1University of Vigo, Applied Physics Department, Campus Lagoas
Marcosende, 36310, Vigo, Spain
2Consejo Superior de Investigaciones Científicas (CSIC),
Instituto de Investigaciones Marinas (IIM), 36208, Vigo, Spain
3Instituto Português do Mar e da Atmosfera (IPMA), Div. Geologia
e Georecursos Marinhos, 1495-006, Lisbon, Portugal
4MARUM, Center for Marine Environmental Sciences, University of
Bremen, 28359, Bremen, Germany
5CCMAR – Centre of Marine Sciences, Universidade do Algarve, Campus de
Gambelas, 8005-139 Faro, Portugal
6Federal Maritime and Hydrographic Agency of Germany, 20359,
7IFREMER, Centre Atlantique (French Research Institute for Exploitation
of the Sea), 44311, Nantes, France
Received: 12 May 2016 – Discussion started: 31 May 2016
Abstract. 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.
Revised: 06 Feb 2017 – Accepted: 23 Feb 2017 – Published: 13 Mar 2017
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.
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Zúñiga, D., Santos, C., Froján, M., Salgueiro, E., Rufino, M. M., De la Granda, F., Figueiras, F. G., Castro, C. G., and Abrantes, F.: Diatoms as a paleoproductivity proxy in the NW Iberian coastal upwelling system (NE Atlantic), Biogeosciences, 14, 1165-1179, doi:10.5194/bg-14-1165-2017, 2017.