# Major sea level fall during the Pliocene M2 glaciation

## TL;DR

This study shows that a major sea level drop occurred during the Pliocene M2 glaciation due to significant ice growth linked to reduced ocean heat transport and lower CO2 levels.

## Contribution

The study improves the benthic foraminiferal Mg/Ca paleothermometer to achieve high-precision temperature reconstructions.

## Key findings

- M2 glaciation involved ~55 m sea-level equivalent ice growth.
- Ice growth was more closely tied to CO2 decline than ocean cooling.
- Reduced ocean heat transport in both hemispheres triggered the glaciation.

## Abstract

The extent of ice growth during the Pliocene M2 glaciation (~3.3 Ma) has been called into question, with benthic foraminiferal oxygen isotope records interpreted primarily as a cooling signal. Here we improve the benthic foraminiferal Mg/Ca paleothermometer, allowing bottom water temperature reconstructions with a precision of ±0.2-0.3°C (1 s.d.). Applying this approach to M2 implies a significant increase in ice volume (~55 m SLE) that was more tightly coupled to a drop in CO2 than to ocean temperature. We suggest that the M2 glaciation was driven by a reduction in northern hemisphere poleward heat transport, and amplified by a reduction in southern hemisphere poleward heat transport caused by restriction of the Indonesian Seaway. The cryosphere growth drove the atmospheric CO2 decrease, which likely contributed to the overall magnitude of ice growth. These results demonstrate the sensitivity of the cryosphere to changes in ocean heat transport in a similar to modern climate.

This study refines benthic foraminiferal Mg/Ca paleothermometry to reduce uncertainties to ±0.2-0.3 °C, which was then applied in Atlantic and Pacific sediment cores to reconstruct Mid-Pliocene M2 glaciation sea-level changes.