Description: Detecting changes of sediment boundaries on the seafloor is important for a better understanding of sediment dynamics and related impacts to benthic habitats. Side-scan sonars (SSS) perform more cost-effectively in shallow waters than other acoustic systems because of their larger swath widths, and the resolution of its images does not change with varying water depth. However, as they are generally towed behind the survey vessel, they tend to have lower positioning accuracy, which makes them unreliable for change detection analyses. In this study, we present a workflow that processes SSS data in a way that makes them fit for change detection analyses. To test the capacity of SSS mosaics for change detection, we used a free software called “Digital Shoreline Analysis System”, which was developed by the United States Geological Survey for ArcGIS version 10.4 onwards. The methods were applied in three areas in the Sylt Outer Reef, German Bight, North Sea. Our results showed that with appropriate processing, SSS mosaics could be used for change detection of sharp sediment boundaries. We found a common trend in the sediment distribution patterns of coarse sediments by monitoring the movement of their boundaries. The boundaries moved in northeast-southwest direction and boundary movements of less than 20 m were typically observed. The methods presented here are semi-automated, repeatable, and replicable, which has potential for wide-scale monitoring of sediment distribution patterns.

Description: The ongoing environmental changes in the Southern Ocean may cause a dramatic decrease in habitat quality. Due to its central position in the food web, Antarctic krill (Euphausia superba) is a key species of the marine Antarctic ecosystem. It is therefore crucial to understand how increasing water temperatures affect important krill life-cycle processes. Here, a long-term (August – March) laboratory acclimation experiment at different temperature scenarios (0.5 ◦C, 1.5 ◦C, 2.5 ◦C, 3.5 ◦C, 5 ◦C, 7 ◦C) was performed and the effects of elevated temperatures on whole animal parameters (O2 consumption, body length, length of the digestive gland) were analyzed. The response of krill oxygen consumption to different experimental temperatures differed between acute/short-term and long-term acclimation. After 8 months, krill oxygen consumption remained unchanged up to temperatures of 3.5 ◦C and was significantly higher at temperatures 〉 3.5 ◦C. Krill acclimated to temperatures ≥ 3.5 ◦C were significantly smaller at the end of the experiment. Limited food intake and/or conversion may have contributed to this effect, especially pronounced after the onset of the reproductive period. In addition, the seasonal growth pattern in males differed from that of females. Together, our findings indicate that warming Southern Ocean waters are likely to increase metabolic rate in krill, possibly altering the amount of energy available for other important life-cycle processes, a finding directly related to future population dynamics and fisheries management.

Description: The Ocean Floor Observation and Bathymetry System (OFOBS) is an underwater survey plat-form, which is designed and developed for research in the Polar Regions by the Alfred Wegener Institute (AWI). The tailored deep tow system brought a new perspective and clarity from Arctic Ocean by its optical and acoustic sensors. During the PS101 expedition at the Karasik seamount, OFOBS provides a novel picture of megafauna’s habitats. In this study, we develop a methodology to convert the imagery dataset to micro-bathymetry in order to provide primary data for object detection and habitat mapping which will provide a better understanding of arctic benthic habitats. The methodology is based on the underwater photogrammetry workflow and two different point cloud classification methods adopted for sponge detec-tion in 3D point clouds, to facilitate habitat mapping with a focus on the central of Kara

Description: Dispersal and foodweb dynamics have long been studied in separate models. However, over the past decades, it has become abundantly clear that there are intricate interactions between local dynamics and spatial patterns. Trophic meta-communities, i.e. meta-foodwebs, are very complex systems that exhibit complex and often counterintuitive dynamics. Over the past decade, a broad range of modelling approaches have been used to study these systems. In this paper, we review these approaches and the insights that they have revealed. We focus particularly on recent papers that study trophic interactions in spatially extensive settings and highlight the common themes that emerged in different models. There is overwhelming evidence that dispersal (and particularly intermediate levels of dispersal) benefits the maintenance of biodiversity in several different ways. Moreover, some insights have been gained into the effect of different habitat topologies, but these results also show that the exact relationships are much more complex than previously thought, highlighting the need for further research in this area. This article is part of the theme issue ‘Integrative research perspectives on marine conservation’.

Description: Whereas the conservation and management of biodiversity has become a key issue in environmental sciences and policy in general, the conservation of marine biodiversity faces additional challenges such as the challenges of accessing field sites (e.g. polar, deep sea), knowledge gaps regarding biodiversity trends, high mobility of many organisms in fluid environments, and ecosystem-specific obstacles to stakeholder engagement and governance. This issue comprises contributions from a diverse international group of scientists in a benchmarking volume for a common research agenda on marine conservation. We begin by addressing information gaps on marine biodiversity trends through novel approaches and technologies, then linking such information to ecosystem functioning through a focus on traits. We then leverage the knowledge of these relationships to inform theory aiming at predicting the future composition and functioning of marine communities. Finally, we elucidate the linkages between marine ecosystems and human societies by examining economic, management and governance approaches that contribute to effective marine conservation in practice. This article is part of the theme issue ‘Integrative research perspectives on marine conservation’.

