Description: Bathymetry (seafloor depth), is a critical parameter providing the geospatial context for a multitude of marine scientific studies. Since 1997, the International Bathymetric Chart of the Arctic Ocean (IBCAO) has been the authoritative source of bathymetry for the Arctic Ocean. IBCAO has merged its efforts with the Nippon Foundation-GEBCO-Seabed 2030 Project, with the goal of mapping all of the oceans by 2030. Here we present the latest version (IBCAO Ver. 4.0), with more than twice the resolution (200 × 200 m versus 500 × 500 m) and with individual depth soundings constraining three times more area of the Arctic Ocean (∼19.8% versus 6.7%), than the previous IBCAO Ver. 3.0 released in 2012. Modern multibeam bathymetry comprises ∼14.3% in Ver. 4.0 compared to ∼5.4% in Ver. 3.0. Thus, the new IBCAO Ver. 4.0 has substantially more seafloor morphological information that offers new insights into a range of submarine features and processes; for example, the improved portrayal of Greenland fjords better serves predictive modelling of the fate of the Greenland Ice Sheet.

Description: Towed camera systems are commonly used to collect photo and video images of the deep seafloor for a wide variety of purposes, from pure exploratory research to the development of management plans. Ongoing technological developments are increasing the quantity and quality of data collected from the deep seafloor. Despite these improvements, the area of seafloor, which towed systems can survey, optically remains limited by the rapid attenuation of visible wavelengths within water. We present an overview of a new towed camera platform integrating additional acoustical devices: the ocean floor observation and bathymetry system (OFOBS). The towed system maintains continuous direct communication via fiber optic cable with a support vessel, operational at depths up to 6000 m. In addition to collecting seafloor photo and video data, OFOBS gathers sidescan data over a 100-m swath width. OFOBS functionality is further augmented by a forward looking sonar, used to aid in hazard avoidance and real-time course correction. Data collected during the first field deployments of OFOBS, at a range of seamounts on the Langseth Ridge/Gakkel Ridge intersection (86° N, 61° E) in the high Arctic in September 2016, are presented to demonstrate the functionality of the system. Collected from a location with near continuous ice cover, this explanatory data set highlights the advantages of the system for deep-sea survey work in environments currently difficult to access for the majority of subsurface research platforms.

Description: Research vessels equipped with fibre optic and copper-cored coaxial cables support the live onboard inspection of high-bandwidth marine data in real time. This allows for towed still-image and video sleds to be equipped with latest-generation higher-resolution digital camera systems and additional sensors. During RV Polarstern expedition PS118 in February–April 2019, the recently developed Ocean Floor Observation and Bathymetry System (OFOBS) of the Alfred Wegener Institute was used to collect still-image and video data from the seafloor at a total of 11 predominantly ice-covered locations in the northern Weddell Sea and Powell Basin. Still images of 26-megapixel resolution and HD (high-definition) quality video data were recorded throughout each deployment. In addition to downward-facing video and still-image cameras, the OFOBS also mounted side-scanning and forward-facing acoustic systems, which facilitated safe deployment in areas of high topographic complexity, such as above the steep flanks of the Powell Basin and the rapidly shallowing, iceberg-scoured Nachtigaller Shoal. To localise collected data, the OFOBS system was equipped with a Posidonia transponder for ultra-short baseline triangulation of OFOBS positions. All images are available from: https://doi.org/10.1594/PANGAEA.911904 (Purser et al., 2020).

Description: The main aim of the MSM95 research expedition was to investigate and map physical impacts on the arctic seafloor in two distinct and contrasting Arctic areas (The Svalbard shelf edge and the HAUSGARTEN time series stations in the FRAM strait) with a range of research equipment. A ‘nested’ data approach was conducted in each research area, with broad seafloor mapping conducted initially with the R/V MARIA S. MERIAN onboard acoustic systems (The EM122 and EM712 bathymetric systems), followed by focused subsequent mapping conducted by PAUL 3000 automated underwater vehicle (AUV) sidescan and camera deployments, Ocean Floor Observation and Bathymetry System (OFOBS) towed sidescan and camera trawls and finally with very high resolution investigations conducted with a new mini-ROV launched directly from the OFOBS for close seafloor visual analysis. These data will be used to produce spatial distribution maps of iceberg and fishery impacts on the seafloor at three locations to the north, south and west of the Svalbard Archipelago, as well as maps of drop stone and topography variations across several of the HAUSGARTEN stations.

