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Highlights: • The cold-water coral Desmophyllum pertusum from reefs off Angola showed the same respiration rates at hypoxic and normoxic oxygen concentration. • The respiration rates measured are in the same order of magnitude as those previously observed for the species under normoxic conditions in other areas. Abstract: Large, well-developed and flourishing reefs dominated by the cold-water coral Desmophyllum pertusum have recently been discovered along the Angola margin in the southeastern Atlantic Ocean living under very low oxygen concentrations (0.6–1.5 mL L−1). This study assessed the respiration rates of this coral in a short-term (10 days) aquarium experiment under naturally low oxygen concentrations (1.4 ± 0.5 mL L−1) as well as under saturated oxygen concentrations (6.1 ± 0.6 mL L−1). We found no significant difference in respiration rates between the two oxygen concentrations. Furthermore, the respiration rates of D. pertusum were in the same order of magnitude as those of the same species living under normoxic conditions in other areas. This work expands the current knowledge on the metabolic activity of cold-water corals under hypoxic conditions, evidencing that low oxygen conditions are not a general limiting factor for the overall distribution of D. pertusum.

The mean cooling of the global ocean during the Last Glacial Maximum (LGM) was recently estimated to 2.6°C using noble gases trapped in ice cores (1). The ocean, however, is highly heterogeneous with respect to its internal temperature varying both in latitude and water depth. While temperature changes in the deep ocean are small at about 2 - 3 °C (1,2), the upper ocean is more dynamic. Regional temperature anomalies of up to 7°C are predicted during the LGM compared to modern interior ocean temperature by global ocean circulation models (3). Due to the temperature drop to near freezing conditions and the global increase in salinity from ice sheet growth, the oceans’ deep interior became strongly haline stratified (2). Temperatures of the glacial ocean thermocline are, however, less well constrained.Here, thermocline temperature reconstructions since the last glacial based on the Li/Mg ratio in cold-water coral skeletons are presented. The coral samples, collected from 300 - 1200 m water depths from different sites in the Atlantic (43°N to 25°S), reveal synchronous 5 - 7°C cooling during the last glacial period compared to today, as well as a dramatic shoaling of the thermocline. At the end of the LGM, warming of the upper thermocline ocean occurred early in the southern hemisphere followed by a fluctuating warming and thermocline deepening in the northern Hemisphere. This supports the oceanic climate seesaw proposed by Stocker and Johnson in 2003 (4). We thus propose dramatic changes in the export of polar waters towards the Equator and an enhanced subsurface ocean stratification leading to a mostly polar Atlantic with a shallow permanent thermocline during the glacial. References:1) Bereiter et al., Nature 553, 39-44 (2018).2) Adkins et al., Science 298, 1769-1773 (2002).3) Ballarotta et al., Clim. Past 9, 2669-2686 (2013).4) Stocker and Johnsen, Paleoceanography 18, 1087 (2003).

This study aims to map the occurrence and distribution of Madrepora oculata and to quantify density and colony sizes across recently discovered coral mounds off Angola. Despite the fact that the Angolan populations of M. oculata thrive under extreme hypoxic conditions within the local oxygen minimum zone, they reveal colonies with remarkable heights of up to 1250 mm—which are the tallest colonies ever recorded for this species—and average densities of 0.53 ± 0.37 (SD) colonies m−2. This is particularly noteworthy as these values are comparable to those documented in areas without any oxygen constraints. The results of this study show that the distribution pattern documented for M. oculata appear to be linked to the specific regional environmental conditions off Angola, which have been recorded in the direct vicinity of the thriving coral community. Additionally, an estimated average colony age of 95 ± 76 (SD) years (total estimated age range: 16–369 years) indicates relatively old M. oculata populations colonizing the Angolan coral mounds. Finally, the characteristics of the Angolan populations are benchmarked and discussed in the light of the existing knowledge on M. oculata gained from the North Atlantic and Mediterranean Sea., SI

Coral mounds formed by framework-forming cold-water corals pierce the seabed along most continental margins of the Atlantic Ocean and new sites are continuously being discovered. Here, we describe an extremely high accumulation of coral mounds at the NW Moroccan Atlantic margin between 35 degrees N and 35.5 degrees N. Within an area of only 1440 km(2), > 3400 mounds were found exposed at the seabed. The coral mounds are nowadays characterized by an almost complete lack of living cold-water corals. In addition, numerous buried mounds were identified in hydroacoustic sub-bottom profiles, and are estimated to be similar to 3.7 times more frequent than the exposed mounds. Consequently, a total of similar to 16,000 buried and exposed mounds is estimated for the entire study area. The exposed mounds are rather small with a mean height of 18 m and show a conspicuous arrangement in two slope-parallel belts that centre in water depths between 720 and 870 m and 890-980 m, respectively, putting them among the deepest mound occurrences discovered so far in the Atlantic. The mostly elongated mounds largely stretch downslope pointing to a significant influence of internal waves in the mound formation process. Moreover, based on their average dimensions, the entire coral mound volume can be estimated as 1.3 km(3), which means the mounds store a considerable amount of coral carbonate highlighting their potentially important role as regional carbonate factories. In combination with further occurrences of coral mounds along the Moroccan margin, both in the Mediterranean and in the Atlantic Ocean, these new findings underline Morocco's role as a hotspot for the occurrence of cold-water coral mounds.

