Investigating the microbial ecology of coastal hotspots of marine nitrogen fixation in the western North Atlantic

AbstractVariation in the microbial cycling of nutrients and carbon in the ocean is an emergent property of complex planktonic communities. While recent findings have considerably expanded our understanding of the diversity and distribution of nitrogen (N2) fixing marine diazotrophs, knowledge gaps remain regarding ecological interactions between diazotrophs and other community members. Using quantitative 16S and 18S V4 rDNA amplicon sequencing, we surveyed eukaryotic and prokaryotic microbial communities from samples collected in August 2016 and 2017 across the Western North Atlantic. Leveraging and significantly expanding an earlier published 2015 molecular dataset, we examined microbial community structure and ecological co-occurrence relationships associated with intense hotspots of N2 fixation previously reported at sites off the Southern New England Shelf and Mid-Atlantic Bight. Overall, we observed a negative relationship between eukaryotic diversity and both N2 fixation and net community production (NCP). Maximum N2 fixation rates occurred at sites with high abundances of mixotrophic stramenopiles, notably Chrysophyceae. Network analysis revealed such stramenopiles to be keystone taxa alongside the haptophyte diazotroph host Braarudosphaera bigelowii and chlorophytes. Our findings highlight an intriguing relationship between marine stramenopiles and high N2 fixation coastal sites.</jats:p

Interactive Impacts of Silver and Phosphorus on Autotrophic Biofilm Elemental and Biochemical Quality for a Macroinvertebrate Consumer

Autotrophic biofilms are complex and fundamental biological compartments of many aquatic ecosystems. In particular, these biofilms represent a major resource for many invertebrate consumers and the first ecological barrier against toxic metals. To date, very few studies have investigated the indirect effects of stressors on upper trophic levels through alterations of the quality of biofilms for their consumers. In a laboratory study, we investigated the single and combined effects of phosphorus (P) availability and silver, a re-emerging contaminant, on the elemental [carbon (C):nitrogen (N):P ratios] and biochemical (fatty acid profiles) compositions of a diatom-dominated biofilm initially collected in a shallow lake. We hypothesized that (1) P and silver, through the replacement of diatoms by more tolerant primary producer species, reduce the biochemical quality of biofilms for their consumers while (2) P enhances biofilm elemental quality and (3) silver contamination of biofilm has negative effects on consumers life history traits. The quality of biofilms for consumers was assessed for a common crustacean species, Gammarus fossarum, by measuring organisms’ survival and growth rates during a 42-days feeding experiment. Results mainly showed that species replacement induced by both stressors affected biofilm fatty acid compositions, and that P immobilization permitted to achieve low C:P biofilms, whatever the level of silver contamination. Gammarids growth and survival rates were not significantly impacted by the ingestion of silver-contaminated resource. On the contrary, we found a significant positive relationship between the biofilm P-content and gammarids growth. This study underlines the large indirect consequences stressors could play on the quality of microbial biomass for consumers, and, in turn, on the whole food web

Zinc isotope fractionation during the inorganic precipitation of calcite - Towards a new pH proxy

International audienceZinc was co-precipitated with calcite in mixed-flow reactors at 25 °C and 6.1 ≤ pH ≤ 8.5 to quantify Zn isotope fractionation between calcite and the reactive fluid. The results suggest that the difference between the isotopic composition of the solid and the fluid (Δ66Zncalcite-fluid = δ66Zncalcite - δ66Znfluid) increases by about 0.6‰ as the solution pH decreases from 8.5 to 6.1. In contrast, based on Zn aqueous speciation and the theoretical values of the reduced partition function ratios for zinc species, lnβ, the isotopic fractionation between calcite and aqueous Zn2+, Δ66Zncalcite-Zn2+ , remains constant at 0.58 ± 0.05‰ over the entire pH range investigated. The constant value of Δ66Zncalcite-Zn2+ suggests that irrespective of the solution pH, the same Zn aqueous species, likely free Zn2+ ions, interacts with calcite surface sites during the growth of this mineral via ion by ion attachment. The enrichment of calcite in 66Zn is consistent with the formation of mononuclear, inner-sphere tetrahedral Zn surface complexes at the calcite surface and the increase of Zn coordination to 6 following its incorporation in the crystal lattice with no further isotopic fractionation. Overall, the results suggest that Zn isotopic composition of natural calcite has the potential to shed light on the prevailing pH at the time of calcite formation in the geological past

