| Summary: | The origin and potential impact of changes in the flow strength and salt discharge of Mediterranean Outflow Waters (MOW) on Atlantic Meridional Overturning Circulation have been long-standing objectives of (paleo-) oceanographers. Late Pliocene changes in the distal advection of MOW were reconstructed on orbital timescales for northeast Atlantic DSDP/ODP Site 548 off Brittany and Site 982 on Rockall Plateau. The proxy records were compared to Western Mediterranean deep-water records of Alboran Sea Site 978 and now supplemented by a MOW record from Site U1389 directly west off Gibraltar. At sites 548 and 982, MOW temperatures and salinities form a prominent rise by 2°–4°C and ~3 psu from ~3.43–3.3 Ma, induced by a preceding and coeval rise in sea surface and deep-water salinity and increased summer aridity in the Western Mediterranean Sea. We suggest that these changes triggering an increased MOW flow were ultimately induced by a persistent 4°C cooling of Indonesian Throughflow waters (Karas et al., 2011). First postulated by Cane and Molnar (2001), the temperature drop resulted from the northward drift of Australia that crossed a threshold value near 3.6–3.3 Ma and led to a large-scale cooling of the eastern subtropical Indian Ocean and in turn, to a reduction of African monsoon rains. Vice versa, we show that the distinct rise in Mediterranean salt export after ~3.4 Ma induced an expected unique long-term rise in the formation of Upper North Atlantic Deep Water, that followed with a phase lag of ~100 ky, finally inducing glacial MIS M2.
|
|---|