Distribution and lability of land-derived organic matter in the surface sediments of the Rhône prodelta and the adjacent shelf (Mediterranean Sea, France): a multi proxy study

The Gulf of Lions is a river-dominated ocean margin that receives high loads of nutrients and particulate matter from the Rhône River but most particulate materials settle rapidly on the nearshore seafloor. One question is raised on the fate of these large quantities of organic carbon delivered by the river to the coastal marine environment. Surface sediments (0–0.5 cm) were collected in the Rhône prodelta and its adjacent shelf during a period of low river discharge (April 2007, 16 stations). The sources, distribution and lability of sedimentary organic matter were examined using bulk (organic carbon, total nitrogen, stable carbon isotope ratios, and grain size) and molecular-level (pigments, amino acids, fatty acids, and δ<sup>13</sup>C of individual fatty acids) analyses. Our results confirmed previous observations of a southwestward Rhodanian imprint in the nearshore sediments, with 97% of terrigenous inputs of organic matter near the river mouth. Isotopic values of bulk organic carbon, as well as fatty acid biomarkers and compound-specific δ<sup>13</sup>C signatures of most fatty acids clearly indicate that the Rhône inputs consist of a mixture of organic matter (OM) from different origins with a strong contribution from terrestrial sources (soil and plant debris), and a smaller input from freshwater microalgae, mostly diatoms. The influence of the Rhône River was prominent within the first ten kilometers, but may still be observed on the outer shelf (~21 km) as indicated by the occurrence of long chain fatty acids, which are derived from vascular plants, and their δ<sup>13</sup>C signatures. In the proximal prodelta, bacteria-specific fatty acids were abundant (1.65 mg g<sup>−1</sup> OC at the mouth site) and were relatively depleted in δ<sup>13</sup>C confirming that bacteria mostly utilize land-derived OM. In the shelf area, the inputs of marine OM and its predominant utilization by the bacteria was confirmed, but the coupling between the pelagic and the benthic compartments appeared limited at this period of the year. <br><br> Overall, degradation indexes based on amino acids (Dauwe's degradation index) and pigments (ratio of intact chlorophyll-<I>a</I> to the sum of chlorophyll-<I>a</I> + phaeopigment-<I>a</I>), as well as isotopic enrichment of source-specific fatty acids reveal an offshore gradient of OM decay reflecting the rapid deposition of the terrestrial material in the prodelta, the low mixing with OM deriving from marine sources and the efficient degradation of the OM. The OM delivered by the Rhône is relatively labile based on the intermediary value of Dauwe's degradation index, the high proportion of bio-available nitrogen and the occurrence of polyunsaturated fatty acids. Deltaic sediments off the Rhône River should thus be of sufficiently high nutritional quality to sustain dense macrofaunal communities

Picophytoplankton biomass distribution in the global ocean

The smallest marine phytoplankton, collectively termed picophytoplankton, have been routinely enumerated by flow cytometry since the late 1980s during cruises throughout most of the world ocean. We compiled a database of 40 946 data points, with separate abundance entries for Prochlorococcus, Synechococcus and picoeukaryotes. We use average conversion factors for each of the three groups to convert the abundance data to carbon biomass. After gridding with 1? spacing, the database covers 2.4% of the ocean surface area, with the best data coverage in the North Atlantic, the South Pacific and North Indian basins, and at least some data in all other basins. The average picophytoplankton biomass is 12 ± 22 µg Cl-1 or 1.9 g Cm-2. We estimate a total global picophytoplankton biomass of 0.53–1.32 Pg C (17–39% Prochlorococcus, 12–15% Synechococcus and 49–69% picoeukaryotes), with an intermediate/best estimate of 0.74 Pg C. Future efforts in this area of research should focus on reporting calibrated cell size and collecting data in undersampled regions

Temporal variability of live (stained) benthic foraminiferal faunas in a river-dominated shelf – Faunal response to rapid changes of the river influence (Rhône prodelta, NW Mediterranean)

