ALBERT

Description: This paper reports a physicochemical study (thermodynamic and kinetic data) describing the ability of Rubus ulmifolius biomass (dead leaves) for metal uptake. The toxicity of aluminum is a major problem for crops in acidic soils and therefore, aluminum has been selected. The results obtained indicate that dead R. ulmifolius leaves uptake up to 10000mg/kg on its surface in less than 60min. This suggests that R. ulmifolius can be an excellent component with adsorbent properties for aquatic environments and in particular for amendments to be used in acidic soils in order to control aluminum levels, thus its toxicity. The results obtained have been critically analyzed and compared with literature on aluminum bioaccumulation. The application of a pseudo-second order kinetic equation, not previously used in toxicity studies, is discussed. Moreover, a good linear correlation between stability constants for Al3+ complexes with several defined ligands and the Langmuir affinity constants obtained from the corresponding adsorption isotherm has been found. Therefore, in addition to its ethno-botanical relevance, applications of R. ulmifolius as a detoxifier for aluminum in a simulated acidic gastrointestinal fluid, as phytostabilization agent in amendments or in natural attenuation cycles or as biomass for wastewater treatment containing aluminum, are suggested.

Description: Concentrations of the toxic element lead (Pb) are elevated in seawater due to historical emissions. While anthropogenic atmospheric emissions are the dominant source of dissolved Pb (dPb) to the Atlantic Ocean, evidence is emerging of a natural source associated with subglacial discharge into the ocean but this has yet to be constrained around Greenland. Here, we show subglacial discharge from the cavity underneath Nioghalvfjerdsbræ floating ice tongue, is a previously unrecognized source of dPb to the NE Greenland Shelf. Contrasting cavity-inflowing and cavity-outflowing waters, we constrain the associated net-dPb flux as 2.2 ± 1.4 Mg·yr−1, of which ∼90% originates from dissolution of glacial bedrock and cavity sediments. We propose that the retreat of the floating ice tongue, the ongoing retreat of many glaciers on Greenland, associated shifts in sediment dynamics, and enhanced meltwater discharges into shelf waters may result in pronounced changes, possibly increases, in net-dPb fluxes to coastal waters. Key Points - Helium and neon show strong evidence for a subglacial source of Pb discharging onto the NE Greenland Shelf - Contrasting inflowing and outflowing waters beneath the floating ice tongue of Nioghalvfjerdsbræ shows a 2-3-fold dPb enrichment - The dissolved Pb flux from Nioghalvfjerdsbræ (2.2 ± 1.4 Mg·yr−1) is comparable to small Arctic rivers, with ∼90% of a sedimentary origin

Description: We present high-resolution profiles of dissolved, labile and total particulate trace metals (TMs) on the Northeast Greenland shelf from GEOTRACES cruise GN05 in August 2016. Combined with radium isotopes, stable oxygen isotopes, and noble gas measurements, elemental distributions suggest that TM dynamics were mainly regulated by the mixing between North Atlantic-derived Intermediate Water, enriched in labile particulate TMs (LpTMs), and Arctic surface waters, enriched in Siberian shelf-derived dissolved TMs (dTMs; Co, Cu, Fe, Mn, and Ni) carried by the Transpolar Drift. These two distinct sources were delineated by salinity-dependent variations of dTM and LpTM concentrations and the proportion of dTMs relative to the total dissolved and labile particulate ratios. Locally produced meltwater from the Nioghalvfjerdsbræ (79NG) glacier cavity, distinguished from other freshwater sources using helium excess, contributed a large pool of dTMs to the shelf inventory. Localized peaks in labile and total particulate Cd, Co, Fe, Mn, Ni, Cu, Al, V, and Ti in the cavity outflow, however, were not directly contributed by submarine melting. Instead, these particulate TMs were mainly supplied by the re-suspension of cavity sediment particles. Currently, Arctic Ocean outflows are the most important source of dFe, dCu and dNi on the shelf, while LpTMs and up to 60% of dMn and dCo are mainly supplied by subglacial discharge from the 79NG cavity. Therefore, changes in the cavity-overturning dynamics of 79NG induced by glacial retreat, and alterations in the transport of Siberian shelf-derived materials with the Transport Drift may shift the shelf dTM-LpTM stoichiometry in the future. Key Points The overall dissolved and particulate trace metal dynamics were mainly regulated by the mixing with Arctic surface waters Resuspension of cavity sediments is a major localized source of labile and total particulate Cd, Co, Fe, Mn, Ni, Cu, Al, V, and Ti Whilst dissolved and particulate trace metals are mostly coupled on the Greenland shelf, cavity outflow decouples both phases

Description: The Arctic Ocean is considered a source of micronutrients to the Nordic Seas and the North Atlantic Ocean through the gateway of Fram Strait. However, there is a paucity of trace element data from across the Arctic Ocean gateways, and so it remains unclear how Arctic and North Atlantic exchange shapes micronutrient availability in the two ocean basins. In 2015 and 2016, GEOTRACES cruises sampled the Barents Sea Opening (GN04, 2015) and Fram Strait (GN05, 2016) for dissolved iron (dFe), manganese (dMn), cobalt (dCo), nickel (dNi), copper (dCu) and zinc (dZn). Together with the most recent synopsis of Arctic-Atlantic volume fluxes, the observed trace element distributions suggest that Fram Strait is the most important gateway for Arctic-Atlantic dissolved micronutrient exchange as a consequence of Intermediate and Deep Water transport. Combining fluxes from Fram Strait and the Barents Sea Opening with estimates for Davis Strait (GN02, 2015) suggests an annual net southward flux of 2.7 ± 2.4 Gg·a-1 dFe, 0.3 ± 0.3 Gg·a-1 dCo, 15.0 ± 12.5 Gg·a-1 dNi and 14.2 ± 6.9 Gg·a-1 dCu from the Arctic towards the North Atlantic Ocean. Arctic-Atlantic exchange of dMn and dZn were more balanced, with a net southbound flux of 2.8 ± 4.7 Gg·a-1 dMn and a net northbound flux of 3.0 ± 7.3 Gg·a-1 dZn. Our results suggest that ongoing changes to shelf inputs and sea ice dynamics in the Arctic, especially in Siberian shelf regions, affect micronutrient availability in Fram Strait and the high latitude North Atlantic Ocean.

