June to October Aerosol Optical Depth over the Arctic at Various Spatial and Temporal Scales in MODIS, MAIAC, CALIOP and GOES Data

The accuracy of the cloud-aerosol lidar with orthogonal polarization (CALIOP), moderate resolution imaging spectroradiometer (MODIS), Multi-Angle Implementation of Atmospheric Correction (MAIAC), and Geostationary Operational Environmental Satellite (GOES) aerosol optical depth (AOD) products for the Arctic north of 59.75°N was examined by means of 35 aerosol robotic network (AERONET) AOD sites. The assessment for June to October 2006 to 2020 showed MAIAC AOD agreed the best with AERONET AOD;CALIOP AOD differed the strongest from the AERONET AOD. Cross-correlations of CALIOP AOD along the satellite path indicated that AOD-values 40 km up-and-down the path often failed to represent the AERONET AOD-values within ±30 min of the overpass in this region dominated by easterly winds. Typically, CALIOP AOD was lower than AERONET AOD and MAIAC AOD at the sites, especially, at sites with mean AOD below 0.1. Generally, MODIS AOD values exceeded those of MAIAC. Comparison of CALIOP, MAIAC, and MODIS products resampled on a 0.25° × 0.25° grid revealed differences among the products caused by their temporal and spatial resolution, sample habit and size. Typically, the MODIS AOD-product showed the most details in AOD distribution. Despite differences in AOD-values, all products provided similar temporal evolution of elevated and lower AOD.

Possible Impacts of the Arctic Oscillation on the Interdecadal Variation of Summer Monsoon Rainfall in East Asia

The influences of the wintertime AO (Arctic Oscillation) on the interdecadal variation of summer monsoon rainfall in East Asia were examined. An interdecadal abrupt change was found by the end of the 1970s in the variation of the AO index and the leading principal component time series of the summer rainfall in East Asia. The rainfall anomaly changed from below normal to above normal in central China, the southern part of northeastern China and the Korean peninsula around 1978. However, the opposite interdecadal variation was found in the rainfall anomaly in North China and South China. The interdecadal variation of summer rainfall is associated with the weakening of the East Asia summer monsoon circulation. It is indicated that the interdecadal variation of the AO exerts an influence on the weakening of the monsoon circulation. The recent trend in the AO toward its high-index polarity during the past two decades plays important roles in the land-sea contrast anomalies and wintertime precipitation anomaly. The mid- and high-latitude regions of the Asian continent are warming, while the low-latitude regions are cooling in winter and spring along with the AO entering its high-index polarity after the late 1970s. In the meantime, the precipitation over the Tibetan Plateau and South China is excessive, implying an increase of soil moisture. The cooling tendency of the land in the southern part of Asia will persist until summer because of the memory of soil moisture. So the warming of the Asian continent is relatively slow in summer. Moreover, the Indian Ocean and Pacific Ocean, which are located southward and eastward of the Asian land, are warming from winter to summer. This suggests that the contrast between the land and sea is decreased in summer. The interdecadal decrease of the land-sea heat contrast finally leads to the weakening of the East Asia summer monsoon circulation.

Geographical inhomogeneity and temporal variability of mixing property and driving mechanism in the Arctic Ocean

Upper ocean mixing plays a key role in the atmosphere-ocean heat transfer and sea ice extent and thickness via modulating the upper ocean temperatures in the Arctic Ocean.Observations of diffusivities in the Arctic that directly indicate the ocean mixing properties are sparse.Therefore,the spatiotemporal pattern and magnitude of diapycnal diffusivities and kinetic energy dissipation rates in the upper Arctic Ocean are important for atmosphere-ocean heat transfers and sea ice changes.These were first estimated from the Ice-Tethered Profilers dataset(2005–2019)using a strain-based fine-scale parameterization.The resultant mixing properties showed signifi cant geographical inhomogeneity and temporal variability.Diapycnal diff usivities and dissipation rates in the Atlantic sector of the Arctic Ocean were stronger than those on the Pacific side.Mixing in the Atlantic sector increased significantly during the observation period;whereas in the Pacific sector,it weakened before 2011 and then strengthened.Potential impact factors include wind,sea ice,near inertial waves,and stratifi cation,while their relative contributions vary between the two sectors of the Arctic Ocean.In the Atlantic sector,turbulent mixing dominated,while in the Pacific sector,turbulent mixing was inhibited by strong stratification prior to 2011,and is able to overcome the stratifi cation gradually after 2014.The vertical turbulent heat fl ux constantly increased in the Atlantic sector year by year,while it decreased in the Pacific sector post 2010.The estimated heat flux variability induced by enhanced turbulent mixing is expected to continue to diminish sea ice in the near future.

