Sea Ice as a Nexus in Polar Seas Between the Ocean and the Atmosphere

Sea ice plays a keystone role in polar oceans and atmospheres, particularly in their coupling. Serving as a transmission belt for the transfer of motion from the atmosphere to the ocean, it modulates the exchange of energy, gases, and moisture. It plays a role in the emission of marine aerosols and controls the transfer of various atmospheric depositions to the ocean. Sea ice also constitutes a distinct ecosystem for a wide range of organisms, from microbes to mammals. The presence of sea ice, for several months or even year-round, shapes the dynamics of the surface ocean over time and space, influencing its biogeochemistry and the epipelagic, mesopelagic, and even benthic ecosystems. The positive and negative feedbacks sea ice promotes have the potential to accelerate or slow down climate change and its consequences. During this fourteenth edition of the GRC on Marine Polar Science, we will examine sea ice from every angle and explore the limits of our most fundamental knowledge about this habitat, which is a key player on Earth and has been omnipresent at times in the past, and which fully covers some moons in our solar system. We will focus particularly on i) how sea ice shapes the distinct identity of polar oceans and atmospheres in terms of physics, biogeochemistry, and ecosystems; ii) the physical and chemical characteristics at micro- to decameter scale that make sea ice a unique ecosystem; iii) the biodiversity sea ice supports within itself and in the ocean; iv) the evolutionary mechanisms sea ice can promote; and v) what it tells us about the potential for life on the icy moons of the solar system. All these topics will be addressed while considering the current and future consequences of climate change. Finally, we will discuss the role that sea ice plays in certain human civilizations. Twenty eight years after the very first conference of this series chaired by Stephen F. Ackley on Sea Ice Ecology, we revisit this crucial element of polar seas, enriched by three decades of discoveries. Following the tradition of the conferences in this series, we will also address the ocean and atmosphere, and delve into physics, chemistry, and biology, all while systematically emphasizing the connections with sea ice. The comparison between the Arctic and the Antarctic will allow us to discern, from these two very different oceans, how the presence of sea ice changes their faces, possibly in similar ways.