Micrometer-scale biomarker and elemental imaging on sediments from the northeastern Arabian Sea – reconstruction of the Indian monsoon evolution on a sub-decadal scale in the Holocene and the Bølling-Allerød interstadial
Oceanography
Final Report Abstract
The project focused on the Indian monsoon dynamics during the Holocene and Bølling-Allerød interstadial. This research aimed to reconstruct Indian monsoon variability and environmental responses at decadal to centennial scales during the Holocene and Bølling-Allerød interstadial phases using advanced imaging techniques, with a particular focus on sea surface temperature reconstruction using mass spectrometry imaging (MSI) on a sediment core from the northeastern Arabian Sea. This region's sediment dynamics is highly influenced by the Indian summer monsoon, which is tied to ITCZ variability, while the annual sea surface temperature is mostly controlled by the Indian winter monsoon, providing a rare opportunity to study their coevolution. The research was conducted on core SO130-289KL off Pakistan, covering the period from ~14,700-12,900 ka BP and 10,000 to 1 ka BP. This core provided an opportunity to study the interaction between the Indian summer and winter monsoons in multidecadal resolution by looking at SST and environmental proxy variability. High-resolution signals from marine sediments were obtained using MSI, which enables detailed detection of biomarkers at micron resolution. MSI provided SST reconstructions at 200 µm resolution, yielding an almost annually resolved SST proxy record. Additional techniques included micro X-Ray Fluorescence Spectroscopy and hyperspectral imaging, which generate multi-proxy maps at micrometre resolution. These methods allowed for a direct comparison of SST, sedimentary dynamics, and primary productivity from the same sediment core at ~annual to multidecadal resolution. Results showed that the SST reconstructions, based on alkenone, provided valuable insights into Indian winter monsoon evolution. A robust age model was constructed with 22 radiocarbon dates, allowing the reconstruction of multidecadal variability. The most significant findings are weakening in the multidecadal SST variability at ~4,000 years BP. Future research will focus on synchronizing records to test the link between solar activity and monsoon variability. Moreover, the study revealed distinctive behaviour between alkenone and GDGT-based SST reconstructions during the Bølling-Allerød interstadial. We observe strong indications that the Indian summer and winter monsoons progressively weakened during the Bølling-Allerød interstadial, potentially suggesting that Indian monsoon intensity was influenced by the gradient between both hemispheres. This project has successfully reconstructed Indian monsoon variability and provided insights into the coevolution of the Indian summer and winter monsoons. The application of advanced imaging techniques has enabled high-resolution analysis of SST and sedimentary dynamics, offering a comprehensive understanding of past climate variability and its driving forces.
Publications
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Subdecadally resolved molecular proxy-based sea surface temperature reconstructions from the northeast Arabian Sea and implications for the Indian monsoon strength between 11,000 and 2,000 years BP. INQUA Conference, Rome, 2023.
Obreht, I., Lückge, A., Wörmer, L., Mohtadi, M. & Hinrichs, K.-U.
