The Quaternary (2.56 Ma to present) is characterized by recurring glacial–interglacial cycles and major reorganizations of the climate system. Two particularly prominent transitions stand out: the Mid-Pleistocene Transition (MPT, ~ 1.2–0.65 Ma), marked by a shift in dominant glacial cyclicity from ~ 41 kyr to ~ 100 kyr, and the Mid-Brunhes Transition (MBT, ~430 ka), associated with a shift toward generally stronger interglacials and changes in atmospheric CO₂, ice volume and ocean–atmosphere interactions.

Both transitions involved profound changes in the climate system, including reorganizations of atmospheric and oceanic circulation, ocean heat redistribution and carbon storage, as well as adjustments in global thermal and hydrological gradients. These were accompanied by significant changes in the cryosphere, including ice sheet extent and dynamics, and in both marine and terrestrial biospheres. However, despite decades of research, the relative roles of orbital forcing, internal feedbacks and changing climate system sensitivity remain debated.

This session aims to bring together new insights from marine and lacustrine sediment cores, ice cores, speleothems and numerical simulations in order to better characterize the paleoenvironmental conditions associated with these key transitions and to constrain the interactions among the different components of the climate system.

We welcome contributions based on geochemical, mineralogical, micropalaeontological, and modelling approaches, covering a broad range of timescales and regions. We particularly encourage contributions addressing orbital and millennial-scale variability as well as regional vs global climate signals. Those integrating multiple archives, proxies or modelling approaches are especially welcome.