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

• Applicant: Dr. Igor Obreht
• Subject Area: Palaeontology ; Oceanography
• Term: from 2021 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 464898428

The Indian monsoon is one of the most important large-scale coupled land-ocean-atmosphere phenomena in the low latitudes. However, the forcing mechanisms of the decadal-scale monsoon variability are not well understood because knowledge of short-term climate oscillations is mostly limited to periods covered by instrumental records. Understanding of the short-scale climate evolution in the more distant past is hampered by the small number of records that preserve undisturbed signals and by methodological limitations to obtain highly resolved records. However, recent developments that interrogate laminated sediments with novel imaging techniques showed great potential to overcome these limitations. In order to reveal subdecadal-scale paleoclimate evolution of the tropics, I propose to apply biomarker and elemental imaging on finely laminated sediment sections from the Arabian Sea spanning the major part of Holocene (from 11.7-2 ka) and Bølling-Allerød interstadial (B-A; 14.7-12.9 ka). The goal of this project is to explore the interplay of the Intertropical Convergence Zone (ITCZ), Indian monsoon intensity and related environmental responses on the subdecadal and decadal-scale during the Holocene and B-A.Sediment core SO130-289KL from the Arabian Sea preserves an undisturbed, laminated record for proposed time intervals, providing an excellent archive for high-resolution studies. I propose to apply mass spectrometry imaging, a novel technique in paleoclimate research that collects mass spectra of organic compounds and visualizes their spatial distribution at the µm-scale, and combine it with congruent µXRF data from sediments deposited during the Holocene and B-A interstadial. The aim is to combine independent biomarker proxies for sea-surface temperature (SST) with proxies of terrestrial vegetation response, aquatic primary productivity and water column anoxia in 200 µm (i.e. annual) resolution and relate this data to elemental ratios indicative of environmental conditions acquired at 50 µm resolution. Obtained annually resolved biomarker and elemental records will reveal previously inaccessible information on monsoon intensity and its relation to ITCZ in interglacial and interstadial climate states, as well as precisely establish monsoon forcing on the environment by detecting leads and lags in the responses of the ocean, atmosphere and land to climate change in an unprecedented level of details. A conservative approach in establishing dominant frequencies of climate variability in warm climate states of the past ~15 ka will be applied to test for the existence of quasi-persistent decadal oscillations. This project will also constrain the rate of SST change and its variability in the tropics over the Holocene and B-A. In summary, this project will provide highly-resolved biomarker and elemental data that could serve as a reference record for subdecadal climate evolution in the tropics during the Holocene and the B-A.

• DFG Programme: Research Grants