Markus Diesing

Norwegian Geological Survey

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Terje Thorsnes

Norwegian Geological Survey

Klaus Schwarzer

Kiel University

David Stephens

University of Memphis

Peter Mitchell

University of the Witwatersrand

John Aldridge

Centre for Environment, Fisheries and Aquaculture Science

Adam Kubicki

Senckenberg am Meer

Lilja Rún Bjarnadóttir

Norwegian Geological Survey

Silke Kröger

Centre for Environment, Fisheries and Aquaculture Science

Roger Coggan

Centre for Environment, Fisheries and Aquaculture Science

Keith Weston

University of Iowa

Cooperative Institutions

Centre for Environment, Fisheries and Aquaculture Science

University of East Anglia

British Geological Survey

GEOMAR Helmholtz Centre for Ocean Research Kiel

Kiel University

South Atlantic Environmental Research Institute

Norwegian Geological Survey

National Oceanography Centre

University of Southampton

Deakin University

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The Croker Carbonate Slabs: extensive methane-derived authigenic carbonate in the Irish Sea—nature, origin, longevity and environmental significance

Geo-Marine Letters (2019)

Alan Judd Tamsyn Noble‐James Neil Golding Andrew Eggett Markus Diesing

Abstract The Croker Carbonate Slabs, in the UK sector of the Irish Sea, has shallow (70 to 100 m) water, strong (> 2 knot) tidal currents, coarse mobile surficial sediments and the most extensive methane-derived authigenic carbonate (MDAC) known in European waters. Multi-disciplinary studies (2004 to 2015) were commissioned specifically to document the benthic habitat, and have resulted in the designation of this site as a Marine Protected Area (MPA) under the European Commission’s Habitats Directive as an example of “ Submarine structures formed by leaking gases ”. However, this paper is focussed on the geoscience aspects of the site: the mineralogy and isotopic composition of the MDAC, its formation and age. It considers the implications of these findings with respect to the timing of the deglaciation of the area since the Last Glacial Maximum (LGM), and the environmental implications of the seepage of methane from the site over a period of at least 17,000 years. Carbon isotope ratios (δ 13 C − 34 to − 54‰) confirm that the carbonate minerals (high-Mg calcite and aragonite) result from the anaerobic oxidation of methane. Widespread shallow gas within post-glacial sediments is sourced from underlying coal-bearing Carboniferous strata. Geophysical (side-scan sonar and multi-beam echo sounder) and visual surveys show that the MDAC occurs as isolated lumps, continuous pavements, and cliffs < 6 m tall, which post-date the post-glacial sediments, but are in places covered by a veneer of coarse mobile surficial sediments. U-Th dates (17,000 ± 5500 to 4000 ± 200 BP) suggest continual MDAC formation since the last glacial maximum, and constrain the postglacial sea level rise in this part of the Irish Sea; the site must have been submarine before MDAC formation started, whether or not methane was escaping. Visual and acoustic evidence of gas seepage is limited, but methane concentrations in the water are high (< 21.4 nmol l −1 ) and suggest present-day export to the atmosphere. It is also implied that significant methane release to the atmosphere occurred immediately after the retreat of the ice that covered the site during the LGM until 21.9 to 20.7 ka BP.

Authigenic

Deglaciation

Dalradian

10.1007/s00367-019-00584-0

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Citations (20)

Application of Geobia to map the seafloor

Markus Diesing

Geographic Object-Based Image Analysis (GEOBIA) has been successfully employed to map terrestrial environments. However,71% of Earth's surface is covered by seawater and standard optical methods suitable for mapping the land surface have limitedapplication in such environments. Application of GEOBIA to marine environments has nevertheless been attempted and cangenerally be subdivided into three domains: 1. The intertidal zone and shallow subtidal zone have been mapped with optical data andapplication of GEOBIA in such environments can be seen as a seaward extension of terrestrial approaches. 2. Photographs of theseafloor give very detailed but spatially limited information. GEOBIA methods have been applied to classify benthic species andhabitats and estimate seafloor complexity among others. 3. Due to the rapid attenuation of light in water, the method of choice tomap the seafloor employs sound. Modern multi-beam echosounders map the seafloor in high detail. Such sensors measure thetopography (water depth) and the strength of the returning signal (backscatter), which can be used to characterise the seafloorsubstrates and habitats. This contribution will focus on the application of GEOBIA to marine acoustic datasets. A generic workflowfor object-based acoustic seafloor mapping will be showcased and the current state of the application of GEOBIA to marine acousticdata will be discussed.

Seafloor Spreading

10.3990/2.405

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Mapping of Cold-Water Coral Carbonate Mounds Based on Geomorphometric Features: An Object-Based Approach

Geosciences (2018)

Markus Diesing Terje Thorsnes

Cold-water coral reefs are rich, yet fragile ecosystems found in colder oceanic waters. Knowledge of their spatial distribution on continental shelves, slopes, seamounts and ridge systems is vital for marine spatial planning and conservation. Cold-water corals frequently form conspicuous carbonate mounds of varying sizes, which are identifiable from multibeam echosounder bathymetry and derived geomorphometric attributes. However, the often-large number of mounds makes manual interpretation and mapping a tedious process. We present a methodology that combines image segmentation and random forest spatial prediction with the aim to derive maps of carbonate mounds and an associated measure of confidence. We demonstrate our method based on multibeam echosounder data from Iverryggen on the mid-Norwegian shelf. We identified the image-object mean planar curvature as the most important predictor. The presence and absence of carbonate mounds is mapped with high accuracy. Spatially-explicit confidence in the predictions is derived from the predicted probability and whether the predictions are within or outside the modelled range of values and is generally high. We plan to apply the showcased method to other areas of the Norwegian continental shelf and slope where multibeam echosounder data have been collected with the aim to provide crucial information for marine spatial planning.

