Percorrer por autor "Balestra, Barbara"
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- Early Pleistocene (1.94–1.46 Ma) records for the upper mediterranean outflow Water branch reveal low and high latitude climate influencesPublication . Voelker, Antje; Ducassou, Emanuelle; Balestra, Barbara; Flores, Jose Abel; Acton, Gary D.; Richter, Carl; Xuan, Chuang; Lofi, Johanna; Alberto, Ana; Kuhnert, Henning; Zarikian, Carlos A. AlvarezThe Mediterranean Outflow Water (MOW), modified by paleoceanographic conditions and tectonic processes, played a significant role in the formation of sediments drifts along the Iberian Margin. Using sediment samples from IODP Hole U1387C, we explore the Early Pleistocene history of the upper MOW core above the central Faro Drift in the Gulf of Cadiz. The time series of benthic foraminifer stable isotope and grain size related data have a rigorous stratigraphic framework consisting of nannofossil biostratigraphy and paleomagnetic and delta 18O stratigraphy. The paleoenvironmental records are supplemented by natural gamma ray downhole logging data. Above the hiatus associated with the youngest dolostone, sandy to muddy contourite sedimentation started at 1.946 Ma, i.e., within Marine Isotope Stage (MIS) 74, at IODP Site U1387, slightly younger than at IODP Site U1389. Formation of contourite layers, reflected in the sortable silt and sand percentage records, strongly reacted to precession forcing, including semi- and quarter-precession cycles. The majority of the contourite beds developed during stadial (colder) climate periods, like previous observations from the Early to Late Pleistocene. Formation of contourite layers within MIS 53, MIS 55 and MIS 65, however, appear to be linked to the prevailing atmospheric conditions over North Africa. Periods of poor ventilation in the upper MOW were linked to insolation maxima and reduced ventilation in the Mediterranean Sea. Here, MIS 51 presents a peculiar case as poor ventilation reached from the surface to the lower North Atlantic Deep Water range, reflecting unique interglacial conditions that merit future exploration.
- Early Pleistocene calcareous nannofossil assemblages from the Gulf of Cadiz reveal glacial-interglacial and millennial-scale variabilityPublication . Trotta, Samanta; Marino, Maria; H L Voelker, Antje; Rodrigues, Teresa; Maiorano, Patrizia; Flores, José-Abel; Girone, Angela; Addante, Marina; Balestra, BarbaraCoccolithophore high resolution (300 years) quantitative analyses have been carried out on Early Pleistocene sediment samples from Integrated Ocean Drilling Program Site U1387 retrieved in the Gulf of Cadiz. The studied interval is well constrained by the delta 18O chronological frame and covers marine isotope stage (MIS) 48 to MIS 45, from 1465.9 ka to 1389.9 ka. The aim is to investigate paleoenvironmental changes during a poorly known interval of the "41 ky world" and understand how climate dynamics controlled coccolithophore abundance and variation at orbital up to millennial scale. Assemblage composition variation and Principal Component Analysis (PCA) indicate that temperature and nutrient availability are the main factors influencing coccolithophores. Precession forcing combined with hydrological and atmospheric dynamics affect changes in coccolithophore assemblage composition and abundance highlighting glacial-interglacial cycles and a millennial scale variability, which is more evident during glacials than during interglacials. Interglacial MIS 47 onset is more abrupt than MIS 45 inception in relation to a more prominent insolation maximum, which favors the sharp increase and highest abundance of warm water taxa in the early MIS 47. Short-term abundance peaks of C. pelagicus spp. pelagicus during glacials document polar-subpolar melting water influx into the Gulf of Cadiz and southward migration of the subpolar front during episodes of high volume ice-sheet in the north hemisphere and reduced Atlantic Meridional Overturning circulation. In late MIS 48 the lowest coccolithophore productivity, induced by colder and stratified surface waters, a terminal stadial has been inferred. Enhanced short-term glacial productivity is favored by higher mixing and nutrient content in surface water due to the strengthened westerly winds during symbolscript phases. This promotes arid condition and upwelling along the studied site. The interglacial short-term coccolithophore productivity increases are associated with insolation maxima and enhanced nutrients of land origin during more humid periods led by -NAO-like phases, which induce the southward position of the westerlies and higher precipitation in the Mediterranean region and North Africa, in agreement with the contemporary sapropel occurrences in Mediterranean Sea. Our data-set suggests a connection between climate dynamics in the Gulf of Cadiz and east of Gibraltar Strait during the Early Pleistocene as well as a relationship with the north hemisphere ice-sheet dynamics.
- High-frequency glacial climate instability during the early pleistocene: insights from IODP site U1387 (Gulf of Cadiz)Publication . Trotta, Samanta; Duque Castaño, Monica Liliana; Rodrigues, Teresa; Voelker, Antje; Maiorano, Patrizia; Balestra, Barbara; Flores, José-Abel; Siniscalchi, Agata; Addante, Marina; Marino, MariaWe provide new high-resolution data on alkenone-derived sea surface temperature (SST) and calcareous plankton key taxa in temporally well constrained, high resolution benthic and planktonic oxygen isotope records at Integrated Ocean Drilling Program site U1387 in the Gulf of Cadiz. The investigated time interval encompasses the Early Pleistocene marine isotope stages (MIS) 48 to MIS 43. The aim is to evidence millennial climate variability during glacial phases of the “41 kyr world” and understand the impact of North Atlantic climate dynamics on the southern Portuguese margin. Neogloboquadrina pachyderma and Coccolithus pelagicus ssp. pelagicus record prominent, short-term abundance peaks concurrent with short-term SST minima and heavier values of ™18O in late MIS 48 and in the middle of MIS 46 and MIS 44. Superimposed on the obliquity and precession forcing, the wavelet analysis carried out on selected proxies (planktonic ™18O, N. pachyderma, C. pelagicus ssp. pelagicus, alkenone derived sea surface temperature) highlighted the occurrence of a higher frequency climate variability.