Variation in Population Structures of Tropical Freshwater Eels, Anguilla Marmorata, A. Bicolor Bicolor and A. Bengalensis Bengalensis, in the Indo-Pacific

Freshwater eels, genus Anguilla, have a distinctive catadromous life history, which could be associated with certain oceanic current systems and offshore spawning sites. Thus, migration and dispersion patterns are believed to be important factors influencing the population structures of each species. Temperate eel species are well studied, while little research has been conducted on the tropical counterparts that comprise two-thirds of all eel species. The population structures of three tropical species, A. marmorata, A. bicolor bicolor and A. bengalensis bengalensis, which are distributed widely in the Indo-Pacific region, were explored by means of DNA sequence analysis of mitochondrial cytochrome c oxidase subunit I (COI). This study found that A. bicolor bicolor had two genetically distinct populations, and these different populations co-occur geographically in the Indo-Pacific region, while A. marmorata and A. bengalensis bengalensis showed a panmictic-population structure in this region. The populations of A. bicolor bicolor were also found to have lower genetic variability than the populations of A. marmorata and A. bengalensis bengalensis. This study is the first to explore the population genetic structure of A. bengalensis bengalensis. The present results also suggest plausible dispersion and migration of these tropical species into their continental habitats.

State-of-the-art of MW-level capacity oceanic current turbines

Marine hydrokinetic turbines of MW-level capacity for harvesting oceanic currents are here reviewed. The best design is 3-blades, open rotor, axial flow turbines, of similar design philosophy to wind turbines, which are anchored to the ocean floor. The best locations are those with the oceanic current resource of higher intensity and stability, non-excessive depth of the ocean floor, proximity to shore, and favorable topography. In these locations, marine hydrokinetic turbines may become competitive with other renewable energy alternatives. It is expected that such turbines will be installed and will start producing electricity, within the next decade, working with power coefficients, the ratio of electric power from the turbine to wind power, around 0.45, similarly to wind turbines. This will pave the road for further progress and significant uptake of technology so far of no impact on the global energy mix.

Impact of the current feedback on the representation of tropical cyclones in coupled models

<p><span>Tropical Cyclones (TCs) are among the most destructive natural phenomena on Earth and severely impact nearly a billion people. Coupled models have become a necessary tool to improve our knowledge on those natural hazards. Improving their ability to statistically represent TCs is of prior importance. In the present study, we investigate the impact of the mechanical interaction between the surface oceanic current and the atmosphere (i.e., the Current FeedBack, CFB) on the statistic of TCs in different basins. We perform sensitivity experiments using the EC-Earth model in its High-Resolution version (1/12˚), by switching on and off CFB. As CFB has been shown to strongly improve the realism of the oceanic circulation at both large scale and mesoscale, we expect an improvement, i.e., a better realism, of the statistical TCs representation when CFB is taken into account in the model. Improving coupled models will help design forecast schemes with lead times longer than those currently provided by operational forecasts centers.</span></p>

Wave-current Interactions in the Aghulas current: Impact on ship behavior

<p>Ocean waves Interacting with large scale ocean currents is a frequent cause of sea-state variability [Ardhuin et al 2017, Quilfen et al 2018, Quilfen and Chapron 2019]. Such situations can lead to sea-state hazards, crucial for shipping security. The Great Agulhas current system is an area of very intensive maritime traffic, where dangerous localized sea-state amplification by the current has quite regularly been reported. </p><p>In absence of wind and wave-induced motions, the heading and drift of every ship along its trajectory can be estimated from the near-surface oceanic current map. This first guess can then be compared with real ship parameters obtained from satellite-collected ship Automatic Identification System (AIS) messages. During Southwestern storm-swell wave conditions, with wind and waves aligned against the current, some ships experience pronounced navigation difficulties, slowing down up to 2 m/s,  and frequently maneuvering to keep their heading perpendicular to dominant waves. Superposed multiple individual ship trajectories can then help map anomalous areas, and to relate them to localized strong wave-current effects such as large refraction of waves by the oceanic current.</p><p>[Ardhuin et al 2017] : Ardhuin, F., S. T. Gille, D. Menemenlis,C. B. Rocha, N. Rascle, B. Chapron, J. Gula, and J. Molemaker (2017), Small-scale open ocean<br>currents have large effects on wind wave heights, J. Geophys. Res. Oceans, 122, 4500–4517, doi:10.1002/2016JC012413.</p><p>[Quilfen et al 2018] :Quilfen Yves, Yurovskaya M., Chapron Bertrand, Ardhuin Fabrice (2018). Storm waves focusing and steepening in the Agulhas current: Satellite observations and modeling. Remote Sensing Of Environment, 216, 561-571. Publisher's official version : </p><p>[Quilfen and Chapron, 2019] : Quilfen, Y., & Chapron, B. (2019). Ocean surface wave-current signatures from satellite altimeter measurements.<br>Geophysical Research Letters, 46. </p><div> </div>

The Structure of Baroclinic Modes in the Presence of Baroclinic Mean Flow

This contribution seeks to understand the vertical structure of linearized quasigeostrophic baroclinic modes when they are modified by the presence of a baroclinic mean flow and associated potential vorticity gradients. It is found that even modest, O(0.05 m s−1), mean flows can give rise to very substantial changes in modal structures, often in the sense of increased surface intensification. The extent to which stable modes are modified depends strongly on the direction of Rossby wave propagation. Further, baroclinically unstable solutions can appear, and a meaningful inviscid critical-layer solution can occur at the transition to instability when the horizontal gradient of potential vorticity changes sign at some depth within the water column. In addition, the gravest, n = 0, vertical stable mode is no longer strictly barotropic, but rather it can carry density variability at frequencies much higher than those possible for baroclinic (higher) Rossby wave modes. This finding appears to be consistent with oceanic current-meter observations that suggest temperature variability propagation even when the frequency is too high for traditional baroclinic Rossby waves to exist.

Single-amino acid variants reveal evolutionary processes that shape the biogeography of a global SAR11 subclade

Members of the SAR11 order Pelagibacterales dominate the surface oceans. Their extensive diversity challenges emerging operational boundaries defined for microbial 'species' and complicates efforts of population genetics to study their evolution. Here, we employed single-amino acid variants (SAAVs) to investigate ecological and evolutionary forces that maintain the genomic heterogeneity within ubiquitous SAR11 populations we accessed through metagenomic read recruitment using a single isolate genome. Integrating amino acid and protein biochemistry with metagenomics revealed that systematic purifying selection against deleterious variants governs non-synonymous variation among very closely related populations of SAR11. SAAVs partitioned metagenomes into two main groups matching large-scale oceanic current temperatures, and six finer proteotypes that connect distant oceanic regions. These findings suggest that environmentally-mediated selection plays a critical role in the journey of cosmopolitan surface ocean microbial populations, and the idea ‘everything is everywhere but the environment selects’ has credence even at the finest resolutions.