Letteratura scientifica selezionata sul tema "Tara-Pacific expedition"

The fire coral Millepora platyphylla Hemprich & Ehrenberg, 1834 (Cnidaria, Hydrozoa) has a widespread Indo-Pacific distribution observed from the surface to 40 m (Razak & Hoeksema 2003). However, its extirpation from the East Pacific (Gulf of Chiriqui, Panama) was documented after the 1982-1983 bleaching event (Glynn & Weerdt 1991). Here, we report the discovery of 5 colonies of M. platyphylla from the eastern Pacific, specifically at Clipperton Atoll, during the TARA Pacific expedition (www.taraexpeditions.org).

During the ‘Tara Pacific 2016–2018 Expedition’, marine benthic diatom samples were collected from several Tuamotu atolls in the South Pacific. Preparation and examination of these samples were conducted following standard methods including light and scanning electron microscopy. A small-celled taxon from the genus Cocconeis Ehrenb. (Bacillariophyceae) is described from the Nukutavake reef, and compared to several other taxa for which the definition is not always clear (e.g., Cocconeis diruptoides Hust. and Cocconeis pseudodiruptoides Foged). The new taxon is present only on one of the investigated Tuamotu atolls, possibly indicating local endemism.

Abstract Marine aerosols play a significant role in the global radiative budget, in clouds’ processes, and in the chemistry of the marine atmosphere. There is a critical need to better understand their production mechanisms, composition, chemical properties, and the contribution of ocean-derived biogenic matter to their mass and number concentration. Here we present an overview of a new dataset of in situ measurements of marine aerosols conducted over the 2.5-yr Tara Pacific Expedition over 110,000 km across the Atlantic and Pacific Oceans. Preliminary results are presented here to describe the new dataset that will be built using this novel set of measurements. It will characterize marine aerosols properties in detail and will open a new window to study the marine aerosol link to the water properties and environmental conditions.

So far, the Futuna Islands located in the Central Indo-Pacific Ocean have not been inventoried for their diversity in marine sponges and associated chemical diversity. As part of the Tara Pacific expedition, the first chemical investigation of the sponge Narrabeena nigra collected around the Futuna Islands yielded 18 brominated alkaloids: seven new bromotryptamine derivatives 1–7 and one new bromotyramine derivative 8 together with 10 known metabolites of both families 9–18. Their structures were deduced from extensive analyses of nuclear magnetic resonance (NMR) and high-resolution mass spectrometry (HRMS) data. In silico metabolite anticipation using the online tool MetWork revealed the presence of a key and minor biosynthetic intermediates. These 18 compounds showed almost no cytotoxic effect up to 10 µM on human neuroblastoma SH-SY5Y and microglia BV2 cells, and some of them exhibited an interesting neuroprotective activity by reducing oxidative damage.

Strain ISS653T, isolated from Atlantic seawater, is a yellow pigmented, non-motile, Gram-reaction-negative rod-shaped bacterium, strictly aerobic and chemoorganotrophic, slightly halophilic (1–15 % NaCl) and mesophilic (4–37 °C), oxidase- and catalase-positive and proteolytic. Its major cellular fatty acids are iso-C15 : 0, iso-C15 : 0 2-OH, and iso-C17 : 0 3-OH; the major identified phospholipid is phosphatidylethanolamine and the major respiratory quinone is MK6. Genome size is 4.28 Mbp and DNA G+C content is 34.9 mol%. 16S rRNA gene sequence similarity places the strain among members of the family Flavobacteriaceae, with the type strains of Mesonia phycicola (93.2 %), Salegentibacter mishustinae (93.1 %) and Mesonia mobilis (92.9 %) as closest relatives. Average amino acid identity (AAI) and average nucleotide identity (ANI) indices show highest values with M. mobilis (81 % AAI; 78.9 % ANI), M. phycicola (76 % AAI; 76.3 % ANI), Mesonia maritima (72 % AAI, 74.9 % ANI), Mesonia hippocampi (64 % AAI, 70.8 % ANI) and Mesonia algae (68 % AAI; 72.2 % ANI). Phylogenomic analysis using the Up-to-date-Bacterial Core Gene set (UBCG) merges strain ISS653T in a clade with species of the genus Mesonia . We conclude that strain ISS653T represents a novel species of the genus Mesonia for which we propose the name Mesonia oceanica sp. nov., and strain ISS653T (=CECT 9532T=LMG 31236T) as the type strain. A second strain of the species, ISS1889 (=CECT 30008) was isolated from Pacific Ocean seawater. Data obtained throughout the Tara oceans expedition indicate that the species is more abundant in the mesopelagic dark ocean than in the photic layer and it is more frequent in the South Pacific, Indian and North Atlantic oceans.

