadas existentes en las penínsulas Byers (isla Livingston) y Barton (isla King George). La datación de la base de los sedimentos recuperados en diferentes lagos emplazados en estas dos penínsulas permite inferir la edad de aparición de cada lago que, integrando el conjunto de dataciones, posibilita la reconstrucción del patrón espacial y temporal de la deglaciación de estas áreas. Las técnicas empleadas para el establecimiento de la cronología de los sedimentos de los lagos se han basado en el uso complementario de dataciones de radiocarbono y termoluminiscencia. En ambas penínsulas la aparición de superficies libres de hielo se inició durante el Holoceno inferior, en torno a los 8 ka. Las áreas más alejadas de los casquetes glaciares actuales y las zonas más elevadas de ambas penínsulas (nunataks) fueron las primeras superficies en quedar expuestas. Durante el Holoceno medio (entre 5 y 6 ka) el sector central de estas áreas fue progresivamente deglaciado. Durante el Holoceno superior los frentes glaciares permanecieron circunscritos a la posición que determinan las morrenas frontales actuales, con avances y retrocesos menores.info:eu-repo/semantics/publishedVersio

Aquatic ecosystems in Byers Peninsula, Livingston Island. An Antarctic Noah’s Ark in a changing world

第6回極域科学シンポジウム[OB] 極域生物圏11月17日（火）　統計数理研究所 セミナー室1（D305

The timing and widespread effects of the largest Holocene volcanic eruption in Antarctica

The caldera collapse of Deception Island Volcano, Antarctica, was comparable in scale to some of the largest eruptions on Earth over the last several millennia. Despite its magnitude and potential for far-reaching environmental effects, the age of this event has never been established, with estimates ranging from the late Pleistocene to 3370 years before present. Here we analyse nearby lake sediments in which we identify a singular event produced by Deception Island’s caldera collapse that occurred 3980 ± 125 calibrated years before present. The erupted tephra record the distinct geochemical composition of ejecta from the caldera-forming eruption, whilst an extreme seismic episode is recorded by lake sediments immediately overlying the collapse tephra. The newly constrained caldera collapse is now the largest volcanic eruption confirmed in Antarctica during the Holocene. An examination of palaeorecords reveals evidence in marine and lacustrine sediments for contemporaneous seismicity around the Antarctic Peninsula; synchronous glaciochemical volcanic signatures also record the eruption in ice cores spread around Antarctica, reaching >4600 km from source. The widespread footprint suggests that this eruption would have had significant climatic and ecological effects across a vast area of the south polar region

Diatom distributions in space and time – a case study from the polar regions

第3回極域科学シンポジウム/第34回極域生物シンポジウム 11月27日（火） 統計数理研究所 ３階セミナー

Petites espèces naviculoïdes de &lt;i&gt;Kobayasiella&lt;/i&gt; Lange-Bertalot, &lt;i&gt;Adlafia&lt;/i&gt; Moser, Lange-Bertalot &amp; Metzeltin, &lt;i&gt;Nupela&lt;/i&gt; Vyverman &amp; Compère and &lt;i&gt;Sellaphora&lt;/i&gt; Mereschowsky du parc national Tursujuq, baie d’Hudson, Nunavik, Québec

Sept espèces des genres Kobayasiella (K. madumensis Jørgensen, K. micropunctata Germain, K. parasubtilissima Kobayasi &amp; Nagumo, K. pseudostauron Lange-Bertalot, K. subtilissima P.T.Cleve), Adlafia (A. bryophila Petersen) et Nupela (N. tenuicephala Hustedt) provenant de lacs oligotrophes de la zone boréale subarctique du parc Tursujuq au Nunavik (nord du Québec, Canada), ont été étudiées par microscopes optique (LM) et électronique à balayage (SEM), et les conditions environnementales de leur lieu de vie ont été caractérisées. Quatre nouvelles espèces, Kobayasiella tursujuqensis sp. nov., Adlafia umiujaqensis sp. nov., Adlafia ossiformis sp. nov., et Sellaphora vincentiana sp. nov., ont été observées et décrites. Bien que similaires à d’autres espèces de leurs genres par observations LM, elles peuvent être différenciées sur la base de traits de caractère indépendants, en combinant des analyses LM et SEM. Les structures morphologiques présentant un intérêt particulier comprennent le contour de la valve, la position des fissures du raphé central et terminal, l’orientation des stries et la formation structurelle des aréoles dans les stries. En raison de la faible abondance des taxons, les schémas de distribution de ces espèces dans le parc ont été difficiles à identifier. Kobayasiella parasubtilissima, K. subtilissima, K. tursujuqensis sp. nov. et N. tenuicephala sont associées aux conditions acides tandis que K. pseudostauron, A. bryophila et S. vincentiana sp. nov. sont associées aux eaux circumneutres. Une meilleure connaissance des espèces naviculoides de petites tailles est nécessaire pour documenter la biogéographie et l’écologie des diatomées afin de mieux comprendre la dynamique de ces organismes dans des conditions environnementales fluctuantes dans un contexte de changement climatique rapide dans les régions boréales.Seven species from the genera Kobayasiella (K. madumensis Jørgensen, K. micropunctata Germain, K. parasubtilissima Kobayasi &amp; Nagumo, K. pseudostauron Lange-Bertalot, K. subtilissima P.T.Cleve), Adlafia (A. bryophila Petersen) and Nupela (N. tenuicephala Hustedt) from oligotrophic lakes of the subarctic boreal zone in Tursujuq National Park in Nunavik (northern Québec, Canada), were studied by light and scanning electron microscopy and linked with environmental conditions. In addition, four new species, Kobayasiella tursujuqensis sp. nov., Adlafia umiujaqensis sp. nov., Adlafia ossiformis sp. nov., and Sellaphora vincentiana sp. nov., were observed and described. The new species are similar in light microscope observations to other species in their associated genera, but can be identified based on independent character traits under a combined LM and SEM analysis. Morphological structures of particular interest include valve outline, position of the central and terminal raphe fissures, orientation of the striae, and the structural formation of the areolae within the striae. Due to low taxon abundances, distribution patterns of these species in the park were difficult to identify. Kobayasiella parasubtilissima, K. subtilissima, K. tursujuqensis sp. nov. and N. tenuicephala were associated with acidic conditions while K. pseudostauron, A. bryophila and S. vincentiana sp. nov. were found in circumneutral waters. A better knowledge of small naviculoid species is necessary to document the circumpolar biogeography and ecology of diatoms for a better understanding of the dynamic of those organisms in changing environmental conditions within the context of rapid climate change in northern regions.</p