Quantification of African monsoon intensity during the last interglacial sapropel S5

Event type: 
Seminar
Date: 
3 April 2018
Time: 
11.00 - 11.30 am
Location: 

Climate Change Research Centre, Seminar Room, Mathews Building 4th floor, UNSW, Sydney

Presenter: 
Jessica Amies
Research School of Earth Sciences, ANU
Host: 
Climate Change Research Centre, UNSW

The Mediterranean has great potential for reconstructing past climate. Due to the geography of a semi-enclosed basin, climate signals are amplified in Mediterranean sedimentary records, and high sedimentation rates enable high resolution records. For example, planktic foraminiferal δ18O records from the Mediterranean have recently been used to reconstruct sea-levels for the past 5.3 Myr. However, the Mediterranean’s sedimentary record is punctuated by sapropels: periodic deep-sea anoxic events strongly associated with times of African monsoon intensification.

The increased freshwater influx to the basin during sapropels decreases the δ18O of surface waters, creating anomalies in foraminiferal δ18O records which prevent robust interpretation of Mediterranean δ18O, and hence of palaeoclimatic reconstructions over these intervals. Despite extensive research on sapropels, the magnitude of monsoonal intensification and freshwater runoff, along with its influence on δ18O, remains elusive.

Using a case study of sapropel S5 (~128-121 ka) which occurred during the last interglacial, we present a method to obtain estimates of African monsoon intensity. Using a box model of the Mediterranean Sea, and proxy records of δ18O, sea-level and sea surface temperature, monsoonal freshwater runoff volume has been calculated for sapropel S5. This method has the potential to be further applied to estimate monsoonal freshwater runoff during other sapropels.

In addition to providing quantification of African monsoon intensification, this study has led to new insights into the stratification and warming of eastern Mediterranean surface waters during sapropels, adding to our understanding of the system dynamics during these events.

 

Speaker Biography: Jessica is doing a PhD at the Climate Change Institute at ANU under the supervision of Dr Katharine Grant and Professor Eelco Rohling. Her project title is "Mediterranean paleoclimate during the last interglacial sapropel S5". Her research involves reconstructing past environmental changes in the oceans. To do this she uses stable isotope measurements of foraminifera shells which are preserved in deep sea sediment cores. Her current work uses samples from the Mediterranean Sea to investigate anoxic events which occurred here in the past. This information will hopefully help improve sea-level records which have been constructed using data from the Mediterranean.