资源环境科技发展态势分析平台

While substantial changes in thermohaline circulation related to deglacial climate variability are well established, the role of this circulation in Holocene climate variability remains uncertain. Here we use two dynamical proxies, Pa-231/Th-230 ratios and mean sortable silt size (SS) to reconstruct Holocene bottom water circulation at the intermediate-depth Carolina Slope. We find no substantial change in deep current speed or Pa-231 export at this site during the Holocene, suggesting consistent Pa-231 export via the Deep Western Boundary Current. (SS) over bar shows increasing millennial-scale variability in the middle-late Holocene, which may reflect Labrador Sea Water contribution to current speed. We conclude that deepwater export from the North Atlantic has remained remarkably stable during the Holocene, decoupled from changing rates of specific water masses, while production of these water masses varied at millennial to centennial time scales. The persistence of the large-scale overturning may reflect the ocean's stabilizing influence on Holocene climate.

Plain Language Summary Atlantic overturning circulation affects Earth's climate by moving heat and salt northward and carrying cold deep water southward. Learning how this circulation has behaved during the last 12,000 years, when climate resembled modern-day climate, can potentially aid in predicting future climate behavior. We investigated how fast the intermediate-depth circulation in the Atlantic moved using a sediment core from the North American continental margin. The overturning circulation has carried the isotope protactinium-231 away from our site at a very constant rate for the past 12,000 years, even when new water masses started contributing to the circulation. No baseline change in the size of silt moved by bottom currents (and thus no baseline change in current speed) occurred during the last 12,000 years, but short-term changes in silt size did occur during the past 6,000 years. Local current speed varied during individual climate events, which might reflect how fast particular water masses are formed in the North Atlantic, but the rate of overall deep circulation of the basin is determined by the combined strength of all these water masses, which has remained stable. Circulation stability may have helped to drive the stable climate the Earth has enjoyed for the last 12,000 years.