Arctic Basin Research Articles

Studies of microplastic content in water and commercial fish: from scientific research to large-scale monitoring

Purpose. The article presents proposals for the development of studies of microplastic pollution of waters and biological resources in the Russian fishery areas. Materials and methods. The materials of VNIRO on the quantitative assessment of the MPs content in the Arctic Seas in August-October 2019–2022 and modern research on this problem are summarized. MPs samples were collected on the surface of the seas with a Manta-trawl 335 and processed according to a single method. Results. The conducted studies pick up knowledge gaps regarding the real level of marine MPs pollution of the Arctic region.Novelty. No large-scale localization of MPs was detected in the observation areas, the level of plastic pollution on the surface of the Russian Arctic seas was lower compared to other areas of the World Ocean. We point out the relevance of the assumption that a significant part of MPs fragments and fibers are transported by Atlantic and Pacific currents to the Arctic basin. A sample survey of fish in commercial catches for MPs contamination confirmed the presence of its fragments and fibers in the digestive tract of some individuals (pink salmon, greenlings, herring, sea bass) caught in the North Pacific seas in 2019, 2021 and 2022.Practical significance. The global increase in MPs content in the Northern hemisphere seas, exacerbated by climate change, requires a transition from exploratory scientific observations to regular multidisciplinary study of plastic pollution of biotopes of ecosystems of the Arctic, North Pacific and Atlantic seas. The key points and tasks of monitoring microplastic pollution of waters and biological resources in the Russian fishing areas provide for objective and comparable assessments based on the use of unified methods of collection and processing of samples, as well as an ecosystem approach to prevent environmental risks and ensure food safety.

Long-Range Atmospheric Transport of Black Carbon from Severe Forest Fires in Siberia to the Arctic Basin

Long-Range Atmospheric Transport of Black Carbon from Severe Forest Fires in Siberia to the Arctic Basin

Detection and attribution of changes in streamflow and snowpack in Arctic river basins

Detection and attribution of changes in streamflow and snowpack in Arctic river basins

FIRST DATA ON PALEOGEOGRAPHICAL SETTINGS AND CHRONOLOGY OF THE LAST INTERGLACIAL ON ZIMNII COAST OF THE WHITE SEA

Field lithostratigraphic studies, microfaunistic and palynological analyses, as well as optically stimulated luminescence (OSL) dating revealed for the first time that the lower part of Quaternary sediment sequences exposed along Zimnii Coast of the White Sea accumulated in marine and nearshore environments during the Boreal transgression at the beginning of the Last Interglacial and thus form the Upper Pleistocene Mikulinian Horizon. This is confirmed by lithology of sediment beds; species composition of foraminifers, ostracods and aquatic palynomorphs; and OSL dates in the range of 118–104 ka. The composition of benthic microfossils indicates that during the early Boreal transgression the entire Zimnii Coast was occupied by an coastal arctic ice-covered basin with water depths of 50 m, high sedimentation rates, and water stratification induced by melt/river water inflow. At the stage of regression, sedimentation in shallow marine environments was dominant along Zimnii Coast.

