The general objective of this project is to better understand the sea ice ecosystem in the northern Canadian Archipelago, in particular the old multiyear ice. Because this old ice is disappearing from the Arctic and changing into thinner annual ice, this has many impacts on the ecosystem. The study will take place on the sea ice off Alert, during the spring of 2018, from end of April to beginning of June. We will use snowmobiles to go a station on the sea ice where ice conditions are safe (see map for tentative location). We will have a temporary shelter tent on the ice; which will be used to process sea ice and water samples. At the station, we will collect sea ice cores and cut them in sections for analysis of the ice conditions. We will also collect water samples using sampling bottles and measure salinity and biological conditions. We will use oceanographic instruments to measure the properties (temperature, salinity) of the water column. We also plan to install instrumentation to measure meteorological conditions, ocean currents, and zooplankton during the spring.. Twice during the study, we will carry out marine mammal surveys using a Twin Otter. The surveys will help identify the use of the sea ice by seals and polar bears. At the end of the spring field season, we will remove all the equipment installed on the ice, including temporary shelter. We plan to return to the station in the fall to deploy the same oceanographic instruments and have measurements until the next spring. We are planning to continue this study over subsequent years, in 2019-2020, to assess year-to-year changes in conditions. The results of this study are needed to better understand the sea ice ecosystem and how it will respond to climate change. This is important since many Arctic marine species depend on the sea ice.