Depth Fluctuations of Mediterranean Outflow Water Along Its Northward Propagation During the Late Pleistocene

Mediterranean Outflow Water (MOW) critically influences the Atlantic Meridional Overturning Circulation, yet its northward transport dynamics along the Iberian Margin remain unclear. Using terrigenous grain-size sortable silt and benthic foraminiferal carbon isotopes from two depth-strategic sites (U1389: 644 m vs. U1588: 1,339 m), we constrain MOW's northward depth fluctuations over the last 250 kyr. Results show that MOW progressively deepened from ∼100 to 60 ka, then stabilized—synchronized with the prevalence of millennial-scale climate variability. During interglacials, MOW directly influenced U1588, while deepened below this site during glacials. Flow speed gradients between Sites U1389 and U1588 show pronounced precession cycles. At precession maxima—Northern Hemisphere summer insolation minima—when flow intensified, MOW underwent enhanced mixing and dilution during northward transport. This results from increased density contrasts between MOW and ambient waters, indicating deeper MOW penetration. We demonstrate precessional forcing on both the strength and depth of MOW's northward propagation.