ALBERT

Beschreibung: New biostratigraphical, geochemical, and magnetic evidence is synthesized with IODP Expedition 352 shipboard results to understand the sedimentary and tectono-magmatic development of the Izu–Bonin outer forearc region. The oceanic basement of the Izu–Bonin forearc was created by supra-subduction zone seafloor spreading during early Eocene (c. 50–51 Ma). Seafloor spreading created an irregular seafloor topography on which talus locally accumulated. Oxide-rich sediments accumulated above the igneous basement by mixing of hydrothermal and pelagic sediment. Basaltic volcanism was followed by a hiatus of up to 15 million years as a result of topographic isolation or sediment bypassing. Variably tuffaceous deep-sea sediments were deposited during Oligocene to early Miocene and from mid-Miocene to Pleistocene. The sediments ponded into extensional fault-controlled basins, whereas condensed sediments accumulated on a local basement high. Oligocene nannofossil ooze accumulated together with felsic tuff that was mainly derived from the nearby Izu–Bonin arc. Accumulation of radiolarian-bearing mud, silty clay, and hydrogenous metal oxides beneath the carbonate compensation depth (CCD) characterized the early Miocene, followed by middle Miocene–Pleistocene increased carbonate preservation, deepened CCD and tephra input from both the oceanic Izu–Bonin arc and the continental margin Honshu arc. The Izu–Bonin forearc basement formed in a near-equatorial setting, with late Mesozoic arc remnants to the west. Subduction-initiation magmatism is likely to have taken place near a pre-existing continent–oceanic crust boundary. The Izu–Bonin arc migrated northward and clockwise to collide with Honshu by early Miocene, strongly influencing regional sedimentation.

Beschreibung: The potential harvest of polymetallic nodules will heavily impact the abyssal, soft sediment ecosystem by removing sediment, hard substrate, and associated fauna inside mined areas. It is therefore important to know whether the ecosystem can recover from this disturbance and if so at which rate. The first objective of this study was to measure recovery of phytodetritus processing by the benthic food web from a sediment disturbance experiment in 1989. The second objective was to determine the role of holothurians in the uptake of fresh phytodetritus by the benthic food web. To meet both objectives, large benthic incubation chambers (CUBEs; 50 × 50 × 50 cm) were deployed inside plow tracks (with and without holothurian presence) and at a reference site (holothurian presence, only) at 4100 m water depth. Shortly after deployment, 13C- and 15N-labeled phytodetritus was injected in the incubation chambers and during the subsequent 3-day incubation period, water samples were taken five times to measure the production of 13C-dissolved inorganic carbon over time. At the end of the incubation, holothurians and sediment samples were taken to determine biomass, densities and incorporation of 13C and 15N into bacteria, nematodes, macrofauna, and holothurians. For the first objective, the results showed that biomass of bacteria, nematodes and macrofauna did not differ between reference sites and plow track sites when holothurians were present. Additionally, meiofauna and macrofauna taxonomic composition was not significantly different between the sites. In contrast, total 13C uptake by bacteria, nematodes and holothurians was significantly lower at plow track sites compared to reference sites, though the number of replicates was low. This result suggests that important ecosystem functions such as organic matter processing have not fully recovered from the disturbance that occurred 26 years prior to our study. For the second objective, the analysis indicated that holothurians incorporated 2.16 × 10−3 mmol labile phytodetritus C m−2 d−1 into their biomass, which is one order of magnitude less as compared to bacteria, but 1.3 times higher than macrofauna and one order of magnitude higher than nematodes. Additionally, holothurians incorporated more phytodetritus carbon per unit biomass than macrofauna and meiofauna, suggesting a size-dependence in phytodetritus carbon uptake.

Beschreibung: Recently, measurements of oxygen concentration in the ocean-one of the most classical parameters in chemical oceanography-are experiencing a revival. This is not surprising, given the key role of oxygen for assessing the status of the marine carbon cycle and feeling the pulse of the biological pump. The revival, however, has to a large extent been driven by the availability of robust optical oxygen sensors and their painstakingly thorough characterization. For autonomous observations, oxygen optodes are the sensors of choice: They are used abundantly on Biogeochemical-Argo floats, gliders and other autonomous oceanographic observation platforms. Still, data quality and accuracy are often suboptimal, in some part because sensor and data treatment are not always straightforward and/or sensor characteristics are not adequately taken into account. Here, we want to summarize the current knowledge about oxygen optodes, their working principle as well as their behavior with respect to oxygen, temperature, hydrostatic pressure, and response time. The focus will lie on the most widely used and accepted optodes made by Aanderaa and Sea-Bird. We revisit the essentials and caveats of in-situ in air calibration as well as of time response correction for profiling applications, and provide requirements for a successful field deployment. In addition, all required steps to post-correct oxygen optode data will be discussed. We hope this summary will serve as a comprehensive, yet concise reference to help people get started with oxygen observations, ensure successful sensor deployments and acquisition of highest quality data, and facilitate post-treatment of oxygen data. In the end, we hope that this will lead to more and higher-quality oxygen observations and help to advance our understanding of ocean biogeochemistry in a changing ocean.

Beschreibung: Increasing interest in deep-sea mineral resources, such as polymetallic nodules, calls for environmental research about possible impacts of mineral exploitation on the deep-sea ecosystem. So far, little geochemical comparisons of deep-sea sediments before and after mining induced disturbances have been made, and thus long-term environmental effects of deep-sea mining are unknown. Here we present geochemical data from sediment cores from an experimental disturbance area at 4,100 m water depth in the Peru Basin. The site was revisited in 2015, 26 years after a disturbance experiment mimicking nodule mining was carried out and compared to sites outside the experimental zone which served as a pre-disturbance reference. We investigated if signs of the disturbance are still visible in the solid phase and the pore water after 26 years or if pre-disturbance conditions have been re-established. Additionally, a new disturbance was created during the cruise and sampled 5 weeks later to compare short- and longer-term impacts. The particulate fraction and pore water were analyzed for major and trace elements to study element distribution and processes in the surface sediment. Pore water and bottom water samples were also analyzed for oxygen, nitrate, dissolved organic carbon, and dissolved amino acids, to examine organic matter degradation processes. The study area of about 11 km2 was found to be naturally more heterogeneous than expected, requiring an analysis of spatial variability before the disturbed and undisturbed sites can be compared. The disturbed sites exhibit various disturbance features: some surface sediments were mixed through, others had the top layer removed and some had additional material deposited on top. Pore water constituents have largely regained pre-disturbance gradients after 26 years. The solid phase, however, shows clear differences between disturbed and undisturbed sites in the top 20 cm so that the impact is still visible in the plowed tracks after 26 years. Especially the upper layer, usually rich in manganese-oxide and associated metals, such as Mo, Ni, Co, and Cu, shows substantial differences in metal distribution. Hence, it can be expected that disturbances from polymetallic nodule mining will have manifold and long-lasting impacts on the geochemistry of the underlying sediment.

Beschreibung: Marine macrophytes are the foundation of algal forests and seagrass meadows-some of the most productive and diverse coastal marine ecosystems on the planet. These ecosystems provide nursery grounds and food for fish and invertebrates, coastline protection from erosion, carbon sequestration, and nutrient fixation. For marine macrophytes, temperature is generally the most important range limiting factor, and ocean warming is considered the most severe threat among global climate change factors. Ocean warming induced losses of dominant macrophytes along their equatorial range edges, as well as range extensions into polar regions, are predicted and already documented. While adaptive evolution based on genetic change is considered too slow to keep pace with the increasing rate of anthropogenic environmental changes, rapid adaptation may come about through a set of non-genetic mechanisms involving the functional composition of the associated microbiome, as well as epigenetic modification of the genome and its regulatory effect on gene expression and the activity of transposable elements. While research in terrestrial plants demonstrates that the integration of non-genetic mechanisms provide a more holistic picture of a species' evolutionary potential, research in marine systems is lagging behind. Here, we aim to review the potential of marine macrophytes to acclimatize and adapt to major climate change effects via intraspecific variation at the genetic, epigenetic, and microbiome levels. All three levels create phenotypic variation that may either enhance fitness within individuals (plasticity) or be subject to selection and ultimately, adaptation. We review three of the most important phenotypic variations in a climate change context, including physiological variation, variation in propagation success, and in herbivore resistance. Integrating different levels of plasticity, and adaptability into ecological models will allow to obtain a more holistic understanding of trait variation and a realistic assessment of the future performance and distribution of marine macrophytes. Such multi-disciplinary approach that integrates various levels of intraspecific variation, and their effect on phenotypic and physiological variation, is of crucial importance for the effective management and conservation of seagrasses and macroalgae under climate change.

Beschreibung: Two different photosystems for performing bacteriochlorophyll-mediated photosynthetic energy conversion are employed in different bacterial phyla. Those bacteria employing a photosystem II type of photosynthetic apparatus include the phototrophic purple bacteria (Proteobacteria), Gemmatimonas and Chloroflexus with their photosynthetic relatives. The proteins of the photosynthetic reaction center PufL and PufM are essential components and are common to all bacteria with a type-II photosynthetic apparatus, including the anaerobic as well as the aerobic phototrophic Proteobacteria. Therefore, PufL and PufM proteins and their genes are perfect tools to evaluate the phylogeny of the photosynthetic apparatus and to study the diversity of the bacteria employing this photosystem in nature. Almost complete pufLM gene sequences and the derived protein sequences from 152 type strains and 45 additional strains of phototrophic Proteobacteria employing photosystem II were compared. The results give interesting and comprehensive insights into the phylogeny of the photosynthetic apparatus and clearly define Chromatiales, Rhodobacterales, Sphingomonadales as major groups distinct from other Alphaproteobacteria, from Betaproteobacteria and from Caulobacterales (Brevundimonas subvibrioides). A special relationship exists between the PufLM sequences of those bacteria employing bacteriochlorophyll b instead of bacteriochlorophyll a. A clear phylogenetic association of aerobic phototrophic purple bacteria to anaerobic purple bacteria according to their PufLM sequences is demonstrated indicating multiple evolutionary lines from anaerobic to aerobic phototrophic purple bacteria. The impact of pufLM gene sequences for studies on the environmental diversity of phototrophic bacteria is discussed and the possibility of their identification on the species level in environmental samples is pointed out. © 2018 Imhoff, Rahn, Künzel and Neulinger.

Beschreibung: The maintenance and resilience of host-associated microbiota during development is a fundamental process influencing the fitness of many organisms. Several host properties were identified as influencing factors on bacterial colonization, including the innate immune system, mucus composition and diet. In contrast, the importance of bacteria-bacteria interactions on host colonization is less understood. Here, we use bacterial abundance data of the marine model organism Nematostella vectensis to reconstruct potential bacteria-bacteria interactions through co-occurrence networks. The analysis indicates that bacteria-bacteria interactions are dynamic during host colonization and change according to the host’s developmental stage. To assess the predictive power of inferred interactions, we tested bacterial isolates with predicted cooperative or competitive behavior for their ability to influence bacterial recolonization dynamics. Within three days of recolonization all tested bacterial isolates affected bacterial community structure, while only competitive bacteria increased bacterial diversity. Already one week after recolonization almost no differences in bacterial community structure could be observed between control and treatments. These results show that predicted competitive bacteria can influence community structure for a short period of time, verifying the in silico predictions. However, within one week, the effects of the bacterial isolates are neutralized, indicating a high degree of resilience of the bacterial community. Hanna Domin1, Yazmín H. Zurita-Gutiérrez2, Marco Scotti3, Jann Buttlar1, Ute Hentschel Humeida2 and Sebastian Fraune1*

Beschreibung: Silicon (Si) is the second most abundant element in the Earth’s crust and is an important nutrient in the ocean. The global Si cycle plays a critical role in regulating primary productivity and carbon cycling on the continents and in the oceans. Development of the analytical tools used to study the sources, sinks, and fluxes of the global Si cycle (e.g., elemental and stable isotope ratio data for Ge, Si, Zn, etc.) have recently led to major advances in our understanding of the mechanisms and processes that constrain the cycling of Si in the modern environment and in the past. Here, we provide background on the geochemical tools that are available for studying the Si cycle and highlight our current understanding of the marine, freshwater and terrestrial systems. We place emphasis on the geochemistry (e.g., Al/Si, Ge/Si, Zn/Si, δ13 C, δ15 N, δ18 O, δ30 Si) of dissolved and biogenic Si, present case studies, such as the Silicic Acid Leakage Hypothesis, and discuss challenges associated with the development of these environmental proxies for the global Si cycle. We also discuss how each system within the global Si cycle might change over time (i.e., sources, sinks, and processes) and the potential technical and conceptual limitations that need to be considered for future studies.

Beschreibung: The surface microlayer (SML) is the uppermost thin layer of the ocean and influencing interactions between the air and sea, such as gas exchange, atmospheric deposition and aerosol emission. Organic matter (OM) plays a key role in air-sea exchange processes, but studying how the accumulation of organic compounds in the SML relates to biological processes is impeded in the field by a changing physical environment, in particular wind speed and wave breaking. Here, we studied OM dynamics in the SML under controlled physical conditions in a large annular wind wave channel, filled with natural seawater, over a period of 26 days. Biology in both SML and bulk water was dominated by bacterioneuston and -plankton, respectively, while autotrophic biomass in the two compartments was very low. In general, SML thickness was related to the concentration of dissolved organic carbon (DOC) but not to enrichment of DOC or of specific OM components in the SML. Pronounced changes in OM enrichment and molecular composition were observed in the course of the study and correlated significantly to bacterial abundance. Thereby, hydrolysable amino acids, in particular arginine, were more enriched in the SML than combined carbohydrates. Amino acid composition indicated that less degraded OM accumulated preferentially in the SML. A strong correlation was established between the amount of surfactants coverage and γ-aminobutric acid, suggesting that microbial cycling of amino acids can control physiochemical traits of the SML. Our study shows that accumulation and cycling of OM in the SML can occur independently of recent autotrophic production, indicating a widespread biogenic control of process across the air-sea exchange.

Beschreibung: The Rare Earth Elements (REEs) have been widely used to investigate marine biogeochemical processes as well as the sources and mixing of water masses. However, there are still important uncertainties about the global aqueous REE cycle with respect to the contributions of highly reactive basaltic minerals originating from volcanic islands and the role of Submarine Groundwater Discharge (SGD). Here we present dissolved REE concentrations obtained from waters at the island-ocean interface (including SGD, river, lagoon and coastal waters) from the island of Tahiti and from three detailed open ocean profiles on the Manihiki Plateau (including neodymium (Nd) isotope compositions), which are located in ocean currents downstream of Tahiti. Tahitian fresh waters have highly variable REE concentrations that likely result from variable water–rock interaction and removal by secondary minerals. In contrast to studies on other islands, the SGD samples do not exhibit elevated REE concentrations but have distinctive REE distributions and Y/Ho ratios. The basaltic Tahitian rocks impart a REE pattern to the waters characterized by a middle REE enrichment, with a peak at europium similar to groundwaters and coastal waters of other volcanic islands in the Pacific. However, the basaltic island REE characteristics (with the exception of elevated Y/Ho ratios) are lost during transport to the Manihiki Plateau within surface waters that also exhibit highly radiogenic Nd isotope signatures. Our new data demonstrate that REE concentrations are enriched in Tahitian coastal water, but without multidimensional sampling, basaltic island Nd flux estimates range over orders of magnitude from relatively small to globally significant. Antarctic Intermediate Water (AAIW) loses its characteristic Nd isotopic signature (-6 to-9) around the Manihiki Plateau as a consequence of mixing with South Equatorial Pacific Intermediate Water (SEqPIW), which shows more positive values (-1 to -2). However, an additional Nd input/exchange along the pathway of AAIW, eventually originating from the volcanic Society, Tuamotu and Tubuai Islands (including Tahiti), is indicated by an offset from the mixing array of AAIW and SEqPIW to more radiogenic Nd isotope compositions.

Beschreibung: The benthic environment is a crucial component of marine systems in the provision of ecosystem services, sustaining biodiversity and in climate regulation, and therefore important to human society. With the contemporary increase in computational power, model resolution and technological improvements in quality and quantity of benthic data, it is necessary to ensure that benthic systems are appropriately represented in coupled benthic-pelagic biogeochemical and ecological modelling studies. In this paper we focus on five topical challenges related to various aspects of modelling benthic environments: organic matter reactivity, dynamics of benthic-pelagic boundary layer, microphytobenthos, biological transport and small-scale heterogeneity, and impacts of episodic events. We discuss current gaps in their understanding and indicate plausible ways ahead. Further, we propose a three-pronged approach for the advancement of benthic and benthic-pelagic modelling, essential for improved understanding, management and prediction of the marine environment. This includes: (A) development of a traceable and hierarchical framework for benthic-pelagic models, which will facilitate integration among models, reduce risk of bias, and clarify model limitations; (B) extended cross-disciplinary approach to promote effective collaboration between modelling and empirical scientists of various backgrounds and better involvement of stakeholders and end-users; (C) a common vocabulary for terminology used in benthic modelling, to promote model development and integration, and also to enhance mutual understanding.

