Ecological and environmental controls on the fine-scale distribution of cold-water corals in the North-East Atlantic

This thesis integrated acoustic, high-definition video and hydrodynamic data to study the distribution, morphology and ecology of cold-water corals (CWC) in the Mingulay Reef area (Chapter 2), the Tisler Reef area (Chapter 3) and the Logachev Mound area (Chapter 4). A new British Geological Survey (BGS) ArcGIS seabed mapping toolbox was developed and quantified semi-automatically the morphometric and acoustic characteristics of CWC reefs. Over 500 Lophelia pertusa reef mounds were delineated and characterised at the Mingulay Reef Complex (Chapter 2), 14 at the Tisler Reef (Norway) (Chapter 3) and 123 in the Logachev Area (Chapter 4). These reefs all had large amounts of small round-shaped mounds. Additionally, the Logachev area had very large dendriform-shaped mounds. A microbathymetric grid of the central area of the Mingulay Reef was used to identify individual live coral colonies (1-7 m) that provided data to predict the likelihood of presence of live coral colonies on biogenic reef mounds (Chapter 2). The distribution and morphology of L. pertusa colonies and the sponges Mycale lingua and Geodia sp. within the Tisler Reef, revealed the importance of local hydrodynamics and substrate availability (Chapter 3). Non-scleractinian corals associated with the Logachev mounds (Chapter 4) proved to be abundant, biodiverse and function as a habitat for associated organisms. Differences in their distribution were found to be related to food supply, the availability and stability of settling substrates. This thesis showed that the BGS Seabed Mapping Toolbox is useful to study the ecology and morphology of reef mounds within and between reefs. Studies on the fine-scale spatial distribution of corals within reefs provided information on the ecology of CWC

Utilizing Extended Continental Shelf (ECS) and Ocean Exploration Mapping Data for Standardized Marine Ecological Classification of the U.S. Atlantic Margin

