Even in the depths of winter, the Arctic Ocean is not a solid sheet of ice. There are persistent areas of open water surrounded by ice called polynyas. Ecological activity in Arctic waters is concentrated in these openings and at the edges of the ice, where an abundance of phytoplankton forms the base of the food chain. Polynyas provide spaces for marine mammals and birds to surface and breathe, while the nearby ice provides a platform for animals to rest, hunt, and give birth. If an oil spill were to occur in broken ice, oil would concentrate in polynyas and at the ice edges that form the heart of the ecosystem, threatening much of the life in the Arctic Ocean. Additionally, oil spill response operations plan to use these open areas to concentrate and burn the oil, a plan that could result in severe impacts to this ecosystem. See the recommendations on assessing spill response capacity.