Cessation of ice-wedge development during the 20th century in spruce forests of eastern Mackenzie Delta, Northwest Territories, Canada

2007 ◽  
Vol 44 (11) ◽  
pp. 1503-1515 ◽  
Author(s):  
S V Kokelj ◽  
M FJ Pisaric ◽  
C R Burn
Keyword(s):  
20Th Century ◽  
Ice Age ◽  
Spruce Forest ◽  
Mackenzie Delta ◽  
Study Region ◽  
Near Surface ◽  
Spruce Forests ◽  
Surface Temperatures ◽  
Forest Sites ◽  
Ice Wedge

Ice wedges are presently inactive in white spruce (Picea glauca) forests of eastern Mackenzie Delta as shown by the absence of vein ice above ice wedges, the maintenance of intact breaking cables, and the abundance of rootlets propagating across ridge–trough sequences. At spruce forest sites, near-surface ground cooling rates and minimum near-surface temperatures from the years 2003–2005 were above ice-wedge cracking thresholds. Ground thermal conditions associated with cracking were recorded at a tundra peatland with active ice wedges. Annual mean permafrost temperatures at the spruce forest sites ranged from –1.8 to –2.9 °C, whereas at the tundra peatland, the permafrost was colder than –6 °C. Although winter air temperatures are similar throughout the study region, deeper snow cover, thicker active layers, and warmer permafrost account for the more gradual seasonal cooling and warmer near-surface temperatures recorded at the subarctic forest sites. The subtle ridge to trough relief, 12–35 cm of permafrost above wedge ice, roots up to 80 years old grown across ice wedges, and negligible tritium levels in wedge ice indicate that thermal contraction cracking in the spruce forests has been infrequent throughout much of the last century. The proximity of wedge ice to the base of the aggrading permafrost table and the absence of old spruce roots spanning ice-wedge troughs suggest that ice-wedge cracking did occur in the forest environments during the cold and dry conditions associated with the Little Ice Age and early part of the 20th century. When these ice wedges cracked, minimum temperatures at the top of permafrost were probably at least 3–8 °C colder than presently observed and similar to present conditions at the tundra peatland.

scholarly journals Regional Patterns and Asynchronous Onset of Ice-Wedge Degradation since the Mid-20th Century in Arctic Alaska

2018 ◽  
Vol 10 (8) ◽  
pp. 1312 ◽  
Author(s):  
Gerald Frost ◽  
Tracy Christopherson ◽  
M. Jorgenson ◽  
Anna Liljedahl ◽  
Matthew Macander ◽  
...  
Keyword(s):  
20Th Century ◽  
Coastal Plain ◽  
Regional Differences ◽  
Environmental Gradients ◽  
Ice Age ◽  
Ground Subsidence ◽  
Ground Ice ◽  
Late 20Th Century ◽  
Regional Patterns ◽  
Ice Wedge

Ice-wedge polygons are widespread and conspicuous surficial expressions of ground-ice in permafrost landscapes. Thawing of ice wedges triggers differential ground subsidence, local ponding, and persistent changes to vegetation and hydrologic connectivity across the landscape. Here we characterize spatio-temporal patterns of ice-wedge degradation since circa 1950 across environmental gradients on Alaska’s North Slope. We used a spectral thresholding approach validated by field observations to map flooded thaw pits in high-resolution images from circa 1950, 1982, and 2012 for 11 study areas (1577–4460 ha). The total area of flooded pits increased since 1950 at 8 of 11 study areas (median change +3.6 ha; 130.3%). There were strong regional differences in the timing and extent of degradation; flooded pits were already extensive by 1950 on the Chukchi coastal plain (alluvial-marine deposits) and subsequent changes there indicate pit stabilization. Degradation began more recently on the central Beaufort coastal plain (eolian sand) and Arctic foothills (yedoma). Our results indicate that ice-wedge degradation in northern Alaska cannot be explained by late-20th century warmth alone. Likely mechanisms for asynchronous onset include landscape-scale differences in surficial materials and ground-ice content, regional climate gradients from west (maritime) to east (continental), and regional differences in the timing and magnitude of extreme warm summers after the Little Ice Age.

