Browsing by Author "Verdugo, Josefa"

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    Climate relevant trace gases (N2O and CH4) in the Eurasian Basin (Arctic Ocean)
    (2016) Verdugo, Josefa; Damm, Ellen; Snoeijs, Pauline; Diez Moreno, Beatriz
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    Coastal Bacterial Community Response to Glacier Melting in the Western Antarctic Peninsula
    (2021) Alcaman-Arias, Maria Estrella; Fuentes-Alburquenque, Sebastian; Vergara-Barros, Pablo; Cifuentes-Anticevic, Jeronimo; Verdugo, Josefa; Polz, Martin; Farias, Laura; Pedros-Alio, Carlos; Diez, Beatriz
    Current warming in the Western Antarctic Peninsula (WAP) has multiple effects on the marine ecosystem, modifying the trophic web and the nutrient regime. In this study, the effect of decreased surface salinity on the marine microbial community as a consequence of freshening from nearby glaciers was investigated in Chile Bay, Greenwich Island, WAP. In the summer of 2016, samples were collected from glacier ice and transects along the bay for 16S rRNA gene sequencing, while in situ dilution experiments were conducted and analyzed using 16S rRNA gene sequencing and metatranscriptomic analysis. The results reveal that certain common seawater genera, such as Polaribacter, Pseudoalteromonas and HTCC2207, responded positively to decreased salinity in both the bay transect and experiments. The relative abundance of these bacteria slightly decreased, but their functional activity was maintained and increased the over time in the dilution experiments. However, while ice bacteria, such as Flavobacterium and Polaromonas, tolerated the increased salinity after mixing with seawater, their gene expression decreased considerably. We suggest that these bacterial taxa could be defined as sentinels of freshening events in the Antarctic coastal system. Furthermore, these results suggest that a significant portion of the microbial community is resilient and can adapt to disturbances, such as freshening due to the warming effect of climate change in Antarctica.
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    Dark Diazotrophy during the Late Summer in Surface Waters of Chile Bay, West Antarctic Peninsula
    (2022) Alcaman-Arias, Maria E.; Cifuentes-Anticevic, Jeronimo; Castillo-Inaipil, Wilson; Farias, Laura; Sanhueza, Cynthia; Fernandez-Gomez, Beatriz; Verdugo, Josefa; Abarzua, Leslie; Ridley, Christina; Tamayo-Leiva, Javier; Diez, Beatriz
    Although crucial for the addition of new nitrogen in marine ecosystems, dinitrogen (N-2) fixation remains an understudied process, especially under dark conditions and in polar coastal areas, such as the West Antarctic Peninsula (WAP). New measurements of light and dark N-2 fixation rates in parallel with carbon (C) fixation rates, as well as analysis of the genetic marker nifH for diazotrophic organisms, were conducted during the late summer in the coastal waters of Chile Bay, South Shetland Islands, WAP. During six late summers (February 2013 to 2019), Chile Bay was characterized by high NO3- concentrations (similar to 20 mu M) and an NH4+ content that remained stable near 0.5 mu M. The N:P ratio was approximately 14.1, thus close to that of the Redfield ratio (16:1). The presence of Cluster I and Cluster III nifH gene sequences closely related to Alpha-, Delta- and, to a lesser extent, Gammaproteobacteria, suggests that chemosynthetic and heterotrophic bacteria are primarily responsible for N-2 fixation in the bay. Photosynthetic carbon assimilation ranged from 51.18 to 1471 nmol C L-1 d(-1), while dark chemosynthesis ranged from 9.24 to 805 nmol C L-1 d(-1). N2 fixation rates were higher under dark conditions (up to 45.40 nmol N L-1 d(-1)) than under light conditions (up to 7.70 nmol N L-1 d(-1)), possibly contributing more than 37% to new nitrogen-based production (>2.5 g N m(-2) y(-1)). Of all the environmental factors measured, only PO43--exhibited a significant correlation with C and N-2 rates, being negatively correlated (p < 0.05) with dark chemosynthesis and N-2 fixation under the light condition, revealing the importance of the N:P ratio for these processes in Chile Bay. This significant contribution of N-2 fixation expands the ubiquity and biological potential of these marine chemosynthetic diazotrophs. As such, this process should be considered along with the entire N cycle when further reviewing highly productive Antarctic coastal waters and the diazotrophic potential of the global marine ecosystem.