Shoaled glacial AMOC despite vigorous tidal Dissipation: Vertical Stratification matters

Abstract. During the Last Glacial Maximum (LGM), tidal dissipation was about threefold higher than today, which could have led to a considerable increase in vertical mixing. This would enhance the glacial Atlantic Meridional Overturning Circulation (AMOC), contradicting the shoaled AMOC as indicated by paleo proxies. Here, we conduct ocean model simulations to investigate the impact of background climate conditions and tidal mixing on the AMOC during LGM. We successfully reproduce the stratified ocean characteristic of the LGM by accurately simulating the elevated salinity of the deep sea and the rapid temperature decrease in the ocean's upper layers. Our findings indicate that show that the shoaled glacial AMOC is mainly due to strong glacial ocean stratification, irrespective of enhanced tidal dissipation. However, glacial tidal dissipation plays a critical role in the intensification of the AABW during the LGM. Given the critical role of AMOC in (de-)glacial climate evolution, our results highlight the complex interactions of ocean stratification and tidal dissipation that have been neglected so far.