Deep ocean microbial communities rely on the organic carbon produced in the sunlit ocean, yet it remains unknown whether surface processes determine the assembly and function of bathypelagic prokaryotes to a larger extent than deep‐sea physicochemical conditions. Here, we explored whether variations in surface phytoplankton assemblages across Atlantic, Pacific and Indian ocean stations can explain structural changes in bathypelagic (ca. 4,000 m) free‐living and particle‐attached prokaryotic communities (characterized through 16S rRNA gene sequencing), as well as changes in prokaryotic activity and dissolved organic matter (DOM) quality. We show that the spatial structuring of prokaryotic communities in the bathypelagic strongly followed variations in the abundances of surface dinoflagellates and ciliates, as well as gradients in surface primary productivity, but were less influenced by bathypelagic physicochemical conditions. Amino acid‐like DOM components in the bathypelagic reflected variations of those components in surface waters, and seemed to control bathypelagic prokaryotic activity. The imprint of surface conditions was more evident in bathypelagic than in shallower mesopelagic (200–1,000 m) communities, suggesting a direct connectivity through fast‐sinking particles that escape mesopelagic transformations. Finally, we identified a pool of endemic deep‐sea prokaryotic taxa (including potentially chemoautotrophic groups) that appear less connected to surface processes than those bathypelagic taxa with a widespread vertical distribution. Our results suggest that surface planktonic communities shape the spatial structure of the bathypelagic microbiome to a larger extent than the local physicochemical environment, likely through determining the nature of the sinking particles and the associated prokaryotes reaching bathypelagic waters.

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Moreno-Ostos, E., Cruz-Pizarro, L., Basanta, A., George, D. G. (2009). Spatial Heterogeneity of Cyanobacteria and Diatoms in a Thermally Stratified Canyon-Shaped Reservoir. International Review of Hydrobiology, 94(3), 245-257.Phytoplankton communities in lakes and reservoirs are seldom homogeneously distributed but usually aggregate in patches and gradients. In this study we have combined the use of in vivo spectrofluorometry and acoustic Doppler current profiling to investigate the effect of water movements on the spatial distribution of cyanobacteria and diatoms in a thermally stratified reservoir in SW Spain. The distinctive canyon-shaped morphometry of the reservoir (El Gergal) favoured the development of a 'conveyor belt' pattern of circulation aligned with the long axis of the reservoir. Under non-regulated conditions, the spatial distribution of phytoplankton was almost entirely dependent on the interactions between advective transport and the buoyancy properties of the different functional groups of phytoplankton. The positively-buoyant cyanobacteria accumulated near the surface and were then transported downwind by the surface drift currents. In contrast, the negatively-buoyant diatoms sank in the water column and were transported upwind by the sub-surface return currents. When deep water was abstracted from the reservoir, these distribution patterns were modified. The results are discussed in relation to the problem of acquiring representative water samples from the reservoir and the application of a simple empirical model to optimize the location of the station used for routine cyanobacteria sampling on the reservoir.Peer reviewe

This work examines the diel change of energy storage and its associated patterns of thermal stratification during the ice-free period in a high mountain lake (La Caldera Lake, Sierra Nevada, Spain), in response to meteorological conditions. Bihourly data have been implemented to a standard methodology of surface heat exchange calculations in lakes. Strong variations have been observed on the diverse components of the energy budget at different time scales, ranging from diel to seasonal. Additionally, time-series analyses have been applied to reveal the underlying periodicities involved in relation to the different variables studied. The results obtained from this study provided realistic M03053; conditions for the environmental modelling of such processes, which are very sensitive in time scale.

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