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Browsing by Author "Zuniga, D."

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  • delta O-18 and Mg/Ca thermometry in planktonic foraminifera: a multiproxy approach toward tracing oastal upwelling dynamics
    Publication . Salgueiro, Emilia; H L Voelker, Antje; Martin, P. A.; Rodrigues, Teresa; Zuniga, D.; Frojan, M.; de la Granda, F.; Villacieros-Robineau, N.; Alonso-Perez, F.; Alberto, A.; Rebotim, A.; Gonzalez-Alvarez, R.; Castro, C. G.; Abrantes, Fatima
    Planktonic foraminifera delta O-18 and Mg/Ca ratios are widely considered as a powerful proxy to reconstruct past seawater-column temperature. Due to the complex interpretation of planktonic foraminifera delta O-18 data in regard to past seawater temperatures, temperature determination based on the foraminifera shell Mg/Ca ratio is believed to be more accurate. Scarce Mg/Ca calibration data exists for coastal upwelling regions, resulting in incoherent results of past seawater reconstructions. The current study along the NW Iberia coastal upwelling system intends to define the best Mg/Ca temperature equation for the most representative species of this region (Neogloboquadrina incompta, Globigerina bulloides, and Globorotalia inflata). Seawater temperature from delta O-18 and Mg/Ca of these three planktonic foraminifera species was compared with the surface sediments alkenone derived SST and with the in situ temperatures measured at the depths where these foraminifera species currently live and calcify. The equations that better reflect each species calcification depth were selected as our regional equations for delta O-18 and Mg/Ca temperature reconstructions. The delta O-18-estimated temperatures for surface sediment specimens were comparable with in situ seawater-column temperature measurements, whereas the Mg/Ca derived temperatures seem to underestimate in situ values, in special for G. bulloides from samples affected by stronger coastal upwelling. The G. bulloides delta O-18 and Mg/Ca estimated temperatures from samples located offshore, further from coastal upwelling influence, are comparable to surface sediment alkenone derived temperatures. Our study shows that in upwelling areas, regional calibration of planktonic foraminifera Mg/Ca temperature equations is necessary for reliable interpretations of high-resolution past temperature variability in these important environments.
    2020-02Journal article Restricted access Show more
  • Particle fluxes in the NW Iberian coastal upwelling system: Hydrodynamical and biological control
    Publication . Zuniga, D.; Villacieros-Robineau, N.; Salgueiro, Emilia; Alonso-Perez, F.; Roson, G.; Abrantes, Fatima; Castro, C. G.
    To better understand sources and transport of particulate material in the NW Iberian coastal upwelling system, a mooring line dotted with an automated PPS 4/3 sediment trap was deployed off Cape Silleiro at the base of the photic zone. The samples were collected from November 2008 through June 2012 over sampling periods of 4-12 days.Our study represents the first automated sediment trap database for the NW Iberian margin. The magnitude and composition of the settling material showed strong seasonal variability with the highest fluxes during the poleward and winter mixing periods (averages of 12.9 +/- 9.6 g m(-2) d(-1) and 5.6 +/- 5.6 g m(-2) d(-1) respectively), and comparatively lower fluxes (3.6 +/- 4.1 gm(-2) d(-1)) for the upwelling season. Intensive deposition events registered during poleward and winter mixing periods were dominated by the lithogenic fraction (80 +/- 3%). They were associated to high energy wave-driven re suspension processes, due to the occurrence of south-westerly storms, and intense riverine inputs of terrestrial material from Minho and Douro rivers.On the other hand, during the spring- summer upwelling season, the share of biogenic compounds (organic matter, calcium carbonate (CaCO3), biogenic silica (bSiO2)) to downward fluxes was higher, reflecting an increase in pelagic sedimentation due to the seasonal intensification of primary production and negligible river inputs and wave-driven resuspended material. Otherwise, the large variations of biogenic settling particles were mainly modulated by upwelling intensity, which by means of upwelling filaments ultimately controlled the offshore transport of the organic carbon fixed by primary producers towards the adjacent ocean. Based on the average downward flux of organic carbon (212 mg C m(-2) d(-1)) and considering an average primary production of 1013 mg C m(-2) d(-1) from literature, we estimated that about 21% of the fixed carbon is vertically exported during the upwelling season. (C) 2016 Elsevier Ltd. All rights reserved.
    2016-07Journal article Restricted access Show more