Light Absorption by Suspended Particles in the Red Sea: Effect of Phytoplankton Community Size Structure and Pigment Composition

The light absorption properties of phytoplankton (aph(λ)) and non-algal particles (anap(λ)) associated with phytoplankton pigments were analyzed across the Red Sea, in the upper 200 m depth, between October 2014 and August 2016. The contribution by non-algal particles to the total particulate light absorption (aph(λ)+ anap(λ)) was highly variable (23 ± 17% at 440 nm) and no relationship between anap(440) and chlorophyll a concentration, [TChl a], was observed. Phytoplankton specific phytoplankton absorption coefficients at 440 and 676 nm for a given [TChl a], aph*(440) and aph*(676), were slightly higher than those derived from average relationships for open ocean waters within the surface layer as well as along the water column. Variations in the concentration of photosynthetic and photoprotective pigments were noticeable by changes in phytoplankton community size structure as well as in aph*(λ). This study revealed that a higher proportion of picophytoplankton and an increase in photoprotective pigments (mainly driven by zeaxanthin) tended to be responsible for the higher aph*(λ) values found in the Red Sea as compared to other oligotrophic regions with similar [TChl a]. Understanding this variability across the Red Sea may help improve the accuracy of biogeochemical parameters, such as [TChl a], derived from in situ measurements and ocean color remote sensing at a regional scale

Particulate Scattering and Backscattering in Relation to the Nature of Particles in the Red Sea

This is the final version. Available on open access from the American Geophysical Union via the DOI in this recordData Availability Statement: The data presented in this study are archived in KAUST repository (https://doi.org/10.25781/KAUST‐PSDX7).European Space AgencyKing Abdullah University of Science and Technology (KAUST), Kingdom of Saudi ArabiaSimons Foundatio

Regionalization of the Red Sea based on phytoplankton phenology: A satellite analysis

The current average state of Red Sea phytoplankton phenology needs to be resolved in order to study future variations that could be induced by climate change. Moreover, a regionalization of the Red Sea could help to identify areas of interest and guide in situ sampling strategies. Here, a clustering method used 21 years of satellite surface chlorophyll-a concentration observations to characterize similar regions of the Red Sea. Four relevant phytoplankton spatiotemporal patterns (i.e., bio-regions) were found and linked to biophysical interactions occurring in their respective areas. Two of them, located in the northern part the Red Sea, were characterized by a distinct winter-time phytoplankton bloom induced by mixing events or associated with a convergence zone. The other two, located in the southern regions, were characterized by phytoplankton blooms in summer and winter which might be under the influence of water advected into the Red Sea from the Gulf of Aden in response to the seasonal monsoon winds. Some observed inter-annual variabilities in these bio-regions suggested that physical mechanisms could be highly variable in response to variations in air-sea heat fluxes and ENSO phases in the northern and southern half of the Red Sea, respectively. This study reveals the importance of sustaining in situ measurements in the Red Sea to build a full understanding about the physical processes that contribute to phytoplankton production in this basin

Organic carbon export and loss rates in the Red Sea

The export and fate of organic carbon in the mesopelagic zone are still poorly understood and quantified due to lack of observations. We exploited data from a BGC‐Argo float that was deployed in the Red Sea to study how a warm and hypoxic environment can affect the fate of the organic carbon in the ocean’s interior. We observed that only 10% of the particulate organic carbon (POC) exported survived at depth due to remineralization processes in the upper mesopelagic zone. We also found that POC exported was rapidly degraded in a first stage and slowly in a second one, which may be dependent on the palatability of the organic matter. We observed that AOU‐based loss rates (a proxy of the remineralization of total organic matter) were significantly higher than the POC‐based loss rates, likely because changes in AOU are mainly attributed to changes in dissolved organic carbon. Finally, we showed that POC‐ and AOU‐based loss rates could be expressed as a function of temperature and oxygen concentration. These findings advance our understanding of the biological carbon pump and mesopelagic ecosystem

Remotely sensing phytoplankton size structure in the Red Sea

Phytoplankton size structure impacts ocean food-web dynamics and biogeochemical cycling, and is thus an important ecological indicator that can be utilised to quantitatively evaluate the state of marine ecosystems. Potential alterations to size structure are predicted to occur in tropical regions under future scenarios of climate change. Therefore, there is an increasing requirement for the synoptic monitoring of phytoplankton size structure in marine systems. The Red Sea remains a comparatively unexplored tropical marine ecosystem, particularly with regards to its large-scale biological dynamics. Using an in situ pigment dataset acquired in the Red Sea, we parameterise a two-component, abundance-based phytoplankton size model and apply it to remotely-sensed observations of chlorophyll-a (Chl-a) concentration, to infer Chl-a in two size classes of phytoplankton, small cells <2 μm in size (picophytoplankton) and large cells >2 μm in size. Satellite-derived estimates of phytoplankton size structure are in good agreement with corresponding in situ measurements and also capture the spatial variability related to regional mesoscale dynamics. Our analysis reveals that, for the estimation of Chl-a in the two size classes, the model performs comparably or in some cases better, to validations in other oceanic regions. Our model parameterisation will be useful for future studies on the seasonal and interannual variability of phytoplankton size classes in the Red Sea, which may ultimately be relevant for understanding trophic linkages between phytoplankton size structure and fisheries, and the development of marine management strategies. © 2019 Elsevier Inc

Remotely sensing phytoplankton size structure in the Red Sea

Phytoplankton size structure impacts ocean food-web dynamics and biogeochemical cycling, and is thus an important ecological indicator that can be utilised to quantitatively evaluate the state of marine ecosystems. Potential alterations to size structure are predicted to occur in tropical regions under future scenarios of climate change. Therefore, there is an increasing requirement for the synoptic monitoring of phytoplankton size structure in marine systems. The Red Sea remains a comparatively unexplored tropical marine ecosystem, particularly with regards to its large-scale biological dynamics. Using an in situ pigment dataset acquired in the Red Sea, we parameterise a two-component, abundance-based phytoplankton size model and apply it to remotely-sensed observations of chlorophyll-a (Chl-a) concentration, to infer Chl-a in two size classes of phytoplankton, small cells 2 μm in size. Satellite-derived estimates of phytoplankton size structure are in good agreement with corresponding in situ measurements and also capture the spatial variability related to regional mesoscale dynamics. Our analysis reveals that, for the estimation of Chl-a in the two size classes, the model performs comparably or in some cases better, to validations in other oceanic regions. Our model parameterisation will be useful for future studies on the seasonal and interannual variability of phytoplankton size classes in the Red Sea, which may ultimately be relevant for understanding trophic linkages between phytoplankton size structure and fisheries, and the development of marine management strategies

Gene transfer in differentiated HepaRGT cells: Application to the modulation of specific hepatocyte functions

International audienc

OS04-03 Gene transfer in differentiated HepaRG™ cells: Application to the modulation of specific hepatocyte functions

International audienc

Gene transfer in differentiated HepaRGT cells: Application to the modulation of specific hepatocyte functions

International audienc