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"Smith, Sharon L"
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Determining TTOP model parameter importance and overall performance across northern Canada
Modelling current permafrost distribution and response to a changing climate depends on understanding which factors most strongly control ground temperatures. The Temperature at the Top of Permafrost (TTOP) model provides an analytical framework for estimating permafrost presence and thermal state, yet its sensitivity to key parameters remains poorly quantified across diverse northern environments. This study evaluates the relative influence of TTOP model parameters using ground and air temperature data from 330 sites across northern Canada. A leave-one-out cross-validation approach to determine model sensitivity was combined with random forest analysis to rank variable importance. Results show that TTOP performance is dominated by freezing-season conditions - particularly the freezing n-factor and freezing degree days - while thaw-season parameters exert less control. Sensitivity varies by region, with thawing parameters becoming more influential where the duration of the freezing and thawing seasons is similar. Machine learning results also highlighted the importance of thermal offset and mean surface temperatures which are strongly influenced by substrate properties. While the model generally reproduces observed ground temperatures well (RMSE of 0.2 °C), parameters derived from landcover classes were not transferable between sites, underscoring the importance of locally calibrated inputs. Overall, this study is the first empirically-based Canada-wide assessment of how different climatic and environmental factors affect the accuracy of permafrost temperature modelling and provides practical guidance for improving parameterization in regional and global permafrost models.
Journal Article
Multi-decadal degradation and persistence of permafrost in the Alaska Highway corridor, northwest Canada
Changes in permafrost distribution in the southern discontinuous zone were evaluated by repeating a 1964 survey through part of the Alaska Highway corridor (56° N-61° N) in northwest Canada. A total of 55 sites from the original survey in northern British Columbia and southern Yukon were located using archival maps and photographs. Probing for frozen ground, manual excavations, air and ground temperature monitoring, borehole drilling and geophysical techniques were used to gather information on present-day permafrost and climatic conditions. Mean annual air temperatures have increased by 1.5-2.0 ° C since the mid-1970s and significant degradation of permafrost has occurred. Almost half of the permafrost sites along the entire transect which exhibited permafrost in 1964 do so no longer. This change is especially evident in the south where two-thirds of the formerly permafrost sites have thawed and the limit of permafrost appears to have shifted northward. The permafrost that persists is patchy, generally less than 15 m thick, has mean annual surface temperatures >0 ° C, mean ground temperatures between −0.5 and 0 ° C, is in peat or beneath a thick organic mat, and appears to have a thicker active layer than in 1964. Its persistence may relate to the latent heat requirements of thawing permafrost or to the large thermal offset of organic soils. The study demonstrates that degradation of permafrost has occurred in the margins of its distribution in the last few decades, a trend that is expected to continue as the climate warms.
Journal Article
Distinctions in the diets and distributions of larval tunas and the important role of appendicularians
Monthly plankton sampling across the Straits of Florida (SOF) allowed for a thorough investigation of the feeding ecologies of four taxa of larval tunas (family Scombridae, tribe Thunnini) and the horizontal and vertical distributions of tuna larvae and their dominant prey. Before piscivory, Thunnus spp. larvae had a mixed diet of crustaceans and appendicularians, whereas skipjack tuna (Katsuwonus pelamis), little tunny (Euthynnus alletteratus), and Auxis spp. displayed highly selective and nearly exclusive feeding on appendicularians. The availability of both appendicularians and larval fish prey declined from west to east across the SOF, and appendicularians were notably patchy. In the western SOF where prey was more abundant, all taxa of tuna larvae co-occurred, indicating the sharing of resources by the larvae, in addition to the adults of these taxa using similar spawning habitat upstream in the Florida Current. In the central and eastern SOF, where prey was less abundant, only Thunnus spp. and skipjack tuna co-occurred, and these two taxa exhibited significantly different vertical distributions. Prey removal rates (estimated from gut evacuation rates and daily rations) occurring in the western SOF where tuna taxa co-occurred are likely to be sustainable by appendicularian levels within this region but would potentially not be by levels in the east. The spatial and trophic characteristics of these four abundant larval taxa highlight the potential influence of feeding-related processes on larval and adult behavior, while also illustrating a critical trophic link to the microbial food web provided by appendicularians in this oligotrophic environment.
Journal Article
The Canadian Permafrost Electrical Resistivity Survey (CPERS) database: 15 years of permafrost resistivity data
Permafrost landscapes are becoming increasingly susceptible to widespread thaw due to climate change. Collating historical and ongoing data are critical for assessing permafrost conditions and spatiotemporal changes. Electrical resistivity tomography (ERT) is a geophysical technique that has become standard practice for characterizing permafrost. However, resistivity data—particularly raw measurements—often go unpublished and unshared, resulting in missed opportunities for knowledge exchange and collaboration. To fill this gap, we created the Canadian Permafrost Electrical Resistivity Survey database and established clear guidelines for data archival and reuse. Here, we present the first release of the database, which currently houses 280 ERT datasets, including standardized metadata, collected between 2008 and 2022 in British Columbia, Labrador, Northwest Territories, Québec, Yukon, and Alaska. These data present unique opportunities to better understand spatial and temporal variability of permafrost conditions across North America.
