scholarly journals Seafloor Characterization Using Multibeam Echosounder Backscatter Data: Methodology and Results in the North Sea

Geosciences ◽  
2019 ◽  
Vol 9 (7) ◽  
pp. 292 ◽  
Author(s):  
Amiri-Simkooei ◽  
Koop ◽  
van der Reijden ◽  
Snellen ◽  
Simons
Keyword(s):  
North Sea ◽  
Sedimentary Environment ◽  
Spline Approximation ◽  
Roughness Parameter ◽  
Scattering Parameter ◽  
Grab Sampling ◽  
Volume Scattering ◽  
Entire Area ◽  
Multibeam Echosounder ◽  
Seafloor Characterization

Seafloor characterization using multibeam echosounder (MBES) backscatter data is an active field of research. The observed backscatter curve (OBC) is used in an inversion algorithm with available physics-based models to determine the seafloor geoacoustic parameters. A complication is that the OBC cannot directly be coupled to the modeled backscatter curve (MBC) due to the correction of uncalibrated sonars. Grab samples at reference areas are usually required to estimate the angular calibration curve (ACC) prior to the inversion. We first attempt to estimate the MBES ACC without grab sampling by using the least squares cubic spline approximation method implemented in a differential evolution optimization algorithm. The geoacoustic parameters are then inverted over the entire area using the OBCs corrected for the estimated ACC. The results indicate that a search for at least three geoacoustic parameters is required, which includes the sediment mean grain size, roughness parameter, and volume scattering parameter. The inverted mean grain sizes are in agreement with grab samples, indicating reliability and stability of the proposed method. Furthermore, the interaction between the geoacoustic parameters and Bayesian acoustic classes is investigated. It is observed that higher backscatter values, and thereby higher acoustic classes, should not only be attributed to (slightly) coarser sediment, especially in a homogeneous sedimentary environment such as the Brown Bank, North Sea. Higher acoustic classes should also be attributed to larger seafloor roughness and volume scattering parameters, which are not likely intrinsic to only sediment characteristics but also to other contributing factors.

scholarly journals Impact of marine sand extraction on benthic communities west off Sylt (SE North Sea)

2020 ◽  
Author(s):  
Finn Mielck ◽  
Rune Michaelis ◽  
Werner Armonies ◽  
H. Christian Hass
Keyword(s):  
North Sea ◽  
Benthic Communities ◽  
Habitat Characteristics ◽  
Western Coast ◽  
Long Term Effects ◽  
Successional Stage ◽  
Grab Sampling ◽  
Effective Measure ◽  
Marine Sand ◽  
Sand Extraction

<p>Ongoing erosion at coasts, beaches and dunes accompanied by a climate change-induced sea-level rise requires extensive protection measures. At the Island of Sylt (SE North Sea) beach nourishments were conducted for almost 50 years to protect the exposed western coast against erosion. Since 1984, the materials for the sand replenishments were dredged from an offshore excavation site approx. 7 km west off Sylt in the German Bight. In this study, we investigate the long-term effects of sand extraction on the local geomorphology, the associated benthic habitats and fauna. Hydroacoustic surveys and grab sampling revealed that after more than 35 years changes in bathymetry (with dredging pits of down to ~15 m below sea floor) and also changes in habitat characteristics are still present. Additionally, the sediment and benthic faunal compositions have changed. A comparison between dredged areas and undisturbed seafloor revealed significant differences in mud content (increasing), the number of individuals and species of macrozoobenthic organisms (decreasing). This indicates that the benthic communities in the dredging areas are in a persistent successional stage. Mud-loving species (e. g. <em>Notomastus latericeus</em> and<em> Kurtiella bidentate</em>) profit from the changed habitats, however sand-preferring organisms (e.g. <em>Pisione remota</em> and <em>Aonides paucibranchiata</em>) largely disappeared. Because of the slow backfill rates, we conclude that a complete backfill of the deep dredging pits is likely to take centuries. The same is expected to apply for the regeneration of the benthic communities. However, since rather coarse-to-medium sand was removed from this area and re-accumulation of this Pleistocene material is not possible because of weak transport rates, a re-establishment of benthic communities that prefer coarser sand seems to be unlikely. Since benthic communities are strongly linked to the habitat characteristics, habitat mapping using hydroacoustic techniques is an efficient and cost-effective measure to monitor the state of regeneration in this study site.</p>

scholarly journals A synthetic map of the northwest European Shelf sedimentary environment for applications in marine science

