Georges and Brown Banks define the seaward edge of the Gulf of Maine, forming a barrier to the North Atlantic. Glacial erosion created the deeper western region of the Gulf of Maine. This higher barrier marks the southern extent of the glaciers during the Ice Age. The deep, cold nutrient-rich water reaches up from the deep ocean, mixes, and washes over this shelf-edge structure, contributing to the Gulf's high biological productivity. Feeding on this "soup" are floating communities of microscopic plants, tiny shrimp-like animals, and jellyfish that concentrate on Georges Bank. This community of animals once sustained abundant populations of Atlantic cod and other groundfish until they were depleted by overfishing during the past 30 years. Between the banks is the Northeast Channel, a deepwater conduit that brings dense, high-salinity, nutrient-rich water from the North Atlantic into the Gulf, where it settles into Jordan, Wilkinson, and Georges Basins.