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Colección de artículos en temáticas antárticas publicados por investigadores de la Universidad de Magallanes en diferentes fuentes, acorde a las políticas del editor.
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Item A 17-year record of meteorological observations across the gran campo nevado ice cap in southern patagonia, Chile, related to synoptic weather types and climate modesWeidemann, Stephanie S.; Sauter, Tobías; Kilian, Rolf; Steger, David; Butorovic, Nicolás; Schneider, Christoph; Burkhart, John F.The network of long-term meteorological observations in Southernmost Patagonia is still sparse but crucial to improve our understanding of climatic variability, in particular in the more elevated and partially glaciated Southernmost Andes. Here we present a unique 17-year meteorological record (2000–2016) of four automatic weather stations (AWS) across the Gran Campo Nevado Ice Cap (53◦S) in the Southernmost Andes (Chile) and the conventional weather station Jorge Schythe of the Instituto de la Patagonia in Punta Arenas for comparison. We revisit the relationship between in situ observations and large-scale climate models as well as mesoscale weather patterns. For this purpose, a 37-year record of ERA Interim Reanalysis data has been used to compute a weather type classification based on a hierarchical correlation-based leader algorithm. The orographic perturbation on the predominantly westerly airflow determines the hydroclimatic response across the mountain range, leading to significant west-east gradients of precipitation, air temperature and humidity. Annual precipitation sums heavily drop within only tens of kilometers from ~7,500 mma−1 to less than 800 mma−1. The occurrence of high precipitation events of up to 620 mm in 5 days and wet spells of up to 61 consecutive days underscore the year-around wet conditions in the Southernmost Andes. Given the strong link between large-scale circulation and orographically controlled precipitation, the synoptic-scale weather conditions largely determine the precipitation and temperature variability on all time scales. Major synoptic weather types with distinct low-pressure cells in the Weddell Sea or Bellingshausen Sea, causing a prevailing southwesterly, northwesterly or westerly airflow, determine the weather conditions in Southernmost Patagonia during 68% of the year. At Gran Campo Nevado, more than 80% of extreme precipitation events occur during the persistence of these weather types. The evolution of the El Niño Southern Oscillation and Antarctic Oscillation impose intra- and inter-annual precipitation and temperature variations. Positive Antarctic Oscillation phases on average are linked to an intensified westerly airflow and warmer conditions in Southernmost Patagonia. Circulation patterns with high-pressure influence leading to colder and dryer conditions in Southernmost Patagonia are more frequent during negative Antarctic Oscillation phases.Item Adjustment of pigment composition in Desmarestia (Desmarestiaceae) species along a sub-Antarctic to Antarctic latitudinal gradient(Taylor & Francis Group, 2016) Mansilla, Andrés; Méndez, Fabio; Murcia, Silvia; Rodríguez, Juan Pablo; Marambio, Johanna; Rosenfeld, Sebastián; Yokoya, Nair; Bischof, KaiPhotosynthesis at high latitudes demands efficient strategies of light utilization to maintain algal fitness and performance. The fitness, and physiological adaptation, of a plant or algae species depends in part on the abundance and efficiency of the pigments it can produce to utilize the light resource from its environment. We quantified pigment composition and concentration in six species of the brown macroalgal genus Desmarestia, collected from sub- Antarctic sites (Strait of Magellan, Beagle Channel Cape Horn Province) and sites on the Antarctic Peninsula and adjacent islands. Sub-Antarctic Desmarestia species exhibited lower concentrations of chlorophyll a, chlorophyll c and fucoxanthin than endemic Antarctic species. Antarctic samples of D. menziesii and D. antarctica collected along a decreasing latitudinal gradient showed spatial and interspecific differences in light-harvesting pigment composition. Our results suggest distinct physiological adjustments in Desmarestia species in response to heterogeneous abiotic environmental conditions. The marine sub- Antarctic and Antarctic ecosystems are characterized by harsh environments (e.g., extreme irradiance, photoperiod, temperature, salinity) to which the