In this work, we introduce HODOR (Hydroacoustic and Optical Dataset for Oceanic Research), a publicly accessible dataset developed for advanced analysis of marine life. It is one of the first datasets to provide synchronized sonar and optical stereo camera videos, comprising over 400 hours of continuous recordings per sensor. The purpose of HODOR is to support the development of machine learning and deep learning algorithms for marine applications, multimodal sensor fusion techniques, biomass quantification, and long-term ecological studies. The data was collected with a stationary underwater fish observatory (UFO) in the Kiel Fjord, an inlet of the Baltic Sea in northern Germany, and includes an 86-day subset of the recordings from 2021, which was selected based on automated detections using the YOLOv5 model.

This study presents a trilateral test array of new opto-acoustic Underwater Fish Observatories (UFOs) that were operated and tested in Kiel Bight as part of the “UFOTriNet” project. While hydroacoustic and optical techniques have so far been used individually to observe and monitor fish stocks, we present a coupled hybrid system consisting of an optical device intended to scan the near-field as a subsample of a spatially larger medium-to-far-field, scanned by an acoustical device. The optical device consists of two residual light amplifying camera modules able to detect and classify various marine species at a high resolution in the range of at max 4 meters in the study area. To compensate for this spatial limitation, the acoustical component consists of a 2D imaging sonar with a maximum range of 50 m, albeit with a lower resolution. Species affiliation, morphometric characteristics of fish and other marine organisms were stereo-optically detected and classified in the nearfield, blended with acoustical activity in medium to far range, and projected onto the entire insonified area using a hybrid algorithm. Through the synchronous acquisition of multiparametric abiotic and biotic data, UFO allows an automatic, continuous, and non-invasive long-term monitoring of various fish and other marine species and their habitats at regional hotspots. An 86-day multiparametric sample revealing an abrupt shift from a clupeid fish to a gelatinous plankton dominated regime in summer/autumn 2021 in Kiel Fjord is used to demonstrate the potential of UFO for various applications.

Spatially distributed underwater sensor systems are important tools to understand long-term trends in marine ecosystems. For example, in the ongoing UFOTriNet project, noninvasive techniques for the purpose of monitoring fish populations are investigated. A challenge within this and related projects is the long-term operation of cameras in brackish and fully saline water. The impact of biofouling, especially on the underwater cameras, should be minimized for reliable imaging. In the context of the UFOTriNet project, for this purpose, an energy-efficient and environmentally friendly antifouling concept based on UVC irradiation was developed and investigated to extend operation times and to reduce energy and maintenance costs. Innovative contributions include LED-based UVC irradiation from the inside of the camera's pressure housing into the water column, periodic UVC irradiation intervals that are significantly shorter than those commonly reported, and an analysis and comparison of the irradiance for internal and external irradiation configurations. The concept was confirmed by a measurement campaign in the Kiel Fjord, located in the southwest Baltic Sea.

The utilization of stationary underwater cameras is a modern and well-adapted approach to provide a continuous and cost-effective long-term solution to monitor underwater habitats of particular interest. A common goal of such monitoring systems is to gain better insight into the dynamics and condition of populations of various marine organisms, such as migratory or commercially relevant fish taxa. This paper describes a complete processing pipeline to automatically determine the abundance, type and estimate the size of biological taxa from stereoscopic video data captured by the stereo camera of a stationary Underwater Fish Observatory (UFO). A calibration of the recording system was carried out in situ and, afterward, validated using the synchronously recorded sonar data. The video data were recorded continuously for nearly one year in the Kiel Fjord, an inlet of the Baltic Sea in northern Germany. It shows underwater organisms in their natural behavior, as passive low-light cameras were used instead of active lighting to dampen attraction effects and allow for the least invasive recording possible. The recorded raw data are pre-filtered by an adaptive background estimation to extract sequences with activity, which are then processed by a deep detection network, i.e., Yolov5. This provides the location and type of organisms detected in each video frame of both cameras, which are used to calculate stereo correspondences following a basic matching scheme. In a subsequent step, the size and distance of the depicted organisms are approximated using the corner coordinates of the matched bounding boxes. The Yolov5 model employed in this study was trained on a novel dataset comprising 73,144 images and 92,899 bounding box annotations for 10 categories of marine animals. The model achieved a mean detection accuracy of 92.4%, a mean average precision (mAP) of 94.8% and an F1 score of 93%.