Highlights • Holocene cold-water coral mound formation started non-synchronous in Belgica province. • Coral mounds and slope sediments record changes in intermediate water mass dynamics. • Increased turbulent bottom currents steered slope erosion and mound formation. • Internal waves at the ENAW-MOW boundary enhance energy supply and particle flux. • Transition zone between the ENAW-MOW shifted 250 m upslope during the last deglacial. Abstract Turbulent bottom currents significantly influence the formation of cold-water coral mounds and sedimentation processes on continental slopes. Combining records from coral mounds and adjacent slope sediments therefore provide an unprecedented palaeo-archive to understand past variations of intermediate water-mass dynamics. Here, we present coral ages from coral mounds of the Belgica province (Porcupine Seabight, NE Atlantic), which indicate a non-synchronous Holocene re-activation in mound formation suggested by a temporal offset of ∼2.7 kyr between the deep (start: ∼11.3 ka BP at 950 m depth) and shallow (start: ∼8.6 ka BP at 700 m depth) mounds. A similar depth-dependent pattern is revealed in the slope sediments close to these mounds that become progressively younger from 22.1 ka BP at 990 m to 12.2 ka BP at 740 m depth (based on core-top ages). We suggest that the observed changes are the consequence of enhanced bottom-water hydrodynamics, caused by internal waves associated to the re-invigoration of the Mediterranean Outflow Water (MOW) and the development of a transition zone (TZ) between the MOW and the overlying Eastern North Atlantic Water (ENAW), which established during the last deglacial. These highly energetic conditions induced erosion adjacent to the Belgica mounds and supported the re-initiation of mound formation by increasing food and sediment fluxes. The striking depth-dependent patterns are likely linked to a shift of the ENAW-MOW-TZ, moving the level of maximum energy ∼250 m upslope since the onset of the last deglaciation.

Cold-water corals (CWC) act as ecosystem engineers and thus contribute to biodiversity on continental margins worldwide. CWC mounds – built over geologic time by the interplay of biological, sedimentological, and oceanographic processes – create ecological niches for a variety of macrobenthic marine taxa (e.g. molluscs, sponges, bryozoans). The growth of CWC mounds is discontinuous over time due to changes in environmental and ecological conditions, such as food supply, water temperature, and dissolved oxygen concentration. While surficial distribution patterns of living and recently-dead mound macrobenthic communities have been described, their temporal ecological relationship with coral growth and mound formation is yet largely unexplored. Therefore, this project aims to determine what effects stagnations in CWC growth (i.e. repeated periods of ecosystem “turn off”) have on the local biodiversity and community structure of other CWC mound taxa, and thus what influences CWC mound development may have on regional biodiversity and biogeography in the deep sea over geologic time. Focusing on a single taxonomic group with high preservation potential, this study 1) quantitatively assesses temporal ecological trends of coral mound molluscan assemblages (bivalves and gastropods), and 2) statistically correlates those data with coral growth and palaeoceanographic records. Preliminary results from two CWC mound gravity cores through Brittlestar Ridge I in the Alboran Sea, western Mediterranean (~13.2 – 2.9 ka) indicate that throughout both cores the molluscan assemblages are typically quantitatively dominated by sessile benthic filter-feeding bivalves, particularly Heteranomia squamula and Hiatella arctica. Although bivalves are more abundant and diverse than gastropods in both cores, these taxonomic groups yield generally similar downcore dynamics in abundance and diversity. Comparisons of total molluscan assemblages (bivalves and gastropods combined) suggest that the older assemblages – those associated with the Bølling-Allerød interstadial (13.5-12.8 ka) and Early Holocene (11.3-9.8 ka) – are more similar to one another than to younger assemblages in the cores. Rotational vector fitting analyses indicate that these older assemblages are significantly related to higher productivity and different hydrodynamics (and sediment input), which are factors that have also been linked to CWC growth in the region. Altogether, our paleoecological reconstructions so far reaffirms the connectivity of benthic communities with local oceanographic conditions and adjacent taxa. Additional ecological assessments will further refine our understanding of the relationships between CWC growth and benthic communities, and in turn the temporal drivers and dynamics of CWC mound biodiversity.

The Last Glacial Maximum (LGM) is marked by significant cooling of the global ocean, which was recently estimated to 2.6°C using noble gases trapped in ice cores (1). This cooling is not equally distributed throughout the world oceans, since global ocean circulation models predict regional temperature anomalies during the LGM of up to 7°C (annually and zonally averaged) when compared to modern interior ocean temperature (2). The oceans deep interior thus became haline stratified (3) due to the drop in temperature to near freezing and the global increase in salinity from ice sheet growth. In contrast to a deepening of the modern thermocline as a result of anthropogenic global warming, cooling causes the thermocline to rise in the sub-tropics as more polar waters enter the mid-depth ocean.Here we present glacial thermocline temperature reconstructions since the LGM based on the Li/Mg ratio in aragonite skeletons of precisely dated cold-water corals. Corals have been collected from 300-1000m water depths from sites in the northern and southern Atlantic (62°N to 25°S) and demonstrate synchronous 5 - 7°C glacial cooling, and a dramatic shoaling of the thermocline. Through the deglaciation the warming of the upper thermocline ocean occurs early in the southern hemisphere followed by fluctuating warming and thermocline deepening in the northern Hemisphere, which supports the oceanic climate seesaw proposed by Stocker and Johnson in 2003 (4). We thus propose dramatic changes in export of polar waters towards the Equator and augmented subsurface ocean stratification leading to a mostly polar Atlantic with a shallow permanent thermocline. This shoaling possibly increased the rate of nutrient recycling causing higher biological surface ocean activity and the cooling promoted carbon storage. During the glacial, we assume an atmospheric forcing, such as equatorward displacement of the Hadley circulation, to steer the glacial polar water advance as mid-depth boundary currents in the northern and southern hemisphere to effectively spread the cold water through the entire mid-depth Atlantic.References:Bereiter et al.: Mean global ocean temperatures during the last glacial transition. Nature 553, 39-44 (2018). Ballarotta et al.: Last Glacial Maximum world ocean simulations at eddy-permitting and coarse resolutions: do eddies contribute to a better consistency between models and palaeoproxies?, Clim. Past 9, 2669-2686 (2013). Adkins et al.: The Salinity, Temperature, and d18O of the Glacial Deep Ocean. Science 298, 1769-1773 (2002). Stocker and Johnsen: A minimum thermodynamic model for the bipolar seesaw, Paleoceanography 18, 1087 (2003).

Reefs formed by scleractinian cold-water corals represent unique biodiversity hot spots in the deep sea, preferring aphotic water depths of 200–1000 m. The distribution of the most prominent reef-building species Lophelia pertusa is controlled by various environmental factors including dissolved oxygen concentrations and temperature. Consequently, the expected ocean deoxygenation and warming triggered by human-induced global change are considered as a serious threat to cold-water coral reefs. Here, we present results on recently discovered reefs in the SE Atlantic, where L. pertusa thrives in hypoxic and rather warm waters. This sheds new light on its capability to adapt to extreme conditions, which is facilitated by high surface ocean productivity, resulting in extensive food supply. Putting our data in an Atlantic-wide perspective clearly demonstrates L. pertusa’s ability to develop population-specific adaptations, which are up to now hardly considered in assessing its present and future distributions.

