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  • 1
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    Plankton networks driving carbon export in the oligotrophic ocean (2016)
    Nature Publishing Group (NPG)
    In: Nature
    Details
    Publication Date: 2016-04-28
    Description: Plankton networks driving carbon export in the oligotrophic ocean Nature 532, 7600 (2016). doi:10.1038/nature16942 Authors: Lionel Guidi, Samuel Chaffron, Lucie Bittner, Damien Eveillard, Abdelhalim Larhlimi, Simon Roux, Youssef Darzi, Stephane Audic, Léo Berline, Jennifer R. Brum, Luis Pedro Coelho, Julio Cesar Ignacio Espinoza, Shruti Malviya, Shinichi Sunagawa, Céline Dimier, Stefanie Kandels-Lewis, Marc Picheral, Julie Poulain, Sarah Searson, Lars Stemmann, Fabrice Not, Pascal Hingamp, Sabrina Speich, Mick Follows, Lee Karp-Boss, Emmanuel Boss, Hiroyuki Ogata, Stephane Pesant, Jean Weissenbach, Patrick Wincker, Silvia G. Acinas, Peer Bork, Colomban de Vargas, Daniele Iudicone, Matthew B. Sullivan, Jeroen Raes, Eric Karsenti, Chris Bowler & Gabriel Gorsky The biological carbon pump is the process by which CO2 is transformed to organic carbon via photosynthesis, exported through sinking particles, and finally sequestered in the deep ocean. While the intensity of the pump correlates with plankton community composition, the underlying ecosystem structure
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 2
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    Reduction of the Powerful Greenhouse Gas N2O in the South-Eastern Indian Ocean (2016)
    In:  EPIC3PLOS ONE, 11(1), pp. e0145996, ISSN: 1932-6203
    Details
    Publication Date: 2017-01-20
    Description: Nitrous oxide (N2O) is a powerful greenhouse gas and a key catalyst of stratospheric ozone depletion. Yet, little data exist about the sink and source terms of the production and reduc- tion of N2O outside the well-known oxygen minimum zones (OMZ). Here we show the pres- ence of functional marker genes for the reduction of N2O in the last step of the denitrification process (nitrous oxide reductase genes; nosZ) in oxygenated surface waters (180–250 O2 μmol.kg-1) in the south-eastern Indian Ocean. Overall copy numbers indicated that nosZ genes represented a significant proportion of the microbial community, which is unexpected in these oxygenated waters. Our data show strong temperature sensitivity for nosZ genes and reaction rates along a vast latitudinal gradient (32°S-12°S). These data suggest a large N2O sink in the warmer Tropical waters of the south-eastern Indian Ocean. Clone sequenc- ing from PCR products revealed that most denitrification genes belonged to Rhodobactera- ceae. Our work highlights the need to investigate the feedback and tight linkages between nitrification and denitrification (both sources of N2O, but the latter also a source of bioavail- able N losses) in the understudied yet strategic Indian Ocean and other oligotrophic systems.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 3
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    A database of marine phytoplankton abundance, biomass and species composition in Australian waters (2016)
    In:  EPIC3Scientific Data, 3, pp. 160043, ISSN: 2052-4463
    Details
    Publication Date: 2017-01-20
    Description: There have been many individual phytoplankton datasets collected across Australia since the mid 1900s, but most are unavailable to the research community. We have searched archives, contacted researchers, and scanned the primary and grey literature to collate 3,621,847 records of marine phytoplankton species from Australian waters from 1844 to the present. Many of these are small datasets collected for local questions, but combined they provide over 170 years of data on phytoplankton communities in Australian waters. Units and taxonomy have been standardised, obviously erroneous data removed, and all metadata included. We have lodged this dataset with the Australian Ocean Data Network (http://portal.aodn.org.au/) allowing public access. The Australian Phytoplankton Database will be invaluable for global change studies, as it allows analysis of ecological indicators of climate change and eutrophication (e.g., changes in distribution; diatom:dinoflagellate ratios). In addition, the standardised conversion of abundance records to biomass provides modellers with quantifiable data to initialise and validate ecosystem models of lower marine trophic levels.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 4
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    Cross-shelf transport, oxygen depletion, and nitrate release within a forming mesoscale eddy in the eastern Indian Ocean (2016)
    AMER SOC LIMNOLOGY OCEANOGRAPHY