Short-Term (7 Day) Beaufort Sea Ice Extent Forecasting with Deep Learning

Abstract Ships inside the Arctic basin require high-resolution (1–5 km), near-term (days to semimonthly) forecasts for guidance on scales of interest to their operations where forecast model predictions are insufficient due to their coarse spatial and temporal resolutions. Deep learning techniques offer the capability of rapid assimilation and analysis of multiple sources of information for improved forecasting. Data from the National Oceanographic and Atmospheric Administration’s Global Forecast System, Multi-scale Ultra-high Resolution Sea Surface Temperature (MEaSUREs), and the National Snow and Ice Data Center’s Multisensor Analyzed Sea ice Extent (MASIE) were used to develop the sea ice extent deep learning forecast model, over the freeze-up periods of 2016, 2018, 2019, and 2020 in the Beaufort Sea. Sea ice extent forecasts were produced for 1–7 days in the future. The approach was novel for sea ice extent forecasting in using forecast data as model input to aid in the prediction of sea ice extent. Model accuracy was assessed against a persistence model. While the average accuracy of the persistence model dropped from 97% to 90% for forecast days 1–7, the deep learning model accuracy dropped only to 93%. A k-fold (fourfold) cross-validation study found that on all except the first day, the deep learning model, which includes a U-Net architecture with an 18-layer residual neural network (Resnet-18) backbone, does better than the persistence model. Skill scores improve the farther out in time to 0.27. The model demonstrated success in predicting changes in ice extent of significance for navigation in the Amundsen Gulf. Extensions to other Arctic seas, seasons, and sea ice parameters are under development. Significance Statement Ships traversing the Arctic require timely, accurate sea ice location information to successfully complete their transits. After testing several potential candidates, we have developed a short-term (7 day) forecast process using existing observations of ice extent and sea surface temperature, with operational forecasts of weather and oceanographic variables, and appropriate machine learning models. The process included using forecasts of atmospheric and oceanographic conditions, as a human forecaster/analyst would. The models were trained for the Beaufort Sea north of Alaska using data and forecasts from 2016 combined with 2018–20. The results showed improvement in short-term forecasts of ice locations over current methods and also demonstrated correctly predicted changes in the sea ice that are important for navigation.

Трансформация процессов развития трансграничных территорий Дальневосточной Арктики и механизмов их регулирования: роль критической инфраструктуры

In this article, on the basis of conceptual approaches derived from research in the field of theories of spatial economy and infrastructure, the problems of naturally occurring significant changes in the pro-cesses of development of natural-economic formations formed in the geostrategic territories of the North-Arctic part of the Far East, representing at the same time the eastern part of the Arctic zone of the Russian Federation (AZRF) are considered. Their transboundary role in the global Arctic basin, as well as at the junction of Russia with the state of Alaska, USA, in the Pacific Arctic, also requires intensification of research in this area, especially at the present stage of the well-known difficulties in international cooperation between our country and the United States. All this requires focusing the attention of specialists on the study of these processes, as well as on the closely related issues of the necessity to adjust the methods and mechanisms of state-regional regulation of the development of these economic entities. In the near future, the regulatory tools used should ensure the transition of these territories from the micro-level of primary, mainly raw material, spatial-economic formations to a new stage, to a higher meso-level of industrial development of economic complexes. As studies show, this transition will occur on the basis of advanced creation of a system-organized critical infrastructure, its main elements, which, due to their new spatial configuration, will provide the necessary conditions for this transition and give the opportunity to maximize the use of exogenous factors and emergent effects of the development of economic entities.

Climate warming enhances chemical weathering in permafrost-dominated eastern Siberia

Understanding the impacts of climate warming on hydrogeochemical processes, particularly in areas dominated by permafrost, is crucial. However, the natural background levels of chemical components in eastern Siberian rivers from permafrost-dominated regions and their responses to climate warming have not been adequately quantified. This study aims to address this knowledge gap by using a comprehensive river water chemistry database (n = 1264) spanning from 1940 to 2019. Our results reveal that the concentration of total dissolved solids (TDS), a key parameter of drinking water quality, in river basins predominantly free of permafrost (194.6 ± 256.4 mg/L) is approximately 2.3 times higher than in permafrost-dominated river basins (83.7 ± 35.8 mg/L) in eastern Siberia. These observations imply potential shifts in freshwater quality resulting from permafrost degradation. We further detect that carbonate weathering, which plays a fundamental role in the global carbon cycle, is a predominant process controlling hydrogeochemical cycles. (Ca2+ + Mg2+) concentrations as a proxy for carbonate weathering intensity are sensitive to climate warming, increasing at a rate of 0.10 mmol/(L·°C). This finding provides evidence that the current acceleration of carbonate weathering, driven by climate warming, is already influencing local water quality. Additionally, (Ca2+ + Mg2+) concentrations and TDS are highly interrelated with temperature-dependent variables (e.g., active layer thickness of permafrost and leaf area index) and basin erosion-controlling factors (e.g., precipitation, elevation and slope of basin). Under a warming climate, river chemical fluxes (e.g., export of TDS and major ions) increase notably, especially during the winter, indicating an increase in mineral-laden groundwater discharge to rivers due to permafrost degradation. Our results demonstrate that climate warming is accelerating hydrogeochemical processes in permafrost-dominated Arctic basins.

