Cold-water corals and hydrochemistry - is there a unifying link?

Physical and chemical parameters were measured in five different regions of the Northeast Atlantic with knownoccurrences of cold-water coral reefs and mounds and in the Mediterranean, where these corals form livingcarpets over existing morphologies. In this study we analyzed 282 bottom water samples regarding delta13CDIC,delta18O, and DIC. The hydrochemical data reveal characteristic patterns and differences for cold-water coralsites with living coral communities and ongoing reef and mound growth at the Irish and Norwegian sites. Whilethe localities in the Mediterranean, in the Gulf of Cadiz, and off Mauritania show only patchy coral growth onmound-like reliefs and various substrates.The analysis of delta13C/delta18O reveals distinct clusters for the different regions and the respective bottomwater masses bathing the delta18O, and especially between delta13CDIC and DIC shows that DIC is a parameterwith high sensitivity to the mixing of bottom water masses. It varies distinctively between sites with livingreefs/mounds and sites with restricted patchy growth or dead corals. Results suggest that DIC and delta13CDICcan provide additional insights into the mixing of bottom water masses.Prolific cold-water coral growth forming giant biogenic structures plot into a narrow geochemical windowcharacterized by a variation of delta13CDIC between 0.45 and 0.79 per mille being associated with the water masshaving a density of sigma-theta of 27.50.15 kg m-3

マルチヒーターを使用した一方向性凝固法による熱流動解析の試み : シリコン多結晶について

This study characterizes the microbial community composition over Haas Mound, one of the most prominent cold-water coral mounds of the Logachev Mound province (Rockall Bank, NE Atlantic). We outline patterns of distribution vertically – from the seafloor to the water column – and laterally – across the mound – and couple these to mound topography and hydrography. Samples of water, sediment and Lophelia pertusa were collected in 2012 and 2013 from locations that were chosen based on high definition video surveys. Temperature and current measurements were obtained at two sites at the summit and foot of Haas Mound to study near-bed hydrodynamic conditions. Overlaying water was collected from depths of 400 m as well as 5 and 10 m above the bottom using a CTD/Rosette system. Near-bottom water, sediment and L. pertusa mucus and skeleton samples were obtained with a box corer. Of all these biotopes, Roche GS-FLX amplicon sequencing targeting both Bacteria and Archaea was carried out, augmenting our understanding of deep sea microbial consortia. The pattern of similarities between samples, visualized by multi-dimensional scaling (MDS), indicates a strong link between the distribution of microbes and the specific biotopes. The microbial operational taxonomic unit (OTU) diversity was the highest in near-bottom water, which was sampled in the coral framework. For the first time, Thaumarchaeota marine group I (MGI) were found in L. pertusa mucus; Endozoicomonas was detected in skeleton, mucus and near-bottom water, whereas Mycoplasma was only detected in skeleton and near-bottom water, however not in mucus. Analysis of similarities (ANOSIM) indicates that overlaying water is well-mixed at 400 m depth but less so at 5 and 10 m above the bottom, where the composition of microbial communities differed significantly between summit, slope and off-mound. At all locations, the near-bottom water differed significantly from water at 5 m above the bottom, illustrating that the near-bottom water in between the coral framework represents a separate microbial habitat. Furthermore, the observed spatial heterogeneity in microbial communities is discussed in relation to environmental conditions

Oceanographic setting and short-timescale environmental variability at an Arctic seamount sponge ground