physiology of macroalgal species must adapt.Item Assessing the impact of retreat mechanisms in a simple antarctic ice sheet model using bayesian calibration(Public Library of Science, 2017-01-12) Ruckert, Kelsey L.; Shaffer, Gary; Pollard, David; Guan, Yaguen; Wong, Tony E.; Forest, Chris E.; Keller, Klaus; Añel, Juan A.The response of the Antarctic ice sheet (AIS) to changing climate forcings is an important driver of sea-level changes. Anthropogenic climate change may drive a sizeable AIS tipping point response with subsequent increases in coastal flooding risks. Many studies analyzing flood risks use simple models to project the future responses of AIS and its sea-level contributions. These analyses have provided important new insights, but they are often silent on the effects of potentially important processes such as Marine Ice Sheet Instability (MISI) or Marine Ice Cliff Instability (MICI). These approximations can be well justified and result in more parsimonious and transparent model structures. This raises the question of how this approximation impacts hindcasts and projections. Here, we calibrate a previously published and relatively simple AIS model, which neglects the effects of MICI and regional characteristics, using a combination of observational constraints and a Bayesian inversion method. Specifically, we approximate the effects of missing MICI by comparing our results to those from expert assessments with more realistic models and quantify the bias during the last interglacial when MICI may have been triggered. Our results suggest that the model can approximate the process of MISI and reproduce the projected median melt from some previous expert assessments in the year 2100. Yet, our mean hindcast is roughly 3/4 of the observed data during the last interglacial period and our mean projection is roughly 1/6 and 1/10 of the mean from a model accounting for MICI in the year 2100. These results suggest that missing MICI and/or regional characteristics can lead to a low-bias during warming period AIS melting and hence a potential low-bias in projected sea levels and flood risks.Item Bioactive monoterpenes from antarctic Plocamium Cartilagineum(Sociedad Chilena de Química, 2013) Rovirosa, Juana; Soler, Agnes; Blanc, Vanessa; León, Rubén; San Martín, AurelioIn a chemical analysis of the red seaweed Plocamium cartilagineum collected in Antarctic Peninsula, four polyhalogenated monoterpenes were isolated. Their structures were established by spectroscopic techniques. Two of them are acyclic monoterpenes and the others are cyclic. We report the antimicrobial, insecticide and acaricide activities of compounds.Item Biogeochemistry of a low-activity cold seep in the Larsen B area, western Weddell Sea, Antarctica(Copernicus Publications on behalf of the European Geosciences Union, 2009-11-02) Niemann, H.; Fisher, D.; Graffe, D.; Knittel, K.; Montiel, Américo; Heilmayer, O.; Knothen, K.; Pape, K.; Kasten, S.; Bohrmann, G.; Boetius, A.; Gutt, J.; Kusel, K.First videographic indication of an Antarctic cold seep ecosystem was recently obtained from the collapsed Larsen B ice shelf, western Weddell Sea (Domack et al., 2005). Within the framework of the R/V Polarstern expedition ANTXXIII-8, we revisited this area for geochemical, microbiological and further videographical examinations. During two dives with ROV Cherokee (MARUM, Bremen), several bivalve shell agglomerations of the seep-associated, chemosynthetic clam Calyptogena sp. were found in the trough of the Crane and Evans glacier. The absence of living clam specimens indicates that the flux of sulphide and hence the seepage activity is diminished at present. This impression was further substantiated by our geochemical observations. Concentrations of thermogenic methane were moderately elevated with 2μM in surface sediments of a clam patch, increasing up to 9μM at a sediment depth of about 1m in the bottom sections of the sediment cores. This correlated with a moderate decrease in sulphate from about 28mM at the surface down to 23.4 mM, an increase in sulphide to up to 1.43mM and elevated rates of the anaerobic oxidation of methane (AOM) of up to 600 pmol cm−3 d−1 at about 1m below the seafloor. Molecular analyses indicate that methanotrophic archaea related to ANME-3 are the most likely candidates mediating AOM in sediments of the Larsen B seep.Item Biogeography in Cellana (Patellogastropoda, Nacellidae) with special emphasis on the relationships of southern hemisphere oceanic island species(PLOS, 2017-01-18) González-Wevar, Claudio