Accurate maps of ocean bathymetry and seafloor habitats are needed to support effective marine ecosystem-based management (EBM) approaches. The central premise of this thesis was to synthesize geomorphological elements of large regions of the deep ocean seafloor to establish standards of characterization for ecosystem-based classification. The approach was to apply semi-automated characterization techniques on seafloor bathymetric data that were originally collected for other purposes. The purpose of generating these maps is ultimately to apply to informing ecosystem-based management for large marine regions. While seafloor classification techniques for habitat classification have been applied in shallow water and generally over more local regions, these techniques have never before been applied at continental-margin scales in such deep water. Over the past decade, the United States has made a substantial investment in seafloor mapping efforts covering over 2.5 million square kilometers of the nation’s potential extended continental shelf (ECS) regions, which extend into deep ocean areas beyond 200 nautical miles from the nation’s shoreline. The entire potential ECS region off the U.S. Atlantic margin has been mapped by researchers at the University of New Hampshire’s Center for Coastal and Ocean Mapping/Joint Hydrographic Center (CCOM/JHC). Extensive complimentary mapping datasets collected by the National Oceanic and Atmospheric Administration’s Office of Ocean Exploration and Research (NOAA OER) have been acquired in adjacent U.S. waters off the East Coast covering the continental slope submarine canyons region and a majority of the Blake Plateau. The focus of this thesis is on demonstrating that data gathered with the initial purpose of establishing a potential extended continental shelf claim can further be used to support EBM efforts and sound marine spatial planning. The approaches developed here could be effectively applied to ECS and ocean exploration data sets collected world-wide to leverage substantial additional value from broad-scale ocean mapping efforts. This thesis posited and tested three hypotheses: 1) Broad-scale bathymetric data of the U.S. Atlantic margin collected for ECS and deep sea exploration purposes are useful to consistently classify ecological marine units of the seafloor and generate value-added characterization maps of large regions. 2) Transparent, repeatable, and efficient semi-automated geomorphic analysis methods employing the Coastal and Marine Ecological Classification Standard (CMECS) as an organizational framework produce useful habitat characterization maps of the U.S. Atlantic margin. 3) Vulnerable cold-water coral (CWC) habitats are identifiable and able to be inventoried and characterized using geomorphic analysis and CMECS classification of bathymetric data. These three research hypotheses were tested through classification and characterization studies of three distinct regions of the U.S. Atlantic margin at different scales (an individual seamount feature, the continental slope and abyssal plains, and a continental margin borderland) ranging across a diversity of marine habitats. An automatic segmentation approach to initially identify landform features from the bathymetry of these study areas was completed and then translated into CMECS classification terminology. Geomorphic terrain classification methods were applied to the continental slope and the abyssal plain of the U.S. Atlantic margin ECS region covering a 959,875 km2 area. Landform features derived from the bathymetry were then translated into complete coverage geomorphology maps of the region utilizing CMECS to define geoforms. Abyssal flats made up more than half of the area (53%), with the continental slope flat class making up another 30% of the total area. Flats of any geoform class (including continental shelf flats and guyot flats) made up 83.06% of the study area. Slopes of any geoform classes make up a cumulative total of 13.26% of the study region (8.27% abyssal slopes, 3.73% continental slopes, 1.25% seamount slopes), while ridge features comprise only 1.82% of the total study area (1.03% abyssal ridges, 0.63 continental slope ridge, and 0.16% seamount ridges). Using methods developed to classify the ECS dataset, bathymetric data from twenty multibeam sonar mapping surveys of the Blake Plateau region were used to derive a standardized geomorphic classification capable of quantifying cold-water coral (CWC) mound habitats. Results documented the most extensive CWC mound province thus far discovered and reported in the literature. Nearly continuous CWC mound features span an area up to 472 km long and 88 km wide, with a core area of high density mounds up to 248 km long by 35 km wide. A total of 59,760 individual peak features were delineated, providing the first estimate of the overall number of potential CWC mounds mapped in the Blake Plateau region to date. Five geomorphic landform classes were mapped and quantified: peaks (342 km2), valleys (2,883 km2), ridges (2,952 km2), slopes (15,227 km2), and flats (49,003 km2). The complex geomorphology of eight subregions was described qualitatively with geomorphic “fingerprints” and quantitatively by measurements of mound density and vertical relief. Ground-truth from 23 submersible dive videos revealed coral rubble to be the dominant substrate component within the peak, ridge, and slope landforms explored, thereby validating the interpretation of these bathymetric features as CWC mounds. Results indicated that the Blake Plateau supports a globally exceptional CWC mound province of heretofore unprecedented scale (at least for now) and diverse morphological complexity. This dissertation has successfully characterized the geomorphology of vast regions of the deep ocean floor off the U.S. Atlantic margin for ecosystem-based management purposes. It has applied techniques and established standards of classification that can be applied to other regions throughout the World. This latter point is critical as there are ongoing international efforts today to map the entirety of the World\u27s oceans at meaningful scales and these techniques can synthesize this information in meaningful ways. Furthermore, the need for such syntheses is paramount in order to successful manage (conserve and preserve) the living and non-living resources of the ocean. This thesis shows a way forward for such endeavors, and emphasizes 1) the applicability of data acquired for other purposes to be applied to this purpose, and 2) the need for standards to define and describe marine habitats so that all governments, managers, biologists, geoscientists, and other ocean stakeholders communicate using the same language

Water mass dynamics around cold-water coral reefs in the North Atlantic

Cold-water coral reefs are distributed all over the world’s oceans and form a high variety of ecosystems depending on their specific environmental factors. The surrounding parameter of cold-water coral reef growth is characterised by hydrophysical signals such as temperature and salinity, both yielded in potential density as a function of temperature, salinity and pressure. Within the past years a serious increase in knowledge on these cold-water coral occurrences and their hydrographic boundary conditions yielded worldwide, especially in the north-east Atlantic. This study investigates in the assessment of the environmental conditions of cold-water coral (CWC) growth in response to geochemical, hydrographic and oceanographic boundary processes. This study aims to unravel the environmental signals that influence CWC growth in different latitudes, which are of great importance for growth and occurrences. For this purpose, cold-water coral reefs in the north Atlantic margin, in the Gulf of Mexico, off Bahamas, in the Bay of Biscay, and off Morocco as well as Mauretania were selected. The comparison of data sets collected with identical tools yielded detailed information on the environmental conditions needed for healthy cold-water-reef growth

Geomorphometric characterization of pockmarks by using a GIS-based semi-automated toolbox

Pockmarks are seabed depressions developed by fluid flow processes that can be found in vast numbers in many marine and lacustrine environments. Manual mapping of these features based on geophysical data is, however, extremely time-consuming and subjective. Here, we present results from a semi-automated mapping toolbox developed to allow more efficient and objective mapping of pockmarks. This ArcGIS-based toolbox recognizes, spatially delineates, and morphometrically describes pockmarks. Since it was first developed, the toolbox has helped to map and characterize several thousands of pockmarks on the UK continental shelf, especially within the central North Sea. This paper presents the latest developments in the functionality of the toolbox and its adaptability for application to other geographic areas (Barents Sea, Norway, and Malin Deep, Ireland) with varied pockmark and seabed morphologies, and in different geological settings. The morphometric characterization of vast numbers of pockmarks allows an unprecedented statistical analysis of their morphology. The outputs from the toolbox provide an objective, quantitative baseline for combining this information with the geological and oceanographical knowledge of individual areas, which can provide further insights into the processes responsible for their development and their influence on local seabed conditions and habitat

