How could ocean circulation have affected Pleistocene climate changes?

During the Pleistocene Epoch, ocean circulation played a critical role in climate variability through complex feedback mechanisms involving the atmosphere, ice sheets, and heat transport.

The strength and pattern of oceanic circulation were significantly altered during glacial stages. Research suggests that thermohaline circulation—the large-scale overturning of the ocean—was considerably weaker during the last glacial maximum compared to the present. This reduction in circulation limited the poleward transfer of heat, which is normally responsible for moderating the climate of regions like northwestern Europe.1

Several factors contributed to these changes:
* Atmospheric Coupling: Large continental ice sheets in North America and Eurasia blocked normal zonal atmospheric circulation, replacing it with meridional patterns that were less effective at driving major oceanic current gyres.2
* Physical Constraints: The eustatic lowering of sea level reduced the effective area of the oceans, while the expansion of sea ice restricted the surface area available for air-ocean coupling.2
* Feedback Loops: Reorganizations of the ocean-atmosphere system, particularly regarding the transport of salt and water vapor, are considered essential to explaining the magnitude of Pleistocene climatic cycles.3

These shifts in circulation were both a response to and a driver of global cooling, influencing the distribution of marine organisms and the rate of sedimentation in ocean basins.24