Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
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Volume 15, issue 1
Biogeosciences, 15, 245-262, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 3.0 License.
Biogeosciences, 15, 245-262, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 11 Jan 2018

Research article | 11 Jan 2018

Spatial and temporal variability in coccolithophore abundance and distribution in the NW Iberian coastal upwelling system

Blanca Ausín1,2, Diana Zúñiga3,4,5, Jose A. Flores1, Catarina Cavaleiro4,5,6, María Froján3, Nicolás Villacieros-Robineau7, Fernando Alonso-Pérez3, Belén Arbones3, Celia Santos4,5,6,8, Francisco de la Granda9, Carmen G. Castro3, Fátima Abrantes4,5, Timothy I. Eglinton2, and Emilia Salgueiro4,5 Blanca Ausín et al.
  • 1Departamento de Geología, Universidad de Salamanca, Salamanca, 37008, Spain
  • 2Department of Earth Sciences, ETH Zurich, Zurich, 8092, Switzerland
  • 3Instituto de Investigaciones Marinas (IIM), Consejo Superior de Investigaciones Científicas (CSIC), Vigo, 36208, Spain
  • 4Div. Geologia e Georecursos Marinhos, Instituto Português do Mar e da Atmosfera (IPMA), Lisbon, 1749-077, Portugal
  • 5CCMAR – Centre of Marine Sciences, Universidade do Algarve, Faro, 8005-139, Portugal
  • 6MARUM, Centre for Marine Environmental Sciences, Bremen, 28359, Germany
  • 7Laboratoire d'Oceanographie et du Clima, Université Pierre et Marie Curie, Paris, 75005, France
  • 8Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Sciences, Bremerhaven, 27570, Germany
  • 9Federal Maritime and Hydrographic Agency, Hamburg, 20359, Germany

Abstract. A systematic investigation of the spatial and temporal variability in coccolithophore abundance and distribution through the water column of the NW Iberian coastal upwelling system was performed. From July 2011 to June 2012, monthly sampling at various water depths was conducted at two parallel stations located at 42°N.

Total coccosphere abundance was higher at the outer-shelf station, where warmer, nutrient-depleted waters favoured coccolithophore rather than phytoplanktonic diatom blooms, which are known to dominate the inner-shelf location.

In seasonal terms, higher coccosphere and coccolith abundances were registered at both stations during upwelling seasons, coinciding with high irradiance levels. This was typically in conjunction with stratified, nutrient-poor conditions (i.e. relaxing upwelling conditions). However, it also occurred during some upwelling events of colder, nutrient-rich subsurface waters onto the continental shelf. Minimum abundances were generally found during downwelling periods, with unexpectedly high coccolith abundance registered in subsurface waters at the inner-shelf station. This finding can only be explained if strong storms during these downwelling periods favoured resuspension processes, thus remobilizing deposited coccoliths from surface sediments, and hence hampering the identification of autochthonous coccolithophore community structure.

At both locations, the major coccolithophore assemblages were dominated by Emiliania huxleyi, small Gephyrocapsa group, Gephyrocapsa oceanica, Florisphaera profunda, Syracosphaera spp., Coronosphaera mediterranea, and Calcidiscus leptoporus. Ecological preferences of the different taxa were assessed by exploring the relationships between environmental conditions and temporal and vertical variability in coccosphere abundance. These findings provide relevant information for the use of fossil coccolith assemblages in marine sediment records, in order to infer past environmental conditions, of particular importance for Paleoceanography. Both E. huxleyi and the small Gephyrocapsa group are proposed as proxies for the upwelling regime with a distinct affinity for different stages of the upwelling event: E. huxleyi was associated with warmer, nutrient-poor and more stable water column (i.e. upwelling relaxation stage) while the small Gephyrocapsa group was linked to colder waters and higher nutrient availability (i.e. early stages of the upwelling event), similarly to G. oceanica. Conversely, F. profunda is suggested as a proxy for the downwelling regime and low-productivity conditions. The assemblage composed by Syracosphaera pulchra, Coronosphaera mediterranea, and Rhabdosphaera clavigera may be a useful indicator of the presence of subtropical waters conveyed northward by the Iberian Poleward Current. Finally, C. leptoporus is proposed as an indicator of warmer, saltier, and oligotrophic waters during the downwelling/winter regime.

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Short summary
A systematic investigation of the coccolithophore ecology was performed for the first time in the NW Iberian Margin to broaden our knowledge on the use of fossil coccoliths in marine sediment records to infer environmental conditions in the past. Coccolithophores proved to be significant primary producers and their abundance and distribution was favoured by warmer and nutrient–depleted waters during the upwelling regime, seasonally controlled offshore and influenced by coastal processes onshore.
A systematic investigation of the coccolithophore ecology was performed for the first time in...