Coral reef islands and atolls. The reef face is the zone above the reef floor or the reef drop-off. This zone is often the reef's most diverse area. Coral and calcareous algae provide complex habitats and areas that offer protection, such as cracks and crevices. Invertebrates and epiphytic algae provide much of the food for other organisms. A common feature on this forereef zone is spur and groove formations that serve to transport sediment downslope. The reef flat is the sandy-bottomed flat, which can be behind the main reef, containing chunks of coral. This zone may border a lagoon and serve as
Open Polar Sea project that by the end of the 21st century, the annual summer withdrawal of the polar ice cap could expose large areas of the Arctic Ocean as open water, and an ice-free Arctic is possible in the future due to Arctic shrinkage. Although the North Pole itself could potentially remain ice-covered in winter, a navigable seasonal sea passage from Europe to the Pacific could develop along the north coast of Asia. Russell Potter, "The Open Polar Sea," "Encyclopedia of the Arctic" (Routledge, 2004) Michael Robinson, "The Coldest Crucible: Arctic Exploration and American Culture" (Chicago, 2006). Michael Robinson, "Reconsidering the Theory