    In:  EPIC3Limnology and Oceanography, AMER SOC LIMNOLOGY OCEANOGRAPHY, ISSN: 0024-3590
    Details
    Publication Date: 2017-01-20
    Description: Mesoscale eddies may drive a significant component of cross-shelf transport important in the ecology of shelf ecosystems and adjacent boundary currents. The Leeuwin Current in the eastern Indian Ocean becomes unstable in the austral autumn triggering the formation of eddies. We hypothesized that eddy formation represented the major driver of cross-shelf transport during the autumn. Acoustic Doppler Current Profiler profiles confirmed periodic offshore movement of 2 Sv of shelf waters into the forming eddy from the shelf, carrying a load of organic particles (〉0.06 mm). The gap between inflow and outflow then closed, such that the eddy became isolated from further direct input of shelf waters. Drifter tracks supported an anticyclonic surface flow peaking at the eddy perimeter and decreasing in velocity at the eddy center. Oxygen and nutrient profiles suggested rapid remineralization of nitrate mid-depth in the isolated water mass as it rotated, with a total drawdown of oxygen of 3.6 mol m22 to 350 m. Depletion of oxygen, and release of nitrate, occurred on the timescale of 1 week. We suggest that N supply and N turnover are rapid in this system, such that nitrate is acting primarily as a regenerated nutrient rather than as a source of new nitrogen. We hypothesize that sources of eddy particulate C and N could include particles sourced from coastal primary producers within 500 km such as macrophytes and seagrasses known to produce copious detritus, which is prone to resuspension and offshore transport.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 5
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    Sources of new nitrogen in the Indian Ocean (2015)
    Wiley
    In:  EPIC3Global Biogeochemical Cycles, Wiley, 29, ISSN: 0886-6236
    Details
    Publication Date: 2019-08-19
    Description: Quantifying the different sources of nitrogen (N) within the N cycle is crucial to gain insights in oceanic phytoplankton production. To understand the controls of primary productivity and the associated capture of CO2 through photosynthesis in the southeastern Indian Ocean, we compiled the physical and biogeochemical data from four voyages conducted in 2010, 2011, 2012, and 2013. Overall, higher NH4 assimilation rates (~530 μmolm-2 h-1) relative to NO3 assimilation rates (~375 μmolm!2 h!1) suggest that the assimilation dynamics of C are primarily regulated by microbial regeneration in our region. N2 fixation rates did not decline when other source of dissolved inorganic nitrogen were available, although the assimilation of N2 is a highly energetic process. Our data showed that the diazotrophic community assimilated ~2 nmol N L!1 h!1 at relative elevated NH4 assimilation rates ~12 nmol L-1 h-1 and NO3 assimilation rates ~6 nmol L!1 h!1. The small diffusive deep water NO3 fluxes could not support the measured NO3 assimilation rates and consequently point toward another source of dissolved inorganic NO3. Highest NO2! values coincided consistently with shallow lower dissolved O2 layers (100–200 m; 100–180 μmol L-1). These results suggest that nitrification above the pycnocline could be a significant component of the N cycle in the eastern Indian Ocean. In our analysis we provide a conceptual understanding of how NO3 in the photic zone could be derived from new N through N2 fixation. We conclude with the hypothesis that N injected through N2 fixation can be recycled within the photic zone as NH4 and sequentially oxidized to NO2 and NO3 in shallow lower dissolved oxygen layers.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 6
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    The 2nd International Indian Ocean Expedition (IIOE-2): Motivating New Exploration in a Poorly Understood Basin. (2016)
    ASLO
    In:  EPIC3Limnology and Oceanography Bulletin, ASLO, 25(4), pp. 117-124, ISSN: 1539-607X
    Details
    Publication Date: 2017-06-23
    Description: Overview The Indian Ocean remains one of the most poorly sampled and overlooked regions of the world ocean. Today, more than 25% of the world’s population lives in the Indian Ocean region and the population of most Indian Ocean rim nations is increasing rapidly. These increases in population are giving rise to mul- tiple stressors in both coastal and open ocean environments. Combined with warming and acidification due to global climate change, these regional stressors are resulting in loss of biodi- versity in the Indian Ocean and also changes in the phenology and biogeography of many spe- cies. These pressures have given rise to an urgent need to understand and predict changes in the Indian