The identification of movement and behaviour patterns, as well as inter- and intra-population connectivity is crucial in order to implement effective and functional management and conservation measures for threatened migratory species such as tope (Galeorhinus galeus). Yet, previous studies struggled to elucidate clear and consistent movement and depth usage patterns of adult tope in the Northeast Atlantic, suggesting a high plasticity in the migration and behaviour. We deployed pop-up satellite archival tags on adult tope during their seasonal summer aggregations in the inner German Bight of the south-eastern North Sea and near a presumed mating site in southwest Scotland. Depth distribution and migration pathways were derived from time series data with location processing. Four individuals followed migration trajectories leaving coastal areas and crossed the European shelf slope into oceanic areas of the Northeast Atlantic, remaining fully pelagic for the rest of the deployment duration. These sharks showed far-ranging migration trajectories and undertook regular and frequent diel vertical migrations, reaching daytime depths of over 700 m. Vertical migration patterns closely overlapped with biological mesopelagic habitat structures and closely tracked the diel migration of organisms from deep scattering layers derived from hydroacoustic recordings. It is hypothesized that adult tope regularly utilize oceanic habitats, foraging on mesopelagic layers in an environment generally considered of low prey density.

Records of backscatter and vertical velocity obtained from moored Acoustic Doppler Current Profilers (ADCP) enabled new insights into the dynamics of deep scattering layers (DSLs) and diel vertical migration (DVM) of mesopelagic biomass between these deep layers and the near-surface photic zone in the southern Norwegian Sea. The DSL exhibits characteristic vertical movement on inter-monthly time scales, which is associated with undulations of the main pycnocline between the warm Atlantic water and the underlying colder water masses. Timing of the DVM is closely linked to the day-night light cycle—decent from the photic zone just before sunrise and ascent immediately after sunset. Seasonal variations are also evident, with the highest DVM activity and lowest depth averaged mean volume backscatter strength (MVBS) during spring. This suggests that both oceanographic and optical conditions are driving the complex dynamics of pelagic and mesopelagic activity in this region. We hypothesize that the increased abundance of calanoid copepods in the near-surface layer during spring increases the motivation for vertical migration of pelagic and mesopelagic species, which therefore can explain the increased DVM activity during this season.

The ocean moderates the world’s climate through absorption of heat and carbon, but how much carbon the ocean will continue to absorb remains unknown. The North Atlantic Ocean west (Baffin Bay/Labrador Sea) and east (Fram Strait/Greenland Sea) of Greenland features the most intense absorption of anthropogenic carbon globally; the biological carbon pump (BCP) contributes substantially. As Arctic sea-ice melts, the BCP changes, impacting global climate and other critical ocean attributes (e.g. biodiversity). Full understanding requires year-round observations across a range of ice conditions. Here we present such observations: autonomously collected Eulerian continuous 24-month time-series in Fram Strait. We show that, compared to ice-unaffected conditions, sea-ice derived meltwater stratification slows the BCP by 4 months, a shift from an export to a retention system, with measurable impacts on benthic communities. This has implications for ecosystem dynamics in the future warmer Arctic where the seasonal ice zone is expected to expand.

This study investigates the relevance of the Elephant Island (EI) region for Southern Hemisphere fin whales (Balaenoptera physalus) in their annual life cycle. We collected 3 years of passive acoustic recordings (January 2013 to February 2016) northwest of EI to calculate time series of fin whale acoustic indices, daily acoustic occurrence, spectrograms, as well as the abundance of their 20 Hz pulses. Acoustic backscatter strength, sea ice concentration and chlorophyll-a composites provided concurrent environmental information for graphic comparisons. Acoustic interannual, seasonal and diel patterns together with visual information and literature resources were used to define the period of occupancy and to infer potential drivers for their behaviour. Spectral results suggest that these fin whales migrate annually to and from offshore central Chile. Acoustic data and visual information reveal their arrival at EI in December to feed without producing their typical 20 Hz pulse. For all 3 years, acoustic activity commences in February, peaks in May and decreases in August, in phase with the onset of their breeding season. Our results emphasize the importance of EI for fin whales throughout most of the year. Our recommendation is to consider EI for establishing a marine protected area to expedite the recovery of this vulnerable species.

