Geographical, seasonal, and depth variation in sinking particle speeds in the North Atlantic

Particle sinking velocity is considered to be a controlling factor for carbon transport to the deep sea and thus carbon sequestration in the oceans. The velocities of the material exported to depth are considered to be high in high-latitude productive systems and low in oligotrophic distributions. We use a recently developed method based on the measurement of the radioactive pair 210Po-210Pb to calculate particle sinking velocities in the temperate and oligotrophic North Atlantic during different bloom stages. Our estimates of average sinking velocities (ASVs) show that slowly sinking particles (<100?m?d?1) contribute significantly to carbon flux at all the locations except in the temperate regions during the bloom. ASVs appear to vary strongly with season, which we propose is caused by changes in the epipelagic community structure. Our results are the first field data to confirm the long-standing theory that particle sinking velocities increase with depth, with increases of up to 90% between 50 and 150?m depth

Segmentation of the Himalayas as revealed by arc-parallel gravity anomalies

International audienceLateral variations along the Himalayan arc are suggested by an increasing number of studies and carry important information about the orogen’s segmentation. Here we compile the hitherto most complete land gravity dataset in the region which enables the currently highest resolution plausible analysis. To study lateral variations in collisional structure we compute arc-parallel gravity anomalies (APaGA) by subtracting the average arc-perpendicular profile from our dataset; we compute likewise for topography (APaTA). We find no direct correlation between APaGA, APaTA and background seismicity, as suggested in oceanic subduction context. In the Himalayas APaTA mainly reflect relief and erosional effects, whereas APaGA reflect the deep structure of the orogen with clear lateral boundaries. Four segments are outlined and have disparate flexural geometry: NE India, Bhutan, Nepal & India until Dehradun, and NW India. The segment boundaries in the India plate are related to inherited structures, and the boundaries of the Shillong block are highlighted by seismic activity. We find that large earthquakes of the past millennium do not propagate across the segment boundaries defined by APaGA, therefore these seem to set limits for potential rupture of megathrust earthquakes

Carbon sequestration in the deep Atlantic enhanced by Saharan dust

sinking rates of particulate organicmatter. Here we present a two-year time series of sediment trap observations of particulate organic carbon flux to 3,000m depth, measured directly in two locations: the dust-rich central North Atlantic gyre and the dust-poor South Atlantic gyre. We find that carbon fluxes are twice as high and a higher proportion of primary production is exported to depth in the dust-rich North Atlantic gyre. Low stable nitrogen isotope ratios suggest that high fluxes result from the stimulation of nitrogen fixation and productivity following the deposition of dust-borne nutrients. Sediment traps in the northern gyre also collected intact colonies of nitrogen-fixing Trichodesmium species. Whereas ballast in Enhanced atmospheric input of dust-borne nutrients and minerals to the remote surface ocean can potentially increase carbon uptake and sequestration at depth. Nutrients can enhance primary productivity, and mineral particles act as ballast, increasing the southern gyre is predominantly biogenic, dust-derived mineral particles constitute the dominant ballast element during the enhanced carbon fluxes in the northern gyre. We conclude that dust deposition increases carbon sequestration in the North Atlantic gyre through the fertilization of the nitrogen-fixing community in surface waters and mineral ballasting of sinking particles

CleanAtlantic sea litter geographical web

A Sea litter data viewer has been developed in the framework of the CleanAtlantic European project. This web application allows access to the litter data of different compartments of the ocean as beach litter, floating litter, and seabed litter. The users can query the statistical distributions of litter concentrations, time series, and the composition of the most frequent types of litter of each geographical item. In order to facilitate access to this type of information to all types of users independently of their data analysis skills, the viewer has developed following criteria of simplicity and usability

Comparison of RANS, DES and DDES Results for ONERA M-6 Wing at Transonic Flow Speed Using an In-House Parallel Code