Dissolved copper binding ligands from seawater samples during POLARSTERN cruise PS100/ GN05 (ARK-XXX/2)

Copper (Cu) is a bio-essential trace metal involved in many phytoplankton metabolic processes. In seawater, its bioavailability is controlled by the formation of organic complexes with binding ligands which also controls the toxicity of free cupric ion (Cu²⁺). Despite this key role, information about Cu speciation is scarce, especially in the Arctic Ocean. However, this oceanographic region is essential to understand the copper biogeochemical cycle. This dataset contains the results of Cu complexation measurements in station depth profiles sampled in Fram Strait and Greenland Shelf. Samples were collected during GEOTRACES expedition GN05 (PS100) between 21 July and 1 September 2016, following GEOTRACES guidelines (https://www.geotraces.org). Copper binding ligand concentrations (LCu) and conditional stability constants (logKcond) were measured by Competitive-Ligand Exchange Adsorptive Cathodic Stripping Voltammetry (CLE-ACSV) using Salicylaldoxime (SA) as competitive ligand (Campos and van den Berg, 1994). The concentration of dissolved copper has been reported by Krisch et al. (2021) (doi:10.1594/PANGAEA.933431)

Influence of secondary metabolites on surface chemistry and metal adsorption of a devitalized lichen biomonitor

Melanised and non-melanised thalli of the devitalized lichen biomonitor Pseudevernia furfuracea have higher binding site concentration than mosses, adsorbing 30% more Zn2+, regardless of melanin presence. Despite the broad use of lichens as biomonitors of airborne trace elements, the surface chemistry and metal adsorption parameters of these organisms are still poorly known. The current investigation is aimed at (i) quantifying the acid-base surface properties and the first-order physical-chemical parameters of Cu2+ and Zn2+ adsorption of devitalized Pseudevernia furfuracea, a lichen commonly used in biomonitoring of airborne trace elements, and (ii) comparing the results with those available for moss biomonitors. Equilibrium constants and metal-binding site concentrations were calculated with a thermodynamic model by taking into account the presence/absence of ancillary extracellular cell wall compounds, namely melanin and acetone-soluble lichen substances. An acid–base titration experiment performed in the pH range of 3–10 showed that melanised and non-melanised P. furfuracea samples have lower pHPZC (3.53–3.99) and higher metal-binding site concentrations (0.96–1.20 mmol g−1) compared to that of the mosses investigated so far at the same experimental conditions. Melanin biosynthesis increased the content of carboxyl and phosphoryl groups and reduces that of amine/polyphenols. Cu2+ and Zn2+ adsorption was unaffected by the degree of melanisation while the removal of extracellular lichen substances slightly decreased Zn2+ adsorption. Although Cu2+ and Zn2+ adsorption parameters related to P. furfuracea surfaces were 3 times lower than in the mosses, lichen samples adsorbed the same amount of Cu2+ and 30% more Zn2+. The present study contributes in understanding the role of ancillary cell wall compounds in Cu2+ and Zn2+ adsorption in a model lichen. It also provides a first comparison between the surface physico-chemical characteristics of lichens and mosses frequently used as biomonitors of trace elements

DataSheet_1_Seasonal variability of coastal pH and CO2 using an oceanographic buoy in the Canary Islands.docx