Composition index of n-alkanes and paleoenvironmental study in sediments of the Arctic

This paper reports different concentration patterns of n-alkanes distribution in the sedi- ments from the Chukchi Sea, the Bering Sea in the Arctic. Factor statistical analysis method is used for studying the source of n-alkanes and paleoenvironment. The result shows that n-alkanes is in the range of nC15-nC33 and n-alkane distribution patterns are characterized by two modes. The first mode belongs to the higher molecular with MH being nC25-nC27, CPI > 1 and with remarkable odd-even dominance. They are of terrigenous plant origin. The second one belongs to lower carbon range with MH being nC17 -nC20, CPI > 1 and with indistinct odd-even dominance. Therefore they are contributed by marine bio- logicla inputs. The contribution of land origin is larger than that of marine source. Pr/Ph is lower than 1 in the investigated area, which indicates the depositional environment of reducing reaction with lower oxygen. The result of factor analysis has good agreement with composition characteristics of n-alkanes in the sediment.

An improved least mean square/fourth direct adaptive equalizer for under-water acoustic communications in the Arctic

An improved least mean square/fourth direct adaptive equalizer(LMS/F-DAE)is proposed in this paper for underwater acoustic communication in the Arctic.It is able to process complex-valued baseband signals and has better equalization performance than LMS.Considering the sparsity feature of equalizer tap coefficients,an adaptive norm(AN)is incorporated into the cost function which is utilized as a sparse regularization.The norm constraint changes adaptively according to the amplitude of each coefficient.For small-scale coefficients,the sparse constraint exists to accelerate the convergence speed.For large-scale coefficients,it disappears to ensure smaller equalization error.The performance of the proposed AN-LMS/F-DAE is verified by the experimental data from the 9th Chinese National Arctic Research Expedition.The results show that compared with the standard LMS/F-DAE,AN-LMS/F-DAE can promote the sparse level of the equalizer and achieve better performance.

Internal solitary wave generation by the tidal flows beneath ice keel in the Arctic Ocean

A series of non-hydrostatic,non-linear numerical simulations were carried out to investigate the generation and evolution of internal solitary waves(ISWs)through the interaction of a barotropic tidal current with an ice keel in the Arctic Ocean.During the interaction process,the internal surge was generated at first,and then the wave gradually steepened due to non-linearity during its propagation away from the ice keel.The internal surge eventually disintegrated into multi-modal and rank-ordered ISW packets with the largest having an amplitude of O(10)m.Sensitivity experiments demonstrated that the ISWs’amplitudes and energy were proportional to the varying ice keel depths and barotropic tidal fl ow amplitudes,but were insensitive to the changing ice keel widths.Typical ISWs can enhance the turbulent dissipation rate of O(10^(-6))W/kg along their propagation path.Further,heat entrainment induced by the wave-ice interaction can reach O(10)MJ/m per tidal cycle.This study reveals a particular ISW generation mechanism and process in the polar ice environment,which could be important in impacting the energy transfer and heat balance in the Arctic Ocean.

Interlinking the Hotspot Track in the Arctic and its Implications for Paleo-plate Reconstrution

The Siberian-Icelandic hotspot track is the only preserved continental hotspot track. Although the track and its associated age progression between 160 Ma and 60 Ma are not yet well understood, this section of the track is closely linked to the tectonic evolution of Amerasian Basin, the Alpha-Mendeleev Ridge and Baffin Bay. Using paleomagnetic data, volcanic structures and marine geophysical data, the paleogeography of Arctic plates （Eurasian plate, North American Plate, Greenland Plate and Alaska Microplate） was reconstructed and the Siberian-Icelandic hotspot track was interlinked between 160 Ma and 60 Ma. Our results suggested that the Alpha-Mendeleev Ridge could be a part of the hotspot track that formed between 160 Ma and 120 Ma. During this period, the hotspot controlled the tectonic evolution of Baffin Bay and the distribution of mafic rock in Greenland. Throughout the Mesozoic Era, the aforementioned Arctic plates experienced clockwise rotation and migrated northeast towards the North Pacific. The vertical influence from the ancient Icelandic mantle plume broke this balance, slowing down some plates and resulting in the opening of several ocean basins. This process controlled the tectonic evolution of the Arctic.

