How do pro- and eukaryotic microbial communities impact nitrogen and carbon processes in the South Indian Ocean and the French Southern and Antarctic Lands?

Nitrogen availability in the open ocean regulates primary productivity and a cascade of associated carbon-nitrogen coupled transformations mediated by both eukaryotic and prokaryotic microorganisms. An understanding of potential alterations at the base of the food chain particularly reductions in planktonic biomass is essential, as a decline or community shift in primary productivity will impact ecosystem services, such as O2 production, carbon sequestration and biogeochemical cycling. This study, as part of the OISO (Ocean Indien Service d'Observation) campaign, aimed to shed light into prokaryotic and photoautotrophic, eukaryotic community composition between four different water masses as well carbon and nitrogen assimilation rates in the Southern Indian Ocean and the French Southern and Antarctic lands. To understand ecosystem dynamics, we linked microbial community composition, using high resolution molecular 16S rDNA amplicon sequencing techniques and functional pigment analysis, to in situ rate measurements of carbon (C) and nitrogen (N). While temperature and salinity were the driving factors for carbon fixation, water masses defined prokaryotic community composition. We could link prokaryotic diversity to high carbon fixation rates emphasizing positive foodweb recoupling and recycling processes. Photoautotrophic community composition clearly separated between the warm Indian Ocean and the Southern Ocean. While the Indian Ocean was vastly dominated by the unicellular cyanobacterium Prochlorococcus, the relative abundance of the diatom diagnostic pigment fucoxanthin increased in the Southern Ocean. C fixation was relatively higher (84.8 ± 44.5 μmol L-1 h-1) in the nutrient-rich Southern Ocean, in comparison to the oligotrophic Indian Ocean (14.2 ± 7.9 μmol L-1 h-1). In general, high variations within-station replicates of C fixation were found, ranging from 43.4 – 134.9 μmol L-1 h-1. We measured N2 fixation at all sampling stations, up to 56°S latitude, supporting the hypothesis that N2 fixation is an ubiquitous process which is not restricted to warm oligotrophic water. N2 fixation rates showed similar patterns as C fixation rates within station replicates, ranging from 0.9 to 7.9 nmol N L-1 d-1. Among other interpretations, this suggests sub-mesoscale dynamics and potential small-scale differences in biochemical conditions. Our observations point out the importance of high resolution (i.e., sub-mesoscale and smaller) in situ studies in combination with remote- sensing techniques, to be able to fully understand the scale of variation in ocean dynamics. ii Collectively our results are another piece of the puzzle of the complex dynamics in the Southern Indian Ocean sector. Understanding biogeochemical and biological processes supports our ability to further understand C and N fluxes to be able to predict and model future climate change scenarios

Towards a Best Practice for Developing Best Practices in Ocean Observation (BP4BP): Supporting Methodological Evolution through Actionable Documentation

IOC Manuals and Guides, 84 Abstract Ever-increasing complexity and multi-dimensionality of ocean investigations present a challenge for the ocean community as we collaboratively (co-)develop methods to research, monitor, and use our oceans. To support transparent sharing of methods, and ultimately agree on best practices in ocean research, operations, and application, the IOC Ocean Best Practices System (OBPS) was initially developed as an Ocean Data Standards project deliverable of the International Oceanographic Data Exchange (IODE) who in 2017 joined with the AtlantOS/ODIP/RCN Best Practices Working Group (BPWG) to develop it into a System. In 2019 the IOC Ocean Best Practices System was approved as a UNESCO/Intergovernmental Oceanographic Commission (IOC) Project, jointly funded by the IODE and GOOS Programmes. In this document, we provide guidance on how to best use the OBPS templates, allowing greater discovery, machine readability, sharing, and understandability of methods and best practices. We clarify how to optimally populate the different sections of an OBPS template, and describe how those sections support the evolution of each OBPS submission, towards a global best practice. Further, we discuss some general challenges in developing methods into community-accepted best practices. While this document focuses on the OBPS, it also offers a perspective on the general challenge of structuring and harmonising method documentation. We invite the community to provide feedback on this document (link to Community review), to contribute towards a generalised best practice for advanced methodological management across the ocean community

