1928 research outputs found
Sort by
Brightness temperature simulation of subarctic lake-ice evolution by HIGHTSI and SMRT model
Full text linkMicrowave brightness temperature (TB) can be used to retrieve lake ice thickness in the Arctic and subarctic regions. However, the accuracy of the retrieval is affected by the physical properties of lake ice. To improve the understanding of how lake ice affects TB, numerical modeling was applied. This study combined a physical thermodynamic ice model HIGHTSI with a microwave radiation transfer model SMRT to simulate the TB and lake ice evolution in 2002–2011 in Hulun Lake, China. The reanalyzed meteorological data were used as atmospheric forcing. The ice season was divided into the growth period, the slow growth period, and the ablation period. The simulations revealed that TB was highly sensitive to ice thickness during the ice season, especially vertical polarization measurement at 18.7 GHz. The quadratic polynomial fit for ice thickness to TB outperformed the linear fit, regardless of whether lake ice contained bubbles or not. A comparison of the simulated TB with space-borne TB showed that the simulated TB had the best accuracy during the slow growth period, with a minimum RMSE of 4.6 K. The results were influenced by the bubble radius and salinity. These findings enhance comprehension of the interaction between lake ice properties (including ice thickness, bubbles, and salinity) and TB during ice seasons, offering insights to sea ice in the Arctic and subarctic freshwater observations
Arctic Value Creation, Employment and Investments
Full text linkThe report covers the Arctic areas (22 regions in total) of eight countries: Norway, the United States, Sweden, Finland, Canada, Iceland, Greenland (Denmark), and Russia. The main objective of this report is to give an overview of the Arctic regional economies with a focus on value creation, employment, and investment trends, as well as basic demographic trends
Middle Eocene chondrichthyan fauna from Antarctic Peninsula housed in the Museo de La Plata, Argentina
Full text linkIn recent years, the taxonomy and systematics of the cartilaginous fish taxa from the Eocene La Meseta Formation of Seymour (Marambio) Island, Antarctica have been extensively discussed in a series of papers, resulting in a complete revision of the Antarctic Eocene ichthyofauna housed in the Vertebrate Paleontology collection of the Museo de La Plata, Argentina. This collection constitutes one of the largest and taxonomically most diverse in the world, with approximately 20000 specimens, which provides a solid database used for the analysis of qualitative and quantitative chondrichthyan taxonomic composition. The information provided herein might be useful to understand the sudden decline in chondrichthyan taxonomic diversity towards the top of La Meseta Formation as well as its potential relationship with environmental changes during the Eocene
Comparison of the precision of glacier flow rates derived from offset-tracking using Sentinel-2 and Landsat-8/9 imagery
Full text linkOffset-tracking is an essential method for deriving glacier flow rates using optical imagery. Sentinel-2 (S2) and Landsat-8/9 (L8/9) are popular optical satellites or constellations for polar studies, offering high spatial resolution with relatively short revisit time, wide swath width, and free accessibility. To evaluate and compare the precision of offset-tracking results yielded with these two kinds of data, in this study S2 and L8/9 imagery observed in Petermann Glacier in Greenland, Karakoram in High-Mountains Asia, and Amery Ice Shelf in the Antarctic are analyzed. Outliers and various systematic error sources in the offset-tracking results including orbital and strip errors were analyzed and eliminated at the pre-process stage. Precision at the off-glacier (bare rock) region was evaluated by presuming that no deformation occurred; then for both glacierized and the off-glacier regions, precision of velocity time series was evaluated based on error propagation theory. The least squares method based on connected components was used to solve flow rates time series based on multi-pair images offset-tracking. The results indicated that S2 achieved slightly higher precision than L8/9 in terms of both single-pair derived displacements and least square solved daily flow rates time series. Generally, the RMSE of daily velocity is 26% lower for S2 than L8/9. Moreover, S2 provided higher temporal resolution for monitoring glacier flow rates
Distribution and abundance of krill in various areas of the Southern Ocean: dataset compilation based on samples collected in CHINARE during 2009–2019
Full text linkThis study investigates the composition, abundance, and basic biological parameters of krill in Prydz Bay, Antarctic Peninsula and Amundsen Sea by analyzing samples and environmental data from the Chinese National Antarctic Research Expeditions conducted between 2009/2010 and 2019/2020. The predominant krill species observed were Euphausia superba, Euphausia crystallorophias, and Thysanoessa macrura. T. macrura, although the most widespread, exhibited the lowest mean abundance (9.96 ind·(1000 m–3)) and biomass (0.31 g·(1000 m–3)), predominantly found in low-latitude regions of the Amundsen Sea while E. crystallorophias was most concentrated in polynyas of Prydz Bay. E. superba, with an average abundance of 34.05 ind·(1000 m–3) and biomass of 11.80 g·(1000 m–3), was mainly distributed in the Antarctic Peninsula and Prydz Bay. This study also identified regional variations in mean body length and frequency distributions of krill. The relationship between krill body length and wet weight followed a power-law pattern. Regional differences were observed in the relationship between krill abundance, biomass, and environmental factors with varying correlations. In the Amundsen Sea, no significant correlation was found between krill abundance and environmental factors. Notably, E. crystallorophias in Prydz Bay demonstrated a significant positive correlation with chlorophyll a concentration, while T. macrura abundance and biomass in the Antarctic Peninsula exhibited a significant negative correlation with ice-free days. The findings contribute valuable regional data on krill distribution, abundance, and biomass in the Southern Ocean, serving as foundational information for the conservation of the Southern Ocean ecosystem and Antarctic krill fishery management on a circumpolar scale
Polar Perspectives No 13 - The Intelligence Community Must Evolve To Meet the Reality of Arctic Change
Full text linkClimate change is accelerating and significant changes are occurring at relatively low levels of warming. 1 The Arctic is warming faster than anywhere on Earth, with tremendous implications for U.S. homeland and national security, as well as U.S. security interests abroad. 2 Future conditions are not well-represented by past experiences so it is important for the U.S. intelligence community (IC) to evolve to meet the demands of this new reality. 3 This includes creating an holistic approach towards the Arctic region, as well as several other targeted, structural interventions pertaining to Arctic engagement and equities. This natural evolution will allow the IC to provide more robust, agile, and comprehensive support to policymakers and the military; properly reflecting the period of unprecedented complexity and consequence we are now within
