152 research outputs found

    The depositional record of the Odyssea drift (Ross Sea, Antarctica)

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    The Ross Sea is one of the major areas for Antarctic Bottom Water formation (the Ross Sea Bottom Water, RSBW), representing the densest ocean water mass, filling the deepest ocean basins connected to the southern ocean. Peri- odic refill of the RSBW occurs through formation of dense, cold and saline water masses (brine) forming on the shelf at the Ross Sea permanent polynya by freezing and salt rejection (high-salinity shelf water, HSSW). The HSSW periodically overspills the shelf area and descends along the slope. This mechanism represents the engine of the global ocean circulation regulating the climate. The Hillary Canyon, crossing the Ross Sea continental slope, represents one of the main conducts through which the HSSW descends the slope to reach the deeper ocean. On its western levee, there is a mounded depocen- tre that was mapped and ground-sampled during the Italian ITRS17-ODYSSEA expedition on board the RV OGS-Explora (January-February 2017). Geophysical data allowed interpreting such feature as a sediment drift (ODYSSEA Drift), generated by along-slope, contour currents sediment transport and accumulation through sev- eral hundred-thousands years. It was inferred that contour currents transported and deposited the sediments that descent the Hillary Canyon by means of the HSSW. Therefore, the depositional sequence of the ODYSSEA Drift potentially contains the record of the variability of HSSW formation, the along slope current intensity in associa- tion to climate change, and the interplay between the two bottom currents. A multidisciplinary investigation was applied to six gravity cores collected in the proximal and distal area of the ODYSSEA Drift. The cores were analysed to reconstruct the age model combining AMS radiocarbon dating on foraminifera tests, biostratigraphy, and the sediment palaeomagnetic record; the sediment physical properties (wet bulk density, water content and grain size); and compositional characteristics (XRF core scan and geochemistry). Three main lithofacies were distinguished and associated to depositional processes and climatic conditions: 1) finely laminated and bioturbated sediments characterized by a relatively high Ca content with common presence of biogenic component. Such facies was associated to contour current deposition during relatively warm conditions. 2) Bioturbated sediments with abundant, sparse and/or layered Ice Rafted Debris, and high Ca content. The onset of this facies is characterized by a prominent Mn peak that was associated to bottom ocean oxygenation through ice sheet melting/decay. 3) Laminated, barren sediments associated to steady strong bottom currents under harsh climate conditions. Further preliminary data interpretations are discussed

    Geomorphology and development of a high-latitude channel system: the INBIS channel case (NW Barents Sea, Arctic)

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    This is a post-peer-review, pre-copyedit version of an article published in Arktos. The final authenticated version is available online at: http://dx.doi.org/https://doi.org/10.1007/s41063-019-00065-9 .The INBIS (Interfan Bear Island and Storfjorden) channel system is a rare example of a deep-sea channel on a glaciated margin. The system is located between two trough mouth fans (TMFs) on the continental slope of the NW Barents Sea: the Bear Island and the Storfjorden–Kveithola TMFs. New bathymetric data in the upper part of this channel system show a series of gullies that incise the shelf break and minor tributary channels on the upper part of the continental slope. These gullies and channels appear far more developed than those on the rest of the NW Barents Sea margin, increasing in size downslope and eventually merging into the INBIS channel. Morphological evidence suggests that the Northern part of the INBIS channel system preserved its original morphology over the last glacial maximum (LGM), whereas the Southern part experienced the emplacement of mass transport glacigenic debris that obliterated the original morphology. Radiometric analyses were applied on two sediment cores to estimate the recent (~ 110 years) sedimentation rates. Furthermore, analysis of grain size characteristics and sediment composition of two cores shows evidence of turbidity currents. We associate these turbidity currents with density-driven plumes, linked to the release of meltwater at the ice-sheet grounding line, cascading down the slope. This type of density current would contribute to the erosion and/ or preservation of the gullies’ morphologies during the present interglacial. We infer that Bear Island and the shallow morphology around it prevented the flow of ice streams to the shelf edge in this area, working as a pin (fastener) for the surrounding ice and allowing for the development of the INBIS channel system on the inter-ice stream part of the slope. The INBIS channel system was protected from the burial by high rates of ice-stream derived sedimentation and only partially affected by the local emplacement of glacial debris, which instead dominated on the neighbouring TMF systems

    Simulated last deglaciation of the Barents Sea Ice Sheet primarily driven by oceanic conditions

