55 research outputs found
Inland dunes on the abandoned bed of Glacial Lake Chicago indicate eolian activity during the Pleistocene-Holocene transition, southwestern Michigan, USA
Inland dune fields have recently emerged as a source of data for reconstructing paleoenvironments and climate in the western Great Lakes region of North America during the Pleistocene-Holocene transition. We employ optically stimulated luminescence (OSL) methods, radiocarbon ages, soils, and landform relationships to determine the age of inland dunes in Ottawa County, Michigan. These dunes rest on the abandoned bed of Glacial Lake Chicago, which is thought to have been exposed after ~13.6 ka. OSL analyses from two inland dunes yield ages ranging from 13.3±1.1 to 11.6±0.9 ka (uncertainty = 2 σ). Fine sand in the parabolic dunes suggests deflation of exposed glaciolacustrine nearshore sand by northwesterly and westerly winds. These new data add to a growing number of studies that demonstrate widespread eolian activity in the western Great Lakes region during the Pleistocene-Holocene transition. OSL ages from dune fields in the western Great Lakes indicate peak eolian activity and dune stabilization occurred during or following the Younger Dryas and Preboreal events. Northwesterly and westerly winds suggest the limited effect of hypothesized easterly anticyclonic winds during the Pleistocene-Holocene transition. Rapidly changing climate and newly deglaciated surfaces provided an ideal environment for dune formation
Calibration and performance of the ISO Long-Wavelength Spectrometer
The wavelength and flux calibration, and the in-orbit performance of the Infrared Space Observatory Long-Wavelength Spectrometer (LWS) are described. The LWS calibration is mostly complete and the instrument's performance in orbit is largely as expected before launch. The effects of ionising radiation on the detectors, and the techniques used to minimise them are outlined. The overall sensitivity figures achieved in practice are summarised. The standard processing of LWS data is described
Calibration and performance of the ISO Long-Wavelength Spectrometer
The wavelength and flux calibration, and the in-orbit performance of the Infrared Space Observatory Long-Wavelength Spectrometer (LWS) are described. The LWS calibration is mostly complete and the instrument's performance in orbit is largely as expected before launch. The effects of ionising radiation on the detectors, and the techniques used to minimise them are outlined. The overall sensitivity figures achieved in practice are summarised. The standard processing of LWS data is described
The Preclinical Natural History of Serous Ovarian Cancer: Defining the Target for Early Detection
Pat Brown and colleagues carry out a modeling study and define what properties a biomarker-based screening test would require in order to be clinically useful
PDRs4All IV. An embarrassment of riches: Aromatic infrared bands in the Orion Bar
(Abridged) Mid-infrared observations of photodissociation regions (PDRs) are
dominated by strong emission features called aromatic infrared bands (AIBs).
The most prominent AIBs are found at 3.3, 6.2, 7.7, 8.6, and 11.2 m. The
most sensitive, highest-resolution infrared spectral imaging data ever taken of
the prototypical PDR, the Orion Bar, have been captured by JWST. We provide an
inventory of the AIBs found in the Orion Bar, along with mid-IR template
spectra from five distinct regions in the Bar: the molecular PDR, the atomic
PDR, and the HII region. We use JWST NIRSpec IFU and MIRI MRS observations of
the Orion Bar from the JWST Early Release Science Program, PDRs4All (ID: 1288).
We extract five template spectra to represent the morphology and environment of
the Orion Bar PDR. The superb sensitivity and the spectral and spatial
resolution of these JWST observations reveal many details of the AIB emission
and enable an improved characterization of their detailed profile shapes and
sub-components. While the spectra are dominated by the well-known AIBs at 3.3,
6.2, 7.7, 8.6, 11.2, and 12.7 m, a wealth of weaker features and
sub-components are present. We report trends in the widths and relative
strengths of AIBs across the five template spectra. These trends yield valuable
insight into the photochemical evolution of PAHs, such as the evolution
responsible for the shift of 11.2 m AIB emission from class B in
the molecular PDR to class A in the PDR surface layers. This
photochemical evolution is driven by the increased importance of FUV processing
in the PDR surface layers, resulting in a "weeding out" of the weakest links of
the PAH family in these layers. For now, these JWST observations are consistent
with a model in which the underlying PAH family is composed of a few species:
the so-called 'grandPAHs'.Comment: 25 pages, 10 figures, to appear in A&
PDRs4All II: JWST's NIR and MIR imaging view of the Orion Nebula
The JWST has captured the most detailed and sharpest infrared images ever
taken of the inner region of the Orion Nebula, the nearest massive star
formation region, and a prototypical highly irradiated dense photo-dissociation
region (PDR). We investigate the fundamental interaction of far-ultraviolet
photons with molecular clouds. The transitions across the ionization front
(IF), dissociation front (DF), and the molecular cloud are studied at
high-angular resolution. These transitions are relevant to understanding the
effects of radiative feedback from massive stars and the dominant physical and
chemical processes that lead to the IR emission that JWST will detect in many
Galactic and extragalactic environments. Due to the proximity of the Orion
Nebula and the unprecedented angular resolution of JWST, these data reveal that
the molecular cloud borders are hyper structured at small angular scales of
0.1-1" (0.0002-0.002 pc or 40-400 au at 414 pc). A diverse set of features are
observed such as ridges, waves, globules and photoevaporated protoplanetary
disks. At the PDR atomic to molecular transition, several bright features are
detected that are associated with the highly irradiated surroundings of the
dense molecular condensations and embedded young star. Toward the Orion Bar
PDR, a highly sculpted interface is detected with sharp edges and density
increases near the IF and DF. This was predicted by previous modeling studies,
but the fronts were unresolved in most tracers. A complex, structured, and