A.; Nakano, Tomoyuki; Palma, Alvaro; Poulin, ElieOceanic islands lacking connections to other land are extremely isolated from sources of potential colonists and have acquired their biota mainly through dispersal from geographically distant areas. Hence, isolated island biota constitutes interesting models to infer biogeographical mechanisms of dispersal, colonization, differentiation, and speciation. Limpets of the genus Cellana (Nacellidae: Patellogastropoda) show limited dispersal capacity but are broadly distributed across the Indo-Pacific including many endemic species in isolated oceanic islands. Here, we examined main distributional patterns and geographic boundaries among Cellana lineages with special emphasis in the relationships of Southern Hemisphere oceanic islands species. Phylogenetic reconstructions based on mtDNA (COI) recognized three main clades in Cellana including taxa from different provinces of the Indo-Pacific. Clear genetic discontinuities characterize the biogeography of Cellana and several lineages are associated to particular areas of the Indo-Pacific supporting the low dispersal capacity of the genus across recognized biogeographical barriers in the region. However, evolutionary relationships within Cellana suggest that long-distance dispersal processes have been common in the history of the genus and probably associated to the origin of the species in Hawaii and Juan FernaÂndez Archipelago. Therefore, the presence of Cellana species in geographically distant Southern Hemisphere oceanic islands, such as the Juan FernaÂndez Archipelago, suggests that long-distance dispersal mediated by rafting may have played an important role in the biogeography of the genus.Item Climate change in antarctic and magellanic regions: Fields and goals of scientific cooperation(Universidad de Magallanes, 2011) Arntz, Wolf E.; Gerdes, DieterItem Colonial life under the Humboldt Current System: deep-sea corals from O’Higgins I seamount(Escuela de Ciencias del Mar, Facultad de Ciencias del Mar y Geografía de la Pontificia Universidad Católica de Valparaíso, 2012) Cañete, Juan I.; Häussermann, VerenaA benthic community constituted by an assemblage of at least four species of deep-sea corals collected in only one trawl carried-out on the summit of the O’Higgins I seamount, central Chile. The corals were collected in only one trawl carried-out during a Chilean-Japanese cruise onboard the R/V” Koyo Maru” in December 29, 2004. Presence of oxygenated and cold Antarctic Intermediate Water (>400 m depth) on the plateau was recorded under of the Equatorial Subsurface Water associated to the oxygen-minimum zone (OMZ, <1 mL O2 L-1). The biogeographic origin of the fauna evidenced a mix of Subantarctic and central Chile continental margin species. The assemblage is represented by two species of anthipatarians (Leiopathes sp. and Chrysopathes sp.), one unidentified species of Paragorgiidae and one species of Isididae (Acanella chilensis). The study demonstrated that deep-water corals of the O’Higgins seamount provide crucial habitat for commercially important crustacean exploited along continental margin off central Chile such as nylon shrimp (Heterocarpus reedi). This resource as well as some fishes such as alfonsino (Beryx splendens) and orange roughy (Hoplostethus atlanticus) could drawing the commercial fishing industry to these fragile areas poorly known Chilean marine benthic communities. Due to a strong economic pressure, fast actions for marine conservation of seamounts are required in Chile.Item Detection and attribution of antarctic climate change(Universidad de Magallanes, 2012) Bracegirdle, Thomas J.El conocimiento actual de los cambios climáticos que han ocurrido en los últimos 50 años sobre la Antártica se presenta con un enfoque sobre: (i) un calentamiento de verano de la región oriental de la Península Antártica, lo que provocó el colapso de la plataforma de hielo Larsen B, (ii) la observación de importante aumento de la extensión total del hielo marino y (iii) una huella antropogénica en el patrón de cambio de temperatura en toda la Antártica. Las implicaciones de esto para las predicciones del futuro se discuten.Item Distribution patterns of macrozoobenthos: a comparison between the Magellan region and the Weddell Sea (Antarctica)(Institut de Ciències del Mar, CSIC, 1999) Gerdes, Dieter; Montiel, AméricoThe Joint Chilean-German-Italian Magellan “Victor Hensen” Campaign in October/November 1994 and the “Polarstern” expedition ANT XIII/4 (May 