A substantial decline in ocean crust production between 15 million and 6 million years ago may have led to a sea level drop of 26–32 metres, comparable to the rise expected if the East Antarctic Ice Sheet were to melt today. Geological processes altering ocean basin volume are believed to have played a crucial role in this shift. Findings suggest that the slowdown in seafloor spreading caused deepening of ocean basins, affecting global sea levels over millions of years.

Tectonic Activity and Ocean Basin Deepening

According to a study published in Geochemistry, Geophysics, Geosystems, ocean crust production declined by 35 percent during this period, primarily due to reduced seafloor spreading. Researchers calculated that this decrease resulted in deeper ocean basins, leading to a sea level drop of 26–32 metres. Various initial conditions for crust formation and destruction were considered to ensure accuracy in estimating the extent of sea level change.

Impact on Oceanic Heat Flow and Chemistry

It has been reported that heat transfer from the mantle to the ocean declined by 8 percent, with a more pronounced 35 percent reduction in hydrothermal flux near oceanic ridges. These changes are thought to have influenced ocean chemistry, potentially affecting marine ecosystems. The study’s findings align with existing geological data from coastal rock formations in New Jersey and Nova Scotia, providing further support for the estimated sea level drop.

Possible Links to Climate Cooling

As per previous research, a slowdown in ocean crust production may have reduced volcanic emissions of greenhouse gases, contributing to global cooling. If this reduction in emissions occurred, the study suggests that additional factors, including thermal contraction of seawater and expansion of ice sheets, could have led to a further sea level drop of over 60 metres.