The Holocene

Our ongoing research is investigating South American summer monsoon (SASM) variability during the last 10,000 years at decadal timescales using a series of alpine lake sediment archives collected along a north-south transect in the Colombian Andes between ~7.5º and 5.5ºN. Despite its vital importance for more than 350 million people, the long-term behavior of the SASM on human timescales is not well understood. This is especially true for the Northern Hemisphere component of the SASM where there are no decadally resolved terrestrial paleoclimate records. Through collaboration with Dr. Escobar of the Universidad del Norte, this work will begin to address this gap in knowledge. Ultimately, this research will provide a paleoclimate context for the SASM mean state and its variability that will allow better predictions of future changes and help guide policy makers when formulating policy to take action to mitigate and/or prevent adverse consequences from future climate change.

Methodologically, this research pairs measurements of sedimentological paleoclimate indicators, including grain size, magnetic susceptibility, and organic matter content with measurements of leaf wax hydrogen isotopes and calcite oxygen isotopes. By combining these methods, this work will investigate local and large-scale changes in SASM precipitation over long periods of time at societally relevant timescales. This is important because it is difficult to distinguish between Andean and Amazonian SASM variability based on isotopic studies alone.

This investigation is testing three hypotheses: (i) Decadal to century-scale changes in SASM precipitation are synchronous between the Northern and Southern Hemisphere Andes. (ii) Variations in Holocene SASM precipitation were similar over the Amazon and Andes, although of greater magnitude over the Andes. (iii) Changes in the location of the Atlantic branch of the Intertropical Convergence Zone (ITCZ) are the primary driver of abrupt SASM variability at decadal to century timescales.

Quaternary SASM Variability at Laguna de Tota

With support from the NSF, an international team of US and Colombian geoscientists will characterize the bathymetry and sedimentary and tectonic structure of Laguna de Tota, Colombia. The Tota survey will provide empirical constraints on the thickness of sediment sequences accumulated in Tota while helping to identify the lake’s depositional center(s) and the presence or absence of lake-level transgression-regression sequences. The data generated by this work will offer a new perspective of the structure and deposits contained in Colombian highland basins. Like Lake Titicaca, these data may provide important paleoclimatic information about the northern Andean tropics in and of themselves through the identification of sedimentary structures that are indicative of past lake-level changes at Tota. The geophysical data are also an essential component of our ultimate goal to developing a Quaternary paleoclimate record from Tota’s sedimentary archive. Ultimately a set of long, continuous sediment cores from Tota has the potential to help illuminate environmental and monsoon variability in the northern South American tropics, thereby allowing a more interhemispheric view of the South American climate, likely over multiple Pleistocene glacial-interglacial cycles. Such information will help refine climate models that simulate tropical South America’s climatic response to continued warming trends.


Lake Records South American Summer Monsoon Variability from the Colombian Andes