2017 ◽  
Author(s):  
Robert J. Wilson ◽  
Douglas C. Speirs ◽  
Alessandro Sabatino ◽  
Michael R. Heath
Keyword(s):  
Grain Size ◽  
North Sea ◽  
Sedimentary Environment ◽  
International Investment ◽  
Marine Policy ◽  
Continuous Variables ◽  
Seabed Sediment ◽  
The North ◽  
Wide Range ◽  
The North Sea

Abstract. Seabed sediment mapping is important for a wide range of marine policy, planning and scientific issues, and there has been considerable national and international investment around the world in the collation and synthesis of sediment data sets. However, in Europe at least, much of this effort has been directed towards seabed classification and mapping of discrete habitats. Scientific users often have to resort to reverse-engineering these classifications to recover continuous variables such as mud content and median grain size that are required for many ecological and biophysical studies. Here we present a new set of 0.125 by 0.125° resolution synthetic maps of continuous properties of the northwest European sedimentary environment, extending from the Bay of Biscay to the northern limits of the North Sea and the Faroe Islands. The maps are a blend of gridded survey data, and statistically modelled values based on distributions of bed shear stress due to tidal currents and waves, and bathymetric properties. Recent work has shown that statistical models can predict sediment composition in British waters and the North Sea with high accuracy, and here we extend this to the entire shelf and to the mapping of other key seabed parameters. The maps include percentage compositions of mud, sand and gravel; porosity and permeability; median grain size of the whole-sediment and of the sand and the gravel fractions; carbon and nitrogen content of sediments; percentage of seabed area covered by rock; mean and maximum depth-averaged tidal velocity and wave-orbital velocity at the seabed; and mean monthly natural disturbance rates. A number of applications for these maps exist, including species distribution modelling and the more accurate representation of seafloor biogeochemistry in ecosystem models. The data products are available from doi:10.15129/07bc686e-a354-40de-8c08-372ced7aad64.

scholarly journals Protecting the North Sea: Cleaver Bank.

2020 ◽  
Author(s):  
Oceana ◽  
Helena Álvarez ◽  
Allison L. Perry ◽  
Jorge Blanco ◽  
Cecilie Petersen ◽  
...  
Keyword(s):  
North Sea ◽  
Ecological Integrity ◽  
Current Management ◽  
Entire Area ◽  
Marine Life ◽  
The North ◽  
Management Measures ◽  
The North Sea ◽  
The Uk ◽  
Benthic Ecosystems

Cleaver Bank represents the largest area of hard substrate in the Dutch North Sea, and its biodiversity importance has been repeatedly recognised. The combination of oceanographic and geological patterns found in the area (e.g., depth, low currents and light penetration) makes Cleaver Bank a unique enclave of marine life in the Dutch EEZ. Thus, it has already been designated under various figures of protection (see Box 4). However, current management measures for these areas fail to secure the preservation of the area’s fragile combination of features. Bearing in mind that the disappearance of the former rocky banks in Dutch waters was caused by their direct removal in bottom trawls, and the threat that fishing activities pose to the fragile and varied seabed of Cleaver Bank, Oceana proposes that the entire area of Klaverbank SAC should be closed to all type of bottom-contacting gears. Continued bottom-contact fishing in Klaverbankrepresents a clear threat to the fragile benthic ecosystems found in the area. On the UK side, Oceana’s findings have further confirmed that Cleaver Bank as a whole (both the Dutch and UK sides) is characterised by very similar habitats and communities. Oceana urges the UK government to carry out more detailed habitat mapping, in order to better identify the range of features present, and determine which conservation and management measures are needed to preserve and restore the ecological integrity of Cleaver Bank.

scholarly journals A synthetic map of the north-west European Shelf sedimentary environment for applications in marine science

2018 ◽  
Vol 10 (1) ◽  
pp. 109-130 ◽  
Author(s):  
Robert J. Wilson ◽  
Douglas C. Speirs ◽  
Alessandro Sabatino ◽  
Michael R. Heath
Keyword(s):  
Grain Size ◽  
North Sea ◽  
Sedimentary Environment ◽  
Marine Policy ◽  
Seabed Sediment ◽  
North West ◽  
The North ◽  
Wide Range ◽  
The North Sea ◽  
West European

