The formation of platelet ice is well known to occur under Antarctic sea ice, where sub-ice platelet layers form from supercooled ice shelf water. In the Arctic however, platelet ice formation has not been extensively observed and its formation and morphology currently remain enigmatic. Here, we present the first comprehensive, long-term in situ observations of a decimeter thick sub-ice platelet layer under free-drifting pack ice of the Central Arctic in winter. Observations carried out with a remotely operated underwater vehicle (ROV) during the midwinter leg of the MOSAiC drift expedition, provide clear evidence of the growth of platelet ice layers from supercooled water present in the ocean mixed layer. This platelet formation takes place under all ice types present during the surveys. Oceanographic data from autonomous observing platforms lead us to the conclusion that platelet ice formation is a widespread but yet overlooked feature of Arctic winter sea ice growth.

Understanding, predicting, and responding to a rapidly changing Arctic requires sustained observations that capture variability and transformative change of the Arctic systems with all its major components. A key challenge for researchers, Arctic communities, and others tasked with effective responses to such change is to achieve structured coordination of numerous individual observing activities and networks. These have different regional and thematic foci. Many are driven from the bottom-up by research interests, while others are mission-oriented operational networks. The Arctic Observing Summit (AOS) is an effort that seeks to help coordinate such disparate activities and support efforts such as the Sustaining Arctic Observing Networks (SAON) initiative. We report on progress as part of an AOS 2018 working group focused on implementation and optimization of sustained observations. Drawing on the Framework on Ocean Observations, our group identified effective approaches and barriers to integration of different observation requirements and activities/platforms into a coherent observing framework. Case studies for benthic communities, sea ice prediction, and permafrost highlighted the importance of allowing for independently driven activities to coalesce into a uniform framework. This in turn requires clearly defined requirements that ideally serve multiple societal benefits. Such clear definitions also aid private-public partnerships and the development of new observing system business models. Prerequisite to better coordination is a comprehensive, international assessment that describes the current set of systems, community-based networks, sensors, networks, and surveys that are used to observe the Arctic today. Pieces of such an endeavor are starting to emerge, and SAON may serve as a home for integrating and building upon these pieces. Essential to this goal is the development of a knowledge map that collates and connects observing resources to societal benefits, helps identify and prioritize essential variables, data management needs, and critical products and services. The AOS 2018 calls for the launch of an optimization and implementation team of experts that would conduct such an effort under the auspices of SAON. We explore different elements of such a team’s portfolio of tasks.

Reliable, high-resolution sea ice forecasts may help contribute to safety of Indigenous marine mammal hunting and community travel in the Arctic. At the same time, sea ice forecasts could also be useful predictors of seasonal harvest success, including potential harvest shortfalls with impacts at the community level. However, large scale measures of sea ice concentration and ice extent are not sufficient indicators for predicting marine mammal harvest success in Bering Strait communities. Weekly sea ice and weather forecasts for Alaskan communities in the Bering Strait were analyzed from the Sea Ice for Walrus Outlook (SIWO) to identify sea ice and weather thresholds that greatly affected Indigenous marine mammal hunting activity and access to marine mammals during the spring harvest. The forecast of the timing for ice-free waters around a coastal community generally aligned with local observations. However some hunters continued to hunt by traveling longer distances from shore to reach marine mammals. This emphasizes the importance of maintaining coastal and marine forecasts even when coastal areas around communities appear ice-free. It was also apparent that while wind forecasts generally predicted the local wind conditions that were observed, the forecasts sometimes omitted important changes in wind direction, speed or ice movement, that occasionally resulted in ocean and ice conditions that required local search and rescue efforts or left hunters “stuck in the ice” overnight. The use of seasonal sea ice forecasts from models have not yet been explored with community partners as a potential tool to plan for upcoming subsistence hunting seasons, although the current use of SIWO is recognized as a tool to record hunter observations in “our words and descriptions” for current events and for future use and analysis. An evaluation of the Sea Ice for Walrus Outlook is being conducted, and the results of this new study will be useful to support future development of forecast information, and avenues for sharing of timely community observations.