Biology subjects

Berman-Frank, I.

Publications and source records attributed to Berman-Frank, I..

3 recordsLinked to original sources

bioRxiv2021

Massive export of diazotrophs across the tropical south Pacific Ocean

Diazotrophs are widespread microorganisms that alleviate nitrogen limitation in 60% of our oceans, regulating marine productivity. Yet, their contribution to organic matter export has not been quantified, making an assessment of their impact on the biological carbon pump impossible. Here, we demonstrate that cyanobacterial and non-cyanobacterial diazotrophs are massively exported down to 1000 m-depth in the western subtropical South Pacific Ocean (WTSP), accounting for up to 52-100% of the total particulate nitrogen export fluxes. We further demonstrate that small size unicellular diazotrophs (UCYN, 1-8 {micro}m) are exported more efficiently than filamentous diazotrophs (>100-1000 {micro}m) under the form of large (>50 {micro}m) aggregates linked by an extracellular organic matrix. Beyond the WTSP, our data are supported by analysis of the Tara Oceans metagenomes collected in other ocean basins, showing that diazotrophs are systematically detected in mesopelagic waters when present at the surface. We thus conclude that diazotrophs are key players in carbon sequestration in the ocean and need to be considered in future studies to improve the accuracy of current regional and global estimates of export.

microbiology↗

bioRxiv2021

Seasonal dynamics of phytoplankton and bacterioplankton at the ultra-oligotrophic southeastern Mediterranean Sea

The Eastern Mediterranean Sea (EMS) is a poorly studied ultra-oligotrophic marine environment, dominated by small-size phyto- and bacterioplankton. Here, we describe the dynamics of a single annual cycle (2018-19) of phyto- and bacterioplankton (abundances, pigments and productivity) in relation to the physical and chemical conditions in the photic water column at an offshore EMS site (Station THEMO-2, [~]1,500m depth, 50km offshore). We show that phytoplankton biomass (as chlorophyll a), primary and bacterial productivity differed between the mixed winter (January-April) and the thermally stratified (May-December) periods. Prochlorococcus and Synechococcus numerically dominated the picophytoplankton populations, with each clade revealing different temporal and depth changes indicative to them, while pico-eukaryotes (primarily haptophytes) were less abundant, yet likely contributed significant biomass. Estimated primary productivity ([~]32 gC m-2 y-1) was lower compared with other well-studied oligotrophic locations, including the north Atlantic and Pacific (BATS and HOT observatories), the western Mediterranean (DYFAMED observatory) and the Red Sea, and was on-par with the ultra-oligotrophic South Pacific Gyre. In contrast, integrated bacterial production ([~]11 gC m-2 y-1) was similar to other oligotrophic locations. Phytoplankton seasonal dynamics were similar to those at BATS and the Red Sea, suggesting an observable effect of winter mixing in this ultra-oligotrophic location. These results highlight the ultra-oligotrophic conditions in the EMS and provide, for the first time in this region, a full-year baseline and context to ocean observatories in the region. HighlightsO_LIBacterioplankton dynamics were assessed monthly in the Eastern Mediterranean Sea C_LIO_LISmall-sized picophytoplankton numerically dominated the phytoplankton community C_LIO_LISeasonal phytoplankton dynamics are similar to BATS and Red Sea, but not to HOT C_LIO_LIAnnual primary productivity is among the lowest in the worlds oceans C_LIO_LIBacterial to primary production ratio is higher than most oligotrophic seas C_LI

microbiology↗

bioRxiv2020

Fine scale sampling unveils diazotroph patchiness in the South Pacific Ocean

Diazotrophs are important contributors to reactive nitrogen availability in the ocean. Oceanographic cruise data accumulated along decades has revealed a heterogeneous distribution of diazotroph species at regional to global scales. However, the role of dynamic fine scale structures in distributing diazotrophs is not well understood. This is due to typical insufficient spatiotemporal resolution sampling and the lack of detailed physical studies in parallel. Here we show the distribution of five groups of diazotrophs in the South Pacific at an unprecedented resolution of 7-16 km. We find a patchy distribution of diazotrophs, with each group being differently affected by parameters describing fine scale structures. The observed variability could not have been revealed with a lower resolution sampling, highlighting the need to consider fine scale physics to resolve the distribution of diazotrophs in the ocean.

microbiology↗