Modelling planktic foraminifer growth and distribution using an ecophysiological multi-species approach

International audienceWe present an eco-physiological model reproducing the growth of eight foraminifer species (Neogloboquad-rina pachyderma, Neogloboquadrina incompta, Neoglobo-quadrina dutertrei, Globigerina bulloides, Globigeri-noides ruber, Globigerinoides sacculifer, Globigerinella si-phonifera and Orbulina universa). By using the main physiological rates of foraminifers (nutrition, respiration, symbi-otic photosynthesis), this model estimates their growth as a function of temperature, light availability, and food concentration. Model parameters are directly derived or calibrated from experimental observations and only the influence of food concentration (estimated via Chlorophyll-a concentration) was calibrated against field observations. Growth rates estimated from the model show positive correlation with observed abundance from plankton net data suggesting close coupling between individual growth and population abundance. This observation was used to directly estimate potential abundance from the model-derived growth. Using satellite data, the model simulate the dominant foraminifer species with a 70.5% efficiency when compared to a data set of 576 field observations worldwide. Using outputs of a biogeochemical model of the global ocean (PISCES) instead of satellite images as forcing variables gives also good results, but with lower efficiency (58.9%). Compared to core tops observations, the model also correctly reproduces the relative worldwide abundance and the diversity of the eight species when using either satellite data either PISCES results. This model allows prediction of the season and water depth at which each species has its maximum abundance potential. This offers promising perspectives for both an improved quantification of paleoceanographic reconstructions and for a better understanding of the foraminiferal role in the marine carbon cycle

Effect of type and concentration of ballasting particles on sinking rate of marine snow produced by the Appendicularian Oikopleura dioica

Ballast material (organic, opal, calcite, lithogenic) is suggested to affect sinking speed of aggregates in the ocean. Here, we tested this hypothesis by incubating appendicularians in suspensions of different algae or Saharan dust, and observing the sinking speed of the marine snow formed by their discarded houses. We show that calcite increases the sinking speeds of aggregates by ~100% and lithogenic material by ~150% while opal only has a minor effect. Furthermore the effect of ballast particle concentration was causing a 33 m d(-1) increase in sinking speed for a 5×10(5) µm(3) ml(-1) increase in particle concentration, near independent on ballast type. We finally compare our observations to the literature and stress the need to generate aggregates similar to those in nature in order to get realistic estimates of the impact of ballast particles on sinking speeds

Multifunctional tribometer development and performance study of CuCrZr-316L material pair for ITER application

Radio-Frequency (RF) contacts are key components on the International Thermonuclear Experimental Reactor (ITER) Ion Cyclotron Resonance Heating (ICRH) antenna, and these components are facing big challenges such as 2 kA operation current load and intensive sliding under up to 250 °C in high vacuum. Stainless steel (SS) 316L and CuCrZr are most likely to be applied as base materials for the conductor and the RF contacts louvers. To evaluate the performance of the selected materials, their electrical and tribological behaviors have to be studied. A multifunctional tribometer which can mimic the ITER ICRH RF contacts' relevant working conditions was designed and built in CEA. The contact resistance (Rc) and coefficient of friction (CoF) of CuCrZr-316L pair were researched on this tribometer

Mistaking plastic for zooplankton: Risk assessment of plastic ingestion in the Mediterranean sea

Floating plastic debris is a pervasive pollutant in seas and oceans, affecting a wide range of animals. In particular, microplastics (<5 mm in size) increase the possibility that marine species consume plastic and enter the food chain. The present study investigates this potential mistake between plastic debris and zooplankton by calculating the plastic debris to zooplankton ratio over the whole Mediterranean Sea. To this aim, in situ data from the Tara Mediterranean Expedition are combined with environmental and Lagrangian diagnostics in a machine learning approach to produce spatially-explicit maps of plastic debris and zooplankton abundance. We then analyse the plastic to zooplankton ratio in regions with high abundances of pelagic fish. Two of the major hotspots of pelagic fish, located in the Gulf of Gabès and Cilician basin, were associated with high ratio values. Finally, we compare the plastic to zooplankton ratio values in the Pelagos Sanctuary, an important hotspot for marine mammals, with other Geographical Sub-Areas, and find that they were among the larger of the Western Mediterranean Sea. Our results indicate a high potential risk of contamination of marine fauna by plastic and advocate for novel integrated modelling approaches which account for potential trophic transfer within the food chain

