One of the main reasons behind our current lack of understanding of iron cycling in the oceans is our inability to characterize the ligands that control iron solubility, photosensitivity, reactivity, and bioavailability. We currently lack consensus about the nature and origin of these ligands. Here, we present the first field application of a new methodological development that allows the selective quantification of the fraction of Fe complexed to humic substances (HS). In the HS-rich surface Arctic waters, including the Fe-rich Transpolar Drift (TPD), we found that HS iron binding groups were largely occupied by iron (49%). The overall contribution of Fe−HS complexes to DFe concentrations was substantial at 80% without significant differences between TPD and non-TPD waters. Stabilization and transport of large concentrations of DFe across the surface of the Arctic Ocean are due to the formation of high concentrations of Fe−HS complexes. Competition of Arctic Fe−HS complexes with desferrioxamine and EDTA indicated that their stability constants are considerably higher than the stability constants previously found for riverine HS in temperate estuaries and HS standard material. This is the first case of identification of the ligand-dominating iron speciation over a specific region of the global ocean.

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Samples inside and outside the Arctic Ocean's TransPolar Drift (TPD) have been analyzed for Fe‐binding organic ligands (Lt) with Competitive Ligand Exchange Adsorptive Stripping Voltammetry (CLE‐AdCSV) using salicylaldoxime (SA). This analysis is compared to prior analyses with CLE‐AdCSV using 2‐(2‐thiazolylazo)‐p‐cresol (TAC). The TPD's strong terrestrial influence is used to compare the performance of both CLE‐AdCSV methods in representing the nature of natural organic ligands. These measurements are compared against direct voltammetric determination of humic substances (HS) and spectral properties of dissolved organic matter. The relationship between the two CLE‐AdCSV derived [Lt] versus HS in the TPD has a comparable slope, with a 40% offset toward higher values obtained with SA. Higher [Lt] values inside the TPD, most probably due to HS, explain high dissolved Fe concentrations transported over the Arctic Ocean by the TPD. Outside of the TPD in the surface Arctic Ocean HS occur as well but at lower concentrations. Here changes in HS relate to changes in dissolved Fe concentration and to [Lt] obtained with SA, whereas [Lt] obtained with TAC remain constant. Moreover, with decreasing HS the offset between the methods using TAC and SA decreases. We surmise that in the presence of HS, the TAC method detects HS only either at higher concentrations or of specific composition. On the other hand, the SA method might overestimate [Lt], as an offset with the TAC method that remains constant where HS are not detected. Regardless, HS are the dominant type of Fe‐binding organic ligand in the surface of the Arctic Ocean.

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The eugenol is the active ingredient of clove oil and it has shown to be effective and safe as fish anesthetic. In this study were evaluated the effects of different concentrations of eugenol for anesthesia, recovery time, blood glucose and hematocrit percentage of pearl cichlid (Geophagus brasiliensis) juveniles. Concentrations of 50, 80, 100, 120, 150, 170 and 200 mg L -1 eugenol were evaluated in terms of time to achieve the different stages of anesthesia and recovery in a completely randomized design (CRD) with 12 repetitions. These results were tested using the Kruskal-Wallis test with subsequent Dunn test. The evaluated concentrations had anesthetic action of the deep induction 172.57 ± 25 s (50 mg L -1 ) and the period of full recovery of 516.25 ± 102 s (200 mg L -1 ), with statistical difference between the treatments at all the stages. The eugenol effect on blood glucose and on hematocrit percentage at 0 h after deep anesthesia was evaluated for concentrations of 0; 50; 80; 100; 150; 200 mg L -1 , in a completely randomized design with five replications, and the results were assessed by One-Way ANOVA. Glucose and percentage of hematocrit: no statistically significant differences (P>0.05) were observed for these variables. All concentrations of eugenol showed to be effective as an anesthetic for G. brasiliensis and did not affect the survival, blood glucose and the percentage of hematocrit. To minimize adverse effects and achieve faster recovery is indicate the use of 50-80 mg L -1 of eugenol for pearl cichlid juveniles.Keywords: anesthesia; clove oil; fish; pearl cichlid UTILIZAÇÃO DE EUGENOL COMO ANESTÉSICO EM JUVENIS DE Geophagus brasiliensis RESUMOO eugenol, substância ativa do óleo de cravo, tem demonstrado ser eficiente e seguro como anestésico para peixes. Neste estudo foram avaliados os efeitos de diferentes concentrações de eugenol na anestesia, tempo de recuperação, glicemia e percentual de hematócrito de cará (Geophagus brasiliensis). Concentrações de 50, 80, 100, 120, 150, 170 e 200 mg L -1 de eugenol foram avaliadas em relação aos tempos para atingir os diferentes estágios de anestesia e de recuperação, em desenho inteiramente casualizado (DIC), com 12 repetições. Os resultados foram analisados pelos testes de Kruskal-Wallis e teste Dunn. As concentrações avaliadas produziram ação anestésica em período de indução profunda de 172,57 ± 25 s (50 mg L -1 ) e no período de total recuperação de 516,25 ± 102 s (200 mg L -1 ), com diferença estatística entre os tratamentos para todas as fases avaliadas. Foi avaliado o efeito do eugenol sobre a glicose no sangue e sobre o percentual de hematócrito, em 0 h após anestesia profunda, nas concentrações 0, 50, 80, 100, 150 e 200 mg L -1 , em DIC com cinco repetições, e os resultados avaliados através de ANOVA uma via. Não foram observadas diferenças estatísticas significativas (P>0,05) para glicose e hematócrito. Todas as concentrações de eugenol avaliadas apresentaram eficiência como anestésico para G. brasiliensis e não afetaram a sobrevivência,...