The deep sea plays a critical role in global climate regulation through uptake and storage of heat and carbon dioxide. However, this regulating service causes warming, acidification and deoxygenation of deep waters, leading to decreased food availability at the seafloor. These changes and their projections are likely to affect productivity, biodiversity and distributions of deep-sea fauna, thereby compromising key ecosystem services. Understanding how climate change can lead to shifts in deep-sea species distributions is critically important in developing management measures. We used environmental niche modelling along with the best available species occurrence data and environmental parameters to model habitat suitability for key cold-water coral and commercially important deep-sea fish species under present-day (1951–2000) environmental conditions and to project changes under severe, high emissions future (2081–2100) climate projections (RCP8.5 scenario) for the North Atlantic Ocean. Our models projected a decrease of 28%–100% in suitable habitat for cold-water corals and a shift in suitable habitat for deep-sea fishes of 2.0°–9.9° towards higher latitudes. The largest reductions in suitable habitat were projected for the scleractinian coral Lophelia pertusa and the octocoral Paragorgia arborea, with declines of at least 79% and 99% respectively. We projected the expansion of suitable habitat by 2100 only for the fishes Helicolenus dactylopterus and Sebastes mentella (20%–30%), mostly through northern latitudinal range expansion. Our results projected limited climate refugia locations in the North Atlantic by 2100 for scleractinian corals (30%–42% of present-day suitable habitat), even smaller refugia locations for the octocorals Acanella arbuscula and Acanthogorgia armata (6%–14%), and almost no refugia for P. arborea. Our results emphasize the need to understand how anticipated climate change will affect the distribution of deep-sea species including commercially important fishes and foundation species, and highlight the importance of identifying and preserving climate refugia for a range of area-based planning and management tools., ATLAS, A Trans-AtLantic Assessment and deep-water ecosystem-based Spatial management plan for Europe, SI

High-precision U-series dating of scleractinian cold-water corals is a key chronological tool for studies of past environmental and climate conditions. Here, we tested and optimized an automated chemical extraction system (ESI prepFAST-MC equipped with an Eichrom TRU-resin chromatographic column) for its ability to purify U and Th isotopes for mass spectrometric U-series dating at the sub-‰ precision level. Chemical yields are constantly high, on average around 90% for both U and Th. Analytical blanks are comparable to manual purification (< 0.15 pg U, 0.15 pg Th for a typical sample of 50 mg) and memory effects due to the recycling of the column are mostly insignificant as the carry-over fraction is about 10− 5 for Th and 10− 3 for U isotopes. However, it was found that the built-in UTh (TRU-resin) column must be pre-conditioned for analysis using > 1 μg g− 1 Th and U in order to achieve the above mentioned chemical yields. This conditioning has no impact on the Th/U data. The automated chemical preparation protocol described here is compared to conventional high precision U-series dating with manual sample purification. For the 34 cold-water corals extracted from a sediment core collected from a coral mound off Angola, the differences between 230Th/238U- and 234U/238U-ratios and U-series ages measured with the two analytical methods are smaller than the respective analytical uncertainty of < 3.0‰, 0.8‰ and 3.0‰, respectively. Overall, ages of the studied corals span 34,000 years and perfectly meet quality control constrains, such as initial seawater δ234U0. Finally, our record of coral ages indicates vigorous coral growth under warm and cold climate conditions in the temperate south-eastern Atlantic, contrasting climate influenced coral occurrences in the north-eastern Atlantic. ISSN:0009-2541 ISSN:1872-6836

Cold-water coral mounds are common seabed features in the North Atlantic Ocean, where they are mainly restricted to water depths between 200 m and 1000 m. Coral mounds consist of coral fragments and hemipelagic sediments, reflecting an often complex history of mound aggradation and erosion linked to coral vitality. In the southern Gulf of Cadiz along the Moroccan margin, a large field (extension: 1800 km2) of 781 comparatively small buried and exposed mounds (average height: about 20 m) has recently been discovered. The mounds in the so-called Atlantic Moroccan Coral Province (AMCP) initiated on at least ten different horizons, all of them most likely related to glacial periods since the Early-Middle Pleistocene Transition. A strong link between the intensification of bottom currents and the number of coral mounds rooting on each of the identified horizons is assumed. Also a shift of the average water depth at which coral mounds initiated towards deeper regions and an accompanied increase in mound height is observed between MIS 14 and MIS 12. Finally, reduced or low sediment input is regarded as one of the main factors causing the rather small size of coral mounds in the AMCP in comparison to other Atlantic mound provinces.

Coral mounds formed by framework-forming scleractinian cold-water corals (CWC; mainly Lopheliapertusa) are a common seabed feature along the Atlantic continental margins. While coral mound areas in the NE Atlantic reveal a climate-dependent temporal pattern of CWC occurrence and mound aggradation that is related to distinct environmental conditions (e.g., productivity, water mass properties, hydrodynamics), the long-term development of CWC and coral mounds at the western side of the Atlantic is less well documented and understood. Here, we present a 260-kyr coral record from the recently described Campeche CWC province in the southern Gulf of Mexico, combined with a reconstruction of the paleo-environmental conditions for the last 140 kyr. Uranium-series dating of 26 coral samples reveals that CWC growth predominantly coincided with interglacial periods. Highest vertical mound aggradation rates of 34 to 40 cm kyr(-1) occurred during the Holocene. The reduced occurrence of CWC and the concurrent almost complete stagnation in mound aggradation during glacial periods could be linked to a diminished presence of Antarctic Intermediate Water at those intermediate depths in which the coral mounds occur. Such setting would have caused a less dynamic bottom current regime resulting in a reduced food supply to the CWC along the Campeche Bank. Deutsche Forschungsgemeinschaft (DFG) [HE 3412/17-1] Fundacao para a Ciencia e Tecnologia (FCT) [SFRH/BD/72149/2010] GLOMAR - the Bremen International Graduate School for Marine Sciences info:eu-repo/semantics/publishedVersion

