Browsing by Author "Sifeddine, Abdelfettah"
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Item Open Access El Fenómeno El Niño durante el último milenio(Instituto Geofísico del Perú, 2015-02) Apaéstegui Campos, James Emiliano; Takahashi, Ken; Ortlieb, Luc; Sifeddine, Abdelfettah; Macharé, JoséEl Fenómeno El Niño-Oscilación Sur (ENSO por sus siglas en inglés) representa la mayor perturbación natural en el sistema climático global. En escala de tiempo interanual, este fenómeno está asociado a procesos de reorganización del sistema océano – atmosférico en el Pacífico Tropical que, a su vez, induce a anomalías climáticas remotas (teleconexiones), tanto en áreas tropicales como extra-tropicales del planeta. Debido a su naturaleza y sus impactos en los ecosistemas y economías globales, este fenómeno ha despertado el interés de varios estudios que se proponen entender los procesos que explican su ocurrencia, intensidad e impactos en base a mediciones instrumentales periódicas en el sistema océano-atmósfera. El presente trabajo tiene como objetivo mostrar algunas de estas evidencias para el último milenio y cómo son utilizadas por la comunidad paleoclimática en vista de incrementar el conocimiento de la evolución del clima y el fenómeno en sí mismo.Item Open Access Monção Sul Americana: Variabilidades e impactos na paleopluviosidade dos Andes orientais durante os últimos 1400 anos a partir de estudos isotópicos em espeleotemas(Universidade Federal Fluminense, 2014) Apaéstegui Campos, James Emiliano; Sifeddine, Abdelfettah; William da Cruz, FranciscoThe caves located in the Peruvian and Bolivian Andes are characterized by the presence of speleothems providing high potential for high resolution paleoclimate and paleohydrologicall reconstructions, which allow understand principally short periods of climate variability. These variability during the last millennium have been widely studied, mainly in correspondance to important recent weather events such as Medieval Climate Anomaly (MCA, AD 900 1200) and the Little Ice Age (LIA - 1400-1850 AD), which were associated to changes in solar and volcanic activities in the Northern Hemisphere. In this work, we used stable oxygen isotopes (δ 18O) in speleothems as a proxy for assessing the stages of change of sources and precipitation intensity related to changes in the activities of the South American Monsoon System. 5 espeleotems were analyzed; 2 in Palestina cave (Peru) and 3 in Chiflonkhakha cave (Bolivia). Our results show changes in δ 18O values suggesting dry conditions in Peru and humid conditions in Bolivia during ACM evidenced by more positive and negative values respectively. Later, during the LIA, results show more negative δ 18O values indicating more humid conditions in both regions. Analysis of frequencies over the studied records showed periodicities around 8, 25 and 64 years. These variations were correlated to ACM and LIA with other paleoclimatic reconstructions in marine and continental areas, in order to understand the influence of the zonal and latitudinal variability of ocean surface temperatures (SSTs) in the Equatorial Pacific and the Atlantic Ocean and it´s influence on distribution of rainfall in relation to the South American Monsoon.Item Restricted Precipitation changes over the eastern Bolivian Andes inferred from speleothem (δ¹⁸O) records for the last 1400 years(Elsevier, 2018-07-15) Apaéstegui Campos, James Emiliano; William Cruz, Francisco; Vuille, Mathias; Fohlmeister, Jens; Espinoza, Jhan Carlo; Sifeddine, Abdelfettah; Strikis, Nicolas; Guyot, Jean Loup; Ventura, Roberto; Cheng, Hai; Edwards, R. LawrenceHere we present high-resolution δ¹⁸ records obtained from speleothems collected in the eastern Bolivian Andes. The stable isotope records are related to the regional- to large-scale atmospheric circulation over South America and allow interpreting changes in δ¹⁸ during the last 1400 yr as a function of changes in precipitation regimes over the southern tropical Andes. Two distinct phases with more negative δ¹⁸ values, interpreted as periods of increased convective activity over the eastern Andean Cordillera in Bolivia are observed concomitantly with periods of global climate anomalies during the last millennium, such as the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA) respectively. Changes in the Bolivian δ¹⁸ record during the LIA are apparently related to a southward displacement of the Intertropical Convergence Zone (ITCZ), which acts as a main moisture driver to intensify convection over the tropical continent. During the MCA, however, the increased convective activity observed in the Bolivian record is likely the result of a different mechanism, which implies moisture sourced mainly from the southern tropical Atlantic. This interpretation