1996) yielded 207 quantitative multibox corer samples from 11 stations in the Paso Ancho (Magellan Straits), 10 stations in the Beagle Channel, and 15 stations of the shelf and continental slope off the eastern entrance of the Beagle Channel. Mean abundance values in the Magellan Region varied from 1591 Ind. m-2 in the Paso Ancho to 3643 Ind. m-2 in the Beagle Channel and 3983 Ind. m-2 on the shelf; the corresponding biomass values were 96.8 g, 301.6 g, and 119.0 g wet weight m-2, respectively. In terms of org. C the corresponding values are 4.8, 11.4, and 4.6 g m-2. Abundance (3806 Ind. m-2) and biomass (222.6 g wet weight m-2 or 7.3 g C) data from the eastern Weddell Sea shelf (“Polarstern” expeditions ANT VI/3, 1987/88 and ANT VII/4, 1989) are in the same range. The composition of the fauna, however, reveals distinct differences.Item Divergence time estimations and contrasting patterns of genetic diversity between antarctic and southern south america benthic invertebrates(Sociedad de Biología de Chile, 2012) González-Wevar, Claudio Alejandro; Díaz, Angie; Gerard, Karin; Poulin, Elie; Cañete, Juan I.Diversity, abundance and composition of taxonomic groups in the Southern Ocean differ from elsewhere in the planet, since the biogeography in this region refl ects the complex interactions of tectonics, oceanography, climate and biological elements since the Eocene. Several groups of marine benthic organisms exhibit high levels of genetic divergence among provinces in this region, supporting the existence of a vicariance process through plate tectonics, while other groups with high dispersive capacity exhibit recent divergence processes. Moreover, the discovery of non- Antarctic decapod larvae in Antarctic Peninsula suggests that some groups can travel across the Antarctic Circumpolar Current. Here we analyzed levels of genetic divergence in congeneric species of three Southern Ocean’s benthic invertebrate groups with dispersive potential. For this purpose we included in the analyses COI sequences of an echinoid (Sterechinus), a gastropod (Nacella), and a bivalve (Yoldia). Considering the levels of genetic differentiation and assuming the molecular clock hypothesis we estimated the separation of invertebrates from the two continents. We also compared levels of genetic variation between Antarctic and sub-Antarctic species of Nacella and Sterechinus to determine the effect of the Quaternary glacial episodes in the demography of these species. We detected clear genetic differences between Antarctic and sub-Antarctic congeneric species of Sterechinus, Nacella, and Yoldia. According to our results, the installation of an effective barrier between Antarctica and sub-Antarctica occurred almost at the same time (between 3.7 and 5.0 Ma) for these groups of organisms, long after the physical separation of both continents. Genetic comparisons between Antarctic and Sub-Antarctic species of Nacella and Sterechinus detected lower levels of genetic diversity in Antarctic species, suggesting more pronounced effects of the glacial episodes in Antarctica than in South America. These results may refl ect the dramatic effect of the Quaternary glacial cycles on Antarctic population sizes, especially in groups with narrow bathymetric ranges. The present study provides new evidence about the differentiation processes between Antarctic and South American organisms. None of the analyzed genera showed evidence for recurrent gene fl ow across the Antarctic Circumpolar Current since the Mio-Pliocene. Genetic comparisons indicate that Antarctic and Sub-Antarctic species were differentially affected by glacial periods.Item Erythemal irradiance at the Magellan’s region and Antarctic ozone hole 1999-2005(Universidad Nacional Autónoma de México, 2008) Casiccia, Claudio; Zamorano, Felix; Hernández, A.La parte más austral del cono sur de Sudamérica, que algunas veces se encuentra bajo la influencia del agujero de ozono antártico (AOA), ocasionalmente recibe altos niveles de radiación ultravioleta B (UV-B: 280-320nm). La Universidad de Magallanes en Punta Arenas, Chile (Lat. 53° S; Long. 70.9° W), ha realizado mediciones de radiación ultravioleta eritémica desde 1999, las cuales se iniciaron con la instalación de cuatro instrumentos en diferentes localidades de la región de Magallanes, la región más austral de Chile y próxima al continente Antártico. En este estudio se muestran los datos obtenidos con instrumentos Solar Light en diferentes puntos de la región de Magallanes desde 1999 hasta 2005, como