The volume, extent and age of Arctic sea ice is in decline, yet winter sea ice production appears to have been increasing, despite Arctic warming being most intense during winter. Previous work suggests that further warming will at some point lead to a decline in ice production, however a consistent explanation of both rise and fall is hitherto missing. Here, we investigate these driving factors through a simple linear model for ice production. We focus on the Kara and Laptev seas-sometimes referred to as Arctic “ice factories” for their outsized role in ice production, and train the model on internal variability across the Community Earth System Model’s Large Ensemble (CESM-LE). The linear model is highly skilful at explaining internal variability and can also explain the forced rise-then-fall of ice production, providing insight into the competing drivers of change. We apply our linear model to the same climate variables from observation-based data; the resulting estimate of ice production over recent decades suggests that, just as in CESM-LE, we are currently passing the peak of ice production in the Kara and Laptev seas.

Atlantic Water (AW) is the largest reservoir of heat in the Arctic Ocean, isolated from the surface and sea ice by a strong halocline. In recent years, AW shoaling and warming are thought to have had an increased influence on sea ice in the Eurasian Basin. In this study, we analyze 59,000 profiles from across the Arctic from the 1970s to 2018 to obtain an observationally based pan‐Arctic picture of the AW layer, and to quantify temporal and spatial changes. The potential temperature maximum of the AW (the AW core) is found to be an easily detectable, and generally effective metric for assessments of AW properties, although temporal trends in AW core properties do not always reflect those of the entire AW layer. The AW core cools and freshens along the AW advection pathway as the AW loses heat and salt through vertical mixing at its upper bound, as well as via likely interaction with cascading shelf flows. In contrast to the Eurasian Basin, where the AW warms (by approximately 0.7°C between 2002 and 2018) in a pulse‐like fashion and has an increased influence on upper ocean heat content, AW in the Canadian Basin cools (by approximately 0.1°C between 2008 and 2018) and becomes more isolated from the surface due to the intensification of the Beaufort Gyre. These opposing AW trends in the Eurasian and Canadian Basins of the Arctic over the last 40 years suggest that AW in these two regions may evolve differently over the coming decades.

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Seafloor observatories enable long-term monitoring of marine soundscapes, modulated by weather, biodiversity, and human impacts (e.g., shipping). High-frequency (96-kHz) measurements at the NEPTUNE node of Folger Deep are processed to compare signatures of shipping and natural events over five tidal cycles, spanning several seasons (2009–2011). Independent meteorological data from local surface stations is also used. Sound levels in third-octave frequency bands centred on 63 Hz and 125 Hz are used to monitor shipping, in line with the European Marine Strategy Framework Directive (MSFD). The contribution from the busy shipping lane 40 km away is affected by the complex, shallow bathymetry, whereas local traffic can increase noise levels by up to 30 dB re. 1 μPa, with strong seasonal variation. The relative contributions of the 63 Hz and 125 Hz bands varied contrary to MSFD expectations for deeper areas. Our results match other studies in shallow, coastal environments, showing the importance of depth in interpreting changes. Principal-Component Analyses show that noise from local vessels is the most significant contributor in all seasons, and weather is the second largest, except in summer when biological noise became prevalent. Biodiversity, measured with the broadband Acoustic Complexity Index, showed a strong correlation with weather.

<p>Observational data from across the Arctic are used to investigate temporal and spatial variability in Atlantic Water throughout the Arctic basin from the 1980s to the present day, with a focus on Atlantic Water heat and its potential influence on the upper water column. MIMOC climatological data are also used in the analysis. The inferred mechanisms behind Atlantic Water spread in the Arctic – both vertically and laterally into sub-basin interiors – are discussed, along with the local and remote influences on the Atlantic Water layer in different Arctic regions. The usefulness of the Atlantic Water core in tracking changes in the Atlantic Water layer is also assessed. </p>