Browsing by Author "Cruz, F. W."
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Item Restricted Calibration of speleothem δ¹⁸O records against hydroclimate instrumental records in Central Brazil(Elsevier, 2016-04) Moquet, Jean Sébastien; Cruz, F. W.; Novello, V. F.; Stríkis, N. M.; Deininger, M.; Karmann, I.; Ventura Santos, R.; Millo, C.; Apaéstegui Campos, James Emiliano; Guyot, J.-L.; Siffedine, A.; Vuille, M.; Cheng, H.; Edwards, R. L.; Santini, W.δ¹⁸O in speleothems is a powerful proxy for reconstruction of precipitation patterns in tropical and sub-tropical regions. The aim of this study is to calibrate the δ¹⁸O record of speleothems against historical precipitation and river discharge data in central Brazil, a region directly influenced by the Southern Atlantic Convergence Zone (SACZ), a major feature of the South American Monsoon System (SAMS). The present work is based on a sub-annual resolution speleothem record covering the last 141 years (the period between the years 1870 and 2011) from a cave in central Brazil. The comparison of this record with instrumental hydroclimate records since 1921 allows defining a strong relationship between precipitation variability and stable oxygen isotope ratios from speleothems. The results from a monitoring program of climatic parameters and isotopic composition of rainfall and cave seepage waters performed in the same cave, show that the rain δ¹⁸O variability is dominated by the amount effect in this region, while δ¹⁸O drip water remains almost constant over the monitored period (1.5 years). The δ¹⁸O of modern calcite, on the other hand, shows clear seasonal variations, with more negative values observed during the rainy season, which implies that other factors also influence the isotopic composition of carbonate. However, the relationship between δ¹⁸O of carbonate deposits and rainwater is supported by the results from the comparison between speleothem δ18O records and historical hydroclimate records. A significant correlation between speleothem δ¹⁸O and monsoon rainfall variability is observed on sub-decadal time scales, especially for the monsoon period (DJFM and NDJFM), once the rainfall record have been smoothed with a 7–9 years running mean. This study confirms that speleothem δ¹⁸O is directly associated with monsoon rainfall variability in central Brazil. The relationship between speleothem δ¹⁸O records and hydroclimatic historical records allows approximation of the absolute changes in mean annual rainfall during the last millennia in the SACZ/SAMS domain.Item Restricted Holocene changes in monsoon precipitation in the Andes of NE Peru based on δ¹⁸O speleothem records(Elsevier, 2016-08-15) Bustamante, M. G.; Cruz, F. W.; Vuille, M.; Apaéstegui Campos, James Emiliano; Strikis, N.; Panizo, G.; Novello, F. V.; Deininger, M.; Sifeddine, A.; Cheng, H.; Moquet, J. S.; Guyot, J. L.; Santos, R. V.; Segura Cajachagua, Hans Mikhail; Edwards, R. L.Two well-dated δ¹⁸O-speleothem records from Shatuca cave, situated on the northeastern flank of the Peruvian Andes (1960 m asl) were used to reconstruct high-resolution changes in precipitation during the Holocene in the South American Summer Monsoon region (SASM). The records show that precipitation increased gradually throughout the Holocene in parallel with the austral summer insolation trend modulated by the precession cycle. Additionally the Shatuca speleothem record shows several hydroclimatic changes on both longer- and shorter-term time scales, some of which have not been described in previous paleoclimatic reconstructions from the Andean region. Such climate episodes, marked by negative excursions in the Shatuca δ¹⁸O record were logged at 9.7–9.5, 9.2, 8.4, 8.1, 5.0, 4.1, 3.5, 3.0, 2.5, 2.1 and 1.5 ka b2k, and related to abrupt multi-decadal events in the SASM. Some of these events were likely associated with changes in sea surface temperatures (SST) during Bond events in the North Atlantic region. On longer time scales, the low δ¹⁸O values reported between 5.1-5.0, 3.5–3.0 and 1.5 ka b2k were contemporaneous with periods of increased sediment influx at Lake Pallcacocha in the Andes of Ecuador, suggesting that the late Holocene intensification of the monsoon recorded at Shatuca site may also have affected high altitudes of the equatorial Andes further north. Numerous episodes of low SASM intensity (dry events) were recorded by the Shatuca record during the Holocene, in particular at 10.2, 9.8, 9.3, 6.5, 5.1, 4.9, 2.5 and 2.3 ka b2k, some of them were synchronous with dry periods in previous Andean records.Item Open Access Hydroclimate variability of the northwestern Amazon Basin near the Andean foothills of Peru related to the South American Monsoon System during the last 1600 years(European Geosciences Union (EGU), 2014-11-19) Apaéstegui Campos, James Emiliano; Cruz, F. W.; Sifeddine, A.; Vuille, M.; Espinoza, Jhan Carlo; Guyot, J. L.; Khodri, M.; Strikis, N.; Santos, R. V.; Cheng, H.; Edwards, L.; Carvalho, E.; Santini, W.In