An exceptionally large cold-water coral mound province (CMP) was recently discovered extending over 80 km along the Namibian shelf (offshore southwestern Africa) in water depths of 160–270 m. This hitherto unknown CMP comprises >2000 mounds with heights of up to 20 m and constitutes the largest CMP known from the southeastern Atlantic Ocean. Uranium-series dating revealed a short but intense pulse in mound formation during the early to mid-Holocene. Coral proliferation during this period was potentially supported by slightly enhanced dissolved oxygen concentrations compared to the present Benguela oxygen minimum zone (OMZ). The subsequent mid-Holocene strengthening of the Benguela Upwelling System and a simultaneous northward migration of the Angola-Benguela Front resulted in an intensification of the OMZ that caused the sudden local extinction of the Namibian corals and prevented their reoccurrence until today., Sí

18 pages, 6 figures, 4 tables, supplementary data https://dx.doi.org/10.1016/j.margeo.2019.02.007.-- Data associated with the article in PANGAEA, Cold-water corals (CWCs) are widely distributed in the entire Alboran Sea (western Mediterranean Sea), but only along the Moroccan margin they have formed numerous coral mounds, which are constrained to the West and the East Melilla CWC mound provinces (WMCP and EMCP). While information already exists about the most recent development of the coral mounds in the EMCP, the temporal evolution of the mounds in the WMCP was unknown up to the present. In this study, we present for the first time CWC ages obtained from four sediment cores collected from different mounds of the WMCP, which allowed to decipher their development since the last deglaciation. Our results revealed two pronounced periods of coral mound formation. The average mound aggradation rates were of 75–176 cm kyr−1 during the Bølling-Allerød interstadial and the Early Holocene, only temporarily interrupted during the Younger Dryas, when aggradation rates decreased to, We wish to acknowledge European Commission Seventh Framework Programme EuroFleets Project for granting the MD194 cruise and related logistics under project grant No. 228344, the Deutsche Forschungsgemeinschaft (DFG) for providing ship time to realize cruise MSM36 and the EC Marie Curie single action “Geo-Habit” (GA29874) for supporting the absolute dating of the MD cores presented in this study. Cruise MSM36 was further supported through the DFG Research Center/Cluster of Excellence “MARUM – The Ocean in the Earth System”. This study received funding from the DFG-project “MoccAMeBo” (HE 3412/18-1). The scholarship of H. Wang is funded by the Chinese Scholar Council

Fossil cold-water coral mounds overgrown by sponges and bryozoans were observed in anoxic conditions on the Namibian margin, while mounds colonized by thriving cold-water coral reefs were found in hypoxic conditions on the Angolan margin. These low oxygen conditions do not meet known environmental ranges favoring cold-water corals and hence are expected to provide unsuitable habitats for cold-water coral growth and therefore reef formation. To explain why the living fauna can nevertheless thrive in both areas, present day environmental conditions at the southwestern African margin were assessed. Downslope CTD transects and the deployment of bottom landers were used to investigate spatial and temporal variations of environmental properties. Temporal measurements in the mound areas recorded oscillating low dissolved oxygen concentrations of 0–0.17 ml l−1 (≙ 0–9 % saturation) on the Namibian and 0.5–1.5 ml l−1 (≙ 7–18 % saturation) on the Angolan margin, which were associated with relatively high temperatures (11.8 13.2 °C and 6.4–12.6 °C respectively). Semi-diurnal barotrophic tides were found to interact with the margin topography producing internal waves with excursions of up to 70 and 130 m for the Namibian and Angolan margins, respectively. These tidal movements temporarily deliver water with more suitable characteristics to the coral mounds from below and above the hypoxic zone. Concurrently, the delivery of high quantity and quality of suspended particulate organic matter was observed, which serves as a food source for cold-water corals. On the Namibian slope organic matter indicates a completely marine source and originates directly from the surface productive zone, whereas on the Angolan margin the geochemical signature of organic material suggest an additional mechanisms of food supply. A nepheloid layer observed above the cold-water coral mound area on the Angolan margin may constitutes a reservoir of fresh organic matter, facilitating a constant supply of food particles by tidal mixing. This suggests that the cold-water coral communities as well as the associated fauna may compensate unfavorable conditions induced by low oxygen levels and high temperatures with an enhanced availability of food. With the expected expansion of oxygen minimum zones in the future due to anthropogenic activities, this study provides an example on how ecosystems could cope with such extreme environmental conditions.

The two scleractinian cold-water corals Lophelia pertusa and Madrepora oculata are widely distributed in the Alboran Sea. They have been found (alive and fossil) on seamounts, volcanic ridges and mud volcanoes, and they formed coral mounds in the geological past. While the cold-water corals show a reduced occurrence during the last glacial period, they experienced a boom since the last deglaciation until the Early Holocene. The proliferation of cold-water corals during this time is expressed in very high vertical mound aggradation rates of >400 cm kyr−1. Since the mid-Holocene coral mound aggradation significantly slowed-down, which is ascribed to the reduced occurrence of cold-water corals likely supplemented by a reduced sediment supply. During the Holocene, a shift in coral species dominance towards a M. oculata-dominated cold-water coral community becomes apparent. It is speculated that in comparison to L. pertusa, M. oculata has a higher tolerance against the increasing Holocene bottom water temperatures, but is not efficient in building-up mounds likely attributed to its thinly branching framework.

Over the recent years, two research fields addressing continental slope sedimentary systems have gained significant momentum: contourites and cold-water coral mounds. Being both related to intense bottom currents and being both dependent on sediment supply, they share some commonalities resulting in their widespread co-occurrence. However, as cold-water coral mounds predominantly occur in shallow to intermediate water depths, this co-occurrence is restricted to these depth levels. For both systems, the available knowledge is derived basically from North Atlantic Ocean settings, indicating the potential to discover such systems hidden in the other ocean basins (as well as still hidden in the Atlantic). Contourites and cold-water coral mounds have the capability of providing high-resolution palaeo-environmental records, although with often differing temporal ranges and/or temporal resolutions. Applying the concept of a joint exploitation of sedimentary records obtained from mounds and contourites offers the unique possibility of analysing contourite and mound development as well as the related palaeo-environmental settings much more comprehensively than done when only considering one of these archives. Thus, after two decades of intense research, providing significant knowledge about contourites and cold-water coral mounds from the North Atlantic, new ideas and concepts may arise from a close collaboration of scientists working in these two fields.

