A lacustrine biomarker record of continental temperature in equatorial Africa over the last 170,000 years

Abstract:

Our understanding of Earth’s climate history during the Quaternary Period is hindered by a shortage of reliable and independently dated proxy records from continental tropical settings. Long-lived lakes are important archives of past environmental change, because their profundal sediments often contain high amounts of organic matter, which allows the application of diverse proxies to study climate change and other processes occurring within the lake and its surroundings. The ICDP project DeepCHALLA recovered a continuous sediment sequence from Lake Chala in eastern equatorial Africa spanning the last c. 250,000 years (250 kyr). Preserved within these sediments are the fossil membrane lipids of archaea and bacteria, glycerol dialkyl glycerol tetraethers (GDGTs), which form the basis for several paleoclimate proxies. Here we present, in unprecedented high resolution (210 years on average) and with an independently established chronology using a variety of dating techniques, a temperature reconstruction for eastern equatorial Africa from the penultimate glacial maximum (MIS6) to the present, based on variations in the down-core distribution of GDGTs. Temperature history in equatorial Africa over the past 170 kyr shows clear influence of orbital insolation forcing at periodicities of ~41k (obliquity) and ~23k (precession). Overall the long-term trend resembles the temperature record of Antarctica, except that during interstadial MIS5c equatorial Africa was still almost as warm as during the peak interglacial period (MIS5e), while high-latitude regions had already cooled significantly, in line with the ~50 ppm decline in atmospheric CO₂. This work demonstrates the potential of lacustrine GDGTs for elucidating the climate history of tropical regions at quaternary timescales, provided the availability of suitable high-quality sediment archives.