Arctic navigability is crucial to the global economy and landscape, while there is an omission in understanding how Arctic navigability changes as a function of 1.5 degrees C of the Paris Agreement. This study investigated the impact of 1.5 degrees C global warming above the preindustrial level on sea ice conditions and accessibility of the Northern Sea Route (NSR) and Northwest Passage (NWP) with the Polar Operational Limit Assessment Risk Indexing System and new risk demarcation criteria. The Arctic is colder on the Canadian side than on the European side under 1.5 degrees C warming. Sea ice is mostly less than three years old, and the younger, thinner and less concentrated ice is mainly in the seas along the NSR. Ships above Polar Class (PC) 6 might be unimpeded along two passages all the year. Besides, the NSR and NWP have great potential for PC6 ships in October-December, while it is only the NSR for PC7 ships. Caution is still required when navigating the western East Siberian Sea, its surrounding straits, and the Parry Channel. These changes in hydrological conditions are important for global shipping, and this work is helpful for supporting coordinated international decision-making.

Arctic river discharge is one of the important factors affecting sea-ice melting of Arctic shelf seas. However, such effects have not been given much attention. In this study, the changes in discharge of the Ob, Yenisei, and Lena Rivers and the sea ice of the Kara and Laptev Seas during 1979-2019 were analyzed. Substantial increases in discharge and heat from the discharge and decreases in sea ice concentration (SIC) were detected. The effects of changes in discharge and riverine heat on sea ice changes were investigated. The results showed that the influence of the discharge, accumulated discharge, heat, and accumulated heat on SIC mainly occurred at the beginning and final stages of sea-ice melting. Discharge accelerated the melting of sea ice by increasing the absorption of solar radiation as the impurities contained in the discharge washed to the sea ice surface during the initial and late stages of sea-ice melting. Changes in cumulative riverine heat from May to September greatly contributed to the SIC changes in the Kara and Laptev Seas at the seasonal scale. The SIC reduced by 1% when the cumulative riverine heat increased by 213.2 x 10(6) MJ, 181.5 x 10(6) MJ, and 154.6 x 10(6) MJ in the Lena, Yenisei, and Ob Rivers, respectively, from May to September. However, even in the plume coverage areas in the Kara and Laptev Seas, discharge changes from the three rivers had a limited contribution to the reduction in SIC at annual scales. This work is helpful for understanding the changes in Arctic sea ice.

While Arctic sea ice has been decreasing in recent decades that is largely due to anthropogenic forcing, the extent of Antarctic sea ice showed a positive trend during 1979-2015, followed by an abrupt decrease. The shortness of the satellite record limits our ability to quantify the possible contribution of anthropogenic forcing and internal variability to the observed Antarctic sea ice variability. In this study, ice core and fast ice records with annual resolution from six sites are used to reconstruct the annualresolved northernmost latitude of sea ice edge (NLSIE) for different sectors of the Southern Ocean, including the Weddell Sea (WS), Bellingshausen Sea (BS), Amundsen Sea (AS), Ross Sea (RS), and the Indian and western Pacific Ocean (IndWPac). The linear trends of the NLSIE are analyzed for each sector for the past 100-200 years and found to be -0.08 degrees, -0.17 degrees, +0.07 degrees, +0.02 degrees, and -0.03 degrees per decade (>95% confidence level) for the WS, BS, AS, RS, and IndWPac, respectively. For the entire Antarctic, our composite NLSIE shows a decreasing trend (-0.03 degrees per decade, 99% confidence level) during the 20th century, with a rapid decline in the mid-1950s. It was not until the early 1980s that the observed increasing trend occurred. A comparison with major climate indices shows that the long-term linear trends in all five sectors are largely dominated by the changes in the Southern Annular Mode (SAM). The multi-decadal variability in WS, BS, and AS is dominated by the Interdecadal Pacific Oscillation, whereas that in the IndWPac and RS is dominated by the SAM. (c) 2021 Science China Press. Published by Elsevier B.V. and Science China Press. All rights reserved.