Statistical study on the spatial - temporal distribution features of the arctic sea ice extent

On the basis of the arctic monthly mean sea ice extent data set during 1953-1984, the arctic region is divided into eight subregions,and the analyses of empirical orthogonal functions, power spectrum and maximum entropy spectrum are made to indentify the major spatial and temporal features of the sea ice fluctuations within 32-year period. And then, a brief appropriate physical explanation is tentatively suggested. The results show that both seasonal and non-seasonal variations of the sea ice extent are remarkable, and iis mean annual peripheral positions as well as their interannu-al shifting amplitudes are quite different among all subregions. These features are primarily affected by solar radiation, o-cean circulation, sea surface temperature and maritime-continental contrast, while the non-seasonal variations are most possibly affected by the cosmic-geophysical factors such as earth pole shife, earth rotation oscillation and solar activity.

Measurements of sea ice thickness and its subice morphology analysis using ice-penetration radar in the Arctic Ocean

Based on radar penetrating measurements and analysis of sea ice in the Arctic Ocean, The potential of radar wave to measure sea ice thickness and map the morphology of the underside of sea ice is investigated. The results indicate that the radar wave can penetrate Arctic summer sea ice of over 6 meters thick; and the propagation velocity of the radar wave in sea ice is in the range of 0.142 m·ns -1 to 0.154 m·ns -1 . The radar images display the roughness and micro-relief variation of sea ice bottom surface. These features are closely related to sea ice types, which show that radar survey may be used to identify and classify ice types. Since radar images can simultaneously display the linear profile features of both the upper surface and the underside of sea ice, we use these images to quantify their actual linear length discrepancy. A new length factor is suggested in relation to the actual linear length discrepancy in linear profiles of sea ice, which may be useful in further study of the area difference between the upper surface and bottom surface of sea ice.

The Lower Cretaceous Giant Dyke Swarms in the Arctic and Its Significance for linking of Siberia-Iceland Hot-Spot Track

Siberia-Iceland hot-spot track is the one of hot-spot track preserved on continent.Although this hot-spot track has clear plume"heads"-Siberia large igneous province,owing to thick continental lithosphere,its continuing

Composition of algal pigments in surface freshen layer after ice melt in the central Arctic

Seasonal meltwater input creates a thin freshen layer in surface seawater under ice, which largely shifts the algae assemblages. Our recent observation of photosynthetic pigments in the high Arctic showed that ice bottom and 5 m of seawater under ice contained relatively high concentration of fucoxanthin, while chlorophyll b and lutein were the major diagnostic pigments in ice-water interface and 0 m of seawater under ice. Additionally, a notable change of dominant phytoplankton occurred in the top 5 m of seawater under ice, from chlorophytes-dominated at surface to diatoms-dominated at 5 m depth, which might attribute to the sharp salinity gradient （salinity from 12.5 to 28.1） in the surface seawater under ice. Our results imply that phytoplankton community in surface layer under ice would become more chlorophytes in the future warming Arctic Ocean.

Frequent central Pacific La Nina events may accelerate Arctic warming since the 1980s

Including significant warming trend,Arctic climate changes also exhibit strong interannual variations in various fields,which is suggested to be related to El Nino and Southern Oscillation(ENSO)events.Previous studies have demonstrated the different impacts on the Arctic of central Pacific(CP)and eastern Pacific(EP)ENSO events,and suggested these impacts are largely of opposite sign for ENSO warm and cold phases.Our results illustrate asymmetrical changes for the cold and warm ENSO events,especially for the La Nina events.Compared to the past frequent basin-wide cooling La Nina events,since the 1980 s the cooling center for the La Nina event has strengthened and moved westward along with the increasing frequency for the canonical and CP La Nina events.Contrary to the basin-wide cooling and canonical La Nina events,the frequent CP La Nina events induce significant warming from the Beaufort Sea to Greenland via the convection center moving northward over the western Pacific.Observation analysis and numerical experiments both suggest that the changes in La Nina type may also accelerate Arctic warming.

