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13 pages, 8 figures, 5 tables ; The small-scale spatial distribution of density and biomass of the crab Liocarcinus depurator off the Ebro delta was analysed using universal kriging (non-linear geostatistics), considering depth as an external trend. In order to understand the spatial distribution of crab size, a third variable was created from the residuals of the non-linear regression between biomass and density. Variogram analysis of crab density and residuals of the biomass/density relationship presented a quadratic relationship with depth, while biomass showed a linear relationship with depth. All experimental variograms were fitted to spherical models. The patch size (range) found was 10.64 km for density, 14.53 km for biomass and 20.49 km for the residual variables. The spatial distribution of 8 sediment variables (temperature, redox potential at 1 and 6 cm depth [R1 and R6], carbonate content [CO3], median grain size [ϕ], sediment sorting [IGSD: inclusive graphic standard deviation] and organic matter content [OM]) was studied. The maps obtained were compared with those calculated for the biological variables of L. depurator using Mantel and partial Mantel tests. Distribution characteristics of this species were significantly affected by most sediment variables considered, particularly by temperature, organic matter content and redox potential, although overall the correlation level was low, coinciding with the generalist ecological role and opportunistic behaviour of the species. Density and biomass, as well as residuals, presented a negative correlation with the sorting coefficient (IGSD) and with carbonates. In relation to IGSD, high densities of L. depurator were found in homogeneous sediments. Residuals (size structure of the population) were significantly correlated with grain size (ϕ), with larger individuals occurring in finer sediments, while juveniles were preferably found in areas with very fine sand sediments. Both density and biomass presented significant positive correlations with the redox potential, indicating that the species favoured well-oxygenated sediments with a low organic content ; We wish to thank all participants in the cruise GEODELTA on board RV 'García del Cid', especially its Chief Scientist, Dr. F. Sardà, for all help and facilities provided. This work was produced while M.M.R. had a PRAXIS PhD grant from the Portuguese government. ; Peer reviewed

15 pages, 5 figures, 2 tables.-- This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY) ; Physical and biogeochemical processes in the Southern Ocean are fundamental for modulating global climate. In this context, a process-based understanding of how Antarctic diatoms control primary production and carbon export, and hence global-ocean carbon sequestration, has been identified as a scientific priority. Here we use novel sediment trap observations in combination with a data-assimilative ocean biogeochemistry model (ECCO-Darwin) to understand how environmental conditions trigger diatom ecology in the iron-fertilized southern Scotia Sea. We unravel the role of diatoms assemblage in controlling the biogeochemistry of sinking material escaping from the euphotic zone, and discuss the link between changes in upper-ocean environmental conditions and the composition of settling material exported from the surface to 1,000 m depth from March 2012 to January 2013. The combined analysis of in situ observations and model simulation suggests that an anomalous sea-ice episode in early summer 2012–2013 favored (via restratification due to sea-ice melt) an early massive bloom of Corethron pennatum that rapidly sank to depth. This event drove high biogenic silicon to organic carbon export ratios, while modulating the carbon and nitrogen isotopic signals of sinking organic matter reaching the deep ocean. Our findings highlight the role of diatom ecology in modulating silicon vs. carbon sequestration efficiency, a critical factor for determining the stoichiometric relationship of limiting nutrients in the Southern Ocean ; This work was funded by the Spanish Polar Program through the Spanish Research and Innovation (I+D+i) National Plan (grant numbers CTM2009-08287-E/ANT and CTM2011-14056- E/ANT), and supported by the Catalan Government Grups de Recerca Consolidats Grant (2017 SGR 315) and the Internal Research and Technology Development program of the Jet Propulsion Laboratory, California Institute of Technology. DZ was funded by a postdoctoral fellowship (Plan I2C) from Xunta de Galicia (Spain) and performed diatom analysis during her stay at Instituto Português do Mar e da Atmosfera (IPMA), Lisbon, Portugal. Diatom analysis was sponsored by Portuguese national funding through FCT-Fundação para a Ciência e a Tecnologia (UIDB/04326/2020 and DiatBIo PTDC/AAG-GLO/3737/2012 projects). GS was supported by the Deutsche Forschungsgemeinschaft (DFG) in the framework of the priority programme "Antarctic Research with comparative investigations in Arctic ice areas" SPP 1158 by Grant SITAnt (365778379) ; Peer reviewed

15 páginas, 1 apéndice, 8 figuras, 3 tablas.-- This work is distributed under the Creative Commons Attribution 3.0 License ; The objective of the current work is to improve our understanding of how water column diatom's abundance and assemblage composition is seasonally transferred from the photic zone to seafloor sediments. To address this, we used a dataset derived from water column, sediment trap and surface sediment samples recovered in the NW Iberian coastal upwelling system. Diatom fluxes (2.2 ( +-5.6) 106 valves m-2 d-1/ represented the majority of the siliceous microorganisms sinking out from the photic zone during all studied years and showed seasonal variability. Contrasting results between water column and sediment trap diatom abundances were found during downwelling periods, as shown by the unexpectedly high diatom export signals when diatom-derived primary production achieved their minimum levels. They were principally related to surface sediment remobilization and intense Minho and Douro river discharge that constitute an additional source of particulate matter to the inner continental shelf. In fact, contributions of allochthonous particles to the sinking material were confirmed by the significant increase of both benthic and freshwater diatoms in the sediment trap assemblage. In contrast, we found that most of the living diatom species blooming during highly productive upwelling periods were dissolved during sinking, and only those resistant to dissolution and the Chaetoceros and Leptocylindrus spp. resting spores were susceptible to being exported and buried. Furthermore, Chaetoceros spp. dominate during spring–early summer, when persistent northerly winds lead to the upwelling of nutrient-rich waters on the shelf, while Leptocylindrus spp. appear associated with late-summer upwelling relaxation, characterized by water column stratification and nutrient depletion. These findings evidence that the contributions of these diatom genera to the sediment's total marine diatom assemblage should allow for the reconstruction of different past upwelling regimes ; This study was sponsored by CAIBEX (CTM2007-66408-C02-01/MAR) and REIMAGE (CTM2011-30155-C03-03) projects funded by the Spanish Government, EXCAPA project (10MDS402013PR) supported by Xunta de Galicia, the EU FEDER funded projects RAIA (INTERREG 2009/2011-0313/RAIA/E) and RAIA.co (INTERREG 2011/2013-052/RAIA.co/1E) and the CALIBERIA project (PTDC/MAR/102045/2008) financed by Fundação para a Ciência e a Tecnologia (FCT-Portugal) and COMPETE/FEDER -FCOMP- 01-0124-FEDER-010599. Diana Zúñiga and Emilia Salgueiro were funded by a postdoctoral fellowship (Plan I2C) from Xunta de Galicia (Spain) and (SFRH/BPD/111433/2015) from FCT, respectively. Celia Santos was funded by a doctoral grant from FCT (Portugal) (SFRH/BD/88439/2012) ; Peer reviewed