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

NASA Planetary Mission Concept Study: Assessing: Dwarf Planet Ceres' past and Present Habitability Potential

The Dawn mission revolutionized our understanding of Ceres during the same decade that has also witnessed the rise of ocean worlds as a research and exploration focus. We will report progress on the Planetary Mission Concept Study (PMCS) on the future exploration of Ceres under the New Frontiers or Flagship program that was selected for NASA funding in October 2019. At the time this writing, the study was just kicked off, hence this abstract reports the study plan as presented in the proposal

Biogeochemical conditions in the equatorial Pacific in late 1994

Quantitative and qualitative investigations of phycoerythrins (PE) were achieved in the Central Southern tropical and equatorial Pacific during the Flux dans l'ouest du Pacifique equatorial (FLUPAC : September-October 1994) and Oligotrophie en Pacifique (OLIPAC : November 1994) cruises. We observed mainly high-phycourobilin (PUB) PE related to small #Synechococcus$spp. (0.6-1.4 micrometers). This PE was characterized by fluorescence excitation peaks at 496 and 550 nm in 50$ did not exceed 31 x 1000 cell/mL. No subpopulations of #Synechococcus$ were evidenced by cytometry. Nevertheless, in a few samples, two new PE spectral types were observed. The first type was a high-PUB PE with two fluorescence excitation peaks at 494 and 564 nm. It appears to be attributable to nonmotile round cells, 2-3 micrometers in size and easily detected by flow cytometry, likely cyanobacteria. They were only observed in very oligotrophic waters South of 15°30'S along 150°W in the top 60 m. In this area, nitrate, nitrite, and ammonia were undetectable above 120 m, while phosphate was always recorded. This suggests that these larger cyanobacteria may fix dinitrogen (N2) to supply their growth and therefore possibly play a significant role in oceanic new production. The second type, a high-phycoerythrobilin (PEB) PE was observed in three samples obtained at or near the equator. It displayed two fluorescence excitation peaks at 496 and 536 nm. The organisms that contained this PE type were not identified. These data suggest that PE is more diverse in oceanic waters than was previously assumed. (Résumé d'auteur

Biogeochemical conditions in the equatorial Pacific in late 1994

Quantitative and qualitative investigations of phycoerythrins (PE) were achieved in the Central Southern tropical and equatorial Pacific during the Flux dans l'ouest du Pacifique equatorial (FLUPAC : September-October 1994) and Oligotrophie en Pacifique (OLIPAC : November 1994) cruises. We observed mainly high-phycourobilin (PUB) PE related to small #Synechococcus$spp. (0.6-1.4 micrometers). This PE was characterized by fluorescence excitation peaks at 496 and 550 nm in 50$ did not exceed 31 x 1000 cell/mL. No subpopulations of #Synechococcus$ were evidenced by cytometry. Nevertheless, in a few samples, two new PE spectral types were observed. The first type was a high-PUB PE with two fluorescence excitation peaks at 494 and 564 nm. It appears to be attributable to nonmotile round cells, 2-3 micrometers in size and easily detected by flow cytometry, likely cyanobacteria. They were only observed in very oligotrophic waters South of 15°30'S along 150°W in the top 60 m. In this area, nitrate, nitrite, and ammonia were undetectable above 120 m, while phosphate was always recorded. This suggests that these larger cyanobacteria may fix dinitrogen (N2) to supply their growth and therefore possibly play a significant role in oceanic new production. The second type, a high-phycoerythrobilin (PEB) PE was observed in three samples obtained at or near the equator. It displayed two fluorescence excitation peaks at 496 and 536 nm. The organisms that contained this PE type were not identified. These data suggest that PE is more diverse in oceanic waters than was previously assumed. (Résumé d'auteur