Trapped tidal currents generate freely propagating internal waves at the Arctic continental slope

Energetic tidal currents in the Arctic play an important role in local mixing processes, but they are primarily confined to the shelves and continental slopes due to topographic trapping north of their critical latitude. Recent studies employing idealized models have suggested that the emergence of higher harmonic tidal waves along these slopes could serve as a conduit for tidal energy transmission into the Arctic Basin. Here we provide observational support from an analysis of yearlong observations from three densely-instrumented oceanographic moorings spanning 30 km across the continental slope north of Svalbard (sim81.3^{circ }N). Full-depth current records show strong barotropic diurnal tidal currents, dominated by the K_1 constituent. These sub-inertial currents vary sub-seasonally and are strongest at the 700-m isobath due to the topographic trapping. Coinciding with the diurnal tide peak in summer 2019, we observe strong baroclinic semidiurnal currents exceeding 10 cm s^{-1} between 500 m and 1000 m depth about 10 km further offshore at the outer mooring. In this semidiurnal band, we identify super-inertial K_2 waves, and present evidence that their frequency, timing, polarization, propagation direction and depths are consistent with the generation as higher harmonics of the topographically trapped K_1 tide at the continental slope.

Revisiting the Potential to Narrow Model Uncertainty in the Projections of Arctic Runoff

AbstractDespite multiple advances in the understanding of the water cycle intensification in a warmer climate, climate models still diverge in their hydrological projections. Here we constrain annual runoff projections over individual and aggregated Arctic river basins. For this purpose, we use two ensembles of global climate models and two statistical methods: a regression scheme assuming similar runoff sensitivities at interannual versus climate change timescales, and a Bayesian method where models are used to derive a posterior runoff response conditioned on historical observations. While both techniques are shown to narrow model uncertainties, more or less substantially depending on rivers, the Bayesian method is less sensitive to the choice of the model ensemble and is more skillful when tested with synthetic observations. It has also been applied over the whole Arctic watershed, showing so far a limited narrowing of the inter‐model spread, but its skill will further improve with increasing climate change.

A model for the Arctic mixed layer circulation under a summertime lead: implications for the near-surface temperature maximum formation

Abstract. Leads in sea ice cover have been studied extensively because of the climatic relevance of the intense ocean–atmosphere heat exchange that occurs during winter. Leads are also preferential locations of heat exchange and melting in early summer, but their oceanography and climate relevance, if any, remains largely unexplored during summertime. In particular, the development of a near-surface temperature maximum (NSTM) layer typically 10–30 m deep under different Arctic basins has been observationally related to the penetration of solar radiation through the leads. These observations reveal that the concatenation of calm and wind events in the leads could facilitate the development of the NSTM layer. Using numerical modeling and an idealized framework, this study investigates the formation of the NSTM layer under a summer lead exposed to a combination of calm and moderate wind periods. During the calm period, solar heat accumulates in the upper layers under the lead. Near-surface convection cells are generated daily, extending from the lead sides to its center. Convection cells affect the heat storage in the mixed layer under the lead and the adjacent ice cap. A subsequent wind event (and corresponding ice drift) mixes and spreads fresh and cold meltwater into the warm layers near the surface. Surface mixing results in temperatures in the near-surface layers that are lower than in the deeper layers, where the impact of the surface stresses is weaker. Additionally, the warm waters initially located under the lead surface stretch and spread horizontally. Thus, an NSTM layer is formed. The study analyzes the sensitivity of the depth and temperature of the NSTM layer to buoyancy forcing, wind intensity, ice drift, stratification, and lead geometry. Numerical results suggest that the NSTM layer appears with moderate wind and ice drift and disappears when the wind intensity is higher than 9 m s−1. Depending on the background stratification, the calm period reinforces or becomes critical in NSTM layer formation. According to the results, ice drift is key to the development of the NSTM layer.