CoMMa: a GIS geomorphometry toolbox to map and measure confined landforms

The Confined Morphologies Mapping (CoMMa) Toolbox, a novel ArcGIS Pro python toolbox expressly created for semi-automated seabed morphological mapping, is presented here. The toolbox includes a selection of tools for the pre-processing, delineation and description of confined features on a digital elevation model (DEM) that are either negative or positive. The CoMMa Toolbox addresses the need for a flexible and multi-faceted solution applicable to different mapping problems, also encapsulating and re-interpreting existing methodologies. This study also evaluates, qualitatively and quantitatively, the performance of CoMMa delineations performed on a synthetic bathymetry DEM with 150 coral mounds of known characteristics against manual digitisations completed by five expert geomorphologists. The results show that the best CoMMa delineation falls within the range of competence demonstrated by the expert manual mappers. Edge evaluation metrics and attribute error scores are comparable or often superior to four of the five human delineations, although the Toolbox never reaches the performance of the best expert. Nevertheless, the semi-automated techniques can be of assistance to any user, providing rapid, visually unbiased and consistent delineations, thus saving time: they can then be optimised manually where desirable. Moreover, while the toolbox was created for marine geomorphometry, it can be applied to any DEM, either marine, terrestrial or extra-terrestrial. The CoMMa Toolbox is available in a public GitHub repository with a thorough user guide

Understanding key geological processes and controls on cold-water coral habitat development in submarine canyons

Cold-water corals are sessile, filter-feeding organisms that baffle water flow inducing sedimentation around their framework. Through geological time, should environmental conditions permit, they can produce positive topographic features on the seafloor called mounds through successive and persistent reef development. These reef ecosystems are considered biodiversity “hotspots” between 200 and 1000 m in the Atlantic Ocean. They are regarded as vulnerable marine ecosystems, providing essential ecosystem services. Over the past two decades, a considerable body of information has been accumulated on understanding the temporal development of CWC reef and mound formation. However, this research is limited in resolution, the range of study sites and datasets analysed. Here, an assessment of the temporal variation of CWC reefs and mounds situated in the west Porcupine Bank (wPB) and Porcupine Bank Canyon (PBC) is presented as well as background palaeoenvironmental information from an off-mound core. Previous studies of the spatial distribution of reefs and mounds reveal that they are dispersed across a variety of geomorphological settings in the region, including the canyon head, along the canyon lip and on the bank. This research broadly aims to understand the temporal distribution of the coral habitats within these contrasting settings. In 2015 and 2016, the QuERCi I and QuERCi II research cruises attempted coring the substrates of the canyon using traditional methods (i.e. gravity and box-corers). However, the acquired cores were insufficient in size and lacked an understanding of what habitat they were taken from. As such, 2 more research cruises (CoCoHaCa I and CoCoHaCa II) were carried out in 2017 and 2018 using sophisticated novel coring systems (ROV-vibrocoring). These methods proved successful, and cores were acquired through various CWC habitats in the canyon (mound summits, flanks, bank, slope and foot of the slope) and presented herein. This data includes novel 3-dimensional computed tomography (CT) derived imagery alongside traditional sedimentological approaches. The CT imagery was used to classify reef and mound formation/cessation. The cores were then split, sampled and investigated using a series of analytical techniques. The phases of formation/cessation were first constrained using radiocarbon dating and the cores were subsequently examined using grain size analysis to interpret the hydrodynamic regime. Stable isotope analysis on planktic and benthic foraminifera was then used to investigate paleoenvironmental conditions, which were contextualized by benthic foraminifera assemblages. An off-mound core was examined to elucidate the impact of the (de)glaciation of the British-Irish Ice Sheet (BIIS) on the wPB. Analysis of the core revealed that several fluxes of ice-rafted debris were deposited to the site. It was found that bottom currents became sluggish during stadial phases. Evidence for iceberg scouring in the core was also identified. Two coral bearing cores acquired from mound summits of variable distance to the canyon were then analysed. It was found that mound growth was twice as fast on the canyon lip than mounds 1 km away on the wPB. Multiproxy data revealed that a high food signal occurs closer to the canyon. This suggests that submarine canyons play a key role in enhancing particle supply and therefore influences coral growth and mound developmenton the margin. The radiocarbon dates acquired from coral bearing cores on the wPB suggest that corals occupied the bank since at least 45.1 ka BP. This finding subsequently resulted in revising our understanding of CWC re-expansion into the NE Atlantic during favourable climatic conditions, highlighting the crucial role played by submarine canyons. Findings outlined in this thesis provides the scientific community with new insights into the tolerances of cold-water corals during ecological tipping points. Furthermore, it highlights the need to investigate other submarine canyons occupied by CWCs in the NE Atlantic using ROV-vibrocoring

