Change in dust and fluvial deposition variability in the Peruvian central continental coast during the last millennium: Response of the ocean atmospheric systems.
Wednesday, 17 December 2014
The particles from aeolian or fluvial origin are a useful proxy for the reconstruction of atmospheric condition patterns in the past. Changes in continental aridity and the atmospheric condition determine the composition and amount of lithogenic material and the way of transport from the continent. Here we present a record of laminated sediments (core B040506) retrieved in the continental shelf off Peru. Wind long-term suspension (regional) and local aeolian transport during the last millennium (transition from Medieval Climate Anomaly (MCA) to Little Ice Age (LIA) and the current warm period (CWP)) at centennial to decadal resolution are characterized. The particle provenance and grain size components are discussed using a mathematical model of fractionation. This model assumes that lithological composition of the sediment is an assemblage of several log-normally distributed particle populations. In this way, an interactive least square fitting routine is used to fit the particle grain size collected with the mathematical expression. This allows inferring the spatial and temporal variation of particle populations and thus the transport mechanisms involved. Our results showed a decrease in aeolian transport from the MCA - LIA transition and during the LIA with except of the local aeolian transport that shows peaks during the LIA. This decrease during LIA is accompanied by an enhanced fluvial transport. During the CWP the aeolian transport (Paracas dust storm and wind long-term suspension) display a high variability and tendency to increase in detriment of runoff. Comparison with other South American records indicates that those changes are linked to change in the shift of the ITCZ and Pacific high at the centennial time resolution. Finally the great increase of the fluvial transport within the transition of the LIA to the CWP is synchronous to severe drought period recorded in the Indo-Pacific region indicating higher frequency of El Niño events. Hence these factors indicate an unambiguous change in the atmospheric regime in relationship with climate changes in the last millennium over the Peruvian continental shelf.