The Atlantic Multidecadal Oscillation (AMO), Arctic Oscillation (AO), and related North Atlantic Oscillation (NAO) have been linked to multidecadal, decadal, and/or interannual sea-ice variability in the arctic, but their relative influences are still under evaluation. While instrumental AMO and reliable AO records are available since the mid-1800s and 1958, respectively, satellite sea-ice concentration datasets start only in 1979, limiting the shared timespan to study their interplay. Growth increments of the coralline algae, Clathromorphum compactum, can provide sea-ice proxy information for years prior to 1979. We present a seasonal 210-year algal record from Lancaster Sound in the Canadian Arctic Archipelago capturing low frequency AMO variability and high frequency interannual AO/NAO prior to 2000. We suggest that sea-ice variability here is strongly coupled to these large-scale climate processes, and that sea-ice cover was greater and the AO more negative in the early and late 19th century compared to the 20th.

During the winter season, stratification in the central Labrador Sea is eroded by surface heat fluxes causing convective overturning exceeding depths of 2km. This is one of the few locations globally in which deep convection occurs, making it an important feature of the climate system and ocean ventilation. Large-scale atmospheric circulation patterns modulate the air-sea interaction that drives the loss of ocean buoyancy. Here we investigate the process by which weather patterns driven by the North Atlantic Oscillation (NAO), and its northern centre of action, the Icelandic Low, modulate convective depths. A one-dimensional ocean model is used to quantify the mixed layer depth’s response to various atmospheric forcing conditions. We find that while net heat flux is the strongest modulating factor of mixed layer depth’s seasonal maximum, it is also strongly affected by the NAO. The Icelandic Low, despite its proximity to the Labrador Sea, does not affect mixed layer deepening as strongly. From geospatial correlation fields with heat flux, NAO, and Icelandic Low time series, it is evident that the NAO more efficiently regulates strong, cold, westerly winds from over the North American continent, which are more effective at cooling the ocean surface boundary layer. These correlations are supported by a compositing approach with a peak-over-threshold technique.

Nares Strait, situated between northwest Greenland and Ellesmere Island is a major sea ice export path from the Arctic Ocean. One of the narrowest parts of the strait --- Kennedy Channel --- is host to several islands. These obstacles' impact on the ice flow along the Strait has yet to be investigated. Here we show that during autumn, these islands can interrupt the relatively homogenous sea ice flow through Kennedy Channel, carried by wind and water currents, and shield downstream regions from becoming ice-covered, resulting in the formation of hitherto unknown transient polynyas, whose size and extent were correlated with the wind's strength and direction along Kennedy Channel. These polynyas likely impact the regional meteorology and oceanography through enhanced air-sea fluxes of heat, moisture, momentum, and carbon dioxide. The presence of open water may also impact the complex and productive regional ecosystem.

The Beaufort Sea High is a high-pressure system located in the Beaufort Sea and influences ocean circulation in the western Arctic known as the Beaufort Gyre. Wrangel Island, located in the western Chukchi Sea, typically experiences easterly sea ice motion due to the Beaufort Gyre. We find that under these climatological conditions, moving ice is blocked by the island and piles up on its eastern side, while ice on its western side continues to drift. This results in an ice thickness dipole across the island. A reversal in the sense of the oceanic and atmospheric circulation across the western Arctic results in a dipole with the opposing sign. We find the dipole is present throughout the year and is strongest in January when the ice thickness difference is approximately 1m. During the spring, it is associated with the transient opening of a polynya to the west of the island. The dipole is the result of opposing ice divergence and convergence across the western Arctic and may impact ocean circulation and ecosystems within the Chukchi Sea.

