Temporal variations of mixed-layer oceanic CO2 at JGOFS-KERFIX time-series station: Physical versus biogeochemical processes

The seasonal and interannual variations in mixed-layer carbon dioxide in the Southern Ocean are analyzed from January 1990 to March 1995 at KERFIX time-series station (50°40S-69°25E). The temperature, salinity and chlorophyll time series are used as constraints on a simple box model to extrapolate total dissolved inorganic carbon (DIC), total alkalinity (TA) and oceanic CO2 fugacity (fCO2) over the five years of the monitoring. Results of the simulation are compared to all available observations. Both measured and simulated DIC and TA give seasonal signals of 25 µmol/kg and 8 µeq/kg, respectively. In spite of a weak primary production about 70 gC/m2/yr, the biological pump appears to play a significant role on seasonal and interannual variations in air-sea CO2 exchanges. Its contribution varies from 10 to 45% of the total sea surface fCO2 variations depending on the period. This area has been a sink for atmospheric CO2 with annual mean values of-0.8 to-3.0 mol/m2/yr during the whole period investigated. Annually the CO2 sink is due to the balance between biological activity and mixing processes on fCO2 inducing thermodynamically mediated variations. The sink\u27s interannual variations appear to be mainly due to the high variability of the wind speeds and hence, of the mixed-layer depth. The impact of the anthropogenic atmospheric CO2 increase on oceanic fCO2 is also investigated. The rate of increase of oceanic fCO2 (0.6 µatm/yr) was half that of atmospheric fCO2 (1.2 µatm/yr). The increase of the air-sea CO2 gradient lead to an increase of the CO2 sink of about 0.07 mol/m2/yr (0.02 GtC/yr) over the five years investigated

Role of plankton communities in sea-air variations in pCO2 in the SW Atlantic Ocean

The influence of the plankton community structure on carbon dynamics was studied in the surface waters of the Argentinean continental shelf (SW Atlantic Ocean) in summer and fall 2002, 2003 and 2004, The horizontal changes in plankton community respiration (R), net community production (NCP) and gross primary production (GPP) were (1) compared with the difference in the partial pressure of CO2 (pCO2) between the sea surface and the atmosphere (ΔpCO2), (2) compared with oxygen saturation and (3) related to the microscopic phytoplankton assemblages, This area, which has recently been shown to be a CO2 sink, had an average surface oxygen saturation of 108.1%, indicating that net photosynthesis could have played a dominant role in the CO2 dynamics. At most stations, the production:respiration (GPP:R) ratio was greater than 1, indicating that planktonic communities were autotrophic; the average GPP:R ratio for the whole study was 2.99, Phytoplankton biomass (chlorophyll a) and NCP showed an inverse relationship with ΔpCO2 and a direct relationship with %O 2 saturation when phytoplankton assemblages were dominated by diatoms (30% of the stations), This was not the case when small (≤5 μm) flagellates were the most abundant organisms, Although NCP was mostly positive for both groups of stations (i.e. diatom-dominated or small flagellate- dominated), other physical and biological processes are thought to modify the CO2 dynamics when small flagellates are the prevailing phytoplankton group.Facultad de Ciencias Naturales y Muse

Campagne océanographique FLUPAC à bord du N.O. l'ATALANTE 23 septembre au 29 octobre 1994. Recueil des données. Tome 1 : météo, courantologie, hydrologie, données de surface

La campagne FLUPAC du N.O. L'Atalante, qui s'est déroulée du 23 septembre au 29 octobre 1994, s'est placée dans le cadre du programme international JGOFS (JOINT GLOBAL OCEAN FLUX STUDY). Elle a comporté deux radiales et deux stations équatoriales de 6-7 jours. La première radiale, le long de 165°E, a parcouru la zone comprise entre 20°S et 6°N. La seconde s'est déroulée le long de l'équateur entre 167°E et 150°W. Les deux stations de longue durée ont eu lieu à O°-167°E et 0°-150°W. Elles ont été l'occasion d'études détaillées des flux impliqués dans le cycle du carbone de la couche superficielle (0-500 m). Le premier tome du recueil de données présente des résultats, sous forme de graphiques et de tableaux, des paramètres enregistrés en continu et de ceux de la sonde CTD. Les paramètres chimiques, la chlorophylle "a" et les observations en cytomètrie de flux obtenus sur l'eau de la "rosette" couplée à la sonde CTD, sont également présentés. (Résumé d'auteur

Role of plankton communities in sea-air variations in pCO2 in the SW Atlantic Ocean

The influence of the plankton community structure on carbon dynamics was studied in the surface waters of the Argentinean continental shelf (SW Atlantic Ocean) in summer and fall 2002, 2003 and 2004, The horizontal changes in plankton community respiration (R), net community production (NCP) and gross primary production (GPP) were (1) compared with the difference in the partial pressure of CO2 (pCO2) between the sea surface and the atmosphere (ΔpCO2), (2) compared with oxygen saturation and (3) related to the microscopic phytoplankton assemblages, This area, which has recently been shown to be a CO2 sink, had an average surface oxygen saturation of 108.1%, indicating that net photosynthesis could have played a dominant role in the CO2 dynamics. At most stations, the production:respiration (GPP:R) ratio was greater than 1, indicating that planktonic communities were autotrophic; the average GPP:R ratio for the whole study was 2.99, Phytoplankton biomass (chlorophyll a) and NCP showed an inverse relationship with ΔpCO2 and a direct relationship with %O 2 saturation when phytoplankton assemblages were dominated by diatoms (30% of the stations), This was not the case when small (≤5 μm) flagellates were the most abundant organisms, Although NCP was mostly positive for both groups of stations (i.e. diatom-dominated or small flagellate- dominated), other physical and biological processes are thought to modify the CO2 dynamics when small flagellates are the prevailing phytoplankton group.Facultad de Ciencias Naturales y Muse

Machine Learning Identifies Stemness Features Associated with Oncogenic Dedifferentiation.

Cancer progression involves the gradual loss of a differentiated phenotype and acquisition of progenitor and stem-cell-like features. Here, we provide novel stemness indices for assessing the degree of oncogenic dedifferentiation. We used an innovative one-class logistic regression (OCLR) machine-learning algorithm to extract transcriptomic and epigenetic feature sets derived from non-transformed pluripotent stem cells and their differentiated progeny. Using OCLR, we were able to identify previously undiscovered biological mechanisms associated with the dedifferentiated oncogenic state. Analyses of the tumor microenvironment revealed unanticipated correlation of cancer stemness with immune checkpoint expression and infiltrating immune cells. We found that the dedifferentiated oncogenic phenotype was generally most prominent in metastatic tumors. Application of our stemness indices to single-cell data revealed patterns of intra-tumor molecular heterogeneity. Finally, the indices allowed for the identification of novel targets and possible targeted therapies aimed at tumor differentiation