Late Holocene Climate of the Andean Altiplano as the Context for Cultural Change: A Paleohydrological Transect Integrating Sedimentary, Geochemical, Stable Isotopic, and Biological Proxies

Collaborative Effort with:

Alexander Wolfe, Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton (awolfe@ualberta.ca)

Donald Rodbell, Department of Geology, Union College (rodbelld@gar.union.edu)

Mathias Vuille, Department of Geosciences, University of Massachusetts, Amherst (mathias@geo.umass.edu)

Project Summary

Our proposed research has two main goals: (1) produce high-resolution multiproxy records documenting changes in the regional P-E balance for the last 5000 years from a network of lakes spanning the range from 14°S to 20°S along the Eastern Cordillera of the Altiplano and (2) expand the number of sites with paleohydrological and modern data that have been studied to date on the north – south transect.  One of the major strengths of the proposed project is in the diversity of the interdisciplinary research team and the proven quality of the network of paleorecords that we propose to study.  We seek to test hypotheses, outlined in the project description, concerning the causes of shifts in the precipitation-evaporation (P-E) balance during the middle and late Holocene across the Andean Altiplano.  We selected lakes in different hydrologic settings in order to derive a range of sensitivities to changes in the moisture balance.  Our past experience in the region has shown that an integrated study of lakes spanning the hydrologic spectrum yields paleoclimate records that capture the full range of shifts in the regional P-E balance.  D and ¹⁸O measurements on modern surface waters across the region illustrate two points: (1) the proposed closed basin sites are sensitive to changes in the P-E balance and (2) the open basins have lake water that plots on the Local Meteoric Water Line (LMWL) indicating that the effects of evaporation are minimal at these sites.

In summary, our past work established the following, which provides the fundamental basis for the present proposal:

(1) The sites targeted for this proposal contain Holocene records. 

(2) The sites are sensitive to changes in effective moisture. 

(3) We can establish reliable ¹⁴C, ¹³⁷ Cs, and ²¹⁰Pb chronologies. 

(4) The sites have sufficient sedimentation rates during the middle and late Holocene to yield the necessary time-resolution (sub-decadal to decadal-scale). 

(5) We are working with a set of reliable paleohydrological proxies (sedimentology, paleomagnetism, elemental and stable isotope geochemistry, and diatoms). 

(6) Down-core interpretations of stable isotope composition and diatom assemblages can be constrained with modern calibration studies. 

(7) Quantitative models are possible by combining the modern calibration sets with the down-core proxies.

The proposed research has six major objectives:

(1) Identify the pattern of decadal to century-scale climate change from a network of 8 sites on a north – south transect from 14 to 20°S across the Central Andes.

(2) Interpret down-core variations in stable isotope composition and diatom assemblages, constrained by modern calibration studies.  We will improve our preliminary modern calibration sets for stable isotopes, diatoms, and limnological measurements by doubling the number of sites from 25 to 50.   

(3) Improve age control by using multiple dating techniques including ¹³⁷Cs, ²¹⁰Pb, ¹⁴C on macrofossils, geomagnetic correlation using U-channels, and tephrochronology from sites at the southern half of the transect.  We will also greatly improve temporal resolution by ¹⁴C dating level 1 sites at approximately 100 year resolution.  Previous work has established that the sites have ample reliable macrofossils and high sedimentation rates.

(4) Use lake water isotope - mass balance models and precipitation ¹⁸O tracer GCMs to quantify the results of our down-core work.

(5) Integrate modern climatology with the results of our paleoclimatic reconstructions to generate synoptic circulation scenarios.

(6) Compare the results with paleorecords of ENSO activity (e.g. Quinn et al., 1987; Ortlieb, 1995; Rodbell et al., 1999; Moy et al., in prep; and others).

We propose to reconstruct the climate history of the Andean Altiplano by applying an integrated methodology that combines sedimentary analyses of lake cores with laboratory analyses of fine-scale sediment features, sediment magnetic characteristics, elemental and isotopic geochemistry, diatoms, and climatology.  We will use AMS ¹⁴C measurements on carefully screened organic constituents (macrofossils).  Recent sediment accumulation rates will be constrained by ¹³⁷Cs and ²¹⁰Pb measurements.
 

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