Beschreibung: In the surface ocean, microorganisms are both a source of extracellular H2O2 and, via the production of H2O2 destroying enzymes, also one of the main H2O2 sinks. Within microbial communities, H2O2 sources and sinks may be unevenly distributed and thus microbial community structure could influence ambient extracellular H2O2 concentrations. Yet the biogeochemical cycling of H2O2 and other reactive oxygen species (ROS) is rarely investigated at the community level. Here, we present a time series of H2O2 concentrations during a 28-day mesocosm experiment where a pCO2 gradient (400–1,450 μatm) was applied to subtropical North Atlantic waters. Pronounced changes in H2O2 concentration were observed over the duration of the experiment. Initially H2O2 concentrations in all mesocosms were strongly correlated with surface H2O2 concentrations in ambient seawaters outside the mesocosms which ranged from 20 to 92 nM over the experiment duration (Spearman Rank Coefficients 0.79–0.93, p-values 〈 0.001–0.015). After approximately 9 days of incubation however, H2O2 concentrations had increased across all mesocosms, later reaching 〉300 nM in some mesocosms (2–6 fold higher than ambient seawaters). The correlation with ambient H2O2 was then no longer significant (p 〉 0.05) in all treatments. Furthermore, changes in H2O2 could not be correlated with inter-day changes in integrated irradiance. Yet H2O2 concentrations in most mesocosms were inversely correlated with bacterial abundance (negative Spearman Rank Coefficients ranging 0.59–0.94, p-values 〈 0.001–0.03). Our results therefore suggest that ambient H2O2 concentration can be influenced by microbial community structure with shifts toward high bacterial abundance correlated with low extracellular H2O2 concentrations. We also infer that the nature of mesocosm experiment design, i.e., the enclosure of water within open containers at the ocean surface, can strongly influence extracellular H2O2 concentrations. This has potential chemical and biological implications during incubation experiments due to the role of H2O2 as both a stressor to microbial functioning and a reactive component involved in the cycling of numerous chemical species including, for example, trace metals and haloalkanes.

Beschreibung: We have assessed how varying CO2 (180, 380, and 720 μatm) and growth light intensity (40 and 400 μmol photons m−2 s−1) affected Trichodesmium erythraeum IMS101 growth and photophysiology over free iron (Fe′) concentrations between 20 and 9,600 pM. We found significant iron dependencies of growth rate and the initial slope and maximal relative PSII electron transport rates (rPm). Under iron-limiting concentrations, high-light increased growth rates and rPm; possibly indicating a lower allocation of resources to iron-containing photosynthetic proteins. Higher CO2 increased growth rates across all iron concentrations, enabled growth to occur at lower Fe′ concentrations, increased rPm and lowered the iron half saturation constants for growth (Km). We attribute these CO2 responses to the operation of the CCM and the ATP spent/saved for CO2 uptake and transport at low and high CO2, respectively. It seems reasonable to conclude that T. erythraeum IMS101 can exhibit a high degree of phenotypic plasticity in response to CO2, light intensity and iron-limitation. These results are important given predictions of increased dissolved CO2 and water column stratification (i.e., higher light exposures) over the coming decades.

Beschreibung: The fluttering shearwater (Puffinus gavia) is an abundant seabird endemic to breeding colonies in northern and central New Zealand. The species remains poorly studied, and here we present the first study to examine its breeding biology in detail. Fluttering shearwater nests were monitored daily from laying in September 2015 to fledging in January 2016 on Burgess Island (Mokohinau Islands group) in the outer Hauraki Gulf, northern New Zealand. Burrows were generally simple and non-branched. Eggs were laid over a period of 39 days with laying peaking 12th September. Incubation was 50 ± 3.7 days and chicks fledged after an average of 74 ± 4.3 days, from late December to the end of January. Chick development corresponds to the pattern observed for other Procellariiformes, gaining body mass rapidly to a maximum of 115% of adult mass, and then losing weight until fledging. Chicks were fed most nights throughout chick-rearing, indicating adult birds have access to a stable food supply close to the colony. Breeding success was 63.8% and similar to other Puffinus species. This study provides baseline biological data for a poorly studied, yet common, New Zealand endemics seabird. The obtained new information will allow for further ecological investigations and improved conservation management for the species

Beschreibung: Salt marshes provide many key ecosystem services that have tremendous ecological and economic value. One critical service is the removal of fixed nitrogen from coastal waters, which limits the negative effects of eutrophication resulting from increased nutrient supply. Nutrient enrichment of salt marsh sediments results in higher rates of nitrogen cycling and, commonly, a concurrent increase in the flux of nitrous oxide, an important greenhouse gas. Little is known, however, regarding controls on the microbial communities that contribute to nitrous oxide fluxes in marsh sediments. To address this disconnect, we generated profiles of microbial communities and communities of micro-organisms containing specific nitrogen cycling genes that encode several enzymes (amoA, norB, nosZ) related to nitrous oxide flux from salt marsh sediments. We hypothesized that communities of microbes responsible for nitrogen transformations will be structured by nitrogen availability. Taxa that respond positively to high nitrogen inputs may be responsible for the elevated rates of nitrogen cycling processes measured in fertilized sediments. Our data show that, with the exception of ammonia-oxidizing archaea, the community composition of organisms involved in the production and consumption of nitrous oxide was altered under nutrient enrichment. These results suggest that previously measured rates of nitrous oxide production and consumption are likely the result of changes in community structure, not simply changes in microbial activity.

Beschreibung: Most eukaryotic species are colonized by a microbial community – the microbiota – that is acquired during early life stages and is critical to host development and health. Much research has focused on the microbiota biodiversity during the host life, however, empirical data on the basic ecological principles that govern microbiota assembly is lacking. Here we quantify the contribution of colonizer order, arrival time and colonization history to microbiota assembly on a host. We established the freshwater polyp Hydra vulgaris and its dominant colonizer Curvibacter as a model system that enables the visualization and quantification of colonizer population size at the single cell resolution, in vivo, in real time. We estimate the carrying capacity of a single Hydra polyp as 2 × 105 Curvibacter cells, which is robust among individuals and time. Colonization experiments reveal a clear priority effect of first colonizers that depends on arrival time and colonization history. First arriving colonizers achieve a numerical advantage over secondary colonizers within a short time lag of 24 h. Furthermore, colonizers primed for the Hydra habitat achieve a numerical advantage in the absence of a time lag. These results follow the theoretical expectations for any bacterial habitat with a finite carrying capacity. Thus, Hydra colonization and succession processes are largely determined by the habitat occupancy over time and Curvibacter colonization history. Our experiments provide empirical data on the basic steps of host-associated microbiota establishment – the colonization stage. The presented approach supplies a framework for studying habitat characteristics and colonization dynamics within the host–microbe setting.

Beschreibung: Seawater rare earth element (REE) concentrations are increasingly applied to reconstruct water mass histories by exploiting relative changes in the distinctive normalised patterns. However, the mechanisms by which water masses gain their patterns are yet to be fully explained. To examine this, we collected water samples along the Extended Ellett Line (EEL), an oceanographic transect between Iceland and Scotland, and measured dissolved REE by offline automated chromatography (SeaFAST) and ICP-MS. The proximity to two continental boundaries, the incipient spring bloom coincident with the timing of the cruise, and the importance of deep water circulation in this climatically sensitive gateway region make it an ideal location to investigate sources of REE to seawater and the effects of vertical cycling and lateral advection on their distribution. The deep waters have REE concentrations closest to typical North Atlantic seawater and are dominated by lateral advection. Comparison to published seawater REE concentrations of the same water masses in other locations provides a first measure of the temporal and spatial stability of the seawater REE signal. We demonstrate the REE pattern is replicated for Iceland-Scotland Overflow Water (ISOW) in the Iceland Basin from adjacent stations sampled 16 years previously. A recently published Labrador Sea Water (LSW) dissolved REE signal is reproduced in the Rockall Trough but shows greater light and mid REE alteration in the Iceland Basin, possibly due to the dominant effect of ISOW and/or continental inputs. An obvious concentration gradient from seafloor sediments to the overlying water column in the Rockall Trough, but not the Iceland Basin, highlights release of light and mid REE from resuspended sediments and pore waters, possibly a seasonal effect associated with the timing of the spring bloom in each basin. The EEL dissolved oxygen minimum at the permanent pycnocline corresponds to positive heavy REE enrichment, indicating maximum rates of organic matter remineralisation and associated REE release. We tentatively suggest a bacterial role to account for the observed heavy REE deviations. This study highlights the need for fully constrained REE sources and sinks, including the temporary nature of some sources, to achieve a balanced budget of seawater REE.

Beschreibung: Coastal marine environments are contaminated globally with a vast quantity of unexploded ordnance and munitions from intentional disposal. These munitions contain organic explosive compounds as well as a variety of metals, and represent point sources of chemical pollution to marine waters. Most underwater munitions originate from World Wars at the beginning of the twentieth century, and metal munitions housings have been impacted by extensive corrosion over the course of the following decades. As a result, the risk of munitions-related contaminant release to the water column is increasing. The behavior of munitions compounds is well-characterized in terrestrial systems and groundwater, but is only poorly understood in marine systems. Organic explosive compounds, primarily nitroaromatics and nitramines, can be degraded or transformed by a variety of biotic and abiotic mechanisms. These reaction products exhibit a range in biogeochemical characteristics such as sorption by particles and sediments, and variable environmental behavior as a result. The reaction products often exhibit increased toxicity to biological receptors and geochemical controls like sorption can limit this exposure. Environmental samples typically show low concentrations of munitions compounds in water and sediments (on the order of ng/L and μg/kg, respectively), and ecological risk appears generally low. Nonetheless, recent work demonstrates the possibility of sub-lethal genetic and metabolic effects. This review evaluates the state of knowledge on the occurrence, fate, and effect of munition-related chemical contaminants in the marine environment. There remain a number of knowledge gaps that limit our understanding of munitions-related contaminant spread and effect, and the need for additional work is made all the more urgent by increasing risk of release to the environment.

Beschreibung: Ocean acidification (OA) is expected to alter plankton community structure in the future ocean. This, in turn, could change the composition of sinking organic matter and the efficiency of the biological carbon pump. So far, most OA experiments involving entire plankton communities have been conducted in meso- to eutrophic environments. However, recent studies suggest that OA effects may be more pronounced during prolonged periods of nutrient limitation. In this study, we investigated how OA-induced changes in low-nutrient adapted plankton communities of the subtropical North Atlantic Ocean may affect particulate organic matter (POM) standing stocks, POM fluxes, and POM stoichiometry. More specifically, we compared the elemental composition of POM suspended in the water column to the corresponding sinking material collected in sediment traps. Three weeks into the experiment, we simulated a natural upwelling event by adding nutrient-rich deep-water to all mesocosms, which induced a diatom-dominated phytoplankton bloom. Our results show that POM was more efficiently retained in the water column in the highest CO2 treatment levels (〉 800 μatm pCO2) subsequent to this bloom. We further observed significantly lower C:N and C:P ratios in post-bloom sedimented POM in the highest CO2 treatments, suggesting that degradation processes were less pronounced. This trend is most likely explained by differences in micro- and mesozooplankton abundance during the bloom and post-bloom phase. Overall, this study shows that OA can indirectly alter POM fluxes and stoichiometry in subtropical environments through changes in plankton community structure.

Beschreibung: Climate models project that the Arctic Ocean may experience ice-free summers by the second half of this century. This may have severe repercussions on phytoplankton bloom dynamics and the associated cycling of carbon in surface waters. We currently lack baseline knowledge of the seasonal dynamics of Arctic microbial communities, which is needed in order to better estimate the effects of such changes on ecosystem functioning. Here we present a comparative study of polar summer microbial communities in the ice-free (eastern) and ice-covered (western) hydrographic regimes at the LTER HAUSGARTEN in Fram Strait, the main gateway between the Arctic and North Atlantic Oceans. Based on measured and modeled biogeochemical parameters, we tentatively identified two different ecosystem states (i.e., different phytoplankton bloom stages) in the distinct regions. Using Illumina tag-sequencing, we determined the community composition of both free-living and particle-associated bacteria as well as microbial eukaryotes in the photic layer. Despite substantial horizontal mixing by eddies in Fram Strait, pelagic microbial communities showed distinct differences between the two regimes, with a proposed early spring (pre-bloom) community in the ice-covered western regime (with higher representation of SAR11, SAR202, SAR406 and eukaryotic MALVs) and a community indicative of late summer conditions (post-bloom) in the ice-free eastern regime (with higher representation of Flavobacteria, Gammaproteobacteria and eukaryotic heterotrophs). Co-occurrence networks revealed specific taxon-taxon associations between bacterial and eukaryotic taxa in the two regions. Our results suggest that the predicted changes in sea ice cover and phytoplankton bloom dynamics will have a strong impact on bacterial community dynamics and potentially on biogeochemical cycles in this region.

Beschreibung: Deep-sea hydrothermal vents may provide one of the largest reservoirs on Earth for hydrogen-oxidizing microorganisms. Depending on the type of geological setting, hydrothermal environments can be considerably enriched in hydrogen (up to millimolar concentrations). As hot, reduced hydrothermal fluids ascend to the seafloor they mix with entrained cold, oxygenated seawater, forming thermal and chemical gradients along their fluid pathways. Consequently, in these thermally and chemically dynamic habitats biochemically distinct hydrogenases (adapted to various temperature regimes, oxygen and hydrogen concentrations) from physiologically and phylogenetically diverse Bacteria and Archaea can be expected. Hydrogen oxidation is one of the important inorganic energy sources in these habitats, capable of providing relatively large amounts of energy (237 kJ/mol H-2) for driving ATP synthesis and autotrophic CO2 fixation. Therefore, hydrogen-oxidizing organisms play a key role in deep-sea hydrothermal vent ecosystems as they can be considerably involved in light-independent primary biomass production. So far, the specific role of hydrogen-utilizing microorganisms in deep-sea hydrothermal ecosystems has been investigated by isolating hydrogen-oxidizers, measuring hydrogen consumption (ex situ), studying hydrogenase gene distribution and more recently by analyzing metatranscriptomic and metaproteomic data. Here we summarize this available knowledge and discuss the advent of new techniques for the identification of novel hydrogen-uptake and - evolving enzymes from hydrothermal vent microorganisms.

Beschreibung: The exchange of trace gases such as carbon dioxide or methane between the atmosphere and the ocean plays a key role for the climate system. However, the investigation of air–sea gas exchange rates lacks fast and accurate measurement techniques that can also be used in the field, e.g., onboard a ship on the ocean. A promising way to overcome this deficiency is to use heat as a proxy tracer for gas transfer. Heat transfer rates across the aqueous boundary layer of the air–water interface can be measured via thermography with unprecedented temporal and spatial resolution in the order of minutes and meters, respectively. Either passive or active measurement schemes can be applied. Passive approaches rely on temperature differences across the water surface, which are caused naturally by radiative and evaporative cooling of the water surface. Active measurement schemes force an artificial heat flux through the aqueous boundary layer by means of heating a patch at the water surface with an appropriate heat source, such as a CO2 laser. The choice of the excitation signal is crucial. It is beneficial to apply periodic heat flux densities with different excitation frequencies. In this way, the air–water interface can be probed for its response in terms of temperature amplitude and phase shift between excitation signal and temperature response. This concept from linear system theory is also well established in the field of non-destructive material testing, where it is known as lock-in thermography. This article gives a short introduction into air–sea gas exchange, before it presents an overview of different thermographic measurement techniques used in wind-wave facilities and at sea starting with early implementations. The article closes with a novel multifrequency excitation scheme for even faster measurements.

