Colloquium: Isla Castañeda

"Terrestrial and marine climate variability in North Africa during the Late Quaternary: Insights from organic geochemical and isotopic proxies"

Abstract: Sedimentary organic matter present in marine environments can contain components derived from both terrestrial and aquatic sources. Molecular fossils (biomarkers) allow for terrestrial and marine components of sedimentary organic matter to be examined separately, and thus paleoenvironmental information regarding conditions both within the water column and on land can be examined simultaneously. The first part of the seminar will examine millennial-scale sea surface temperature (SST) and land surface temperature variability in the Eastern Mediterranean region during the last 27 kyr. Past SSTs are reconstructed using the Uk’37 index, based on long-chain alkenones produced by haptophyte algae, and TEX86, based on glycerol dialkyl glycerol tetraethers (GDGTs) produced by marine Thaumarchaeota. The recently developed MBT and CBT proxies, based on branched GDGTs produced by anaerobic soil bacteria, are used to examine changes in mean annual air temperature and soil pH, respectively.  These proxies provide insights into the response of the Eastern Mediterranean region to global climate events including the Last Glacial Maximum, Heinrich event 1, and the Younger Dryas. The second part of the seminar will examine relationships between the strength of Atlantic Meridional Overturning Circulation (AMOC) and vegetation type in central North Africa during the past 200 kyr. Uk’37 and TEX86 SSTs, in combination with benthic carbon isotope data (C. wuellerstorfi), provide insights into past AMOC variability. The carbon isotopic composition of plant leaf waxes, present in dust blown to offshore N Africa from the Sahara and Sahel, is used to examine changes in the distribution of C3 (trees) and C4 (grasses) vegetation. Increased inputs of C3 vegetation are noted within Marine Isotope Stage (MIS) 3 (~50-45 ka) and MIS 5 (~120-110 ka), suggesting wetter conditions at these times and coinciding with major human migration events out of sub-Saharan Africa.

Isla Castañeda, Postdoctoral Research Associate
Department of Marine Organic Biogeochemistry, Royal Netherlands Institute for Sea Research (NIOZ)