Isotopic Variations and Internal Storm Dynamics in the Amazon Basin

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  • a Department of Environmental Sciences, University of Virginia, Charlottesville, Virginia
  • b Department of Physics, University of Virginia, Charlottesville, Virginia
  • c Instituto Nacional Pesquisas da Amazônia, Manaus, Brazil
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Abstract

Rainwater samples taken every 10 min, protected from fractionation by a hydrocarbon layer and collected every 12 h, are subjected to isotopic analyses to obtain a time series of oxygen and deuterium values through successive rain events in the eastern and central Amazon basin. Satellite imagery is used to characterize the rain events, and rain rates from recording rain gauges are used to delineate changes in internal rain production within each storm.

Three clear isotopic signals are seen in the storm systems examined. These three responses consist of depletion of heavy isotopes by as much as −6.7% in a single storm, depletion followed by enrichment, and little change in the isotopic signal. Each of these changes in isotopic content of the rainwater can be related to the internal rain-rate production, evaporation/condensation processes together with the implied convective/stratiform circulations of the storm. The storm-related isotopic results suggest, in addition to illuminating the internal dynamics of these storm systems, that sampling of rain from any given rain-producing system can yield significantly different isotopic values. Conclusions about the large-scale hydrologic cycle and the sources and pathways followed by water contained within rain must take these internal storm variations in isotopic values into account.

Abstract

Rainwater samples taken every 10 min, protected from fractionation by a hydrocarbon layer and collected every 12 h, are subjected to isotopic analyses to obtain a time series of oxygen and deuterium values through successive rain events in the eastern and central Amazon basin. Satellite imagery is used to characterize the rain events, and rain rates from recording rain gauges are used to delineate changes in internal rain production within each storm.

Three clear isotopic signals are seen in the storm systems examined. These three responses consist of depletion of heavy isotopes by as much as −6.7% in a single storm, depletion followed by enrichment, and little change in the isotopic signal. Each of these changes in isotopic content of the rainwater can be related to the internal rain-rate production, evaporation/condensation processes together with the implied convective/stratiform circulations of the storm. The storm-related isotopic results suggest, in addition to illuminating the internal dynamics of these storm systems, that sampling of rain from any given rain-producing system can yield significantly different isotopic values. Conclusions about the large-scale hydrologic cycle and the sources and pathways followed by water contained within rain must take these internal storm variations in isotopic values into account.

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