Beschreibung: Glyoxalase is one of two enzymes of the glyoxalase detoxification system against methylglyoxal and other aldehydes, the metabolites derived from glycolysis. The glyoxalase system is found almost in all living organisms: bacteria, protozoa, plants, and animals, including humans, and is related to the class of ‘life essential proteins’. The enzyme belongs to the expanded Glyoxalase/Bleomycin resistance protein/Dioxygenase superfamily. At present the GenBank contains about 700 of amino acid sequences of this enzyme type, and the Protein Data Bank includes dozens of spatial structures. We have offered a novel approach for structural identification of glyoxalase I protein family, which is based on the selecting of basic representative proteins with known structures. On this basis, six new subfamilies of these enzymes have been derived. Most populated subfamilies A1 and A2 were based on representative human Homo sapiens and bacterial Escherichia coli enzymes. We have found that the principle feature, which defines the subfamilies’ structural differences, is conditioned by arrangement of N- and C-domains inside the protein monomer. Finely, we have deduced the structural classification for the glyoxalase I and assigned about 460 protein sequences distributed among six new subfamilies. Structural similarities and specific differences of all the subfamilies have been presented. This approach can be used for structural identification of thousands of the so-called hypothetical proteins with the known PDB structures allowing to identify many of already existing atomic coordinate entrees.

Beschreibung: All around the world, beneath the seafloor, there are huge volumes of natural gas. But these are not the normal gas reservoirs that we collect to use for cooking, heating our homes, and making electricity in power stations. This gas is locked up in what we call gas hydrates. Gas hydrates are a solid form of water, rather like ice, that contains gas molecules locked up in a “cage” of water molecules. Gas hydrates are found on continental shelves around the world and in permafrost in the arctic. We are interested in gas hydrates because they could be used as a future source of natural gas. They are also important because they can cause large landslides on the seafloor, damaging offshore pipelines and cables and contributing to the formation of tsunami waves.

Beschreibung: Morphological variability in gorgonians is frequent and commonly associated with habitat variability, often resulting in segregated morphotypes. Paramuricea macrospina is an endemic Mediterranean gorgonian species found on rocky bottoms between 40 and 160 m depth and has recently been reported as one of the most abundant species in continental shelf and shelf edge environments. Three different chromatic forms of P. macrospina were observed in the Menorca Channel: a yellow form and a light purple form occurring on maërl beds of the continental shelf, and a dark purple form occurring on rocky substrates of the shelf edge. The objective of the present work is to verify if these P. macrospina forms may represent distinct taxonomic units by analysing differences in colony morphology and sclerite size and shape of the three chromatic forms. No significant differences were found in colony shape, suggesting that environmental variability between the continental shelf and the shelf edge is not influential enough to significantly alter colony morphology. Significant differences in sclerite size and shape were found amongst all forms, suggesting that sclerites may be influenced by environmental conditions. However, the co-occurrence of the yellow and light purple forms side by side on the continental shelf may indicate a certain degree of genetic differentiation.

Beschreibung: The feeding habits of two sympatric squid species, Uroteuthis (Photololigo) chinensis and Uroteuthis (Photololigo) duvaucelii from the southwestern Gulf of Thailand were studied. They fed on low numbers of food types (AF) and had a low diet breadth; 1.18 and 0.01 for U. (P.) chinensis and 1.49 and 0.05 for U. (P.) duvaucelii, respectively. Three major prey types (fishes, crustaceans and molluscs) were always detected and cannibalism was observed. Fish was the greatest contributor to the diet of both species, contributing 89.5% for U. (P.) chinensis and 69.9% for U. (P.) duvaucelii. Fish size significantly affected fullness index (FL) and AF for U. (P.) chinensis (P 〈 0.001) and U. (P.) duvaucelii (P 〈 0.001). Depth affected the FL of U. (P.) chinensis (P 〈 0.001) but not of U. (P.) duvaucelii (P 〉 0.05). Maturity stages of both male and female U. (P.) chinensis influenced FL (male: P 〈 0.001; female: P 〈 0.05) and AF (male: P 〈 0.05; female: P 〈 0.01). The FL of squid from cast nets was higher than those from trawls. The multivariate results showed dietary grouping between size classes of both species.

Beschreibung: Indian squid, Uroteuthis (Photololigo) duvaucelii (Loliginidae) constitute an important component of the inshore cephalopod fisheries along the eastern Arabian Sea. Local environmental variation plays an important role in species–environment interactions in neritic squids, which inhabit nearshore/coastal waters. Such ‘active’ and ‘passive’ responses of squids to environmental changes is crucial in understanding their relationships and influence on the biological processes, distribution and abundance of the fast-growing short-lived coastal loliginids. The empirical relationship between squid abundance and the variability in rainfall and sea surface temperature (SST) were explored in a tropical monsoon fishery. Monthly catch rates (catch per fishing hour) of squids in commercial trawl during 1987–2009 were used as the abundance index. Linear regression models with ARIMA errors were fitted with catch per unit hour time series as dependent variable and rainfall and SST as exogenous variables. While rainfall was observed to have a negative effect on squid abundance, the SST recorded a positive impact. ARIMA models provided satisfactory fit to observed data and forecast of 22 months. Given that the squid life-cycle is a function of their environment, this result is relevant in forecasting squid biomass for the management of tropical monsoon fisheries.

Beschreibung: The distribution pattern of purpleback flying squid and the relationship between its abundance and environmental variables in the south-eastern Arabian Sea were analysed using a geographical information system (GIS) and a generalised additive model (GAM). Highest abundances were observed during December and January within 10 and 13°N and 71 and 72°E around the Lakshadweep Islands. The mean abundance in the area was 4.21 tonnes/km2 and the maximum sustainable yield (MSY) was estimated as 0.63 million tonnes. GAM indicated that very high squid abundance was associated with low values of dissolved oxygen (6.01–6.27 mg/L), sea surface temperature (28.03–28.62°C), pH (7.75–8.56), salinity (30.42–34.48 psu), chlorophyll-a (0.4–0.6 mg/m3), zooplankton biomass (0.23–0.64 mL/m3), and shallow 20°C isotherm (101.2–134.7 m) and mixed layer depth (17.8–29.8 m). As a carnivore from paralarval stages, S. oualaniensis depends on secondary and tertiary production to sustain its population for which primary production is used up. In the tropical Arabian Sea where temperature differences are not so pronounced, S. oualaniensis distribution was found to be related to a low but very narrow sea surface temperature (SST) band. There is sufficient fishable biomass in the area to possibly launch a new targeted oceanic squid fishery from the western seaboard of India.

Beschreibung: The sea surface microlayer (SML) is located at the air-sea interface, with microorganisms and organic matter in the SML influencing air-sea exchange processes. Yet understanding of the SML bacterial (bacterioneuston) community composition and assembly remains limited. Availability of organic matter, UV radiation and wind speed have previously been suggested to influence the community composition of bacterioneuston. Another mechanism potentially controlling bacterioneuston dynamics is bacterioplankton attached to gel-like particles that ascend through the water column into the SML. We analyzed the bacterial community composition, Transparent Exopolymer Particles (TEP) abundance and nutrient concentrations in the surface waters of the Peruvian upwelling region. The bacterioneuston and bacterioplankton communities were similar, suggesting a close spatial coupling. Four Bacteroidetes families were significantly enriched in the SML, two of them, the Flavobacteriaceae and Cryomorphaceae, were found to comprise the majority of SML-enriched operational taxonomic units (OTUs). The enrichment of these families was controlled by a variety of environmental factors. The SML-enriched bacterial families were negatively correlated with water temperature and wind speed in the SML and positively correlated with nutrient concentrations, salinity and TEP in the underlying water (ULW). The correlations with nutrient concentrations and salinity suggest that the enriched bacterial families were more abundant at the upwelling stations.

Beschreibung: The environmental system of the northern Nordic Seas is very sensitive to oceanographic and climatic changes at the contact of cold Arctic and warmer North Atlantic waters. These contrasts are reflected in the associations of marine microorganisms and archived in the bottom sediments. A microfossil study (diatoms, coccoliths) of late Holocene sediments in core MSM5/5-712-1 from the eastern Fram Strait provides a better understanding of marine ecosystems and palaeoenvironments during Arctic warming events of the last two millennia. Indicative diatom species and groups of species revealed a high variability of sea-surface conditions. Based on the diatom distribution, three warming periods could be detected, corresponding to the time intervals of 0 to 440 CE (the later part of the Roman Warm Period), 1200 to1420 CE (the final part of the Medieval Climate Anomaly) and 1730 CE to present (including the Recent Warming). The various micropalaeontological proxies used in this study and other publications describe the Roman Warm Period and, especially, the Recent Warming as the most pronounced warm events in the area during the last 2000 years. A comparison of data from the different microfossil groups, indicators of sea-surface and subsurface conditions, reveals variable, complicated and non-simultaneous palaeoenvironmental signals within the warm periods. This can potentially be explained by changes in the surface/subsurface water structure during the events (variations in the cold/warm water advection, stratification, availability of nutrients, seasonal succession of bioproductivity, etc.), which are reflected by changes in the microplankton communities.

Beschreibung: Did you know that we have better maps of the moon, Mars, and Venus than we do of the seafloor on Earth? Since oceans cover 71% of the Earth’s surface, understanding what the seafloor looks like, and where different processes, such as ocean currents are active, is hugely important. Mapping the seafloor helps us to work out things like where different types of fish live, where we might find resources, such as rare metals and fossil fuels, and whether there is a risk of underwater landslides happening that might cause a tsunami. Mapping the seafloor is very challenging, because we cannot use the same techniques that we would use on land. To map the deep ocean, we use a tool called a multibeam echo-sounder, which is attached to a ship or a submarine vessel.

Beschreibung: Geoengineering is regarded by advocates as a creative and responsible technological option in the face of a climate emergency. Critics often see it as a hubristic attempt to play God, with disastrous consequences for the planet and humanity. These antipodal perspectives are represented by the ideal types of Prometheans and Gaians. Prometheans and Gaians typically talk past each other. The geoengineering debate can be made more fruitful by well articulating their respective positions and subsequently situating them in the discourse of sustainability. A sustainability orientation does not answer the troubling question whether geoengineering should be developed and deployed. But it can foster a ‘fusion of horizons’ between Prometheans and Gaians, providing common ground in an otherwise polarized debate and making a more productive dialogue possible.

Beschreibung: Wind, chemical enhancement, phytoplankton activity, and surfactants are potential factors driving the air-sea gas exchange of carbon dioxide (CO2). We investigated their effects on the gas transfer velocity of CO2 in a large annular wind-wave tank filled with natural seawater from the North Atlantic Ocean. Experiments were run under 11 different wind speed conditions (ranging from 1.5 ms−1 to 22.8 ms−1), and we increased the water pCO2 concentration twice by more than 950 μatm for two of the seven experimental days. We develop a conceptual box model that incorporated the thermodynamics of the marine CO2 system. Surfactant concentrations in the sea surface microlayer (SML) ranged from 301 to 1015 μgL−1 (as Triton X-100 equivalents) with enrichments ranged from 1.0 to 5.7 in comparison to the samples from the underlying bulk water. With wind speeds up to 8.5 ms−1, surfactants in the SML can reduce the gas transfer velocity by 54%. Wind-wave tank experiments in combination with modeling are useful tools for obtaining a better understanding of the gas transfer velocities of CO2 across the air-sea boundary. The tank allowed for measuring the gas exchange velocity under extreme low and high wind speeds; in contrast, most previous parametrizations have fallen short because measurements of gas exchange velocities in the field are challenging, especially at low wind conditions. High variability in the CO2 transfer velocities suggests that gas exchange is a complex process not solely controlled by wind forces, especially in low wind conditions.

Beschreibung: Microplastic contamination of aquatic environments has become an increasingly alarming problem. These, defined as particles 〈5 mm, are mostly formed due to the cracking and embrittlement of larger plastic particles. Recent reports show that the increasing presence of microplastics in the environment could have significant deleterious consequences over the health of marine organisms, but also across the food chain. Herein, we have studied the effects of artificial seawater on polyethylene (PE)-based beads by exposing them up to eight weeks to saltwater in stirred batch reactors in the dark and examined the structural and morphological changes these endured. Electron microscopy observations showed that artificial seawater induces severe microcracking of the pellets' surfaces. Additionally, Fourier transform infrared spectroscopy (FTIR) analyses evidenced the formation of oxidized groups whenever these particles were exposed to water and an increase in organic matter content of the waters in which the pellets were kept was evidenced by Raman spectroscopy. There were also noticeable consequences in the thermal stability of the polyethylene pellets, as determined by thermogravimetric studies (TGA). Furthermore, the parallel exposure of polyethylene pellets to UV radiation yielded less pronounced effects, thus underscoring its lower preponderance in the degradation of this material. These results highlight the importance of determining the mechanisms of degradation of microplastics in marine settings and what the implications may be for the environment. Overall, the herein presented results show that a relatively short period of time of accelerated exposure can yield quantifiable chemical and physical impacts on the structural and morphological characteristics of PE pellets.

Beschreibung: Hydroacoustic and optical remote sensing have been commonly used to map shallow nearshore benthic features. However, the number, type, scale, and accuracy of the mapping products that can be obtained from the two sensors differ; as such, there can be limited agreement between their mapping products. These differences can be further accentuated if the hydroacoustic data are interpolated to produce a map. Interpolation introduces spatial uncertainty and reduces map accuracy. Consequently, maps generated from the two sensors may provide dissimilar spatial and temporal representations of the same benthic features. We therefore compared the performance of a random forest regression (RFr) and a universal kriging (UK) interpolation method and a post-classification enhancement that can be used to increase the accuracy and complementarity of benthic habitat maps derived from hydroacoustic data. First, we used single beam echosounder (SBES) survey bathymetry data from the Bluefields Bay marine protected area (MPA) in western Jamaica (13.82 km2 in size), to create a bathymetric surface model (BSM), from which rugosity and bathymetric position index (BPI) maps were generated. Next, the RFr was used to create submerged aquatic vegetation (SAV) percentage cover maps from the SBES SAV cover data by predicting cover at un-sampled locations. Predictors included auxiliary data such as depth, BPI, survey points coordinates and radiometrically corrected, deglinted and water column corrected image reflectance index values from each of the following: WorldView-2, Geoeye-1 and Landsat 8. Additionally, a SAV map was created using the UK. The most accurate SAV cover thresholds were identified and were used to create binary maps from the RFr and UK maps. A rugosity derived coral reef map was then added to the binary maps. The resulting benthic habitat maps had comparable accuracies and class coverage to benthic maps classified from GeoEye-1 and WorldView-2 images using pixel and object-based classifiers. However, map accuracies were calculated using a suboptimal number of reference points (〈50) for two of the benthic map classes (SAV absent and coral reef). This was not considered to be problematic as the addition of the coral reef class to the binary maps resulted in a significant decrease in uncertainty (standard error and confidence interval width of the overall accuracy) and a significant increase in the user’s accuracy of the SAV absent map class. Also, the difference in uncertainty and accuracy between the map classes did not change. The methods used in this study can therefore be used to increase the accuracy (and to decrease the uncertainty) and the complementarity of maps derived from hydroacoustic data.

Beschreibung: A series of triaxial compression tests of frozen sandy soil are carried out under five confining pressures (1 MPa, 4 MPa, 6 MPa, 8 MPa and 10 MPa) at –6 °C. By comparing the grain size distribution curves of frozen sandy soil before and after shearing, it is found that significant particle breakage can occur during triaxial shearing. Particle breakage changes internal structure of geomaterials and has a significant effect on their stress–strain relationships. In order to accurately describe the effect of particle breakage of frozen sandy soil on the stress–strain relationships, an elastoplastic constitutive model for frozen sandy soil considering particle breakage is proposed. Based on the energy balance equation established by Indraratna and Salim, the constant critical state stress ratio (Mcr) in the energy balance equation is modified to the stress ratio (M) which changed with shear strain during the shearing process. A yield function, considering particle breakage, is proposed using the modified energy balance equation. The hardening law is determined based on the rebound test results of frozen sandy soil, and the associated flow rule is adopted in the model. Compared with experimental data, the model can well simulate the stress–strain relationships under different confining pressures for frozen sandy soil. • Highlights • The particle breakage characteristics of frozen sandy soil are studied. • The energy balance equation considering particle breakage is modified to calculate the energy dissipation of frozen sandy soil. • An elastoplastic constitutive model for frozen sandy soil considering particle breakage is proposed.

