Abstract The results of a multi-proxy study, including quantitative planktonic foraminifera faunal analysis, geochemistry of foraminifera tests, and lithogenic counts (IRD) are presented for two open marine sites. The sites are located in the eastern South Atlantic (ODP Leg 177 Site 1088) and the western tropical North Atlantic (ODP Leg 154 Site 925). Both sedimentary records span the interval 5.7–5.2Ma (i.e. late Miocene to early Pliocene), which encompasses the time of deposition of the upper evaporites (UE) in the Mediterranean basin. The observations confirm a major oceanographic and climatologic event which occurred during the Messinian at the transition between the glacial TG12 and the prominent TG11 warm interglacial at 5.5Ma. However, some oceanographic changes also occurred at the Miocene–Pliocene (M–P) transition in the northern tropical Atlantic and in the Southern Ocean with the first input of IRD at ODP Site 1088. In contrast to the termination across the lower evaporites (LE) at 5.5Ma, the M–P transition may not have involved a large change in ice volume. The potential causes behind the data across the major climatic transient are examined in the light of published information, including evidence from polar areas with focus on the climatic impact of fluctuating meridional oceanic circulation (MOC). A thermal seesaw mechanism in pre-Quaternary times is hypothesised as part of the large late Messinian deglaciation across the TG12–TG11 transition. An implication of the major Southern Atlantic warming before 5.5Ma is that an abrupt event freshening the surface of the North Atlantic might be present in the sub-polar Northern Hemisphere, but this has yet to be verified. This deglaciation may have been reinforced by a freshening of the North Atlantic as a result of discontinuous connection of the Mediterranean Sea.