Articles | Volume 13, issue 18
Biogeosciences, 13, 5357–5377, 2016
Biogeosciences, 13, 5357–5377, 2016

Research article 27 Sep 2016

Research article | 27 Sep 2016

Palaeohydrological changes over the last 50 ky in the central Gulf of Cadiz: complex forcing mechanisms mixing multi-scale processes

Aurélie Penaud1, Frédérique Eynaud2, Antje Helga Luise Voelker3,4, and Jean-Louis Turon2 Aurélie Penaud et al.
  • 1University of Brest, CNRS, UMR6538 Domaines Océaniques, IUEM, 29280, Plouzané, France
  • 2University of Bordeaux, CNRS, UMR5805 EPOC, Allée Geoffroy St Hilaire, 33615, Pessac, France
  • 3Divisão de Geologia e Georecursos Marinhos, Instituto Português do Mar e da Atmosfera (IPMA), Rua Alfredo Magalhães Ramalho 6, 1495-006 Lisbon, Portugal
  • 4CCMAR, Centro de Ciencias do Mar, Universidade do Algarve, Campus de Gambelas, 8005-139 Faro, Portugal

Abstract. New dinoflagellate cyst (dinocyst) analyses were carried out at high resolution in core MD99-2339, retrieved from a contouritic field in the central part of the Gulf of Cadiz, for the Marine Isotope Stage (MIS) 3 interval, allowing for discussion of palaeohydrological changes over the last 50 ky in the subtropical NE Atlantic Ocean. Some index dinocyst taxa, according to their (palaeo)ecological significance, shed light on significant sea-surface changes. Superimposed on the general decreasing pattern of dinocyst export to the seafloor over the last 50 ky, paralleling the general context of decreasing aeolian dust fertilization, a complex variability in dinocyst assemblages was detected at the millennial timescale. Enhanced fluvial discharges occurred during Greenland Interstadials (GIs), especially GI 1, 8 and 12, while enhanced upwelling cell dynamics were suggested during the Last Glacial Maximum and Heinrich Stadials. Finally, during the early Holocene, and more specifically during the Sapropel 1 interval (around 7–9 ka BP), we evidenced a strong decrease in dinocyst fluxes, which occurred synchronously to a strong reduction in Mediterranean Outflow Water strength and which we attributed to an advection of warm and nutrient-poor subtropical North Atlantic Central Waters. Over the last 50 ky, our study thus allows for capturing and documenting the fine tuning existing between terrestrial and marine realms in North Atlantic subtropical latitudes, in response to not only the regional climate pattern but also monsoonal forcing interfering during precession-driven Northern Hemisphere insolation maxima. This mechanism, well expressed during the Holocene, is superimposed on the pervasive role of the obliquity as a first major trigger for explaining migration of dinocyst productive centres in the NE Atlantic margin to the subtropical (temperate) latitudes during glacial (interglacial) periods.

Short summary
This paper presents new analyses conducted at high resolution in the Gulf of Cadiz over the last 50 ky. Palaeohydrological changes in these subtropical latitudes are discussed through dinoflagellate cyst assemblages but also dinocyst transfer function results, implying sea surface temperature and salinity as well as annual productivity reconstructions. This study is thus important for our understanding of past and future productivity regimes, also implying consequences on the biological pump.
Final-revised paper