también datos de la columna total de ozono medida en Punta Arenas con el instrumento Brewer (Serie 180) además de datos del Total Ozone Mapping Spectrometer (TOMS). Estos datos muestran un número significativo de días en 2004 con baja concentración de ozono, señalando que la recuperación de la columna de ozono en estas latitudes en todavía incierta. Se han analizado datos de mediciones de radiación eritémica obtenidos de las estaciones de la red de medidores instalada en la región de Magallanes, con especial atención al periodo primavera verano, en el que la actividad del AOA es más intensa. En algunas ocasiones se observaron disminuciones entre 20 y 53% en la columna total de ozono. Durante estos periodos también se observaron aumentos de la radiación UV-B. Al comparar estos con los valores de radiación para aquelos días considerados normales, los niveles de radiación UV-B son mayores aproximadamente entre 50 y 200% en las diferentes estaciones.Item Evolution of the austral-antarctic flora during the cretaceous: New insights from a paleobiogeographic perspective(Sociedad de Biología de Chile, 2012) Leppe, Marcelo; Mihoc, Maritza; Varela, Natalia; Stinnesbeck, Wolfgang; Mansilla, Héctor; Bierma, Hessel; Cisterna, Katherine; Frey, Eberhard; Jujihara, ThoshiroFores t environments have continuously existed in Antarctica since the late Paleozoic and only disappeared from this continent since the Neogene. Nevertheless, the structure of these forests underwent substantial evolutionary changes. During the late Cretaceous, forests dominated by conifers and pteridophytes were gradually replaced by angiospermdominated forests. Elements common to these Antarctic forests are important constituents of the recent Valdivian Forest. During the Turonian stage of the Late Cretaceous, the Antarctic Peninsula and Patagonia were reconnected by a land bridge after a separation since the end of the Jurassic. Using biogeographic tools applied to the palynological and leaf imprint record, outcrops of Campanian-Maastrichtian age were studied from the Snow Hill, James Ross and Seymour (Marambio) Islands in the James Ross basin, Antarctica; Skua Bay, Half Three Point, Price Point and Zamek Hill on King George Island, Antarctica, and Rocallosa Point, Cerro Guido, Las Chinas, Dorotea Hill, Cazador Hill and La Irene in Chilean-Argentinian Patagonia, comparing the current distribution and the paleogeography, as well as the infl uence of potential areas of endemism and vicariants events. The analysis indicates that vegetation evolved under environmental conditions subject to intense volcanic and climatic disturbances, with changes from a period with extreme greenhouse climate (Turonian-Campanian) to strong cooling during the Maastrichtian. We suggest that a continuous forest existed in southern South America and Antarctica, which was shaped during the Latest Cretaceous by the presence of marine basins and and intermittent connection and disconnection of the flora.Item Extreme sunbathing: three weeks of small total O3 columns and high UV radiation over the southern tip of South America during the 2009 Antarctic O3 hole season(American Geophysical Union, 2010-07-27) Laat, A.T.J. de; Van der A., R.J.; Alaart, M.A.F.; Van Wheele, M.; Benítez, G.C.; Casiccia, Claudio; Paes Leme, N.M.; Quel, E.; Salvador, J.; Wolfram, E.This paper presents an analysis of satellite and groundbased measurements of total O3 columns and the UV index of a unique event during the 2009 Antarctic O3 hole season. From 11 to 30 November 2009 the Antarctic vortex was located just south of the southern tip of South America rather than at its climatological position over Antarctica. Analysis of 30 years of assimilated total O3 column and UV index measurements shows that this 20‐day event was unique in the history of the ozone hole for these latitudes. During this period, small total O3 columns and large UV index values were observed over the southern tip of South America. Comparison of ground‐based and satellite measurements of total O3 columns and satellite based calculations of the UVI index – never designed nor validated for such extreme Southern Hemisphere conditions – show excellent agreement.Item Flora marina bentónica de la región austral de sudamérica y la antártica(Universidad de Magallanes, 2010) Ramírez, María ElianaEl conocimiento taxonómico de la flora marina bentónica de la región austral de Sudamérica, incluida la Antártica, está basado fundamentalmente en los registros de las expediciones europeas que recorrieron los mares