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Feng Ling - One of the best experts on this subject based on the ideXlab platform.

  • Quantifying Impacts of Mean Annual Lake Bottom Temperature on Talik Development and Permafrost Degradation below Expanding Thermokarst Lakes on the Qinghai–Tibet Plateau
    Water, 2019
    Co-Authors: Feng Ling, Feifei Pan
    Abstract:

    Variations in thermokarst lake area, lake water depth, lake age, air Temperature, permafrost condition, and other environmental variables could have important influences on the mean annual lake Bottom Temperature (MALBT) and thus affect the ground thermal regime and talik development beneath the lakes through their direct impacts on the MALBT. A lake expanding model was employed for examining the impacts of variations in the MALBT on talik development and permafrost degradation beneath expanding thermokarst lakes in the Beiluhe Basin on the Qinghai–Tibetan Plateau (QTP). All required boundary and initial conditions and model parameters were determined based on field measurements. Four simulation cases were conducted with different respective fitting sinusoidal functions of the MALBTs at 3.75 °C, 4.5 °C, 5.25 °C, and 6.0 °C. The simulated results show that for lakes with MALBTs of 3.75 °C, 4.5 °C, 5.25 °C, and 6.0 °C, the maximum thicknesses of bowl-shaped talik below the lakes at year 300 were 27.2 m, 29.6 m, 32.0 m, and 34.4 m; funnel-shaped open taliks formed beneath the lakes at years 451, 411, 382, and 356 after the formation of thermokarst lakes, with mean downward thaw rates of 9.1 m/year, 10.2 m/year, 11.2 m/year, and 12.0 m/year, respectively. Increases in the MALBT from 3.75 °C to 4.52 °C, 4.25 °C to 5.25 °C, and 5.25 °C to 6.0 °C respectively resulted in the permafrost with a horizontal distance to lake centerline less than or equal to 45 m thawing completely 36 years, 32 years, and 24 years in advance, and the maximum ground Temperature increases at a depth of 40 m below the lakes at year 600 ranged from 2.16 °C to 2.80 °C, 3.57 °C, and 4.09 °C, depending on the MALBT. The ground Temperature increases of more than 0.5 °C at a depth of 40 m in year 600 occurred as far as 74.9 m, 87.2 m, 97.8 m, and 106.6 m from the lake centerlines. The simulation results also show that changes in the MALBT almost have no impact on the open talik lateral progress rate, although the minimum distances from the open talik profile to lake centerlines below the lakes with different MALBTs exhibited substantial differences.

  • numerical simulation of permafrost thermal regime and talik development under shallow thaw lakes on the alaskan arctic coastal plain
    Journal of Geophysical Research, 2003
    Co-Authors: Feng Ling, Tingjun Zhang
    Abstract:

    [1] Thaw lakes are one of the most obvious manifestations of the hydrological system at work in the tundra regions of the Alaskan Arctic Coastal Plain, but the extent of the role of thaw lakes in Arctic land-atmosphere interactions and feedback has yet to be fully understood. This study uses a two-dimensional heat transfer model with phase change under a cylindrical coordinate system to simulate the long-term influence of shallow thaw lakes on the thermal regime of permafrost and talik development on the Alaskan Arctic Coastal Plain. On the basis of previous studies of permafrost and thaw lakes at Barrow, Alaska, a series of simulation cases was conducted using different combinations of long-term mean lake Bottom Temperature and lake depth. The simulated results indicate that shallow thaw lakes are a significant heat source to permafrost and talik. For a thaw lake with a long-term mean lake Bottom Temperature of greater than 0.0°C a talik forms under the thaw lake. The maximum talik thicknesses (vertical distance from the ground surface to the permafrost surface) are 28.0, 43.0, and 53.2 m 3000 years after the formation of a shallow thaw lake with long-term mean lake Bottom Temperatures of 1.0°, 2.0°, and 3.0°C, respectively. Talik development rate is very high in the first several years after a thaw lake formation and decreases gradually with time. No talik forms below a thaw lake with a long-term mean lake Bottom Temperature equal to or lower than 0.0°C, but the Temperature of permafrost below the thaw lake increases with time. Three thousand years after the formation of a thaw lake with a long-term mean lake Bottom Temperature of greater than or equal to −2.0°C, ground Temperature increases of more than 0.5°C occur as far as 300 m from the lake shore and as deep as about 400 m below the ground surface. It is concluded that variation of long-term mean lake Bottom Temperature has a significant influence on permafrost thermal regime and talik development. Continued monitoring for thaw lake Bottom Temperature and ground Temperature under shallow thaw lakes is needed to further improve the simulation.