This study presents aggradation rates supplemented for the first time by carbonate accumulation rates from Mediterranean cold-water coral sites considering three different regional and geomorphological settings: (i) a cold-water coral ridge (eastern Melilla coral province, Alboran Sea), (ii) a cold-water coral rubble talus deposit at the base of a submarine cliff (Urania Bank, Strait of Sicily) and (iii) a cold-water coral deposit rooted on a predefined topographic high overgrown by cold-water corals (Santa Maria di Leuca coral province, Ionian Sea). The mean aggradation rates of the respective cold-water coral deposits vary between 10 and 530 cm kyr−1 and the mean carbonate accumulation rates range between 8 and 396 g cm−2 kyr−1 with a maximum of 503 g cm−2 kyr−1 reached in the eastern Melilla coral province. Compared to other deep-water depositional environments the Mediterranean cold-water coral sites reveal significantly higher carbonate accumulation rates that were even in the range of the highest productive shallow-water Mediterranean carbonate factories (e.g. Cladocora caespitosa coral reefs). Focusing exclusively on cold-water coral occurrences, the carbonate accumulation rates of the Mediterranean cold-water coral sites are in the lower range of those obtained for the prolific Norwegian coral occurrences, but exhibit much higher rates than the cold-water coral mounds off Ireland. This study clearly indicates that cold-water corals have the potential to act as important carbonate factories and regional carbonate sinks within the Mediterranean Sea. Moreover, the data highlight the potential of cold-water corals to store carbonate with rates in the range of tropical shallow-water reefs. In order to evaluate the contribution of the cold-water coral carbonate factory to the regional or global carbonate/carbon cycle, an improved understanding of the temporal and spatial variability in aggradation and carbonate accumulation rates and areal estimates of the respective regions is needed.

The largest coherent cold-water coral (CWC) mound province in the Atlantic Ocean exists along the Mauritanian margin, where up to 100 m high mounds extend over a distance of similar to 400 km, arranged in two slope-parallel chains in 400-550 m water depth. Additionally, CWCs are present in the numerous submarine canyons with isolated coral mounds being developed on some canyon flanks. Seventy-seven Uranium-series coral ages were assessed to elucidate the timing of CWC colonisation and coral mound development along the Mauritanian margin for the last similar to 120,000 years. Our results show that CWCs were present on the mounds during the Last Interglacial, though in low numbers corresponding to coral mound aggradation rates of 16 cm kyr(-1). Most prolific periods for CWC growth are identified for the last glacial and deglaciation, resulting in enhanced mound aggradation (>1000 cm kyr(-1)), before mound formation stagnated along the entire margin with the onset of the Holocene. Until today, the Mauritanian mounds are in a dormant state with only scarce CWC growth. In the canyons, live CWCs are abundant since the Late Holocene at least. Thus, the canyons may serve as a refuge to CWCs potentially enabling the observed modest re-colonisation pulse on the mounds along the open slope. The timing and rate of the pre-Holocene coral mound aggradation, and the cessation of mound formation varied between the individual mounds, which was likely the consequence of vertical/lateral changes in water mass structure that placed the mounds near or out of oxygen-depleted waters, respectively. (C) 2018 The Authors. Published by Elsevier Ltd.

Highlights: • Basin-wide assessment of Lophelia and Madrepora since the last glacial. • Corals were most prolific during the Younger Dryas in the eastern Mediterranean. • Lophelia was most prolific during the deglaciation and Early Holocene in the Alboran Sea. • Temporary decline of Lophelia in the Alboran Sea during the Younger Dryas. • Mediterranean cold-water corals are related to high productivity conditions. • Link between cold-water corals and intensified intermediate water mass circulation. Abstract: This study presents newly obtained coral ages of the cold-water corals Lophelia pertusa and Madrepora oculata collected in the Alboran Sea and the Strait of Sicily (Urania Bank). These data were combined with all available Mediterranean Lophelia and Madrepora ages compiled from literature to conduct a basin-wide assessment of the spatial and temporal occurrence of these prominent framework-forming scleractinian species in the Mediterranean realm and to unravel the palaeo-environmental conditions that controlled their proliferation or decline. For the first time special focus was placed on a closer examination of potential differences occurring between the eastern and western Mediterranean sub-basins. Our results clearly demonstrate that cold-water corals occurred sparsely in the entire Mediterranean during the last glacial before becoming abundant during the Bolling-Allerod warm interval, pointing to a basin-wide, almost concurrent onset in (re-)colonisation after ~13.5 ka. This time coincides with a peak in meltwater discharge originating from the northern Mediterranean borderlands which caused a major reorganisation of the Mediterranean thermohaline circulation. During the Younger Dryas and Holocene, some striking differences in coral proliferation were identified between the sub-basins such as periods of highly prolific coral growth in the eastern Mediterranean Sea during the Younger Dryas and in the western basin during the Early Holocene, whereas a temporary pronounced coral decline during the Younger Dryas was exclusively affecting coral sites in the Alboran Sea. Comparison with environmental and oceanographic data revealed that the proliferation of the Mediterranean corals is linked with enhanced productivity conditions. Moreover, corals thrived in intermediate depths and showed a close relationship with intermediate water mass circulation in the Mediterranean sub-basins. For instance, reduced Levantine Intermediate Water formation hampered coral growth in the eastern Mediterranean Sea during sapropel S1 event as reduced Winter Intermediate Water formation did in the westernmost part of the Mediterranean (Alboran Sea) during the Mid-Holocene. Overall, this study clearly demonstrates the importance to consider region-specific environmental changes as well as species-specific environmental preferences in interpreting coral chronologies. Moreover, it highlights that the occurrence or decline of cold-water corals is not controlled by one key parameter but rather by a complex interplay of various environmental variables.

