temporarily blocked the outflow of pack ice from McMurdo Sound, according to news reports. Iceberg B-15A's grounding at the mouth of McMurdo Sound also blocked the path for thousands of penguins to reach their food source in open water. Moreover, pack ice built up behind the iceberg in the Ross Sea creating a nearly frozen barrier that blocked two cargo ships en route to supply McMurdo Station, according to the National Science Foundation. The icebreakers USCGC Polar Star and the Russian Krasin were required to open a ship channel through ice up to thick. The last leg of the channel followed a route along the eastern shoreline of McMurdo Sound adjacent to Ross Island. The icebreakers escorted the tanker USNS Paul Buck to McMurdo Station's ice pier in late January. The freighter MV American Tern followed on 3 February. Similar pack ice blocked a National Geographic expedition aboard the Braveheart from reaching B-15A. However, expedition divers were able to explore the underwater world of another grounded tabular iceberg. They encountered a surprising environment of fish and other sea life secreted within a deep iceberg crevasse. Discoveries included starfish, crabs, and ice fish. The latter were found to have burrowed thumb-sized holes into the ice. The expedition reported an exceedingly rare and seldom witnessed occurrence of an iceberg exploding. Shards of ice erupted into the air as if a bomb went off, this only hours after divers surfaced and after the Braveheart moved away from the iceberg (National Geographic). Pollution More than 50 years of continuous operation of the United States and New Zealand bases on Ross Island have left pockets of severe pollution in McMurdo Sound's. Until 1981, McMurdo Station residents simply towed their garbage out to the sea ice and let nature take its course. The garbage sank to the sea floor when the ice broke up in the spring, according to news reports. A 2001 survey of the seabed near McMurdo revealed 15 vehicles, 26 shipping containers, and 603 fuel drums, as well as some 1,000 miscellaneous items dumped on an area of some . Findings by scuba divers were reported in the State of the Environment Report, a New Zealand sponsored study. The study by the government agency Antarctica New Zealand revealed that decades of daily pumping thousands of gallons of raw sewage from 1,200 summer residents into the sound had fouled Winter Quarters Bay, the harbor