113 research outputs found
Praeorbulina-like specimens" in sediments of the Northern Arabian Sea during the last glacial period
Date du colloque : 06/2009International audienc
Palaeoclimatology and palaeohydrography of the glacial stages on Celtic and Armorican margins over the last 360 000 yrs
Core MD03-2692 was retrieved in a water-depth of 4064 m on the Celtic margin (Bay of Biscay) during the SEDICAR cruise onboard the RV Marion Dufresne II. It covers the last 360 ka in a total length of 39 m. Multidisciplinary analyses have been applied to this sequence with the aim of studying the palaeoclimatic and palaeoenvironmental signals of the last few climatic cycles. The analyses undertaken include: (1) non-destructive logging with: physical properties (magnetic susceptibility, sediment colour), X-ray radiography and measurement of the major elements by X-ray-fluorescence, (2) analyses of planktonic and benthic foraminifera, lithic grains and stable isotopic measurements (oxygen and carbon). We have focused on the long-term evolution of glacial stages (with special attention to terminations and Heinrich events). The results obtained confirm the close correlation between deep-sea sedimentation recorded on the Celtic margin and changes in the terrestrial environment of the adjacent continent. Heinrich layers have been identified in MIS 2, 3, 6 and 8. We note the occurrence of laminated facies within deglacial sequences deposited during Termination I and MIS 6. These facies are closely linked to disintegration phases of the British–Irish Ice Sheet (BIS). The laminations contain lower ice-rafted detritus (IRD) concentrations than the equivalent Heinrich layers and are linked to abrupt changes in sea-surface palaeotemperatures. We suggest that the laminations are formed by an annual cycle of meltwater and iceberg release from the disintegrating BIS generating cascading plumes of dense turbid meltwater coeval with IRD release
Northward advection of Atlantic water in the eastern Nordic Seas over the last 3000 yr
Three marine sediment cores distributed along the
Norwegian (MD95-2011), Barents Sea (JM09-KA11-GC),
and Svalbard (HH11-134-BC) continental margins have been
investigated in order to reconstruct changes in the poleward
flow of Atlantic waters (AW) and in the nature of upper
surface water masses within the eastern Nordic Seas over
the last 3000 yr. These reconstructions are based on a limited
set of coccolith proxies: the abundance ratio between
Emiliania huxleyi and Coccolithus pelagicus, an index of Atlantic
vs. Polar/Arctic surface water masses; and Gephyrocapsa
muellerae, a drifted coccolith species from the temperate
North Atlantic, whose abundance changes are related
to variations in the strength of the North Atlantic Current.
The entire investigated area, from 66 to 77 N, was affected
by an overall increase in AWflow from 3000 cal yr BP
(before present) to the present. The long-term modulation
of westerlies’ strength and location, which are essentially
driven by the dominant mode of the North Atlantic Oscillation
(NAO), is thought to explain the observed dynamics of
poleward AW flow. The same mechanism also reconciles the
recorded opposite zonal shifts in the location of the Arctic
front between the area off western Norway and the western
Barents Sea–eastern Fram Strait region.
The Little Ice Age (LIA) was governed by deteriorating
conditions, with Arctic/Polar waters dominating in the surface
off western Svalbard and western Barents Sea, possibly
associated with both severe sea ice conditions and a strongly
reduced AW strength. A sudden short pulse of resumed high
WSC (West Spitsbergen Current) flow interrupted this cold
spell in eastern Fram Strait from 330 to 410 cal yr BP. Our
dataset not only confirms the high amplitude warming of
surface waters at the turn of the 19th century off western
Svalbard, it also shows that such a warming was primarily
induced by an excess flow of AW which stands as unprecedented
over the last 3000 yr
Assessment of sea surface temperature changes in the Gulf of Cadiz during the last 30 ka: Implications for glacial changes in the regional hydrography
New dinocyst analyses were conducted on
core MD99-2339 retrieved from the central Gulf of Cadiz.
Dinocyst and foraminiferal assemblages from this core are
combined with existing data off SW Portugal and NW Morocco to investigate past hydrological and primary productivity regimes in the subtropical NE Atlantic Ocean over the
last 30 ka. Our results have revealed highest upwelling intensity during Heinrich Stadial 1 (HS 1) and the Younger Dryas
and weaker upwelling cells during the Last Glacial Maximum (LGM) and HS 2, off the SW Iberian and NW Moroccan margins. Similar assemblages between the Gulf of Cadiz
and the NW Moroccan margin, and distinct species off Portugal, were observed during the cold climatic extremes that
punctuated the last 30 ka. This pattern has been linked to the
occurrence of a hydrological structure between SW Iberia
and Cadiz during the last glacial period, perhaps similar to
the modern Azores Front. This front was probably responsible locally for heterotrophic dinocysts found in the Gulf
of Cadiz during the last glacial period, even if this sector is
not conductive to upwelling phenomena by Ekman transport.
Regional reconstructions of paleo-sea-surface temperatures
(SSTs) using dinocyst and foraminiferal transfer functions,
as well as alkenones, are also discussed and depict coherent scenarios over the last 30 ka. Seasonal reconstructions
Correspondence to: A. Penaud
([email protected].)
of LGM SSTs obtained with this multi-proxy panel are discussed jointly with model outputs in order to contribute to
ongoing efforts in model-data comparisonC2007-FCT/319/2006info:eu-repo/semantics/publishedVersio
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