Mass occurrences of large sponges, or ‘sponge grounds’, are found globally in a range of oceanographic settings. Interest in these grounds is growing because of their ecological importance as hotspots of biodiversity, their role in biogeochemical cycling and bentho-pelagic coupling, the biotechnological potential of their constituent sponges, and their perceived vulnerability to physical disturbance and environmental change. Little is known about the environmental conditions required for sponges to persist and for grounds to form, and very few studies have explicitly characterised and interpreted the importance of oceanographic conditions. Here, results are presented of the first observational oceanographic campaign at a known sponge ground on the Schultz Massif Seamount (SMS; Arctic Mid-Ocean Ridge, Greenland / Norwegian Seas). The campaign consisted of water column profiling and short-term deployment of a benthic lander. It was supported by multibeam echosounder bathymetry and remotely operated vehicle video surveys. The seamount summit hosted several environmental factors potentially beneficial to sponges. It occurred within relatively nutrient-rich waters and was regularly flushed from above with slightly warmer, oxygen-enriched Norwegian Arctic Intermediate Water. It was exposed to elevated suspended particulate matter levels and oscillating currents (with diurnal tidal frequency) likely to enhance food supply and prevent smothering of the sponges by sedimentation. Elevated chlorophyll a concentration was observed in lenses above the summit, which may indicate particle retention by seamount-scale circulation patterns. High sponge density and diversity observed on the summit is likely explained by the combination of several beneficial factors, the coincidence of which at the summit arises from interaction between seamount geomorphology, hydrodynamic regime, and water column structure. Neighbouring seamounts along the mid-ocean ridge are likely to present similarly complex oceanographic settings and, as with the SMS, associated sponge ground ecosystems may therefore be sensitive to changes over a particularly broad range of abiotic factor

Distributions and habitat associations of deep-water corals in Norfolk and Baltimore Canyons, Mid-Atlantic Bight, USA

A multi-disciplinary study of two major submarine canyons, Baltimore Canyon and Norfolk Canyon, off the US mid-Atlantic coast focused on the ecology and biology of canyon habitats, particularly those supporting deep-sea corals. Historical data on deep-sea corals from these canyons were sparse with less than 750 records for the mid-Atlantic region, with most being soft sediment species. This study substantially increased the number of deep-sea coral records for the target canyons and the region. Large gorgonians were the dominant structure-forming coral taxa on exposed hard substrates, but several species of scleractinians were also documented, including first observations of Lophelia pertusa in the mid-Atlantic Bight region. Coral distribution varied within and between the two canyons, with greater abundance of the octocoral Paragorgia arborea in Baltimore Canyon, and higher occurrence of stony corals in Norfolk Canyon; these observations reflect the differences in environmental conditions, particularly turbidity, between the canyons. Some species have a wide distribution (e.g., P. arborea, Primnoa resedaeformis, Anthothela grandiflora), while others are limited to certain habitat types and/or depth zones (e.g., Paramuricea placomus, L. pertusa, Solenosmilia variabilis). The distribution of a species is driven by a combination of factors, which include availability of appropriate physical structure and environmental conditions. Although the diversity of the structure-forming corals (gorgonians, branching scleractinians and large anemones) was low, many areas of both canyons supported high coral abundance and a diverse coral-associated community. The canyons provide suitable habitat for the development of deep-sea coral communities that is not readily available elsewhere on the sedimented shelf and slope of the Mid-Atlantic Bight

Structure and development of carbonate mounds along the NE Atlantic margin

Giant carbonate mounds between 500-1200 m water depth along both the SE and SW margins of Rockall Trough rise 5 to 300 m above the surrounding seafloor and have diameters at their basis of up to 5 km. Buried mounds, at relatively shallow depth below the seafloor are also found. Both individual and complex clusters of mounds can be recognized. Smaller and individual, sometimes buried mounds are found at the upper slope. On the SW Rockall Trough margin, higher, steeper and individual mounds are found deeper downslope (900-1100 m). At the middle slope the mounds merge into a complex structure and form complex clusters with a very irregular upper surface and an apparent lack of internal reflectors (600-1000 m depth). These clusters are oriented perpendicular and slightly oblique to the prevailing bathymetry, and show on TOBI profiles as linear ridges. Further results of the TOBI survey in summer 2002 show that the distribution of mounds along the flanks of SW Rockall Trough is considerably more widespread than previously considered, and also that the mounds appear to form constructional elements on a large plateau. Erosional channels between mounds identify the strong interaction between mound shape and strong bottom currents along the slopes of mounds. On the upper flank the mounds are delineated by a field of large gravelly sediment waves of 500m wavelength oriented parallel to the margin in the central part and more curved to the north. On their lower flank slide scars do locally occur