Ocean, but the measurements that are needed to do this are still lacking. In response, SCOR, IOC, and IOGOOS have stimulated a second International Indian Ocean Expedition (IIOE-2). An international Science Plan and an Implementation Strategy for IIOE-2 have been developed, the formulation of national plans is well underway in several countries, and new research initiatives are being motivated. An Early-Career Scientist Network for Indian Ocean Research has self-organized to support the Expedition. The success of IIOE-2 will be gauged not just by how much it advances our understanding of the complex and dynamic Indian Ocean system, but also by how it con- tributes to sustainable development of marine resources, environmental stewardship, ocean and climate forecasting, and training of the next generation of ocean scientists. We encourage ASLO members to get involved.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , peerRev
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  • 7
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    The 2nd International Indian Ocean Expedition (IIOE-2): Motivating New Exploration in a Poorly Understood Basin. (2017)
    Association for the Sciences of Limnology and Oceanography (ASLO)
    Details
    Publication Date: 2021-05-19
    Description: The Indian Ocean remains one of the most poorly sampled and overlooked regions of the world ocean. Today, more than 25% of the world’s population lives in the Indian Ocean region and the population of most Indian Ocean rim nations is increasing rapidly. These increases in population are giving rise to multiple stressors in both coastal and open ocean environments. Combined with warming and acidification due to global climate change, these regional stressors are resulting in loss of biodiversity in the Indian Ocean and also changes in the phenology and biogeography of many species. These pressures have given rise to an urgent need to understand and predict changes in the Indian Ocean, but the measurements that are needed to do this are still lacking. In response, SCOR, IOC, and IOGOOS have stimulated a second International Indian Ocean Expedition (IIOE-2). An international Science Plan and an Implementation Strategy for IIOE-2 have been developed, the formulation of national plans is well underway in several countries, and new research initiatives are being motivated
    Description: Article pdf provided by authors via ResearchGate. Article published in Limnology and Oceanography Bulletin Volume 25 Number 4 pp.97–138, November 2016.
    Description: Published
    Keywords: IIOE-2 ; IIOE ; Historical account ; Indian Ocean Observing System (IndOOS) ; Early career scientists ; ASFA_2015::E::Expeditions (multiship)
    Repository Name: AquaDocs
    Type: Conference Material , Refereed
    Format: pp.117-124
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  • 8
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    Hydrographic fronts shape productivity, nitrogen fixation, and microbial community composition in the southern Indian Ocean and the Southern Ocean (2021)
    In:  EPIC3Biogeosciences, 18(12), pp. 3733-3749, ISSN: 1726-4189
    Details
    Publication Date: 2021-11-16
    Description: Biogeochemical cycling of carbon (C) and nitrogen (N) in the ocean depends on both the composition and activity of underlying biological communities and on abiotic factors. The Southern Ocean is encircled by a series of strong currents and fronts, providing a barrier to microbial dispersion into adjacent oligotrophic gyres. Our study region straddles the boundary between the nutrient-rich Southern Ocean and the adjacent oligotrophic gyre of the southern Indian Ocean, providing an ideal region to study changes in microbial productivity. Here, we measured the impact of C and N uptake on microbial community diversity, contextualized by hydrographic factors and local physico-chemical conditions across the Southern Ocean and southern Indian Ocean. We observed that contrasting physico-chemical characteristics led to unique microbial diversity patterns, with significant correlations between microbial alpha diversity and primary productivity (PP). However, we detected no link between specific PP (PP normalized by chlorophyll-a concentration) and microbial alpha and beta diversity. Prokaryotic alpha and beta diversity were correlated with biological N2 fixation, which is itself a prokaryotic process, and we detected measurable N2 fixation to 60◦S. While regional water masses have distinct microbial genetic fingerprints in both the eukaryotic and prokaryotic fractions, PP and N2 fixation vary more gradually and regionally. This suggests that microbial phylogenetic diversity is more strongly bounded by physical oceanographic features, while microbial activity responds more to chemical factors. We conclude that concomitant assessments of microbial diversity and activity are central to understanding the dynamics and complex responses of microorganisms to a changing ocean environment.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , peerRev