The very first thought that comes to the mind with the application area of the DES and DDES schemes is a massively separated flow with highly unsteady flowfield. However, for various complex three dimensional cases, there is no prior knowledge of the flowfield in the domain and it may have mild separation or no separation at all with a steady domain. This study is carried out to see that what will be the behaviour of the DES and DDES schemes in comparison with the URANS scheme if they are applied to a steady state case. An in-house mpi code DG-DES is used for the present study. Three different flux computational schemes named Roe, AUSM and HLLC schemes within DES formulation are compared to check the response for the flows without massive separation and unsteadiness. The cases are run in both single and double precision mode for DES formulation using Roe flux computational scheme to appreciate the accuracy of the solver. A good comparison of pressure distribution with the experimental data is obtained for all URANS, DES and DDES simulations. The pressure distribution results for DES scheme using single and double precision agree well with the experimental data. The pressure distribution predicted by DES using Roe, AUSM and HLLC schemes agree well with the experimental data. The computed values of Cl and Cd are also in close approximity to the other studies. The drag predicted by all DES and DDES simulations is lower than the URANS scheme. It indicates that the DES and DDES schemes generate lower dissipation due to switching to the LES mode and hence result in lower drag prediction as compared with the URANS solution. There is no anomaly observed in the flow due to the use of DES or DDES for steady flow case

Attenuation of particulate organic carbon flux in the Scotia Sea, Southern Ocean, is controlled by zooplankton fecal pellets

The Southern Ocean (SO) is an important CO2 reservoir, some of which enters via the production, sinking and remineralization of organic matter. Recent work suggests the fraction of production that sinks is inversely related to production in the SO, a suggestion we confirm from 20 stations in the Scotia Sea. The efficiency with which exported material is transferred to depth (transfer efficiency) is believed to be low in high latitude systems. However, our estimates of transfer efficiency are bimodal, with stations in the seasonal ice zone showing intense losses and others displaying increases in flux with depth. Zooplankton fecal pellets dominated organic carbon flux and at stations with transfer efficiency >100 % fecal pellets were brown, indicative of fresh phytodetritus. We suggest that active flux mediated by zooplankton vertical migration and the presence of sea ice regulate the transfer of organic carbon into the oceans interior in the Southern Ocean

Overview of the marine litter status in the Atlantic Area: beach, floating and seabed litter

CleanAtlantic is an INTERREG Atlantic Area Programme project that aimed at protecting biodiversity and ecosystem services in the Atlantic Area by improving capabilities to monitor, prevent and remove (macro) marine litter. Besides, the project also contributed to raise awareness and change attitudes among stakeholders and to improve marine litter managing systems. To achieve these aims, the work was organised in 8 work packages. The present deliverable aims at synthesizing the main results obtained on the frame of the action 1 of work package 4, which focused on the Regional characterisation of marine litter in the Atlantic Area. With this purpose, an overview of marine litter status in beach, floating and seabed compartments in the Atlantic Area is presented. Additionally, the major key findings, gaps on monitoring and research as well as potential improvements and recommendations are identified. Links to the complete dedicated reports for each compartment are included in the references section. Also, an interactive map for spatial visualization of data on beach, floating and seabed litter composition and abundance in the Atlantic Area was created and is presented at the end of this report

Cytopathic effects of the cytomegalovirus-encoded apoptosis inhibitory protein vMIA

Replication of human cytomegalovirus (CMV) requires the expression of the viral mitochondria–localized inhibitor of apoptosis (vMIA). vMIA inhibits apoptosis by recruiting Bax to mitochondria, resulting in its neutralization. We show that vMIA decreases cell size, reduces actin polymerization, and induces cell rounding. As compared with vMIA-expressing CMV, vMIA-deficient CMV, which replicates in fibroblasts expressing the adenoviral apoptosis suppressor E1B19K, induces less cytopathic effects. These vMIA effects can be separated from its cell death–inhibitory function because vMIA modulates cellular morphology in Bax-deficient cells. Expression of vMIA coincided with a reduction in the cellular adenosine triphosphate (ATP) level. vMIA selectively inhibited one component of the ATP synthasome, namely, the mitochondrial phosphate carrier. Exposure of cells to inhibitors of oxidative phosphorylation produced similar effects, such as an ATP level reduced by 30%, smaller cell size, and deficient actin polymerization. Similarly, knockdown of the phosphate carrier reduced cell size. Our data suggest that the cytopathic effect of CMV can be explained by vMIA effects on mitochondrial bioenergetics