This work aims at characterising the seamount physiography and biology in the OSPAR Convention limits (north-east Atlantic Ocean) and Mediterranean Sea. We first inferred potential abundance, location and morphological characteristics of seamounts, and secondly, summarized the existing biological, geological and oceanographic in situ research, identifying examples of well-studied seamounts. Our study showed that the seamount population in the OSPAR area (north-east Atlantic) and in the Mediterranean Sea is large with around 557 and 101 seamount-like features, respectively. Similarly, seamounts occupy large areas of about 616 000 km2 in the OSPAR region and of about 89 500 km2 in the Mediterranean Sea. The presence of seamounts in the north-east Atlantic has been known since the late 19th century, but overall knowledge regarding seamount ecology and geology is still relatively poor. Only 37 seamounts in the OSPAR area (3.5% of all seamounts in the region), 22 in the Mediterranean Sea (9.2% of all seamounts in the region) and 25 in the north-east Atlantic south of the OSPAR area have in situ information. Seamounts mapped in both areas are in general very heterogeneous, showing diverse geophysical characteristics. These differences will likely affect the biological diversity and production of resident and associated organisms.

The neodymium isotopic composition (εNd) of mixed planktonic foraminifera species and scleractinian cold-water corals (CWC; Madrepora oculata, Lophelia pertusa) collected at 280–620 m water depth in the Balearic Sea, the Alboran Sea and the south Sardinian continental margin was investigated to constrain hydrological variations at intermediate depths in the western Mediterranean Sea during the last 20 ka. Planktonic (Globigerina bulloides) and benthic (Cibicidoides pachyderma) foraminifera were also analyzed for stable oxygen (δ18O) and carbon (δ13C) isotopes. The foraminiferal and coral εNd values from the Balearic Sea and the Alboran Sea are comparable over the past ~ 13 ka, with mean values of −8.94 ± 0.26 (1σ; n = 24) and −8.91 ± 0.18 (1σ; n = 25), respectively. Before 13 ka BP, the foraminiferal εNd values are slightly lower (−9.28 ± 0.15) and tend to reflect a higher mixing between intermediate and deep waters, characterized by more unradiogenic εNd values. The slight εNd increase after 13 ka BP is associated to a marked difference in the benthic foraminiferal δ13C composition of intermediate and deeper depths, which started at ~ 16 ka BP. This suggests an earlier stratification of the water masses and a subsequent reduced contribution of unradiogenic εNd from deep waters. The CWC from the Sardinia Channel show a much larger scattering of εNd values, from −8.66 ± 0.30 to −5.99 ± 0.50, and a lower average (−7.31 ± 0.73; n = 19) compared to the CWC and foraminifera from the Alboran Sea and Balearic Sea, indicative of intermediate waters sourced from the Levantine basin. At the time of sapropel S1 deposition (10.2 to 6.4 ka), the εNd values of the Sardinian CWC become more unradiogenic (−8.38 ± 0.47; n = 3 at ~ 8.7 ka BP), suggesting a significant contribution of intermediate waters originated from the western basin. Accordingly, we propose here that western Mediterranean intermediate waters replaced the Levantine Intermediate Water (LIW), which was strongly reduced during the mid-sapropel (~ 8.7 ka BP). This observation supports a notable change of Mediterranean circulation pattern centered on sapropel S1 that needs further investigations to be confirmed.

Continuous sedimentary records from an eastern Mediterranean cold-water coral ecosystem thriving in intermediate water depths (∼600 m) reveal a temporary extinction of cold-water corals during the Early to Mid Holocene from 11.4–5.9 cal kyr BP. Benthic foraminiferal assemblage analysis shows low-oxygen conditions of 2 ml l −1 during the same period, compared to bottom-water oxygen values of 4–5 ml l −1 before and after the coral-free interval. The timing of the corals' demise coincides with the sapropel S1 event, during which the deep eastern Mediterranean basin turned anoxic. Our results show that during the sapropel S1 event low oxygen conditions extended to the rather shallow depths of our study site in the Ionian Sea and caused the cold-water corals temporary extinction. This first evidence for the sensitivity of cold-water corals to low oceanic oxygen contents suggests that the projected expansion of tropical oxygen minimum zones resulting from global change will threaten cold-water coral ecosystems in low latitudes in the same way that ocean acidification will do in the higher latitudes.

Article history:Received 17 June 2010Received in revised form 29 October 2010Accepted 11 December 2010Available online 21 December 2010Communicated by G.J. de LangeKeywords:Lopheliacold-water coralscarbonate moundsBanda Mound ProvinceNW-Africaprimary productivity Cold-water corals are widely distributed along the Atlantic continental margin with varying growth patternsinrelationtotheirspecificenvironment.Here,weinvestigatethelong-termdevelopmentofcold-watercoralsthat once thrived on a low-latitude (17°40′N) cold-water coral mound in the Banda Mound Province offMauritania duringthelastglacial–interglacialcycle. U/Thdatesobtained from20specimensofthecold-watercoral Lophelia pertusa, revealed three distinct periods of coral growth during the last glacial at 65 to 57 kyr BP,45 to 32 kyr BP and 14 kyr BP, thus comprising the cool periods of Marine Isotopic Stages (MIS) 2–4. Thesecoral growth periods occur during periods of increased productivity in the region, emphasizing thatproductivity seems to be the major steering factor for coral growth off Mauritania, which is one of the majorupwelling regions in the world. This pattern differs from the well studied coral mounds off Ireland, where thecurrent regime predominantly influences the prosperity of the cold-water corals. Moreover, coral growth offIreland takes place during rather warm interglacial and interstadial periods, whereas off Mauritania coralgrowth is restricted to glacial and stadial periods. However, the on-mound sedimentation patterns offMauritania largely resemble the observations reported from the Irish mounds. The bulk of the preservedsediments derives from periods of coral growth, whereas during periods without corals hardly any netsedimentation or mound growth took place.© 2011 Elsevier B.V. All rights reserved.

International audience; U-series age patterns obtained on reef framework-forming cold-water corals collected over a nearly 6000-km-long continental margin sector, extending from off Mauritania (17 degrees N; northwest Africa) to the southwestern Barents Sea (70 degrees N; northeastern Europe), reveal strong climate influences on the geographical distribution and sustained development of these ecosystems. Over the past three glacial-interglacial cycles, framework-forming cold-water corals (Lophelia pertusa and Madrepora oculata) seem to have predominantly populated reefs, canyons, and patches in the temperate East Atlantic and the Mediterranean Sea. Above 50 degrees N corals colonize reefs in the northern East Atlantic primarily during warm climate periods with the biogeographic limit advancing from similar to 50 degrees N to similar to 70 degrees N. We propose that north-south oscillations of the biogeographic limit of reef developments are paced by ice ages and may occur synchronously with north-south displacement of cold nutrient-rich intermediate waters and surface productivity related to changes of the polar front.