Coral-based reconstructions of reef- to regional-scale ocean surface conditions in the Atlantic Warm Pool since the late 19th century

Climate variability in the tropical Atlantic region produces numerous impacts on society and the environment of the surrounding continents. Understanding past tropical climate variability beyond the period of instrumental observations or within regions lacking instrumental data requires the use of climate proxies. The geochemistry of coral skeletons provides such proxies, recording environmental fluctuations in ambient seawater during growth. This thesis investigates seasonal-scale proxy records of surface ocean conditions in order to study past changes in tropical Atlantic climate variability and reef scale environmental variability extending beyond the period of instrumental data. Monthly resolved coral records from the central Caribbean (Cayman Islands) are generated using the massive growing hermatypic species Diploria strigosa. The potential of coral proxy time series to capture local environmental signals is assessed. These time series are used to examine how local environmental parameters may affect and be imprinted in the coral record and which may be specific for different reef environments. The isotopic and trace elemental composition of two coral cores drilled in adjacent but distinct reef environments (fore reef and lagoon) are examined. The measured geochemical proxies are compared to in situ and gridded SST data and used to reconstruct seasonal- to decadal-scale SST variations. Furthermore, the potential of Little Cayman Island as a qualified reference site for the investigation of past large-scale climate signals and of the influence of external climate modes on the Caribbean and regions beyond is assessed. For this purpose the geochemical record from the fore reef environment is analyzed for decadal to multidecadal signals of climate variability and examined in combination with coral proxy records from other Caribbean sites

Korallenbasierte Rekonstruktionen riff- bis regionalmaßstäblicher Meeresoberflächenbedingungen im Atlantic Warm Pool seit dem späten 19. Jahrhundert

Climate variability in the tropical Atlantic region produces numerous impacts on society and the environment of the surrounding continents. Understanding past tropical climate variability beyond the period of instrumental observations or within regions lacking instrumental data requires the use of climate proxies. The geochemistry of coral skeletons provides such proxies, recording environmental fluctuations in ambient seawater during growth. This thesis investigates seasonal-scale proxy records of surface ocean conditions in order to study past changes in tropical Atlantic climate variability and reef scale environmental variability extending beyond the period of instrumental data. Monthly resolved coral records from the central Caribbean (Cayman Islands) are generated using the massive growing hermatypic species Diploria strigosa. The potential of coral proxy time series to capture local environmental signals is assessed. These time series are used to examine how local environmental parameters may affect and be imprinted in the coral record and which may be specific for different reef environments. The isotopic and trace elemental composition of two coral cores drilled in adjacent but distinct reef environments (fore reef and lagoon) are examined. The measured geochemical proxies are compared to in situ and gridded SST data and used to reconstruct seasonal- to decadal-scale SST variations. Furthermore, the potential of Little Cayman Island as a qualified reference site for the investigation of past large-scale climate signals and of the influence of external climate modes on the Caribbean and regions beyond is assessed. For this purpose the geochemical record from the fore reef environment is analyzed for decadal to multidecadal signals of climate variability and examined in combination with coral proxy records from other Caribbean sites.Klimaschwankungen im tropischen Nordatlantik haben großen Einfluss auf die Umweltbedingungen und die menschliche Gesellschaft auf den umliegenden Kontinenten. Um vergangene Klima- und Umweltbedingungen in den Tropen über die Zeit instrumenteller Beobachtungen hinaus verstehen zu können, werden geochemische Klimaproxies benötigt. Die Geochemie von Korallenskeletten liefert solche Proxies, die während des Wachstums Umweltschwankungen im umgebenden Meerwasser aufzeichnen. In dieser Arbeit werden saisonal aufgelöste Proxy-Zeitreihen der Meeresoberflächenbedinungen erstellt, um vergangene Klimaschwankungen im tropischen Nordatlantik sowie Riff-maßstäbliche Umweltschwankungen zu untersuchen, die über den Zeitraum instrumenteller Daten hinausgehen. Basierend auf der Steinkorallenart Diploria strigosa werden monatlich aufgelöste Korallen-Zeitreihen aus der zentralen Karibik (Cayman Islands) erzeugt. Das Potenzial der geochemischen Proxy-Zeitreihen zur Erfassung lokaler Umweltsignale wird bewertet. Anhand dieser Zeitreihen wird untersucht, wie lokale Umweltparameter das Korallenarchiv beeinflussen und von diesem aufgezeichnet werden und welche für verschiedene Riffumgebungen spezifisch sein können. Die Isotopen- und Spurenelementzusammensetzung von zwei Korallenkernen, die in benachbarten, aber unterschiedlichen Riffumgebungen (Vorriff und Lagune) geborgen wurden, werden untersucht. Die Proxydaten werden mit In-situ- und Reanalyse-SST-Daten verglichen und zur Rekonstruktion von saisonalen bis dekadischen SST-Variationen verwendet. Zudem wird das Potenzial von Little Cayman Island als qualifizierter Referenzstandort für die Untersuchung von großräumigen Klimasignalen und des Einflusses externer Klimamodi auf die Karibik und darüber hinaus bewertet. Zu diesem Zweck werden die geochemischen Daten aus dem Vorriff auf dekadische bis multidekadische Klimasignale analysiert und in Kombination mit Korallen-Proxydatensätzen anderer karibischer Standorte untersucht