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  • 9
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    HIGH-RESOLUTION OCEANOGRAPHIC AND MICROBIAL DIVERSITY ANALYSES WITHIN TROPHIC GROUPS REVEAL NEW PROVINCIALISM ACROSS THE ATLANTIC OCEAN (2021)
    In:  EPIC3ASLO 2021 Aquatic Sciences Meeting, online, 2021-06-22-2021-06-27
    Details
    Publication Date: 2021-11-16
    Description: Ocean currents, fronts, and eddies shape the distribution of phylogenetic and functional microbial biodiversity, sustaining a mosaic of ecosystem structures with both high and low productivity. Major sampling campaigns have created a wealth of knowledge about the Atlantic microbiome; however, we lack in-depth understanding of how microbial diversity and primary productivity covary at fine spatial scales (~10-100 km). Here, we present results from an Atlantic Ocean transect ( ~50°S - 50°N), sampled at every ~0.5° latitude. We combined in-situ rate measurements of primary productivity, 16S and 18S rRNA gene sequencing, and physicochemical analyses to investigate associations between hydrography and microbial diversity We detected boundaries of ecological regions - partially coincident with Longhurst provinces – with high and low chl a signatures. Eukaryotic autotrophs and prokaryotic heterotrophs showed higher beta diversity in high chl a provinces, while beta diversity of mixotrophs, cyanobacteria and eukaryotic heterotrophs was higher in low chl a provinces. Additionally, we calculated productivity-specific length scales to assess key dimensions of biological-physical coupling across our transect. We observed a link between advection driven by surface currents and patchiness of microbial diversity signals within provinces. Our integrative approach suggests that evaluating trophically disaggregated diversity alongside productivity and advection will improve our understanding of the mosaic nature of microbial provincialism.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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  • 10
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    Day length is a significant driver of seasonal bacterial diversity in polar, temperate and tropical marine time-series (2022)
    In:  EPIC3Ocean Sciences Meeting, online event
    Details
    Publication Date: 2022-05-30
    Description: Unravelling the relationship between biological diversity and ecosystem resilience is a timeless topic dating back to Alexander von Humboldt’s expeditions in the early 19th century. While global oceanographic expeditions and basin-wide transects show positive correlations between microbial diversity and temperature or productivity, they often lack temporal replication, and include few high latitude observations especially during winter months. Here, using seasonal amplicon sequence data from six time-series in the northern and southern hemispheres, we show that on a multiannual basis marine microbial alpha-diversity (species richness and evenness) correlate most strongly with day length, rather than with temperature and chlorophyll a (as proxy for primary production), independent of the targeted 16S rRNA hypervariable region. By integrating data from 2003 to 2020, our evidence suggests that microbial diversity and annually recurring community composition are governed by similar principles, from subtropic to polar oceans. These global trends are consistent regardless of the collection methods, DNA extraction chemistry, sequencing technologies or bioinformatic pipelines. Hence, to understand drivers of marine microbial diversity, larger-scale studies need to embed their analyses into the context of regional seasonal variations. Overall, our synthesis reframes the fundamental drivers of marine microbial diversity as phenological, and suggests that although the state of the temperature and chlorophyll spectra should be considered, it is regular sampling over seasonal cycles that can disentangle these effects. Our findings support the idea that microbial diversity patterns and ecosystem stability are regulated by holistic feedback systems. Or as Alexander von Humboldt already stated, Nature is interconnected, linking ‘the little things’ with global interactions and patterns will allow us to place the observed microbial diversity into the bigger picture.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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