Quaternary geological features and oceanographic conditions supporting coral and sponge gardens in the northern Labrador Sea and Baffin Bay

Abstract

Deep-sea corals and sponges are a diverse group of habitat-structuring organisms found at continental slope depths in most of the world's ocean basins. Their distributions are influenced by oceanographic parameters such as temperature and salinity at coarse scales, and by surficial and bedrock geology and intermediate and fine scales. Recent remotely operated vehicle (ROV) video surveys focusing on twelve cold-water coral and sponge habitat sites in the northern Labrador Sea and Baffin Bay, Canada, were accompanied by acquisition of multibeam sonar and sub-bottom profiles, enabling analysis of the geological features upon which the coral and sponge habitats have grown. CTD casts in the same locations gathered data on temperature, salinity, seawater density, nutrient concentrations, and calcium carbonate saturation state. Most of the Northern Labrador Sea coral and sponge habitats are developed on glacially deposited materials. On the NE Saglek Bank, the site with the highest abundance of large gorgonian corals in the region, a diverse coral fauna occurs on current-swept bouldery gravels of glacial or glaciofluvial origin, with channels resembling glacial outwash fan channels between 300 and 400 m water depth. Further north in the Labrador Sea, near the Hatton Basin, SE Baffin shelf and slope, and Cape Dyer sites, diverse sponge-rich habitats appear to be most common on ice-contact bouldery gravels that have been extensively scoured by icebergs. On the outer side of the Hatton Basin sill, Primnoa resedaeformis-rich coral faunas are well developed on bouldery gravels that are interpreted as the grounding-line facies. CTD profiles at some of these northern Labrador Sea locations suggest sharp thermoclines associated with water mass boundaries, which likely also influence the distribution of the corals. Dense Keratoisis sp. bamboo corals in SE Baffin Bay are developed on muddy bottoms overlying a trough-mouth fan in SE Baffin Bay. Although the bamboo corals baffle sediments, creating small-scale topography, the ridges observed in multibeam and sub-bottom profile are glaciomarine in origin, likely till-tongues or glacigenic debris flows. Multibeam sonar and sub-bottom profiles were used to examine the geology of two sites with reported possible cold-seep related mounds, on the NE Saglek Bank and the SE Hatton Basin. Both sites are found within the iceberg-scoured ice-contact sediment facies. No evidence of authigenic carbonates or cold-seep related mounds was observed in multibeam sonar, sub-bottom profile, or box-core. Multibeam and sub-bottom profiles of the reported possible mound field in SE Hatton Basin revealed an iceberg-scoured ice-contact bouldery gravel facies, consistent with that observed at the NE Hatton basin sponge-dominated site. Methane bubbles and microbial mats were confirmed at a known hydrocarbon seep from Scott Inlet, in NW Baffin Bay. Bedrock exposures along cliffs in Scott Inlet support abundant Cladorhiza carnivorous sponges. Diverse sponge gardens were found on rill-and-gully morphology glaciomarine gravelly sands in SW Baffin Bay. The species composition of these sponge gardens appears to be quite different from that found in the northern Labrador Sea and in Frobisher Bay. Both the coral and sponge gardens contribute to benthic biodiversity throughout the region.