Changes of the streamflow of northern river basins of Siberia and their teleconnections to climate patterns

AbstractThe Arctic rivers contribute more than one‐third of the total freshwater streamflow into the Arctic Ocean and play an essential role in the heat and mass circulation of the Arctic atmosphere/ocean system. As the Arctic is warming faster than the global average, the streamflow from Arctic basins increases. This study analyzed the streamflow of the three largest Siberian rivers: the Lena, Yenisei, and Ob', at multiple temporal scales. Results show that the annual streamflow of each river basin exhibits statistically significant increasing trends, while the seasonal streamflow of sub‐basins generally decreases in the summer but increases in the winter. Both autocorrelation and long‐term persistency are often found in the streamflow time series, which indicates significant changes in the large‐scale climatological environment. Therefore, wavelet coherence between the streamflow and large‐scale climate patterns, including the El Niño–Southern Oscillation (ENSO), North Pacific pattern (NP), Arctic Oscillation (AO), and the Pacific/North America Pattern (PNA), have been conducted. NP and ENSO are found to have positive relationships with the precipitation and the ratio of potential evapotranspiration over the precipitation. AO and the PNA are found to have positive relationships with the streamflow of the Ob' and Yenisei rivers at decadal and multidecadal scales. This study demonstrates that the existence of nonstationarities within the Siberian streamflow as the combined impact of climate change alters the hydroclimatological and terrestrial environment of Siberia. These findings provide new insights into the mechanisms underlying the hydrologic changes to warming trends and oscillations of climate patterns, which contribute to our understanding and the prediction of streamflow of these northern rivers.

Response of ocean climate to different heat-flux perturbations over the North Atlantic in FAFMIP

The diversity of surface-flux perturbations, especially for heat-flux perturbations, notably leads to uncertainties surrounding the responses of ocean climate under global warming scenarios projected by climate/Earth system models. However, when imposing heat-flux perturbations on the models, strong feedback persists between the atmosphere and the ocean, resulting in nearly doubled heat-flux perturbation over the North Atlantic (NA). Herein, quantitative evaluation of the influences of magnitude change of heat-flux perturbations over the NA on the changes in the Atlantic Meridional Overturning Circulation (AMOC), ocean heat uptake (OHU) and dynamic sea level (DSL) has been conducted by analysis of eight coupled model responses to the heat-flux perturbation experiments in the Flux-Anomaly-Forced Model Inter-comparison Project. It has been demonstrated that the magnitude of the AMOC change is extremely sensitive to the magnitude change of imposed NA heat-flux perturbation, and the weakening amplitude of the AMOC is nearly halved as the imposed heat-flux perturbation F is halved over the NA. The most remarkable responses of both DSL and OHU to the magnitude changes of NA heat-flux perturbation have been primarily found in the Atlantic and Arctic basins, especially for the NA region. Both the added ocean heat uptake (OHUa) and redistributed ocean heat uptake (OHUr) play key roles in OHU changes among the various NA heat-flux perturbation experiments. The magnitude change of NA-mean OHUa is almost linearly related to the imposed NA heat-flux perturbation, while the magnitude change of NA-mean OHUr, which is primarily caused by AMOC change and redistributed heat flux, is not proportional to the imposed NA heat-flux perturbation. There is a nearly linear relationship between the magnitude of AMOC change and the OHUr in tropical regions, including the regions in the low-latitude South Atlantic, the tropical Pacific Ocean and the Indian Ocean.

Understanding Arctic Sea Ice Thickness Predictability by a Markov Model

Abstract The Arctic sea ice decline and associated change in maritime accessibility have created a pressing need for sea ice thickness (SIT) predictions. This study developed a linear Markov model for the seasonal prediction of model-assimilated SIT. It tested the performance of physically relevant predictors by a series of sensitivity tests. As measured by the anomaly correlation coefficient (ACC) and root-mean-square error (RMSE), the SIT prediction skill was evaluated in different Arctic regions and across all seasons. The results show that SIT prediction has better skill in the cold season than in the warm season. The model performs best in the Arctic basin up to 12 months in advance with ACCs of 0.7–0.8. Linear trend contributions to model skill increase with lead months. Although monthly SIT trends contribute largely to the model skill, the model remains skillful up to 2-month leads with ACCs of 0.6 for detrended SIT predictions in many Arctic regions. In addition, the Markov model’s skill generally outperforms an anomaly persistence forecast even after all trends were removed. It also shows that, apart from SIT itself, upper-ocean heat content (OHC) generally contributes more to SIT prediction skill than other variables. Sea ice concentration (SIC) is a relatively less sensitive predictor for SIT prediction skill than OHC. Moreover, the Markov model can capture the melt-to-growth season reemergence of SIT predictability and does not show a spring predictability barrier, which has previously been observed in regional dynamical model forecasts of September sea ice area, suggesting that the Markov model is an effective tool for SIT seasonal predictions.

