Aditya Narayanan

Bio: Aditya Narayanan is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topic(s): Water mass & Circumpolar deep water. The author has an hindex of 2, co-authored 3 publication(s) receiving 15 citation(s).

Water Mass Characteristics of the Antarctic Margins and the Production and Seasonality of Dense Shelf Water

Abstract: Conductivity-temperature-depth data from instrumented seals of the Marine Mammals Exploring Oceans from Pole to Pole program are analyzed to characterize the water masses and the seasonality of the marginal seas. Bottom temperatures are found to be in a cold regime in Dense Shelf Water (DSW) producing regions, identified in this study as the southern Weddell Sea, Cape Darnley, Prydz Bay, Adélie Coast, and the western Ross Sea. DSW occupies the bottom of the Weddell and Ross Sea continental shelves throughout the year: Production of DSW and vertical overturning occur only during the winter. In the other DSW producing regions, salinity is reduced more markedly during the summer. We identify the Princess Martha Coast, Leopold and Astrid Coast, and the Knox Coast as Low Salinity Shelf Water producing regions, where modified Circumpolar Deep Water (CDW) intrudes onto the continental shelf, reaching areas close to the ice shelves keeping the bottom temperatures in an intermediate regime. The Prince Harald Coast, the Amundsen Sea, and the Bellingshausen Sea experience more intense CDW intrusion, which keeps them in a warm regime year-round. CDW layer thicknesses correlate with the meridional winds over the shelf sea, and with the zonal winds at the slope, while DSW layer thicknesses correlate with the meridional winds over the shelf seas and the curl of the wind stress over the slope. Locations of DSW on the continental shelf coincide with an absence of warmer CDW near the ice shelves.

Antarctica and the Southern Ocean

Abstract: Author(s): Stammerjohn, Sharon; Scambos, Ted A; Adusumilli, Susheel; Barreira, Sandra; Bernhard, Germar H; Bozkurt, Deniz; Bushinsky, Seth M; Clem, Kyle R; Colwell, Steve; Coy, Lawrence; De Laat, Jos; du Plessis, Marcel D; Fogt, Ryan L; Foppert, Annie; Fricker, Helen Amanda; Gardner, Alex S; Gille, Sarah T; Gorte, Tessa; Johnson, Bryan; Keenan, Eric; Kennett, Daemon; Keller, Linda M; Kramarova, Natalya A; Lakkala, Kaisa; Lazzara, Matthew A; Lenaerts, Jan TM; Lieser, Jan L; Li, Zhi; Liu, Hongxing; Long, Craig S; MacFerrin, Michael; Maclennan, Michelle L; Massom, Robert A; Mikolajczyk, David; Montgomery, Lynn; Mote, Thomas L; Nash, Eric R; Newman, Paul A; Petropavlovskikh, Irina; Pitts, Michael; Reid, Phillip; Rintoul, Steven R; Santee, Michelle L; Shadwick, Elizabeth H; Silvano, Alessandro; Stierle, Scott; Strahan, Susan; Sutton, Adrienne J; Swart, Sebastiaan; Tamsitt, Veronica; Tilbrook, Bronte; Wang, Lei; Williams, Nancy L; Yuan, Xiaojun

Auto-Zeroing Static Phase Offset in DLLs Using a Digitally Programmable Sensing Circuit

Abstract: This brief presents a static phase offset (SPO) reduction technique through auto-zeroing in a delay-locked loop (DLL). We propose a self-calibrated, digitally programmable, sensing circuit that can measure both the polarity and the magnitude of the SPO. The SPO is suppressed by tuning a pair of digital-to-time converters (DTCs) at the input of the phase frequency detector (PFD). The proposed technique enables run-time background calibration and can suppress the SPO caused by artifacts from the PFD, charge pump, and loop filter capacitor. Monte Carlo simulation results show that the SPO in a conventional DLL implementation improves from 12.92 ps to 0.90 ps when the proposed auto-zeroing technique is employed.