Echo sounding

Seamount

Marine Spatial Planning

10.3390/geosciences8020034

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Citations (38)

A Spatially Explicit Comparison of Quantitative and Categorical Modelling Approaches for Mapping Seabed Sediments Using Random Forest

Geosciences (2019)

Benjamin Misiuk Markus Diesing Alec E. Aitken Craig J. Brown Evan Edinger

Seabed sediment composition is an important component of benthic habitat and there are many approaches for producing maps that convey sediment information to marine managers. Random Forest is a popular statistical method for thematic seabed sediment mapping using both categorical and quantitative supervised modelling approaches. This study compares the performance and qualities of these Random Forest approaches to predict the distribution of fine-grained sediments from grab samples as one component of a multi-model map of sediment classes in Frobisher Bay, Nunavut, Canada. The second component predicts the presence of coarse substrates from underwater video. Spatial and non-spatial cross-validations were conducted to evaluate the performance of categorical and quantitative Random Forest models and maps were compared to determine differences in predictions. While both approaches seemed highly accurate, the non-spatial cross-validation suggested greater accuracy using the categorical approach. Using a spatial cross-validation, there was little difference between approaches—both showed poor extrapolative performance. Spatial cross-validation methods also suggested evidence of overfitting in the coarse sediment model caused by the spatial dependence of transect samples. The quantitative modelling approach was able to predict rare and unsampled sediment classes but the flexibility of probabilistic predictions from the categorical approach allowed for tuning to maximize extrapolative performance. Results demonstrate that the apparent accuracies of these models failed to convey important differences between map predictions and that spatially explicit evaluation strategies may be necessary for evaluating extrapolative performance. Differentiating extrapolative from interpolative prediction can aid in selecting appropriate modelling methods.

Categorical variable

Seabed

10.3390/geosciences9060254

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Citations (56)

Spatially predicted concentrations of particulate organic carbon in surface (0-10cm) sediments of parts of the north-west European continental shelf (1996-2015)

Markus Diesing Silke Kröger Ruth Parker Chris Jenkins Claire Mason

Particulate organic carbon

Carbon fibers

10.1594/pangaea.871584

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Sensitivity of macrobenthic secondary production to trawling in the English sector of the Greater North Sea: A biological trait approach

Journal of Sea Research (2013)

Stefan G. Bolam R.C. Coggan J.D. Eggleton Markus Diesing David Stephens

Demersal zone

Bottom trawling

10.1016/j.seares.2013.05.003

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Citations (85)

Mapping the Oceans: Progress in Semi-Automated Seabed Classification Required

AGUOS (2016)

Markus Diesing

Seabed

Source

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Citations (0)

Rock Ridges in the Central English Channel

Elsevier eBooks (2011)

Roger Coggan Markus Diesing

10.1016/b978-0-12-385140-6.00033-5

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Citations (10)

Legacy Data: How Decades of Seabed Sampling Can Produce Robust Predictions and Versatile Products

Geosciences (2019)

Peter Mitchell John Aldridge Markus Diesing

Sediment maps developed from categorical data are widely applied to support marine spatial planning across various fields. However, deriving maps independently of sediment classification potentially improves our understanding of environmental gradients and reduces issues of harmonising data across jurisdictional boundaries. As the groundtruth samples are often measured for the fractions of mud, sand and gravel, this data can be utilised more effectively to produce quantitative maps of sediment composition. Using harmonised data products from a range of sources including the European Marine Observation and Data Network (EMODnet), spatial predictions of these three sediment fractions were generated for the north-west European continental shelf using the random forest algorithm. Once modelled these sediment fraction maps were classified using a range of schemes to show the versatility of such an approach, and spatial accuracy maps were generated to support their interpretation. The maps produced in this study are to date the highest resolution quantitative sediment composition maps that have been produced for a study area of this extent and are likely to be of interest for a wide range of applications such as ecological and biophysical studies.

Seabed

Marine Spatial Planning

Categorical variable

10.3390/geosciences9040182

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Citations (45)

Organic carbon in surface sediments of the North Sea and Skagerrak

Markus Diesing Terje Thorsnes Lilja Rún Bjarnadóttir

Abstract. Continental shelf sediments are places of both rapid organic carbon turnover and accumulation, while at the same time increasingly subjected to human-induced disturbances. Recent research suggests that shelf sediments might have a role to play as a natural climate solution, e.g. by protecting the seafloor against human-induced disturbance. However, we have an incomplete understanding about the centres of organic carbon accumulation and storage on continental shelves. To better constrain the rate of accumulation and the mass of organic carbon that is stored in sediments, we developed and applied a spatial modelling framework that allows to estimate those quantities from sparse observations and predictor variables known or suspected to influence the spatial patterns of these parameters. This paper presents spatial distribution patterns of organic carbon densities and accumulation rates in the North Sea and Skagerrak. We found that organic carbon stocks and accumulation rates are highest in the Norwegian Trough, while large parts of the North Sea are characterised by low stocks and zero net-accumulation. The total stock of organic carbon that is stored in the upper 0.1 m of sediments amounted to 230.5 ± 134.5 Tg, of which approximately 26 % are stored in the Norwegian Trough. Rates of organic carbon accumulation in the Norwegian Trough are on par with those reported from nearby fjords. We provide baseline datasets that could be used in marine management, e.g. for the establishment of carbon protection zones. Additionally, we highlight the complex nature of continental shelves with zones of rapid carbon cycling and accumulation juxtaposed, which will require further detailed and spatially explicit analyses to constrain sedimentary organic carbon stocks and accumulation rates globally.

Fjord

Trough (economics)

Seafloor Spreading

Carbon fibers

10.5194/bg-2020-352

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Citations (3)