Palaeohydrological changes over the last 50 ky in the central Gulf of Cadiz: complex forcing mechanisms mixing multi-scale processes
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...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2016-09-01
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| Series: | Biogeosciences |
| Online Access: | http://www.biogeosciences.net/13/5357/2016/bg-13-5357-2016.pdf |
| Summary: | 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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| ISSN: | 1726-4170 1726-4189 |