Kai Wieland - One of the best experts on this subject based on the ideXlab platform.

  • changes in recruitment growth and stock size of northern shrimp pandalus borealis at west greenland Temperature and density dependent effects at released predation pressure
    Ices Journal of Marine Science, 2005
    Co-Authors: Kai Wieland
    Abstract:

    Stock size of northern shrimp (Pandalus borealis) in West Greenland waters has been fairly stable from the late 1980s to the mid-1990s. Thereafter, survey estimates of biomass increased substantially, and the exploitation rate declined slightly in the most recent years. The present analysis was carried out on a spatially disaggregated basis in order to account for the latitudinal differences in Bottom Temperature and shrimp density. Changes in recruitment and, with a lag of 2 years, in stock biomass were most pronounced in the northern part of its distributional range, while Bottom Temperature increased in all survey regions since the mid-1990s. Length-at-age was positively correlated with Temperature in general, but a trend towards slower growth was observed in areas with the highest stock densities in the most recent years. It is concluded that the moderate increase in Temperature above a lower threshold of the optimal range in the northern regions has extended the distributional area that is most favourable for northern shrimp. This, together with a decreasing rate of exploitation and a continuous low predation pressure, resulted in an increase of the stock to a level at which density-dependent effects have become prominent in parts of study area.

  • length at sex transition in northern shrimp pandalus borealis off west greenland in relation to changes in Temperature and stock size
    Fisheries Research, 2004
    Co-Authors: Kai Wieland
    Abstract:

    Abstract Length at sex transition of northern shrimp (Pandalus borealis) off West Greenland decreased in the years 1991–2002. A pronounced increase in Bottom Temperature occurred in the middle of this period, and stock size increased substantially during the past years. Length at sex transition differed within the area and the possible effects of changing Temperature and abundance were studied for five different regions on the West Greenland shelf. On average, length at sex transition declined by 1.7 mm carapace length (CL) and mean Bottom Temperature increased by 1.9 °C. The change in length at sex transition was significantly correlated with Bottom Temperature in three out of the five regions and for all regions combined. No clear density-dependence was detected despite of a substantial increase in northern shrimp density in parts of the area and no evidence was found that northern shrimp decrease size at sex change during periods of low female abundance to compensate for a decreased reproductive potential. The observed change in length at sex transition was apparently independent from the fishery. Earlier maturation due to higher Temperature was identified as the principal cause for the decrease in the length at sex transition. Because maximum female length is regarded to be proportional to length at sex transition and female fecundity increases with size, total egg production of a given year class over its lifespan would be lower when sex transition occurs at a smaller size if not compensated otherwise, e.g. through an increase of the proportion of females that spawn in each instead of every second year.

Tingjun Zhang - One of the best experts on this subject based on the ideXlab platform.

  • numerical simulation of permafrost thermal regime and talik development under shallow thaw lakes on the alaskan arctic coastal plain
    Journal of Geophysical Research, 2003
    Co-Authors: Feng Ling, Tingjun Zhang
    Abstract:

    [1] Thaw lakes are one of the most obvious manifestations of the hydrological system at work in the tundra regions of the Alaskan Arctic Coastal Plain, but the extent of the role of thaw lakes in Arctic land-atmosphere interactions and feedback has yet to be fully understood. This study uses a two-dimensional heat transfer model with phase change under a cylindrical coordinate system to simulate the long-term influence of shallow thaw lakes on the thermal regime of permafrost and talik development on the Alaskan Arctic Coastal Plain. On the basis of previous studies of permafrost and thaw lakes at Barrow, Alaska, a series of simulation cases was conducted using different combinations of long-term mean lake Bottom Temperature and lake depth. The simulated results indicate that shallow thaw lakes are a significant heat source to permafrost and talik. For a thaw lake with a long-term mean lake Bottom Temperature of greater than 0.0°C a talik forms under the thaw lake. The maximum talik thicknesses (vertical distance from the ground surface to the permafrost surface) are 28.0, 43.0, and 53.2 m 3000 years after the formation of a shallow thaw lake with long-term mean lake Bottom Temperatures of 1.0°, 2.0°, and 3.0°C, respectively. Talik development rate is very high in the first several years after a thaw lake formation and decreases gradually with time. No talik forms below a thaw lake with a long-term mean lake Bottom Temperature equal to or lower than 0.0°C, but the Temperature of permafrost below the thaw lake increases with time. Three thousand years after the formation of a thaw lake with a long-term mean lake Bottom Temperature of greater than or equal to −2.0°C, ground Temperature increases of more than 0.5°C occur as far as 300 m from the lake shore and as deep as about 400 m below the ground surface. It is concluded that variation of long-term mean lake Bottom Temperature has a significant influence on permafrost thermal regime and talik development. Continued monitoring for thaw lake Bottom Temperature and ground Temperature under shallow thaw lakes is needed to further improve the simulation.