Ocean acidification, caused by the absorption of carbon dioxide (CO2) from the atmosphere into the ocean, ranks among the most critical consequences of climate change for marine ecosystems. Most studies have examined pH and CO2 trends in the open ocean through oceanic time-series research. The analysis in coastal waters, particularly in island environments, remains relatively underexplored. This gap in our understanding is particularly important given the profound implications of these changes for coastal ecosystems and the blue economy. The present study focuses on the ongoing monitoring effort that started in March 2020 along the east coast of Gran Canaria, within the Gando Bay, by the CanOA-1 buoy. This monitoring initiative focuses on the systematic collection of multiple variables within the CO2 system, such as CO2 fugacity (fCO2), pH (in total scale, pHT), total inorganic carbon (CT), and other hydrographic variables including sea surface salinity (SSS), sea surface temperature (SST) and wind intensity and direction. Accordingly, the study allows the computation of the CO2 flux (FCO2) between the surface waters and the atmosphere. During the study period, stational (warm and cold periods) behavior was found for all the variables. The lowest SST values were recorded in March, with a range of 18.8-19.3°C, while the highest SST were observed in September and October, ranging from 24.5-24.8°C. SST exhibited an annual increase with a rate of 0.007°C yr-1. Warmer months increased SSS, while colder periods, influenced by extreme events like tropical storms, led to lower salinity (SSS=34.02). The predominant Trade Winds facilitated the arrival of deeper water, replenishing seawater. The study provided insights into atmospheric CO2. Atmospheric fCO2 averaged 415 ± 4 µatm (2020-2023). Surface water fCO2sw presented variability, with the highest values recorded in September and October, peaking at 437 µatm in September 2021. The lowest values for fCO2sw were found in February 2021 (368 µatm). From 2020 to 2023, surface water fCO2sw values displayed an increasing rate of 1.9 µatm yr-1 in the study area. The assessment of fCO2sw decomposition into thermal and non-thermal processes revealed the importance of SST on the fCO2sw. Nevertheless, in the present study, it is crucial to remark the impact of non-thermal factors on near-shallow coastal regions. Our findings highlight the influence of physical factors such as tides, and wind effect to horizontal mixing in these areas. The CT showed a mean concentration of 2113 ± 8 μmol kg-1 and pH at in-situ temperature (pHT,IS) has a mean value of 8.05 ± 0.02. The mean FCO2 from 2020 to 2023 was 0.34 ± 0.04 mmol m-2 d-1 (126 ± 13 mmol m-2 yr-1) acting as a slight CO2 source. In general, between May and December were the months when the area was a source of CO2. Extrapolating to the entire 6 km2 of Gando Bay, the region sourced 33 ± 4 Tons of CO2 yr-1.</p

Storage and recycling of major and trace element in mangroves

The role of mangroves in sequestering metal and nutrients in sediment has been described in the past, but knowl-edge gaps still exist on storage capacity and recycling fluxes of elements in plant biomass, notably concerning their magnitude in root uptake and loss by litterfall. This study addresses the storage and transport pathways of 16 elements, classified as macro-nutrients (Ca, Mg, Na, K), micro-nutrients (Fe, Mn, Ni, Co, Cu, Cr, Zn, Mo), and potential toxicants (Al, Cd, Sn, Pb) in the world's largest mangroves, the Sundarbans. Elemental concentra-tions in plant organs were generally lower than in the sediment. The stock of macro and micro-nutrients in plant biomass varied from 60 to 2717 and 0.003 to 37.7 Mg ha(-1) respectively, with highest values observed for Na and lowest for Cd. The Avicennia species exhibited the maximal accumulation of all elements. Translocation of major elements to different plant organs increased with increasing their concentrations in the sediment. Ele-mental loss via litterfall indicated that Sundarbans mangrove could act as a source, particularly of Mn, to the Bay of Bengal. Moreover, belowground uptake of the 16 elements showed 2-3 fold higher fluxes than their loss via litterfall. There was a significant retention of some trace elements (notably Mo, Cd, and Sn) in plant biomass, which might allow one to use these mangroves for phytoremediation and restoration purposes. We conclude that mangroves efficiently store and remobilize major and trace elements from the sediments by root uptake and recycle back to sediment surface via litterfall

Chemical and structural characterization of copper adsorbed on mosses (Bryophyta)

The adsorption of copper on passive biomonitors (devitalized mosses Hypnum sp., Sphagnum denticulatum, Pseudoscleropodium purum and Brachythecium rutabulum) was studied under different experimental conditions such as a function of pH and Cu concentration in solution. Cu assimilation by living Physcomitrella patents was also investigated. Molecular structure of surface adsorbed and incorporated Cu was studied by X-ray Absorption Spectroscopy (XAS). Devitalized mosses exhibited the universal adsorption pattern of Cu as a function of pH, with a total binding sites number 0.05-0.06 mmolg and a maximal adsorption capacity of 0.93-1.25 mmolg for these devitalized species. The Extended X-ray Absorption Fine Structure (EXAFS) fit of the first neighbor demonstrated that for all studied mosses there are ~4.5 O/N atoms around Cu at ~1.95 Å likely in a pseudo-square geometry. The X-ray Absorption Near Edge Structure (XANES) analysis demonstrated that Cu(II)-cellulose (representing carboxylate groups) and Cu(II)-phosphate are the main moss surface binding moieties, and the percentage of these sites varies as a function of solution pH. P. patens exposed during one month to Cu yielded ~20% of Cu(I) in the form of Cu-S(CN) complexes, suggesting metabolically-controlled reduction of adsorbed and assimilated Cu.This study was supported by the MOSSclone project by the European Union in the Seventh Framework Program (FP7-ENV.2011.3.1.9-1) for Research and Technological Development as well as by BIO-GEO-CLIM grant No 14.B25.31.0001 and RSF grant no. 15-17-10009 (30%)

