– Paleoenvironmental and paleoclimatological research using molecular fossils and compound-specific isotope analysis from lake sediments

Speaker: Dr. Rienk Smittenberg, Univ. Docent at the Department of Geological Science

Photo: Barbara Wohlfarth

Abstract
In this seminar, a case study will be presented showcasing the use and application of organic geochemistry - the analysis of molecular fossils and their isotopic composition, extracted from lake and ocean sediments - in paleo-environmental and paleoclimate research. Below is the abstract of the paper under discussion.

Climate and human-induced environmental change promote biological regime shifts between alternate stable states, with implications for ecosystem resilience, function, and services. While these effects have been shown for present-day ecosystems, the long-term response of microbial communities has not been investigated in detail. This study assessed the decadal variations in phytoplankton communities in a ca. 150 year long sedimentary archive of Lake Nong Thale Prong (NTP), southern Thailand using a combination of bulk geochemical analysis, quantitative polymerase chain reaction (qPCR) and lipid biomarkers techniques including compound-specific hydrogen isotope analysis as a proxy for precipitation. Relatively drier and warmer conditions from ca. 1857-1916 Common Era (CE) coincided with a dominance of the green algae Botryococcus braunii, indicating lower nutrient levels in the oxic lake surface waters, possibly related to lake water stratification. A change to higher silica (Si) input around 1916 CE was linked to increased rainfall and concurs with an abrupt takeover by diatom blooms lasting for 50 years. These were increasingly outcompeted by cyanobacteria from the 1970s onwards, most likely because of increased levels of anthropogenic phosphate and a reduction in rainfall. Our results showcase that the multi-proxy approach applied here provides an efficient way to track centennial-scale limnological, geochemical and microbial change, as influenced by hydroclimatic and anthropogenic forcing.

Reference
Yamoah, K.A., Callac, N., Chi Fru, E., Wohlfarth, B., Wiech, A., Chabangborn, A., Smittenberg, R.H., A 150-year record of phytoplankton community succession controlled by hydroclimatic variability in a tropical lake. Biogeosciences 13, 3971-3989. https://bg.copernicus.org/articles/13/3971/2016

IGV Seminar Series organizers
Wei-Li Hong, wei-li.hong@geo.su.se
Paola Manzotti, paola.manzotti@geo.su.se
Christian Stranne, christian.stranne@geo.su.se