Deconstruction of tropospheric chemical reactivity using aircraft measurements: the Atmospheric Tomography Mission (ATom) data

Abstract. The NASA Atmospheric Tomography Mission (ATom) completed four seasonal deployments (August 2016, February 2017, October 2017, May 2018), each with regular 0.2–12 km profiling by transecting the remote Pacific Ocean and Atlantic Ocean basins. Additional data were also acquired for the Southern Ocean, the Arctic basin, and two flights over Antarctica. ATom in situ measurements provide a near-complete chemical characterization of the ∼ 140 000 10 s (80 m by 2 km) air parcels measured along the flight path. This paper presents the Modeling Data Stream (MDS), a continuous gap-filled record of the 10 s parcels containing the chemical species needed to initialize a gas-phase chemistry model for the budgets of tropospheric ozone and methane. Global 3D models have been used to calculate the Reactivity Data Stream (RDS), which is comprised of the chemical reactivities (production and loss) for methane, ozone, and carbon monoxide, through 24 h integration of the 10 s parcels. These parcels accurately sample tropospheric heterogeneity and allow us to partially deconstruct the spatial scales and variability that define tropospheric chemistry from composition to reactions. This paper provides a first look at and analysis of the up-to-date MDS and RDS data including all four deployments (Prather et al., 2023, https://doi.org/10.7280/D1B12H). ATom's regular profiling of the ocean basins allows for weighted averages to build probability densities for the key species and reactivities presented here. These statistics provide climatological metrics for global chemistry models, e.g., the large-scale pattern of ozone and methane loss in the lower troposphere and the more sporadic hotspots of ozone production in the upper troposphere. The profiling curtains of reactivity also identify meteorologically variable and hence deployment-specific hotspots of photochemical activity. Added calculations of the sensitivities of the production and loss terms relative to each species emphasize the few dominant species that control the ozone and methane budgets and whose statistical patterns should be key model–measurement metrics. From the sensitivities, we also derive linearized lifetimes of ozone and methane on a parcel-by-parcel basis and average over the basins, providing an observational basis for these previously model-only diagnostics. We had found that most model differences in the ozone and methane budgets are caused by the models calculating different climatologies for the key species such as O3, CO, H2O, NOx, CH4, and T, and thus these ATom measurements make a substantial contribution to the understanding of model differences and even identifying model errors in global tropospheric chemistry.

Some patterns of formation of extreme surface air temperature in the area of the Spitzbergen (Svalbard) archipelago during the cold period

The article presents research findings of meteorological conditions during the formation of extreme surface air temperature (SAT) in the cold period from October to May in the Barentsburg area, the Spitzbergen (Svalbard) archipelago. Six extremely cold periods and six extremely warm periods for the weather sequence from 1912 to 2022 are considered. Correlation coefficients of extreme SAT in Barentsburg with extreme SAT in the points of Longyearbyen, Hornsund, Isfjord Radio, Pyramiden, Nu-Alesund, located in the west of Spitzbergen (Svalbard), were calculated. Also, characteristics of atmospheric circulation at the surface level, the level of the geopotential surface 500 hPa and 700 hPa and air temperature anomalies are analyzed, the results of comparing atmospheric circulation indices NAO and AO in the formation of extreme SAT are presented. Characteristic localizations of the polar vortex were found during the formation of negative and positive anomalies of SAT. For cold periods with extremely low temperatures, the localization of the polar vortex in the northeast of the Kara Sea and Severnaya Zemlya archipelago is observed. At the surface level the baric trough from the Atlantic depression is shifted to the coast of Scandinavia and the southern part of the Barents Sea. The Svalbard region is under the influence of the periphery of the anticyclonic field over the Arctic basin, Greenland, over the western Arctic Seas, conditions are formed for the deviation of SAT by 3–4 degrees below normal. In the case of extremely high SAT, the polar vortex is shifted to the eastern part of the Canadian Arctic Archipelago and the Baffin Sea. At the surface level, the baric trough from the Icelandic depression develops over the Greenland, Norwegian and Barents Seas, which leads to the moving of warm air masses from the Atlantic to polar latitudes and the formation of average SAT in the Spitzbergen (Svalbard) region above long-term values by 1–2 degrees. The estimates of macroprocesses obtained can be used for preparing long-term forecasts for the northern polar region and detailing them for the Spitzbergen (Svalbard) region.

