A newly published study shows the correlation between the melting of ancient ice sheets, the migration of the Earth's rotation axis and sea levels between 2000 and 8000 years ago.
The shift of the Earth's rotation axis, determined in ancient times by the processes triggered by the progressive retreat of the glaciers, it is able to modulate the height of the sea level due to the complex interactions between the various components of the Earth system during deglaciations.
This is what emerges from the study “Earth's rotation impacted the mid-Holocene sea-level highstand”, just published in the scientific journal 'Communications Earth & Environment' by a team of researchers from theIstituto Nazionale di Geofisica e Vulcanologia (INGV),University of Salzburg e of the Department of Physics and Astronomy "Augusto Righi" of the University of Bologna.
The research concerned, in particular, the so-called “highstand” of the Holocene, that is, evidence of sea level rise to a level higher than today, typically observed at mid- and low-latitudes, in coastal areas far from ancient ice sheets.
At the height of the last Ice Age, about 21.000 years ago, immense ice sheets covered North America and Northern Europe, while the average sea level was about 130 meters lower than today. As the glaciers gradually retreated, A huge amount of meltwater has flowed into the oceans, but their levels have not risen uniformly everywhere.In fact, the response of the solid Earth to the stresses due to the loads acting on its surface and the mutual gravitational attraction between oceans and glaciers have caused the melting of the great continental ice sheets to produce a complex distribution of rising and falling ocean levels.
The movement of enormous masses from the continental ice sheets to the oceans has also determined a progressive migration of the Earth's rotation axis, which moved towards Hudson Bay, near the northeastern coast of Canada.
These phenomena, collectively known as “glacio-isostatic adjustment” (Glacial Isostatic Adjustment, or GIA), are described quantitatively by physical models that are able to explain very well the general trend of geological observations of sea levels in the past: nevertheless, some aspects of the distribution in space and time of ancient coastlines still remain unclear today.
“With our study, we have systematically analyzed for the first time the effect of the Earth's rotational pole drift on the formation of highstands.”, explains Daniel Melini, researcher at INGV and first author of the article. “The results, obtained through numerical models, have shown that the shift of the rotation axis due to deglaciation modulates the height of highstands, and in some regions of the globe it may even be the mechanism that determines their appearance (or their absence)”.
In particular, the rotation pole drift increases the height of the highstand in the southwest Atlantic, northeastern Pacific, and northern Indian Ocean, and decreases in the southern Indian Ocean and parts of the Pacific.
Analysis of geological data on past sea levels confirms the predictions of physical models: in regions where they indicate an amplifying effect from the Earth's rotation, highstands are, on average, higher than those in regions where the models instead predict a weakening.
"Data on ancient coastlines in regions far from the Pleistocene ice sheets are increasingly abundant and of better quality. These findings allow us to better understand the physical mechanisms that determine sea level variations during a glacial cycle, thus proving of considerable importance in the future interpretation of new data."he concludes Giorgio Spada, Professor of the Department of Physics and Astronomy “Augusto Righi” of the University of Bologna and co-author of the article.
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Figure: The figure shows the maximum sea level rise between 2000 and 8000 years ago, predicted by numerical models, both including the effect of Earth's rotational pole drift (top) and ignoring it (bottom). Comparing the two simulations shows how the effect of pole drift is essential for the emergence of highstands along the Asia-Pacific coast.