42 research outputs found
Recommended from our members
Past water flow beneath Pine Island and Thwaites glaciers, West Antarctica
Abstract. Outburst floods from subglacial lakes beneath the Antarctic Ice Sheet
modulate ice-flow velocities over periods of months to years. Although
subglacial lake drainage events have been observed from
satellite-altimetric data, little is known about their role in the
long-term evolution of ice-sheet basal hydrology. Here, we
systematically map and model past water flow through an extensive area
containing over 1000 subglacial channels and 19 former lake basins exposed
on over 19 000 km2 of seafloor by the retreat of Pine Island and
Thwaites glaciers, West Antarctica. At 507 m wide and 43 m deep on average,
the channels offshore of present-day Pine Island and Thwaites glaciers
are approximately twice as deep, 3 times as wide, and cover an area over
400 times larger than the terrestrial meltwater channels comprising the
Labyrinth in the Antarctic Dry Valleys. The channels incised into bedrock
offshore of contemporary Pine Island and Thwaites glaciers would have been
capable of accommodating discharges of up to 8.8×106 m3 s−1. We suggest that the channels were formed by episodic discharges
from subglacial lakes trapped during ice-sheet advance and retreat over
multiple glacial periods. Our results document the widespread influence of
episodic subglacial drainage events during past glacial periods, in
particular beneath large ice streams similar to those that continue to
dominate contemporary ice-sheet discharge.
UK Natural Environment Research Council’s iSTAR programme (grant nos. NE/J005703/1, NE/J005746/1, and NE/J005770/1).
James D. Kirkham: Debenham Scholarship from the Scott Polar Research Institute, University of Cambridge, and a UK Natural Environment Research Council Ph.D. studentship awarded through the Cambridge Earth System Science Doctoral Training Partnership (grant no. NE/L002507/1
Revealing the former bed of Thwaites Glacier using sea-floor bathymetry: Implications for warm-water routing and bed controls on ice flow and buttressing
Abstract. The geometry of the sea floor immediately beyond
Antarctica's marine-terminating glaciers is a fundamental control on
warm-water routing, but it also describes former topographic pinning points
that have been important for ice-shelf buttressing. Unfortunately, this
information is often lacking due to the inaccessibility of these areas for
survey, leading to modelled or interpolated bathymetries being used as
boundary conditions in numerical modelling simulations. At Thwaites Glacier
(TG) this critical data gap was addressed in 2019 during the first cruise of
the International Thwaites Glacier Collaboration (ITGC) project. We present more than 2000 km2 of new multibeam
echo-sounder (MBES) data acquired in exceptional sea-ice conditions
immediately offshore TG, and we update existing bathymetric compilations.
The cross-sectional areas of sea-floor troughs are under-predicted by up to
40 % or are not resolved at all where MBES data are missing, suggesting that
calculations of trough capacity, and thus oceanic heat flux, may be
significantly underestimated. Spatial variations in the morphology of
topographic highs, known to be former pinning points for the floating ice
shelf of TG, indicate differences in bed composition that are supported by
landform evidence. We discuss links to ice dynamics for an overriding ice
mass including a potential positive feedback mechanism where erosion of
soft erodible highs may lead to ice-shelf ungrounding even with little
or no ice thinning. Analyses of bed roughnesses and basal drag contributions
show that the sea-floor bathymetry in front of TG is an analogue for extant
bed areas. Ice flow over the sea-floor troughs and ridges would have been
affected by similarly high basal drag to that acting at the grounding zone
today. We conclude that more can certainly be gleaned from these 3D
bathymetric datasets regarding the likely spatial variability of bed
roughness and bed composition types underneath TG. This work also addresses
the requirements of recent numerical ice-sheet and ocean modelling studies
that have recognised the need for accurate and high-resolution bathymetry to
determine warm-water routing to the grounding zone and, ultimately, for
predicting glacier retreat behaviour.