Using long-term moorings data together with wind and sea ice measurements, we document the characteristics and variations of upwelling in Barrow Canyon and investigate the upwelled Atlantic Water (AW) on the Chukchi Sea shelf and how it impacts the ice cover. Driven by strong northeasterly winds, upwelling occurs more often in the cold months, and the occurrence tends to increase interannually since 2001. Over the 12-year mooring record at the mouth of Barrow Canyon, roughly 10% of the upwelling events can drive AW onto the Chukchi Sea shelf. Both AW and non-AW upwelling events have more occurrence and stronger strength in the cold months, but do not present a significant interannual trend. These variations are associated with the northeasterly winds. Comparing to the non-AW upwelling, the AW upwelling is generally characterized by more vertical displacement of the AW layer at the mouth of Barrow Canyon, and stronger up-canyon volume and heat transport. In the ice-covered period, these two types of upwelling have different consequences for forming polynyas on the shelf. Under similar wind forcing, the ice reduction appears confined in the coastal region in the non-AW upwelling events, while during AW upwelling events, the sea ice declines dramatically in the shelf interior with 15% more ice loss. It elucidates that the heat carried by the upwelled AW plays a considerable role in modulating the ice cover in the shelf interior.

Recent research has shown that snow cover induces extreme wintertime cooling and has detrimental impacts. Although the dramatic loss of Arctic sea ice certainly has contributed to a more extreme climate, the mechanism connecting sea-ice loss to extensive snow cover is still up for debate. In this study, a significant relationship between sea ice concentration (SIC) in the Barents-Kara (B-K) seas in November and snow cover extent over Eurasia in winter (November-January) has been found based in observational datasets and through numerical experiments. The reduction in B-K sea ice gives rise to a negative phase of Arctic Oscillation (AO), a deepened East Asia trough, and a shallow trough over Europe. These circulation anomalies lead to colder-than-normal Eurasian mid-latitude temperatures, providing favorable conditions for snowfall. In addition, two prominent cyclonic anomalies near Europe and Lake Baikal affect moisture transport and its divergence, which results in increased precipitation due to moisture advection and wind convergence. Furthermore, anomalous E-P flux shows that amplified upward propagating waves associated with the low SIC could contribute to the weakening of the polar vortex and southward breakouts of cold air. This work may be helpful for further understanding and predicting the snowfall conditions in the middle latitudes.

The cryosphere is the term used to describe the frozen areas of the Earth, including all forms of snow and ice, which are primarily influenced by anthropogenic pollutants through atmospheric transport. In this review, we described the current status of newly emergent pollutant-microplastics-in the snow and ice of typical cryospheric regions (e.g., Arctic, Antarctic, Alps, Tibetan Plateau, and Andes), discussed their transport pathways, and provided perspectives for future research. A brief summary of snow and ice sampling, pretreatment, and the identification of microplastics in cryospheric regions suggested that standard procedures were inadequate and urgently required improvement. Microplastics were widely distributed in snow and ice across the typical cryospheric regions, indicating the ubiquitous distribution of microplastics in such environments. However, the abundance, size distribution, shape, and polymer composition of the microplastics in snow and ice showed significant differences. Sea ice was especially important for the temporal storage, transport, and release of microplastics in the Arctic and Antarctic. Microplastics in land snow cover and mountain glaciers emphasized the importance of atmospheric transport in the transferal of microplastics to cryospheric regions. In particular, the non-polar cryospheric regions (e.g., Tibetan Plateau, Andes, or Alps) were highlighted as important receptors of mid-latitude emissions of microplastics, which might indicate a future climatic risk considering the ability of microplastics to absorb radiation and accelerate the melting of snow. Microplastics retrieved from mountain glacier ice cores may also provide new insights into the historical variations of anthropogenic pollutants. The potential impact of microplastics in snow and ice on the carbon cycle and the climatic risk needs to be further addressed in the future.

Although a rapid decrease in sea ice due to global warming has improved the navigable potential of the Arctic passages, the extent to which this area will become viable for commercial shipping in the future remains unclear. This study investigated the accessibility of the Northern Sea Route and Northwest Passage under global warming of 2 degrees C and 3 degrees C. We applied the Polar Operational Limit Assessment Risk Indexing System to measure navi-gability by considering the impacts of sea ice and ice resistance of ships. Except for the Parry Channel, surface air temperature is positive in the Seas along two passages in September under 2 degrees C warming. With global warming of 3 degrees C, the warming area extends northward, and the concentration of sea ice drops below 20%. The thickness of the sea ice is still substantial in the eastern Beaufort Sea and the waters within the Canadian Arctic Archipelago and north of Greenland, both of which can restricting the opening of the Arctic passages. Temperature increases cause sea ice to be younger and are more pronounced in the seas on the European side of the Arctic. The results indicate that changes in sea ice improve the navigability of the Arctic passages. Ships in Polar Class 6 may be unimpeded along two Arctic passages in November from 2 degrees C warming onward, whereas ordinary ships may be capable of passing the Northern Sea Route with global warming of 3 degrees C, with maximum potential in September. This study provides an important reference for planning global shipping in the Arctic in the future, even with some uncertainty in the model projections.