Abstract. Seabed sediment mapping is important for a wide range of marine policy, planning and scientific issues, and there has been considerable national and international investment around the world in the collation and synthesis of sediment datasets. However, in Europe at least, much of this effort has been directed towards seabed classification and mapping of discrete habitats. Scientific users often have to resort to reverse engineering these classifications to recover continuous variables, such as mud content and median grain size, that are required for many ecological and biophysical studies. Here we present a new set of 0.125∘ by 0.125∘ resolution synthetic maps of continuous properties of the north-west European sedimentary environment, extending from the Bay of Biscay to the northern limits of the North Sea and the Faroe Islands. The maps are a blend of gridded survey data, statistically modelled values based on distributions of bed shear stress due to tidal currents and waves, and bathymetric properties. Recent work has shown that statistical models can predict sediment composition in British waters and the North Sea with high accuracy, and here we extend this to the entire shelf and to the mapping of other key seabed parameters. The maps include percentage compositions of mud, sand and gravel; porosity and permeability; median grain size of the whole sediment and of the sand and the gravel fractions; carbon and nitrogen content of sediments; percentage of seabed area covered by rock; mean and maximum depth-averaged tidal velocity and wave orbital velocity at the seabed; and mean monthly natural disturbance rates. A number of applications for these maps exist, including species distribution modelling and the more accurate representation of sea-floor biogeochemistry in ecosystem models. The data products are available from https://doi.org/10.15129/1e27b806-1eae-494d-83b5-a5f4792c46fc.

scholarly journals Seafloor change detection using multibeam echosounder backscatter: case study on the Belgian part of the North Sea

2017 ◽  
Vol 39 (1-2) ◽  
pp. 229-247 ◽  
Author(s):  
Giacomo Montereale-Gavazzi ◽  
Marc Roche ◽  
Xavier Lurton ◽  
Koen Degrendele ◽  
Nathan Terseleer ◽  
...  
Keyword(s):  
Change Detection ◽  
North Sea ◽  
Multibeam Echosounder ◽  
The North ◽  
The North Sea

scholarly journals Sequence stratigraphy of the Jurassic of the Danish Central Graben

2003 ◽  
Vol 1 ◽  
pp. 265-300 ◽  
Author(s):  
Jan Andsbjerg ◽  
Karen Dybkjær
Keyword(s):  
Sea Level ◽  
North Sea ◽  
Sedimentary Environment ◽  
Structural Rearrangement ◽  
Upper Jurassic ◽  
Lower Jurassic ◽  
High Rate ◽  
Border Zone ◽  
Stratigraphic Correlation ◽  
Sequence Stratigraphic

A sequence stratigraphic framework is established for the Jurassic of the Danish Central Graben based primarily on petrophysical log data, core sedimentology and biostratigraphic data from about 50 wells. Regional seismic lines are used to assist in the correlation of some wells and in the construction of isochore maps. In the Lower Jurassic (Hettangian–Pliensbachian) succession, five sequences have been identified. The Middle Jurassic is subdivided into four sequences that together span the uppermost Aalenian/lowermost Bajocian to the Callovian. In the Upper Jurassic, better well coverage permits greater stratigraphic resolution, and 11 sequences are identified and mapped. On the basis of the sequence stratigraphic correlation and the construction of isochore maps for individual sequences, the Jurassic basin history of the Danish Central Graben can be subdivided into seven discrete phases: (1) Shallow marine and offshore sediments deposited in a prerift basin extending from the North Sea to the Fennoscandian Border Zone (Hettangian–Pliensbachian). (2) Uplift and erosion in association with a Toarcian–Aalenian North Sea doming event. A major hiatus represents this phase in the study area. (3) Terrestrial and marginal marine sedimentation during initial rifting (latest Aalenian/earliest Bajocian – Late Callovian). (4) Early Oxfordian – Early Kimmeridgian transgression during and after a rift pulse. The sedimentary environment changed from coastal plain and marginal marine to fully marine. (5) Regression associated with a cessation or slowing of subsidence during a structural rearrangement that took place in the Late Kimmeridgian during a break in the main rift climax. Shallow to marginal marine sandstones were deposited above an erosion surface of regional extent. (6) Deep-water mudstones deposited in a composite graben with high subsidence rates related to rift pulses (latest Late Kimmeridgian – middle Middle Volgian). (7) Deposition of organic-rich mudstones and turbidite sandstones during the late Middle Volgian – Early Ryazanian. The main basin shallowed, became more symmetrical and experienced a decreasing rate of subsidence, recording the onset of the post-rift stage. A relative sea-level curve is constructed for the Middle–Late Jurassic. It shows close similarity to published eustatic (global) and relative (North Atlantic area) sea-level curves in the latest Bathonian – late Early Kimmeridgian, but differs in the Late Kimmeridgian – Middle Volgian interval, probably due to the high rate of subsidence in the study area.

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