Beschreibung: Surfactant-mediated extraction (SME), pressurized liquid extraction (PLE), and enzyme-assisted extraction (EAE) have been compared to improve the isolation of phlorotannins from the brown algae Lobophora variegata. Enzymatic treatment with Alcalase 2.4 L FG, Carezyme 4500 L, protease from Streptomyces griseus, pectinase from Aspergillus niger, Celluclast 1.5 L, protease from Bacillus licheniformis; surfactant extraction with triacetin and guaiacol and PLE with ethanol:water as extracting solvent, have been studied in terms of total phenolic content by the Folin–Ciocalteu method and total phlorotannin content using the DMBA assay. The results showed that SME yields the highest amount of phenols and phlorotannins by using food grade guaiacol as the surfactant. An extraction protocol was developed to maximize the amount of extract obtained from L. variegata. The effects of various parameters such as the type of surfactant, efficacy of surfactant, and optimum pH, on the extraction efficiency of polyphenols were examined. The simultaneous use of the enzyme and surfactant was also investigated. However, a synergistic effect between the enzymes and the surfactant for the extraction of polyphenols has not been observed. Considering total phenols and total phlorotannins in the extract, the extraction yield were obtained for total phenols as SME 〉 EAE 〉 PLE and for total phlorotannins as SME 〉 PLE 〉 EAE.

Beschreibung: The Ponto-Caspian round goby (Neogobius melanostomus Pallas, 1814) is a prominent invasive species in many European waters. Eggs of the Western Baltic Spring Spawning Atlantic herring might be attractive prey for the invasive round goby during the spawning season. However, investigations of the small fish fauna in an important spawning area of herring, which was characterized by high densities of macrophytes, indicated a spatio-temporal mismatch of round goby and herring spawn in spring, at least on some of the known important spawning beds situated on vegetated sandy bottoms. In contrast, a spatio-temporal overlap between round gobies and herring spawn was observed in a more structured area, characterized with stones, where round gobies’ stomachs were sampled. Further field study results suggest that large round gobies (〉 10 cm) do not feed on herring eggs, while smaller round gobies (〈 10 cm) do so. To support these results, we conducted laboratory feeding experiments with round gobies. When C. crangon, M. edulis and herring eggs were offered simultaneously, round gobies preferred C. crangon. M. edulis was preferred over herring eggs when C. crangon was absent. The predatory impact of the round goby on herring eggs seems to be of minor importance compared to other species, such as three-spined stickleback or perch. Applying the same data, different food ‘preference indices’ revealed a discrepancy in preference between indices. Therefore, we propose a modified food preference index (mE), taking into account four important parameters and combining benefits of two commonly applied indices.

Beschreibung: Gas hydrates continue to attract enormous attention throughout the energy industry, as both a hindrance in conventional production and a substantial unconventional resource. Scientists continue to be fascinated by the hydrates’ ability of sequestering large amounts of hydrophobic gases, unusual thermal transport properties and unique molecular structures. Technologically, clathrate hydrates promise advantages in applications as diverse as carbon sequestration and water desalination. The communities interested in hydrates span traditional academic disciplines, including earth science, physical chemistry and petroleum engineering. The studies on this field are equally diverse, including field expeditions to attempt the production of natural gas from hydrate deposits accumulated naturally on the seafloor, to lab-scale studies to exchange CO2 for CH4 in hydrates; from theoretical studies to understand the stability of hydrates depending on the guest molecules, to molecular simulations probing nucleation mechanisms. This review highlights a few fundamental questions, with focus on knowledge gaps representing some of the barriers that must be addressed to enable growth in the practical applications of hydrate technology, including natural gas storage, water desalination, CO2 – CH4 exchange in hydrate deposits and prevention of hydrate plugs in conventional energy transportation.

Beschreibung: To enable successful management of marine bioinvasions, timely and robust scientific advice is required. This knowledge should inform managers and stakeholders on the magnitude of a pressure (rate of human-mediated introductions), the environmental state of an ecosystem (impacts of non-indigenous species), and the success of management response (prevention, eradication, mitigation). This advice often relies on baseline biodiversity information in the form of measureable parameters (metrics). This can be derived from conventional approaches such as visual surveys, but also by utilizing environmental DNA/RNA-based molecular techniques, which are increasingly being touted as promising tools for assessing biodiversity and detecting rare or invasive species. Depending on the stage of incursion, each approach has merits and limitations. In this review we assess the performance of biosecurity-relevant biodiversity parameters derived from eDNA/eRNA samples and discuss the results in relation to different stages of invasion and management applications. The overall performance of considered methods ranged between 42 and 90% based on defined criteria, with target-specific approaches scoring higher for respective biosecurity applications, followed by eDNA metabarcoding. Caveats are discussed along with avenues which may enhance these techniques and their successful uptake for marine biosecurity surveillance and management. To facilitate and encourage uptake of these techniques, there is a need for an international collaborative framework aimed at unifying molecular sampling and analysis methodologies. Improvement of quantitative capacity and cost-efficiency will also enhance their integration in biosecurity programmes.

Beschreibung: Little is known about the ecosystem effects of locally adapted populations. The filter feeding copepod Eurytemora affinis is an abundant and important zooplankton in coastal waters that consist of a cryptic species complex with locally adapted populations. We used a mesocosm setup to investigate population and ecosystem interactions of two populations from the Baltic Sea with different morphology and life history traits. One population is laterally wider, larger-sized, more fecund, and have higher growth rate than the other. The experimental ecosystems varied in algae community (pelagic algae, and pelagic algae + benthic diatoms) with two resource supply scenarios. Results showed that the large-sized population is a more effective grazer. In low resource supply the small-sized population starved, whereas the large-sized population was unaffected, resulting in a larger population increase of both nauplii and copepodites than for the small-sized population. Addition of benthic diatoms to the pelagic algae community had much more negative effects on the reproduction of the large-sized population. This suggests that the large-sized population feeds near benthic to a greater extent than the small-sized population, and that filamentous benthic diatoms interfere with the grazing process. Despite the negative effects of benthic diatoms, the large-sized population could maintain similar or higher reproduction than the small-sized population. In addition, the high grazing efficiency of the large-sized population resulted in a different community composition of algae. Specifically, flagellated species and small sized benthic diatoms were more grazed upon by the large-sized population. Our results show that morphologically divergent, yet phylogenetically closely related zooplankton populations can have different ecosystem functions, and in turn have different population increase in response to resource supply and algae community.

Beschreibung: Fermentation plays a fundamental role in organic carbon degradation on a global scale. However, little is known about how environmental variables influence this process. In a step towards quantifying how temperature and composition influence fermentation, we have calculated the Gibbs energies of 47 fermentation reaction, ΔGr, from 0–150 °C for a broad range of compositions representing microbial habitats as variable as sediments, estuaries, soils, and crustal rocks. The organic compounds in these reactions include amino acids, nucleic acid bases, monosaccharides, carboxylates, methanogenic compounds and more. The amount of energy available varies considerably, from +54 kJ (mol C)−1 for palmitate fermentation, to −184 kJ (mol C)−1 for methylamine disproportionation. For some reactions, there is little difference in ΔGr between low and high energy systems (e.g., the monosaccharide reactions) while others span a much broader range (e.g., the nucleic acid bases). There is no clear-cut trend between exergonicity and temperature, and the values of standard state Gibbs energies of reactions, ΔG0r, for nearly half of the reactions lie outside the range of ΔGr values. To carry out some of these calculations, the thermodynamic properties for six organic compounds were estimated: dimethylamine, trimethylamine, resorcinol, phloroglucinol and cyclohexane carboxylate and its conjugate acid.

Beschreibung: Staphylococcus epidermidis, the common inhabitant of human skin and mucosal surfaces has emerged as an important pathogen in patients carrying surgical implants and medical devices. Entering the body via surgical sites and colonizing the medical devices through formation of multi-layered biofilms leads to refractory and persistent device-related infections (DRIs). Staphylococci organized in biofilms are more tolerant to antibiotics and immune responses, and thus are difficult-to-treat. The consequent morbidity and mortality, and economic losses in health care systems has strongly necessitated the need for development of new anti-bacterial and anti-biofilm-based therapeutics. In this study, we describe the biological activity of a marine sponge-derived Streptomyces sp. SBT348 extract in restraining staphylococcal growth and biofilm formation on polystyrene, glass, medically relevant titan metal, and silicone surfaces. A bioassay-guided fractionation was performed to isolate the active compound (SKC3) from the crude SBT348 extract. Our results demonstrated that SKC3 effectively inhibits the growth (MIC: 31.25 μg/ml) and biofilm formation (sub-MIC range: 1.95–〈31.25 μg/ml) of S. epidermidis RP62A in vitro. Chemical characterization of SKC3 by heat and enzyme treatments, and mass spectrometry (HRMS) revealed its heat-stable and non-proteinaceous nature, and high molecular weight (1258.3 Da). Cytotoxicity profiling of SKC3 in vitro on mouse fibroblast (NIH/3T3) and macrophage (J774.1) cell lines, and in vivo on the greater wax moth larvae Galleria mellonella revealed its non-toxic nature at the effective dose. Transcriptome analysis of SKC3 treated S. epidermidis RP62A has further unmasked its negative effect on central metabolism such as carbon flux as well as, amino acid, lipid, and energy metabolism. Taken together, these findings suggest a potential of SKC3 as a putative drug to prevent staphylococcal DRIs.

Beschreibung: The impacts of biochemicals driving food web processes are under investigation for just the last few decades. In addition, as jellyfish are drawing increasing attentions because of their mass developments and of their potential capacity of driving food web structures and energy flow by ‘top-down’ and ‘bottom-up’ controls. We here show that the provision with the biochemical complex thiamin (vitamin B1) to the common phytoplankton Rhodomonas baltica altered its fatty acid (FA) pattern towards 3-highly-unsaturated FAs (3-HUFA) and that this pattern was further transferred up to the zooplankton consumer, the copepod Acartia tonsa. However, polyps of the Jellyfish Aurelia aurita feeding on A. tonsa only had a low relative 3-HUFA content, especially due to a reduction in 22:63 (DHA), but elevated levels of 20:46 (ARA). The high proportion of the -6 HUFA, ARA in polyps may provide evidence for preferential conversion of ARA in polyps, eventually from DHA in a so far unknown pathway. In contrast to A. tonsa, newly hatched A. salina nauplii used as food for A. aurita polyps were almost devoid of HUFA, but contained high levels of C18 polyunsaturated FAs (C18-PUFA). Consequently, polyps feeding on them contained few HUFA, while high levels of C18-PUFA predominated. This suggests that A. aurita polyps cannot efficiently convert 3 C18-PUFA to 3-HUFA. In addition, besides a decrease in saturated FAs, especially an increase in HUFA in A. aurita polyps with decreasing temperature was observed, for which the dietary provision with HUFA seemed to be critical. Altering the FA pattern as a response of temperature reflects an adaptation to seasonal changes and may be related to their life history plasticity.

Beschreibung: A large number of remarkable studies on the secondary metabolites of fungi have been conducted in recent years. This review gives an overview of one hundred and sixty-seven molecules with novel skeletons and their bioactivities that have been reported in seventy-nine articles published from 2013 to 2017. Our statistical data showed that endophytic fungi and marine-derived fungi are the major sources of novel bioactive secondary metabolites.

Beschreibung: Long-term time series data show that ocean acidification is occurring in the subtropical oceans. As a component of an in situ mesocosm experiment carried out offGran Canaria in the subtropical North Atlantic, we examined the influence of ocean acidification on the net production of dimethylsulfide (DMS). Over 23 days under oligotrophic conditions, time-integrated DMS concentrations showed an inverse relationship of -0.21 ± 0.02 nmol DMS nmol-1 H+ across the gradient of H+ concentration of 8.8-23.3 nmol l-1, equivalent to a range of pCO2 of 400-1,252 atm. Proportionally similar decreases in the concentrations of both dissolved and particulate dimethylsulfoniopropionate (DMSP) were observed in relation to increasing H+ concentration between the mesocosms. The reduced net production of DMSP with increased acidity appeared to result from a decrease in abundance of a DMSP-rich nanophytoplankton population. A 35S-DMSP tracer approach was used to determine rates of dissolved DMSP catabolism, including DMS production, across the mesocosm treatments. Over a phase of increasing DMS concentrations during the experiment, the specific rates of DMS production were significantly reduced at elevated H+ concentration. These rates were closely correlated to the rates of net DMS production indicating that transformation of dissolved DMSP to DMS by bacteria was a major component of DMS production. It was not possible to resolve whether catabolism of DMSP was directly influenced by H+ concentrations or was an indirect response in the bacterial community composition associated with reduced DMSP availability. There is a pressing need to understand how subtropical planktonic communities respond to the predicted gradual prolonged ocean acidification, as alterations in the emission of DMS from the vast subtropical oceans could influence atmospheric chemistry and potentially climate, over a large proportion of the Earth's surface.

Beschreibung: As an important DNA source, herbarium specimens have been widely used in plant phylogenetics due to their easy accessibility and richness. However, contamination is a constant risk owing to low quality and/or quantity of DNA extracted from old samples. The inclusion of contaminant sequences can mislead phylogenetic reconstruction, and thereby affect subsequent analyses, such as divergence time estimates and biogeographic inferences. To employ appropriately herbarium specimens in plant phylogenetics, we outline here several suggestions regarding DNA extraction, PCR amplification and sequencing. We hope that these suggestions will serve as a guide for researchers using herbarium specimens in plant phylogenetics and help them identify from the early steps potential contaminant sequences from other plants or other organisms.

Beschreibung: The subtropical oceans are home to one of the largest ecosystems on Earth, contributing to nearly one third of global oceanic primary production. Ocean warming leads to enhanced stratification in the oligotrophic ocean but also intensification in cross-shore wind gradients and thus in eddy kinetic energy across eastern boundary regions of the subtropical gyres. Phytoplankton thriving in a future warmer oligotrophic subtropical ocean with enhanced CO2 levels could therefore be patchily fertilized by increased mesoscale and submesoscale variability inducing nutrient pumping into the surface ocean. Under this premise, we have tested the response of three size classes (0.2-2, 2-20, and 〉 20 μm) of subtropical phytoplankton communities in terms of primary production, chlorophyll and cell biomass, to increasing CO2 concentrations and nutrient fertilization during an in situ mesocosm experiment in oligotrophic waters offof the island of Gran Canaria. We found no significant CO2-related effect on primary production and biomass under oligotrophic conditions (phase I). In contrast, primary production, chlorophyll and biomass displayed a significant and pronounced increase under elevated CO2 conditions in all groups after nutrient fertilization, both during the bloom (phase II) and post-bloom (phase III) conditions. Although the relative increase of primary production in picophytoplankton (250%) was 2.5 higher than in microphytoplankton (100%) after nutrient fertilization, comparing the high and low CO2 treatments, microphytoplankton dominated in terms of biomass, contributing 〉 57% to the total. These results contrast with similar studies conducted in temperate and cold waters, where consistently small phytoplankton benefitted after nutrient additions at high CO2, pointing to different CO2-sensitivities across plankton communities and ecosystem types in the ocean.

Beschreibung: Fungi represent a rich source of bioactive metabolites and some are marketed as alternatives to synthetic agrochemicals against plant pathogens. However, the culturability of fungal strains in artificial laboratory conditions is still limited and the standard mono-cultures do not reflect their full spectrum chemical diversity. Phytopathogenic fungi and bacteria have successfully been used in the activation of cryptic biosynthetic pathways to promote the production of new secondary metabolites in co-culture experiments. The aim of this study was to map the fungal diversity of Windebyer Noor, a brackish lake connected to Baltic Sea (Germany), to induce the chemical space of the isolated marine-adapted fungi by co-culturing with phytopathogens, and to assess their inhibitory potential against six commercially important phytopathogens. Out of 123 marine-adapted fungal isolates obtained, 21 were selected based on their phylogenetic and metabolite diversity. They were challenged with two phytopathogenic bacteria (Pseudomonas syringae and Ralstonia solanacearum) and two phytopathogenic fungi (Magnaporthe oryzae and Botrytis cinerea) on solid agar. An in-depth untargeted metabolomics approach incorporating UPLC–QToF–HRMS/MS-based molecular networking (MN), in silico MS/MS databases, and manual dereplication was employed for comparative analysis of the extracts belonging to nine most bioactive co-cultures and their respective mono-cultures. The phytopathogens triggered interspecies chemical communications with marine-adapted fungi, leading to the production of new compounds and enhanced expression of known metabolites in co-cultures. MN successfully generated a detailed map of the chemical inventory of both mono- and co-cultures. We annotated overall 18 molecular clusters (belonging to terpenes, alkaloids, peptides, and polyketides), 9 of which were exclusively produced in co-cultures. Several clusters contained compounds, which could not be annotated to any known compounds, suggesting that they are putatively new metabolites. Direct antagonistic effects of the marine-adapted fungi on the phytopathogens were observed and anti-phytopathogenic activity was demonstrated.The untargeted metabolomics approach combined with bioactivity testing allowed prioritization of two co-cultures for purification and characterization of marine fungal metabolites with crop-protective activity. To our knowledge, this is the first study employing plant pathogens to challenge marine-adapted fungi.