A chronology of the Little Ice Age in the tropical Andes of Bolivia (16°S) and its implications for climate reconstruction

2008 ◽  
Vol 70 (2) ◽  
pp. 198-212 ◽  
Author(s):  
Antoine Rabatel ◽  
Bernard Francou ◽  
Vincent Jomelli ◽  
Philippe Naveau ◽  
Delphine Grancher
Keyword(s):  
20Th Century ◽  
Little Ice Age ◽  
18Th Century ◽  
Extreme Values ◽  
Ice Age ◽  
Tropical Andes ◽  
Equilibrium Line Altitude ◽  
Mountain Areas ◽  
Study Region ◽  
Glacier Recession

AbstractDating moraines by lichenometry enabled us to reconstruct glacier recession in the Bolivian Andes since the Little Ice Age maximum. On the 15 proglacial margins studied, we identified a system of ten principal moraines that marks the successive positions of glaciers over the last four centuries. Moraines were dated by performing statistical analysis of lichen measurements based on the extreme values theory. Like glaciers in many mid-latitude mountain areas, Bolivian glaciers reached their maximal extent during the second half of the 17th century. This glacier maximum coincides with the Maunder minimum of solar irradiance. By reconstructing the equilibrium-line altitude and changes in mass-balance, we think the glacier maximum may be due to a 20 to 30% increase in precipitation and a 1.1 to 1.2 °C decrease in temperature compared with present conditions. In the early 18th century, glaciers started to retreat at varying rates until the late 19th to early 20th century; this trend was generally associated with decreasing accumulation rates. By contrast, glacier recession in the 20th century was mainly the consequence of an increase in temperature and humidity. These results are consistent with observations made in the study region based on other proxies.

scholarly journals A ring-width-based reconstruction of June–July minimum temperatures since AD 1245 from white spruce stands in the Mackenzie Delta region, northwestern Canada

2013 ◽  
Vol 80 (2) ◽  
pp. 167-179 ◽  
Author(s):  
Trevor J. Porter ◽  
Michael F.J. Pisaric ◽  
Steven V. Kokelj ◽  
Peter deMontigny
Keyword(s):  
20Th Century ◽  
Large Scale ◽  
Ring Width ◽  
White Spruce ◽  
Mackenzie Delta ◽  
Delta Region ◽  
Late 20Th Century ◽  
Climate History ◽  
Study Region ◽  
June July

We present a reconstruction of June–July minimum temperatures since AD 1245 for the Mackenzie Delta region based on a 29-site network of white spruce (Picea glauca) ring-width series. Most but not all trees experienced a divergent temperature–growth response, similar to the divergence that has affected other white spruce trees across Yukon and Alaska. However, divergence in the study region began as early as AD 1900 and we have documented our methods to avoid including divergent signals in the reconstruction. Calibration/verification testing based on local temperature data, and multi-century coherence with nearby and large-scale temperature proxy records, confirm that our reconstruction is robust. The reconstruction shows cool conditions in the late 13th, early 18th and early 19th centuries, corresponding with solar minima and increased volcanism. These cool periods are interrupted by warm periods consistent with early to mid-20th century warmth. The late 20th century is the warmest interval, and the last decade is estimated to be 1.4°C warmer than any decade before the mid-20th century. The reconstructed climate history corroborates other proxy-based inferences and supports the notion that high-latitude regions such as the Mackenzie Delta have experienced rapid warming in recent decades that is exceptional in the last eight centuries.

The Western Tibetan Vortex as an emergent feature of near-surface temperature variations

2020 ◽  
Author(s):  
Remco de Kok ◽  
Walter Immerzeel
Keyword(s):  
Surface Temperature ◽  
20Th Century ◽  
Large Scale ◽  
High Mountain ◽  
Net Radiation ◽  
Near Surface ◽  
Temperature Variations ◽  
Surface Temperatures ◽  
Emergent Feature ◽  
Main Driver

<p>Glaciers are growing in a part of High Mountain Asia (HMA), contrary to the demise of glaciers worldwide. A proposed explanation for this behaviour is the decreasing strength of the "Western Tibetan Vortex" (WTV), a circular motion of air in the troposphere around northwestern High Mountain Asia, which is proposed to drive near-surface temperatures. Here, we show that the WTV is the change of wind field resulting from changes in near-surface temperature, and that it is not unique to northwestern HMA, but is generally applicable to large parts of the globe. Instead, we argue that net radiation is likely the main driver of near-surface temperatures in Western HMA in summer and autumn, and that the WTV is the response of the atmosphere to changes in temperature. The decreasing strength of the WTV, as seen during summer in the 20th century, is thus likely the result of changing net radiation, and not the main driver of cooling itself. We do argue that the WTV is a useful concept to understand large scale climate variability in the region, and that such an approach could yield important insights in other mid-latitude regions as well.</p>