Environmental effects of ozone depletion, UV radiation and interactions with climate change: UNEP Environmental Effects Assessment Panel, update 2017

Abstract: This assessment, by the United Nations Environment Programme (UNEP) Environmental Effects Assessment Panel (EEAP), one of three Panels informing the Parties to the Montreal Protocol, provides an update, since our previous extensive assessment (Photochem. Photobiol. Sci., 2019, 18, 595-828), of recent findings of current and projected interactive environmental effects of ultraviolet (UV) radiation, stratospheric ozone, and climate change. These effects include those on human health, air quality, terrestrial and aquatic ecosystems, biogeochemical cycles, and materials used in construction and other services. The present update evaluates further evidence of the consequences of human activity on climate change that are altering the exposure of organisms and ecosystems to UV radiation. This in turn reveals the interactive effects of many climate change factors with UV radiation that have implications for the atmosphere, feedbacks, contaminant fate and transport, organismal responses, and many outdoor materials including plastics, wood, and fabrics. The universal ratification of the Montreal Protocol, signed by 197 countries, has led to the regulation and phase-out of chemicals that deplete the stratospheric ozone layer. Although this treaty has had unprecedented success in protecting the ozone layer, and hence all life on Earth from damaging UV radiation, it is also making a substantial contribution to reducing climate warming because many of the chemicals under this treaty are greenhouse gases.

State of the Climate in 2019

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Age and composition of Antarctic bedrock reflected by detrital zircons, erratics, and recycled microfossils in the Prydz Bay-Wilkes Land-Ross Sea-Marie Byrd Land sector (70°-240°E)

Abstract: The age and composition of the 14 × 10 6 km 2 of Antarctica's surface obscured by ice is unknown except for some dates on detrital minerals. In remedy, we bring together proxies of Antarctic bedrock in the form of (1) detrital zircons analysed for U–Pb age, T DM C , eHf, and rock type, including five new analyses of Neogene turbidites, (2) erratics that reflect age, composition, and metamorphism, and (3) recycled microfossils that reflect age, facies, and metamorphism. Each sample is located in its ice-drainage basin for backtracking to the potential provenance. Gaps in age between sample and upslope exposure are specifically attributable to the provenance. This work indicates that the central Antarctic provenance about a core of the Gamburtsev Subglacial Mountains (GSM) and Vostok Subglacial Highlands (VSH) contains a basement that includes igneous (mafic granitoids) and metamorphic rocks with peak U–Pb ages of 0.5–0.7, 0.9–1.3, 1.4–1.7, 1.9–2.1, 2.2–2.3, 2.6–2.8, and 3.15–3.35 Ga, T DM C 1.3–3.6 Ga, and eHf + 12 to − 40. Other modelled cratons with similar ages are set in a matrix of foldbelts of 0.5–0.7 Ga age. The basement in the core is surmounted by Permian red beds, at the periphery by Permian and Triassic sedimentary rocks unaffected by igneous heating or load metamorphism, and west of the Transantarctic Mountains (TAM) in the Wilkes Basin arguably by Late Cretaceous through Pliocene marine sediments. Erratics of undated red sandstone along the coast of Wilkes Land and George V Land indicate a red-bed provenance in the interior. The Prince Charles Mountains (PCM) provide an exposed example of a crust of Precambrian igneous and metamorphic rocks and Permian and Triassic sedimentary rocks.

