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Chilean salmon farms release inorganic nutrients excreted by the fish into the surrounding water in Patagonian fjords. The objective of this experiment from the Comau Fjord (42.2° S) in southern Chile was to study how increased input of ammonium (NH4) and phosphate (PO4) from salmon farms might affect the community structure of bacteria in surface waters where fish farms are located. We used microcosms (35 l) with NH4-N and PO4-P added to the natural seawater in a gradient of nutrient-loading rates, with the same N:P ratio as in salmon aquaculture effluents. Additionally, we measured bacterial community structure at different depths in the Comau Fjord to assess the natural variation to compare with our experiment. We used denaturing gradient gel electrophoresis (DGGE) to create 16S rDNA fingerprints of the bacterial communities and monitored biological and environmental variables (chlorophyll a, inorganic nutrients, pH, microbial abundance). The nutrient-loading rate had a significant impact on the bacterial community structure, and the community dissimilarity between low and high nutrient additions was up to 78%. Of the measured environmental variables, phytoplankton abundance and increased pH from photosynthesis had a significant effect. We observed no significant changes in bacterial diversity, which remained at the same level as in the unmanipulated community. Thus, the bacterial community of the fjord was not resistant, but resilient within the time frame and nutrient gradient of our experiment.

Marine sediment is a significant sink for the global pollutant mercury. In a rapidly changing Arctic region, mercury (Hg) bioaccumulation in the marine ecosystem remains a prominent environmental issue. Here, we report surface sediment (0-2 cm) concentrations of Hg and other toxic elements of interest (Cr, Ni, Zn, Cu, As, Cd, Pb) in the northern Barents Sea and Eurasian Basin. We observed average Hg concentrations of 65 ± 23 ng/g with the highest concentration of 116 ng/g in the Eurasian Basin. Our calculated enrichment factors suggest low anthropogenic enrichment for mercury, chromium, nickel, and copper. Mercury and trace element geographic patterns are best explained by the origin and transportation of fine grain sediment towards the Eurasian Basin, with scavenging by both particulate organic carbon and metal oxides as significant delivery mechanisms., Competing Interests: Declaration of competing interest The authors declare no competing interests., (Copyright © 2022 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Fjord systems in higher latitudes are unique coastal water ecosystems that facilitate the study of dissolved organic matter (DOM) dynamics from surface to deeper waters. The current work was undertaken in the Trondheim fjord characterized by North Atlantic waters, and compared DOM fractions from three depths - surface (3 m), intermediate (225 m) and deep (440 m) in four seasons, from late spring to winter in 2017. The high-resolution mass spectrometry data showed that DOM composition varies significantly in different seasons rather than in different depths in the fjord systems. The bacterial community composition was comparable except at spring surface and summer intermediate depths. Bacterial production was minimal below the euphotic layer, even with sufficient availability of inorganic nutrients. The bacterial production rate in the surface waters was about 7 times and over 50 times higher than that of the aphotic zone in the winter and the summer seasons, respectively. The surface heterotrophic microbial communities might have rapidly consumed the available labile DOM, with the production of more refractory DOM limiting bacterial production in aphotic layers. The greater number of CRAM-like formulas determined in the surface waters compared to other depths supports our hypothesis. The refractory DOM sequestered in the water column may either be exported into sediments attached to particulate matter and marine gels, or may escape into the atmosphere as carbon dioxide/monoxide during the photochemical oxidation pathways, suggesting that it is involved in climate change scenarios., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 The Authors. Published by Elsevier B.V. All rights reserved.)