Beschreibung: Developing enduring capacity to monitor ocean life requires investing in people and their institutions to build infrastructure, ownership, and long-term support networks. International initiatives can enhance access to scientific data, tools and methodologies, and develop local expertise to use them, but without ongoing engagement may fail to have lasting benefit. Linking capacity development and technology transfer to sustained ocean monitoring is a win-win proposition. Trained local experts will benefit from joining global communities of experts who are building the comprehensive Global Ocean Observing System (GOOS). This two-way exchange will benefit scientists and policy makers in developing and developed countries. The first step toward the GOOS is complete: identification of an initial set of biological Essential Ocean Variables (EOVs) that incorporate the Group on Earth Observations (GEO) Essential Biological Variables (EBVs), and link to the physical and biogeochemical EOVs. EOVs provide a globally consistent approach to monitoring where the costs of monitoring oceans can be shared and where capacity and expertise can be transferred globally. Integrating monitoring with existing international reporting and policy development connects ocean observations with agreements underlying many countries' commitments and obligations, including under SDG 14, thus catalyzing progress toward sustained use of the ocean. Combining scientific expertise with international capacity development initiatives can help meet the need of developing countries to engage in the agreed United Nations (UN) initiatives including new negotiations for the conservation and sustainable use of marine biological diversity of areas beyond national jurisdiction, and the needs of the global community to understand how the ocean is changing.

Beschreibung: As an emerging technology, hyperspectral imaging (HSI), which combines both advanced spectroscopy and imaging techniques, provides sufficient information for spectral and spatial analysis and is thus suitable for distribution and property investigation of nanoscale materials. Considering the applications of HSI have spread from remote sensing to quality control of macro products such as food and milk, this article reviews recent research of HSI in a new field of nanoscale materials. On the basis of fundamental parts of a HSI system, new techniques fitting specifically for nanoscale materials imaging such as dark field and Raman spectroscopy are introduced. Nanoscale materials, including metal nanoparticles, carbon nanotubes and graphene, biological components in cells and tissues, as well as multi-layer nanoscale materials, are the research hotspots utilizing HSI technology. Related research reports of the above materials are reviewed based on the physical distinction of these nanoscale materials. It is believed that HSI technology is a strongly potential technique for property investigation and manipulation of nanomaterial for various applications.

Beschreibung: Anthropogenic Marine Debris (AMD) in the SE Pacific has primarily local origins from land-based sources, including cities (coastal and inland), beach-goers, aquaculture, and fisheries. The low frequency of AMD colonized by oceanic biota (bryozoans, lepadid barnacles) suggests that most litter items from coastal waters of the Humboldt Current System (HCS) are pulled offshore into the South Pacific Subtropical Gyre (SPSG). The highest densities of floating micro- and macroplastics are reported from the SPSG. An extensive survey of photographic records, unpublished data, conference proceedings, and published studies revealed interactions with plastics for 97 species in the SE Pacific, including 20 species of fish, 5 sea turtles, 53 seabirds, and 19 marine mammals. Sea turtles are most affected by interactions with plastics, underlined by the fact that 4 of the 5 species suffer both from entanglement and ingestion. Reports gathered in this review suggest that interactions along the continental coast are mostly via entanglement. High frequencies of microplastic ingestion have been reported from planktivorous fish and seabirds inhabiting the oceanic waters and islands exposed to high densities of microplastics concentrated by oceanic currents in the SPSG. Our review also suggests that some species from the highly productive HCS face the risk of negative interactions with AMD, because food and plastic litter are concentrated in coastal front systems. In order to improve the conservation of marine vertebrates, especially of sea turtles, urgent measures of plastic reduction are needed.

Beschreibung: The feeding habits of two sympatric squid species, Uroteuthis (Photololigo) chinensis and Uroteuthis (Photololigo) duvaucelii from the southwestern Gulf of Thailand were studied. They fed on low numbers of food types (AF) and had a low diet breadth; 1.18 and 0.01 for U. (P.) chinensis and 1.49 and 0.05 for U. (P.) duvaucelii, respectively. Three major prey types (fishes, crustaceans and molluscs) were always detected and cannibalism was observed. Fish was the greatest contributor to the diet of both species, contributing 89.5% for U. (P.) chinensis and 69.9% for U. (P.) duvaucelii. Fish size significantly affected fullness index (FL) and AF for U. (P.) chinensis (P 〈 0.001) and U. (P.) duvaucelii (P 〈 0.001). Depth affected the FL of U. (P.) chinensis (P 〈 0.001) but not of U. (P.) duvaucelii (P 〉 0.05). Maturity stages of both male and female U. (P.) chinensis influenced FL (male: P 〈 0.001; female: P 〈 0.05) and AF (male: P 〈 0.05; female: P 〈 0.01). The FL of squid from cast nets was higher than those from trawls. The multivariate results showed dietary grouping between size classes of both species.

Beschreibung: Climate change has profound impacts on marine biodiversity and biodiversity changes in turn might affect the community sensitivity to impacts of abiotic changes. We used mesocosm experiments and Next Generation Sequencing to study the response of the natural Baltic and Mediterranean unicellular eukaryotic plankton communities (control and +6oC heat shock) to subsequent salinity changes (-5 psu, +5 psu). The impact on Operational Taxonomic Unit (OTU) richness, taxonomic and functional composition and rRNA:rDNA ratios were examined. Our results showed that heat shock leads to lower OTU richness (21% fewer OTUs in the Baltic and 14% fewer in the Mediterranean) and a shift in composition towards pico- and nanophytoplankton and heterotrophic related OTUs. Heat shock also leads to increased rRNA:rDNA ratios for pico- and micrograzers. Less than 18% of shared OTUs were found among the different salinities indicating the crucial role of salinity in shaping communities. The response of rRNA:rDNA ratios varied highly after salinity changes. In both experiments the diversity decrease brought about by heat shock influenced the sensitivity to salinity changes. The heat shock either decreased or increased the sensitivity of the remaining community, depending on whether it removed the more salinity-sensitive or the salinity-tolerant taxa.

Beschreibung: Iron is required for microbial growth and proliferation. To survive in low-iron environments, some microorganisms secrete ferric iron chelators called siderophores. Siderophore biosynthesis occurs via two pathways: the non-ribosomal peptide synthetase (NRPS) pathway and the NRPS-independent siderophore (NIS) synthetase pathway. NIS enzymes function by adenylating a carboxylic acid substrate, typically citrate, or a derivative, followed by nucleophilic capture of an amine or alcohol and displacement of a citryl intermediate. In this review, we summarize recent advances in NIS biochemistry with a particular focus on structural biology and confirm the classification of NIS enzymes into Types A, A', B, and C based on substrate specificity. Based on a phylogenetic analysis, we also propose a new subclass of NIS enzymes, Type C', responsible for dimerization and macrocyclization of complex and substituted amine or amide intermediates. Finally, we describe the role of NIS enzymes in virulence of pathogenic microbes and discuss NIS inhibitors as potential anti-microbial agents.

Beschreibung: Fixed nitrogen (N) limits productivity across much of the low-latitude ocean. The magnitude of its inventory results from the balance of N input and N loss, the latter largely occurring in regionally well-defined low-oxygen waters and sediments (denitrification and anammox). The rate and distribution of N input by biotic N2 fixation, the dominant N source, is not well known. Here we compile N2 fixation estimates from experimental measurements, tracer-based geochemical and modelling approaches, and discuss their limitations and uncertainties. The lack of adequate experimental data coverage and the unsufficient understanding of the controls of marine N2 fixation result in high uncertainties, which make the assessment of the current N-balance a challenge. We suggest that a more comprehensive understanding of the environmental and ecological interaction of marine N2 fixers is required to advance the field towards robust N2 fixation rates estimates and predictions.

Beschreibung: The subtropical oceans are home to the largest phytoplankton biome on the planet. Yet, little is known about potential impacts of ocean acidification (OA) on phytoplankton community composition in the vast oligotrophic ecosystems of the subtropical gyres. To address this question, we conducted an experiment with 9 in situ mesocosms (~35 m3) off the coast of Gran Canaria in the eastern subtropical North Atlantic over a period of 9 weeks. By establishing a gradient of pCO2 ranging from ~350 to 1025 µatm, we simulated carbonate chemistry conditions as projected until the end of the 21st century. Furthermore, we injected nutrient-rich deep water into the mesocosms halfway through the experiment to simulate a natural upwelling event, which regularly leads to patchy nutrient fertilization in the study region. The temporal developments of major taxonomic groups of phytoplankton were analyzed by flow cytometry, pigment composition and microscopy. We observed distinct shifts in phytoplankton community structure in response to high CO2, with markedly different patterns depending on nutrient status of the system. Phytoplankton biomass during the oligotrophic phase was dominated by picocyanobacteria (Synechococcus), which constituted 60-80% of biomass and displayed significantly higher cell abundances at elevated pCO2. The addition of deep water triggered a substantial bloom of large, chain-forming diatoms (mainly Guinardia striata and Leptocylindrus danicus) that dominated the phytoplankton community during the bloom phase (70-80% of biomass) and until the end of the experiment. A CO2 effect on bulk diatom biomass became apparent only in the highest CO2 treatments (〉800 µatm), displaying elevated concentrations especially in the stationary phase after nutrient depletion. Notably, these responses were tightly linked to distinct interspecific shifts within the diatom assemblage, particularly favoring the largest species Guinardia striata. Other taxonomic groups contributed less to total phytoplankton biomass, but also displayed distinct responses to OA treatments. For instance, higher CO2 favored the occurrence of prymnesiophyceae (Phaeocystis globosa) and dictyochophyceae, whereas dinoflagellates were negatively affected by increasing CO2. Altogether, our findings revealed considerable shifts in species composition in response to elevated CO2 and indicated that phytoplankton communities in the subtropical oligotrophic oceans might be profoundly altered by ocean acidification.

Beschreibung: This work presents two new methods to estimate oceanic alkalinity (AT), dissolved inorganic carbon (CT), pH, and pCO2 from temperature, salinity, oxygen, and geolocation data. “CANYON-B” is a Bayesian neural network mapping that accurately reproduces GLODAPv2 bottle data and the biogeochemical relations contained therein. “CONTENT” combines and refines the four carbonate system variables to be consistent with carbonate chemistry. Both methods come with a robust uncertainty estimate that incorporates information from the local conditions. They are validated against independent GO-SHIP bottle and sensor data, and compare favorably to other state-of-the-art mapping methods. As “dynamic climatologies” they show comparable performance to classical climatologies on large scales but a much better representation on smaller scales (40–120 d, 500–1,500 km) compared to in situ data. The limits of these mappings are explored with pCO2 estimation in surface waters, i.e., at the edge of the domain with high intrinsic variability. In highly productive areas, there is a tendency for pCO2 overestimation due to decoupling of the O2 and C cycles by air-sea gas exchange, but global surface pCO2 estimates are unbiased compared to a monthly climatology. CANYON-B and CONTENT are highly useful as transfer functions between components of the ocean observing system (GO-SHIP repeat hydrography, BGC-Argo, underway observations) and permit the synergistic use of these highly complementary systems, both in spatial/temporal coverage and number of observations. Through easily and robotically-accessible observations they allow densification of more difficult-to-observe variables (e.g., 15 times denser AT and CT compared to direct measurements). At the same time, they give access to the complete carbonate system. This potential is demonstrated by an observation-based global analysis of the Revelle buffer factor, which shows a significant, high latitude-intensified increase between +0.1 and +0.4 units per decade. This shows the utility that such transfer functions with realistic uncertainty estimates provide to ocean biogeochemistry and global climate change research. In addition, CANYON-B provides robust and accurate estimates of nitrate, phosphate, and silicate. Matlab and R code are available at https://github.com/HCBScienceProducts/. Introduction

Beschreibung: The Paris Agreement target of limiting global surface warming to 1.5–2∘C compared to pre-industrial levels by 2100 will still heavily impact the ocean. While ambitious mitigation and adaptation are both needed, the ocean provides major opportunities for action to reduce climate change globally and its impacts on vital ecosystems and ecosystem services. A comprehensive and systematic assessment of 13 global- and local-scale, ocean-based measures was performed to help steer the development and implementation of technologies and actions toward a sustainable outcome. We show that (1) all measures have tradeoffs and multiple criteria must be used for a comprehensive assessment of their potential, (2) greatest benefit is derived by combining global and local solutions, some of which could be implemented or scaled-up immediately, (3) some measures are too uncertain to be recommended yet, (4) political consistency must be achieved through effective cross-scale governance mechanisms, (5) scientific effort must focus on effectiveness, co-benefits, disbenefits, and costs of poorly tested as well as new and emerging measures.

Beschreibung: Hydrothermal precipitates and hydrothermal alteration products could record important information about temporal variations of seafloor hydrothermal systems. Geochemistry, mineralogy, and microscopic features of three pumice samples (T3-1, T3-2, and T3-3) near the Iheya North hydrothermal field were analyzed in this article. The results show that T3-3 sample has undergone at least two-stage influences by hydrothermal fluids. In the first stage, pure amorphous silica from hydrothermal fluid precipitated in the vesicles of all three T3 samples as a result of conductive cooling and fluid–seawater mixing. The precipitation temperatures according to oxygen isotope thermometer are approximately 13–21°C. In the second stage, T3-3 pumice underwent low-temperature hydrothermal alteration, during which the amorphous silica precipitates were redissolved, together resulting in losses of FeO and SiO2 and gains of MgO, Pb, Zn, and Cu. Furthermore, ferruginous filamentous silica, which might be related to activities of Fe-oxidizing bacteria, was formed in the altered pumice. The transformation from pure amorphous silica precipitation to redissolution of the silica in T3-3 pumice might indicate a rise of temperature and/or decrease in silica concentrations in hydrothermal fluids, implying a changing hydrothermal environment.

Beschreibung: In coastal temperate regions such as the Baltic Sea, calcifying bivalves dominate benthic communities playing a vital ecological role in maintaining biodiversity and nutrient recycling. At low salinities, bivalves exhibit reduced growth and calcification rates which is thought to result from physiological constraints associated with osmotic stress. Calcification demands a considerable amount of energy in calcifying molluscs and estuarine habitats provide sub-optimal conditions for calcification due to low concentrations of calcification substrates and large variations in carbonate chemistry. Therefore, we hypothesize that slow growth rates in estuarine bivalves result from increased costs of calcification, rather than costs associated with osmotic stress. To investigate this, we estimated the cost of calcification for the first time in benthic bivalve life stages and the relative energy allocation to calcification in three Mytilus populations along the Baltic salinity gradient. Our results indicate that calcification rates are significantly reduced only in 6 psu populations compared to 11 and 16 psu populations, coinciding with ca. 2–3-fold higher calcification costs at low salinity and temperature. This suggests that reduced growth of Baltic Mytilus at low salinities results from increased calcification costs rather than osmotic stress related costs. We also reveal that shell growth (both calcification and shell organic production) demands 31–60% of available assimilated energy from food, which is significantly higher than previous estimates. Energetically expensive calcification represents a major constraint on growth of mytilids in the estuarine and coastal seas where warming, acidification and desalination are predicted over the next century.

Beschreibung: Planktonic Foraminifera and thecosome pteropods are major producers of calcite and aragonite in the ocean and play an important role for pelagic carbonate flux. The responses of planktonic foraminifers to ocean acidification (OA) are variable among the species tested and so far do not allow for reliable conclusion. Thecosome pteropods respond with reduced calcification and shell dissolution to OA and are considered at high risk especially at high latitudes. The present investigation was part of a large-scale in situ mesocosm experiment in the oligotrophic waters of the eastern subtropical North Atlantic. Over 62 days, we measured the abundance and vertical flux of pelagic foraminifers and thecosome pteropods as part of a natural plankton community over a range of OA scenarios. A bloom phase was initiated by the introduction of deep-water collected from approx. 650 m depth simulating a natural up-welling event. Foraminifers occurred throughout the entire experiment in both the water column and the sediment traps. Pteropods were present only in small numbers and disappeared after the first two weeks of the experiment. No significant CO2 related effects were observed for foraminifers, but cumulative sedimentary flux was reduced at the highest CO2 concentrations. This flux reduction was most likely accompanying an observed flux reduction of particulate organic matter (POM) so that less foraminifers were intercepted and transported downward.