Abstract. Eastern boundary upwelling systems are characterized by high productivity that often leads to subsurface hypoxia on the shelf. Mesoscale eddies are important, frequent, and persistent features of circulation in these regions, transporting physical, chemical and biological properties from shelves to the open ocean. In austral fall of 2011, during the Tara Oceans expedition, a subsurface layer (200–400 m) in which the concentration of oxygen was very low (< 2 μmol kg−1 of O2) was observed in the eastern South Pacific, ~ 900 km offshore (30° S, 81° W). Satellite altimetry combined with CTD observations associated the local oxygen anomaly with an intrathermocline, anticyclonic, mesoscale eddy with a diameter of about 150 km. The eddy contained Equatorial Subsurface Water (ESSW) that at this latitude is normally restricted near the coast. Undersaturation (44 %) of nitrous oxide (N2O) and nitrite accumulation (> 0.5 μM) gave evidence for denitrification in this water mass. Based on satellite altimetry, we tracked the eddy back to its region of formation on the coast of central Chile (36.1° S, 74.6° W). We estimate that the eddy formed in April 2010. Field studies conducted on the Chilean shelf in June 2010 provided approximate information on initial O2 and N2O concentrations of "source water" in the region at the time of eddy formation. Concentrations of both O2 and N2O in the oxygen minimum zone (OMZ) of the offshore eddy were lower than its surroundings or "source water" on the shelf, suggesting that these chemical species were consumed as the eddy moved offshore. Estimates of apparent oxygen utilization rates at the OMZ of the eddy ranged from 0.29 to 44 nmol L−1 d−1 and the rate of N2O consumption was 3.92 nmol L−1 d−1. Our results show that mesoscale eddies in the ESP not only transport physical properties of the ESSW from the coast to the ocean interior, but also export and transform biogeochemical properties, creating suboxic environments in the oligotrophic region of the eastern South Pacific. Suboxic water masses that are advected by eddies act as hotspots for denitrification and loss of fixed nitrogen from the system.

Abstract. Aerosol size distribution has major effects on warm cloud processes. Here, we use newly acquired marine aerosol size distributions (MSDs), measured in situ over the open ocean during the Tara Pacific expedition (2016–2018), to examine how the total aerosol concentration (Ntot) and the shape of the MSDs change warm clouds' properties. For this, we used a toy model with detailed bin microphysics initialized using three different atmospheric profiles, supporting the formation of shallow to intermediate and deeper warm clouds. The changes in the MSDs affected the clouds' total mass and surface precipitation. In general, the clouds showed higher sensitivity to changes in Ntot than to changes in the MSD's shape, except for the case where the MSD contained giant and ultragiant cloud condensation nuclei (GCCN, UGCCN). For increased Ntot (for the deep and intermediate profiles), most of the MSDs drove an expected non-monotonic trend of mass and precipitation (the shallow clouds showed only the decreasing part of the curves with mass and precipitation monotonically decreasing). The addition of GCCN and UGCCN drastically changed the non-monotonic trend, such that surface rain saturated and the mass monotonically increased with Ntot. GCCN and UGCCN changed the interplay between the microphysical processes by triggering an early initiation of collision–coalescence. The early fallout of drizzle in those cases enhanced the evaporation below the cloud base. Testing the sensitivity of rain yield to GCCN and UGCCN revealed an enhancement of surface rain upon the addition of larger particles to the MSD, up to a certain particle size, when the addition of larger particles resulted in rain suppression. This finding suggests a physical lower bound can be defined for the size ranges of GCCN and UGCCN.

Abstract. Mesoscale eddies are important, frequent, and persistent features of the circulation in the eastern South Pacific (ESP) Ocean, transporting physical, chemical and biological properties from the productive shelves to the open ocean. Some of these eddies exhibit subsurface hypoxic or suboxic conditions and may serve as important hotspots for nitrogen loss, but little is known about oxygen consumption rates and nitrogen transformation processes associated with these eddies. In the austral fall of 2011, during the Tara Oceans expedition, an intrathermocline, anticyclonic, mesoscale eddy with a suboxic (< 2 µmol kg−1 of O2), subsurface layer (200–400 m) was detected ∼ 900 km off the Chilean shore (30° S, 81° W). The core of the eddy's suboxic layer had a temperature-salinity signature characteristic of Equatorial Subsurface Water (ESSW) that at this latitude is normally restricted to an area near the coast. Measurements of nitrogen species within the eddy revealed undersaturation (below 44 %) of nitrous oxide (N2O) and nitrite accumulation (> 0.5 µM), suggesting that active denitrification occurred in this water mass. Using satellite altimetry, we were able to track the eddy back to its region of formation on the coast of central Chile (36.1° S, 74.6° W). Field studies conducted in Chilean shelf waters close to the time of eddy formation provided estimates of initial O2 and N2O concentrations of the ESSW source water in the eddy. By the time of its offshore sighting, concentrations of both O2 and N2O in the subsurface oxygen minimum zone (OMZ) of the eddy were lower than concentrations in surrounding water and “source water” on the shelf, indicating that these chemical species were consumed as the eddy moved offshore. Estimates of apparent oxygen utilization rates at the OMZ of the eddy ranged from 0.29 to 44 nmol L−1 d−1 and the rate of N2O consumption was 3.92 nmol L−1 d−1. These results show that mesoscale eddies affect open-ocean biogeochemistry in the ESP not only by transporting physical and chemical properties from the coast to the ocean interior but also during advection, local biological consumption of oxygen within an eddy further generates conditions favorable to denitrification and loss of fixed nitrogen from the system.