Carbon capture and storage (CCS) is one of the most promising mitigation strategies for reducing the emissions of carbon dioxide (CO 2 ) to the atmosphere and may substantially help to decelerate global warming. There is an increasing demand for CCS sites. Nevertheless, there is a lack of knowledge of the environmental risk associated with potential leakage of CO 2 from the storage sites; and even more, what happens when the seepage stops. Can the environment return to the initial equilibrium? Potential effects on native macrofauna were studied under a scenario of a 50-day CO 2 leakage, and the subsequent leak closure. To accomplish the objective, Trondheim Fjord sediments and clams were exposed to an acidified environment (pH 6.9) at 29 atm for 7 weeks followed by a 14-day recovery at normal seawater conditions (pH 8.0, 29 atm). Growth and survival of clams exposed to pressure (29 atm) and reduced pH (6.9) did not significantly differ from control clams kept at 1 atm in natural seawater. Furthermore, bioaccumulation of elements in the soft tissue of clams did not register significant variations for most of the analysed elements (Cd, Cr, Pb, and Ti), while other elements (As, Cu, Fe, Ni) had decreasing concentrations in tissues under acidified conditions in contrast to Na and Mg, which registered an uptake (Ku) of 111 and 9.92 μg g -1 dw d -1 , respectively. This Ku may be altered due to the stress induced by acidification; and the element concentration being released from sediments was not highly affected at that pH. Therefore, a 1 unit drop in pH at the seafloor for several weeks does not appear to pose a risk for the clams., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Iron is an essential, yet scarce, nutrient in marine environments. Phytoplankton, and especially cyanobacteria, have developed a wide range of mechanisms to acquire iron and maintain their iron-rich photosynthetic machinery. Iron limitation studies often utilize either oceanographic methods to understand large scale processes, or laboratory-based, molecular experiments to identify underlying molecular mechanisms on a cellular level. Here, we aim to highlight the benefits of both approaches to encourage interdisciplinary understanding of the effects of iron limitation on cyanobacteria with a focus on avoiding pitfalls in the initial phases of collaboration. In particular, we discuss the use of trace metal clean methods in combination with sterile techniques, and the challenges faced when a new collaboration is set up to combine interdisciplinary techniques. Methods necessary for producing reliable data, such as High Resolution Inductively Coupled Plasma Mass Spectrometry (HR-ICP-MS), Flow Injection Analysis Chemiluminescence (FIA-CL), and 77K fluorescence emission spectroscopy are discussed and evaluated and a technical manual, including the preparation of the artificial seawater medium Aquil, cleaning procedures, and a sampling scheme for an iron limitation experiment is included. This paper provides a reference point for researchers to implement different techniques into interdisciplinary iron studies that span cyanobacteria physiology, molecular biology, and biogeochemistry.

Carbon capture and storage sites in Barents Sea shelf are currently in progress as part of climate change mitigation activities. However environmental impacts of a possible CO 2 seepage on bacterial community are lacking knowledge. This work addressed potential consequences on bacterial communities from Snøvit region in Barents Sea sediments. Long-term experiment (92 days) was carried out mimicking realistic conditions of pressure (∼30 bars) using the unique hyperbaric chamber (Karl Erik TiTank). The experiment was divided in three stages: i) 21 days of no CO 2 , ii) 50 days of simulation of carbon dioxide leakage (depletion of pH to 7.0) and iii) 14 days emulating a leakage cessation. Results suggested that bacterial communities can adapt to a CO 2 leakage in short term. However, bacteria showed negative effects in terms of activity, community structure, and number of cells after long term CO 2 exposure. After CO 2 leakage cessation, bacterial communities did not show a significant recovery. These findings highlighted that, even though marine bacteria showed adaptation to the new conditions (acidified environment), in case of a small but continuous CO 2 leakage marine bacteria might not be recovered upon pre-exposure status., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Carbon capture and storage (CCS) is the third contributor to cumulative carbon emission reductions required by the second half of this century. Although this is a promising technology for reducing atmospheric CO 2 , it is only affordable if the confinement of the gas is guaranteed for hundreds of years. Hence, it