Examinando por Autor "Martínez, J.I."
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Ítem LATE HOLOCENE PALEOXYGENATION AND PALEOPRODRUCTIVITY OF THE PANAMA GULF(Universidad Industrial de Santander, 2016-04-01) Patarroyo, G.D.; Martínez, J.I.; Universidad EAFIT. Departamento de Geología; Ciencias del MarPaleocenographic conditions in the Panama Bight for the past 4000 years were inferred by using the micropaleontological record from the deep sea core KNR176-2-MC4 (7.27 degrees N, 78.24 degrees W; water depth 2121 m). The epifauna-infauna relationship of deep-sea benthic foraminifera and their diversity gradually increase up-core, which is interpreted as a result of: (1) a decrease in the dissolved oxygen content towards the recent and, (2) higher taphonomic effects which modify the original composition of the microfauna. Indicative taxa of moderate oxygen conditions, such as Uvigerina proboscidea and Oridorsalis umbonatus were found at the base of the core. In contrast, lower oxygenation and higher productivity conditions are inferred by the common presence of Globobulimina affinis and Uvigerina proboscidea. Additional paleoproductivity indicators such as Epistominella spp. and Uvigerina peregrina were more common in the middle part of the core. The comparison of the MC4 core micropaleontological record with several paleoclimatic records from the Panama isthmus (the Woodhouse Lake, and the Chilibrillo stalagmite) illustrates that a higher recurrence of El Nino events since 5000 years BP, could be related to a higher frequency and intensity of upwelling processes in the Panama Gulf. However, themagnetic susceptibility of the MC4 core presents variations which cannot be related with to a reduction in local rainfall.Ítem Late quaternary sea bottom conditions in the southern Panama basin, Eastern Equatorial Pacific(PERGAMON-ELSEVIER SCIENCE LTD, 2015-11-01) Patarroyo, G.D.; Martínez, J.I.; Universidad EAFIT. Departamento de Geología; Ciencias del MarA paleoceanographic reconstruction of the southern Panama Basin for the last 23.000 years, based on the benthic foraminiferal analysis from the deep sea core ME0005A-24JC (0.01 degrees N, 86.28 degrees W, water depth 2941) is presented. Cluster and SHEBI (SHE Analysis for Biozone Identification) analyses performed on the benthic foraminiferal assemblages, evidence a faunal turnover in the early Holocene at 14 Icy BR Between 23 and 14 ky BP, Fursenkoina rotundata, Hoeglundina elegans, Globobulimina affinis, Globobulimina pacifica, Cibicidoides wuellerstorfi and Uvigerina hispidocostata were common. Conversely, from 14 ky to the present, the assemblage is represented by Chilostomella oolina, Laticarinina pauperata, and Uvigerina proboscidea. This faunal turnover suggests significant fluctuations in oxygen content at the sea floor and the organic matter (OM) influx, which could reflect: (1) fluctuations in the surface productivity related to the equatorial divergence and, (2) OM advection caused by the dynamic of the deep sea currents. Paleoproductivity estimates and benthic foraminiferal rates depict a general trend towards lower values since the Last Glacial Maximum (LGM) with a conspicuous change at 14 ky BP. Therefore, the paleoceanographic reconstructions of the ME0005A-24JC core suggest a transition from La Nina-like conditions during the LGM to El Nino-like conditions in the recent, as previously proposed for the Eastern Equatorial Pacific. Estimates of the paleo-intensity of deep sea currents based on the relative percentage abundance of the epifaunal foraminifera Cibicidoides wuellerstorfi suggest stronger deep sea currents on the Carnegie Ridge before 14 Icy BR (C) 2015 Elsevier Ltd. All rights reserved.Ítem Palaeoceanography of the last glacial maximum in the eastern Indian Ocean: Planktonic foraminiferal evidence(ELSEVIER SCIENCE BV, 1999-01-01) Martínez, J.I.; De Deckker, P.; Barrows, T.T.; Universidad EAFIT. Departamento de Geología; Ciencias del MarPalaeoceanographic conditions in the eastern Indian Ocean for the last ~30 kyr are documented by means of planktonic foraminiferal analyses of 10 gravity cores. Quantitative foraminiferal analysis (%), Q-mode factor analysis, the modern analog technique (MAT) and oxygen-isotope analyses are used. A conspicuous increase during the last glacial maximum (LGM) of foraminiferal fragmentation resulting from a more productive Java upwelling system and/or a more corrosive Antarctic Intermediate Water (AAIW) was found at intermediate water depths (~1000 m). Contrasting Q-mode factors based on foraminifera between today and the LGM suggest changes in the thermocline depth, sea-surface temperature (SST), upwelling, and the strength of both the Australasian Mediterranean Water (AAMW) and the Indian Central Water (ICW). The decrease in the percentage abundance of shallow-dwelling and symbiont-bearing planktonic foraminifera, the increase in percentage of the upwelling-related species Globorotalia cultrata and Neogloboquadrina dutertrei, and factor 3 (dominated by Globorotalia tumida and Globigerinella siphonifera) suggest a stronger Java upwelling system during the LGM. A steeper, steric latitudinal gradient (in the presence of a weak Leeuwin Current), and a geostrophic flow similar to today's is postulated for the LGM, and this must have prevented upwelling offshore Western Australia. Today's AAMW-ICW sharp front was weaker during the LGM when the AAMW was saltier, cooler, and nutrient richer and more similar to the ICW. During the LGM, a more gentle SST latitudinal gradient over the ~16 to ~23°S region contrasts with today's steeper conditions at the AAMW-ICW Front. Also, for the LGM, a nutrient-rich ICW may explain previously documented increases in mass accumulation rates of CaCO3, organic carbon and benthonic foraminifera in a region where the nutricline was deep and within the lower euphotic zone.