The image shows the global nitrogen cycle, illustrating how nitrogen moves through the atmosphere, land, oceans, and rocks. Atmospheric nitrogen (N₂), the largest reservoir, is fixed into usable forms by biological processes on land and in the ocean. Fixed nitrogen accumulates in soils and surface oceans , and moves through rivers, upwelling, downwelling, and the biological pump. The deep ocean holds a large nitrogen pool, while denitrification returns nitrogen to the atmosphere both on land and in the ocean. Some nitrogen is buried in sediments and stored long-term in sedimentary rocks , with weathering slowly releasing it back to land.