Siliceous sponge communities, biological zonation, and Recent sea-level change on the Arctic margin: Ice Island results: Discussion
Bathymetric profiles, bottom-camera photographs, surface-sediment samples, and biological samples were obtained through a 44 m long hydrohole in the Canadian Ice Island as it drifted over the Canadian polar margin from western Ellesmere Island to Meighen Island. Continuous bathymetric profiles show a 300 km wide shelf with a narrow, dissected, shallow (< 200 m) inner shelf and a deep (300–800 m), sloping outer shelf. Extensive areas of siliceous sponge communities are present on the seafloor beneath the polar pack ice on the central shelf. A clear biological zonation is evident: above 130 m, large living sponges support a diverse benthic community and form reef mounds up to 10 m high; from 130 to 150 m, there are few living sponges, but extensive mats of sponge spicules are present; from 150 to 300 m, there are few, small living sponges, and radiocarbon dating of mud-covered spicule mats indicates that formerly extensive sponge communities have died during the past 500–2000 years. This zonation may reflec...