High-resolution physical--biogeochemical structure of a filament and an eddy of upwelled water off northwest Africa

Nutrient rich water upwells offshore of Northwest Africa and is subsequently advected westwards. There it forms eddies and filaments with a rich spatial structure of physical and biological/biogeochemical properties. Here we present a high resolution (2.5 km) section through upwelling filaments and an eddy obtained in May 2018 with a Triaxus towed vehicle equipped with various oceanographic sensors. Physical processes at the mesoscale and submesoscale such as symmetric instability, trapping of fluid in eddies, and subduction of low potential vorticity (which we use as a water mass tracer) water can explain the observed distribution of biological production and export. We found a nitrate excess (higher nitrate concentrations than would be expected from oxygen values if only influenced by production and remineralization processes) core of an anti-cyclonic mode water eddy. We also found a high nitrate concentration region of ~5 km width in the mixed layer where symmetric instability appears to have injected nutrients from below into the euphotic zone. A similar region a little further south had high chlorophyll-a concentrations suggesting that nutrients had been injected there a few days earlier. Considering that such interactions of physics and biology are ubiquitous in the world's upwelling regions, we assume that they have strong influences on the productivity of such systems and their role in CO2 uptake. The intricate interplay of different parameters at kilometer scale needs to be taken into account when interpreting single profile and/or bottle data in dynamically active regions of the ocean

Publisher Correction: Carbon dioxide sink in the Arctic Ocean from cross-shelf transport of dense Barents Sea water

In the version of this article initially published, author Cora Hörstmann was wrongly listed with a second affiliation with the Department of Ecoscience–Applied Marine Ecology and Modelling, Aarhus University rather than the Mediterranean Institute of Oceanography (MIO), Marseille, France. Furthermore, references 83–97, now found in the Supplementary Tables caption, were wrongly cited in the Data Availability section. The errors have been corrected in the HTML and PDF versions of the article

Evolving and Sustaining Ocean Best Practices to Enable Interoperability in the UN Decade of Ocean Science for Sustainable Development

The UN Decade of Ocean Science for Sustainable Development (Ocean Decade) challenges marine science to better inform and stimulate social and economic development while conserving marine ecosystems. To achieve these objectives, we must make our diverse methodologies more comparable and interoperable, expanding global participation and foster capacity development in ocean science through a new and coherent approach to best practice development. We present perspectives on this issue gleaned from the ongoing development of the UNESCO Intergovernmental Oceanographic Commission (IOC) Ocean Best Practices System (OBPS). The OBPS is collaborating with individuals and programs around the world to transform the way ocean methodologies are managed, in strong alignment with the outcomes envisioned for the Ocean Decade. However, significant challenges remain, including: (1) the haphazard management of methodologies across their lifecycle, (2) the ambiguous endorsement of what is "best" and when and where one method may be applicable vs. another, and (3) the inconsistent access to methodological knowledge across disciplines and cultures. To help address these challenges, we recommend that sponsors and leaders in ocean science and education promote consistent documentation and convergence of methodologies to: create and improve context-dependent best practices; incorporate contextualized best practices into Ocean Decade Actions; clarify who endorses which method and why; create a global network of complementary ocean practices systems; and ensure broader consistency and flexibility in international capacity development

Marine microbes on the map: Defining spatial scales of functional microbial biogeography in the ocean

Marine microorganisms have markedly great functional and phylogenetic diversity and sustain major elemental cycles, including those of carbon and nitrogen. However, a major challenge in microbial observation is that the spatial scales of microbial biodiversity patterns and microbial activity differentially change within their physical oceanographic environment, which requires sampling across multiple scales. In this thesis, I applied a combination of metabarcoding (16S and 18S rRNA gene sequencing) and stable isotope C and N2 fixation measurements of surface ocean samples (0 - 40m) against the backdrop of chemical (dissolved inorganic nutrients, particulate organic matter) and physical (temperature, salinity, and surface currents) environmental variables in the Atlantic, Indian and the Arctic Ocean. I demonstrate how functional activity can be decoupled from phylogenetic diversity. I show that beta diversity patterns generally reflect ocean provinces and can also be used to refine oceanographic boundaries. In a pan-Arctic study, I show how microbial communities disperse and form regional and within-fjord signals, with different co-occurrence patterns between fjords with and without marine-terminating glaciers. The presented calculations of a productivity-specific length scale can help identify sample patchiness and scale sample diversity in relation to marine ecosystem structure. In order to harmonize research in meta-analyses and across global scales, we provided perspectives on best practices in method documentation. In conclusion, my work helps to better understand pelagic microbial ecosystems, taking into account the patchiness and ecosystem boundaries and their impact on productivity and food web interactions that are typically overlooked in marine microbial ecology. The presented approaches will support mapping microbiomes to relevant oceanographic scales and have potential implications for researching, observing, and monitoring marine ecosystem structures

