Varied terrestrial sources of branched tetraether lipids in sediments of the Lower Bengal Fan affect the temperature reconstruction proxy
Year: 2025
Type: article
Abstract: Sedimentary branched glycerol dialkyl glycerol tetraether (brGDGT) lipids are commonly used to reconstruct continental paleotemperatures. However, the influence of varied terrestrial sources of brGDGTs either from highland or floodplain in a river basin on paleotemperature reconstruction has not been addressed. In this study, brGDGT lipids were analyzed in a gravity core taken from the active channel of the Lower Bengal Fan to evaluate the source effect on paleotemperature reconstruction during three distinct stages over the past 15 ka: stage I (15-10 ka), stage II (10 - 2 ka), and stage III (2-0 ka). The positive correlation between smectite/ (illite + chlorite) and methylation index of 5-methyl branched tetraethers (MBT’ 5ME ) (stage I: R 2 = 0.64, p < 0.01; stages II and III: R 2 = 0.69, p < 0.01) indicated that the reconstructed paleotemperatures were intimately associated with shifts in sediment sources. At stage I, enriched highland sediment sources with low smectite/ (illite + chlorite) ratio at the low sea level during the Bølling-Allerød event led to an underestimation of the paleotemperature (15 °C) compared to the Younger Dryas (17 °C) event. During late stage II (6-2 ka), gradually waning highland sediments indicated by the increasing smectite/ (illite + chlorite) ratio along with rising sea level and deltaic subsidence, resulted in a progressive overestimation of the reconstructed temperatures (19 to 20 °C) than the early stage II (18 °C at 10-6 ka). Stage III (2-0 ka) marked an incrementally increasing contribution from highland sediments due to progressive river relocation, leading to a cooling paleotemperature reconstruction from 20 °C to 18 °C. All pointed to the importance of distinguishing varied terrestrial sources of branched tetraether lipids in large-elevation river basins to reconstruct paleotemperature by MBT’ 5ME proxy.
Source: Applied Geochemistry
Language: English
Subfield: Atmospheric Science
Field: Earth and Planetary Sciences
Domain: Physical Sciences
Open Access status: hybrid
Estimated APC paid: $3,490
Funders: National Natural Science Foundation of China, Science, Technology and Innovation Commission of Shenzhen Municipality, Southern University of Science and Technology, China Geological Survey, Key Technologies Research and Development Program, National Key Research and Development Program of China
OpenAlex ID: W4416118608