The migration of the Earth's rotational pole has affected sea levels

The shift in the Earth’s axis of rotation, which was historically caused by processes triggered by the gradual retreat of glaciers, can influence sea levels. This phenomenon is the result of complex interactions among the various components of the Earth system during deglaciations.

This is the finding of a study conducted by a team of researchers from the National Institute of Geophysics and Volcanology (INGV), the University of Salzburg, and the “Augusto Righi” Department of Physics and Astronomy - DIFA at the University of Bologna. Published in Communications Earth & Environment, the study focused on the so-called “Holocene highstands”, i.e., evidence of sea-level rises exceeding current levels They are typically observed at mid- and low-latitudes, in coastal areas far from ancient ice sheets.

At the peak of the last ice age, about 21,000 years ago, vast ice sheets covered North America and Northern Europe, and the average sea level was about 130 meters lower than it is today. As the glaciers have gradually receded, a huge amount of meltwater has flowed into the oceans, though sea levels have not risen uniformly everywhere. Instead, a complex combination of rising and falling sea levels has occurred, caused by the response of the Earth’s solid crust to the stresses resulting from the increased water loads on its surface and the mutual gravitational pull between the oceans and glaciers.

In addition, the shifting of enormous masses from the continental ice sheets to the oceans resulted in a gradual displacement of the Earth's axis of rotation, which moved toward Hudson Bay, near the northeastern coast of Canada. In particular, the drift of the Earth’s rotational pole has increased the height of the highstands in the southwestern Atlantic, the northeastern Pacific, and the northern Indian Ocean, and has decreased it in the southern Indian Ocean and in some parts of the Pacific.

“Data on ancient coastlines in regions far from the Pleistocene ice sheets are becoming increasingly abundant and of higher quality,” explained Giorgio Spada, a professor in the “Augusto Righi” Department of Physics and Astronomy - DIFA at the University of Bologna and co-author of the article. “The results of this study allow us to better understand the physical mechanisms that drive sea-level changes during a glacial cycle. Therefore, they are of considerable importance for the future interpretation of new data”.

Analysis of geological data on past sea levels confirms the findings of physical models: in regions where the models indicate an amplification effect due to Earth’s rotation, the highstands are, on average, higher than those in regions where the models predict a weakening effect.

“In this study, we systematically analysed for the first time the effect of the Earth's rotational pole drift on the formation of highstands”, said Daniele Melini, a researcher at the INGV and the article's lead author. “The results, obtained using numerical models, showed that the shift in the axis of rotation caused by deglaciation influences the height of glacial highstands, and in some regions of the globe may even be the mechanism that determines their occurrence (or absence)”.

The study was published in Communications Earth & Environment with the title “Earth’s rotation impacted the mid-Holocene sea-level highstand”. The authors are Daniele Melini from the National Institute of Geophysics and Volcanology (INGV), Barbara Mauz from the University of Salzburg and Giorgio Spada from the “Augusto Righi” Department of Physics and Astronomy - DIFA at the University of Bologna.