Weakening of northeast trade winds during the Heinrich stadial 1 event recorded by dune field stabilization in tropical Brazil

摘要

The identification, characterization, and mapping of large areas of stabilized eolian features along the tropical northeastern Brazilian coast enabled recognition of the existence of one of the largest Quaternary dune fields (16,000 km(2)) in South America. This paleodune system is observed inland of the Lencois Maranhenses transgressive dune field (2.5 degrees S, 43 degrees W) and comprises deflation plains, stabilized parabolic dunes, and barchanoid chains developed under the action of northeast (NE) trade winds. Optically stimulated luminescence ages coupled with geomorphological analysis were used to constrain the time of dune field stabilization. Ages of stabilization of parabolic dunes and barchanoid chains throughout this paleodune system range between 19 to 14 ka showing heterogeneous dune stabilization by vegetation growth during a 5 ka time interval. Dune field stabilization is related to a decrease in NE trade wind strength and increase in precipitation as a consequence of the southward shift of the Intertropical Convergence Zone during the Heinrich stadial 1 event (18-15 ka), which resulted in a lower eolian drift potential, less sand input by alongshore transport, and low sediment availability to eolian transport, due to an increase in moisture to support vegetation growth and rising relative sea level.