australes durante los siglos XVIII, XIX y principios del siglo XX. Debido a la lejanía de estos territorios y a las dificultades logísticas para la realización de nuevas recolecciones en el área, poco se ha avanzado en la revisión crítica de los taxa publicados en la literatura hasta la fecha. El presente trabajo da a conocer un listado actualizado de esta flora marina, en base a las publicaciones y exploraciones recientes en el área. Adicionalmente y en base a este listado, se presenta un análisis biogeográfico con el objeto de establecer las relaciones entre la flora marina de la región austral de Sudamérica y aquélla de la región antártica.Item Foraminíferos textuláridos en sedimentos someros recientes de la península antártica y su relación con el área subantártica sudamericana(Universidad de Magallanes, 2012) Hromic, Tatiana; Camblor, María; Quezada, LytaForty nine samples, of superficial marine sediments (< 50m.) from 3 localities: Deception Island, Chile Bay and Fildes Bay, Antarctic península were analysed in order to investigate the foraminiferers of suborder Textulariina Delage y Herouard, 1886. Twenty two species were identified and classiffied en 12 families and 15 generas. The most abundant species were Trochammina malovensis (53,2%), Miliammina arenácea (16,3%) y Reophax dentaliniformis (6,7%). Deception Island contributed with most of the specimens (57%) and Chile Bay with the highest number of species. Thes most common species in the area were Trochammina malovensis (95,9% of the samples), Miliammina arenácea (73,5%), Spiroplectammina biformis (63,3%) and Trochammina squamata (61,2%). Hierarchical cluster analysis and ANOSIM showed there is not communities differences between bays. Ten species (from 22) could not be found in the southernmost southamerica: Alveolophragmiun columbiense, Deuterammina glabra, Eggerella minuta, Pseudobolivina antarctica, Reophax nodulosus, Rhabdammina linnearis, Saccammina sphaerica, Textularia wiesneri, Trochammina malovensis and T. quadriloba. Probably they are endemic species for the Antarctic region.Item Genetic structure and demographic inference of the regular sea urchin Sterechinus neumayeri (Meissner, 1900) in the southern ocean: The role of the last glaciation(Tzen-Yuh Chiang, National Cheng Kung University, Taiwan, 2018-06-06) Díaz, Angie; Gerard, Karin; González-Wevar, Claudio; Maturana, Claudia; Féral, Jean-Pierre; David, Bruno; Saucède, Thomas; Poulin, ElieOne of the most relevant characteristics of the extant Southern Ocean fauna is its resiliency to survive glacial processes of the Quaternary. These climatic events produced catastrophic habitat reductions and forced some marine benthic species to move, adapt or go extinct. The marine benthic species inhabiting the Antarctic upper continental shelf faced the Quaternary glaciations with different strategies that drastically modified population sizes and thus affected the amount and distribution of intraspecific genetic variation. Here we present new genetic information for the most conspicuous regular sea urchin of the Antarctic continental shelf, Sterechinus neumayeri. We studied the patterns of genetic diversity and structure in this broadcast-spawner across three Antarctic regions: Antarctic Peninsula, the Weddell Sea and Ade lie Land in East Antarctica. Genetic analyses based on mitochondrial and nuclear markers suggested that S. neumayeri is a single genetic unit around the Antarctic continent. The species is characterized by low levels of genetic diversity and exhibits a typical star-like haplotype genealogy that supports the hypothesis of a single in situ refugium. Based on two mutation rates standardized for this genus, the Bayesian Skyline plot analyses detected a rapid demographic expansion after the Last Glacial Maximum. We propose a scenario of rapid postglacial expansion and recolonization of Antarctic shallow areas from a less ice-impacted refugium where the species survived the LGM. Considering the patterns of genetic diversity and structure recorded in the species, this refugium was probably located in East Antarctica.Item Georeferenciación de datos obtenidos a través de radio eco-sondaje al norte de la península antártica(Universidad de Magallanes, 2011) Cárdenas, Carlos; Carvallo, Rubén; Dodman, Cristian; Johnson, Erling; Hernández, JorgeThis investigation presents data from working with Global Positioning System (GPS) to complement the work of Radio Echo Sounding from January 2009 at the area next to the Chilean Base Station Bernardo O’Higgins