Using MAN and Coastal AERONET Measurements to Assess the Suitability of MODIS C6.1 Aerosol Optical Depth for Monitoring Changes from Increased Arctic Shipping

Collocated data of the moderate resolution imaging spectroradiometer (MO-DIS) Collection 6.1 aerosol optical depths (AOD) at 3 km × 3 km north of 59.9°N over ocean were assessed at 550 nm by aerosol robotic network (AERONET) data from coastal sites and marine aerosol network (MAN) data from vessels during June to October 2006 to 2018. Typically, MODIS AOD was higher at low and lower at high values than the AERONET AOD. Discrepancies were largest for sites where the Earth’s surface around the site is very heterogeneous (Canadian Archipelago, coast of Greenland). Due to the higher likelihood for sea-ice, MAN and MODIS AOD differed stronger west of Greenland and over the Beaufort Sea than at location in the Greenland and Norwegian Seas and Atlantic. MODIS AOD well captured the inter-seasonal variability found in the AERONET AOD data (R = 0.933). At all sites, MO-DIS and AERONET AOD agreement improved as time progressed in the shipping season, hinting at errors in sea-ice vs. open water classification. Overall 75.3% of the MODIS AOD data fell within the limits of the error envelops of the AERONET/MAN AOD data with MAN ranging between 87.5% and 100%. Changes in both MODIS and AERONET mean AOD between two periods of same length (2006-2011, 2013-2018) were explainable by changes in emissions for all sites.

As the Arctic Warms

冰雪皑皑的北极现正在逐步变暖,这不仅对全球气温产生影响,更危害到了生活在北极的动物,如北极熊和其他哺乳动物等。本文为美国北极气候影响评估中心最新的调查报告,通过数据揭示了发生在北极的变化。

Climatology of Air Quality in Arctic Cities—Inventory and Assessment

Freely available data of sulfur dioxide (SO2), ammonia (NH3), nitrogen dioxide (NO2), ozone (O3), and particulate matter (PM) observed in Arctic cities (north of 59.99 N) between 1972 and 2016 were compiled into an air-quality inventory of samples taken for limited periods. For cities with multiple years of data, air-quality climatology was determined in terms of daily means in the annual course. Mean urban air-quality climatology was calculated for regions of similar insolation, emission standards, topography, K&#246ppen-Geiger classification, and city size. Urban concentrations of PM precursors (SO2, NH3, NO2), PM2.5 and PM10 (PM with diameter less than 2.5 and 10 μm) were assessed in the sense of climatology with evidence from current knowledge. Typically, annual SO2 and NO2 means were lower for small than large Arctic cities, but can vary more than an order of magnitude over short distance. Cities seeing seasonal sea-ice had W-shaped mean annual courses of daily O3, while other cities had a spring maximum. Typically, annual means of urban pollutants in North America exceeded those in Scandinavia except for O3, where the opposite was true. Annual mean urban PM2.5 and PM10 concentrations varied from 1.6 to 21.2 μg·m-3 and 2 to 18.2 μg·m-3, respectively. Since PM10 encompasses PM2.5, annual PM10 means must be at least 21.2 μg·m-3. According to rural-to-urban ratios of species, seasonal transport of pollutants from wildfires, shipping, and the Kola Peninsula mining area occurred at some sites in Interior Alaska, western and northern Norway, respectively. Concurrent SO2 and PM or NO2 and PM measurements revealed combustion or traffic as major contributors to urban concentrations. Recommendations for potential future measurements of Arctic urban air quality were given based on the assessments of climatology and inventory.

Chinese science diplomacy in Arctic climate governance based on a survey and interviews with Chinese scientists

Science diplomacy is attracting increasing attention in the international relations literature.This study investigates how Chinese scientists understand this term and explores China’s dynamic praxis in Arctic climate governance.It conducts a theoretical and practical examination of science diplomacy in terms of three dimensions—science in diplomacy,diplomacy for science,and science for diplomacy—thus achieving a high degree of consistency.A multi-method approach,combining qualitative and quantitative research methodologies and involving the adoption of a literature review,participant interviews,and questionnaires,is adopted.Data were collected from interviews with 16 Chinese scientists involved in Arctic climate governance and from 130 valid questionnaires collected from Chinese natural scientists working in the climate change field.Drawing on qualitative and quantitative findings,the study reveals that the three-dimensional framework of science diplomacy can provide insight into Chinese scientists’understandings of the topic.In contrast to the participants’vague theoretical responses,the outlines of China’s Arctic climate governance can be clearly identified within this framework.The study concludes by underlining the tension between theory and practice in terms of science diplomacy and highlighting the emerging challenges for China in developing its Arctic science diplomacy against the background of the COVID-19 pandemic and Russia-Ukraine conflict.Moreover,it is suggested that,to further develop China’s Arctic science diplomacy,it is vital to take account of the deficiencies in China’s science diplomacy.The study’s empirical results contribute to an understanding of the dynamic nature of science diplomacy in the Chinese context.