Beschreibung: We propose a geochemical parameter, “metal flux” in evaluating hydrogenetic Co-rich ferromanganese crust deposits in the Pacific seamount area, that is based on physical, chemical, and geological characterization of the integrated growth piles of crusts. We calculated the metal flux for fifteen sites from different depths ranging between 900-6000m from different seamounts. The secular and areal variations of metal flux indicate a strong geological controls, and also can be a reliable tool for estimating an economic potential of the crusts. The Co flux decreases with increasing water depth, followed by almost constant flux of Ni and Mn. The Al and Fe fluxes vary with regions, indicating higher values in the western regions near the island arc probably related to a supply from the Asian continents. The results imply that Co, a redox sensitive metal element, is controlled by redox conditions of seawater, while Fe and Al are by terrigenous input. The metal flux reflects global and regional conditions and controls the compositional diversity of metals, thus consequently, the parameter can be a reliable powerful tool to estimate or single out more potential areas.

Beschreibung: The enzymatic electron transport system (ETS) assay is frequently used as a proxy of respiratory activity in planktonic communities. It is thought to estimate the maximum overall activity of the enzymes associated with the respiratory ETS systems in both eukaryotic and prokaryotic organisms. Thus, in order to derive actual respiration rates (R) from ETS it is necessary to determine empirical R/ETS conversion algorithms. In this study we explore the temporal development of R and ETS activity in natural plankton communities (from bacteria to large phytoplankton) enclosed in mesocosms, treated with different CO2 concentrations. The experiment lasted 30 days, during which abrupt changes in community structure and biomass occurred through a sharp transition from oligotrophy (phase I) to highly eutrophic conditions (phase II) after nutrient-induced fertilization (day 18). R and ETS did not show any response to CO2 under oligotrophic conditions, but R increased significantly more in the two high CO2 mesocosms after fertilization, coinciding with a sharp rise in large phytoplankton (mostly diatoms). R and ETS were significantly correlated only during the eutrophic phase. The R/ETS ranged more than threefold in magnitude during the experiment, with phase-averaged values significantly higher under oligotrophic conditions (0.7-1.1) than after nutrient fertilization (0.5-0.7). We did not find any significant relationship between R/ETS and community structure or biomass, although R correlated significantly with total biomass after fertilization in the four mesocosms. Multiple stepwise regression models show that large phytoplankton explains most of the variance in R during phases I (86%) and II (53%) and of ETS (86%) during phase II, while picophytoplankton contributes up to 73% to explain the variance in the ETS model during phase I. Our results suggest that R/ETS may be too variable in the ocean as to apply constant values to different communities living under contrasting environmental conditions. Controlled experiments with natural communities, like the present one, would help to constrain the range of variability of the R/ETS ratio, and to understand the factors driving it.

Beschreibung: Submarine volcanic eruptions are difficult to detect because they are hidden from view at the bottom of the ocean and far from land-based sensors. However, most of Earth’s volcanic activity is in the oceans along tectonic plate boundaries, and modern tools of oceanography now allow us to find and study recent eruptions in the deep sea. The first known historical eruption on the Mariana back-arc spreading center was discovered in December 2015 during exploration of the southern back-arc for new hydrothermal vent sites. A water-column survey along the axis of the back-arc showed hydrothermal plumes over the site characterized by low particle concentrations and relatively high reduced chemical anomalies. A dive with the autonomous underwater vehicle Sentry collected high-resolution (1 m) multibeam sonar bathymetry over the site, followed by a near-bottom photographic survey of a smaller area. The photo survey revealed the presence of a pristine, dark, glassy lava flow on the seafloor with no sediment cover. Venting of milky hydrothermal fluid indicated that the lava flow was still warm and therefore very young. A comparison of multibeam sonar bathymetry collected by R/V Falkor in December 2015, to the most recent previous survey of the area by R/V Melville in February 2013, revealed large depth changes in the same area, effectively bracketing the timing of the eruption within a window of less than 3 years. The bathymetric comparison shows the eruption produced a string of lava flows with maximum thicknesses of 40–138 m along a distance of 7.3 km (from latitude 15∘22.3′ to 15∘26.3′N) between depths of 4050–4450 m bsl (meters below sea level), making this the deepest known historical submarine volcanic eruption on Earth. The cross-axis width of the lava flows is 200–800 m. The Sentry bathymetry shows that the new lava flows are constructed of steep-sided hummocky pillow mounds and are surrounded by older flows with similar morphology. In April and December 2016, two dives were made on the new lava flows by remotely operated vehicles Deep Discoverer and SuBastian. The pillow lavas have many small glassy buds on the steep flanks of the mounds, locally thick accumulations of hydrothermal sediment near the tops of mounds, and small cones of radiating pillows at their summits. The 2015–2016 observations show a rapidly declining hydrothermal system on the lava flows, suggesting that the eruption had occurred only months before its discovery in December 2015. The morphology of the pillow lavas is similar to other historical eruption sites, so the greater depth and ambient pressure of this site had no apparent effect on the processes of lava extrusion and emplacement. This study reveals that some segments of the Mariana back-arc have active magmatic systems despite the relatively low spreading rate, and that other eruptions are possible in the near future.

Beschreibung: Digestive system functionality of fish larvae relies on the onset of genetically pre-programmed and extrinsically influenced digestive functions. This study explored how algal supplementation (green-water) until 14 days post hatch (dph) and the ingestion of food [enriched rotifer (Brachionus plicatilis) paste] from 15 dph onward affects molecular maturation and functionality of European eel larval ingestion and digestion mechanisms. For this, we linked larval biometrics to expression of genes relating to appetite [ghrelin (ghrl), cholecystokinin (cck)], food intake [proopiomelanocortin (pomc)], digestion [trypsin (try), triglyceride lipase (tgl), amylase (amyl)], energy metabolism [ATP synthase F0 subunit 6 (atp6), cytochrome-c-oxidase 1 (cox1)], growth [insulin-like growth factor (igf1)] and thyroid metabolism [thyroid hormone receptors (thrαA, thrβB)]. Additionally, we estimated larval nutritional status via nucleic acid analysis during transition from endogenous and throughout the exogenous feeding stage. Results showed increased expression of ghrl and cck on 12 dph, marking the beginning of the first-feeding window, but no benefit of larviculture in green-water was observed. Moreover, expression of genes relating to protein (try) and lipid (tgl) hydrolysis revealed essential digestive processes occurring from 14 to 20 dph. On 16 dph, a molecular response to initiation of exogenous feeding was observed in the expression patterns of pomc, atp6, cox1, igf1, thrαA and thrβB. Additionally, we detected increased DNA contents, which coincided with increased RNA contents and greater body area, reflecting growth in feeding compared to non-feeding larvae. Thus, the here applied nutritional regime facilitated a short-term benefit, where feeding larvae were able to sustain growth and better condition than their non-feeding conspecifics. However, RNA:DNA ratios decreased from 12 dph onward, indicating a generally low larval nutritional condition, probably leading to the point-of-no-return and subsequent irreversible mortality due to unsuccessful utilization of exogenous feeding. In conclusion, this study molecularly identified the first-feeding window in European eel and revealed that exogenous feeding success occurs concurrently with the onset of a broad array of enzymes and hormones, which are known to regulate molecular processes in feeding physiology. This knowledge constitutes essential information to develop efficient larval feeding strategies and will hopefully provide a promising step toward sustainable aquaculture of European eel.

Beschreibung: Ocean acidification (OA) is affecting marine ecosystems through changes in carbonate chemistry that may influence consumers of phytoplankton, often via trophic pathways. Using a mesocosm approach, we investigated OA effects on a subtropical zooplankton community during oligotrophic, bloom, and post-bloom phases under a range of different pCO2 levels (from ∼400 to ∼1480 μatm). Furthermore, we simulated an upwelling event by adding 650 m-depth nutrient-rich water to the mesocosms, which initiated a phytoplankton bloom. No effects of pCO2 on the zooplankton community were visible in the oligotrophic conditions before the bloom. The zooplankton community responded to phytoplankton bloom by increased abundances in all treatments, although the response was delayed under high-pCO2 conditions. Microzooplankton was dominated by small dinoflagellates and aloricate ciliates, which were more abundant under medium- to high-pCO2 conditions. The most abundant mesozooplankters were calanoid copepods, which did not respond to CO2 treatments during the oligotrophic phase of the experiment but were found in higher abundance under medium- and high-pCO2 conditions toward the end of the experiment, most likely as a response to increased phyto- and microzooplankton standing stocks. The second most abundant mesozooplankton taxon were appendicularians, which did not show a response to the different pCO2 treatments. Overall, CO2 effects on zooplankton seemed to be primarily transmitted through significant CO2 effects on phytoplankton and therefore indirect pathways. We conclude that elevated pCO2 can change trophic cascades with significant effects on zooplankton, what might ultimately affect higher trophic levels in the future.

Beschreibung: Rapid mass loss from the Greenland Ice Sheet (GrIS) is affecting sea level and, through increased freshwater and sediment discharge, ocean circulation, sea-ice, biogeochemistry, and marine ecosystems around Greenland. Key to interpreting ongoing and projecting future ice loss, and its impact on the ocean, is understanding exchanges of heat, freshwater, and nutrients that occur at the GrIS marine margins. Processes governing these exchanges are not well understood because of limited observations from the regions where glaciers terminate into the ocean and the challenge of modeling the spatial and temporal scales involved. Thus, notwithstanding their importance, ice sheet/ocean exchanges are poorly represented or not accounted for in models used for projection studies. Widespread community consensus maintains that concurrent and long-term records of glaciological, oceanic, and atmospheric parameters at the ice sheet/ocean margins are key to addressing this knowledge gap by informing understanding, and constraining and validating models. Through a series of workshops and documents endorsed by the community-at-large, a framework for an international, collaborative, Greenland Ice sheet-Ocean Observing System (GrIOOS), that addresses the needs of society in relation to a changing GrIS, has been proposed. This system would consist of a set of ocean, glacier, and atmosphere essential variables to be collected at a number of diverse sites around Greenland for a minimum of two decades. Internationally agreed upon data protocols and data sharing policies would guarantee uniformity and availability of the information for the broader community. Its development, maintenance, and funding will require close international collaboration. Engagement of end-users, local people, and groups already active in these areas, as well as synergy with ongoing, related, or complementary networks will be key to its success and effectiveness.

Beschreibung: The tropical Atlantic is home to multiple coupled climate variations covering a wide range of timescales and impacting societally relevant phenomena such as continental rainfall, Atlantic hurricane activity, oceanic biological productivity, and atmospheric circulation in the equatorial Pacific. The tropical Atlantic also connects the southern and northern branches of the Atlantic meridional overturning circulation and receives freshwater input from some of the world’s largest rivers. To address these diverse, unique, and interconnected research challenges, a rich network of ocean observations has developed, building on the backbone of the Prediction and Research Moored Array in the Tropical Atlantic (PIRATA). This network has evolved naturally over time and out of necessity in order to address the most important outstanding scientific questions and to improve predictions of tropical Atlantic severe weather and global climate variability and change. The tropical Atlantic observing system is motivated by goals to understand and better predict phenomena such as tropical Atlantic interannual to decadal variability and climate change; multidecadal variability and its links to the meridional overturning circulation; air-sea fluxes of CO2 and their implications for the fate of anthropogenic CO2; the Amazon River plume and its interactions with biogeochemistry, vertical mixing, and hurricanes; the highly productive eastern boundary and equatorial upwelling systems; and oceanic oxygen minimum zones, their impacts on biogeochemical cycles and marine ecosystems, and their feedbacks to climate. Past success of the tropical Atlantic observing system is the result of an international commitment to sustained observations and scientific cooperation, a willingness to evolve with changing research and monitoring needs, and a desire to share data openly with the scientific community and operational centers. The observing system must continue to evolve in order to meet an expanding set of research priorities and operational challenges. This paper discusses the tropical Atlantic observing system, including emerging scientific questions that demand sustained ocean observations, the potential for further integration of the observing system, and the requirements for sustaining and enhancing the tropical Atlantic observing system.

Beschreibung: Ultraslow spreading ridges account for one-third of the global mid-ocean ridges. Their impact on the diversity and connectivity of benthic deep-sea microbial assemblages is poorly understood, especially for hydrothermally inactive, magma-starved ridges. We investigated bacterial and archaeal diversity in sediments collected from an amagmatic segment (10∘–17∘E) of the Southwest Indian Ridge (SWIR) and in the adjacent northern and southern abyssal zones of similar water depths within one biogeochemical province of the Indian Ocean. Microbial diversity was determined by 16S ribosomal RNA (rRNA) gene sequencing. Our results show significant differences in microbial communities between stations outside and inside the SWIR, which were mostly explained by environmental selection. Community similarity correlated significantly with differences in chlorophyll a content and with the presence of upward porewater fluxes carrying reduced compounds (e.g., ammonia and sulfide), suggesting that trophic resource availability is a main driver for changes in microbial community composition. At the stations in the SWIR axial valley (3,655–4,448 m water depth), microbial communities were enriched in bacterial and archaeal taxa common in organic matter-rich subsurface sediments (e.g., SEEP-SRB1, Dehalococcoida, Atribacteria, and Woesearchaeota) and chemosynthetic environments (mainly Helicobacteraceae). The abyssal stations outside the SWIR communities (3,760–4,869 m water depth) were dominated by OM1 clade, JTB255, Planctomycetaceae, and Rhodospirillaceae. We conclude that ultraslow spreading ridges create a unique environmental setting in sedimented segments without distinct hydrothermal activity, and play an important role in shaping microbial communities and promoting diversity, but also in connectivity among deep-sea habitats.

Beschreibung: Oceanic oxygen decline due to anthropogenic climate change is a matter of growing concern. A quantitative oxygen proxy is highly desirable in order to identify and monitor recent dynamics as well as to reconstruct pre-Anthropocene changes in amplitude and extension of oxygen depletion. Geochemical proxies like foraminiferal I/Ca ratios seem to be promising redox proxies. Nevertheless, recent studies on microanalyses of benthic foraminiferal I/Ca ratios at the Peruvian oxygen minimum zone (OMZ) measured with secondary-ion mass spectrometry (SIMS) revealed a possible association of iodine with organic accumulations within the test. Here, we present a new study on the micro-distribution of nitrogen, sulfur, and iodine within the test walls of Uvigerina striata from the Peruvian OMZ measured with Nano-SIMS. A quantification of the foraminiferal I/Ca ratios from our NanoSIMS study is in good agreement with quantitative results from a previous SIMS study. Additionally, we compared uncleaned specimens with specimens that have been treated with an oxidative cleaning procedure. Both nitrogen and sulfur, which are used as tracer for organic matter, show a patchy distribution within the test walls of the uncleaned specimens and a statistically significant correlation with the iodine distribution. This patchy organic-rich phase has a different geochemical signature than the pristine calcitic parts of the test and another phase that shows a banding-like structure and that is characterized by a strong sulfur enrichment. All three elements, sulfur, nitrogen, and iodine, are strongly depleted in the cleaned specimens, even within the massive parts of the test walls that lack the connection with the test pores. These results indicate that the organic parts of the test walls are located inside a microporous framework within the foraminiferal calcite. This has to be considered in the interpretation of geochemical proxies on foraminiferal calcite, especially for microanalytical methods, since the chemical signature of these organic parts likely alters some element-to-calcium ratios within the foraminiferal test.

Beschreibung: Marine sponges (Phylum Porifera) are globally distributed within marine and freshwater ecosystems. In addition, sponges host dense and diverse prokaryotic communities, which are potential sources of novel bioactive metabolites and other complex compounds. Those sponge-derived natural products can span a broad spectrum of bioactivities, from antibacterial and antifungal to antitumor and antiviral compounds. However, most analyses concerning sponge-associated prokaryotes have mainly focused on conveniently accessible relatively shallow sampling locations for sponges. Hence, knowledge of community composition, host-relatedness and biotechnological potential of prokaryotic associations in temperate and cold-water sponges from greater depths (mesophotic to mesopelagic zones) is still scarce. Therefore, we analyzed the prokaryotic community diversity of four phylogenetically divergent sponge taxa from mesophotic to mesopelagic depths of Antarctic shelf at different depths and locations in the region of the South Shetland Islands using 16S rRNA gene amplicon-based sequencing. In addition, we predicted functional profiles applying Tax4Fun from metagenomic 16S rRNA gene data to estimate their biotechnological capability and possible roles as sources of novel bioactive compounds. We found indications that cold and deep-water sponges exhibit host-specific prokaryotic communities, despite different sampling sites and depths. Functional prediction analysis suggests that the associated prokaryotes may enhance the roles of sponges in biodegradation processes of xenobiotics and their involvement in the biosynthesis of secondary metabolites.