and Jakenau Mountain at north of the Antarctic peninsula (63° 19’ S, 57° 51’ W). The main objective was to georeference the information onto crevasses zones identified by Radio Eco Sounding, using two topographic GPS equipment. The measured points correspond to a grid draw on the area that is normally used for Twin Otter aircraft landing thus, surface and subglacier topographyItem Glacial reduction and millennial-scale variations in Drake Passage throughflow(National Academy of Sciences, 2015-11-03) Lamy, Frank; Arz, Helge W.; Kilian, Rolf; Lange, Carina B.; Lembke-Jene, Lester; Wengler, Marc; Kaiser, Jerôme; Baeza-Urrea, Oscar; Hall, Ian R.; Harada, Naomi; Tiedemann, Ralf; Thiemens, Mark H.The Drake Passage (DP) is the major geographic constriction for the Antarctic Circumpolar Current (ACC) and exerts a strong control on the exchange of physical, chemical, and biological properties between the Atlantic, Pacific, and Indian Ocean basins. Resolving changes in the flow of circumpolar water masses through this gateway is, therefore, crucial for advancing our understanding of the Southern Ocean’s role in global ocean and climate variability. Here, we reconstruct changes in DP throughflow dynamics over the past 65,000 y based on grain size and geochemical properties of sediment records from the southernmost continental margin of South America. Combined with published sediment records from the Scotia Sea, we argue for a considerable total reduction of DP transport and reveal an up to ∼40% decrease in flow speed along the northernmost ACC pathway entering the DP during glacial times. Superimposed on this long-term decrease are high-amplitude, millennial- scale variations, which parallel Southern Ocean and Antarctic temperature patterns. The glacial intervals of strong weakening of the ACC entering the DP imply an enhanced export of northern ACC surface and intermediate waters into the South Pacific Gyre and reduced Pacific–Atlantic exchange through the DP (“cold water route”). We conclude that changes in DP throughflow play a critical role for the global meridional overturning circulation and interbasin exchange in the Southern Ocean, most likely regulated by variations in the westerly wind field and changes in Antarctic sea ice extent.Item Historically unprecedented global glacier decline in the early 21st century(International Glaciological Society, 2015) Zemp, Michael; Frey, Holger; Garnert-Roer, Isabelle; Nussbaumer, Samuel U.; Hoelzle, Martin; Paul, Frank; Haeberli, Wilfried; Denzinger, Florian; Anderson, Brian; Bajracharya, Samjwal; Baroni, Carlo; Braun, Ludwing N.; Cáceres, Bolívar E.; Casassa, Gino; Dávila, Luzmila R.; Delgado Granados, Hugo; Demuth, Michael N.; Espizua, Lydia; Fisher, Andrea; Fujita, Koji; Gadek, Bogdan; Ghazanfar, Ali; Hagen, Jon Ovi; Holmlund, Per; Karimi, Neamat; Li, Zhonqin; Pelto, Mauri; Pitte, Pierre; Popovnin, Victor V.; Portocarrero, Cesar A.; Prinz, Rainer; Sangewar, Chandrashekhar; Severskiy, Igor; Sigurdsson, Oddur; Soruco, Alvaro; Usubaliev, Ryskul; Vincent, Christian; Ahlstrom, Andreas P.; Cobos, GuillermoObservations show that glaciers around the world are in retreat and losing mass. Internationally coordinated for over a century, glacier monitoring activities provide an unprecedented dataset of glacier observations from ground, air and space. Glacier studies generally select specific parts of these datasets to obtain optimal assessments of the mass-balance data relating to the impact that glaciers exercise on global sea-level fluctuations or on regional runoff. In this study we provide an overview and analysis of the main observational datasets compiled by the World Glacier Monitoring Service (WGMS). The dataset on glacier front variations (~42 000 since 1600) delivers clear evidence that centennial glacier retreat is a global phenomenon. Intermittent readvance periods at regional and decadal scale are normally restricted to a subsample of glaciers and have not come close to achieving the maximum positions of the Little Ice Age (or Holocene). Glaciological and geodetic observations (~5200 since 1850) show that the rates of early 21st-century mass loss are without precedent on a global scale, at least for the time period observed and probably also for recorded history, as indicated also in reconstructions from written and illustrated documents. This strong imbalance implies that glaciers in many regions will very likely suffer further ice loss, even if climate remains stable.
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