Enigmatic Mounds of Orphan Knoll

Diversity, biogeography, and biomineralisation of cold-water car

bonate producers in Canadian waters: overview and new directio

Edinger, E.N., Layne, G.D., Neuweiler, F. (order alphabetical)

Abstract

Cold-water carbonate producing organisms, sediments and rocks have received limited study in

Canada, compared to the cold-water scleractinian bioherms of the northeast Atlantic, the main fo cus of COCARDE (Cold-water Carbonates in Shallow and Deep time), the eastern US and Gulf of Mexico, or the extensive cold-water carbonate systems of southern Australia, the Gulf of Calif ornia or the Mediterranean. Canada’s climate, oceanography, and glacial inheritance may limit th e organisms and their sedimentary products.

Dominant cold-water carbonate producing organisms in Canadian waters include the corallin e red algae, bryozoans, bivalve and gastropod molluscs, sponges (indirectly) and corals - similar to the general bryomol assemblage described from other broad cold-water carbonate shelves. Cor alline algae, producing magnesian calcite skeletons, are ubiquitous members of Canadian shallo w marine hard-substrate communities. Branching corallines produce large amounts of carbonate sediment in some fjords, while compact domal coralline algae may record high-latitude climatic or ecological chaanges. Dominantly calcitic erect and encrusting bryozoans are common epibent hos in shelf-depth waters, and are often found associated with cold-water corals and sponges, but remain vastly understudied. Carbonate-skeletoned cold-water corals include aragonitic scleractin ians, aragonitic or calcitic stylasterids, and calcitic gorgonians. Solitary scleractinians have a rel atively low diversity, while colonial scleractinians occur mainly as isolated colonies, rather than i n bioherms. Stylasterid hydrocorals are common and relatively diverse in some British Columbia waters, but rare in Atlantic Canada and the Arctic. The most common carbonate-skeletoned gorg onian corals include Primnoids in shallow, high-current settings, and Isidids in deeper, calmer set tings. Cold-water gorgonians construct ‘coral forests’, whose habitat importance far surpasses th eir sedimentary production. Sponges, especially demosponges and hexactinellids, make an impor tant contribution to habitat throughout Canadian waters, and build glass sponge bioherms in shelf depth British Columbia waters.

Modern cold-water carbonate sediment deposits appear relatively rare in Canadian waters, p erhaps due to dilution by the vast amounts of siliciclastic sediments delivered to Canadian contin ental shelves by Pleistocene glaciations. Preservation potential of cold-water scleractinians and c arbonate-skeletoned gorgonian corals may be relatively high, as evidenced by sub-fossil skeleton s several thousands of years old found exposed on the seafloor, but the preservation potential of t he environments in which most of these organisms live is generally low. Many areas remain unex plored, however, especially in the Arctic.

Emerging questions surrounding Canadian cold-water carbonates include biomineralisation an d skeletal microchemistry, rates of skeletal growth and carbonate production, mineralogy, pattern s of distribution and abundance, and sedimentology and diagenesis of mound construction and ot her habitat formation.