Calibration of speleothem delta O-18 records against hydroclimate instrumental records in Central Brazil

2016

Article référencé dans le Web of Science WOS:000374626700013

Moquet J. S., Cruz F. W., Novello V. F., Strikis N. M., Deininger M., Karmann I., Santos R. V., Millo C., Apaestegui J., Guyot Jean-Loup, Sifeddine Abdelfettah, Vuille M., Cheng H., Edwards R. L., Santini William

Global and Planetary Change, 2016, 139, p. 151-164 ISSN 0921-8181

delta O-18 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 delta O-18 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 delta O-18 variability is dominated by the amount effect in this region, while delta O-18 drip water remains almost constant over the monitored period (1.5 years). The delta O-18 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 delta O-18 of carbonate deposits and rainwater is supported by the results from the comparison between speleothem delta O-18 records and historical hydroclimate records. A significant correlation between speleothem delta O-18 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 delta O-18 is directly associated with monsoon rainfall variability in central Brazil. The relationship between speleothem delta O-18 records and hydroclimatic historical records allows approximation of the absolute changes in mean annual rainfall during the last millennia in the SACZ/SAMS domain.

Sciences du milieu [021] ; Hydrologie [062] ; Géologie et formations superficielles [064]

BRESIL

Fonds IRD [F B010066804]

fdi:010066804