Arctic climate warming: discrepancies between global climate
 models and observations and possible causes

Global climate models are used to predict anthropogenic climate change and to plan social and economic activities under changing climatic conditions. At the same time, there are discrepancies between model projections and observed climate changes, especially in low latitudes and polar regions. One reason for the discrepancy may be insufficient attention to natural forcings on the climate system. Therefore, studies of the role of natural factors in the development of modern warming are relevant for
 improving the reliability of forecasts for the development of the climatic situation on Earth. Particular attention is paid to the impact of climate change in low latitudes on the Arctic. A significant contribution to these changes can be made by a long-term increase in low-latitude insolation. Most of the low latitudes
 are occupied by the ocean, which absorbs the bulk of the incoming solar radiation. The contribution of the increase in insolation to the increase in ocean surface temperature at low latitudes is estimated from the available data on insolation of the upper boundary of the atmosphere. The changes in SST at low latitudes are compared according to reanalysis data and calculations of global climate models. Comparison of climate changes in low latitudes and in the Arctic is made. The influence from low latitudes on the reduction in the area of sea ice and the increase in water temperature in the Arctic basin is estimated. Changes in the characteristics of the atmosphere and ocean at low latitudes, associated with an increase in insolation, after
 3 years are manifested in changes in the characteristics of the climate and sea ice in the Arctic. This indicates the potential for improved global modeling of warming in the Arctic and at low latitudes when taking into account slow changes in radiative forcing at the upper boundary of the atmosphere due to the Earth’s orbital dynamics. Insolation trends at low latitudes are maximum in spring, i.e., in the vicinity of the vernal equinox in the Earth’s orbit. This indicates the influence of precession — a slow shift of the equinox point, when the influx of solar radiation to low latitudes is maximum, to the perihelion, where it will be 3 W/m2more.

Учет сезонности и маршрутов плавания для обеспечения аварийно-спасательных работ в акватории Севморпути

Development of the navigation in the Arctic basin in the changed geopolitical conditions is a national task, the solution of which ensures an uncomplicated, and in some cases, more economical access of the Russian products to the Asian markets. The transition to year-round navigation determines the development of new routes in the eastern sector of the Northern Sea Route, as well as the expansion of the navigation window. The condition for the development of navigation, both seasonal and year-round, is to ensure its safety. This applies both to the own navigation of ships and the ability of emergency rescue teams to provide their vessels with easy access to all the sections of shipping routes. The analysis was carried out concerning the ice classes of the existing and under construction emergency rescue fleet of the Federal State Budgetary Institution «Morspassluzhba» of the ice classes Arc5, Icebreaker6 and Icebreaker7. It was concluded that in accordance with the current Rules for navigation in the waters of the Northern Sea Route they have significant restrictions on independent work. Emergency rescue vessels of the Arctic ice class Arc5 cannot conduct independent operations in the winter-spring period in the eastern sector of the Northern Sea Route in the medium type of ice conditions (in the heavy type of ice conditions, their navigation is completely prohibited), requiring icebreaking support. Ice class vessels Icebreaker6 (as well as the most powerful multifunctional emergency rescue vessel of the project IBSV02 of ice class Icebreaker7) cannot perform independent operations in case of heavy type of ice conditions. To carry out rescue operations, they will need the support of nuclear-powered icebreakers of ice class Icebreaker8 and Icebreaker9 or diesel icebreakers Icebreaker8, for which there are no restrictions on navigation in the waters of the Northern Sea Route. During the period of the most difficult navigation conditions (winter-spring period), it is proposed to place emergency rescue teams on the linear icebreakers, not only nuclear, but also diesel icebreakers of the Icebreaker8 of ice class, as well as their use as jumping helicopter platforms for conducting emergency rescue operations.

