Local ice caps in Finderup Land,North Greenland,survived the Holocene Thermal Maximum

Local glaciers and ice caps (GICs) comprise only ~5.4% of the total ice volume, but account for ~14–20% of the current ice loss in Greenland. The glacial history of GICs is not well constrained, however, and little is known about how they reacted to Holocene climate changes. Specifically, in North Greenland, there is limited knowledge about past GIC fluctuations and whether they survived the Holocene Thermal Maximum (HTM, ~8 to 5 ka). In this study, we use proglacial lake records to constrain the ice‐marginal fluctuations of three local ice caps in North Greenland including Flade Isblink, the largest ice cap in Greenland. Additionally, we have radiocarbon dated reworked marine molluscs in Little Ice Age (LIA) moraines adjacent to the Flade Isblink, which reveal when the ice cap was smaller than present. We found that outlet glaciers from Flade Isblink retreated inland of their present extent from ~9.4 to 0.2 cal. ka BP. The proglacial lake records, however, demonstrate that the lakes continued to receive glacial meltwater throughout the entire Holocene. This implies that GICs in Finderup Land survived the HTM. Our results are consistent with other observations from North Greenland but differ from locations in southern Greenland where all records show that the local ice caps at low and intermediate elevations disappeared completely during the HTM. We explain the north–south gradient in glacier response as a result of sensitivity to increased temperature and precipitation. While the increased temperatures during the HTM led to a complete melting of GICs in southern Greenland, GICs remained in North Greenland probably because the melting was counterbalanced by increased precipitation due to a reduction in Arctic sea‐ice extent and/or increased poleward moisture transport.     

Wetland hydroperiod classification in the western prairies using multitemporal synthetic aperture radar

Wetlands represent one of the world's most biodiverse and threatened ecosystem types and were diminished globally by about two‐thirds in the 20th century. There is continuing decline in wetland quantity and function due to infilling and other human activities. In addition, with climate change, warmer temperatures and changes in precipitation and evapotranspiration are reducing wetland surface and groundwater supplies, further altering wetland hydrology and vegetation. There is a need to automate inventory and monitoring of wetlands, and as a study system, we investigated the Shepard Slough wetlands complex, which includes numerous wetlands in urban, suburban, and agricultural zones in the prairie pothole region of southern Alberta, Canada. Here, wetlands are generally confined to depressions in the undulating terrain, challenging wetlands inventory and monitoring. This study applied threshold and frequency analysis routines for high‐resolution, single‐polarization (HH) RADARSAT‐2, synthetic aperture radar mapping. This enabled a growing season surface water extent hyroperiod‐based wetland classification, which can support water and wetland resource monitoring. This 3‐year study demonstrated synthetic aperture radar‐derived multitemporal open‐water masks provided an effective index of wetland permanence class, with overall accuracies of 89% to 95% compared with optical validation data, and RMSE between 0.2 and 0.7 m between model and field validation data. This allowed for characterizing the distribution and dynamics of 4 marsh wetlands hydroperiod classes, temporary, seasonal, semipermanent, and permanent, and mapping of the sequential vegetation bands that included emergent, obligate wetland, facultative wetland, and upland plant communities. Hydroperiod variation and surface water extent were found to be influenced by short‐term rainfall events in both wet and dry years. Seasonal hydroperiods in wetlands were particularly variable if there was a decrease in the temporary or semipermanent hydroperiod classes. In years with extreme rain events, the temporary wetlands especially increased relative to longer lasting wetlands (84% in 2015 with significant rainfall events, compared with 42% otherwise).     

The isotopic signature of monsoon conditions,cloud modes,and rainfall type

This work provides a comprehensive physically based framework for the interpretation of the north Australian rainfall stable isotope record (δ¹⁸O and δ²H). Until now, interpretations mainly relied on statistical relationships between rainfall amount and isotopic values on monthly timescales. Here, we use multiseason daily rainfall stable isotope and high resolution (10 min) ground‐based C‐band polarimetric radar data and show that the five weather types (monsoon regimes) that constitute the Australian wet season each have a characteristic isotope ratio. The data suggest that this is not only due to changes in regional rainfall amount during these regimes but, more importantly, is due to different rain and cloud types that are associated with the large scale circulation regimes. Negative (positive) isotope anomalies occurred when stratiform rainfall fractions were large (small) and the horizontal extent of raining areas were largest (smallest). Intense, yet isolated, convective conditions were associated with enriched isotope values whereas more depleted isotope values were observed when convection was widespread but less intense. This means that isotopic proxy records may record the frequency of which these typical wet season regimes occur. Positive anomalies in paleoclimatic records are most likely associated with periods where continental convection dominates and convection is sea‐breeze forced. Negative anomalies may be interpreted as periods when the monsoon trough is active, convection is of the oceanic type, less electric, and stratiform areas are wide spread. This connection between variability of rainfall isotope anomalies and the intrinsic properties of convection and its large‐scale environment has important implications for all fields of research that use rainfall stable isotopes.     

Analytical study of ground motion caused by seismic wave propagation across faulted rock masses

Studying seismic wave propagation across rock masses and the induced ground motion is an important topic, which receives considerable attention in design and construction of underground cavern/tunnel constructions and mining activities. The current study investigates wave propagation across a rock mass with one fault and the induced ground motion using a recursive approach. The rocks beside the fault are assumed as viscoelastic media with seismic quality factors, Q_p and Q_s. Two kinds of interactions between stress waves and a discontinuity and between stress waves and a free surface are analyzed, respectively. As the result of the wave superposition, the mathematical expressions for induced ground vibration are deduced. The proposed approach is then compared with the existing analysis for special cases. Finally, parametric studies are carried out, which includes the influences of fault stiffness, incident angle, and frequency of incident waves on the peak particle velocities of the ground motions.     

