André Freiwald

Grounding Pleistocene icebergs shape recent deep-water coral reefs

The widespread view that scleractinian corals in cold and deep waters of high latitudes are slow growing organisms that do not form reefs is challenged by the discovery of a huge coral reef over 13 km in length, 10 to 35 m in height and up to 300 m in width formed by the coral Lophelia pertusa in water depths of 270 to 310 m at 64°N on the Sula Ridge, Mid-Norwegian Shelf. Cruises in 1994, 1995 and manned submersible operations in May 1997 provide data and observations from which the structure and development of the Sula Ridge coral reef have been determined. The Fennoscandian icesheet retreated from the Mid-Norwegian shelf prior to 12,000 years before present and modern oceanographic conditions were established at 8000 years before present. Coral growth since that time has resulted in a large deep-water shelf reef for which recent stable isotopic studies have demonstrated high growth rates for these azooxanthellate cold-water corals. Information on the geometry of deep-water coral reefs and their environmental controls is still fragmentary, controversial and raises issues of conservation in this area of active fishing and oil exploration. This paper reports on the discovery of what is probably one of the largest deep-water coral reefs existing in the northeast Atlantic and indicates that its siting is due to post-glacial structures (iceberg plough marks), events (the second Storegga Slide) and local conditions on the seafloor. Surprisingly, reef accumulation rates on the Sula Ridge are comparable with those measured on tropical coral reefs.

Controls on modern carbonate sedimentation on warm-temperate to arctic coasts, shelves and seamounts in the Northern Hemisphere: Implications for fossil counterparts

SummaryIn contrast to the well studied tropical carbonate environments, interest in non-tropical carbonate deposition was rather low until the basic ideas of theForamol-concept were outlined byLees & Buller (1972). In the following two decades studies on non-tropical carbonate settings evolved as a new and exciting branch of carbonate sedimentology (seeNelson 1988). This is archieved in a great number of publications dealing on temperate carbonate deposits from numerous coastal and open shelf settings on both hemispheres. The existence of wide extended carbonate depositional systems and even reefal frameworks in Subarctic and Arctic seas which are in focus by our research group made it possible to study modern non-tropical carbonate settings along a latitudinal transect from the warm-temperate Mediterranean Sea to the cold Nordic Seas. Because of increasing seasonality in environmental conditions towards high latitudes, the major controls in biogenic carbonate production can be more clearly addressed in these areas. After the initiation of the priority program “Global and regional controlling processes of biogenic sedimentation-evolution of reefs” by the German Science Foundation four years ago, a set of modern case studies were comparatively analysed specifically with regard to their principle controlling processes:(1)Modern and Holocene coralline algal reefs and rhodolith pavements formed in wave-protected shallow waters along the coast of the Brittany and northern Norway. Their finetuned interaction with herbivores resulted in the development of widespread but low-diverse, slowly growing coralline algal frameworks with high competitive value against the rapid-growing phaeophytic communities.(2)The MediterraneanCladocora caespitosa-banks provide an instructive example of non-tropical hermatypic coral framework construction out of the subtropical-tropical coral reef belt.(3)The geometry and environmental controls of several kilometer long coral reefs formed by the azooxanthellateLophelia pertusa andMadrepora oculata are studied in more than 250 m water depth in mid and northern Norway.(4)ModernBryomol-sediments are widely distributed on non-tropical deeper shelf settings. The formational processes converting bryozoan-thickets into huge piles of sand and gravel dunes are recently studied on the outer shelves off northern Brittany and off northern Norway.(5)Arctic sponge-bryozoan buildups on the seamount Vesterisbank in the Greenland Sea and(6)balanid-dominated open shelf carbonates on the Spitsbergen Bank form the Arctic endmembers of modernForamol-deposits. Seasonalice-edge phytoplankton blooms and efficient mechanisms of pelagic-benthic food transfer characterize these depositional settings. Fossil counterparts of each of these modern case studies are discussed in context with their paleoceanographic and environmental settings.

Taphonomy of modern deep, cold‐temperate water coral reefs

Deep‐water corals are widely distributed along the cold‐temperate northeastern Atlantic continental margin. Despite the widespread occurrence of these aphotic coral constructions in deep shelf settings, the processes of framework formation and postmortem alterations which result in different preservational styles are still poorly known. Detailed mapping surveys on probably one of the largest Lophelia reef structures were carried out on the Sula Ridge, Mid‐Norwegian Shelf in 270 to 300 m depth. Side scan sonar records and camera surveys yield information at various scales of resolution on the reef complex which is more than 9 km long and up to 45 m high. Living Lophelia colonies effectively prevent colonization by other organisms and are successful in the rejection of passing detrital material from the soft tissue. In a healthy condition the coral is able to encrust repetitively attached organisms by selectively secreted sclerenchyme layers, thus, this defensive reaction results in the thickening of the sk...