Les coraux tropicaux sont des archives naturelles qui permettent d’une part, de reconstruire la variabilité océanique et, d’autre part, d’évaluer les impacts du réchauffement climatique et de l’acidification des océans sur ces organismes calcifiants.À partir d'un jeu de données unique issu de 40 colonies de corail massif couvrant l’ensemble de l'Océan Pacifique, de nouvelles calibrations de température ont été développées via l’analyse géochimique élémentaire de leur squelette pour la période 2010-2016. Ainsi, l’utilisation de l’approche « multi-traceurs » couplant Sr/Ca-Li/Mg permet de réduire les incertitudes de reconstruction des températures à ± 0,87 °C. Grâce à cela, deux séries temporelles de température dérivées de colonies de Porites et de Diploastrea de Palaos (Micronésie) ont été comparées. Celles-ci révèlent une discordance marquée des variations temporelles selon le traceur utilisé ou le genre étudié et donc, la nécessité de mieux comprendre les processus de bio-minéralisation. Pour cela, l'analyse géochimique (B/Ca et δ11B) de squelettes coralliens a été réalisée afin de reconstruire les propriétés chimiques des carbonates au sein du fluide de calcification (cf).Ce travail doctoral met en évidence la capacité des coraux massifs à réguler la chimie des carbonates de leur cf avec, pour Porites une hausse du pHcf (~ 8,41) à la fois sur un site témoin (pHsw ~ 8,03) et sur un site naturellement acide de Palaos (pHsw ~ 7,85), favorisant ainsi le processus de calcification.À l’échelle du bassin Pacifique, il en résulte que la température conjointement à la chimie des carbonates de l’eau de mer (pHsw, DICsw et Ωsw) pilotent cette régulation interne ainsi que les paramètres de croissance. Parmi eux, la densité du squelette des Porites diminue de 14 % en condition acide, ce qui pourrait à terme, les rendre plus vulnérables.En revanche, la régulation interne du genre Diploastrea semble plus sensible au réchauffement de l'océan et mérite donc une attention particulière dans les études futures afin d’évaluer leur capacité à supporter ce réchauffement conjugué à l'acidification des océans
Tropical corals provide natural archives to reconstruct oceanic variability and evaluate the impacts of global warming and ocean acidification on these calcifying organisms.From a unique dataset of 40 massive coral colonies across the Pacific Ocean, I developed temperature calibrations via elemental geochemical analysis of their skeletons for the period 2010-2016. The use of a "multi-proxy" approach coupling Sr/Ca-Li/Mg reduces the reconstructed temperature uncertainties to ± 0.87 °C. Thereby, two temperature time series derived from Porites and Diploastrea colonies from Palau (Micronesia) were reconstructed and compared. These reveal a substantial discrepancy in temporal variations by proxy or genus of interest and hence, the need to better understand bio-mineralization processes. With this aim, I analysed the B/Ca and δ11B of the coral skeletons in order to determine the carbonate system properties of the calcifying fluid (cf).My results highlight the ability of massive corals to regulate the carbonate chemistry of their cf with, for Porites, an increase in pHcf (~ 8.41) both at a control site (pHsw ~ 8.03) and at a naturally acidic site in Palau (pHsw ~ 7.85), promoting the calcification process.At the Pacific Ocean level, it emerges that temperature together with seawater carbonate chemistry (pHsw, DICsw and Ωsw) influence this internal regulation as well as the growth parameters. In particular, the skeletal density of Porites decreases by 14% under acidic conditions, which might ultimately lead to a greater vulnerability to further damages.In contrast, internal regulation of the genus Diploastrea is more likely to be sensitive to ocean warming and therefore, deserve forefront attention in the future studies to assess their ability to endure increasing global ocean warming and acidification