Seasonal variability in the source and composition of particulate matter in the depositional zone of Baltimore Canyon, U.S. Mid-Atlantic Bight

Submarine canyons are often hotspots of biomass due to enhanced productivity and funneling of organic matterof marine and terrestrial origin. However, most deep-sea canyons remain poorly studied in terms of their role asconduits of terrestrial and marine particles. A multi-tracer geochemical investigation of particles collectedyearlong by a sediment trap in Baltimore Canyon on the US Mid-Atlantic Bight (MAB) revealed temporalvariability in source, transport, and fate of particulate matter. Both organic biomarker composition (sterol and nalkanes)and bulk characteristics (δ13C, Δ14C, Chl-a) suggest that while on average the annual contribution ofterrestrial and marine organic matter sources are similar, 42% and 52% respectively, marine sources dominate.Elevated Chlorophyll-a and sterol concentrations during the spring sampling period highlight a seasonal influx ofrelatively fresh phytodetritus. In addition, the contemporaneous increase in the particle reactive micronutrientscadmium (Cd) and molybdenum (Mo) in the spring suggest increased scavenging, aggregation, and sinking ofphytodetrital biomass in response to enhanced surface production within the nutricline. While tidally drivencurrents within the canyon resuspend sediment between 200 and 600 m, resulting in the formation of a nepheloidlayer rich in lithogenic material, near-bed sediment remobilization in the canyon depositional zone wasminimal. Instead, vertical transport and lateral transport across the continental margin were the dominantprocesses driving seasonal input of particulate matter. In turn, seasonal variability in deposited particulate organicmatter is likely linked to benthic faunal composition and ecosystem scale carbon cycling

Cold-water coral growth under extreme environmental conditions, the Cape Lookout area, NW Atlantic

The Cape Lookout cold-water coral area off thecoast of North Carolina forms the shallowest and northernmostcold-water coral mound area on the Blake Plateau inthe NW Atlantic. Cold-water coral habitats near Cape Lookoutare occasionally bathed in the Gulf Stream, which is characterisedby oligotrophic warm water and strong surface currents.Here, we present the first insights into the mound distributionand morphology, sedimentary environment and coralcover and near-bed environmental conditions as recordedby bottom landers from this coral area. The mounds occurbetween 320 and 550m water depth and are characterisedby high acoustic backscatter indicating the presenceof hard structure. Three distinct mound morphologies wereobserved: (1) a mound with a flattened top at 320 m, (2)multi-summited mounds with a teardrop shape in the middlepart of the area and (3) a single mound at 540m water depth.Echosounder profiles show the presence of a strong reflectorunderneath all mound structures that forms the base of themounds. This reflector cropped out at the downstream side ofthe single mound and consists of carbonate slabs. Video analysisrevealed that all mounds are covered by Lophelia pertusaand that living colonies only occur close to the summitsof the SSW side of the mounds, which is the side that facesthe strongest currents. Off-mound areas were characterisedby low backscatter and sediment ripples, indicating the presenceof relatively strong bottom currents. Two bottom landerswere deployed amidst the coral mounds between December2009 and May 2010. Both landers recorded prominentevents, characterised by large fluctuations in environmentalconditions near the seabed as well as in the overlyingwater column. The period between December and April wascharacterised by several events of increasing temperature andsalinity, coinciding with increased flow and near-bed acousticbackscatter. During these events temperature fluctuatedby up to 9 ?C within a day, which is the largest temperaturevariability as measured so far in a cold-water coral habitat.Warm events, related to Gulf Stream meanders, had the durationof roughly 1 week and the current during these eventswas directed to the NNE. The consequences of such eventsmust be significant given the strong effects of temperature on the metabolism of cold-water corals. Furthermore, elevatedacoustic backscatter values and high mass fluxes werealso recorded during these events, indicating a second stressorthat may affect the corals. The abrasive nature of sand incombination with strong currents might sand blast the corals.We conclude that cold-water corals near Cape Lookout liveunder extreme conditions that limit mound growth at present