Journal Article
Spatial and thermal characteristics of mountain permafrost, northwest canada
Lewkowicz, A.G., Bonnaventure, P.P., Smith, S.L. and Kuntz, Z., 2012. Spatial and thermal characteristics of mountain permafrost, northwest Canada. Geografiska Annaler: Series A, Physical Geography, **, **-**. doi:10.1111/j.1468-0459.2012.00462.x
An extensive network of monitoring stations was used to develop a mean annual air temperature map for the complex mountainous terrain in the southern Yukon and northern British Columbia, Canada (latitude 59° to 65° N). Air temperature lapse rates measured at screen height from valley bottoms up to treeline are normal in the maritime extreme southwest, normal but weak in much of the region, and inverted in the highly continental northernmost sites. Relationships between air and ground surface temperatures, expressed as freezing and thawing n-factors, vary significantly with vegetation type and hence elevational band, with the lowest values for the forested zone and the highest for non-maritime alpine tundra. Equilibrium modelling carried out for one site in the southern part of the region and one in the northern part illustrates the impacts of the differing n-factors on trends in mean ground surface temperature with elevation. Ground thermal regimes determined at borehole locations vary greatly due to these climatic controls but are also affected by substrate. Valley-bottom permafrost in the south is scattered, at temperatures just below 0°C, has a depth of zero annual amplitude of 2-3 m (due to latent heat effects) and may be only a few metres in thickness. Permafrost on bedrock summits is cold, has active layers >5 m thick, is >50 m thick and may be locally continuous. Given the range of air temperatures and n-factors, permafrost is possible throughout the Yukon but higher temperatures southward and stronger lapse rates mean that a lower elevational limit exists in northern British Columbia.
Journal Article
Implications of Climate Change for Economic Development in Northern Canada: Energy, Resource, and Transportation Sectors
Northern Canada is projected to experience major changes to its climate, which will have major implications for northern economic development. Some of these, such as mining and oil and gas development, have experienced rapid expansion in recent years and are likely to expand further, partly as the result of indirect effects of changing climate. This article reviews how a changing climate will affect several economic sectors including the hydroelectric, oil and gas, and mining industries as well as infrastructure and transportation, both marine and freshwater. Of particular importance to all sectors are projected changes in the cryosphere, which will create both problems and opportunities. Potential adaptation strategies that could be used to minimize the negative impacts created by a climate change are also reviewed.
Journal Article
Quantifying Surface Temperature Inversions and Their Impact on the Ground Thermal Regime at a High Arctic Site
Air and ground temperature data collected at Canadian Forces Station Alert, Nunavut, Canada, have been analyzed to investigate the potential role that air temperature inversions play in influencing the spatial variation of permafrost thermal conditions in coastal areas of the High Arctic. Frequent, persistent air temperature inversions have been documented using a series of weather stations deployed along an elevation gradient inland from the coast. During inversion periods, which may last several days, air temperatures in valley bottoms can be up to 10 °C lower than adjacent stations located at elevations 47 to 130 m higher. The occurrence of air temperature inversions during the winter combined with thin snow cover suggest a mechanism explaining the observation of lower winter ground-surface temperatures and colder permafrost conditions in valley bottoms compared to higher elevations.
Journal Article
Twenty-five year results of the national cancer institute randomized breast conservation trial
Breast conservation therapy (BCT) consisting of lumpectomy and postoperative radiation has become an accepted alternative to mastectomy (MRM) for the treatment of early stage breast cancer. We currently report the 25 year outcomes of a single institution, prospective, randomized clinical trial at the National Cancer Institute. 237 women with pathologically confirmed invasive breast tumors 5 cm or less were accrued between 1979 and 1987 and randomized to receive either BCT or MRM. Overall survival was the primary endpoint. Patients with node positive disease were included and treated with doxorubicin and cyclophosphamide. Both arms received axillary dissection. BCT patients had radiation to the whole breast followed by a boost. At a median follow-up of 25.7 years, overall survival was 43.8% for the MRM group and 37.9% for BCT (
P
= 0.38). Although the cumulative incidence of a disease-free survival event was higher in BCT patients (29.0% MRM vs. 56.4% BCT,
P
= 0.0017), the additional treatment failures were primarily isolated ipsilateral breast tumor recurrences (IBTR’s) requiring salvage mastectomy. 22.3% of BCT patients experienced an IBTR. Distant disease and second cancers were similar in both arms. After 25 years, long term survival between BCT and MRM continues to be similar in patients treated for early stage breast cancer. Patients receiving BCT may be at risk for additional treatment-related morbidity, which may occur as a late event. Further studies are required to delineate patients at higher risk for these events, and prolonged follow up should be encouraged after treatment for all women.
Journal Article