Feifei Pan - One of the best experts on this subject based on the ideXlab platform.

  • Quantifying Impacts of Mean Annual Lake Bottom Temperature on Talik Development and Permafrost Degradation below Expanding Thermokarst Lakes on the Qinghai–Tibet Plateau
    Water, 2019
    Co-Authors: Feng Ling, Feifei Pan
    Abstract:

    Variations in thermokarst lake area, lake water depth, lake age, air Temperature, permafrost condition, and other environmental variables could have important influences on the mean annual lake Bottom Temperature (MALBT) and thus affect the ground thermal regime and talik development beneath the lakes through their direct impacts on the MALBT. A lake expanding model was employed for examining the impacts of variations in the MALBT on talik development and permafrost degradation beneath expanding thermokarst lakes in the Beiluhe Basin on the Qinghai–Tibetan Plateau (QTP). All required boundary and initial conditions and model parameters were determined based on field measurements. Four simulation cases were conducted with different respective fitting sinusoidal functions of the MALBTs at 3.75 °C, 4.5 °C, 5.25 °C, and 6.0 °C. The simulated results show that for lakes with MALBTs of 3.75 °C, 4.5 °C, 5.25 °C, and 6.0 °C, the maximum thicknesses of bowl-shaped talik below the lakes at year 300 were 27.2 m, 29.6 m, 32.0 m, and 34.4 m; funnel-shaped open taliks formed beneath the lakes at years 451, 411, 382, and 356 after the formation of thermokarst lakes, with mean downward thaw rates of 9.1 m/year, 10.2 m/year, 11.2 m/year, and 12.0 m/year, respectively. Increases in the MALBT from 3.75 °C to 4.52 °C, 4.25 °C to 5.25 °C, and 5.25 °C to 6.0 °C respectively resulted in the permafrost with a horizontal distance to lake centerline less than or equal to 45 m thawing completely 36 years, 32 years, and 24 years in advance, and the maximum ground Temperature increases at a depth of 40 m below the lakes at year 600 ranged from 2.16 °C to 2.80 °C, 3.57 °C, and 4.09 °C, depending on the MALBT. The ground Temperature increases of more than 0.5 °C at a depth of 40 m in year 600 occurred as far as 74.9 m, 87.2 m, 97.8 m, and 106.6 m from the lake centerlines. The simulation results also show that changes in the MALBT almost have no impact on the open talik lateral progress rate, although the minimum distances from the open talik profile to lake centerlines below the lakes with different MALBTs exhibited substantial differences.

A F Sinclair - One of the best experts on this subject based on the ideXlab platform.

  • effect of water Temperature on catchability of atlantic cod gadus morhua to the Bottom trawl survey in the southern gulf of st lawrence
    Journal of Materials Science, 2000
    Co-Authors: D P Swain, G A Poirier, A F Sinclair
    Abstract:

    Correlations between catch rates in Bottom-trawl surveys and indices of environmental conditions or fish distribution have been attributed to effects of the environmental conditions or fish distribution on catchability to the survey. We tested this hypothesis using data on cod in the southern Gulf of St Lawrence. Survey catch rates of cod were significantly correlated with indices of Bottom Temperature and of cod Temperature and depth distributions. Correlations were in the directions expected on the basis of predicted effects on catchability or availability to the survey. However, tests involving calibrations of sequential population analysis (SPA) or residuals from multiplicative analyses of the survey catch rates (with terms for yearclass, age and cumulative mortality) did not support the hypothesis that these correlations resulted from effects on catchability to the survey. These tests provided no support for an effect of cod Temperature or depth distribution on catchability. They provided some support for an effect of Bottom Temperature conditions on availability to the survey, but this effect on availability was not reflected by the correlations observed between Bottom Temperature indices and survey catch rates. We conclude that adjustments for effects on catchability should be based on relationships with inconsistencies in survey catch rates instead of relationships with the catch rates themselves. These adjustments could be incorporated in calibration of the SPA or calculated based on relationships with residuals from models relating survey catch rate to yearclass, age and fishing mortality. However, such adjustments were negligible in the case of southern Gulf of St Lawrence cod. 2000 International Council for the Exploration of the Sea