Actual organization of forest communities with broad-leaved trees in broad-leaved-coniferous zone (with Moscow Region as an example)

2018 ◽  
pp. 107-130 ◽  
Author(s):  
T. V. Chernenkova ◽  
O. V. Morozova ◽  
N. G. Belyaeva ◽  
M. Yu. Puzachenko
Keyword(s):  
Tree Species ◽  
Forest Cover ◽  
Activity Index ◽  
Plant Cover ◽  
Moscow Region ◽  
Pine Forests ◽  
Coniferous Forests ◽  
Oak Forests ◽  
Study Region ◽  
Spruce Forests

This study aimed at an investigation of the structure, ecology and mapping of mixed communities with the participation of spruce, pine and broad-leave trees in one of the regions of broad-leave–coniferous zone. Despite the long history of the nature use of the study area, including forestry practices (Kurnayev, 1968; Rysin, Saveliyeva, 2007; Arkhipova, 2014; Belyaeva, Popov, 2016), the communities kept the main features of the indigenous forests of the broad-leave–coniferous zone ­— the tree species polydominance of the stands, the multilayer structure of communities and the high species diversity. In the course of field works in the southwestern part of the Moscow Region (2000–2016) 120 relevés were made. Spatial structure, species composition as well as cover values (%) of all vascular plants and bryophytes were recorded in each stand. The relevés were analysed following the ecology-phytocenotic classification approach and methods of multivariate statistical analysis that allowed correctly to differentiate communities according the broad-leave species participation. The accuracy of the classification based on the results of discriminant analysis was 95.8 %. Evaluation of the similarity of the selected units was carried out with the help of cluster analysis (Fig. 12). Clustering into groups is performed according to the activity index of species (A) (Malyshev, 1973) within the allocated syntaxon using Euclidean distance and Ward’s method. The classification results are corrected by DCA ordination in PC-ORD 5.0 (McCune, Mefford, 2006) (Fig. 1). Spatial mapping of forest cover was carried out on the basis of ground data, Landsat satellite images (Landsat 5 TM, 7 ETM +, 8 OLI_TIRS), digital elevation (DEM) and statistical methods (Puzachenko et al., 2014; Chernenkova et al., 2015) (Fig. 13 а, б). The obtained data and the developed classification refine the existing understanding of the phytocenotic structure of the forest cover of the broad-leave–coniferous zone. Three forest formation groups with different shares of broad-leave species in the canopy with seven groups of associations were described: a) coniferous forests with broad-leave species (small- and broad-herb spruce forests with oak and lime (1)); broad-herb spruce forests with oak and lime (2); small- and broad-herb pine forests with spruce, lime, oak and hazel (3); broad-herb pine forests with lime, oak and hazel (4)), b) broad-leave–coniferous forests (broad-herb spruce–broad-leave forests (5)), and c) broad-leave forests (broad-herb oak forests (6), broad-herb lime forests (7)). In the row of discussed syntaxa from 1 to 7 group, the change in the ratio of coniferous and broad-leave species of the tree layer (A) reflects re­gular decrease in the participation of spruce in the plant cover (from 66 to 6 %; Fig. 3 A1, A2) and an increase in oak and lime more than threefold (from 15 to 65 %; Fig. 4 a). Nemoral species predominate in the composition of ground layers, the cove­rage of which increases (from 40 to 80 %) in the range from 1 to 7 group, the coverage of the boreal group varies from 55 to 8 % (Fig. 11) while maintaining the presence of these species, even in nemoral lime and oak forests. In forests with equal share of broad-leave and coniferous trees (group 5) the nemoral species predominate in herb layer. In oak forests (group 6) the species of the nitro group are maximally represented, which is natural for oak forests occurring on rich soils, and also having abundant undergrowth of hazel. Practically in all studied groups the presence of both coniferous (in particular, spruce) and broad-leave trees in undergrowth (B) and ground layer (C) were present in equal proportions (Fig. 3). This does not confirm the unambiguity of the enrichment with nemoral species and increase in their cover in complex spruce and pine forests in connection with the climate warming in this region, but rather indicates on natural change of the main tree species in the cenopopulations. Further development of the stand and the formation of coni­ferous or broad-leave communities is conditioned by landscape. It is proved that the distribution of different types of communities is statistically significant due to the relief. According to the results of the analysis of remote information, the distribution areas of coniferous forests with broad-leave species, mixed and broad-leave forest areas for the study region are represented equally. The largest massifs of broad-leave–coniferous forests are located in the central and western parts of the study area, while in the eastern one the broad-leave forests predominate, that is a confirmation of the zonal ecotone (along the Pakhra River: Petrov, Kuzenkova, 1968) from broad-leave–coniferous forests to broad-leave forests.