</jats:p
Magnetism, FeS colloids, and Origins of Life
A number of features of living systems: reversible interactions and weak
bonds underlying motor-dynamics; gel-sol transitions; cellular connected
fractal organization; asymmetry in interactions and organization; quantum
coherent phenomena; to name some, can have a natural accounting via
interactions, which we therefore seek to incorporate by expanding the horizons
of `chemistry-only' approaches to the origins of life. It is suggested that the
magnetic 'face' of the minerals from the inorganic world, recognized to have
played a pivotal role in initiating Life, may throw light on some of these
issues. A magnetic environment in the form of rocks in the Hadean Ocean could
have enabled the accretion and therefore an ordered confinement of
super-paramagnetic colloids within a structured phase. A moderate H-field can
help magnetic nano-particles to not only overcome thermal fluctuations but also
harness them. Such controlled dynamics brings in the possibility of accessing
quantum effects, which together with frustrations in magnetic ordering and
hysteresis (a natural mechanism for a primitive memory) could throw light on
the birth of biological information which, as Abel argues, requires a
combination of order and complexity. This scenario gains strength from
observations of scale-free framboidal forms of the greigite mineral, with a
magnetic basis of assembly. And greigite's metabolic potential plays a key role
in the mound scenario of Russell and coworkers-an expansion of which is
suggested for including magnetism.Comment: 42 pages, 5 figures, to be published in A.R. Memorial volume, Ed
Krishnaswami Alladi, Springer 201
Technology-dependency among patients discharged from a children's hospital: a retrospective cohort study
BACKGROUND: Advances in medical technology may be increasing the population of children who are technology-dependent (TD). We assessed the proportion of children discharged from a children's hospital who are judged to be TD, and determined the most common devices and number of prescription medications at the time of discharge. METHODS: Chart review of 100 randomly selected patients from all services discharged from a children's hospital during the year 2000. Data were reviewed independently by 4 investigators who classified the cases as TD if the failure or withdrawal of the technology would likely have adverse health consequences sufficient to require hospitalization. Only those cases where 3 or 4 raters agreed were classified as TD. RESULTS: Among the 100 randomly sampled patients, the median age was 7 years (range: 1 day to 24 years old), 52% were male, 86% primarily spoke English, and 54% were privately insured. The median length of stay was 3 days (range: 1 to 103 days). No diagnosis accounted for more than 5% of cases. 41% were deemed to be technology dependent, with 20% dependent upon devices, 32% dependent upon medications, and 11% dependent upon both devices and medications. Devices at the time of discharge included gastrostomy and jejeunostomy tubes (10%), central venous catheters (7%), and tracheotomies (1%). The median number of prescription medications was 2 (range: 0–13), with 12% of cases having 5 or more medications. Home care services were planned for 7% of cases. CONCLUSION: Technology-dependency is common among children discharged from a children's hospital
On the Origin and Trigger of the Notothenioid Adaptive Radiation
Adaptive radiation is usually triggered by ecological opportunity, arising
through (i) the colonization of a new habitat by its
progenitor; (ii) the extinction of competitors; or
(iii) the emergence of an evolutionary key innovation in
the ancestral lineage. Support for the key innovation hypothesis is scarce,
however, even in textbook examples of adaptive radiation. Antifreeze
glycoproteins (AFGPs) have been proposed as putative key innovation for the
adaptive radiation of notothenioid fishes in the ice-cold waters of Antarctica.
A crucial prerequisite for this assumption is the concurrence of the
notothenioid radiation with the onset of Antarctic sea ice conditions. Here, we
use a fossil-calibrated multi-marker phylogeny of nothothenioid and related
acanthomorph fishes to date AFGP emergence and the notothenioid radiation. All
time-constraints are cross-validated to assess their reliability resulting in
six powerful calibration points. We find that the notothenioid radiation began
near the Oligocene-Miocene transition, which coincides with the increasing
presence of Antarctic sea ice. Divergence dates of notothenioids are thus
consistent with the key innovation hypothesis of AFGP. Early notothenioid
divergences are furthermore congruent with vicariant speciation and the breakup
of Gondwana
Neuron-glial Interactions
Although lagging behind classical computational neuroscience, theoretical and computational approaches are beginning to emerge to characterize different aspects of neuron-glial interactions. This chapter aims to provide essential knowledge on neuron-glial interactions in the mammalian brain, leveraging on computational studies that focus on structure (anatomy) and function (physiology) of such interactions in the healthy brain. Although our understanding of the need of neuron-glial interactions in the brain is still at its infancy, being mostly based on predictions that await for experimental validation, simple general modeling arguments borrowed from control theory are introduced to support the importance of including such interactions in traditional neuron-based modeling paradigms.Junior Leader Fellowship Program by “la Caixa” Banking Foundation (LCF/BQ/LI18/11630006
Tectonic Reconstructions of the Southernmost Andes and the Scotia Sea During the Opening of the Drake Passage
Study of the tectonic development of the Scotia Sea region started with basic lithological and structural studies of outcrop geology in Tierra del Fuego and the Antarctic Peninsula. To nineteenth- and early twentieth-century geologists, the results of these studies suggested the presence of a submerged orocline running around the margins of the Scotia Sea. Subsequent increases in detailed knowledge about the fragmentary outcrop geology from islands distributed around the margins of the Scotia Sea, and later their interpretation in the light of the plate tectonic paradigm led to large modifications in the hypothesis such that by the present day the concept of oroclinal bending in the region persists only in vestigial form. Of the early comparative lithostratigraphic work in the region, only the likenesses between Jurassic–Cretaceous basin floor and fill sequences in South Georgia and Tierra del Fuego are regarded as strong enough to be useful in plate kinematic reconstruction by permitting the interpretation of those regions’ contiguity in mid-Mesozoic times. Marine and satellite geophysical data sets reveal features of the remaining, submerged, 98 % of the Scotia Sea region between the outcrops. These data enable a more detailed and quantitative approach to the region’s plate kinematics. In contrast to long-used interpretations of the outcrop geology, these data do not prescribe the proximity of South Georgia to Tierra del Fuego in any past period. It is, however, possible to reinterpret the geology of those two regions in terms of the plate kinematic history that the seafloor has preserved
Neuron-Glial Interactions
Although lagging behind classical computational neuroscience, theoretical and
computational approaches are beginning to emerge to characterize different
aspects of neuron-glial interactions. This chapter aims to provide essential
knowledge on neuron-glial interactions in the mammalian brain, leveraging on
computational studies that focus on structure (anatomy) and function
(physiology) of such interactions in the healthy brain. Although our
understanding of the need of neuron-glial interactions in the brain is still at
its infancy, being mostly based on predictions that await for experimental
validation, simple general modeling arguments borrowed from control theory are
introduced to support the importance of including such interactions in
traditional neuron-based modeling paradigms.Comment: 43 pages, 2 figures, 1 table. Accepted for publication in the
"Encyclopedia of Computational Neuroscience," D. Jaeger and R. Jung eds.,
Springer-Verlag New York, 2020 (2nd edition