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

Type Article
Date 2016-09
Language English
Author(s) Penaud Aurelie1, Eynaud Frederique2, Luise Voelker Antje Helga3, 4, Turon Jean-Louis2
Affiliation(s) 1 : Univ Brest, CNRS, Domaines Ocean UMR6538, IUEM, F-29280 Plouzane, France.
2 : Univ Bordeaux, CNRS, EPOC UMR5805, Allee Geoffroy St Hilaire, F-33615 Pessac, France.
3 : IPMA, Div Geol & Georecursos Marinhos, Rua Alfredo Magalhaes Ramalho 6, P-1495006 Lisbon, Portugal.
4 : Univ Algarve, Ctr Ciencias Mar, CCMAR, Campus Gambelas, P-8005139 Faro, Portugal.
Source Biogeosciences (1726-4170) (Copernicus Gesellschaft Mbh), 2016-09 , Vol. 13 , N. 18 , P. 5357-5377
DOI 10.5194/bg-13-5357-2016
WOS© Times Cited 5
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.

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