Cabled coastal observatories are often seen as future-oriented marine technology that enables science to conduct observational and experimental studies under water year-round, independent of physical accessibility to the target area. Additionally, the availability of (unrestricted) electricity and an Internet connection under water allows the operation of complex experimental setups and sensor systems for longer periods of time, thus creating a kind of laboratory beneath the water. After successful operation for several decades in the terrestrial and atmospheric research field, remote controlled observatory technology finally also enables marine scientists to take advantage of the rapidly developing communication technology. The continuous operation of two cabled observatories in the southern North Sea and off the Svalbard coast since 2012 shows that even highly complex sensor systems, such as stereo-optical cameras, video plankton recorders or systems for measuring the marine carbonate system, can be successfully operated remotely year-round facilitating continuous scientific access to areas that are difficult to reach, such as the polar seas or the North Sea. Experience also shows, however, that the challenges of operating a cabled coastal observatory go far beyond the provision of electricity and network connection under water. In this manuscript, the essential developmental stages of the “COSYNA Shallow Water Underwater Node” system are presented, and the difficulties and solutions that have arisen in the course of operation since 2012 are addressed with regard to technical, organizational and scientific aspects.

Summertime visual observations suggest that the region around Elephant Island may serve as an important feeding area for fin whales. To explore its year-round relevance, passive acoustic recordings collected northwest of Elephant Island (61°0.88’S, 55°58.53’W) from January 2013 to February 2016 were analysed for seasonal and diel patterns of fin whale 20 Hz calls. Calls were detected year-round, although in some years calls were not present during all months. For all years, fin whale calls were consistently present from March to July for more than 90% of days per month. From August to January, percentage of days with calls varied between years, with presence exceeding 75% of days per month throughout 2014, whereas in 2015 calls were absent in October and November. In 2013, fin whale calling dropped in August and increased again towards October and November. Quantitative analyses of power spectral density for the 20-Hz and 89-Hz fin whale bands, showed that fin whale acoustic power in both frequency bands followed a Gaussian-like temporal pattern, increasing in late January, peaking during April-May and decreasing in late August for all years. A second shoulder peak in PSD seemed to occur during the second part of July showing strongest for the upper fin whale band, followed by a rapid decrease, after which SNR for both bands dropped to zero. Diel patterns in call activity were analysed for a 10-month subset of the data from 2013. Fluctuations in call rates did not follow a diel pattern nor correspond to local insolation. The observed peaks in fin whale call activity correspond to the periods during which fin whale super groups have been observed visually in this region. Our year-round acoustic analysis indicates that the Elephant Island region likely carries an important role for fin whales throughout the entire year.

The ICES (International Council for the Exploration of the Sea) Working Group on Oceanic Hydrography (WGOH) was established in the late 1970’s with the aim of gathering experts in physical oceanography to provide regular science-based assessments of the North Atlantic hydrographical condition (basically termohaline fields). From the beginning, the WGOH has relied on repeated long-term in-situ sampling at key sites around the North Atlantic, the Nordic Seas and adjacent shelf seas. An annual Report on Ocean Climate (IROC), produced by the WGOH since the late 1990’s, summarizes trends in regional hydrography and identifies patterns linking these changes across the North Atlantic. Regional analyses are prepared by local experts who are directly involved in the monitoring programs responsible for collecting data presented in the report. An interactive webpage created in 2013 allows users to browse and download data that inform the IROC. Within the last two decades the physical oceanography community has evolved quickly incor- porating technological advances such as autonomous devices into classical in-situ sampling programs. The WGOH has embraced such technological developments without diverting focus from ongoing in-situ long-term monitoring programs. Having longstanding experience synthe- sizing data and expertise from a large number of operational programs spanning an extensive international footprint, the WGOH has a unique perspective to offer the global ocean observing community. Here we discuss how we might foster connections with ICES to benefit the GOOS (Global Ocean Observing System) community.