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    The Barents Sea Ice Sheet was part of an interconnected complex of ice sheets, collectively referred to as the Eurasian Ice Sheet, which covered north-westernmost Europe, Russia and the Barents Sea during the Last Glacial Maximum (around 21 ky BP). Due to common geological features, the Barents Sea component of this ice complex is seen as a paleo-analogue for the present-day West Antarctic Ice Sheet. Investigating key processes driving the last deglaciation of the Barents Sea Ice Sheet represents an important tool to interpret recent observations in Antarctica over the multi-millennial temporal scale of glaciological changes. We present results from a perturbed physics ensemble of ice sheet model simulations of the last deglaciation of the Barents Sea Ice Sheet, forced with transient atmospheric and oceanic conditions derived from AOGCM simulations. The ensemble of transient simulations is evaluated against the data-based DATED-1 reconstruction to construct minimum, maximum and average deglaciation scenarios. Despite a large model/data mismatch at the western and eastern ice sheet margins, the simulated and DATED-1 deglaciation scenarios agree well on the timing of the deglaciation of the central and northern Barents Sea. We find that the simulated deglaciation of the Barents Sea Ice Sheet is primarily driven by the oceanic forcing, with prescribed eustatic sea level rise amplifying the ice sheet sensitivity to sub-shelf melting over relatively short intervals. Our results highlight that the sub-shelf melting has a very strong control on the simulated grounding-line flux, showing that a slow, gradual ocean warming trend is capable of triggering sustained grounded ice discharge over multi-millennial timescales, even without taking into account marine ice sheet or ice cliff instability

    Санитарно-эпидемиологическая экспертиза импортной пищевой продукции и продовольственного сырья как составляющая профилактического направления транспортной медицины

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    Санітарно епідеміологічна експертиза імпортної харчової продукції й продовольчої сировини (далі експертиза) є одним з пріоритетних напрямів діяльності транспортних підрозділів санепідслужби. Здійснюючи функцію по контролю, виявленню та попередженню впливу небезпечних факторів, пов’язаних з перевезенням вантажів, вона є однією зі складових частин профілактичного напряму транспортної медицини. Експертиза імпортованої продукції харчового призначення нерозривно пов’язана та базується на загальних принципах всієї державної політики у сфері безпеки харчової продукції та продовольчої сировини. Основою для проведення усього комплексу робіт санітарно епідеміологічного направлення є нормативна база, яка була сформована в нашій країні кілька десятиліть назад. Механізм визначення безпеки продукції та ті критерії оцінки, які були закладені в її основі, вимагають перегляду у відповідності з вимогами сьогодення та враховуючи розвиток міжнародних відносин. Зроблені деякі кроки у цьому напрямку. Наприклад, визначення експертизи у законі «Про внесення змін до закону України «Про якість та безпеку харчових продуктів та продовольчої сировини» поряд зі встановленням відповідності продукції нормативним вимогам передбачає оцінку ризику дії шкідливих факторів у процесі обігу харчових продуктів, що відповідає сучас ним вимогам до вирішення задач профілактичного напрямку, запобігання шкідливого впливу факторів, керування санітарно-епідеміологічною ситуацією взагалі та на етапі транспортування харчових грузів зокрема. Такий підхід потрібно враховувати при подальшому необхідному перегляді та формуванні нової нормативної бази.Sanіtarу epidemiological examination of imported foodstuffs and edible raw materials (then «examination») is one of the priority directions of transport sanіtarу epidemiological servise. Examination controls, discovers and prevents an influence of dangerous factors while in transportation of loads. So it’s one of the component of the transport medicine preventive activity. Examination of import foodstuffs and edible raw materials inseparably linked with and based on general principles of the food safety state policy. The foundation of the sanitary service work is the normative base, that was formed in our country about twenty years ago. It is necessary to review the mechanism of the food safety determination and its criteria in accordance with requirements of present day time and with account of the development of the international relations. One of taken steps in this direction is a characteristic of examination in law «About contributing the modification to law of the Ukraine «About quality and safety of foodstuffs and foodraw materials» where along with determination of the products correspondence to the normative requirements is provided forrisk assessment of the harmful factors in process of the turn of the food stuffs. Such approach corresponds with modern requests to decision of the prophylactic problems, prevention bad influence dangerous factors, management sanіtarу epidemiological situation in general and in step of transportation food cargo in particular. And it should be taken into account during the further necessary process of revision and forming the new normative base

