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<p>Marine heatwaves (MHWs) are periods of extreme warm ocean temperatures that can have devastating impacts on marine<br>organisms and socio-economic systems. Despite recent advances in understanding the underlying processes of individual events, a<br>global view of the local oceanic and atmospheric drivers of MHWs is currently missing. Here, we use daily-mean output of<br>temperature tendency terms from a comprehensive fully coupled Earth system model to quantify the main local processes leading<br>to the buildup and decay of MHWs in the surface ocean. Our analysis reveals that net ocean heat uptake associated with more<br>shortwave heat absorption and less latent heat loss is the primary driver of the buildup of MHWs in the subtropics and mid-to-high<br>latitudes. Reduced vertical mixing from the nonlocal portion of the KPP boundary layer scheme partially dampens the temperature<br>increase. In contrast, ocean heat uptake is reduced during the MHW build-up in the tropics, where reduced vertical local mixing<br>and diffusion cause the warming. In the subsequent decay phase, ocean heat loss to the atmosphere dominates the temperature<br>decrease globally. The processes leading to the buildup and decay of MHWs are similar for short and long MHWs. Different types of<br>MHWs with distinct driver combinations are identified within the large variability among events. Our analysis contributes to a<br>better understanding of MHW drivers and processes and may therefore help to improve the prediction of high-impact marine<br>heatwaves.</p>

Marine microbes play fundamental roles in nutrient cycling and climate regulation at a planetary scale. The field of marine microbial ecology has experienced major breakthroughs following the application of high-throughput sequencing and cultureindependent methodologies that have pushed the exploration of the marine microbiome to an unprecedented scale. This chapter overviews how the advances in gene- and genome-centric approaches as well as in culturing and single cell physiological methodologies in conjunction with global oceanographic circumnavigation expeditions and long-term time series are fueling our understanding of the biogeography, temporal dynamics, functional diversity, and evolutionary processes of microbial populations. We discuss how the joint effort of all those integrative approaches will help to boost our knowledge of the marine microbiome to reach a predictive understanding of how it is going to evolve in future scenarios.

AbstractAimThe distribution of zooplankton functional traits is a key factor for regulating food web dynamics and carbon cycling in the oceans. Yet, we lack a clear understanding of how many functional groups (FGs) exist in the zooplankton and how their traits are distributed on a global scale. Here, we model and map the environmental habitats of copepod (i.e. the main component of marine zooplankton) FGs to identify regions sharing similar functional trait expression, at the community level.TaxonMarine planktonic Neocopepoda.LocationGlobal ocean.MethodsFactor analysis on mixed data and hierarchical clustering were used to identify copepod FGs based on five species-level functional traits. An ensemble of species distribution models was used to estimate the environmental niches of the species modelled and the community weighted mean values of the traits studied. Ocean regions were defined based on their community-level mean trait expression using a principal component analysis and hierarchical clustering.ResultsEleven global copepod FGs were identified. They displayed contrasting latitudinal patterns in mean annual habitat suitability that could be explained by differences in environmental niche preferences: two FGs were associated with polar conditions, one followed the global temperature gradient, five were associated with tropical oligotrophic gyres, and the remaining three with boundary currents and counter currents. Four main regions of varying community weighted mean trait values emerged: the Southern Ocean, the northern and southern high latitudes, the tropical gyres, and the boundary currents and upwelling systems.ConclusionsThe present FGs will improve the representation of copepods in global marine ecosystem models. This study improves the understanding of the patterns and drivers of copepods trait biogeography and will serve as a basis for studying links between zooplankton biodiversity and ecosystem functioning in a context of climate change.

The role of the Arctic Ocean ecosystem in climate regulation may depend on the responses of marine microorganisms to environmental change. We applied genome-resolved metagenomics to 41 Arctic seawater samples, collected at various depths in different seasons during the Tara Oceans Polar Circle expedition, to evaluate the ecology, metabolic potential and activity of resident bacteria and archaea. We assembled 530 metagenome-assembled genomes (MAGs) to form the Arctic MAGs catalogue comprising 526 species. A total of 441 MAGs belonged to species that have not previously been reported and 299 genomes showed an exclusively polar distribution. Most Arctic MAGs have large genomes and the potential for fast generation times, both of which may enable adaptation to a copiotrophic lifestyle in nutrient-rich waters. We identified 38 habitat generalists and 111 specialists in the Arctic Ocean. We also found a general prevalence of 14 mixotrophs, while chemolithoautotrophs were mostly present in the mesopelagic layer during spring and autumn. We revealed 62 MAGs classified as key Arctic species, found only in the Arctic Ocean, showing the highest gene expression values and predicted to have habitat-specific traits. The Artic MAGs catalogue will inform our understanding of polar microorganisms that drive global biogeochemical cycles. ispartof: NATURE MICROBIOLOGY vol:6 issue:12 pages:1561-+ ispartof: location:England status: published