Bacteria-induced carbonate degradation; a taphonomic case study of Cibicides lobatulus from a high-boreal carbonate setting

The process of bacterial degradation of skeletal-binding organic matter forces selective carbonate dissolution in aerobic and turbulent coarsegrained environments. This is demonstrated in a Scanning Electron Microscope study on the benthic foraminifer Cibicides lobatulus from a coastal platform in northern Norway. High CO2 partial pressures are created by rod-shaped bacteria colonies under the protective extracellular polymer surface (EPS) film. The impact of degradative bacteria on biogenic carbonates is strongly controlled by a) the microstructural composition of the infested particles, and b) the distribution and supply of organic compounds on and within the skeletal construction. Both factors have strong influences on variations in rates of decay, biasing fossil preservation. In aerobic systems, carbonate dissolution may be regarded as a metabolic by-product through bacterial-induced decomposition of skeletal-binding organic matter. This study supports the increasing amount of evidence pointing to carbonate dissolution and maceration phenomena from shelf environments, especially from cold sea environments, and stresses microbial input in early diagenesis. INTRODUCTION

Substrate pitting and boring pattern of Hyrrokkin sarcophaga Cedhagen, 1994 (Foraminifera) in a modern deep-water coral reef mound

Colonization structures of the large parasitic foraminifer Hyrrokkin sarcophaga Cedhagen, 1994 on Lophelia pertusa, Acesta excavata and Delectopecten vitreus are described from a deep-water coral reef mound on the mid-Norwegian shelf at 240 to 300 m water depth. Hyrrokkin sarcophaga is the only epibiont which is capable of attaching itself on the soft tissue-protected coral skeleton where it tends to form clusters of 3 to 8 specimens close to the tentacles of Lophelia. The foraminifer excavates a pit up to 1.5 mm deep and etches a straight channel through the skeleton of the host which ends within the soft tissue. In contrast to Lophelia, infested bivalves show a strong wound repair reaction and seal the etched channels by intense calcification. The etching is only performed by adult specimens. Substrate pitting is considered to improve the attachment strength while boring enables the parasite to secure a persistent nutrient source.

Composition of soluble mineralizing matrices in zooxanthellate and non-zooxanthellate scleractinian corals: Biochemical assessment of photosynthetic metabolism through the study of a skeletal feature

SummarySoluble organic matrices extracted from aragonitic skeletons produced by recent zooxanthellate and non-zooxanthellate scleractinian corals were studied after suitable hydrolyses, by HPLC chromatographies allowing characterization of their amino acid and monasaccharide compositions. Clear compositional differences can be correlated with the symbiotic or non-symbiotic character in both proteic (via Asp, Glu, Ala and Ser) and glucidic phases of soluble matrices (via GalN, GlcN and Gal), providing new criteria to assess the impact of photosynthetic metabolism on skeletal features of scleractinian corals.

Coralline algal maerl frameworks-Islands within the phaeophytic kelp belt

SummaryIn the subtropical belt highly productive ecosystems are formed by coral reefs in oligotrophic seas. Towards more eutrophic conditions, coral reefs diminish and are subsequently replaced by highly productive kelp forests. In high latitudes framework constructing carbonate production is enhanced by the growth of branching coralline algae which predominantly generate maerl-type deposits. On a global view, these coralline algal ecosystems show an island-like distribution pattern within the phaeophytic kelp belt. Compared to kelp ecosystems, coralline-algaldominated ecosystems have low rates of productivity. Therefore, it is reasonable to seek the pronounced competitive value of the extremely slow-growing corallines. Due to their low annual growth increment, the coralline algae studied are very endangered by abiotic physical disturbances and by overgrowth of rapidly growing filamentous algae or sessile invertebrates. To overcome fouling pressure and storm-triggered physical disturbances, coralline algae thrive well in wave-sheltered headlands or skerry areas and generate characteristic ‘denuded areas’ by intense herbivory. This general distributional pattern is also true for high-boreal to subarctic coralline algal bioherms in northern Norway. Such a complex biological feedback maintains a high potential of self-regulation or self-organization in the algal reef bioherms. The different proponents involved in feedback processes include bacterial colonization, diatom microfouling and selective induction of larval metamorphosis. The negative impact of diatom microfouling and the important role of herbivores are relevant activities in the feedback system on a microscopic scale. Macroscopically, intense herbivory on coralline algae create denuded conditions, which are a widespread phenomenon in coralline algal ecosystems.