    Climate-controlled submarine landslides on the Antarctic continental margin

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    Antarctica’s continental margins pose an unknown submarine landslidegenerated tsunami risk to Southern Hemisphere populations and infrastructure. Understanding the factors driving slope failure is essential to assessing future geohazards. Here, we present a multidisciplinary study of a major submarine landslide complex along the eastern Ross Sea continental slope (Antarctica) that identifies preconditioning factors and failure mechanisms. Weak layers, identified beneath three submarine landslides, consist of distinct packages of interbedded Miocene- to Pliocene-age diatom oozes and glaciomarine diamicts. The observed lithological differences, which arise from glacial to interglacial variations in biological productivity, ice proximity, and ocean circulation, caused changes in sediment deposition that inherently preconditioned slope failure. These recurrent Antarctic submarine landslides were likely triggered by seismicity associated with glacioisostatic readjustment, leading to failure within the preconditioned weak layers. Ongoing climate warming and ice retreat may increase regional glacioisostatic seismicity, triggering Antarctic submarine landslides

    Role of dense shelf water in the development of Antarctic submarine canyon morphology

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    Increased ocean heat supply to the Antarctic continental shelves is projected to cause accelerated ice sheet loss and contribute significantly to global sea-level rise over coming decades. Changes in temperature or salinity of dense shelf waters around Antarctica, resulting from increased glacial meltwater input, have the potential to significantly impact the location and structure of the global Meridional Overturning Circulation, with seabed irregularities such as submarine canyons, driving these flows toward the abyss. Submarine canyons also influence the location of intruding warm water currents by acting as preferential routes for rising Circumpolar Deep Water. These global changes have implications for large-scale effects to atmospheric and oceanic circulation. The ability for numerical modellers to predict these future behaviours is dependent upon our ability to understand both modern and past oceanic, sedimentological and glaciological processes. This knowledge allows ocean models to better predict the flux and pathways of Circumpolar Deep Water delivery to the shelf, and consequently to ice shelf cavities where melt is concentrated. Here we seek to understand how dense shelf water and other continental slope processes influence submarine canyon morphology by analysing newly collected geophysical and oceanographic data from a region of significant and prolonged dense shelf water export, the Hillary Canyon in the Ross Sea. We find that cascading flows of dense shelf water do not contribute to significant gully incision at the shelf edge during interglacial periods, however, are strong enough to prevent gully infilling and contribute to canyon-levee aggradation down-slope. We find buried paleo-gullies beneath gullies incising the modern seafloor. Paleo-gullies occur as single gullies and in complexes indicating that gully activity was continuous over multiple glacial cycles and formed an important role in the development of the shelf edge and upper slope. Glacial cycles likely drive large-scale shifts in canyon head processes with periods of intense seafloor erosion and significant gully incision likely occurring when ice grounded near to the shelf edge, during glacial and deglacial periods, when sediment-laden subglacial meltwater was released at the shelf edge. We put slope morphology observed at the Hillary Canyon head into global perspective to show that cascading flows of dense shelf water do not exert consistent patterns of erosion on high-latitude continental margins

    Climate-controlled submarine landslides on the Antarctic continental margin

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    Antarctica’s continental margins pose an unknown submarine landslide-generated tsunami risk to Southern Hemisphere populations and infrastructure. Understanding the factors driving slope failure is essential to assessing future geohazards. Here, we present a multidisciplinary study of a major submarine landslide complex along the eastern Ross Sea continental slope (Antarctica) that identifies preconditioning factors and failure mechanisms. Weak layers, identified beneath three submarine landslides, consist of distinct packages of interbedded Miocene- to Pliocene-age diatom oozes and glaciomarine diamicts. The observed lithological differences, which arise from glacial to interglacial variations in biological productivity, ice proximity, and ocean circulation, caused changes in sediment deposition that inherently preconditioned slope failure. These recurrent Antarctic submarine landslides were likely triggered by seismicity associated with glacioisostatic readjustment, leading to failure within the preconditioned weak layers. Ongoing climate warming and ice retreat may increase regional glacioisostatic seismicity, triggering Antarctic submarine landslides

    Modelled ocean changes at the Plio-Pleistocene transition driven by Antarctic ice advance

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    The Earth underwent a major transition from the warm climates of the Pliocene to the Pleistocene ice ages between 3.2 and 2.6 million years ago. The intensification of Northern Hemisphere Glaciation is the most obvious result of the Plio-Pleistocene transition. However, recent data show that the ocean also underwent a significant change, with the convergence of deep water mass properties in the North Pacific and North Atlantic Ocean. Here we show that the lack of coastal ice in the Pacific sector of Antarctica leads to major reductions in Pacific Ocean overturning and the loss of the modern North Pacific Deep Water (NPDW) mass in climate models of the warmest periods of the Pliocene. These results potentially explain the convergence of global deep water mass properties at the Plio-Pleistocene transition, as Circumpolar Deep Water (CDW) became the common source
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