An increasing number of researchers support reproducibility by including pointers to and descriptions of datasets, software and methods in their publications. However, scientific articles may be ambiguous, incomplete and difficult to process by automated systems. In this paper we introduce RO-Crate, an open, community-driven, and lightweight approach to packaging research artefacts along with their metadata in a machine readable manner. RO-Crate is based on Schema$.$org annotations in JSON-LD, aiming to establish best practices to formally describe metadata in an accessible and practical way for their use in a wide variety of situations. An RO-Crate is a structured archive of all the items that contributed to a research outcome, including their identifiers, provenance, relations and annotations. As a general purpose packaging approach for data and their metadata, RO-Crate is used across multiple areas, including bioinformatics, digital humanities and regulatory sciences. By applying "just enough" Linked Data standards, RO-Crate simplifies the process of making research outputs FAIR while also enhancing research reproducibility. An RO-Crate for this article is available at https://www.researchobject.org/2021-packaging-research-artefacts-with-ro-crate/ Comment: 42 pages. Submitted to Data Science

Vertical variations in physical and chemical conditions drive changes in marine zooplankton community composition. In turn, zooplankton communities play a critical role in regulating the transfer of organic matter produced in the surface ocean to deeper layers. Yet, the links between zooplankton community composition and the strength of vertical fluxes of particles remain elusive, especially on a global scale. Here, we provide a comprehensive analysis of variations in zooplankton community composition and vertical particle flux in the upper kilometer of the global ocean. Zooplankton samples were collected across five depth layers and vertical particle fluxes were assessed using continuous profiles of the Underwater Vision Profiler (UVP5) at 57 stations covering seven ocean basins. Zooplankton samples were analysed using a Zooscan and individual organisms were classified into 19 groups for the quantitative analyses. Zooplankton abundance, biomass and vertical particle flux decreased from the surface to 1000 m depth at all latitudes. The zooplankton abundance decrease rate was stronger at sites characterised by oxygen minima (2.kg−1) where most zooplankton groups showed a marked decline in abundance, except the jellyfishes, molluscs, annelids, large protists and a few copepod families. The attenuation rate of vertical particle fluxes was weaker at such oxygen-depleted sites. Canonical redundancy analyses showed that the epipelagic zooplankton community composition depended on the temperature, on the phytoplankton size distribution and the surface large particulate organic matter while oxygen was an additional important factor for structuring zooplankton in the mesopelagic. Our results further suggest that future changes in surface phytoplankton size and taxa composition and mesopelagic oxygen loss might lead to profound shift in zooplankton abundance and community structure in both the euphotic and mesopelagic ocean. These changes may affect the vertical export and hereby the strength of the biological carbon pump. International audience

AbstractProviding standard definitions of what should be considered as a node in food webs is still an unsolved problem. Especially for comparative and predictive food web modelling, a more systematic understanding is needed for the effects of trophic aggregation procedures. Aggregation is unavoidable during data management. Therefore, it is crucial to know whether food web properties are conserved during this process.Here, we study how different aggregation methods change the positional importance of species in food webs. In particular, we investigated the effects of various aggregation algorithms on 24 indices of importance. Our work was carried out on 76 aquatic food webs coming from the Ecopath with Ecosim database (EcoBase). We considered six main types of aggregation, according to the way that the nodes were clustered. These were (i) hierarchical clustering based on the Jaccard index, (ii) hierarchical clustering based on the regular equivalence index (REGE), (iii) maximisation of directed modularity, (iv) maximisation of modularity according to modules in which species fed on the same preys, (v) maximisation of modularity according to modules in which species are fed upon by the same predators, and (vi) clustering through the group model.Hierarchical clustering based on the Jaccard index and REGE index outperformed the other four methods on maintaining the relative importance of species for all the indices of importance (except for the contrastatus index (s′) and betweenness centrality (BC)). The choice between these two methods should follow our research question and the importance index we are interested in studying. The other four aggregation methods change more the centrality of species, especially the one based on maximising directed modularity. When using these aggregation algorithms, one has to keep in mind that the network will not only be smaller but also provides different information.