New Issues in Polar Tourism : Communities, Environments, Politics

Abstract: 1. Introduction: New Issues in Polar Tourism Dieter K. Muller*, Linda Lundmark & Raynald H. Lemelin 2. Looking Back, Venturing Forward: Challenges For Academia, Community and Industry in Polar Tourism Research Patrick T. Maher* 3. What is Arctic Tourism, and Who Should Define It? Arvid Viken* 4. Narrative Frameworks of Consideration: Horizontal and Vertical Approaches to Conceptualising the Sub-Antarctic Eric J. Shelton* 5. Reaching Consensus on Antarctic Tourism Regulation Kees Bastmeijer & Machiel Lamers* 6. The Effectiveness of Environmental Impact Assessments on Visitor Activity in the Ross Sea Region of Antarctica Tanya A. O'Neill*, Megan R. Balks & Jeronimo Lopez-Martinez 7. German Tourism Activities in the Antarctic Area - A Governmental Perspective Manuela Krakau & Heike Herata* 8. The Wild North - Network Cooperation for Sustainable Tourism in a Fragile Marine Environment in the Arctic Region Sandra Magdalena Granquist & Per Ake Nilsson* 9. Tourism Resolving Crisis? Exploring Tourism Development in Iceland in the Wake of Economic Recession Gunnar Thor Johannesson* & Edward H. Huijbens 10. A (Ski) Trip into the Future - Climate Change and Winter Tourism in Polar Sweden in 2040 Patrick Brouder & Linda Lundmark* 11. Conflicting Discourses in Tourism Development - A Case of Kilpisjarvi Village, Finnish Lapland Tuukka Makitie & Anna-Liisa Ylisirnio* 12. Will 'Free Entry into the Forest' Remain? Argumentation Analysis of Finnish and Swedish Discussions on Everyman's Rights Seija Tuulentie* & Outi Rantala 13. National Parks for Tourism Development in Sub-Arctic Areas - Curse or Blessing? The Case of a Proposed National Park in Northern Sweden Dieter K. Muller* 14. Indigenous People: Discussing the Forgotten Dimension of Dark Tourism and Battlefield Tourism Raynald H. Lemelin*, Anna Thompson-Carr, Margaret Johnston, Emma Stewart & Jackie Dawson 15. New Issues in Polar Tourism: Conclusion Linda Lundmark, Raynald H. Lemelin & Dieter K. Muller* Index

Age and composition of Antarctic sub-glacial bedrock reflected by detrital zircons, erratics, and recycled microfossils in the Ellsworth Land–Antarctic Peninsula–Weddell Sea–Dronning Maud Land sector (240°E–0°–015°E)

Abstract: The age and composition of the 14 × 10 6 km 2 of Antarctica's surface obscured by ice is unknown except for some dated detrital minerals and erratics. In remedy, we present four new analyses (U–Pb age, T DM C , eHf, and rock type) of detrital zircons from Neogene turbidites as proxies of Antarctic bedrock, and review published proxies: detrital hornblendes analysed for Ar–Ar age and bulk Sm–Nd isotopes; Pb isotope compositions of detrital K-feldspars; erratics and dropstones that reflect age and composition; and recycled microfossils that reflect age and facies. This work deals with the 240°E–0°–015°E sector, and complements Veevers and Saeed's (2011) analysis of the 70°E–240°E sector. Each sample is located in its ice-drainage basin for backtracking to the potential provenance. Gaps in age between sample and upslope exposure are specifically attributable to the provenance. The major provenance of detritus west of the Antarctic Peninsula (AP) is West Antarctica, and of detritus east of the AP East Antarctica. We confirm that the Central Antarctic provenance about a core of the Gamburtsev Subglacial Mountains (GSM) and the Vostok Subglacial Highlands (VSH) contains a basement that includes igneous (mafic granitoids) and metamorphic rocks with peak U–Pb ages of 0.65–0.50, 1.20–0.9, 2.1–1.9, 2.8–2.6, and 3.35–3.30 Ga, T DM C of 3.6–1.3 Ga, and mainly negative eHf. The potential provenance of zircons of 650–500 Ma age with T DM C ages of 1.55 Ga, and of zircons of 1200–900 Ma age with positive eHf lies beneath the ice in East Antarctica south and southeast of Dronning Maud Land within the Antarctic part of the East African–Antarctic Orogen. Zircons with the additional ages of 1.7–1.4 Ga, 2.1–1.9 Ga, and 3.35–3.00 Ga have a potential provenance in the GSM.