Description: An accurate identification of species and communities is a prerequisite for analysing and recording biodiversity and community shifts. In the context of marine biodiversity conservation and management, this review outlines past, present and forward-looking perspectives on identifying and recording planktonic diversity by illustrating the transition from traditional species identification based on morphological diagnostic characters to full molecular genetic identification of marine assemblages. In this process, the article presents the methodological advancements by discussing progress and critical aspects of the crossover from traditional to novel and future molecular genetic identifications and it outlines the advantages of integrative approaches using the strengths of both morphological and molecular techniques to identify species and assemblages. We demonstrate this process of identifying and recording marine biodiversity on pelagic copepods as model taxon. Copepods are known for their high taxonomic and ecological diversity and comprise a huge variety of behaviours, forms and life histories, making them a highly interesting and well-studied group in terms of biodiversity and ecosystem functioning. Furthermore, their short life cycles and rapid responses to changing environments make them good indicators and core research components for ecosystem health and status in the light of environmental change. This article is part of the theme issue ‘Integrative research perspectives on marine conservation’.

Description: During the 1-year MOSAiC (Multidisciplinary drifting Observatory for the Study of Arctic Climate) expedition, the German icebreaker Polarstern drifted through Arctic Ocean ice from October 2019 to May 2020, mainly at latitudes between 85 and 88.5∘ N. A multiwavelength polarization Raman lidar was operated on board the research vessel and continuously monitored aerosol and cloud layers up to a height of 30 km. During our mission, we expected to observe a thin residual volcanic aerosol layer in the stratosphere, originating from the Raikoke volcanic eruption in June 2019, with an aerosol optical thickness (AOT) of 0.005–0.01 at 500 nm over the North Pole area during the winter season. However, the highlight of our measurements was the detection of a persistent, 10 km deep aerosol layer in the upper troposphere and lower stratosphere (UTLS), from about 7–8 to 17–18 km height, with clear and unambiguous wildfire smoke signatures up to 12 km and an order of magnitude higher AOT of around 0.1 in the autumn of 2019. Case studies are presented to explain the specific optical fingerprints of aged wildfire smoke in detail. The pronounced aerosol layer was present throughout the winter half-year until the strong polar vortex began to collapse in late April 2020. We hypothesize that the detected smoke originated from extraordinarily intense and long-lasting wildfires in central and eastern Siberia in July and August 2019 and may have reached the tropopause layer by the self-lifting process. In this article, we summarize the main findings of our 7-month smoke observations and characterize the aerosol in terms of geometrical, optical, and microphysical properties. The UTLS AOT at 532 nm ranged from 0.05–0.12 in October–November 2019 and 0.03–0.06 during the main winter season. The Raikoke aerosol fraction was estimated to always be lower than 15 %. We assume that the volcanic aerosol was above the smoke layer (above 13 km height). As an unambiguous sign of the dominance of smoke in the main aerosol layer from 7–13 km height, the particle extinction-to-backscatter ratio (lidar ratio) at 355 nm was found to be much lower than at 532 nm, with mean values of 55 and 85 sr, respectively. The 355–532 nm Ångström exponent of around 0.65 also clearly indicated the presence of smoke aerosol. For the first time, we show a distinct view of the aerosol layering features in the High Arctic from the surface up to 30 km height during the winter half-year. Finally, we provide a vertically resolved view on the late winter and early spring conditions regarding ozone depletion, smoke occurrence, and polar stratospheric cloud formation. The latter will largely stimulate research on a potential impact of the unexpected stratospheric aerosol perturbation on the record-breaking ozone depletion in the Arctic in spring 2020.

Description: Low-level mixed-phase clouds (MPCs) are common in the Arctic. Both local and large-scale phenomena influence the properties and lifetime of MPCs. Arctic fjords are characterized by complex terrain and large variations in surface properties. Yet, not many studies have investigated the impact of local boundary layer dynamics and their relative importance on MPCs in the fjord environment. In this work, we used a combination of ground-based remote sensing instruments, surface meteorological observations, radiosoundings, and reanalysis data to study persistent low-level MPCs at Ny-Ålesund, Svalbard, for a 2.5-year period. Methods to identify the cloud regime, surface coupling, and regional and local wind patterns were developed. We found that persistent low-level MPCs were most common with westerly winds, and the westerly clouds had a higher mean liquid (42 g m−2) and ice water path (16 g m−2) compared to those with easterly winds. The increased height and rarity of persistent MPCs with easterly free-tropospheric winds suggest the island and its orography have an influence on the studied clouds. Seasonal variation in the liquid water path was found to be minimal, although the occurrence of persistent MPCs, their height, and their ice water path all showed notable seasonal dependency. Most of the studied MPCs were decoupled from the surface (63 %–82 % of the time). The coupled clouds had 41 % higher liquid water path than the fully decoupled ones. Local winds in the fjord were related to the frequency of surface coupling, and we propose that katabatic winds from the glaciers in the vicinity of the station may cause clouds to decouple. We concluded that while the regional to large-scale wind direction was important for the persistent MPC occurrence and properties, the local-scale phenomena (local wind patterns in the fjord and surface coupling) also had an influence. Moreover, this suggests that local boundary layer processes should be described in models in order to present low-level MPC properties accurately.