Beschreibung: DNA barcoding analysis, using tufA, revealed considerable differences between the expected and observed species inventory of Ulva sensu lato in the Baltic and North Sea areas of the German state of Schleswig-Holstein. Of 20 observed genetic entities, at least four (U. australis, U. californica, U. gigantea and Umbraulva dangeardii) had been introduced recently, whereas three others (one Ulva sp. and two Blidingia spp.) could not be identified at the species level and could also represent recently introduced species. In addition, the observed distributions of Kornmannia leptoderma and U. rigida were much more extensive than indicated by historical records, whereas Blidingia minima and Gayralia oxysperma were absent or much less common than expected. Barcoding analysis also revealed that both U. tenera (type material) and U. pseudocurvata (historical vouchers) from Helgoland, an off-shore island in the North Sea, actually belong to U. lactuca, a species that appears to be restricted to this island. Furthermore, past morphological descriptions of U. intestinalis and U. compressa have apparently been too restrictive and have been responsible for numerous misidentifications. The same is true for U. linza, which, in northern Germany, clusters into two genetically closely related but morphologically indistinguishable entities. One of these entities is present on Helgoland, while the second is present on North Sea and Baltic Sea mainland coasts.

Beschreibung: N2-fixing cyanobacteria mediate H2 fluxes through the opposing processes of H2 evolution, which is a by-product of the N2 fixation reaction, and H2 uptake, which is driven by uptake hydrogenases. Here, we used microelectrodes to characterize H2 and O2 dynamics in single natural colonies of the globally important N2 fixer Trichodesmium collected from the Gulf of Eilat. We observed gradually changing H2 dynamics over the course of the day, including both net H2 evolution and net H2 uptake, as well as large differences in H2 fluxes between individual colonies. Net H2 uptake was observed in colonies amended with H2 in both light and dark. Net H2 evolution was recorded in the light only, reflecting light-dependent N2 fixation coupled to H2 evolution. Both net H2 evolution and H2 uptake rates were higher before 2 pm than later in the day. These pronounced H2 dynamics in the morning coincided with strong net O2 uptake and the previously reported diel peak in N2 fixation. Later in the afternoon, when photosynthesis rates determined by O2 measurements were highest, and N2 fixation rates decrease according to previous studies, the H2 dynamics were also less pronounced. Thus, the observed diel variations in H2 dynamics reflect diel changes in the rates of O2 consumption and N2 fixation. Remarkably, the presence of H2 strongly stimulated the uptake of mineral iron by natural colonies. The magnitude of this effect was dependent on the time of day, with the strongest response in incubations that started before 2 pm, i.e., the period that covered the time of highest uptake hydrogenase activity. Based on these findings, we propose that by providing an electron source for mineral iron reduction in N2-fixing cells, H2 may contribute to iron uptake in Trichodesmium colonies.

Beschreibung: Heme b is an iron-containing co-factor in hemoproteins. Heme b concentrations are low (〈1 pmol L-1) in iron limited phytoplankton in cultures and in the field. Here, we determined heme b in marine particulate material (〉0.7 μm) from the North Atlantic Ocean (GEOVIDE cruise – GEOTRACES section GA01), which spanned several biogeochemical regimes. We examined the relationship between heme b abundance and the microbial community composition, and its utility for mapping iron limited phytoplankton. Heme b concentrations ranged from 0.16 to 5.1 pmol L-1 (median = 2.0 pmol L-1, n = 62) in the surface mixed layer (SML) along the cruise track, driven mainly by variability in biomass. However, in the Irminger Basin, the lowest heme b levels (SML: median = 0.53 pmol L-1, n = 12) were observed, whilst the biomass was highest (particulate organic carbon, median = 14.2 μmol L-1, n = 25; chlorophyll a: median = 2.0 nmol L-1, n = 23) pointing to regulatory mechanisms of the heme b pool for growth conservation. Dissolved iron (DFe) was not depleted (SML: median = 0.38 nmol L-1, n = 11) in the Irminger Basin, but large diatoms (Rhizosolenia sp.) dominated. Hence, heme b depletion and regulation is likely to occur during bloom progression when phytoplankton class-dependent absolute iron requirements exceed the available ambient concentration of DFe. Furthermore, high heme b concentrations found in the Iceland Basin and Labrador Sea (median = 3.4 pmol L-1, n = 20), despite having similar DFe concentrations to the Irminger Basin, were attributed to an earlier growth phase of the extant phytoplankton populations. Thus, heme b provides a snapshot of the cellular activity in situ and could both be used as indicator of iron limitation and contribute to understanding phytoplankton adaptation mechanisms to changing iron supplies.

Beschreibung: Our civilization needs a clean, resilient, productive, safe, well-observed, documented and predicted ocean. “The ocean we need for the future we want” was the motto of the Intergovernmental Oceanographic Commission proposal to the United Nations to consider the merit of an Ocean Science Decade. By proclaiming the Decade, the UN General Assembly offered the oceanographic community a unique, once in a life-time, opportunity to change the way we do things, make oceanography fit for purpose of effectively supporting sustainable development, and energize the ocean sciences for future generations. The Decade is the chance to put in place a more complete and sustainable observing system and feed the resulting data into a science-based informed decision-making system allowing increased reliance of our civilization on the ocean, its ecosystem services and, at the same time, preserving ocean health. Strong and proactive engagement of the oceanographic community in the design of the Decade and its observing component and subsequent energetic implementation of the ideas are sought. Participants in OceanObs’19 are invited to consider the additional possibilities and requirements associated with the Decade in their contributions to and brainstorming at the Conference. It is essential to use collective wisdom of OceanObs’19 to help developing an ambitious and also realistic implementation plan for the Decade, with a strong observational component.

Beschreibung: Climate change and variability are major societal challenges, and the ocean is an integral part of this complex and variable system. Key to the understanding of the ocean's role in the Earth's climate system is the study of ocean and sea-ice physical processes, including its interactions with the atmosphere, cryosphere, land and biosphere. These processes include those linked to ocean circulation; the storage and redistribution of heat, carbon, salt and other water properties; and air-sea exchanges of heat, momentum, freshwater, carbon and other gasses. Measurements of ocean physics variables are fundamental to reliable earth prediction systems for a range of applications and users. In addition, knowledge of the physical environment is fundamental to growing understanding of the ocean's biogeochemistry and biological/ecosystem variability and function. Through the progress from OceanObs'99 to OceanObs'09, the ocean observing system has evolved from a platform centric perspective to an integrated observing system. The challenge now is for the observing system to evolve to respond to an increasingly diverse end user group. The Ocean Observations Physics and Climate panel (OOPC), formed in 1995, has undertaken many activities that led to observing system-related agreements. Here, OOPC will explore the opportunities and challenges for the development of a fit-for-purpose, sustained and prioritized ocean observing system, focusing on physical variables that maximize support for fundamental research, climate monitoring, forecasting on different timescales, and society. OOPC recommendations are guided by the Framework for Ocean Observing (Lindstrom et al. 2012) which emphasizes identifying user requirements by considering time and space scales of the Essential Ocean Variables. This approach provides a framework for reviewing the adequacy of the observing system, looking for synergies in delivering an integrated observing system for a range of applications and focusing innovation in areas where existing technologies do not meet these requirements

Beschreibung: The pelagic ocean receives terrigenous inputs of a range of organic compounds; however, the role that this terrigenous material plays in the ocean carbon cycle and biological pump is not entirely understood, and questions remain as to how oceanic cycles of terrigenous and autochthonous carbon interact. A significant portion of organic carbon that cannot be utilized by marine microbes in the epipelagic ocean escapes microbial remineralization to be sequestered in the deep ocean as refractory dissolved organic matter (DOM). Lignin, a “model” terrigenous compound, is thought to be refractory in the open ocean unless chemically altered. However, in this study, incubation experiments performed using lignin-amended oligotrophic seawater from the Sargasso Sea exhibited bacteria and archaea growth that doubled compared to unamended control treatments. The increase in bacteria and archaea cell abundance in lignin-amended treatments coincided with a 21–25% decrease in absorbance (250–400 nm) of chromophoric dissolved organic matter (CDOM), suggesting that certain microbes may be capable of altering fractions of this ostensibly recalcitrant organic matter. Furthermore, the microbial response to the lignin-amended treatments appears to be taxon-specific. Two phyla of Archaea, Euryarchaeota and Thaumarchaeota, exhibited an increase in abundance of 7-fold and 28-fold (from 2.42 × 106 cells L–1 to 1.72 × 107 cells L–1, and from 1.60 × 106 cells L–1 to 4.54 × 107 cells L–1, respectively), over 4 days of incubation in lignin-amended treatments. Additionally, an increase of 11-fold and 13-fold (from 2.93 × 106 cells L–1 to 3.30 × 107 cells L–1, and from 3.26 × 106 cells L–1 to 4.28 × 107 cells L–1, respectively), was observed in the abundance of these phyla in treatments containing lignin with added nitrogen and phosphorus, thus raising questions regarding primary and/or secondary responses to lignin degradation. Our findings indicate that marine bacteria and archaea play a role in the transformation of the optical properties of lignin in the open ocean and that they may serve as a potential sink for a portion of the lignin macromolecule.

Beschreibung: Multidisciplinary ocean observing activities provide critical ocean information to satisfy ever-changing socioeconomic needs and require coordinated implementation. The upper oxycline (transition between high and low oxygen waters) is fundamentally important for the ecosystem structure and can be a useful proxy for multiple observing objectives connected to eastern boundary systems (EBSs) that neighbor oxygen minimum zones (OMZs). The variability of the oxycline and its impact on the ecosystem (VOICE) initiative demonstrates how societal benefits drive the need for integration and optimization of biological, biogeochemical, and physical components of regional ocean observing related to EBS. In liaison with the Global Ocean Oxygen Network, VOICE creates a roadmap toward observation-model syntheses for a comprehensive understanding of selected oxycline-dependent objectives. Local to global effects, such as habitat compression or deoxygenation trends, prompt for comprehensive observing of the oxycline on various space and time scales, and for an increased awareness of its impact on ecosystem services. Building on the Framework for Ocean Observing (FOO), we present a first readiness level assessment for ocean observing of the oxycline in EBS. This was to determine current ocean observing design and future needs in EBS regions (e.g., the California Current System, the Equatorial Eastern Pacific off Ecuador, the Peru–Chile Current system, the Northern Benguela off Namibia, etc.) building on the FOO strategy. We choose regional champions to assess the ocean observing design elements proposed in the FOO, namely, requirement processes, coordination of observational elements, and data management and information products and the related best practices. The readiness level for the FOO elements was derived for each EBS through a similar and very general ad hoc questionnaire. Despite some weaknesses in the questionnaire design and its completion, an assessment was achievable. We found that fisheries and ecosystem management are a societal requirement for all regions, but maturity levels of observational elements and data management and information products differ substantially. Identification of relevant stakeholders, developing strategies for readiness level improvements, and building and sustaining infrastructure capacity to implement these strategies are fundamental milestones for the VOICE initiative over the next 2–5 years and beyond.

Beschreibung: Corals exert a strong biological control over their calcification processes, but there is a lack of knowledge on their capability of long-term acclimatization to ocean acidification (OA). We used a dual geochemical proxy approach to estimate the calcifying fluid pH (pHcf) and carbonate chemistry of a Mediterranean coral (Balanophyllia europaea) naturally growing along a pH gradient (range: pHTS 8.07–7.74). The pHcf derived from skeletal boron isotopic composition (δ11B) was 0.3–0.6 units above seawater values and homogeneous along the gradient (mean ± SEM: Site 1 = 8.39 ± 0.03, Site 2 = 8.34 ± 0.03, Site 3 = 8.34 ± 0.02). Also carbonate ion concentration derived from B/Ca was homogeneous [mean ± SEM (μmol kg–1): Site 1 = 579 ± 34, Site 2 = 541 ± 27, Site 3 = 568 ± 30] regardless of seawater pH. Furthermore, gross calcification rate (GCR, mass of CaCO3 deposited on the skeletal unit area per unit of time), estimated by a “bio-inorganic model” (IpHRAC), was homogeneous with decreasing pH. The homogeneous GCR, internal pH and carbonate chemistry confirm that the features of the “building blocks” – the fundamental structural components – produced by the biomineralization process were substantially unaffected by increased acidification. Furthermore, the pH up-regulation observed in this study could potentially explain the previous hypothesis that less “building blocks” are produced with increasing acidification ultimately leading to increased skeletal porosity and to reduced net calcification rate computed by including the total volume of the pore space. In fact, assuming that the available energy at the three sites is the same, this energy at the low pH sites could be partitioned among fewer calicoblastic cells that consume more energy given the larger difference between external and internal pH compared to the control, leading to the production of less building blocks (i.e., formation of pores inside the skeleton structure, determining increased porosity). However, we cannot exclude that also dissolution may play a role in increasing porosity. Thus, the ability of scleractinian corals to maintain elevated pHcf relative to ambient seawater might not always be sufficient to counteract declines in net calcification under OA scenarios.

Beschreibung: The presence of optically active water constituents is known to attenuate the light penetration in the ocean and impact the ocean heat content. Here, we investigate the influence of colored dissolved organic matter (CDOM) and total suspended matter (TSM) on the radiative heating of the Laptev Sea shelf waters. The Laptev Sea region is heavily influenced by the Lena River, one of the largest river systems in the Arctic region. We simulate the radiative heating by using a coupled atmosphere-ocean radiative transfer model (RTM) and in situ measurements from the TRANSDRIFT XVII expedition carried out in September 2010. The results indicate that CDOM and TSM have significant influence on the energy budget of the Laptev Sea shelf waters, absorbing most of the solar energy in the first 2 m of the water column. In the station with the highest CDOM absorption (aCDOM(443) = 1.77 m−1) ~43% more energy is absorbed in the surface layer compared to the station with the lowest aCDOM(443) (~0.2 m−1), which translates to an increased radiative heating of ~0.6°C/day. The increased absorbed energy by the water constituents also implies increased sea ice melt rate and changes in the surface heat fluxes to the atmosphere. By using satellite remote sensing and RTM we quantify the spatial distribution of the radiative heating in the Laptev Sea for a typical summer day. The combined use of satellite remote sensing, RT modeling and in situ observations can be used to improve parameterization schemes in atmosphere-ocean circulation models to assess the role of the ocean in the effect of Arctic amplification.

Beschreibung: To resolve historical misinterpretations of species descriptions and to comprehend the morphological diversity together with the distribution of Ulva compressa Linnaeus in northern Germany, a morphological and molecular study was undertaken of recently collected specimens and herbarium vouchers. Phylogenetic analyses from sequences of the plastid encoded tufA gene confirmed that U. compressa is abundant along the German Baltic Sea and North Sea coasts. We were able to genetically confirm the presence of U. compressa in the Baltic Sea below salinities of 15 PSU. However, we detected morphologies agreeing with the attached and branched tubular type material only in the North Sea, while U. compressa on Baltic Sea coasts indiscriminately exhibited a very distinct morphology of sheet-like thalli that were always unattached, with the exception of one collection site. Drifting forms were also frequently detected in the Wadden Sea, but not on the island of Helgoland. The tufA sequences of attached and tubular forms of U. compressa from the German Wadden Sea were identical to the drifting sheets found in the Wadden and Baltic Seas and the sequence divergence was extremely small at ≤0.9%. The proliferating, blade-like thalli of U. compressa appear as a nuisance ecotype that is able to form massive accumulations associated with oxygen depletion. Mass accumulations were observed to cause severe damage and increased mortality of habitat forming Zostera and Ruppia populations.

Beschreibung: We investigated how future ocean conditions, and specifically the interaction between temperature and CO2, might affect marine aggregate formation and physical properties. Initially, mesocosms filled with coastal seawater were subjected to three different treatments of CO2 concentration and temperature: (1) 750 ppm CO2, 16°C, (2) 750 ppm CO2, 20°C, and (3) 390 ppm CO2, 16°C. Diatom-dominated phytoplankton blooms were induced in the mesocosms by addition of nutrients. In aggregates produced in roller tanks using seawater taken from the mesocosms during different stages of the bloom, we measured sinking velocity, size, chlorophyll a, particulate organic carbon and nitrogen, and exopolymer particle content; excess density and mass were calculated from the sinking velocity and size of the aggregates. As has been seen in previous experiments, no discernable differences in overall nutrient uptake, chlorophyll-a concentration, or exopolymer particle concentrations could be related to the acidification treatment in the mesocosms. In addition, in the aggregates formed during the roller tank experiments (RTEs), we observed no statistically significant differences in chemical composition among the treatments during Pre-Bloom, Bloom, and Post-Bloom periods. However, physical characteristics were different and showed a synergistic effect of warmer temperature and higher CO2 during the Pre-Bloom period; at this time, temperature had a larger effect than CO2 on aggregate sinking velocity. In RTEs with warmer and acidified treatment (future conditions), aggregates were larger, heavier, and settled faster than aggregates formed at present-day or only acidified conditions. During the Post-Bloom, however, aggregates formed under present and future conditions had similar physical properties. In acidified tanks at ambient temperature, aggregates were slower, smaller and less dense than those formed at the same temperature but under present CO2 or under warmer and acidified conditions. Thus, the sinking velocity of aggregates formed in acidified tanks at ambient temperature was slower than the other two cases. Our findings point out the potential of ocean acidification and warming to modify physical properties of sinking aggregates but also emphasize the need of future experiments investigating multiple environmental stressors to clarify the importance of each factor.