is of paramount importance to figure out and predict the chemical and biological effects associated with potential CO 2 leakage, to provide decision makers with a good basis for choosing technology and potential storage sites. To this end, a titanium reactor (1.4 m 3 ) was used to study CO 2 seepage under realistic sub-seabed conditions (30 bar pressure and 7 °C). The injection of CO 2 was calibrated to decrease the pH value from 8.1 to 7.3, which may be the pH found near a leakage point. This pH value also coincides with predictions for near-future ocean pH under current CO 2 emissions worldwide. The results from this study demonstrate that there are some elements, i.e., Fe, Co, Pb, Ce, Zn and Cu, present in deep marine sediments, that are strongly affected by the reduced pH levels related to CO 2 addition. The dissolved concentrations of Fe, Pb and, to a lesser extent, Cr increased, due probably to weakening of the Fe/Mn shuttle by increased dissolved concentrations of CO 2 . Desorption processes from oxyhydroxide surfaces due to acidification may explain the release of Co, Ni and Ce observed during the experiment. The increased CO 2 concentration also led to increased metal bioavailability, suggested by higher values for labile metal species. Conversely, Cd mobility seems not to be affected by CO 2 -associated acidification. It is concluded that the determination of those elements most affected by CO 2 -related acidification in a sub-seabed CO 2 storage perimeter (i.e., sediment, sediment-water interface and water column) would be a simple and effective technique to verify suspected leakage., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Hazardous substances entering the sea, and ultimately deposited in bottom sediments, pose a growing threat to marine ecosystems. The present study characterized two coastal areas exposed to significant anthropogenic impact - Gulf of Gdańsk (Poland), and Oslofjord/Drammensfjord (Norway) - by conducting a multi-proxy investigation of recent sediments, and comparing the results in light of different available thresholds for selected contaminants. Sediment samples were analyzed for benzo(a)pyrene (B(a)P) and other polycyclic aromatic hydrocarbons (PAHs), nonylphenols (NPs), organotin compounds (OTs), toxic metals (Cd, Hg, Pb), as well as mutagenic, genotoxic and endocrine-disrupting activities (in CALUX bioassays). In general, a declining trend in the deposition of contaminants was observed. Sediments from both basins were not highly contaminated with PAHs, NPs and metals, while OT levels may still give rise to concern in the Norwegian fjords. The results suggest that the contamination of sediments depends also on water/sediment conditions in a given region., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

The impact of CO(2) leakage on solubility and distribution of trace metals in seawater and sediment has been studied in lab scale chambers. Seven metals (Al, Cr, Ni, Pb, Cd, Cu, and Zn) were investigated in membrane-filtered seawater samples, and DGT samplers were deployed in water and sediment during the experiment. During the first phase (16 days), "dissolved" (<0.2 microm) concentrations of all elements increased substantially in the water. The increase in dissolved fractions of Al, Cr, Ni, Cu, Zn, Cd and Pb in the CO(2) seepage chamber was respectively 5.1, 3.8, 4.5, 3.2, 1.4, 2.3 and 1.3 times higher than the dissolved concentrations of these metals in the control. During the second phase of the experiment (10 days) with the same sediment but replenished seawater, the dissolved fractions of Al, Cr, Cd, and Zn were partly removed from the water column in the CO(2) chamber. DNi and DCu still increased but at reduced rates, while DPb increased faster than that was observed during the first phase. DGT-labile fractions (Me(DGT)) of all metals increased substantially during the first phase of CO(2) seepage. DGT-labile fractions of Al, Cr, Ni, Cu, Zn, Cd and Pb were respectively 7.9, 2.0, 3.6, 1.7, 2.1, 1.9 and 2.3 times higher in the CO(2) chamber than that of in the control chamber. Al(DGT), Cr(DGT), Ni(DGT), and Pb(DGT) continued to increase during the second phase of the experiment. There was no change in Cd(DGT) during the second phase, while Cu(DGT) and Zn(DGT) decreased by 30% and 25%, respectively in the CO(2) chamber. In the sediment pore water, DGT labile fractions of all the seven elements increased substantially in the CO(2) chamber. Our results show that CO(2) leakage affected the solubility, particle reactivity and transformation rates of the studied metals in sediment and at the sediment-water interface. The metal species released due to CO(2) acidification may have sufficiently long residence time in the seawater to affect bioavailability and toxicity of the metals to biota.