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Paleoenvironmental reconstruction in Madagascar

Periodic Reporting for period 1 - PALEOMADA (Paleoenvironmental reconstruction in Madagascar)

Reporting period: 2019-03-01 to 2021-02-28

Climate and environmental changes are among important challenges facing our society today. Inhabitants of our planet Earth may suffer from the negative impact of climate changes if preventative measures are not taken. This is the motivation behind project PALEOMADA, which stands for PALEOenvironmental reconstruction in MADAgascar. Our understanding of past climate changes depends on linking together paleoclimate records from several locations worldwide, including Madagascar, to test and evaluate climate models. Paleoclimate and paleoenvironmental studies are among fundamental scientific disciplines that can help us understand the causes and the nature of the changes before the instrumental records. Knowledge from paleoclimate studies, in turn, can be used to refine global or local climate models to better predict climate in the near future.

Madagascar is an excellent location for paleoenvironmental study because of its unique topography, climate, and environment. However, it is among understudied regions worldwide, and even though substantial paleoenvironmental conclusions have been drawn from separate investigation of speleothem proxies and lake sediments proxies, such conclusions have not yet been fully validated. Validation requires data calibration from modern monitoring and information cross-check across a range of complementary proxies between speleothems and lake sediments. PALEOMADA is a multidisciplinary approach, and it consists of combining state-of-the-art modern and paleo approach to produce a more robust paleoenvironmental interpretation in NW Madagascar using speleothems and lake sediments.

The objective of PALEOMADA is to (1) calibrate paleo-proxy data, i.e. using knowledge of modern biogeochemical processes as a tool to reconstruct paleoenvironmental changes, and (2) cross-check paleoenvironmental interpretations on a range of geochemical signatures between speleothems and lake sediments.
PALEOMADA combines field and laboratory activities.

Field work consists of setting up monitoring stations in each setting (lake and rivers, caves, and meteorological station), training Malagasy and Belgian Master's students and local collaborators (field technicians and meteorological staff collaborators) in the sample collection and storage processes, in situ measurements of various physico-chemical parameters during field expedition, and physical samples collection (lake sediments, speleothems, and various water samples from the lake, the surrounding rivers, and from the cave drips and pools). All these activities have received permission from the local authorities.

Lab activities consist of preparing and analyzing the physical samples collected from the field to produce interpretable geochemical data. Water samples were analyzed for various stable isotope composition (d2H, d18O, d13C) and for various major and trace elemental composition (Ca, Mg, Sr, Ba). Speleothem samples were analyzed for d18O, d13C, major and trace elemental composition, and clumped isotope). Lake sediment samples were analyzed for TOC, TN, C/N, %C, %N, δ2H, δ13C and δ15N. Records from lake sediments and modern lake environment have been used by a Belgian MSc student for her MSc. thesis, which was defended in June 2020. Records from stalagmites samples and cave monitoring are currently used by a Malagasy MSc student in the preparation of her MSc. thesis. Another Malagasy student assistant has been benefiting from the project and my mentoring and has defended a Master's thesis on physico-chemical characterization and valorization of caves in December 2020.
Up to this final report, three manuscripts using data from this PALEOMADA project have been submitted. Two manuscripts are first authored (with one sole author). They are under review at Geochemica Cosmochimica Acta and at Science of the Total Environment. The 3rd manuscript is co-authored and is currently under review at Nature, the results presented in which are beyond the original scope of the project because it looks at methane and greenhouse gas emission from tropical lakes. Four conference abstracts have been submitted and presented, except one that had been cancelled due to COVID. In addition to this, the researcher has been invited to give a seminar talk at the Institute of Earth Sciences, Johannes Gutenberg University Mainz, in Germany.
Other peer-reviewed scientific publications indirectly linked to PALEOMADA have been published during the course of the Fellowship, one of them is an invited review contribution to Malagasy Nature by Prof. David Burney, a well-known scientific researcher in Madagascar, looking at the Malagasy monsoon over the Holocene using speleothem δ18O records. Another paper is published in Science Advances aiming at providing a multi-millennial climatic context for the megafaunal extinctions in Madagascar and Mascarene Islands. A significant paper aiming at demystifying main controls on the stable carbon isotope composition of Speleothems was published in 2020, in collaboration with members of the speleothem community.
Efforts have been made to partially share relevant information from the project on social media (Twitter and Research Gate, and even on the ARTE France). We are still dedicated to reach out to the general public via outreach activity when it is safe to do so. In collaboration with the Geological Society of Madagascar that I founded, and which became an official non-profit organization in Madagascar since July 2019, an outreach activity with high school students was performed in March and December of 2020, and this effort is planned to continue this year and the following years.
Selected photograph of the two study locations.