Carbon mineralization and carbonate preservation in modern cold-water coral reef sediments on the Norwegian shelf

Abstract

Abstract. Cold-water coral ecosystems are considered hotspots of biodiversity and biomass production and may be a regionally important contributor to carbonate production. The impact of these ecosystems on biogeochemical processes and carbonate preservation in associated sediments were studied at Røst Reef and Traenadjupet Reef, two modern (post-glacial) cold-water coral reefs on the MidNorwegian shelf. Sulfate and iron reduction as well as carbonate dissolution and precipitation were investigated by combining pore-water geochemical profiles, steady state modeling, as well as solid phase analyses and sulfate reduction rate measurements on gravity cores of up to 3.25 m length. Low extents of sulfate depletion and dissolved inorganic carbon (DIC) production, combined with sulfate reduction rates not exceeding 3 nmol S cm −3 d −1 , suggested that overall anaerobic carbon mineralization in the sediments was low. These data showed that the coral fragment-bearing siliciclastic sediments were effectively decoupled from the productive pelagic ecosystem by the complex reef surface framework. Organic matter being mineralized by sulfate reduction was calculated to consist of 57% carbon bound in CH 2 O groups and 43% carbon in -CH 2 -groups. Methane concentrations were below 1 µM, and failed to support the hypothesis of a linkage between the distribution of coldwater coral reefs and the presence of hydrocarbon seepage. Reductive iron oxide dissolution linked to microbial sulfate reduction buffered the pore-water carbonate system and inhibited acid-driven coral skeleton dissolution. A large pool of reactive iron was available leading to the formation of iron

Aggradation and carbonate accumulation of Holocene Norwegian cold‐water coral reefs

“…Information on the Holocene evolution of the Norwegian cold‐water coral (CWC) reefs is still limited, and is restricted to a few gravity cores from Lopphavet shelf (Stalder et al ., ), Stjernsund reef (López Correa et al ., ), Røst reef (Wehrmann et al ., ), Træna reef (López Correa et al ., ) and Sula Ridge (Hovland et al ., ). Additional information about dated CWCs is available from sea floor and land outcrop specimens from Trondheimsfjord, Oslofjord and Kosterfjord (Mikkelsen et al ., ; Schröder‐Ritzrau et al ., ).…”

“…The reef complex itself is about 35 to 40 km long and up to 3 km wide (Fosså et al ., ). The small circular reefs developed on the uppermost ridges of the Trænadjupet submarine slide headwall and subordinately on iceberg plough marks on the adjacent shelf (Laberg & Vorren, ; Thorsnes & Fosså, ; Fosså et al ., ; Nordgulen et al ., ; Wehrmann et al ., ).…”

Microhabitat and shrimp abundance within a Norwegian cold-water coral ecosystem

“…The Røst Reef complex, the largest discovered worldwide to date Nordgulen et al, 2006;Wehrmann et al, 2009;Fosså et al, 2010;Tong et al, 2012a), was the focus of this study. The complex is situated on the edge of the continental shelf, and is marked by vigorous Lophelia pertusa scleractinian coral growth on a series of seafloor crests formed by the Traenadjupet landslide during the Cenozoic (Laberg and Vorren, 2000).…”

“…The complex is situated on the edge of the continental shelf, and is marked by vigorous Lophelia pertusa scleractinian coral growth on a series of seafloor crests formed by the Traenadjupet landslide during the Cenozoic (Laberg and Vorren, 2000). Between these scleractinian reef crests are regions of coral rubble and areas of low density Lophelia pertusa coverage on dead, exposed coral framework (Wehrmann et al, 2009) with the gorgonian coral species Primnoa arborea and Paragorgia arborea also abundant (Tong et al, 2012a).…”

“…4): live Lophelia pertusa (a), live Paragorgia arborea (b), live Primnoa resedaeformis (c), dead structure (d), coral rubble (e), gravel/pebbles (f), wall (g), dead gorgonian (h), soft seabed (i) and hard ground (j). These microhabitat categories were selected as all were previously reported for the Røst Reef and the Norwegian margin reefs in general (Mortensen et al, 1995;Wehrmann et al, 2009;Tong et al, 2012b).…”