The pathways of plastic in the Mediterranean Sea and its potential impact on marine biota

International audiencePlastic debris is a ubiquitous pollutant found from the sea surface to the seafloor. Understanding the mechanisms driving its pollution is a difficult task mostly due to the complex oceanic circulation, which affects plastic debris in manifold ways. The Lagrangian approach is hence a natural framework to study this problem. Here, I will show the results of TrackMPD, a Lagrangian model simulating the pathways of plastic debris in the Mediterranean Sea, and validated with the most extensive dataset of plastic measurements in this region to date. The Mediterranean Sea lacks in zones of plastic accumulation despite being one of the most polluted basins worldwide. Here, we adopt a different paradigm, by identifying crossroad regions through which large amounts of plastic debris flow. We find that around 20% of Mediterranean plastic debris passed through 1% of the basin surface. The most important crossroads intercepted plastic debris from multiple sources, which had often traveled long distances. During its travel, plastic debris can be colonised by marine organisms, and eventually sink. We found that the locations where debris leaves the surface are significantly different from those where it reaches the seafloor: debris travels hundreds of kilometers during its sinking. In the water column, plastic debris can potentially be mistaken for zooplankton and be ingested, thus impacting marine biota. To quantify this risk, we estimated the plastic debris to zooplankton ratio over the entire Mediterranean Sea, showing a high risk of contamination for both pelagic fish and whales

Tara Mediterranena expedition: Assessing the impact of microplastics on Mediterrnanean ecosystem

The accumulation of plastic debris on the surface of the oceans is widely recognizedas a newly emerging problem for worldwide marine systems. Yet, too little isknown about the fate of this plastic and its role in ecosystem dynamics to predictthe inevitable impacts on the marine biodiversity and on human health. Under theeffect of circular oceanic currents, plastic accumulate in the world’s oceans, withfive main accumulation zones in the subtropical gyres but also even the most remotepolar seas areas are submerged with plastics debri

Patterns of invasive ctenophore Mnemiopsis leidyi distribution and variability in different recipient environments of the Eurasian seas: A review

23 pages, 10 figures, 5 tables, supplementary data https://doi.org/10.1016/j.marenvres.2019.104791Harmful invader ctenophore Mnemiopsis leidyi's expansions in the Eurasian Seas, its spatio-temporal population dynamics depending on environmental conditions in recipient habitats have been synthesized. M. leidyi found suitable temperature, salinity and productivity conditions in the temperate and subtropical environments of the semi-enclosed seas, in the coastal areas of open basins and in closed water bodies, where it created autonomous populations. M. leidyi changes its phenology depending on seasonal temperature regime in different environments. We assessed ranges of sea surface temperature, sea surface salinity and sea surface chlorophyll values, sufficient for M. leidyi general occurrence and reproduction based on comprehensive long-term datasets, contributed by co-authors. This assessment revealed that there are at least two eco-types (Southern and Northern) in the recipient seas of Eurasia with features specific for their donor areas. The range of thresholds for M. leidyi establishment, occurrence and life cycle in both eco-types depends on variability of environmental parameters in their native habitatsT.A. Shiganova performed this study within the framework of State assignment of the Ministry of Education and Science of the Russian Federation - theme #0149-2019-0010. A.S. Kazmin performed assessment of current advection, contributing to species dispersal within the framework of State assignment of the Ministry of Education and Science of the Russian Federation - theme #0149-2019-0004Peer Reviewe