δ 18 O in speleothems is a powerful proxy for reconstruction of precipitation patterns in tropica... more δ 18 O in speleothems is a powerful proxy for reconstruction of precipitation patterns in tropical and subtropical regions. The aim of this study is to calibrate the δ 18 O 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 δ 18 O variability is dominated by the amount effect in this region, while δ 18 O drip water remains almost constant over the monitored period (1.5 years). The δ 18 O 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 δ 18 O of carbonate deposits and rainwater is supported by the results from the comparison between speleothem δ 18 O records and historical hydroclimate records. A significant correlation between speleothem δ 18 O 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 δ 18 O is directly associated with monsoon rainfall variability in central Brazil. The relationship between speleothem δ 18 O records and hydroclimatic historical records allows approximation of the absolute changes in mean annual rainfall during the last millennia in the SACZ/SAMS domain.
Hydrology and Earth System Sciences Discussions, 2011
For the past 30 years, a process of glacier retreat has been observed in the Andes, raising alarm... more For the past 30 years, a process of glacier retreat has been observed in the Andes, raising alarm among regional water resources managers. The purpose of this paper is to develop a model of the role of Andean glaciers in the hydrology of their associated watersheds, which is appropriate for application at a river basin scale, with an 5 20 the historical contribution of groundwater accretions to river flows; and (vi) reproducing a reasonable simulation of recent hydropower operations in the Rio Santa system. In pursuit objective (i), a split sample calibration-validation of the model was conducted by comparing the simulated glacier area to Landsat images taken in 1987 and 1998 and observed and simulated river flow at 16 control points in the Rio Santa watershed. At 25 the global scale of the watershed, the glacier retreat is correctly simulated for the period 1970/1999 with a calculated retreat equals to −23% when the observed retreat is of −24%. Having established that the model can respond to these scientific objectives,
The Medieval Climate Anomaly (MCA: 800-1300 CE) was the most recent pre-industrial warm interval ... more The Medieval Climate Anomaly (MCA: 800-1300 CE) was the most recent pre-industrial warm interval of European climate, yet it remains less well-known in South America. Various studies from continental and marine late Holocene proxy records from South America show heterogeneous changes during this period. The main goal of this study is to explore for evidence of inter-hemispheric teleconnections and possible
δ 18 O in speleothems is a powerful proxy for reconstruction of precipitation patterns in tropica... more δ 18 O in speleothems is a powerful proxy for reconstruction of precipitation patterns in tropical and subtropical regions. The aim of this study is to calibrate the δ 18 O 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 δ 18 O variability is dominated by the amount effect in this region, while δ 18 O drip water remains almost constant over the monitored period (1.5 years). The δ 18 O 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 δ 18 O of carbonate deposits and rainwater is supported by the results from the comparison between speleothem δ 18 O records and historical hydroclimate records. A significant correlation between speleothem δ 18 O 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 δ 18 O is directly associated with monsoon rainfall variability in central Brazil. The relationship between speleothem δ 18 O records and hydroclimatic historical records allows approximation of the absolute changes in mean annual rainfall during the last millennia in the SACZ/SAMS domain.
Hydrology and Earth System Sciences Discussions, 2011
For the past 30 years, a process of glacier retreat has been observed in the Andes, raising alarm... more For the past 30 years, a process of glacier retreat has been observed in the Andes, raising alarm among regional water resources managers. The purpose of this paper is to develop a model of the role of Andean glaciers in the hydrology of their associated watersheds, which is appropriate for application at a river basin scale, with an 5 20 the historical contribution of groundwater accretions to river flows; and (vi) reproducing a reasonable simulation of recent hydropower operations in the Rio Santa system. In pursuit objective (i), a split sample calibration-validation of the model was conducted by comparing the simulated glacier area to Landsat images taken in 1987 and 1998 and observed and simulated river flow at 16 control points in the Rio Santa watershed. At 25 the global scale of the watershed, the glacier retreat is correctly simulated for the period 1970/1999 with a calculated retreat equals to −23% when the observed retreat is of −24%. Having established that the model can respond to these scientific objectives,
The Medieval Climate Anomaly (MCA: 800-1300 CE) was the most recent pre-industrial warm interval ... more The Medieval Climate Anomaly (MCA: 800-1300 CE) was the most recent pre-industrial warm interval of European climate, yet it remains less well-known in South America. Various studies from continental and marine late Holocene proxy records from South America show heterogeneous changes during this period. The main goal of this study is to explore for evidence of inter-hemispheric teleconnections and possible
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Papers by J. Apaestegui