In August 1978, a large tundra lake was drained to study the aggradation of permafrost into newly exposed lake-bottom sediments. Ice-wedge growth, which started in the first winter following ...drainage, had ceased in most of the lake bottom within about twelve years. The gradual cessation of thermal contraction cracking can be attributed to rapid vegetation growth, snow entrapment, an increase in winter ground temperatures, and a decrease in the linear coefficient of thermal contraction associated with freeze-thaw consolidation of the initially saturated lake-bottom sediments. The tilt and separation of markers in the active layer revealed gradual convergence towards the troughs even after ice-wedge growth had ceased. For the first few years the ice-wedge growth rate was up to 3 cm/a as determined by excavation, drilling, separation of the bottoms of benchmarks installed into permafrost, and divergence of free-floating inductance coils placed on the sides of ice wedges well below the bottom of the active layer. The vertical extent of most ice wedges was probably about 2 m, as deduced from the depths of ice-wedge cracks and the geometries of the wedge tops. Many thermal contraction cracks propagated upward to the ground surface from the tops of the ice wedges rather than downward from the ground surface. Small, upward facing, horizontal steps and vertical slickensided surfaces in permafrost on both sides of an excavated ice wedge near its top indicated that the adjacent permafrost had moved upward, relative to the wedge, from thermal expansion during the warming period.
Near‐surface wedges of massive ice commonly outline polygons in tundra lowlands, but such polygons have been difficult to identify on hillslopes because soil movement flattens the ridges and infills ...the troughs that form beside and above the ice wedges. Over the past three decades, the active layer has thickened near the western Arctic coast of Canada and consequent thawing of ice wedges has been detected by remote sensing for flat terrain but not, generally, on hillslopes. Annual field surveys (1996–2018) at the Illisarvik field site of thaw depth and ground surface elevation show the mean subsidence rate above hillslope ice wedges has been up to 32 mm a−1 since thaw depth reached the ice‐wedge tops in 2007. Annual mean ground temperatures at the site are about −3.0°C beneath late‐winter snow depths characteristic of the ice‐wedge troughs but about −5.3°C under conditions of the intervening polygons. The rate of thaw subsidence is high for natural, subaerial disturbances because meltwater from the ice wedges runs off downslope. The rate is constant, because the thickness of seasonally thawed ground above the ice wedges and the ice content of the ground remain the same while the troughs develop. Observations of changes in surface elevation in northern Banks Island between the late 1970s and 2019 show troughs on hillslopes where none was previously visible. Development of these troughs creates regional thermokarst landscapes, distinct from the widely recognized results of thawing relict glacier ice, that are now widespread over Canada's western Arctic coastlands. Recognition of ice‐wedge occurrence and accelerated thaw subsidence on hillslopes is important in the design of infrastructure proposed for construction in rolling permafrost terrain.
Context.
Recent observational findings have suggested a positive correlation between the occurrence rates of inner super-Earths and outer giant planets. These results raise the question of whether ...this trend can be reproduced and explained by planet formation theory.
Aims.
Here, we investigate the properties of inner super-Earths and outer giant planets that form according to a core accretion scenario. We study the mutual relations between these planet species in synthetic planetary systems and compare them to the observed exoplanet population.
Methods.
We invoked the Generation 3 Bern model of planet formation and evolution to simulate 1000 multi-planet systems. We then confronted these synthetic systems with the observed sample, taking into account the detection bias that distorts the observed demographics.
Results.
The formation of warm super-Earths and cold Jupiters in the same system is enhanced compared to the individual appearances, although it is weaker than what has been proposed through observations. We attribute the discrepancy to warm and dynamically active giant planets that frequently disrupt the inner systems, particularly in high-metallicity environments. In general, a joint occurrence of the two planet types requires intermediate solid reservoirs in the originating protoplanetary disk. Furthermore, we find differences in the volatile content of planets in different system architectures and predict that high-density super-Earths are more likely to host an outer giant. This correlation can be tested observationally.
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