is consistent with paleoclimate records further to the north in the tropical Andes that show progressively drier conditions during this time period, indicating a more northerly position of the ITCZ. The transition period between the MCA and the LIA shows a slight tendency toward increased δ¹⁸ values, indicating weakened convective activity. Our results also reveal a non-stationary anti-phased behavior between the δ¹⁸ reconstructions from Bolivia and northeastern Brazil that confirms a continental-scale east–west teleconnection across South America during the LIA.Item Restricted Speleothem records decadal to multidecadal hydroclimate variations in southwestern Morocco during the last millennium(Elsevier, 2017-10-15) Ait Brahim, Yassine; Cheng, Hai; Sifeddine, Abdelfettah; Wassenburg, Jasper A.; Cruz, Francisco W.; Khodri, Myriam; Sha, Lijuan; Pérez-Zanón, Núria; Hassane Beraaouz, El; Apaéstegui Campos, James Emiliano; Guyot, Jean-Loup; Jochum, Klaus Peter; Bouchaou, LhoussaineThis study presents the first well-dated high resolution stable isotope (δ¹⁸O and δ¹³C) and trace element (Mg and Sr) speleothem records from southwestern Morocco covering the last 1000 yrs. Our records reveal substantial decadal to multidecadal swings between dry and humid periods, consistent with regional paleorecords with prevailing dry conditions during the Medieval Climate Anomaly (MCA), wetter conditions during the second part of the Little Ice Age (LIA), and a trend towards dry conditions during the current warm period. These coherent regional climate signals suggest common climate controls. Statistical analyses indicate that the climate of southwestern Morocco remained under the combined influence of both the North Atlantic Oscillation (NAO) and the Atlantic Multidecadal Oscillation (AMO) over the last millennium. Interestingly, the generally warmer MCA and colder LIA at longer multidecadal timescales probably influenced the regional climate in North Africa through the influence on Sahara Low which weakened and strengthened the mean moisture inflow from the Atlantic Ocean during the MCA and LIA respectively.Item Restricted System controls of coastal and open ocean oxygen depletion(Elsevier, 2021-09-09) Pitcher, Grant C.; Aguirre-Velarde, Arturo; Breitburg, Denise; Cardich, Jorge; Carstensen, Jacob; Conley, Daniel J.; Dewitte, Boris; Engel, Anja; Espinoza-Morriberón, Dante; Flores, Georgina; Garçon, Véronique; Graco, Michelle; Grégoire, Marilaure; Gutiérrez, Dimitri; Hernandez-Ayon, José Martin; Huang, Huai-Hsuan May; Isensee, Kirsten; Jacinto, María Elena; Levin, Lisa; Lorenzo, Alberto; Machu, Eric; Merma, Lander; Montes Torres, Ivonne; Naqvi, S. W. A.; Paulmier, Aurelien; Roman, Michael; Rose, Kenneth; Hood, Raleigh; Rabalais, Nancy N.; Salvanves, Anne Gro V.; Salvatteci, Renato; Sánchez, Sonia; Sifeddine, Abdelfettah; Tall, Abdoul Wahab; van der Plas, Anja K.; Yasuhara, Moriaki; Zhang, Jing; Zhu, Z. Y.The epoch of the Anthropocene, a period during which human activity has been the dominant influence on climate and the environment, has witnessed a decline in oxygen concentrations and an expansion of oxygen-depleted environments in both coastal and open ocean systems since the middle of the 20th century. This paper provides a review of system-specific drivers of low oxygen in a range of case studies representing marine systems in the open ocean, on continental shelves, in enclosed seas and in the coastal environment. Identification of similar and contrasting responses within and across system types and corresponding oxygen regimes is shown to be informative both in understanding and isolating key controlling processes and provides a sound basis for predicting change under anticipated future conditions. Case studies were selected to achieve a balance in system diversity and global coverage. Each case study describes system attributes, including the present-day oxygen environment and known trends in oxygen concentrations over time. Central to each case study is the identification of the physical and biogeochemical processes that determine oxygen concentrations through the tradeoff between ventilation and respiration. Spatial distributions of oxygen and time series of oxygen data provide the opportunity to identify trends in oxygen availability and have allowed various drivers of low oxygen to be distinguished through correlative and causative relationships. Deoxygenation results from a complex interplay of hydrographic and biogeochemical processes and the superposition of these processes, some additive and others subtractive, makes attribution to any particular driver challenging. System-specific models are therefore required to achieve a quantitative understanding of these processes and of the feedbacks between processes at varying scales.