How do long-term climate changes affect the magnitude/frequency of sediment density flows? Insights from the Dead Sea ICDP drilling

Sediment density flows (ρ_flow<ρ_water, overflows: flood plumes; ρ_flow>ρ_water, underflows: including turbidity currents and debris flows) are major processes for transporting sediments and organic carbon from rivers, coasts or continental shelves into deep basins. These flows can also have serious socioeconomic consequences such as breaking seabed communications cables and pipelines. Given the potential impacts of climate change, it is important to quantify how sediment density flow processes are impacted by changing environmental conditions.

Lab-simulations and/or field monitoring campaigns on the timescales of seconds to years are helpful for understanding specific triggers for sediment density flows and how their magnitude/frequency may change under different conditions. However, these methods cannot be applied to longer timescales, which are of great interest to geologists and palaeoclimatologists trying to understand the past. It is unclear whether, and if so how, long-term climate changes affect the magnitude/frequency or type of sediment density flows within a specific water body. One approach to answering this question is to analyze a comprehensive geological record that comprises deposits that can be reliably linked to modern sediment flow processes.

To address this question, we analyzed the unique ICDP Core 5017-1 from the Dead Sea (the largest and deepest hypersaline lake on Earth -- ρ_water:1240 g/L) depocenter covering MIS 7-1. Based on an understanding of modern sediment density flow processes in the lake, we link homogeneous muds in the core to overflows (surface flood plumes, ρ_flow<ρ_water), and link graded turbidites and debrites to underflows (ρ_flow>ρ_water). Our dataset reveals (1) overflows are more prominent during interglacials, while underflows are more prominent during glacials; (2) orbital-scale climate changes affected the magnitude/frequency of the flows via changing salinity and density of lake brine and lake-level (Lu et al., 2022).

The current research bridges the gap between our understanding of modern sediment density flow processes and deposits preserved in a long-term geological record in the Dead Sea, a tectonically active subaqueous environment (Lu et al., 2020). It has wider implications for turbidite paleoseismology and implies that to develop prehistoric turbidites as a reliable paleoearthquake indicator, comprehensive modern sediment flow monitoring is essential. It also has wider implications for paleoclimate research in a tectonically active subaqueous environment. A sedimentary archive is filtered to remove significant instantaneous event deposits such as turbidites and debrites could help paleoclimatologists to better reconstruct paleoclimate change.

 

Refs.:

Lu, Y., Wetzler, N., Waldmann, N.D., Agnon, A., Biasi, G.P., and Marco, S., 2020. A 220,000-year-long continuous large earthquake record on a slow-slipping plate boundary. Science Advances, 6 (48), doi: 10.1126/sciadv.aba4170

Lu, Y., Pope E., Moernaut, J., Bookman, R., Waldmann, N., Agnon, A., Marco, S., Strasser, M., 2022. Stratigraphic record reveals contrasting roles of overflows and underflows over glacial cycles in a hypersaline lake (Dead Sea). Earth and Planetary Science Letters, 594, 117723, doi: 10.1016/j.epsl.2022.117723