Baseline Study on Microplastic Distribution in the Open Surface Waters of the Korean Southwest Sea

This study investigated microplastic distribution characteristics by collecting surface seawater from sea areas to the south of Jeju Island in August 2020. The average microplastic abundance was 0.46 ± 0.27 particles/L (n = 23), and PE had a high ratio, averaging 53%. The levels of fragments and fibers were observed to be 69% and 31% on average, respectively. The most common size of the microplastics was on average 0.02–0.30 mm at a level of 69%. We found a higher abundance of microplastics in the study area than in other open waters such as the Arctic Central Basin and the Atlantic Ocean, whereas the abundance was lower than that in previous studies on coastal areas. We studied an area of open sea connecting China, Japan, and the Pacific Ocean, and, in this region, the microplastic distribution varies depending on sea currents in the surrounding areas. In the summer, the western and central regions of the study sea area have low salinity levels due to discharge from China’s Yangtze River. This generally indicates that high-density plastic deposits are found in the Yangtze River estuary, and low-density plastics are found in the study area. Furthermore, this implies that low- and high-density plastics are transported in water for long periods of time due to the Taiwan Warm Current and because the eastern sea area has high salinity.

Estimation of summer pan-Arctic ice draft from satellite passive microwave observations

Pan-Arctic observations of summer sea ice thickness have been a challenging problem despite their global significance in weather/climate analysis and prediction. To solve this problem, this study developed a method for estimating the pan-Arctic ice draft (depth of sea ice below sea surface level) using spaceborne passive microwave-measured brightness temperatures (TBs). This study found that the time series of TBs is highly correlated with the corresponding time series of ice draft (D)s measured by three upward-looking sonar (ULS) sites over the Beaufort Sea during the ice melting season. Based on this finding, a D estimation equation was derived by relating satellite-measured TBs at microwave frequencies to Ds. Pan-Arctic D distributions from June to August obtained from this study describe well the general thinning process of Arctic sea ice during the summer of 2021. The validation of estimated Ds with other ULS measurements, which were not used for training data, showed good agreement between them suggesting the robustness of the developed estimation method over the Arctic basin. In addition, validation was made against ice mass balance buoy-measured sea ice thickness, and result shows a good agreement between buoy-measured ice thickness and estimated ice thickness converted from the D. Meanwhile, relatively high uncertainty in D estimation above 2 m shown in the result and validation suggests the potential for future improvement of D estimation in the early melting period. As the proposed method can provide summer pan-Arctic D distributions on a daily basis, the D from this study can be applied for generating the initial field for the sea ice and global climate models through data assimilation.

Observed Spatio‐Temporal Variability of the Eddy‐Sea Ice Interactions in the Arctic Basin

AbstractIn the Arctic Basin, the ocean dynamics at mesoscale and submesoscale under sea ice are poorly quantified and understood. Here, we analyze comprehensive data sets from Ice Tethered Profilers and moorings from the Beaufort Gyre Observing System spanning the period 2004–2019 in order to characterize the space and time variations of the (sub)mesoscale flow. In seasonally ice‐covered regions, the dynamics in the surface layer is largely determined by the presence of sea ice, with an increased eddy kinetic energy and numerous eddies in summer. Beyond these regions, the influence of the sea ice conditions on the first order dynamics is less clear. A wavenumber spectra analysis of observations at the surface and at depth under the sea ice pack reveals that a large variety of regimes can be found, independently of the time and space variations of the sea ice conditions. Focusing on a census of individual eddies, and their potential signature in sea ice, we found that around 500 eddies can be detected in the subsurface layer over 2004–2019, including both submesoscale (radius between 3 and 10 km) and mesoscale (up to 80 km) structures. Based on simple scaling calculations, we quantify the dynamical or thermodynamical signature that these eddies may imprint at the surface. While they do not induce any significant heat flux and subsequent sea ice melt, subsurface eddies can induce a dynamic height anomaly of the order of a few centimetres, resulting into a surface vorticity anomaly strong enough to impact sea ice locally.