Abstract. Measuring temperature and salinity profiles in the world's oceans is crucial to understanding ocean dynamics and its influence on the heat budget, the water cycle, the marine environment and on our climate. Since 1983 the German research vessel and icebreaker Polarstern has been the platform of numerous CTD (conductivity, temperature, depth instrument) deployments in the Arctic and the Antarctic. We report on a unique data collection spanning 33 years of polar CTD data. In total 131 data sets (1 data set per cruise leg) containing data from 10 063 CTD casts are now freely available at doi:10.1594/PANGAEA.860066 . During this long period five CTD types with different characteristics and accuracies have been used. Therefore the instruments and processing procedures (sensor calibration, data validation, etc.) are described in detail. This compilation is special not only with regard to the quantity but also the quality of the data – the latter indicated for each data set using defined quality codes. The complete data collection includes a number of repeated sections for which the quality code can be used to investigate and evaluate long-term changes. Beginning with 2010, the salinity measurements presented here are of the highest quality possible in this field owing to the introduction of the OPTIMARE Precision Salinometer.

The success of any efforts to determine the effects of climate change on marine ecosystems depends on understanding in the first instance the natural variations, which contemporarily occur on the interannual and shorter time scales. Here we present results on the environmental controls of zooplankton distribution patterns and behaviour in the eastern Weddell Sea, Southern Ocean. Zooplankton abundance and vertical migration are derived from the mean volume backscattering strength (MVBS) and the vertical velocity measured by moored acoustic Doppler current profilers (ADCPs), which were deployed simultaneously at 64 degrees S, 66.5 degrees S and 69 degrees S along the Greenwich Meridian from February, 2005, until March, 2008. While these time series span a period of full three years they resolve hourly changes.A highly persistent behavioural pattern found at all three mooring locations is the synchronous diel vertical migration (DVM) of two distinct groups of zooplankton that migrate between a deep residence depth during daytime and a shallow depth during nighttime. The DVM was closely coupled to the astronomical daylight cycles. However, while the DVM was symmetric around local noon, the annual modulation of the DVM was clearly asymmetric around winter solstice or summer solstice, respectively, at all three mooring sites. DVM at our observation sites persisted throughout winter, even at the highest latitude exposed to the polar night. Since the magnitude as well as the relative rate of change of illumination is minimal at this time, we propose that the ultimate causes of DVM separated from the light mediated proximal cue that coordinates it. In all three years, a marked change in the migration behaviour occurred in late spring (late October/early November), when DVM ceased. The complete suspension of DVM after early November is possibly caused by the combination of two factors: (1) increased availability of food in the surface mixed layer provided by the phytoplankton spring bloom, and (2) vanishing diurnal enhancement of the threat from visually oriented predators when the illumination is quasi-continuous during the polar and subpolar summer.Zooplankton abundance in the water column, estimated as the mean MVBS in the depth range 50-300 m, was highest end of summer and lowest mid to end winter on the average annual cycle. However, zooplankton abundance varied several-fold between years and between locations. Based on satellite and in situ data of chlorophyll and sea ice as well as on hydrographic measurements, the inter annual and spatial variations of zooplankton mean abundance can be explained by differences in the magnitude of the phytoplankton spring bloom, which develops during the seasonal sea ice retreat. Whereas the vernal ice melt appears necessary to stimulate the blooming of phytoplankton, it is not the determinator of the blooms magnitude, its areal extent and duration. A possible explanation for the limitation of the phytoplankton bloom in some years is top-down control. We hypothesise that the phytoplankton spring development can be curbed by grazing when the zooplankton had attained high abundance by growth during the preceding summer. (C) 2016 Elsevier Ltd. All rights reserved.