Description: To describe the seafloor topography, a number of different bathymetric methods can be applied. These methods vary greatly in coverage, resolution, and topographic uncertainty. Satellite-based gravimetry and radar altimetry can give large-scale structural estimates of the seafloor topography, yet, with a very low resolution and without real depth measurements. Ship-based swath bathymetry systems greatly improve the topographic uncertainty and increase the knowledge on geomorphology and depth of the seafloor. In shallow waters, ship mounted echosounders can produce high-resolution data on a submeter level. However, in deep-sea environments, the resolution deteriorates due to large acoustic footprints and a reduced number of measurement points with respect to the mapped area. In order to conduct high-resolution habitat mapping and to resolve small-scale topographic seafloor features, subsea survey vehicles need to be employed. Next to remotely operated or autonomous underwater vehicles, towed camera systems present a comparatively cheap method, both financially and with regards to support requirements, to collect close-range optical seafloor data. Nonetheless, optical sensors have very limited coverage capabilities in the deep sea, due to the nature of the sensors and the high attenuation of light in the water column. Acoustic sensors on the other hand can achieve much wider survey swaths, depending on their operation frequency. The Ocean Floor Observation and Bathymetry System (OFOBS), developed at the Alfred Wegener Institute for Polar and Marine Research, Germany, offers a novel survey technology for deep-towed multisensor microbathymetric habitat mapping. To augment the traditional optical sensors, the OFOBS was equipped with additional acoustic and navigational sensors. A bathymetric side scan sonar collects lateral seafloor reflection intensity and bathymetry at ranges up to 100 m to both sides of the vehicle. A forward looking sonar records acoustic imagery ahead of the system, which can be used for hazardous obstacle avoidance in rough terrain. This thesis introduces the newly developed system along with processing workflows for the acquired datasets. Underwater photogrammetric methods are utilized for the optical data, to reconstruct the three dimensional morphology of the seabed. The camera pose estimations of the employed bundle adjustment algorithms are used for local navigation corrections of the acoustic datasets, to achieve best possible data alignment. The resulting multilayer product consists of wide-swath acoustic bathymetry (submeter resolution), multi-frequency side scan mosaics (subdecimeter resolution), photogrammetric microbathymetry (subcentimeter resolution), and geometrically corrected, georeferenced photo mosaics (submillimeter resolution). These results offer a wide variety of use cases in high-resolution habitat analyses by the associated scientific working groups. The data used for developing the presented workflow was collected during the RV Polarstern expedition PS101 in the extreme environment of the volcanic seamounts along the Langseth Ridge in the high Arctic (87°N, 60°E).

Description: This comment presents acoustic and visual data showing deep seafloor depression chains similar to those reported in Marsh et al. (R. Soc. open sci. 5: 180286), though from a different deep-sea setting. Marsh et al. present data collected during cruise JC120 from polymetallic nodule rich sites within the Clarion-Clipperton Fracture Zone (CCFZ), at water depths of between 3999 and 4258 m. Within this comment, we present data collected with equivalent acoustic and imaging devices on-board the RV Sonne (SO261—March/April 2018) from the Atacama Trench, approximately 4000 m depth, which shows comparable depression chains in the seafloor. In contrast with the CCFZ observations, our study area was wholly free of polymetallic nodules, an observation therefore weakening the ‘ballast collection’ by deep-sea diving mammals formation hypothesis discussed in their paper. We support their alternate hypothesis that if these features are indeed generated by deep-diving megafauna, then they are more likely the resultant traces of infauna feeding or marks made during opportunistic capture of benthic fish/cephalopods. We observed these potential prey fauna with lander and towed camera systems during the cruise, with example images of these presented here. Both the SO261 and JC120 cruises employed high-resolution sidescan systems at deployment altitudes seldom used routinely until the last few years during scientific deep-sea surveys. Given that both cruises found these depression chains in contrasting physical regions of the East Pacific, they may have a more ubiquitous distribution than at just these sites. Thus, the impacts of cetacean foraging behaviour on deep seafloor communities, and the potential relevance of these prey sources to deep-diving species, should be considered.