this paper we explore a speleothem δ ¹⁸O record from Palestina cave, northwestern Peru, at a site on the eastern side of the Andes cordillera, in the upper Amazon Basin. The δ ¹⁸O record is interpreted as a proxy for South American Summer Monsoon (SASM) intensity and allows the reconstruction of its variability during the last 1600 years. Two periods of anomalous changes in the climate mean state corresponding to the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA) periods identified in the Northern Hemisphere are recognized in the record, in which decreased and increased SASM activity, respectively, have been documented. Variations in SASM activity between the MCA and the LIA seem to be larger over the northern part of the continent, suggesting a latitudinal dependence of the MCA footprint. Our results, based on time series, composite and wavelet analyses, suggest that the Atlantic Multidecadal Oscillation (AMO) plays an relevant role for SASM modulation on multidecadal scales (∼ 65 years), especially during dry periods such as the MCA. Composite analyses, applied to evaluate the influence of the AMO on the Palestina cave δ¹⁸O and other δ¹⁸O-derived SASM reconstructions, allow insight into the spatial footprints of the AMO over tropical South America and highlight differences between records during key studied periods. This work also reveals that replicating regional climate signals from different sites, and using different proxies is absolutely essential for a comprehensive understanding of past changes in SASM activity.Item Open Access Hydroclimate variability of the northwestern Amazon Basin near the Andean foothills of Peru related to the South American Monsoon System during the last 1600 years(European Geosciences Union (EGU), 2014) Apaéstegui Campos, James Emiliano; Cruz, F. W.; Sifeddine, A.; Vuille, M.; Espinoza, Jhan Carlo; Guyot, J. L.; Khodri, M.; Strikis, N.; Santos, R. V.; Cheng, H.; Edwards, L.; Carvalho, E.; Santini, W.In this paper we explore a speleothem δ¹⁸O record from Palestina Cave, North Eastern Peru, at a site on the eastern side of the Andes cordillera, upper Amazon Basin, interpreted as a proxy for South America Summer Monsoon (SASM) intensity. This record 5 allows reconstructing SASM activity with ∼ 5 yr time resolution over the last 1600 yr, spanning two major periods of climate variability: the Medieval Climate Anomaly (MCA; 900–1200 AD) and Little Ice Age (LIA 1400–1850 AD) recognized as periods of decrease and increase SASM activity respectively. Time series and wavelet analyses reveal decadal to multidecadal frequencies. Our results suggest that Atlantic Multi10 decadal Oscillation mode (AMO) plays an important role for SASM modulation on multidecadal scale (∼ 65 yr), especially over dry periods such as observed during MCA. Frequencies of 8 and 25 yr simultaneously with multidecadal signal (65 yr) are found over the LIA. and suggest that those modes could be related to North Atlantic Oscillation (NAO) and Interdecadal Pacific Oscillation mode (IPO). Comparison with other 15 South American Paleoprecipitation records shows that the Atlantic and Pacific decadal to multidecadal variability and their teleconnections play an important role in the intensity and the regional patterns of rainfall distribution during the last 1600 yr.Item Restricted The forest effects on the isotopic composition of rainfall in the northwestern Amazon Basin(American Geophysical Union (AGU), 2020-02-27) Ampuero, A.; Stríkis, N. M.; Apaéstegui Campos, James Emiliano; Vuille, M.; Novello, V. F.; Espinoza, Jhan Carlo; Cruz, F. W.; Vonhof, H.; Mayta, V. C.; Martins, V. T. S.; Cordeiro, R. C.; Azevedo, V.; Sifeddine, A.In the Amazon basin, intense precipitation recycling across the forest significantly modifies the isotopic composition of rainfall (δ¹⁸O, δD). In the tropical hydrologic cycle, such an effect can be identified through deuterium excess (dxs), yet it remains unclear what environmental factors control dxs, increasing the uncertainty of dxs‐based paleoclimate reconstructions. Here we present a 4‐year record of the isotopic composition of rainfall, monitored in the northwestern Amazon basin. We analyze the isotopic variations as a function of the air mass history, based on atmospheric back trajectory analyses, satellite observations of precipitation upstream, leaf area index, and simulated moisture recycling along the transport pathway. We show that the precipitation recycling in the forest exerts a significant control on the isotopic composition of precipitation in the northwestern Amazon basin, especially on dxs during the dry season (r = 0.71). Applying these observations to existing speleothem and pollen paleorecords, we conclude that winter precipitation increased after the mid‐Holocene, as the expansion of the forest allowed for more moisture recycling. Therefore, forest effects should be considered when interpreting paleorecords of past precipitation changes.