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Title: Registro de paleontemperaturas na plataforma continental de Cabo Frio, Rio de Janeiro, ao longo dos últimos 13.000 anos
Keywords: Foraminífero;  Paleoclima;  Holoceno;  Produção intelectual;  Paleo-oceanografia;  Planctônicos;  Cabo Frio;  Paleotemperaturas;  Planktic foraminífera;  Paleoceanographic;  Cabo Frio;  Paleotemperature;  Holocene
Issue Date: 30-Jul-2008
Abstract: Planktonic Foraminifera and isotopic composition (δ18O) of Globigerinoides ruber(Gr) and Globigerina bulloides (Gb) were used to reconstruct SST variations in the coastal shelf of Cabo Frio (23º11´ S and 42º47´ W) for the past 13.000 cal yr. For this, two cores(CF02-01B e CF02-02B) were drilled. CF02-02B core covered the last 13000 years cal and registered the late Pleistocene and the whole Holocene. It presented six litologics units which registered the evolution of the coastal shelf during the Holocene. CF02-01B core covered the last 4000 years and allowed a better SST resolution. The species Globigerinoides ruber (Gr) and Globigerina bulloides (Gb) were consider dominants in the planktic foraminifera assemblages. These species are markers of the TW (Tropical Water) and SACW (South Atlantic Central Water), respectively. The average calcification temperature of G.ruber and of G.bulloides confirmed the preference of these species for warm waters and cold waters, respectively, justifying the use of the ratio Gb:Gr as marker of the SST. The SST varibility estimate was based on the ratio Gb:Gr, on the G.bulloides flux, on the δ18O G.ruber and G.bulloides. The absolute SST was estimate based and on the Method Analog Technique (MAT). According to these markers, three phases are characterized. Phase (1) between 13000 and 7000 years BP, the estimated SST was associated to the intense variations on the level of the sea and the thermohaline circulation changes and variations in the atmosferic temperature. This phase is characterized by the high amplitude of the SST variability, in which Younger Dryas was registered, around 12000 years cal BP and the gradual influence of the SACW in the region of Cabo Frio during the earlier Holocene. According MAT, the estimated SST ranged from 26,4 to 10,3 ºC during phase I. Phase II, between 7000 and 3500 years cal BP was characterized by low variability of the SST, as well as the higher SST which indicates the predominance of TW on the coastal shelf of Cabo Frio, suggesting, a upwelling weak phase. According MAT, the estimated SST ranged from 25,6 to 18,2 ºC. Phase III, after 3500 years cal BP, presents again high SST variability, however, showing a tendency to low temperatures, which indicates the predominance of the SACW on the coastal shelf of Cabo Frio, suggesting stronger upwelling phase. According MAT, the estimated SST ranged from 26,4 to 16,0 ºC. The SST variability observed over the last 13000 years cal BP was similar to the Total Organic Carbon (TOC). The high correlation between the TOC and the flux of G. bulloides confirms the relation between the SST and the upwelling of Cabo Frio. Among the factors that have conditioned the SST pattern of variability of Cabo Frio, it can list: the intensity and the frequency of the NE winds that promote the upwelling; the cold fronts system that control the pattern of the winds, and thus inhibiting the upwelling; the SACZ (South Atlantic Converge Zone) that promotes the blocking of the polar systems, favoring the upwelling and the El Niño-Oscillation South (ENSO) events that were very likely to be the responsible for the high SST variability observed in the third phase. The variability of SST in Cabo Frio along the Holocene seems to exhibit a correlation with climatic events of the North Atlantic and provides evidences for the existence of teleconnections between the regional and global climates. Then, planktic foraminifera showed an efficient tool for the study of the paleooceanographic conditions of Cabo Frio coastal shelf.
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