Browsing by Author "Farias, Laura"

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    Biogeochemical characteristics of a long-lived anticyclonic eddy in the eastern South Pacific Ocean
    (2016) Cornejo D'Ottone, Marcela; Bravo, Luis; Ramos, Marcel; Pizarro, Oscar; Karstensen, Johannes; Gallegos, Mauricio; Correa-Ramirez, Marco; Silva, Nelson; Farias, Laura; Karp-Boss, Lee
    Mesoscale eddies are important, frequent, and persistent features of the circulation in the eastern South Pacific (ESP) Ocean, transporting physical, chemical and biological properties from the productive shelves to the open ocean. Some of these eddies exhibit subsurface hypoxic or suboxic conditions and may serve as important hotspots for nitrogen loss, but little is known about oxygen consumption rates and nitrogen transformation processes associated with these eddies. In the austral fall of 2011, during the Tara Oceans expedition, an intrathermocline, anticyclonic, mesoscale eddy with a suboxic (< aEuro-2aEuro-A mu molaEuro-kg(-1) of O-2), subsurface layer (200-400aEuro-m) was detected similar to aEuro parts per thousand aEuro-900aEuro-km off the Chilean shore (30A degrees aEuro-S, 81A degrees aEuro-W). The core of the eddy's suboxic layer had a temperature-salinity signature characteristic of Equatorial Subsurface Water (ESSW) that at this latitude is normally restricted to an area near the coast. Measurements of nitrogen species within the eddy revealed undersaturation (below 44aEuro-%) of nitrous oxide (N2O) and nitrite accumulation (> aEuro-0.5aEuro-A mu M), suggesting that active denitrification occurred in this water mass. Using satellite altimetry, we were able to track the eddy back to its region of formation on the coast of central Chile (36.1A degrees aEuro-S, 74.6A degrees aEuro-W). Field studies conducted in Chilean shelf waters close to the time of eddy formation provided estimates of initial O-2 and N2O concentrations of the ESSW source water in the eddy. By the time of its offshore sighting, concentrations of both O-2 and N2O in the subsurface oxygen minimum zone (OMZ) of the eddy were lower than concentrations in surrounding water and "source water" on the shelf, indicating that these chemical species were consumed as the eddy moved offshore. Estimates of apparent oxygen utilization rates at the OMZ of the eddy ranged from 0.29 to 44aEuro-nmolaEuro-L(-1)aEuro-d(-1) and the rate of N2O consumption was 3.92aEuro-nmolaEuro-L(-1)aEuro-d(-1). These results show that mesoscale eddies affect open-ocean biogeochemistry in the ESP not only by transporting physical and chemical properties from the coast to the ocean interior but also during advection, local biological consumption of oxygen within an eddy further generates conditions favorable to denitrification and loss of fixed nitrogen from the system.
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    Climate projections of oceanographic variables in the Exclusive Economic Zone of Ecuador: A 21st century perspective to inform impact and adaptation assessment
    (2024) Winckler, Patricio; Farias, Laura; Vicuna, Sebastian; Esparza, Cesar; Mora, Javiera; Chubretovic, Rosario; Cabrera, Francisco; Zambrano-Sanchez, Nicolas; Caza, Pablo; Gonzalez, Rosa Ana
    Climate projections of ocean variables are essential to inform adaptation strategies and plans involving open and coastal oceanic regions. Assessment of baseline and projections of sea surface temperature (SST), pH, dissolved oxygen (DO), mean sea level (MSL), waves coastal flooding within Ecuador's Exclusive Economic Zone, including Galapagos Islands are reported herein. With different magnitudes of change, both near-future (2021-2050) and far-future projections (2051-2080) show a statistically robust increase in SST, MSL rise and a reduction in pH, a proxy for acidification. In contrast, DO decrease is only observed in surface (0-100 m) but not in subsurface waters (100-400 m). The likelihood of extreme sea level events in the coastal cities of La Libertad, Manta and Esmeraldas would remain almost unchanged for near-future projections (2026-2045) whereas, for end-ofcentury projections (2081-2100), historical 1 in a 100-year extreme flooding events would become yearly occurrences. The generated data product offers a state-of-the-art research and management tool for the 21st century under the combined stressors of global climate change. Since the eastern Tropical Pacific Ocean is one of the most productive and biodiverse worldwide due to the equatorial upwelling system, possible impacts on marine biodiversity, social, and economic systems are discussed.
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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.