Micromechanical approach to effective viscoelastic properties of micro‐fractured geomaterials

The aim of this paper is to formulate a micromechanics‐based approach to non‐aging viscoelastic behavior of materials with randomly distributed micro‐fractures. Unlike cracks, fractures are discontinuities that are able to transfer stresses and can therefore be regarded from a mechanical viewpoint as interfaces endowed with a specific behavior under normal and shear loading. Making use of the elastic‐viscoelastic correspondence principle together with a Mori‐Tanka homogenization scheme, the effective viscoelastic behavior is assessed from properties of the material constituents and damage parameters related to density and size of fractures. It is notably shown that the homogenized behavior thus formulated can be described in most cases by means of a generalized Maxwell rheological model. For practical implementation in structural analyses, an approximate model for the isotropic homogenized fractured medium is formulated within the class of Burger models. Although the approximation is basically developed for short‐term and long‐term behaviors, numerical applications indicate that the approximate Burger model accurately reproduce the homogenized viscoelastic behavior also in the transient conditions.     

Symplectic Mappings of Co-orbital Motion in the Restricted Problem of Three Bodies

The dynamics of co-orbital motion in the restricted three-body problem are investigated by symplectic mappings. Analytical and semi-numerical mappings have been developed and studied in detail. The mappings have been tested by numerical integration of the equations of motion. These mappings have been proved to be useful for a quick determination of the phase space structure reflecting the main characteristics of the dynamics of the co-orbital problem.     

Subglacial and subaqueous processes near a glacier grounding line: sedimentological evidence from a former ice-dammed lake, Achnasheen Scotland

Subglacial and subaqueous sediments deposited near the margin of a Late-glacial ice-dammed lake near Achnasheen, northern Scotland, are described and interpreted. The subglacial sediments consist of deformation tills and glacitectonites derived from pre-existing glaciolacustrine deposits, and the subaqueous sediments consist of ice-proximal outwash and sediment flow deposits, and distal turbidites. Sediment was delivered from the glacier to the lake by two main processes: (1) subglacial till deformation, which fed debris flows at the grounding line; and (2) meltwater transport, which fed sediment-gravity flows on prograding outwash fans. Beyond the ice-marginal environment, deposition was from turbidity currents, ice-rafting and settling of suspended sediments. The exposures support the conclusion that the presence of a subglacial deforming layer can exert an important influence on sedimentation at the grounding lines of calving glaciers.     

Spatial measurements of stream baseflow,a relevant method for aquifer characterization and permeability evaluation. Application to a hard‐rock aquifer,the Oman ophiolite

The structure, functioning and hydrodynamic properties of aquifers can be determined from an analysis of the spatial variability of baseflow in the streams with which they are associated. Such analyses are based on simple low‐cost measurements. Through interpreting the hydrological profiles (Q = f(A)) it is possible to locate the aquifer(s) linked to the stream network and to determine the type of interrelated flow, i.e. whether the stream drains or feeds the aquifer. Using an analytical solution developed for situations with a positive linear relationship, i.e. where the baseflow increases linearly with increasing catchment size, it is also possible to estimate the permeability of the aquifer(s) concerned at catchment scale. Applied to the hard‐rock aquifers of the Oman ophiolite, this method shows that the ‘gabbro’ aquifer is more permeable than the ‘peridotite’ aquifer. As a consequence the streams drain the peridotites and ‘leak’ into the gabbro. The hydrological profiles within the peridotite are linear and positive, and indicate homogeneity in the hydrodynamic properties of these formations at the kilometre scale. The permeability of the peridotite is estimated at 5 · 10^?7 to 5 · 10^?8 m/s. Copyright © 2004 John Wiley & Sons, Ltd.     

A measurement of the 362 GHz absorption line of Mars atmospheric H2O2

The 362.156 GHz absorption spectrum of H₂O₂ in the Mars atmosphere was observed on September 4 of 2003, employing the James Clerk Maxwell Telescope (JCMT) sub-millimeter facility on Mauna Kea, Hawaii. Radiative transfer analysis of this line absorption yields an average volume mixing ratio of 18±0.4 ppbv within the lower (0-30 km) Mars atmosphere, in general accordance with standard photochemical models (e.g., Nair et al., 1994, Icarus 111, 124-150). Our derived H₂O₂ abundance is roughly three times greater than the upper limit retrieved by Encrenaz et al. (2002, Astron. Astrophys. 396, 1037-1044) from infrared spectroscopy, although part of this discrepancy may result from the different solar longitudes (L_s) of observation. Aphelion-to-perihelion thermal forcing of the global Mars hygropause generates substantial (>200%) increases in HO_x abundances above ∼10 km altitudes between the L_s=112° period of the Encrenaz et al. upper limit measurement and the current L_s=250° period of detection (Clancy and Nair, 1996, J. Geophys. Res. 101, 12785-12590). The observed H₂O₂ line absorption weakens arguments for non-standard homogeneous (Encrenaz et al., 2002, Astron. Astrophys. 396, 1037-1044) or heterogeneous (Krasnopolsky, 2003a, J. Geophys. Res. 108; 2003b, Icarus 165, 315-325) chemistry, which have been advocated partly on the basis of infrared (8 μm) non-detections for Mars H₂O₂. Observation of Mars H₂O₂ also represents the first measurement of a key catalytic specie in a planetary atmosphere other than our own.