scholarly journals Thermal Submeso Motions in the Nocturnal Stable Boundary Layer. Part 2: Generating Mechanisms and Implications

2021 ◽  
Author(s):  
Lena Pfister ◽  
Karl Lapo ◽  
Larry Mahrt ◽  
Christoph K. Thomas
Keyword(s):  
Boundary Layer ◽  
Stable Boundary Layer ◽  
Side Wall ◽  
Cold Pool ◽  
Continuous Data ◽  
Valley Bottom ◽  
Near Surface ◽  
Cold Air ◽  
Stable Boundary ◽  
Surface Temperatures

AbstractIn the stable boundary layer, thermal submesofronts (TSFs) are detected during the Shallow Cold Pool experiment in the Colorado plains, Colorado, USA in 2012. The topography induces TSFs by forming two different air layers converging on the valley-side wall while being stacked vertically above the valley bottom. The warm-air layer is mechanically generated by lee turbulence that consistently elevates near-surface temperatures, while the cold-air layer is thermodynamically driven by radiative cooling and the corresponding cold-air drainage decreases near-surface temperatures. The semi-stationary TSFs can only be detected, tracked, and investigated in detail when using fibre-optic distributed sensing (FODS), as point observations miss TSFs most of the time. Neither the occurrence of TSFs nor the characteristics of each air layer are connected to a specific wind or thermal regime. However, each air layer is characterized by a specific relationship between the wind speed and the friction velocity. Accordingly, a single threshold separating different flow regimes within the boundary layer is an oversimplification, especially during the occurrence of TSFs. No local forcings or their combination could predict the occurrence of TSFs except that they are less likely to occur during stronger near-surface or synoptic-scale flow. While classical conceptualizations and techniques of the boundary layer fail in describing the formation of TSFs, the use of spatially continuous data obtained from FODS provide new insights. Future studies need to incorporate spatially continuous data in the horizontal and vertical planes, in addition to classic sensor networks of sonic anemometry and thermohygrometers to fully characterize and describe boundary-layer phenomena.

scholarly journals Summer temperature response to extreme soil water conditions in the Mediterranean transitional climate regime

2021 ◽  
Author(s):  
Stefano Materia ◽  
Constantin Ardilouze ◽  
Chloé Prodhomme ◽  
Markus G. Donat ◽  
Marianna Benassi ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Soil Moisture ◽  
Soil Water ◽  
Land Surface ◽  
Heat Waves ◽  
Climate Regime ◽  
Seasonal Forecasts ◽  
Near Surface ◽  
Surface Temperatures ◽  
The Mediterranean

AbstractLand surface and atmosphere are interlocked by the hydrological and energy cycles and the effects of soil water-air coupling can modulate near-surface temperatures. In this work, three paired experiments were designed to evaluate impacts of different soil moisture initial and boundary conditions on summer temperatures in the Mediterranean transitional climate regime region. In this area, evapotranspiration is not limited by solar radiation, rather by soil moisture, which therefore controls the boundary layer variability. Extremely dry, extremely wet and averagely humid ground conditions are imposed to two global climate models at the beginning of the warm and dry season. Then, sensitivity experiments, where atmosphere is alternatively interactive with and forced by land surface, are launched. The initial soil state largely affects summer near-surface temperatures: dry soils contribute to warm the lower atmosphere and exacerbate heat extremes, while wet terrains suppress thermal peaks, and both effects last for several months. Land-atmosphere coupling proves to be a fundamental ingredient to modulate the boundary layer state, through the partition between latent and sensible heat fluxes. In the coupled runs, early season heat waves are sustained by interactive dry soils, which respond to hot weather conditions with increased evaporative demand, resulting in longer-lasting extreme temperatures. On the other hand, when wet conditions are prescribed across the season, the occurrence of hot days is suppressed. The land surface prescribed by climatological precipitation forcing causes a temperature drop throughout the months, due to sustained evaporation of surface soil water. Results have implications for seasonal forecasts on both rain-fed and irrigated continental regions in transitional climate zones.

