<p>Geogenic reefs are hotspots for benthic organisms including fish. Given their ecosystem importance, the European Union has protected them by law and demands an area-wide mapping. The German federal agency for nature conservation together with scientific experts has lately published a guideline to map reefs in the Baltic Sea. Reef delineation is based on hydroacoustic backscatter mosaics which are divided and interpreted in 50x50 m cells. Each cell is categorized according to the number of boulders present:  none, 1-5, and more than 5 boulders. The categorization is strongly dependent on the data quality, hydroacoustic frequency used and technique of boulder identification (manual or automatic). By comparing data with different frequencies interpreted each manually and automatically we will demonstrate the importance of appropriate data for reef delineation.</p>
No abstract is provided for this article.
. Tsunami, storm and flash-flood event layers, which have been deposited over the last century on the shelf offshore Khao Lak (Thailand, Andaman Sea), are identified in sediment cores based on sedimentary structures, grain size compositions, Ti / Ca ratios and 210Pb activity. Individual offshore tsunami deposits are 12 to 30 cm in thickness and originate from the 2004 Indian Ocean Tsunami. They are characterized by (1) the appearance of sand layers enriched in shells and shell debris and (2) the appearance of mud and sand clasts. Storm deposits found in core depths between 5 and 82 cm could be attributed to recent storm events by using 210Pb profiles in conjunction with historical data of typhoons and tropical storms. Massive sand layers enriched in shells and shell debris characterize storm deposits. The last classified type of event layer represents reworked flash-flood deposits, which are characterized by a fining-upward sequence of muddy sediment. The most distinct difference between storm and tsunami deposits is the lack of mud and sand clasts, mud content and terrigenous material within storm deposits. Terrigenous material transported offshore during the tsunami backwash is therefore an important indicator to distinguish between storm and tsunami deposits in offshore environments.
Understanding the development of shallow seas is essential, as they provide a major environmental and economic resource. An investigation of the Holocene development and the present conditions of the Andaman Sea shelf was carried out based on hydroacoustic surveys and sedimentological sampling. The results show that the relative sea level in the offshore Phang Nga province (Thailand) was at a present-day water depth of approximately 63 m at 13 cal ka BP. This agrees with the sea level development of the Sunda Shelf. Since that time, the Andaman Sea continental shelf developed as a sediment-starved environment, with less than 2 m thickness of sediment deposited during the Holocene on the crystalline basement over large areas between 60 m and 20 m water depth. Between 28 and 17 m water depth, a series of moribund asymmetrical sand ridges exist. These ridges were formed around 9.0 ka cal BP. They strike oblique to the coastline. On the seaward side of the sand ridges, small NW-SE directed submarine dunefields developed, shaped by monsoon-induced currents.
The bathymetric data were collected on the 27<sup>th</sup> of June 2020 as underway research data on a 1.5 km track during the cruise EMB239 with the German research vessel Elisabeth Mann Borgese. The objective of the data acquisition was to survey seafloor scars resulting from the controlled detonation of ground mines. For data acquisition, the ship’s hull-mounted Sonic 2024 (R2Sonic Inc.) multibeam echosounder was used. The raw sonar data were loaded in Qimera v2.4.3 (Quality Positioning Services B.V.) and automatically processed to compute sounding footprint location under consideration of sound velocity, position, motion, and heading information. To make the data usable without any specific software, the georeferenced soundings were exported without any bathymetric data cleaning as comma-separated ASCII file in the coordinate reference system EPSG: 32632 - WGS84 / UTM zone 32N. For more details please refer to Papenmeier, S., Darr, A., Feldens, P. (in prep): Geomorphological data from detonation craters in the Fehmarnbelt, German Baltic Sea.
The black coral Anthipatella wollastoni forms marine animal forests in the mesophotic zone. The spatial extent of black coral forests is not well known in many regions. Due to its protein and chitin skeleton, the coral is difficult to image using acoustic remote sensing techniques compared to corals with carbonate skeletons. Several manufacturers have recently introduced an additional data type to their multibeam echosounders, called “multi-detection,” which provides additional target detections per beam in addition to the primary bottom detection. In this study, we used a Norbit chirp multibeam echosounder in multi-detect mode to acquire up to three targets in each beam in an area of black coral below 45 m depth off the coast of Lanzarote (Canary Islands, Spain). Multi-detect allows features above and below the primary bottom detection to be identified without the need to store and process water-column data. Black coral can be detected by comparing “multi-detection” data with ground truthing by technical divers and underwater cameras. However, the repeatability of the detections is limited and further sensitivity studies are required.
