117 research outputs found
Workshop on Science Opportunities for a Multidisciplinary Long-Range Aircraft for Antarctic Research: Program and Abstract Volume
No full textOrganizing Committee: Bea Csatho, David H. Bromwich, Michael Studinger, Thomas R. Parish, Robin Muench, and Jeff StithOffice of Polar Programs, National Science Foundatio
Point: Counterpoint: Cardiovascular variability is/is not an index of autonomic control of circulation
No full textThis series of debates was initiated for the Journal of Applied Physiology because we believe an important means of searching for truth is through debate where contradictory viewpoints are put forward. This dialectic process whereby a thesis is advanced, then opposed by an antithesis, with a synthesis subsequently arrived at, is a powerful and often entertaining method for gaining knowledge and for understanding the source of a controversy. Before reading these Point: Counterpoint manuscripts or preparing a brief commentary on their content (see below for instructions), the reader should understand that authors on each side of the debate are expected to advance a polarized viewpoint and to select the most convincing data to support their position. This approach differs markedly from the review article where the reader expects the author to present balanced coverage of the topic. Each of the authors has been strictly limited in the lengths of both the manuscript (1,200 words) and the rebuttal (400). The number of references to publications is also limited to 30, and citation of unpublished findings is prohibited
Influx of meltwater to subglacial Lake Concordia, East Antarctica
No full textWe present evidence for melting at the base of the ice that overlies Lake Concordia, an 800 km2 subglacial lake near Dome Concordia, East Antarctica, via a combination of glaciohydraulic melting (associated with the tilted ice ceiling and its influence on lake circulation/melting temperature) and melting by extreme strain heating (where the ice sheet is grounded). An influx of water is necessary to provide nutrients, material and biota to support subglacial lake ecosystems but has not been detected previously. Freezing is the dominant observed basal process at over 60% of the surface area above the lake. The total volume of accreted ice above the lake surface is estimated as 50-60 km3, roughly 25-30% of the 200 ± 40 km3 estimated lake volume. Estimated rates of melting and freezing are very similar, ±2-6 mm a−1. The apparent net freezing may reflect the present-day response of Lake Concordia to cooling associated with the Last Glacial Maximum, or a large influx of water either via a subglacial hydrological system or from additional melting of the ice sheet. Lake Concordia is an excellent candidate for subglacial exploration given active basal processes, proximity to the Dome Concordia ice core and traverse resupply route
Rift in Antarctic Glacier: A Unique Chance to study Ice Shelf Retreat
No full textIt happened again, but this time it was caught in the act. During the last week of September 2011 a large transverse rift developed across thefloating terminus of West Antarcticas PineIsland Glacier, less than 5 years after its lastlarge calving event, in 2007 (Figure 1). PineIsland Glaciers retreat has accelerated substantiallyin the past 2 decades, and it is nowlosing 50 gigatons of ice per year, or roughly 25 of Antarcticas total annual contributionto sea level rise [Rignot et al., 2008]. The glaciers recent accelerated retreat is likely triggered by ocean warming and increased submarine melting. As such, it is of significant interest to glaciologists and of heightened societal relevance
Tectonically controlled subglacial lakes on the flanks of the Gamburtsev Subglacial Mountains, East Antarctica
No full textThe morphology of surface lakes strongly influences their ecology and limnology (Wetzel, 2001). This morphology is a result of both the geologic processes that produce topographic basins and the regional climatic and local hydrologic processes that control water depth and sediment infilling (Carroll and Bohacs, 1999). Although basin forming processes range from glacial scour to meteorite impacts (Cohen, 2003), the deepest, oldest surface lakes are tectonically controlled (Meybeck, 1995) and contain diverse exotic ecosystems (Rossiterm and Kawanabe, 2000). Subglacial lakes are also thought to be ancient systems that may contain exotic biota (Bulat et al., 2004; Karl et al., 1999; Priscu et al., 1999). Here we present evidence for the scale and configuration of 2 large subglacial lakes in East Antarctica that together with Lake Vostok define a province of major lakes on the flanks of the Gamburtsev Subglacial Mountains. Spatially-defined in the new Moderate Resolution Imaging Spectroradiometer (MODIS) imagery of Antarctica (T. Scambos et al., A MODIS-based mosaic of Antarctica: MOA, submitted to Remote Sensing of Environment, 2005, hereinafter referred to as Scambos et al., submitted manuscript, 2005), these lakes are aligned parallel to Lake Vostok. Other data shows that they are distinguished by distinct gravity lows, flat ice surface slopes and have estimated water depths of at least 900 m. Surface elevation data indicates that large deep subglacial lakes have a profound influence on the regional ice sheet topography and probably ice sheet flow. These deep subglacial lakes with elongate, rectilinear morphology are tectonically controlled features. Unlike the shallow lakes in West Antarctica and beneath Dome Concordia, these deep subglacial lakes remained stable environments through many glacial cycles since their origin 10–35 Ma enabling the development of novel ecosystems.Bell and Studinger were supported by the Doherty Endowment of LDEO and the Palisades Geophysical Institute. Fahnestock and Shuman were supported by NASA's Cryospheric program for work on mosaic production and altimetry. We thank NASA's Science Mission Directorate, Cryospheric Sciences Program, and the ICESat Mission for both support and data. The aquisition of the radar data has been supported by NSF as part of the study of Lake Vostok. We thank the NSIDC and Ted Scambos for providing data. LDEO contribution 6851.https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2005GL02520