folded DF surface was traced by the H2 lines. This dataset was used to revisit
the commonly adopted 2D PDR structure of the Orion Bar. JWST provides us with a
complete view of the PDR, all the way from the PDR edge to the substructured
dense region, and this allowed us to determine, in detail, where the emission
of the atomic and molecular lines, aromatic bands, and dust originate
PDRs4All III: JWST's NIR spectroscopic view of the Orion Bar
(Abridged) We investigate the impact of radiative feedback from massive stars
on their natal cloud and focus on the transition from the HII region to the
atomic PDR (crossing the ionisation front (IF)), and the subsequent transition
to the molecular PDR (crossing the dissociation front (DF)). We use
high-resolution near-IR integral field spectroscopic data from NIRSpec on JWST
to observe the Orion Bar PDR as part of the PDRs4All JWST Early Release Science
Program. The NIRSpec data reveal a forest of lines including, but not limited
to, HeI, HI, and CI recombination lines, ionic lines, OI and NI fluorescence
lines, Aromatic Infrared Bands (AIBs including aromatic CH, aliphatic CH, and
their CD counterparts), CO2 ice, pure rotational and ro-vibrational lines from
H2, and ro-vibrational lines HD, CO, and CH+, most of them detected for the
first time towards a PDR. Their spatial distribution resolves the H and He
ionisation structure in the Huygens region, gives insight into the geometry of
the Bar, and confirms the large-scale stratification of PDRs. We observe
numerous smaller scale structures whose typical size decreases with distance
from Ori C and IR lines from CI, if solely arising from radiative recombination
and cascade, reveal very high gas temperatures consistent with the hot
irradiated surface of small-scale dense clumps deep inside the PDR. The H2
lines reveal multiple, prominent filaments which exhibit different
characteristics. This leaves the impression of a "terraced" transition from the
predominantly atomic surface region to the CO-rich molecular zone deeper in.
This study showcases the discovery space created by JWST to further our
understanding of the impact radiation from young stars has on their natal
molecular cloud and proto-planetary disk, which touches on star- and planet
formation as well as galaxy evolution.Comment: 52 pages, 30 figures, submitted to A&
Preliminary results of a study of sapping valleys in Ottawa County, Michigan
Sapping valleys are valleys eroded by springs and their streams and contribute to water resources and landscape evolution. Springs along the Pigeon River, in western Ottawa County, erode dune sand and form numerous small valleys with the signature amphitheater shape of previously documented sapping valleys. These springs are important for providing clean and cool water for micro-environments and the larger watershed. We investigate whether small valleys in Hemlock Crossing Park were formed by spring sapping, and document and quantify sapping processes that include spring discharge and sediment transport.
A detailed geomorphic map and topographic profile of one small valley was created using a Trimble M3 total station and data were mapped in ArcMap 10.3. A high resolution digital elevation model, our geomorphic map, and topographic profiles were then compared to previously described sapping valleys, to distinguish common morphologic traits and test whether this small valley is likely formed by sapping processes. Spring discharge was estimated and monitored with staff gauges, and a 90-degree notch weir. Two sets of nested wells were installed at the heads of two small valleys near spring heads. Staff gauges and wells were monitored from May to August of 2018. HOBO© and Odyssey© data loggers were deployed in the nested wells and stream beds to monitor hydraulic head, water temperature, and conductivity at ~30-minute intervals over the ~4 month period. Bedload transport was estimated using sediment traps and bedload virtual velocimetry determined from GoPro time-lapse images.
Three small valleys at Hemlock Crossing Park possess most criteria previously described for sapping valleys. The valleys possess seven out of the eleven characteristics including: light-bulb shape of basin, low basin-area to canyon- area ratio, theater or cirque-like valley heads, steep valley walls and flat valley floors, dendritic drainage pattern, and high tributary junction angles with the main trunk stream. We observed only small daily and seasonal variations in hydraulic head, temperature, discharge, conductivity, and stage in the springs and their streams. The hydraulic head and stream discharge increased in early May and then steadily declined from late May to late August. Temperature of the groundwater increased gradually over May to August. One set of nested wells (site #2) indicated a gradual overall decline of upward gradient, while the gradient in another set of nested wells (site #1) declined more rapidly, until it was zero by mid-August. Because of an increase in precipitation at the end of August, the gradient at site #1, indicating recharge of the aquifer. The wells at site #2 show a decline in gradient, but the groundwater still flowed upward at the end of August.
Daily water level variations in wells can be explained by diurnal cycles in transpiration rates of the forest cover. Seasonal variations are hypothesized to depend on seasonal recharge rates of the shallow aquifer and the inherent lag times of the aquifer system. Bedload transport rates are notoriously difficult to estimate, but our virtual velocimetry measurements and volumetric sediment transport calculations suggest that valley volumes could be excavated given the rates we calculated. We observed very low bedload transport rates during the month of August. The flow at that time was so low that little bedload was being transported. We interpret that these valleys are being formed by spring sapping based upon their morphology, and their observed discharge of water and sediment. These springs and sapping valleys provide cool, moist, and moderating micro-environments for plants and animals along the Pigeon River and are important controls on surface water temperature and chemistry
A numerical investigation of ice-lobe–permafrost interaction around the southern Laurentide ice sheet
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