Starting in January 2020, the novel coronavirus, now known as acute respiratory syndrome coronavirus (SARS-CoV-2) and the disease that it causes (COVID-19) has had significant impacts on human health, the environment and the economy globally. The rapid lockdown that occurred as well as its well documented timing in various locations allows for an unprecedented opportunity to examine the impact of air pollution from densely populated regions has on adjacent and pristine environments. Here we use in-situ and satellite observations to show that there was a step function decrease in two key indicators of air quality, nitrogen dioxide and airborne particulates, in locations within the Indo-Gangetic Plan (IGP) as a result of the Spring 2020 lockdown. Based on anomaly patterns, we find a dipole response with a statistically significant reduction in air pollution along the western IGP and Himalaya and an increase in air pollution in the eastern IGP and Himalaya. We show that spatial variability in the reductions in economic activity across northern India and the adjoining countries of Nepal, Pakistan and Bangladesh contributed to this dipole as did a persistent atmospheric circulation anomaly across the region during the lockdown.

Nares Strait is the long and narrow strait bounded by steep topography that connects the Arctic Ocean’s Lincoln Sea to the North Atlantic’s Baffin Bay. The winds that blow along the strait play an important role in modulating ice and water exports from the Arctic Ocean as well as in helping to establish the Arctic’s largest and most productive polynya that forms at its southern terminus. However, its remote location has limited our knowledge of the winds along the strait. Here we use weather station data from the region as well as 3 numerical models with horizontal resolutions that vary from ~30km to ~2.5 km to characterize the wind field in the vicinity of the strait. The strait has a width that varies from ~40km to ~100 km and as such the wind field is typically ageostrophic and controlled by the pressure gradient in the along-strait direction. We show that model resolution plays a role in the representation of both the mean and extreme winds along the strait through the ability to represent this ageostrophic flow. Higher windspeeds occur in the vicinity of Smith Sound and are the result of a left-hand corner jet. Kane Basin, the widest section of the strait, is characterized by a pronounced zonal windspeed gradient that is the result of the steep topography of the upstream Washington Land peninsula.

The area to the north of Ellesmere Island and Greenland contains the Arctic's thickest ice and it is predicted to be the last to lose its perennial ice, thus providing an important refuge for ice-dependent species. There is however evidence that this Last Ice Area is, like the entire Arctic, undergoing rapid changes that may reduce its suitability as a refuge. During May 2020, a polynya developed to the north of Ellesmere Island in a region where there are no reports of a previous development during May. We use a variety of remotely sensed data as well as atmospheric models to document the evolution and the dynamics responsible for the polynya. In particular, we argue that anomalously strong divergent winds associated with an intense and long-lived Arctic anti-cyclone contributed to the development of the polynya as well as a similar previously unreported event in May 2004.

The planetary boundary layer height (PBLH) is a diagnostic field related to the effective heat capacity of the lower atmosphere and it constrains motion in this layer as well as impacting surface warming. Here we used radiosonde data from five icebreaker cruises to the Chukchi and Beaufort Seas during both spring and fall to derive PBLH that were compared with results from the ERA5 reanalysis. The ERA5 PBLH was similar to but slightly lower than the observation. Clear and consistent seasonal changes were found in both the observation and the reanalysis: PBLH decreases from mid-May to mid-June and subsequently increases after August. The comparison with ERA5 shows that biases in PBLH are a function of wind direction that are largest for northerly flow conditions, suggesting that the availability of upwind observations is important in representing processes active in the planetary boundary layer over the Arctic Ocean.

The Arctic Ocean's Wandel Sea is the easternmost sector of the Last Ice Area, where thick, old sea ice is expected to endure longer than elsewhere. Nevertheless, in August 2020 the area experienced record-low sea ice concentration. Here we use satellite data and sea ice model experiments to determine what caused this record sea ice minimum. In our simulations there was a multi-year sea-ice thinning trend due to climate change. Natural climate variability expressed as wind-forced ice advection and subsequent melt added to this trend. In spring 2020, the Wandel Sea had a mixture of both thin and---unusual for recent years---thick ice, but this thick ice was not sufficiently widespread to prevent the summer sea ice concentration minimum. With continued thinning, more frequent low summer sea ice events are expected. We suggest that the Last Ice Area, an important refuge for ice-dependent species, is less resilient to warming than previously thought.