Beschreibung: Marine transform faults and associated fracture zones (MTFFZs) cover vast stretches of the ocean floor, where they play a key role in plate tectonics, accommodating the lateral movement of tectonic plates and allowing connections between ridges and trenches. Together with the continental counterparts of MTFFZs, these structures also pose a risk to human societies as they can generate high magnitude earthquakes and trigger tsunamis. Historical examples are the Sumatra-Wharton Basin Earthquake in 2012 (M8.6) and the Atlantic Gloria Fault Earthquake in 1941 (M8.4). Earthquakes at MTFFZs furthermore open and sustain pathways for fluid flow triggering reactions with the host rocks that may permanently change the rheological properties of the oceanic lithosphere. In fact, they may act as conduits mediating vertical fluid flow and leading to elemental exchanges between Earth’s mantle and overlying sediments. Chemicals transported upward in MTFFZs include energy substrates, such as H2 and volatile hydrocarbons, which then sustain chemosynthetic, microbial ecosystems at and below the seafloor. Moreover, up- or downwelling of fluids within the complex system of fractures and seismogenic faults along MTFFZs could modify earthquake cycles and/or serve as “detectors” for changes in the stress state during interseismic phases. Despite their likely global importance, the large areas where transform faults and fracture zones occur are still underexplored, as are the coupling mechanisms between seismic activity, fluid flow, and life. This manuscript provides an interdisciplinary review and synthesis of scientific progress at or related to MTFFZs and specifies approaches and strategies to deepen the understanding of processes that trigger, maintain, and control fluid flow at MTFFZs.

Beschreibung: We revisit the challenges and prospects for ocean circulation models following Griffies et al. (2010). Over the past decade, ocean circulation models evolved through improved understanding, numerics, spatial discretization, grid configurations, parameterizations, data assimilation, environmental monitoring, and process-level observations and modeling. Important large scale applications over the last decade are simulations of the Southern Ocean, the Meridional Overturning Circulation and its variability, and regional sea level change. Submesoscale variability is now routinely resolved in process models and permitted in a few global models, and submesoscale effects are parameterized in most global models. The scales where nonhydrostatic effects become important are beginning to be resolved in regional and process models. Coupling to sea ice, ice shelves, and high-resolution atmospheric models has stimulated new ideas and driven improvements in numerics. Observations have provided insight into turbulence and mixing around the globe and its consequences are assessed through perturbed physics models. Relatedly, parameterizations of the mixing and overturning processes in boundary layers and the ocean interior have improved. New diagnostics being used for evaluating models alongside present and novel observations are briefly referenced. The overall goal is summarizing new developments in ocean modeling, including: how new and existing observations can be used, what modeling challenges remain, and how simulations can be used to support observations.

Beschreibung: Cytospora is a genus including important phytopathogens causing severe dieback and canker diseases distributed worldwide with a wide host range. However, identification of Cytospora species is difficult since the currently available DNA sequence data are insufficient. Aside the limited availability of ex-type sequence data, most of the genetic work is only based on the ITS region DNA marker which lacks the resolution to delineate to the species level in Cytospora. In this study, three fresh strains were isolated from the symptomatic branches of Elaeagnus angustifolia in Xinjiang Uygur Autonomous Region, China. Morphological observation and multi-locus phylogenetic analyses (ITS, LSU, ACT and RPB2) support these specimens are best accommodated as a distinct novel species of Cytospora. Cytospora elaeagnicola sp. nov. is introduced, having discoid, nearly flat, pycnidial conidiomata with hyaline, allantoid conidia, and differs from its relatives genetically and by host association.

Beschreibung: The translocation of non-indigenous species around the world, especially in marine systems, is a matter of concern for biodiversity conservation and ecosystem functioning. While specific traits are often recognized to influence establishment success of non-indigenous species, the impact of the associated microbial community for the fitness, performance and invasion success of basal marine metazoans remains vastly unknown. In this study we compared the microbiota community composition of the invasive ctenophore Mnemiopsis leidyi in different native and invasive sub-populations along with characterization of the genetic structure of the host. By 16S rRNA gene amplicon sequencing we showed that the sister group to all metazoans, namely ctenophores, harbored a distinct microbiota on the animal host, which significantly differed across two major tissues, namely epidermis and gastrodermis. Additionally, we identified significant differences between native and invasive sub-populations of M. leidyi, which indicate, that the microbiota community is likely influenced by the genotypic background of the ctenophore. To test the hypothesis that the microbiota is genotypically selected for by the ctenophore host, experiments under controlled environments are required.

Beschreibung: Apicomplexans are a group of microbial eukaryotes that contain some of the most well-studied parasites, including the causing agents of toxoplasmosis and malaria, and emergent diseases like cryptosporidiosis or babesiosis. Decades of research have illuminated the pathogenic mechanisms, molecular biology, and genomics of model apicomplexans, but we know little about their diversity and distribution in natural environments. In this study we analyze the distribution of apicomplexans across a range of both host-associated and free-living environments. Using publicly available small subunit (SSU) rRNA gene databases, high-throughput environmental sequencing (HTES) surveys, and our own generated HTES data, we developed an apicomplexan reference database, which includes the largest apicomplexan SSU rRNA tree available to date and encompasses comprehensive sampling of this group and their closest relatives. This tree allowed us to identify and correct incongruences in the molecular identification of apicomplexan sequences. Analyzing the diversity and distribution of apicomplexans in HTES studies with this curated reference database also showed a widespread, and quantitatively important, presence of apicomplexans across a variety of free-living environments. These data allow us to describe a remarkable molecular diversity of this group compared with our current knowledge, especially when compared with that identified from described apicomplexan species. This is most striking in marine environments, where potentially the most diverse apicomplexans apparently exist, but have not yet been formally recognized. The new database will be useful for microbial ecology and epidemiological studies, and provide valuable reference for medical and veterinary diagnosis especially in cases of emerging, zoonotic, and cryptic infections.

Beschreibung: In the Peruvian upwelling system, the mesopelagic oxygen minimum zone (OMZ) is the main vertically structuring feature of the pelagic habitat. Several zooplankton and nekton species undertake diel vertical migrations (DVMs) into anoxic depths. It has been argued that these migrations contribute substantially to the oxygen consumption and release of dissolved compounds (in particular ammonium) in subsurface waters. However, metabolic suppression as a response to low ambient oxygen partial pressure (pO2) has not been accounted for in these estimates. Here, we present estimates of zooplankton- and nekton-mediated oxygen consumption and ammonium release based on vertically stratified net hauls (day/night, upper 1,000 m). Samples were scanned, followed by image analysis and size-/taxon-specific estimation of metabolic rates of all identified organisms as a function of their biomass as well as ambient temperature and pO2. The main crustacean migrants were euphausiids (mainly E. mucronata) on offshore stations and the commercially exploited squat lobster Pleuroncodes monodon on the upper shelf, where it often undertakes migration to the seafloor during the day. Correction for metabolic suppression results in a substantial reduction of both respiration and ammonium excretion within the OMZ core. Ignoring this mechanism leads to a 10-fold higher estimate of DVM-mediated active export of carbon by respiration to below 100 m depth at deep-water stations. The DVM-mediated release of ammonium by euphausiids into the 200–400 m depth layer ranges between 0 and 36.81 μmol NH4 m−2 d−1, which is insufficient to balance published estimates of ammonium uptake rates due to anammox. It seems critical to account for the modulation of zooplankton metabolic activity at low oxygen in order to correctly represent the contribution of migrating species to the biological pump.

Beschreibung: The ecological impacts of meltwater produced by icebergs and sea ice in the waters around Greenland are poorly understood, due in part to limited observations. Current field sampling methods are resource and labor-intensive, and not without significant risk. We developed a small, unoccupied, and robotic platform to retrieve ice samples, while simultaneously eliminating safety risks to scientists and their support infrastructure. The IceDrone consists of a modified commercial hexcopter that retrieves ice samples. We describe the design requirements, construction, and testing of the IceDrone. IceDrone's capabilities were validated in the laboratory and during a field test in January 2019 near Nuuk (southwest Greenland). IceDrone retrieved samples in hard and dry glacial ice in harsh winter conditions. The field test led to modifications in the drilling head design and drilling process that enable it to retrieve samples in thin sea ice. All design files and software are provided in an attempt to rapidly enhance our collective understanding of ice-ocean interactions while improving the safety and productivity of field sampling campaigns.

Beschreibung: The long-term trend of diurnal temperature range (DTR) over Nigeria was examined using daily station-based datasets for the period 1971–2013. The results show that the regionally averaged DTR has decreased significantly (−0.34°C per decade) over the Nigerian Sahel (north of 10°N), but there has been a slight increasing trend (0.01°C per decade) over the Nigerian Guinea Coast. The annual decreasing trend of DTR in the Nigerian Sahel is mainly attributable to the significant increasing trend in daily minimum temperature (Tmin, 0.51°C per decade), which far outstrips the rate of increase in the daily maximum (Tmax, 0.17°C per decade). In contrast, the comparable trends in Tmin (0.19°C per decade) and Tmax (0.20°C per decade) may explain the non-significant trend of the DTR averaged over the Guinea Coast region. It is observed that the DTR has decreased more in boreal summer (June–July–August) than in boreal winter (December–January–February) for the regions. Furthermore, it is found that the significant DTR declining trend over the Nigerian Sahel is closely associated with an increasing trend of annual and summer precipitation in the region, but the increasing DTR trend in the Nigerian Guinea Coast region can be attributed to the decreasing trend of cloud cover over the region.

Beschreibung: While burial diagenetic processes of tropical corals are well investigated, current knowledge about factors initiating early diagenesis remains fragmentary. In the present study, we focus on recent Porites microatolls, growing in the intertidal zone. This growth form represents a model organism for elevated sea surface temperatures (SSTs) and provides important but rare archives for changes close to the seawater/atmosphere interface with exceptional precision on sea level reconstruction. As other coral growth forms, microatolls are prone to the colonization by endolithic green algae. In this case, the algae can facilitate earliest diagenetic alteration of the coral skeleton. Algae metabolic activity not only results in secondary coral porosity due to boring activities, but may also initiate reprecipitation of secondary aragonite within coral pore space, a process not exclusively restricted to microatoll settings. In the samples of this initial study, we quantified a mass transfer from primary to secondary aragonite of around 4% within endolithic green algae bands. Using δ18O, δ13C, Sr/Ca, U/Ca, Mg/Ca, and Li/Mg systematics suggests that the secondary aragonite precipitation followed abiotic precipitation principles. According to their individual distribution coefficients, the different isotope and element ratios showed variable sensitivity to the presence of secondary aragonite in bulk samples, with implications for microatoll-based SST reconstructions. The secondary precipitates formed on an organic template, presumably originating from endolithic green algae activity. Based on laboratory experiments with the green algae Ostreobium quekettii, we propose a conceptual model that secondary aragonite formation is potentially accelerated by an active intracellular calcium transport through the algal thallus from the location of dissolution into coral pore spaces. The combined high-resolution imaging and geochemical approach applied in this study shows that endolithic algae can possibly act as a main driver for earliest diagenesis of coral aragonite starting already during a coral’s life span.

Beschreibung: A realistic estimation of uncertainty is an essential requirement for all analytical measurements. It is common practice, however, for the uncertainty estimate of a chemical measurement to be based on the instrumental precision associated with the analysis of a single or multiple samples, which can lead to underestimation. Within the context of chemical oceanography such an underestimation of uncertainty could lead to an over interpretation of the result(s) and hence impact on, e.g., studies of biogeochemical cycles, and the outputs from oceanographic models. Getting high quality observational data with a firm uncertainty assessment is therefore essential for proper model validation. This paper describes and compares two recommended approaches that can give a more holistic assessment of the uncertainty associated with such measurements, referred to here as the “bottom up” or modeling approach and the “top down” or empirical approach. “Best practice” recommendations for the implementation of these strategies are provided. The “bottom up” approach combines the standard uncertainties associated with each stage of the entire measurement procedure. The “top down” approach combines the uncertainties associated with day to day reproducibility and possible bias in the complete data set and is easy to use. For analytical methods that are routinely used, laboratories will have access to the information required to calculate the uncertainty from archived quality assurance data. The determination of trace elements in seawater is a significant analytical challenge and iron is used as an example for the implementation of both approaches using real oceanographic data. Relative expanded uncertainties of 10 – 20% were estimated for both approaches compared with a typical short term precision (rsd) of≤5%.

Beschreibung: Trace metal micronutrients are integral to the functioning of marine ecosystems and the export of particulate carbon to the deep ocean. Although much progress has been made in mapping the distributions of metal micronutrients throughout the ocean over the last 30 years, there remain information gaps, most notable during seasonal transitions and in remote regions. The next challenge is to develop in situ sensing technologies necessary to capture the spatial and temporal variabilities of micronutrients characterized with short residence times, highly variable source terms, and sub-nanomolar concentrations in open ocean settings. Such an effort will allow investigation of the biogeochemical processes at the necessary resolution to constrain fluxes, residence times, and the biological and chemical responses to varying metal inputs in a changing ocean. Here, we discuss the current state of the art and analytical challenges associated with metal micronutrient determinations and highlight existing and emerging technologies, namely in situ chemical analyzers, electrochemical sensors, passive preconcentration samplers, and autonomous trace metal clean samplers, which could form the basis of autonomous observing systems for trace metals within the next decade. We suggest that several existing assets can already be deployed in regions of enhanced metal concentrations and argue that, upon further development, a combination of wet chemical analyzers with electrochemical sensors may provide the best compromise between analytical precision, detection limits, metal speciation, and longevity for autonomous open ocean determinations. To meet this goal, resources must be invested to: (1) improve the sensitivity of existing sensors including the development of novel chemical assays; (2) reduce sensor size and power requirements; (3) develop an open-source “Do-It-Yourself” infrastructure to facilitate sensor development, uptake by end-users and foster a mechanism by which scientists can rapidly adapt commercially available technologies to in situ applications; and (4) develop a community-led standardized protocol to demonstrate the endurance and comparability of in situ sensor data with established techniques. Such a vision will be best served through ongoing collaborations between trace metal geochemists, analytical chemists, the engineering community, and commercial partners, which will accelerate the delivery of new technologies for in situ metal sensing in the decade following OceanObs’19.

Beschreibung: The Arctic Ocean plays a key role in regulating the global climate, while being highly sensitive to climate change. Temperature in the Arctic increases faster than the global average, causing a loss of multiyear sea-ice and affecting marine ecosystem structure and functioning. As a result, Arctic primary production and biogeochemical cycling are changing. Here, we investigated inter-annual changes in the concentrations of particulate and dissolved organic carbon (POC, DOC) together with biological drivers, such as phyto- and bacterioplankton abundance in the Fram Strait, the Atlantic gateway to the Central Arctic Ocean. Data have been collected in summer at the Long-Term Ecological Research observatory HAUSGARTEN during eight cruises from 2009 to 2017. Our results suggest that the dynamic physical system of the Fram Strait induces strong heterogeneity of the ecosystem that displays considerable intra-seasonal as well as inter-annual variability. Over the observational period, DOC concentrations were significantly negatively related to temperature and salinity, suggesting that outflow of Central Arctic waters carrying a high DOC load is the main control of DOC concentration in this region. POC concentration was not linked to temperature or salinity but tightly related to phytoplankton biomass as estimated from chlorophyll-a concentrations (Chl-a). For the years 2009–2017, no temporal trends in the depth-integrated (0–100 m) amounts of DOC and Chl-a were observed. In contrast, depth-integrated (0–100 m) amounts of POC, as well as the ratio [POC]:[TOC], decreased significantly over time. This suggests a higher partitioning of organic carbon into the dissolved phase. Potential causes and consequences of the observed changes in organic carbon stocks for food-web structure and CO2 sequestration are discussed.