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    Distribution of dissolved methane and nitrous oxide in Chilean coastal systems of the Magellanic Sub-Antarctit region (50°-55°S)
    (2018) Farias, Laura; Bello, Estrella; Arancibia, Gresel; Fernandez, Josseline
    Nitrous oxide (H2O) and methane (CH4()) are greenhouse gases and active in the depletion of the ozone layer. These gases, originating from both anthropogenic and natural sources, are mainly released to the atmosphere from coastal areas, including continental shelves, estuaries and cords. Surface distribution of dissolved N2O and CH4 during the austral spring were described within the Magellanic Sub -Antarctic region (50-55 degrees S, Chile) with a coastal area that has a complex system of Cords, channels, gulf and, bays. A narrow range of N2O concentrations were observed from under-saturations (similar to 65%), as result of freshwater/glacial flow into fjord heads, to slight super-saturations (similar to 120-150%) in cord mouths and adjacent marine zones. One exception was Otway Sound, where a penguin colony is situated, with N2O levels of up to 218%. In contrast, CH4 concentrations presented a wide range of saturations between 47.9% and 483%, with a spatial distribution that mainly corresponded to the type of hydrographic/geomorphologic basin; in the southern Patagonian Andes (mostly covered by the southern Ice Fields) CH4 levels varied between 65 and 80% in the marine area, and 180% saturation in the channels and Cords; whereas in the southern Patagonian tableland (Magellan Strait) higher CH4 concentrations, up to 483% saturation, were observed apparently associated with continental inputs (peatland and tundra vegetation). N2O concentrations were positively correlated with salinity and nutrients, indicating that the majority of N2O and nutrients (except silicate) originated from the Sub-Antarctic Water Mass (SAAW), which mixes with N2O-de-pleated freshwater. However, CH4 concentrations did not correlate with any oceanographic variables, suggesting that they originate from local marine/terrestrial interactions, The Magellanic Sub -Antarctic region acts as a modest source of N2O and CH4, to the atmosphere with effluxes of 6.20 +/- 10.13 and 16.88 +/- 27.04 mu mol m(-2) d(-1) respectively. Due to climate change and a growth in anthropogenic activities such as salmon farming, future emissions of N2O and CH4 within this remote region remain uncertain.
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    Dust fluxes and iron fertilization in Holocene and Last Glacial Maximum climates
    (2015) Lambert, Fabrice; Tagliabue, Alessandro; Shaffer, Gary; Lamy, Frank; Winckler, Gisela; Farias, Laura; Gallardo, Laura; De Pol-Holz, Ricardo
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    Proteorhodopsin Phototrophy in Antarctic Coastal Waters
    (2021) Cifuentes-Anticevic, Jeronimo; Alcaman-Arias, Maria E.; Alarcon-Schumacher, Tomas; Tamayo-Leiva, Javier; Pedros-Alio, Carlos; Farias, Laura; Diez, Beatriz
    Microbial proton-pumping rhodopsins are considered the simplest strategy among phototrophs to conserve energy from light. Proteorhodopsins are the most studied rhodopsins thus far because of their ubiquitous presence in the ocean, except in Antarctica, where they remain understudied. We analyzed proteorhodopsin abundance and transcriptional activity in the Western Antarctic coastal seawaters. Combining quantitative PCR (qPCR) and metagenomics, the relative abundance of proteorhodopsin-bearing bacteria accounted on average for 17, 3.5, and 29.7% of the bacterial community in Chile Bay (South Shetland Islands) during 2014, 2016, and 2017 summer-autumn, respectively. The abundance of proteorhodopsin-bearing bacteria changed in relation to environmental conditions such as chlorophyll a and temperature. Alphaproteobacteria, Gammaproteobacteria, and Flavobacteriia were the main bacteria that transcribed the proteorhodopsin gene during day and night. Although green light-absorbing proteorhodopsin genes were more abundant than blue-absorbing ones, the latter were transcribed more intensely, resulting in .50% of the proteorhodopsin transcripts during the day and night. Flavobacteriia were the most abundant proteorhodopsin-bearing bacteria in the metagenomes; however, Alphaproteobacteria and Gammaproteobacteria were more represented in the metatranscriptomes, with qPCR quantification suggesting the dominance of the active SAR11 clade. Our results show that proteorhodopsin-bearing bacteria are prevalent in Antarctic coastal waters in late austral summer and early autumn, and their ecological relevance needs to be elucidated to better understand how sunlight energy is used in this marine ecosystem.
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    Surface Ammonia-Oxidizer Abundance During the Late Summer in the West Antarctic Coastal System
    (2022) Alcaman-Arias, Maria E.; Cifuentes-Anticevic, Jeronimo; Diez, Beatriz; Testa, Giovanni; Troncoso, Macarena; Bello, Estrella; Farias, Laura
    Marine ammonia oxidizers that oxidize ammonium to nitrite are abundant in polar waters, especially during the winter in the deeper mixed-layer of West Antarctic Peninsula (WAP) waters. However, the activity and abundance of ammonia-oxidizers during the summer in surface coastal Antarctic waters remain unclear. In this study, the ammonia-oxidation rates, abundance and identity of ammonia-oxidizing bacteria (AOB) and archaea (AOA) were evaluated in the marine surface layer (to 30 m depth) in Chile Bay (Greenwich Island, WAP) over three consecutive late-summer periods (2017, 2018, and 2019). Ammonia-oxidation rates of 68.31 nmol N L-1 day(-1) (2018) and 37.28 nmol N L-1 day(-1) (2019) were detected from illuminated 2 m seawater incubations. However, high ammonia-oxidation rates between 267.75 and 109.38 nmol N L-1 day(-1) were obtained under the dark condition at 30 m in 2018 and 2019, respectively. During the late-summer sampling periods both stratifying and mixing events occurring in the water column over short timescales (February-March). Metagenomic analysis of seven nitrogen cycle modules revealed the presence of ammonia-oxidizers, such as the Archaea Nitrosopumilus and the Bacteria Nitrosomonas and Nitrosospira, with AOA often being more abundant than AOB. However, quantification of specific amoA gene transcripts showed number of AOB being two orders of magnitude higher than AOA, with Nitrosomonas representing the most transcriptionally active AOB in the surface waters. Additionally, Candidatus Nitrosopelagicus and Nitrosopumilus, phylogenetically related to surface members of the NP-epsilon and NP-gamma clades respectively, were the predominant AOA. Our findings expand the known distribution of ammonium-oxidizers to the marine surface layer, exposing their potential ecological role in supporting the marine Antarctic system during the productive summer periods.