Interpretation und Analyse von Potentialfelddaten im Weddellmeer, Antarktis: der Zerfall des Superkontinents Gondwana = Compilation and analysis of potential field data from the Weddell Sea, Antarctica: implications for the break-up of Gondwana
No full textIncorporation of particulates into accreted ice above subglacial Vostok lake, Antarctica
No full textThe nature of microscopic particulates in meteoric and accreted ice from the Vostok (Antarctica) ice core is assessed in conjunction with existing ice-core data to investigate the mechanism by which particulates are incorporated into refrozen lake water. Melted ice samples from a range of icecore depths were filtered through 0.2 m polycarbonate membranes, and secondary electron images were collected at ×500 magnification using a scanning electron microscope. Image analysis software was used to characterize the size and shape of particulates. Similar distributions of major-axis lengths, surface areas and shape factors (aspect ratio and compactness) for particulates in all accreted ice samples suggest that a single process may be responsible for incorporating the vast majority of particulates for all depths. Calculation of Stokes settling velocities for particulates of various sizes implies that 98% of particulates observed could 'float' to the ice–water interface with upward water velocities of 0.0003 m s−1 where they could be incorporated by growing ice crystals, or by rising frazil ice crystals. The presence of particulates that are expected to sink in the water column (2%) and the uneven distribution of particulates in the ice core further implies that periodic perturbations to the lake's circulation, involving increased velocities, may have occurred in the past
Crustal structure of the Filchner-Ronne Shelf and Coats Land, Antarctica, from gravity and magnetic data implications for the break-up of Gondwana
No full textA Quantum Mechanical Description of the Diffusion Properties of C1-C2 Hydrocarbon Molecules in MOF-74-Mg
No full textAmong the numerous metal organic framework (MOF) families, of significant importance is the MOF-74-M series (M = metal, -also known as CPO-27-M), characterized by a high density of not fully coordinated open metal site centers; this peculiarity has been demonstrated to translate into a higher hydrocarbons’ separation potential than other known MOFs and zeolites. To provide a more comprehensive description of the behavior of the hydrocarbon molecules within the MOF-74 cavity, diffusion processes and corresponding diffusion barriers of small hydrocarbons in the MOF-74-Mg were modeled. This work provides a description of the molecular transport processes of CH4, C2H2, C2H4 and C2H6 within and along the cavity of MOF-74-Mg; in addition, the influence of pre-adsorbed water molecules is also addressed. Density functional theory (DFT), as implemented within a plane-wave (PW) approach under periodic boundary conditions (PBC), has been used to investigate the diffusion mechanisms using the climbing-image nudge elastic band (CI-NEB) method, coupled with the van der Waals functional (vdW-DF) and ultra-soft pseudopotentials. Two transport mechanisms were identified: M1, referring to the molecular migrations within the MOF cavity; and M2, referring to the molecular migrations along the MOF longitudinal channel. The M1 transport mechanism was further analyzed to address the molecular migration from one metal atom to its adjacent one (M1a), and with respect to the second metal over (M1b). All the transport mechanisms considered show that the diffusion of paraffin molecules in MOF-74-Mg is energetically more favorable than that of olefin molecules. An interesting trend is observed across all the diffusion mechanisms where the stronger the molecule binds to the open metal site, the higher the diffusion barrier it needs to overcome. For all the small hydrocarbons considered in this study, transport mechanism M1a is significantly more energetically favorable than M1b, showing that it is easier for molecules to drift along the longitudinal cavity than to remain trapped cross-sectionally within the cavity itself. This work shows how this computational approach can be successfully applied not only to reveal the molecular transport in other MOF-74 isostructural species, but also in the fundamental understanding of the screening of MOFs and other nano-porous materials for gas separation applications
Gridded pan-Arctic total neutral atmospheric 10-m drag coefficient estimates derived from ICESat-2 ATL07 sea ice height data
No full textThis data-set contains average drag coefficient estimates for the whole of the Arctic (resampled onto a 25 km polar stereographic grid) for each month from 11.2018 to 06.2022. The total drag coefficients are referenced to a height of 10 meters and a neutrally stratified atmosphere is assumed. The total drag is the sum of open water drag scaled with (1-A) where A is sea ice concentration (Spreen et al., 2008), drag due to floe edges incorporated via a constant derived from parameterization (Lüpkes et al., 2012) and scaled with A(1-A), sea ice skin drag scaled with A, and sea ice form drag due to obstacles (e.g. ridges) computed from sea ice feature averages (Garbrecht et al., 2002) derived from ICESat-2 ATL07 sea ice heights (for all 25 km grid cells filled by ICESat-2 ATL07 data) (Kwok et al., 2021). Each individual component is also given as a separate variable in the data-set. In addition, the sea ice feature averages (10-km average obstacle height and obstacle spacing) used to derive form drag due to obstacles is also gridded and included in the data files. Obstacles below a threshold value of 20 cm and those that do not fulfill the Rayleigh Criterion (wherein if the trough between two peaks is smaller than the higher of two crests, only the higher one is considered) are omitted. Lastly, we scale up the ICESat-2 ATL07-derived form drag coefficients via a regression derived from comparing them to drag coefficients derived from topographic data collected during the 04.2019 NASA airborne Operation IceBridge ICESat-2 under-flights (Studinger, 2013). This is to deal with the sampling issues associated with resolution differences
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