This study aimed to constrain the source area of fluids responsible for the formation of a pockmark field in the eastern Red Sea. The newly discovered fiel
Bottom trawling represents the largest anthropogenic source of physical disturbance to seafloor morphology, sediment texture and composition, and benthic habitats. Past studies have shown that the morphological traces left by bottom trawling in the Baltic Sea remain stable for a year to more than a decade depending on area. The persistence of trawling-induced morphology is particularly relevant with the currently declining fishing pressure. The steeply declining trawling intensity provides the opportunity to establish baseline maps of trawling impacts and investigate how a trawled seafloor re-naturalizes after trawling has stopped. Here, we train a convolutional neural network to map trawl marks in bathymetric grids of 1 m resolution largely provided by the German Federal Maritime Agency for Kiel Bay, Fehmarn Belt, Mecklenburg Bay and Arkona Basin in the Western Baltic Sea. The model operates directly on bathymetric grids and is robust to artifacts, allowing monitoring of trawl marks with low effort. The calculated trawl mark density is a measure of the cumulative morphological impact of trawling in the different areas. For the Fehmarn Belt marine protected area, where bottom trawling was excluded in 2025, differential bathymetric data show no substantial seafloor recovery after one year, and new trawl marks are observed. Small areas of low trawling activity around seafloor obstacles such as pockmarks, boulders and wrecks allow the direct comparison of a pristine (Holocene-like) seafloor with an adjacent heavily trawled seafloor. Here, seafloor roughness decreases with increasing trawling intensity, potentially related to sediment resuspension and flattening by ground ropes that are not directly image by acoustic surveys. Untrawled seafloor locally elevates slightly above the surrounding trawled seafloor, potentially caused by long-term erosive effects of sediment reworking by bottom trawling. Initial results suggest a relationship of near-subseafloor free methane fronts to areas of intense trawling, suggesting that trawling can also effect the flux of climate relevant trace-gases into the water column. We further analyze vertical profiles of benthic microbial communities at stations with different trawling intensity.
Accurate mapping of seafloor morphological features, such as pockmarks, is essential for marine spatial planning, geological hazard assessment, and environmental monitoring. Traditional manual delineation methods are often subjective and inefficient when applied to large, high-resolution bathymetric datasets. This study presents a semi-automated workflow based on the CoMMa (Confined Morphologies Mapping) toolbox to classify pockmarks in Flensburg Fjord, Germany–Denmark. Initial detection employed the Bathymetric Position Index (BPI) with intentionally permissive parameters to ensure high recall of morphologically diverse features. Morphometric descriptors were then extracted and used to train a Random Forest classifier, enabling noise reduction and refinement of overinclusive delineations. Validation against expert-derived mappings showed that the model achieved an overall classification accuracy of 86.16%, demonstrating strong performance across the validation area. These findings highlight how integrating a GIS-based geomorphometry toolbox with machine learning yields a reproducible, objective, and scalable approach to seabed mapping, supporting decision-making processes and advancing standardized methodologies in marine geomorphology.
Backscatter mosaics based on a multi-frequency multibeam echosounder survey in the continental shelf setting of the North Sea were compared. The uncalibrated backscatter data were recorded with frequencies of 200, 400 and 600 kHz. The results showed that the seafloor appears mostly featureless in acoustic backscatter mosaics derived from 600 kHz data. The same area surveyed with 200 kHz reveals numerous backscatter anomalies with diameters of 10–70 m deviating between −2 dB and +4 dB from the background sediment. Backscatter anomalies were further subdivided based on their frequency-specific texture and were attributed to bioturbation within the sediment and the presence of polychaetes on the seafloor. While low frequencies show the highest overall contrast between different seafloor types, a consideration of all frequencies permits an improved interpretation of subtle seafloor features.