Description: The physicochemical characteristics of dissolved organic matter (DOM) strongly influence its interactions with inorganic species such as protons and trace elements in natural waters. We collected water samples at Boknis Eck, a time series station in the Baltic Sea with a low exposure to freshwater inputs, to investigate how seasonal fluctuations impact the proton binding properties of the isolated DOM. We used potentiometric titrations to assess the binding properties of solid-phase extracted DOM (SPE–DOM) over a seasonal cycle. We report and critically analyze the first NICA parameters estimates of carboxylic-like and phenolic-like sites for brackish water SPE–DOM. The total amount of functional groups (QmaxH,tot) showed no seasonal fluctuations and an average value of 136 ± 5.2 mmol·mol C–1. The average proton affinity (logKH) and binding site heterogeneity (m) showed a relatively minor variability for samples obtained between April and September, when the water remained stratified. These results contribute to a better understanding of the ion binding characteristics of DOM in natural brackish waters.

Description: Marine dissolved organic matter (DOM) presents key thermodynamic properties that are not yet fully constrained. Here, we report the distribution of binding sites occupied by protons (i.e., proton affinity spectra) and parametrize the median intrinsic proton binding affinities (log K̅H) and heterogeneities (m), for DOM samples extracted from the North Atlantic. We estimate that 11.4 ± 0.6% of C atoms in the extracted marine DOM have a functional group with a binding site for ionic species. The log K̅H of the most acidic groups was larger (4.01–4.02 ± 0.02) than that observed in DOM from coastal waters (3.82 ± 0.02), while the chemical binding heterogeneity parameter increased with depth to values (m1= 0.666 ± 0.009) ca. 10% higher than those observed in surface open ocean or coastal samples. On the contrary, the log K̅H for the less acidic groups shows a difference between the surface (10.01 ± 0.08) and deep (9.22 ± 0.35) samples. The latter chemical groups were more heterogeneous for marine than for terrestrial DOM, and m2 decreased with depth to values of 0.28 ± 0.03. Binding heterogeneity reflects aromatic carbon compounds’ persistence and accumulation in diverse, low-abundance chemical forms, while easily degradable low-affinity groups accumulate more uniformly in the deep ocean.

Description: The substance Tris (or THAM, 2-amino-2-hydroxymethyl-1,3-propanediol) is used in the preparation of pH buffer solutions for applications in natural water chemistry, including seawater. The development of a chemical speciation model of buffer solutions containing Tris, TrisH+, and the major ions of seawater is desirable, so that the effects of changes in the composition and concentration of the medium on pH can be calculated. The Pitzer activity coefficient equations, commonly used in such speciation models, describe the thermodynamic properties of solutions in terms of interactions between dissolved ions and uncharged solute species. To determine some of these interactions, we have measured solubilities of Tris(s) in water and aqueous solutions of NaCl, TrisHCl, and (TrisH)2SO4 and the solubility of NaCl(s) in aqueous Tris(aq), from 5 to 45 °C. We report measurements of the water activities of Tris solutions at 293.5 K to high supersaturation with respect to the solid. Using the Pitzer equations, we compare our results to literature data yielding stoichiometric dissociation constants of TrisH+ in aqueous NaCl, and to electromotive forces of cells containing dissolved Tris, TrisHCl, and NaCl. Values of parameters for the interactions of Tris with the ions TrisH+, Na+, and SO42– at 25 °C are determined.

Description: Climate change has led to a ~ 40% reduction in summer Arctic sea-ice cover extent since the 1970s. Resultant increases in light availability may enhance phytoplankton production. Direct evidence for factors currently constraining summertime phytoplankton growth in the Arctic region is however lacking. GEOTRACES cruise GN05 conducted a Fram Strait transect from Svalbard to the NE Greenland Shelf in summer 2016, sampling for bioessential trace metals (Fe, Co, Zn, Mn) and macronutrients (N, Si, P) at ~ 79°N. Five bioassay experiments were conducted to establish phytoplankton responses to additions of Fe, N, Fe + N and volcanic dust. Ambient nutrient concentrations suggested N and Fe were deficient in surface seawater relative to typical phytoplankton requirements. A west-to-east trend in the relative deficiency of N and Fe was apparent, with N becoming more deficient towards Greenland and Fe more deficient towards Svalbard. This aligned with phytoplankton responses in bioassay experiments, which showed greatest chlorophyll-a increases in + N treatment near Greenland and + N + Fe near Svalbard. Collectively these results suggest primary N limitation of phytoplankton growth throughout the study region, with conditions potentially approaching secondary Fe limitation in the eastern Fram Strait. We suggest that the supply of Atlantic-derived N and Arctic-derived Fe exerts a strong control on summertime nutrient stoichiometry and resultant limitation patterns across the Fram Strait region.