In the context of the French research project CHACCRA (Climate and Human-induced Alterations in Carbon Cycling at the River-seA connection), living (rose Bengal-stained) benthic foraminifera were investigated at two stations (24 and 67 m depth) in the Rhône prodelta (NW Mediterranean, Gulf of Lions). The aim of this study was to precise the response of benthic foraminiferal faunas to temporal changes of the Rhône River inputs (e.g. organic and terrigeneous material). Each site was sampled in April 2007, September 2007, May 2008 and December 2008, permitting to observe foraminiferal faunas of the 63–150 and >150 μm size fractions under a wide range of environmental conditions. Obvious variations in foraminiferal faunal composition were observed during the four investigated periods at the shallowest Station A located in the close vicinity of the Rhône River mouth. After major Rhône River flood events, different colonisation stages were observed with foraminiferal faunas responding with an opportunistic strategy few days to weeks after the creation of a peculiar sedimentary environment (<i>Leptohalysis scottii</i>, May 2008) or high organic matter supplies (<i>Ammonia tepida</i>, December 2008). Under more stable conditions, relatively diverse and equilibrated faunas grew in the sediments. Species benefited from noticeable input of riverine phytodetritus to the sediment during spring bloom conditions (April 2007; e.g. <i>Bolivina dilatata</i>, <i>Nonionella stella</i>, <i>Stainforthia fusiformis</i>), or high amounts of still bio-available organic matter under more oligotrophic conditions (September 2007; e.g. <i>Ammonia tepida</i>, <i>Psammosphaera fusca</i>). The reduced influence of the Rhône River input at the farther Station N led to less contrasted environmental conditions during the four sampling periods, and so to less obvious variations in foraminiferal faunal composition. During reduced riverine influence (i.e. low Rhône discharge), species able to feed on fresh phytodetritus (e.g. <i>Clavulina cylindrica</i>, <i>Hopkinsina atlantica</i>, <i>Nonionella iridea</i> and <i>Nonionella turgida</i>) benefited from eutrophic conditions of the spring bloom (April 2007, May 2008). Conversely, the occurrence of <i>Nouria polymorphinoides</i> under oligotrophic conditions (September 2007, December 2008) was indicative of a benthic environment potentially disturbed by bottom currents. This study put into evidence the extremely rapid response of benthic foraminiferal faunas to strong variations in environmental conditions mostly induced by the Rhône dynamics

Wavrin – La Vallée et Château de la Vallée

Un projet de création d’une zone maraîchère et horticole biologique porté par la MEL est à l’origine des 2 opérations de diagnostic réalisées par l’Inrap à Wavrin en septembre et octobre 2015, sur un ensemble de terrains situés aux lieux-dits « La Vallée » et « Château de la Vallée ». Le projet concerne 2 parcelles. Il prévoit notamment la réalisation d’une plate-forme pour assoir un bâtiment agricole et le drainage de la partie basse des terrains, travaux qui font porter la prescription sur ..

Potential Cislunar and Interplanetary Proving Ground Excursion Trajectory Concepts

NASA has been investigating potential translunar excursion concepts to take place in the 2020s that would be used to test and demonstrate long duration life support and other systems needed for eventual Mars missions in the 2030s. These potential trajectory concepts could be conducted in the proving ground, a region of cislunar and near-Earth interplanetary space where international space agencies could cooperate to develop the technologies needed for interplanetary spaceflight. Enabled by high power Solar Electric Propulsion (SEP) technologies, the excursion trajectory concepts studied are grouped into three classes of increasing distance from the Earth and increasing technical difficulty: the first class of excursion trajectory concepts would represent a 90-120 day round trip trajectory with abort to Earth options throughout the entire length, the second class would be a 180-210 day round trip trajectory with periods in which aborts would not be available, and the third would be a 300-400 day round trip trajectory without aborts for most of the length of the trip. This paper provides a top-level summary of the trajectory and mission design of representative example missions of these three classes of excursion trajectory concepts

Nivelle – Rue Achille-Dufresne

Un projet de construction d’un groupe scolaire est à l’origine du diagnostic réalisé par l’Inrap sur la commune de Nivelle en mai 2015 sur un terrain d’une surface annoncée de 2 460 m2 mais qui totalise en réalité 4 588 m2. L’emprise est localisée à l’est de la commune de Nivelle, à proximité de la salle des sports et de la salle polyvalente ; il s’agit de l’ancien terrain de football de la commune. Au sud-est, elle est bordée par un chemin de halage qui longe en rive gauche la Scarpe canalis..

Carvin – Rue des Colibris

Un projet d’extension de lotissement est à l’origine du diagnostic réalisé par l’Inrap sur la commune de Carvin en décembre 2015 sur un terrain d’une surface de 4 884 m2 situé à l’extrémité de la rue des Colibris ; cette prescription vient en complément d’une intervention réalisée en septembre 2015 sur des parcelles contiguës au sud. L’emprise concernée par l’intervention archéologique se situe au sud-est de l’agglomération de Carvin, au lieu-dit « Le Willerval » en bordure immédiate d’une zo..

Wattignies – Rue Sadi-Carnot

Un projet de construction d’un lotissement par la société Promogim est à l’origine du diagnostic réalisé par l’Inrap sur la commune de Wattignies en juin 2015 sur un terrain d’une surface de 12 161 m2 situé rue Sadi Carnot. L’emprise destinée à être aménagée est localisée au sud de la commune de Wattignies entre les lieux-dits « Le Marais », « La Jappe » et « Bargues » ; il s’agit d’un terrain encore récemment occupé par un horticulteur installé de l’autre côté de la rue. Plusieurs mentions d..

Saint-Amand-les-Eaux – Chemin de l’Empire

Opération négative Le projet d’extension du parking du Port de Plaisance de Saint-Amand-les-Eaux, est à l’origine de la prescription d’un diagnostic archéologique d’une surface totale de 7 753 m2, partiellement accessible. Elle se situe à l’est de l’agglomération de Saint-Amand, entre le centre-ville et le quartier du Mont des Bruyère, entre le Port de Plaisance et le nouveau casino. La zone étudiée est localisée en rive droite de la Scarpe canalisée, en partie basse du versant ouest du Mont ..