Spring means it's suppertime in the Great South Channel, an undersea canyon between Nantucket Shoals and Georges Bank. During this time, a relatively fresh coastal current (right) flows south along the New England coast, bringing a swarm of tiny animals called copepods. In the channel, the coastal current meets saltier, denser water (left). The water masses don't mix; they form an ocean front. Denser, saltier water sinks beneath the lighter, fresher water. Copepods sinking with the saltier water swim back toward the surface, aggregating along the front in dense, protein-rich patches that attract whales, basking sharks, cod, and halibut.
(Illustration by Amy Caracappa-Qubeck, Woods Hole Oceanographic Institution)