For nine miles along a submerged ridge, the corals rise in lumpy hillocks that spread out 100 yards or more, resembling heaped scoops of rainbow sherbet and Neapolitan ice cream. The mounds, some 100 feet tall, sprout delicate treelike gorgonians that sift currents for a plankton meal. Fish, worms and other creatures dart or crawl in every crevice. This description could apply to thousands of coral reefs in shallow, sun-streaked tropical waters from Australia to the Bahamas. But this is the Sula Ridge, 1,000 feet down in frigid darkness on the continental shelf 100 miles off Norway's coast.