Past Temperature Reconstructions at Lake Malawi During the Past 75,000 years



Presenter: Magnus Kendall

Faculty Sponsor: Isla S. Castañeda

School: UMass Amherst

Research Area: Geology and Earth Sciences

Session: Poster Session 4, 2:15 PM - 3:00 PM, 163, C4

ABSTRACT

Earth’s climate is rapidly changing. Available instrumental climate records are short – most only go back to around ~1900 AD, although in some places there are older records. To put the natural climate variability into context, we need longer records than the current instrumental record. Understanding the natural range of variability over different timescales is therefore critical to grasping what the future has in store. It is particularly uncertain in tropical Africa where observations are limited.

Past conditions can be determined from organic compounds (biomarkers) preserved in lake sediment, which provide important information on past climates.  This study examines a long sedimentary record collected from Lake Malawi in tropical East Africa in 2005. Core MAL05-2A was collected from the northern basin of the lake and spans the past 75,000 years, which captures a period of stark temperature change. Particularly abundant in this core are branched glycerol dialkyl glycerol tetraether lipids (brGDGTs), which are a group of biomarkers produced by bacteria. The number of methyl groups in different brGDGTs is controlled by temperature and by examining changes in the distributions of brGDGTs, past temperatures can be reconstructed. In addition, the temperature index TEX86, which is based on isoprenoid GDGTs (iGDGTs) produced by archaea, is another technique for reconstructing past temperature.

This study generates a new temperature reconstruction spanning the last 75,000 years by analyzing both brGDGTs and iGDGTs. By looking at past temperatures in East Africa, one can better understand how climate change will impact this region in the future.

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