Nitrogen and carbon processes in the South Indian Ocean and the French Southern and Antarctic Lands

Our data, as part of the OISO (Ocean Indien Service d'Observation) campaign, contributes to a better understanding of the physical and biological factors controlling N2 fixation in the Southern Indian Ocean and the French Southern and Antarctic lands during Austral summer January and February 2017. We measured N2 and C fixation as well as NH4+ and NO3- assimilation in 3-6 replicates per station. Additionally, we measured diagnostic pigment concentrations to evaluate phtosynthetic community composition. For pigment analysis 4L water was filtered through 25mm Whatman GF/F filters (pressure drop <10kPa). Samples were stored at -80°C until analysis. Pigments were analysed using High Performance Liquid Chromatography (HPLC). Pigment concentration were calculated according to Kilias et al (2013, doi:10.1111/jpy.12109). N2 fixation experiments were carried out in three to six replicates for each station. Incubations were done in pre-acid washed polycarbonate bottles on deck with ambient light conditions. All polycarbonate incubation bottles were rinsed with deionized water, and seawater prior to incubation. We used the combination of the bubble approach (Montoya et al., 1996) and the dissolution method (Mohr et al., 2010, doi:10.1371/journal.pone.0012583) proposed by Klawonn et al. (2015, doi:10.3389/fmicb.2015.00769). Bottles were filled up to capacity to avoid air contamination. Incubations were initialized by adding a 10 ml 15-15N gas bubble. Bottles were gently rocked for 15 minutes. Finally, the remaining bubble was removed to avoid equilibration between gas and aqueous phase. after 24 hours a water subsample was taken to a 12 ml exetainer and preserved with 100 µl HgCl2 solution for later determination of exact 15N-15N concentration. Natural 15N2 was determined using Membrane Inlet Mass Spectrometry (MIMS; GAM200, IPI) for each station. Analysis of 15N2 incorporated was carried out by the Isotopic Laboratory at the UC Davis, California campus. We used stable isotope tracers (15N) to measure dissolved inorganic nitrogen (DIN) assimilation rates. Experiments were initiated by adding a known concentration of 0.05 of K15NO3 and 15NH4Cl for oligotrophic waters of the IO and 0.625 µmol L-1 for HNLC regions in the ACC and PF (Knap et al., 1994, Waite et al., 2007, doi:10.1016/j.dsr2.2006.12.010) to one litre polycarbonate bottles. For C assimilation experiments, we added 20 µmol L-1 of NaH13CO3 to one of each of N2 fixation, NH4+ and NO3- assimilation experiment bottles. For incubation, we followed the same procedure as for N2 fixation experiments. Findings reveal that N2 fixation occurs throughout the whole sampling area up to 55°S latitude. In addition, variations of N2 fiaxation rates between replicates were relatively high indicating a great heterogeneity of the French Southern and Antarctic waters. References: Montoya 1996: Montoya, Joseph P., et al. "A Simple, High-Precision, High-Sensitivity Tracer Assay for N (inf2) Fixation." Applied and environmental microbiology 62.3 (1996): 986-993. Knap et al 1994: Knap, A., Michaels, A., Close, A., Ducklow, H. & Dickson, A. 1994. Protocols for the Joint Global Ocean Flux Study (JGOFS) Core Measurements, JGOFS, Reprint of the IOC Manuals and Guides No. 29. UNESCO, 19, 1