Browsing by Author "Bassinot, Franck"
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- Modern relationships between microscopic charcoal in marine sediments and fire regimes on adjacent landmasses to refine the interpretation of marine paleofire records: an Iberian case studyPublication . Genet, Marion; Daniau, Anne-Laure; Mouillot, Florent; Hanquiez, Vincent; Schmidt, Sabine; David, Valérie; Georget, Muriel; Abrantes, Fatima; Anschutz, Pierre; Bassinot, Franck; Bonnin, Jérome; Dennielou, Bernard; Eynaud, Frédérique; Hodell, David A.; Mulder, Thierry; Naughton, Filipa; Rossignol, Linda; Tzedakis, Polychronis; Sánchez-Goñi, Maria FernandaMarine microcharcoal records provide invaluable information to understand changes in biomass burning and its drivers over multiple glacial and interglacial cycles and to evaluate fire models under warmer climates than today. However, quantitative reconstructions of burnt area, fire intensity and frequency from these records need calibration studies of the current fire-microcharcoal relationship. Here, we present the analysis of microcharcoal concentration and morphology in 102 core-top sediment samples collected in the Iberian margin and the Gulf of Cadiz. We show that microcharcoal concentrations are influenced by the water depth or the distance from the river mouth. At regional scale, the mean microcharcoal concentrations and microcharcoal elongation (length to width ratio) show a marked latitudinal variation in their distribution, primarily controlled by the type of burnt vegetation in the adjacent continent. High microcharcoal concentrations in marine sediments represent rare, large and intense fires in open Mediterranean woodlands. Based on these results, the increasing trend of microcharcoal concentrations recorded since 8 ka in the well-known marine sedimentary core MD95-2042 off the Iberian margin indicates the occurrence of large and infrequent fires of high intensity due to the progressive degradation of the Mediterranean forest and the expansion of shrublands.
- Multiproxy record of suborbital-scale climate changes in the Algero-Balearic Basin during late MIS 20-Termination IXPublication . Quivelli, Ornella; Marino, Maria; Rodrigues, Teresa; Girone, Angela; Maiorano, Patrizia; Bertini, Adele; Niccolini, Gabriele; Trotta, Samanta; Bassinot, FranckHigh-resolution quantitative analyses have been carried out in samples from the Ocean Drilling Program (ODP) Site 975 in the Algero-Balearic basin through late Marine Isotope Stage (MIS 20)-Termination IX (800-784 ka). The multi-proxy study combines data of planktonic delta O-18, delta C-13, calcareous plankton (coccolithophores, foraminifera), palynomorphs, alkenone-based sea surface temperature (SST), % alkenone tetraunsatured (% C-37:4), and terrigenous biomarkers (C-23-C-31 n-alkanes, C-22-C-30 n-alkanols) with the aim to reconstruct climate-induced paleoenvironmental changes at orbital-submillennial scale, in a crucial time interval of the Early-Midde Pleistocene transition. The surface water delta O-18(sw) has been reconstructed from delta O-18(G.bulloides) and alkenone-based SST as a proxy for salinity changes. The late MIS 20 has been subdivided in several phases based on evidence of (i) meltwater events of polar origin or from surrounding mountain glaciers, (ii) changes in the production rate of Western Mediterranean Deep Water (WMDW) and in deep water ventilation, (iii) variation in terrestrial input and river discharge, and iv) variations in the strength of the north westerlies, and polar front shift. Following a glacial stadial (lasting ca 3 kyr) marked by the strongest WMDW production, coeval with a boreal summer insolation minimum and a marked low sea level, the latest MIS 20 is characterized by a terminal stadial event (lasting ca 3.5 kyr), which is traced by the occurrence of cold-low salinity water, pointing to meltwater advection at the site location. Short-term warm and cool events occurred through Termination IX during sea level rise and insolation increase, preceding the onset of full MIS 19c, characterized by an organic rich layer (ORL) associated with insolation cycle 74. The succession of these climate and oceanographic events has been compared to evidences from other Mediterranean sites, highlighting similar basin-wide patterns, which recall the climate evolution of Termination I. The comparison of our results with the climate proxies from the Integrated Ocean Drilling Program (IODP) Site U1385 located west of Iberian margin made it possible to point at the connection between Mediterranean oceanographic and atmospheric dynamics and the northern hemisphere ice-sheet instability, providing insight on the relationship with the Atlantic meridional overturning circulation and thermal front migration. (C) 2021 Elsevier Ltd. All rights reserved.
- Paleoproductivity proxies and alkenone precursors in the Western Mediterranean during the Early-Middle Pleistocene transitionPublication . Marino, Maria; Rodrigues, Teresa; Quivelli, Ornella; Girone, Angela; Maiorano, Patrizia; Bassinot, FranckMultidisciplinary analyses (taxonomic analysis of coccolithophore assemblages, stable oxygen isotopes, marine and terrestrial biomarkers) have been carried out on sediments from Ocean Drilling Program Site 975 in the Algero-Balearic basin, through late marine isotope stage (MIS) 20-19 (800-756 ka). The aim is to compare coccolithophore paleoproductivity proxies, such as C-37 alkenone concentration and nannofossil accumulation rate (NAR), and understand their relationship with paleoceanographic condition and paleoenvironmental changes, alkenone-producing precursors and unsaturated C-37 alkenone compounds. The patterns of C-37 alkenones and NAR provide reliable information on past paleoproductivity changes since coccolith dissolution and organic matter preservation were excluded as relevant processes at the site. This is testified by the high values of Nannofossil Dissolution Index and relation between C-37 alkenone concentration and Alcohol Preservation Index, the latter used as a proxy of sea bottom ventilation in the basin. A weak mismatching between NAR and C-37 alkenone concentration records has been observed and related to paleoenvironmental factors and ecological preferences of alkenone-producing species. Temperature variations mostly controlled the alternating interspecific abundance variations of these taxa through glacial-interglacial and stadial-interstadial climate phases. The percentage abundances of alkenone-producing species, Gephyrocapsa caribbeanica and Gephyrocapsa with open central area (mainly G. margerelii-G. muellerae) strongly co-varied with the percentages of C-37:2 and C-37:3, respectively during warm and cool-cold periods, suggesting their prominent role in producing these unsaturated C-37 alkenone compounds. Moreover, Gephyrocapsa spp. with open central area > 3 mu m were likely the main C-37:4 producers during the colder late MIS 20 stadial and stadial phases. Other factors in addition to temperature influenced the paleoproductivity proxy patterns. The oceanographic condition established during MIS 20-MIS 19 deglaciation and the more nutrient-rich surface waters during the orbitally-controlled organic-rich layer deposition in the early MIS 19 enhanced primary productivity leading to higher production and preservation of total C-37 alkenones.