ALBERT

Description: Sediment delivery to the abyssal regions of the oceans is an integral process in the source to sink cycle of material derived from adjacent continents and islands. The Zambezi River, the largest in southern Africa, delivers vast amounts of material to the inner continental shelf of central Mozambique. The aim of this contribution is to better constrain sediment transport pathways to the abyssal plains using the latest, regional, high-resolution multibeam bathymetry data available, taking into account the effects of bottom water circulation, antecedent basin morphology and sea-level change. Results show that sediment transport and delivery to the abyssal plains is partitioned into three distinct domains; southern, central and northern. Sediment partitioning is primarily controlled by changes in continental shelf and shelf-break morphology under the influence of a clockwise rotating shelf circulation system. However, changes in sealevel have an overarching control on sediment delivery to particular domains. During highstand conditions, such as today, limited sediment delivery to the submarine Zambezi Valley and Channel is proposed, with increased sediment delivery to the deepwater basin being envisaged during regression and lowstand conditions. However, there is a pronounced along-strike variation in sediment transport during the sea-level cycle due to changes in the width, depth and orientation of the shelf. This combination of features outlines a sequence stratigraphic concept not generally considered in the strike-aligned shelf-slope-abyssal continuum.

Description: The Chilean fjord region, situated between 42 and 56 °S, forms one of the most ragged shorelines and belongs to the ecologically and biogeographically least understood marine regions of the world. A labyrinth of fjords, channels, and islands extends over 240,000 km2 and creates a coastline of more than 80,000 km. Due to strong abiotic gradients, numerous habitats are created, which are further diversified by temporal dynamics (tidal cycle, seasonal changes in precipitation, temperature, radiation, etc.). The region is a biodiversity hotspot hosting unique and fragile ecosystems. Among the species living here, several are species forming habitats in the ecosystem. These organisms can reach high densities conforming the so-called marine animal forests. Examples are marine animal forests dominated by cold-water stony corals, gorgonians, hydrocorals, brachiopods, polychaetes, giant barnacles, sponges, and ascidians. Many of these communities have been discov- ered only recently. There is also a singular characteristic in this area: exceptionally low pH levels of the waters of Patagonian fjords provide the opportunity to study calcifying organisms in an environment with pH conditions in the same range as the ones predicted by the IPCC for the world oceans in 2100. Despite the scarce ecological and biogeographical knowledge of this area, it encounters an unparalleled economic development including high-impact industry-scale salmonid farming, ambitious infrastructure and industrialization projects, and increasing extractive activities. Baseline research on the abiotic and biotic environment of the region is needed to reach sustainability in the use of the marine resources. Management plans including the establishment of marine protected areas to preserve benthic diversity and ecosystem services are urgently needed.

Description: Mineral ballasting enhances carbon export from the surface to the deep ocean; however, little is known about the role of this process in the ice-covered Arctic Ocean. Here, we propose gypsum ballasting as a new mechanism that likely facilitated enhanced vertical carbon export from an under-ice phytoplankton bloom dominated by the haptophyte Phaeocystis. In the spring 2015 abundant gypsum crystals embedded in Phaeocystis aggregates were collected throughout the water column and on the sea floor at a depth below 2 km. Model predictions supported by isotopic signatures indicate that 2.7 g m−2 gypsum crystals were formed in sea ice at temperatures below −6.5°C and released into the water column during sea ice melting. Our finding indicates that sea ice derived (cryogenic) gypsum is stable enough to survive export to the deep ocean and serves as an effective ballast mineral. Our findings also suggest a potentially important and previously unknown role of Phaeocystis in deep carbon export due to cryogenic gypsum ballasting. The rapidly changing Arctic sea ice regime might favour this gypsum gravity chute with potential consequences for carbon export and food partitioning between pelagic and benthic ecosystems.

Description: Sea-ice ecosystems are among the most extensive of Earth’s habitats; yet its autotrophic and heterotrophic activities remain poorly constrained. We employed the in situ aquatic eddy-covariance (AEC) O2 flux method and laboratory incubation techniques (H14CO3−, [3H] thymidine and [3H] leucine) to assess productivity in Arctic sea-ice using different methods, in conditions ranging from land-fast ice during winter, to pack ice within the central Arctic Ocean during summer. Laboratory tracer measurements resolved rates of bacterial C demand of 0.003–0.166 mmol C m−2 day−1 and primary productivity rates of 0.008–0.125 mmol C m−2 day−1 for the different ice floes. Pack ice in the central Arctic Ocean was overall net autotrophic (0.002–0.063 mmol C m−2 day−1), whereas winter land-fast ice was net heterotrophic (− 0.155 mmol C m−2 day−1). AEC measurements resolved an uptake of O2 by the bottom-ice environment, from ~ − 2 mmol O2 m−2 day−1 under winter land-fast ice to~ − 6 mmol O2 m−2 day−1 under summer pack ice. Flux of O2-deplete meltwater and changes in water flow velocity masked potential biological-mediated activity. AEC estimates of primary productivity were only possible at one study location. Here, productivity rates of 1.3 ± 0.9 mmol O2 m−2 day−1, much larger than concurrent laboratory tracer estimates (0.03 mmol C m−2 day−1), indicate that ice algal production and its importance within the marine Arctic could be underestimated using traditional approaches. Given careful flux interpretation and with further development, the AEC technique represents a promising new tool for assessing oxygen dynamics and sea-ice productivity in ice-covered regions.

