A model study of convergent dynamics in the marginal ice zone.

With the increasing resolution of operational forecasting models, the marginal ice zone (MIZ), the area where waves and sea ice interact, can now be better represented. However, the proper mechanics of wave propagation and attenuation in ice, and especially their influence on sea ice dynamics, still remain poorly understood and constrained in models. Observations have shown exponential wave energy decrease with distance in sea ice, particularly strong at higher frequencies. Some of this energy is transferred to the ice, breaking it into smaller floes and weakening it, as well as exerting a stress on the ice similar to winds and currents. In this article, we present a one-dimensional, fully integrated wave and ice model that has been developed to test different parameterizations of wave-ice interactions. The response of the ice cover to the wind and wave radiative stresses is investigated for a variety of wind, wave and ice conditions at different scales. Results of sensitivity analyses reveal the complex interplay between wave attenuation and rheological parameters and suggest that the compressive strength of the MIZ may be better represented by a Mohr-Coulomb parameterization with a nonlinear dependence on thickness. This article is part of the theme issue 'Theory, modelling and observations of marginal ice zone dynamics: multidisciplinary perspectives and outlooks'.

Marginal ice zone dynamics: history, definitions and research perspectives.

Despite enormous scientific and technological progress in numerical weather and climate prediction, sea ice still remains unreliably predicted by models, both in short-term forecasting and climate projection applications. The total ice extent in both hemispheres is tied to the location of the ice edge, and consequently to what happens in the portion of the ice cover immediately adjacent to the open ocean that is called the marginal ice zone (MIZ). There is mounting evidence that processes occurring in the MIZ might play an important role in the polar climate of both hemispheres, yet some key physical processes are still missing in models. As sea ice models developed for climate studies are increasingly used for operational forecasting, the missing physics also impede short-term sea ice prediction skills. This paper is a mini-review that provides a historical perspective on how MIZ research has progressed since the 1970s, with a focus on the fundamental importance of the interactions between sea ice and surface gravity waves on sea ice dynamics. Completeness is not achieved, as the body of literature is huge, scattered and rapidly growing, but the intention is to inform future collaborative research efforts to improve our understanding and predictive capabilities of sea ice dynamics in the MIZ. This article is part of the theme issue 'Theory, modelling and observations of marginal ice zone dynamics: multidisciplinary perspectives and outlooks'.

Sea-air transfer of a tracer dye observed during the Tracer Release Experiment with implications for airborne contaminant exposure.

Rhodamine water tracer (RWT) released during the 2021 Tracer Release Experiment in the St. Lawrence Estuary provides a proxy for the water-soluble fractions of contaminant spills. Measurements of total and size-resolved aerosols were taken onboard a research vessel throughout the experiment. Size-resolved aerosol measurements show airborne transmission of water-soluble RWT in a bimodal distribution peaking at 5.2 µm and 0.9 µm. Highest aerosol RWT (30.5 pg m-3) was observed in the 12-hour daytime period following the first dye release (Sept. 5), while the lowest (8.8 pg m-3) was observed in the subsequent nighttime sample. Available wind and RWT patch information were used to identify factors contributing to the factor-of-three variation in aerosol RWT concentrations. Negligible correlations were found between aerosol RWT and wind speed and sample time-of-day. Wind direction is isolated as the key variable for consideration in identifying the impact of contaminant spills on coastal and inland communities.

Toward Food Sovereignty for Coastal Communities of Eastern Québec: Co-designing A Website to Support Consumption of Edible Resources from the St. Lawrence River, Estuary, and Gulf.

Background. Despite the abundance and proximity of edible marine resources, coastal communities along the St. Lawrence in Eastern Québec rarely consume these resources. Within a community-based food sovereignty project, Manger notre Saint-Laurent ("Sustenance from our St. Lawrence"), members of participating communities (3 non-Indigenous, 1 Indigenous) identified a need for a web-based decision tool to help make informed consumption choices. Methods. We thus aimed to co-design a prototype website that facilitates informed choices about consuming local edible marine resources based on seasonal and regional availability, food safety, nutrition, and sustainability, with community members, regional stakeholders, and experts in user experience design and web development. We conducted 48 interviews with a variety of people over 3 iterative cycles, assessing the prototype's ease of use with a validated measure, the System Usability Scale. Results. Community members, regional stakeholders, and other experts identified problematic elements in initial versions of the website (e.g., confusing symbols). We resolved issues and added features people identified as useful. Usability scores reached "best imaginable" for both the second and the third versions and did not differ significantly between sociodemographic groups. The final prototype includes a tool to explore each species and index cards to regroup accurate evidence relevant to each species. Conclusions. Engaging co-designers with different sociodemographic characteristics brought together a variety of perspectives. Several components would not have been included without co-designers' input; other components were greatly improved thanks to their feedback. Co-design approaches in research and intervention development are preferable to foster the inclusion of a variety of people. Once the prototype is programmed and available online, we hope to evaluate the website to determine its effects on food choices.

Shells of the bivalve Astarte moerchi give new evidence of a strong pelagic-benthic coupling shift occurring since the late 1970s in the North Water polynya.

Climate changes in the Arctic may weaken the currently tight pelagic-benthic coupling. In response to decreasing sea ice cover, arctic marine systems are expected to shift from a 'sea-ice algae-benthos' to a 'phytoplankton-zooplankton' dominance. We used mollusc shells as bioarchives and fatty acid trophic markers to estimate the effects of the reduction of sea ice cover on the food exported to the seafloor. Bathyal bivalve Astarte moerchi living at 600 m depth in northern Baffin Bay reveals a clear shift in growth variations and Ba/Ca ratios since the late 1970s, which we relate to a change in food availability. Tissue fatty acid compositions show that this species feeds mainly on microalgae exported from the euphotic zone to the seabed. We, therefore, suggest that changes in pelagic-benthic coupling are likely due either to local changes in sea ice dynamics, mediated through bottom-up regulation exerted by sea ice on phytoplankton production, or to a mismatch between phytoplankton bloom and zooplankton grazing due to phenological change. Both possibilities allow a more regular and increased transfer of food to the seabed. This article is part of the theme issue 'The changing Arctic Ocean: consequences for biological communities, biogeochemical processes and ecosystem functioning'.