Ocean iron fertilization experiments enable the quantitative study of processes shaping the structure and functioning of pelagic ecosystems following perturbation under in situ conditions. EIFEX was conducted within a stationary eddy adjacent to the Antarctic Polar Front over 38 days in February/March 2004 and induced a massive diatom bloom. Here, we present the responses in abundance and biomass of all identifiable protozooplankton taxa (heterotrophic protists ranging from 2 to 500 mm) during the bloom. Acantharia, dinoflagellates and ciliates together contributed >90% of protozooplankton biomass in the upper 100 m throughout the experiment with heterotrophic nanoflagellates, nassellaria, spumellaria, phaeodaria, foraminifera and the taxopodidean Sticholonche zanclea providing the remainder. Total protozooplankton biomass increased slightly from 1.0 to 1.3 g C m(-2) within the fertilized patch and remained at 0.7+0.04 g C m(-2) outside it. However, distinct trends in population build-up or decline were observed within the dominant taxa in each group. In general, smaller less-defended groups such as aloricate ciliates and athecate dinoflagellates declined, whereas the biomass of large, spiny and armoured groups, in particular acantharia, large tintinnids and thecate dinoflagellates increased inside the patch. We attribute the higher accumulation rates of defended taxa to selective, heavy grazing pressure by the large stocks of copepods. Of the defended taxa, acantharia had the lowest mortality rates and the highest biomass. Large stocks of tintinnid loricae in the deep water column identify this group as a relevant contributor to deep organic carbon export. Highest accumulation rates (0.11 day(-1)) were recorded in S. zanclea.

In the European Iron Fertilization Experiment (EIFEX), the iron hypothesis was tested by an open ocean perturbation experiment. The success of EIFEX owes to the applied experimental strategy; namely to use the closed core of a mesoscale eddy for the iron injection. This strategy not only allowed tracking the phytoplankton bloom within the fertilized patch of mixed-layer water, but also allowed the export of biologically fixed carbon to the deep ocean to be quantified. In this present study, least-squares techniques are used to fit a regional numerical ocean circulation model with four open boundaries to temperature, salinity, and velocity observations collected during EIFEX. By adjusting the open boundary values of temperature, salinity and velocity, an optimized model is obtained that clearly improves the simulated eddy and its mixed layer compared to a first guess representation of the cyclonic eddy. A biogeochemical model, coupled to the optimized circulation model, simulates the evolution of variables such as chlorophyll a and particular organic carbon in close agreement with the observations. The estimated carbon export, however, is lower than the estimates obtained from observations without numerical modeling support. Tuning the sinking parameterization in the model increases the carbon export at the cost of unrealistically high sinking velocities. Repeating the model experiment without adding iron allows more insight into the effects of the iron fertilization. In the model this effect is about 40% lower than in previous estimates in the context of EIFEX. The likely causes for these discrepancies are potentially too high remineralization, inaccurate representation of the bloom-termination in the model, and ambiguity in budget computations and averaging. The discrepancies are discussed and improvements are suggested for the parameterization used in the biogeochemical model components.

This study provides evidence of the influence of hydrography and large scale ocean circulation on the geographical distribution of beaked redfish (Sebastes mentella) in the Irminger Sea on the interannual time scale, from 1992 to 2011. The results reveal the average relationship of adult pelagic redfish to their physical habitat from 100 to 800m depth: the most preferred latitude, longitude, depth, temperature and salinity for redfish are approximately 58°N, 41°W, 557m, 4.5°C and 34.87, respectively. The redfish habitat corresponds in a temperature–salinity (TS) diagram to a mixing triangle between East Greenland Current Water (EGCW), Labrador Sea Water (LSW) and Irminger Current Water (ICW). The geographical centre of mass of the redfish distribution (as revealed by acoustic fish density) indicates displacements from year to year. Changes in hydrographic conditions were investigated in detail for possible reasons for these displacements. Empirical Orthogonal Analysis reveals that maximum variations of water mass volume on an interannual time-scale in the study region correspond to ICW and LSW changes, while EGCW remains comparatively stable. Indices of redfish geographical centroid, LSW volume, ICW temperature and Subpolar Gyre (SPG) intensity suggest that the geographical redfish displacements are closely related to interannual changes of ICW modulated by the SPG intensity with a lag of 1 or 2 years. In comparison, LSW seems to have no impact on the redfish distribution at the studied depth range. The time lag between ICW and redfish displacements indicates an indirect influence of temperature on redfish. Hence, changes of chlorophyll-a (from satellite imagery), as a proxy for primary production, were used in a first approach to study the role of food availability. The analysis is based on acoustic and trawl data from nine expeditions coordinated by the International Council for the Exploration of the Sea (ICES), around 71,000 hydrographic stations from the Integrated Climate Data Center, World Ocean Database 2009 and Coriolis (among others), 60 years of circulation data from the Max-Planck Institute Ocean Model and 14 years of satellite chlorophyll-a from SeaWiFS, MODIS-Aqua and MERIS.