The negative freeboard of sea ice (i.e., the height of ice surface below sea level) with subsequent flooding is widespread in the Southern Ocean, as opposed to the Arctic, due to the relatively thicker ice and thinner snow. In this study, we used the observations of snow and ice thickness from 103 ice mass balance buoys (IMBs) and NASA Operation IceBridge Aircraft Missions to investigate the spatial distribution of negative freeboard of Arctic sea ice. The Result showed that seven IMBs recorded negative freeboards, which were sporadically located in the seas around Northeast Greenland, the Central Arctic Ocean, and the marginal areas of the Chukchi-Beaufort Sea. The observed maximum values of negative freeboard could reach -0.12 m in the seas around Northeast Greenland. The observations from IceBridge campaigns also revealed negative freeboard comparable to those of IMBs in the seas around North Greenland and the Beaufort Sea. We further investigated the large-scale distribution of negative freeboard using NASA CryoSat-2 radar altimeter data, and the result indicates that except for the negative freeboard areas observed by IMBs and IceBridge, there are negative freeboards in other marginal seas of the Arctic Ocean. However, the comparison of the satellite data with the IMB data and IceBridge data shows that the Cryosat-2 data generally overestimate the extent and magnitude of the negative freeboard in the Arctic.

Remote sensing can be helpful in defining the dynamic of a high-latitude coastal environment where the role of cryogenic processes like sea-ice or permafrost are the main drivers together with storm surge and wind action. Here we examined the geomorphological dynamics of a beach located at Edmonson Point (74 degrees S) not far from the Italian Antarctic Station Mario Zucchelli between 1993 and 2019 using different remote sensing techniques and field measurements. Our data demonstrate that the average rate of surficial increase of the beach (0.002 +/- 0.032 m yr(-1)) was slightly higher than the uplift rate determined by previous authors (0-1 cm yr(-1)) in case of pure isostatic rebound. However, we suggest that the evolution of EPNB is likely due to the couple effect of vertical uplift and high wave-energy events. Indeed, the coastline accumulation could be related to the subsurface sea water infiltration and annually freezing at the permafrost table interface as aggradational ice as suggested by the ERT carried out in 1996. This ERT suggests the occurrence of saline frozen permafrost or hypersaline brines under the sea level while permafrost with ice occurred above the sea level. The beach also revealed areas that had quite high subsidence values (between 0.08 and 0.011 m yr(-1)) located in the area where ice content was higher in 1996 and where the active layer thickening and wind erosion could explain the measured erosion rates. Here, we also dated at the late morning of 15 February 2019 coastal flooding and defined a significant wave height of 1.95 m. During the high oceanic wave event the sea level increased advancing shoreward up to 360 m, three times higher than the previous reported storm surge (81 m) and with a sea level rise almost five times higher than has been previously recorded in the Ross Sea.

The navigation potential of the Arctic has improved with the rapid retreat of sea ice under continuous warming. The comprehensive evaluation of Arctic accessibility for low ice-breaking ships (civil use) in the mid-century is important to support coordinated international decision-making. In this study, the hydrological conditions and navigation potential in key areas and crucial straits along the Northern Sea Route (NSR) and Northwest Passage (NWP) were assessed under Shared Socioeconomic Pathways (SSPs) using the Polar Operational Limit Assessment Risk Indexing System. The results showed that the most critical areas for navigation in the mid-century (2046-2055) are the waters around the New Siberian Islands and within the Parry Channel. Arctic navigability improves from SSP1-2.6 to SSP2-4.5 to SSP5-8.5, and the accessibility for PC7 ships under SSP2-4.5 is even better for OW ships under SSP5-8.5. The route on the north side of the New Siberian Islands is a relatively good choice within the NSR, and the southern route has a better navigation potential than the Parry Channel within the NWP. In addition, the accessibility of the Dmitrii Laptev Strait is better than that of the Sannikov Strait at a monthly scale, although the latter has more navigable days. However, there is little difference in accessibility between the eastern and western parts of the Parry Channel. The best navigation potential through the above straits is in September for ordinary ships, and the optimal time window is delayed and extended for PC7 ships. The results can serve as references for policy-making and navigation planning in the Arctic.