An integrated study of Quaternary sedimentary processes on the eastern slope of the Porcupine Seabight, SW of Ireland

A wide range of geophysical and sedimentological investigations on upper slope sediments of the eastern Porcupine Seabight, SW of Ireland, allowed to evaluate the local importance of bottom currents throughout the Upper Paleogene to recent times, as well as the influence of, and interplay with other deep-water sedimentary processes. The tools available for this study mainly allowed to focus on the nature and characteristics of the Quaternary deposits of seismic unit U1, but also documented buried Middle Eocene to Pliocene sediment drifts and sediment waves. A Late Pliocene erosional event (RD1) created a highly irregular discontinuity, observed from the northern part of the Belgica mound province towards the southern Gollum channel and Goban Spur. During this event, the basis of all major channels was created. They remained to be major current pathways, although their seismic characteristics suggest that the vigour of these currents seems to have decreased. The local Quaternary sedimentary environment has been dominated by a dynamic bottom current environment and by the paleotopography of the underlying unit U2. In the Belgica mound province, this unique geographic and hydrodynamic setting was responsible for the deposition of several sediment and contourite drifts. South of the Belgica mounds, the evolution and construction of the flanks of the broad Kings channels is seen to be influenced by downslope flowing currents. It is thought to be affected by periodic turbidite currents, possibly already weakened by northward flowing bottom currents. The main Gollum channel system shows similarities with a submarine fan channel system. The channel deposits are predominantly turbidites and mass-wasting deposits. This study also strengthens the idea that this system is located directly downstream of a (still undiscovered) feeding glacial fluvial system located on the Irish mainland shelf. A SE to NW transect of five long cores demonstrates the variability and distribution of British-Irish Ice Sheet (BIIS) sourced IRD in the Porcupine Seabight. Two cores located on the eastern slope almost exclusively contain BIIS-sourced material. Six ice-rafting events (IRE) were described and can be compared with the North Atlantic Heinrich Events. These regional events carry a very strong BIIS signature with mainly sands originating from Devonian and Carboniferous sandstones. The abundance of the IRD record shows a millennial-scaled disintegration of the BIIS from 25 ka onwards with distinct ice-rafting pulses about 17.4 and 15 ka BP. Moreover, all cores from the Belgica mound province show that the glacial deposits are muddy contourites in which several peak current episodes could be distinguished. More specifically, a core located on the small mounded contourite drift contains an amplified record of this bottom current variability. The presence of a massive sandy contourite between 1500 and 2625 cm suggests that during interglacial times the bottom current regime is similar as the present day situation. A similar conclusion was drawn from a core within one of the Gollum channel heads. During glacial times (especially during the last glacial maximum), turbidity currents were active due to a lowered sea-level. These fine-grained turbidites were deposited in a hemipelagic background sediment with IRD. During interglacial times, reversing bottom currents were active in this channel, creating muddy-silty contourites or even reworking the glacial turbidite deposits