Fine-scale timing of environmental changes at the BA-YD transition in the Cariaco Basin revealed by molecular stratigraphy at sub-annual resolution

Brenna Boehman1,2, Lars W├Ârmer1, Jenny Wendt1, Gerald Hermann Haug3,4 and Kai-Uwe Hinrichs1, (1)MARUM / University of Bremen, Bremen, Germany, (2)Massachusetts Institute of Technology / Woods Hole Oceanographic Institution, Boston, MA, United States, (3)Max Planck Institute for Chemistry, Mainz, Germany, (4)ETH Swiss Federal Institute of Technology Zurich, Zurich, Switzerland
Molecular stratigraphy using biomarkers produced by marine or terrestrial organisms is a useful tool to explore paleoenvironmental conditions. However, traditional techniques require sample volumes that limit the temporal resolution when reconstructing past climate. Using mass spectrometry imaging (MSI), we can generate ultra-high resolution records with up to sub-annual resolution of environmental changes. We examined the abrupt climate change during the transition from the Bølling-Allerød (BA) to the Younger Dryas (YD) on laminated sediments from the Cariaco Basin off the northern shelf of Venezuela. The onset of the YD in the Cariaco Basin is expressed by dramatic changes in the elemental composition and sediment reflectance owed to the southward migration of the Intertropical Convergence Zone (ITCZ), leading to decreased rainfall and increased trade-wind induced upwelling in the region. To explore the precise timing of environmental changes at the BA/YD transition, we utilized microXRF for elemental mapping and MSI for molecular proxies representing marine and terrestrial paleoenvironmental conditions.

Sequence and magnitude of environmental changes in response to the BA/YD transition were evaluated by a multi-proxy approach, including (a) sea surface temperature (SST) proxies based on long chain alkenones from Haptophyta and on thaumarchaeal lipids, and (b) long chain fatty acids originating from leaf waxes of higher plant, which can inform on vegetation change. Divergence among the two SST proxies, and also from previous SST estimates based on foraminiferal Mg/Ca ratios, is discussed in the context of abrupt changes in water column characteristics.

Combined with existing records, the extremely high temporal resolution (100 µm, ~monthly) of the MSI approach provides us with a more nuanced understanding of the timing and interplay of the dominant climate feedbacks that affect tropical and global climate at the BA-YD transition.