Lessons and prospects of Sino-Russian Arctic cooperation

The strategic partnership between China and Russia is creating solid ground for the cooperative development of the Arctic. These two states＇ joint development of the Northern Sea Route will not only provide additional impulse to the export- oriented economy of China and allow further diversification of supply routes to China, but will also promote investment into the infrastructure and economic growth of Russian northern territories. Climate change in the Arctic has forced China and Russia to acknowledge the sustainable use of the Arctic. On the one hand, exploration of the region should not harm indigenous people＇s rights and should help this population improve their standard of living by providing qualified healthcare and opportunities for commercial fulfillment of traditional crafts. On the other hand, this exploration should also include elimination of harmful anthropogenic impact and provide support for environment self-restoration. Sino-Russian Arctic cooperation will help humans discover eco-friendly approaches to use Arctic resources, promote rational use of the Arctic and inspire sustainable development of the region.

Geographical distribution of general aerobic heterotrophic bacteria in surficial sediments from the Chukchi Sea and Canadian Basin

This paper determined the abundance of General Aerobic heterotrophic Bacteria （GAB） in surficial sediments from the Chukchi Sea and the Canadian basin by using MPN and discussed their geographical distribution. The result shows that the determination percentages of the GAB were high, even till 100 percentage. The abundance range and averages of GAB for 4℃and 25℃ were from 4.00 × 10^2 to 2.40× 10^6 , 1.71×10^6 ind.·g^-1 （wet sample ） and from 2.40 ×10^5 to 2.40×10^7 , 1.10×10^7 ind. ·g^-1 （wet sample ） respectively. Not only the abundance range but also the averages of GAB in 25℃ were higher than that in 4℃. The abundance of GAB in sediments show a tendency that it is roughly greater in the lower latitudinal area than in the higher latitudinal area. The abundance of GAB increased from east to west as for the longitudinal distribution. With the water depth increasing, the abundance of GAB at 4℃ decreased, but GBA at 25℃ is not changed obviously with water depth. It seems that warmer circumstantial temperature is more suitable for some GAB.

Chinese investment in Greenland

In 2009 Greenland moved to a more extensive degree of self-government in relation to the Kingdom of Denmark （the Realm）, and most policy areas related to business activities and investment are now under the control of Greenland. Under the Self-Government Act, Greenland has issued legislation within several business sectors and other business-related policy areas, including the mineral resources sector. Today, Greenland is highly dependent on fishing and fish exports; however, the government is quite ambi-tious in its desire to develop new business sectors and attract foreign investment, including investment from China, especially to develop its mineral resources. China is now the second largest economy in the world, and outbound investments by Chinese companies present unprecedented opportunities for both the Chinese companies and their global partners. However, Chinese outbound investment faces many hurdles, both at home and elsewhere. It is highly advisable for Chinese companies to evaluate the regulatory, political, environmental, labor, and financial conditions and under-stand what remedies may mitigate the risks they identify before investing in Green land. This paper investigates and analyzes the hurdles faced by Chinese investors in both Greenland and the Danish Realm. The paper focuses on but is not limited to investments in the mining industry.

Evaluation of the relationships and uncertainties of airborne and ground-based sea ice surface temperature measurements against remotely sensed temperature records

Sea ice surface temperature(IST)is an important indicator of environmental changes in the Arctic Ocean.In this study,the relative performance of four mainstream IST records,i.e.airborne IST,infrared radiometer measured IST(IR IST),longwave radiation derived IST(LWR IST),and snow and ice mass balance array buoy derived IST(Buoy IST),were evaluated against the MODIS IST product.Bias,standard deviation(STD),and root mean square error(RMSE)were used to evaluate the data quality.Results revealed that airborne IST had the best accuracy,which was 0.21 K colder than MODIS IST,with STD of 1.46 K and RMSE of 1.47 K.Ground-based ISTs were biased with each other but all warmer than the MODIS IST.The IR IST had the best overall accuracy(bias=0.55 K;STD=1.52 K;RMSE=1.61 K),while the LWR IST was the noisiest measurement with the largest outlier data percent.Besides,co-located IR and LWR ISTs were more consistent than any type of evaluated IST against MODIS IST(correlation coefficient=0.99).Airborne and IR ISTs are thus the premier choice for monitoring the rapidly changing Arctic sea ice,together with satellite observations.