Description: The study investigates the in-situ strength of sediments across a plate boundary décollement using drilling parameters recorded when a 1180-m-deep borehole was established during International Ocean Discovery Program (IODP)Expedition 370, Temperature-Limit of the Deep Biosphere off Muroto (T-Limit). Information of the in-situ strength of the shallow portion in/around a plate boundary fault zone is critical for understanding the development of accretionary prisms and of the décollement itself. Studies using seismic reflection surveys and scientific ocean drillings have recently revealed the existence of high pore pressure zones around frontal accretionary prisms, which may reduce the effective strength of the sediments. A direct measurement of in-situ strength by experiments, however, has not been executed due to the difficulty in estimating in-situ stress conditions. In this study, we derived a depth profile for the in-situ strength of a frontal accretionary prism across a décollement from drilling parameters using the recently established equivalent strength (EST) method. At site C0023, the toe of the accretionary prism area off Cape Muroto, Japan, the EST gradually increases with depth but undergoes a sudden change at ~ 800 mbsf, corresponding to the top of the subducting sediment. At this depth, directly below the décollement zone, the EST decreases from ~ 10 to 2 MPa, with a change in the baseline. This mechanically weak zone in the subducting sediments extends over 250 m (~ 800–1050 mbsf), corresponding to the zone where the fluid influx was discovered, and high-fluid pressure was suggested by previous seismic imaging observations. Although the origin of the fluids or absolute values of the strength remain unclear, our investigations support previous studies suggesting that elevated pore pressure beneath the décollement weakens the subducting sediments.

Description: Our knowledge on distribution, habitats and behavior of Southern Ocean fishes living at water depths beyond scuba-diving limits is still sparse, as it is difficult to obtain quantitative data on these aspects of their biology. Here, we report the results of an analysis of seabed images to investigate species composition, behavior, spatial distribution and preferred habitats of demersal fish assemblages in the southern Weddell Sea. Our study was based on a total of 2736 high-resolution images, covering a total seabed area of 11,317 m2, which were taken at 13 stations at water depths between 200 and 750 m. Fish were found in 380 images. A total of 379 notothenioid specimens were recorded, representing four families (Nototheniidae, Artedidraconidae, Bathydraconidae, Channichthyidae), 17 genera and 25 species. Nototheniidae was the most speciose fam- ily, including benthic species (Trematomus spp.) and the pelagic species Pleuragramma antarctica, which was occasionally recorded in dense shoals. Bathydraconids ranked second with six species, followed by artedidraconids and channichthyids, both with five species. Most abundant species were Trematomus scotti and T. lepidorhinus among nototheniids, and Dol- loidraco longedorsalis and Pagetopsis maculatus among artedidraconids and channichthyids, respectively. Both T. lepi- dorhinus and P. maculatus preferred seabed habitats characterized by biogenous debris and rich epibenthic fauna, whereas T. scotti and D. longedorsalis were frequently seen resting on fine sediments and scattered gravel. Several fish species were recorded to make use of the three-dimensional structure formed by epibenthic foundation species, like sponges, for perching or hiding inside. Nesting behavior was observed, frequently in association with dropstones, in species from various families, including Channichthyidae (Chaenodraco wilsoni and Pagetopsis macropterus) and Bathydraconidae (Cygnodraco mawsoni).

Description: Due to its year-round accessibility and excellent on-site infrastructure, Kongsfjorden and the Ny-Ålesund Research and Monitoring Facility have become established as a primary location to study the impact of environmental change on Arctic coastal ecosystems. Due to its location right at the interface of Arctic and Atlantic oceanic regimes, Kongsfjorden already experiences large amplitudes of variability in physico/chemical conditions and might, thus, be considered as an early warning indicator of future changes, which can then be extrapolated in a pan-Arctic perspective. Already now, Kongsfjorden represents one of the best-studied Arctic fjord systems. However, research conducted to date has concentrated largely on small disciplinary projects, prompting the need for a higher level of integration of future research activities. This contribution, thus, aims at identifying gaps in knowledge and research priorities with respect to ecological and adaptive responses to Arctic ecosystem changes. By doing so we aim to provide a stimulus for the initiation of new international and interdisciplinary research initiatives.

Description: This open access book presents the proceedings volume of the YOUMARES 8 conference, which took place in Kiel, Germany, in September 2017, supported by the German Association for Marine Sciences (DGM). The YOUMARES conference series is entirely bottom-up organized by and for YOUng MARine RESearchers. Qualified early career scientists moderated the scientific sessions during the conference and provided literature reviews on aspects of their research field. These reviews and the presenters’ conference abstracts are compiled here. Thus, this book discusses highly topical fields of marine research and aims to act as a source of knowledge and inspiration for further reading and research.

Description: Marine microbial biogeography has been studied intensively; however few studies address community variation across temporal and spatial scales simultaneously so far. Here we present a yearlong study investigating the dynamics of the free-living and particle-attached bacterioplankton community across a 100 km transect in the German Bight reaching from the Elbe estuary towards the open North Sea. Community composition was assessed using automated ribosomal intergenic spacer analysis and linked to environmental parameters applying multivariate statistical techniques. Results suggest that the spatial variation of the bacterioplankton community is defined by hydrographic current conditions, which separate the inner German Bight from the open North Sea and lead to pronounced differences in the coastal and offshore bacterioplankton community. However this spatial variation is overwhelmed by a strong temporal variation which is triggered by temperature as the main driving force throughout the whole transect. Variation in the free-living community was predominantly driven by temperature, whereas the particle-attached community exhibited stronger spatial variation patterns.