BIOCLASTIC CARBONATE SEDIMENTS ON THE SOUTHWESTERN SVALBARD SHELF

The poleward continuation of one of the largest known Arctic carbonate factories, the western Spitsbergenbank of the Barents Sea, has been surveyed along the narrow SW Svalbard shelf. On this shelf, formation of cold-water carbonate sediments occurs under glaciomarine environmental conditions. Mya truncata and Hiatella arctica colonized a soft glacio marine diamicton 3000-6000 years after the final retreat of the icedome from the SW Svalbard shelf. Since 2600 yr B.P., an increase of along-shelf bottom currents washed out the fine terrigenous deposits leaving behind a shelly lag-deposit and winnowed boulders on a morainic shelf topography. The most favourable depth interval promoting the establishment of an amalgamated bioclastic blanket is located in 50-80 m water depth. In this interval, strong bottom currents prevent sedimentation, thus, facilitating colonisation of filter-feeding benthic communities dominated by Balanus balanus and Chlamys islandica. Additional skeletal components are supplied by echinoderms, bryozoans, serpulids, brachiopods and gastropods. In shallower water depths, carbonate production is hampered by intense iceberg-scouring and release of ice-rafted debris from the still glaciated hinterland of Svalbard. In deeper water (>80 m), olive grey muds with dispersed pebbles rich in benthic foraminiferans, Clinocardium ciliatum and taxodont bivalves are present on all surveyed shelf banks. The deepest unit is a blue mud in water depths > 120 m with benthic foraminiferans, taxodont bivalves and sipunculids. Compared to Spitsbergenbank, carbonate production is much more restricted and impoverished on the SW Svalbard shelf, but is still an instructive modern example for the formation of skeletal carbonates resting on tillites in the geological record.

Serpula aggregates and their role in deep-sea coral communities in the southern Adriatic Sea

We document a remarkable abundance of the tubeworm Serpula vermicularis Linnaeus, 1767, in bathyal coral habitats from the Bari Canyon System in the southern Adriatic Sea. Here, the specimens of S. vermicularis grow from muddy substrate either as isolated individuals or as localized clusters of multiple individuals. Peculiar tube aggregations are also associated with Madrepora oculata build-ups and other stony corals including Desmophyllum dianthus. Three types of coral-serpulid (C–S) frameworks have been recognized based upon size and shape. The abundance of S. vermicularis increases with the size of C–S frameworks, which results from superimposition, overgrowth, and/or intergrowth of scleractinians and serpulids. Several generations of S. vermicularis contribute to the C–S frameworks, each most probably accounting for more than 8xa0years and presumably existing in the area for the last hundreds of years. At a meso-scale, the distribution pattern of serpulids seems to be mainly governed by currents and siltation. A further constraint is the co-occurring solitary coral D. dianthus within frameworks. The successful sea-bottom colonization by S. vermicularis and associated C–S frameworks is possibly related to a high oxygen content and food supply derived from the North Adriatic Dense Water (NAdDW). The flourishing populations of S. vermicularis as well as the peculiarity of C–S frameworks suggest that deep-sea canyons provide important benthic habitats in bathyal environments.

Ostracods in a cold-temperate coastal environment, Western Troms, Northern Norway: Sedimentary aspects and assemblages

SummaryThis study presents sedimentological and micropaleontological data on ostracods from a cold-temperate inner shelf setting in the Troms District, northern Norway. The coarse fraction analyses carried out on sediment surface samples from coastal platforms and adjacent outer fjord troughs reveal a considerable contribution from ostracods to the accumulation of skeletal carbonates in distinct depositional settings. Ostracod accumulation is highest along wave-sheltered areas of coastal platforms where fleshy seaweed and coralline algal communities thrive in 10 to 30 m water depth. Current-exposed slopes of outer fjord troughs show a highly mixed ostracod assemblage consisting of imported species from the shallow coastal platform which is mixed with the trough assemblage. The hydrodynamic transport of ostracods into deeper areas results from the strong tidal current regime. Because of this mixing process, only the end members, the coastal platform and the fjord trough assemblages can be defined. The former is characterized byBaffinicythere emarginata, Cythere lutea, Finmarchinella angulata, Hemicytherura clathrata, Robertsonites tuberculatus, Sclerochilus rudjakovi, Semicytherura undata andXestoleberis cf.depressa. The outer fjord trough assemblage is characterized byCluthia cluthae, Cytherella abyssorum, Cytheropteron alatum, Krithe cf.adelspergi, Muellerina abyssicola, Cytherella cf.vulgatella andCytheropteron testudo. Members of the northern Norwegian trough assemblage are known to occur in deeper open shelf environments of the NE-Atlantic.