This paper constitutes a first detailed and systematic facies and biota description of an isolated carbonate knoll (Pee Shoal) in the Timor Sea (Sahul Shelf, NW Australia). The steep and flat-topped knoll is characterized by a distinct facies zonation comprising (A) soft sediments with scattered debris and scarce sponges, hydrozoans and crinoids (320–210 m water depth), (B) hardground outcrops (step-like banks, vertical cliffs) that are mainly colonized by octocorals and sponges (210–75 m), and (C) the summit region (75–21 m) where the slopes merge gently into the flat-topped summit that is densely colonized by massive and encrusting zooxanthellate corals and the octocoral Heliopora coerulea. In contrast, the sediments recovered from the summit are dominated by the green alga Halimeda, subordinate components are corals, benthic foraminifers, mollusks, and coralline red algae. Thus, the sediments are classified as chlorozoan grain assemblage. However, non-skeletal grains (fecal pellets, ooids) are almost completely absent. This discrepancy between the living biota and the sediment composition could reflect a disruption by the severe tropical cyclone Ingrid that hit the northern Australian shelf in March 2005, just before the sampling for this study took place (September 2005).

Cold-water coral carbonate mounds are widespread along the Irish continental margin. Whereas the Porcupine Seabight and the Rockall Trough are relatively well studied with regard to mound topography, coral coverage, and benthic life diversity, the situation on the western Rockall Bank is rather unknown. Detailed facies and biocoenoses mapping based on video footage analyses was conducted on the newly-discovered Franken Mound. Facies were identified ranging between cliff-like to planar hardgrounds and soft sediments that are partly rippled. A variety of biocoenoses are associated with these facies comprising discrete live coral colonies, dense live and dead coral framework coverage, abundant to scattered coral debris, and a soft sediment faunal community, whereas the latter is three times less speciose as biocoenoses containing live framework-building corals. The facies and biocoenosis classes are supplemented by exposed dropstones, lost fishery nets, and rubbish. The distribution of the classes clearly indicates a close relationship with local current effects and current intensification. Due to the dominance of dead coral framework and the partially exposed internal sediment sequences on the mound flanks, it is assumed that Franken Mound is approaching the “mound retirement” mound growth state.

Acoustic seabed classification provides a sophisticated technique to discriminate seabed characteristics and to map their distribution at high spatial and temporal resolution. In the present study, the seabed classification system QTC View/Impact was applied to investigate a 9- km 2 area at water depths between 6 and 20 m in the outer Weser Estuary (German Bight, southeastern North Sea). The survey area comprises parts of a routinely dredged shipping channel as well as of a dredge spoil disposal site. The acoustic data, collected by means of a singlebeam 200-kHz echosounder combined with a QTC system, were classified into three acoustic classes. These classes are identified with (1) fine to medium sand, with a low content of shell fragments; (2) medium sand, with a moderate content of shell fragments; and (3) medium to coarse sand, with a high content of shell fragments. By comparing this point-related acoustic classification with sidescan sonographs, it can be convincingly demonstrated that the acoustic data obtained by the QTC system reflect more than simply sediment type distribution, but that rather the occurrence of bedforms also appears to be important. Furthermore, in a time series of three QTC surveys in a period of 14 months, it is apparent that dredging as well as the disposal of dredge spoil constitute a strong impact on the sediment distribution and seabed morphology of the study site.

The impact of dredge spoil disposal on asymmetrical large-scale dunes has been studied at a disposal site in a shallow subtidal area of the outer Weser Estuary (German Bight, southeastern North Sea). Between June and December 1998, this site was used for the disposal of ~3×106 m3 dredge spoil. Repeated bathymetric surveys with a multibeam echosounder system reveal that the artificial supply of sediment provoked significant morphological changes in the dune field, including the infill of dune troughs and even the complete burial of individual dunes. However, even completely buried dunes began to regenerate within a few months. In addition, slow migration of the dunes toward the open sea was observed, indicating net seaward sediment transport in the survey area. Since the dumped sediment does not appear to have a persistent effect on the bedforms and, in all likelihood, will be exported from the estuarine system on medium- to long-term timescales, the investigated area constitutes a suitable disposal site.

With the development of high-resolution multibeam echosounder systems (MBES) for surveying shallow-water areas a new tool is available to monitor rapid changes in seabed morphology as, e.g., caused by the dumping of dredge spoil in coastal waters. In this study, four data sets of repeated bathymetric surveys with a MBES were processed and analyzed. The data were collected in a 1.94-km2 dumping site in the outer Weser Estuary (German Bight). Between June and December 1998, 2.6 million m3 of dredged sediment were deposited there. The bathymetric maps generated in the course of this study reveal features such as subaqueous dunes, scour holes, and mounds of dumped dredge spoil. The mean water depth decreased by about 1 m during the dumping period. Furthermore, difference grids showing changes in sediment volume allowed a calculation of the sediment budget for the monitored area. After a time period of only 5 months, 0.5 million m3 of the originally dumped 2.6 million m3 of dredge spoil had already been removed from the dumping site.