scholarly journals Neoglacial history of Robson Glacier, British Columbia

2017 ◽  
Vol 54 (11) ◽  
pp. 1153-1164 ◽  
Author(s):  
B.H. Luckman ◽  
M.H. Masiokas ◽  
K. Nicolussi
Keyword(s):  
British Columbia ◽  
Little Ice Age ◽  
Ice Age ◽  
Tree Line ◽  
Canadian Rockies ◽  
The Holocene ◽  
Forest Sites ◽  
History Of ◽  
Subfossil Wood ◽  
Glacier Advance

As glaciers in the Canadian Rockies recede, glacier forefields continue to yield subfossil wood from sites overridden by these glaciers during the Holocene. Robson Glacier in British Columbia formerly extended below tree line, and recession over the last century has progressively revealed a number of buried forest sites that are providing one of the more complete records of glacier history in the Canadian Rockies during the latter half of the Holocene. The glacier was advancing ca. 5.5 km upvalley of the Little Ice Age terminus ca. 5.26 cal ka BP, at sites ca. 2 km upvalley ca. 4.02 cal ka BP and ca. 3.55 cal ka BP, and 0.5–1 km upvalley between 1140 and 1350 A.D. There is also limited evidence based on detrital wood of an additional period of glacier advance ca. 3.24 cal ka BP. This record is more similar to glacier histories further west in British Columbia than elsewhere in the Rockies and provides the first evidence for a post-Hypsithermal glacier advance at ca. 5.26 cal ka BP in the Rockies. The utilization of the wiggle-matching approach using multiple 14C dates from sample locations determined by dendrochronological analyses enabled the recognition of 14C outliers and an increase in the precision and accuracy of the dating of glacier advances.

scholarly journals Record of Little Ice Age sea surface temperatures at Bermuda using a growth-dependent calibration of coral Sr/Ca

2005 ◽  
Vol 20 (4) ◽  
pp. n/a-n/a ◽  
Author(s):  
Nathalie F. Goodkin ◽  
Konrad A. Hughen ◽  
Anne L. Cohen ◽  
Struan R. Smith
Keyword(s):  
Little Ice Age ◽  
Sea Surface ◽  
Ice Age ◽  
Sea Surface Temperatures ◽  
Surface Temperatures

Storm-induced circulation in the Pearl River Estuary of China during super Typhoon Koryn

2012 ◽  
Vol 47 (3-4) ◽  
pp. 314-332 ◽  
Author(s):  
Liqun Tang ◽  
Jinyu Sheng ◽  
Yuhan Cai
Keyword(s):  
Northern South China Sea ◽  
River Estuary ◽  
Pearl River Estuary ◽  
Horizontal Resolution ◽  
Pearl River ◽  
Study Region ◽  
Near Surface ◽  
The Pearl River Estuary ◽  
Super Typhoon ◽  
The Pearl River

This study presents a numerical investigation of storm-induced circulation and hydrographic distributions over the Pearl River Estuary (PRE) in South China's Guangdong Province during super Typhoon Koryn in June 1993. The nested-grid modelling system used in this study has three downscaling subcomponents: an outer-most sub-model with a coarse horizontal resolution of ∼7 km for simulating surface elevations and depth-mean currents forced by wind and tides over China Seas from Bohai Sea to the northern South China Sea; and an inner-most sub-model with a fine resolution of ∼1.2 km for simulating the three-dimensional estuarine circulation and hydrographic distributions in the PRE and adjacent waters. A parametric vortex is inserted into the coarse-resolution (0.5°) numerical weather forecast products to better represent the atmospheric pressure and wind stress associated with Koryn. Model results demonstrate that large surface elevations and intense surface currents are generated over the area of influence of the storm. Lagrange velocities of near-surface particles are also used to examine the effect of the storm on the movements and dispersion of near-surface particles over the study region.

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