Distribution of copper-binding ligands in Fram Strait and influences from the Greenland Shelf (GEOTRACES GN05)

Highlights • Cu complexation was measured for the first time in the Fram Strait region. • Cu-binding ligand concentrations and binding strength varied longitudinally in the Fram Strait. • More than 99 % of dCu was organically complexed by strong ligands. • On the Greenland shelf the Transpolar Drift and the coastal processes were the main sources of Cu ligands. Abstract The Fram Strait represents the major gateway of Arctic Ocean waters towards the Nordic Seas and North Atlantic Ocean and is a key region to study the impact of climate change on biogeochemical cycles. In the region, information about trace metal speciation, such as copper, is scarce. This manuscript presents the concentrations and conditional stability constants of copper-binding ligands (LCu and log KcondCu2+L) in the water column of Fram Strait and the Greenland shelf (GEOTRACES cruise GN05). Cu-binding ligands were analysed by Competitive Ligand Exchange-Adsorptive Cathodic Stripping Voltammetry (CLE-ACSV) using salicylaldoxime (SA) as competitive ligand. Based on water masses and the hydrodynamic influences, three provinces were considered (coast, shelf, and Fram Strait) and differences were observed between regions and water masses. The strongest variability was observed in surface waters, with increasing LCu concentrations (mean values: Fram Strait = 2.6 ± 1.0 nM; shelf = 5.2 ± 1.3 nM; coast = 6.4 ± 0.8 nM) and decreasing log KcondCu2+L values (mean values: Fram Strait = 15.7 ± 0.3; shelf = 15.2 ± 0.3; coast = 14.8 ± 0.3) towards the west. The surface LCu concentrations obtained above the Greenland shelf indicate a supply from the coastal environment to the Polar Surface Water (PSW) which is an addition to the ligand exported from the central Arctic to Fram Strait. The significant differences (in terms of LCu and log KcondCu2+L) between shelf and coastal samples were explained considering the processes which modify ligand concentrations and binding strengths, such as biological activity in sea-ice, phytoplankton bloom in surface waters, bacterial degradation, and meltwater discharge from 79NG glacier terminus. Overall, the ligand concentration exceeded those of dissolved Cu (dCu) and kept the free copper (Cu2+) concentrations at femtomolar levels (0.13–21.13 fM). This indicates that Cu2+ toxicity limits were not reached and dCu levels were stabilized in surface waters by organic complexes, which favoured its transport to the Nordic Seas and North Atlantic Ocean and the development of microorganism

Chemical and structural characterization of copper adsorbed on mosses (Bryophyta)

The adsorption of copper on passive biomonitors (devitalized mosses Hypnum sp., Sphagnum denticulatum, Pseudoscleropodium purum and Brachythecium rutabulum) was studied under different experimental conditions such as a function of pH and Cu concentration in solution. Cu assimilation by living Physcomitrella patents was also investigated. Molecular structure of surface adsorbed and incorporated Cu was studied by X-ray Absorption Spectroscopy (XAS). Devitalized mosses exhibited the universal adsorption pattern of Cu as a function of pH, with a total binding sites number 0.05–0.06 mmolgdry−1 and a maximal adsorption capacity of 0.93–1.25 mmolgdry−1 for these devitalized species. The Extended X-ray Absorption Fine Structure (EXAFS) fit of the first neighbor demonstrated that for all studied mosses there are ∼4.5 O/N atoms around Cu at ∼1.95 Å likely in a pseudo-square geometry. The X-ray Absorption Near Edge Structure (XANES) analysis demonstrated that Cu(II)-cellulose (representing carboxylate groups) and Cu(II)-phosphate are the main moss surface binding moieties, and the percentage of these sites varies as a function of solution pH. P. patens exposed during one month to Cu2+ yielded ∼20% of Cu(I) in the form of Cu–S(CN) complexes, suggesting metabolically-controlled reduction of adsorbed and assimilated Cu2+