An unconformity-bound glacial sequence (135 cm thick) of a coral-bearing sediment core collected from the flank of a cold-water coral mound in the Banda Mound Province off Mauritania was analysed. In order to study the relation between coral framework growth and its filling by hemipelagic sediments, U-series dates obtained from the cold-water coral species Lophelia pertusa were compared to C-14 dates of planktonic foraminifera of the surrounding matrix sediments. The coral ages, ranging from 45.1 to 32.3 ka BP, exhibit no clear depositional trend, while on the other hand the C-14 dates of the matrix sediment provide ages within a much narrower time window of

International audience; The neodymium (Nd) isotopic composition (expressed in epsilon units, ɛNd) of reef framework-forming cold-water corals provides unique measures of water mass provenance and mixing within the Northeast Atlantic today and in the past. A reconstruction of near thermocline water ɛNd from cold-water corals of the Gulf of Cádiz and Porcupine Seabight spanning over the past 300,000 years, now revealed that climate cooling during Marine Isotope Stages (MIS) 7.2 and MIS 8/9 led to a retraction of the mid-depth Subpolar Gyre (mSPG) to the west. Conversely, Northern Hemisphere warming and increasing fresh water fluxes to the northwest (Labrador Sea) favor a stronger eastward extension of the mSPG blocking the northward flow of temperate Atlantic water as observed during the early MIS 1 and the early stage MIS 5.5. These changes are likely the result of large-scale south-north displacement of the westerlies similar to present-day observations that the North Atlantic Oscillation (NAO) is linked with mid-depth ocean circulation. Based on these observations, we hypothesize that further climate warming will also strengthen the mSPG leading to a salt and temperature decrease in the Northeast Atlantic whereas salinity and temperature will increase in the temperate Atlantic. However, the amplitude of such changes on North Atlantic overturning remains to be tested.

International audience; A set of 40 Uranium-series datings obtained on the reef-forming scleractinian cold-water corals Lophelia pertusa and Madrepora oculata revealed that during the past 400 kyr their occurrence in the Gulf of Cádiz (GoC) was almost exclusively restricted to glacial periods. This result strengthens the outcomes of former studies that coral growth in the temperate NE Atlantic encompassing the French, Iberian and Moroccan margins dominated during glacial periods, whereas in the higher latitudes (Irish and Norwegian margins) extended coral growth prevailed during interglacial periods. Thus it appears that the biogeographical limits for sustained cold-water coral growth along the NE Atlantic margin are strongly related to climate change. By focussing on the last glacial–interglacial cycle, this study shows that palaeo-productivity was increased during the last glacial. This was likely driven by the fertilisation effect of an increased input of aeolian dust and locally intensified upwelling. After the Younger Dryas cold event, the input of aeolian dust and productivity significantly decreased concurrent with an increase in water temperatures in the GoC. This primarily resulted in reduced food availability and caused a widespread demise of the formerly thriving coral ecosystems. Moreover, these climate induced changes most likely caused a latitudinal shift of areas with optimum coral growth conditions towards the northern NE Atlantic where more suitable environmental conditions established with the onset of the Holocene.

This paper presents the first compilation of information on the spatial distribution of scleractinian cold-water corals in the Gulf of Cádiz based on literature research and own observations (video footage, sediment samples). Scleractinian cold-water corals are widely distributed along the Spanish and Moroccan margins in the Gulf of Cádiz, where they are mainly associated with mud volcanoes, diapiric ridges, steep fault escarpments, and coral mounds. Dendrophyllia cornigera, Dendrophyllia alternata, Eguchipsammia cornucopia, Madrepora oculata and Lophelia pertusa are the most abundant reef-forming species. Today, they are almost solely present as isolated patches of fossil coral and coral rubble. The absence of living scleractinian corals is likely related to a reduced food supply caused by low productivity and diminished tidal effects. In contrast, during the past 48 kyr scleractinian corals were abundant in the Gulf of Cádiz, although their occurrence demonstrates no relationship with main climatic or oceanographic changes. Nevertheless, there exists a conspicuous relationship when the main species are considered separately. Dendrophylliids are associated with periods of relatively stable and warm conditions. The occurrence of L. pertusa mainly clusters within the last glacial when bottom current strength in the Gulf of Cádiz was enhanced and long-term stable conditions existed in terms of temperature. Madrepora oculata shows a higher tolerance to abrupt environmental changes. © 2009 Elsevier Ltd. All rights reserved.

During the past decade, knowledge about the ecology and the environment of giant carbonate mounds has been growing continuously. However, still little is known about their growth dynamics. Three gravity cores from Galway Mound, Belgica Mound Province in the Porcupine Seabight off Ireland, were investigated for their sedimentological, geophysical and geochemical properties to get insight into the long-term development of this cold-water coral covered carbonate mound. These data were supplemented by radiometric age determinations on planktonic foraminifera and coral skeletons. The records from three different settings on Galway Mound reveal a coherent growth history that in general is similar to what is known from other carbonate mounds at the Irish margin. However, whereas other cores are often disturbed by numerous and not correlateable hiatuses, Galway Mound, in contrast, appears to be characterised by only one major hiatus representing a time gap of ~ 250 kyr. Several mechanisms are discussed in this study as possible causes for the observed stratigraphic record at Galway Mound. The most likely explanation is that the hiatus has its origin in a major mass wasting event on an instable, possibly glacial, unit that could have acted as a slip plane. The overall Late Quaternary growth history of Galway Mound fits well into existing cyclical mound development models, pointing to Galway Mound being an ‘actively growing’ mound (“coral bank stage”) at present.

The characterisation of trophic nets in the deep-sea is challenging due to the remoteness and the logistic constraints to reach and sample these habitats. Stable carbon and nitrogen isotope (δ13C and δ15N) analysis has proven to be a useful tool in identifying trophic relationships. The benthic trophic network of the fauna in the recently discovered Angolan cold-water coral (CWC) mounds is being investigated through carbon and nitrogen isotopic characterization. Samples were collected in 2016 during the M122 ("ANNA") expedition on board the R/V METEOR. Organisms belonging to different functional groups of Porifera, Cnidaria, Mollusca, Annelida, Bryozoa, Arthropoda, Echinodermata, and Chordata, as well as potential food sources (suspended particulate organic matter and organic matter of sediments) were analysed. The main aims of the study are: (1) to describe the megabenthic trophic guilds of the Angolan CWC mounds, (2) to estimate the total number of trophic levels, and (3) to compare this unexplored area with previous results from other CWC dominated communities. Our first results show that particulate organic matter presented a marine signature (δ13C from -20 to -25‰ V.P.D.B.). However, the analysed CWC species seem to prefer a diet which combined a mix of detrital and resuspended organic matter (δ13C from -15 to -20‰ V.P.D.B.), similar to what has been observed for Antarctic gorgonians and other CWC habitats. Porifera presented the highest δ15N ratios (20.19±1.81‰). We hypothesise this could be due to the assimilation of bacterioplankton as a food source which has been already documented for Porifera.