Between 15 million and 6 million years ago, a drop in ocean crust production collapsed the sea level, which lowered between 26 to 32 meters.
At the moment, Watch a quick climb of sea level worldwide, mainly attributable to the fusion of ice cloaks and glaciers caused by climate change and thermal expansion of seawater.
However, the change in sea level also occurs over millions of years, as geological processes gradually reshape the Earth’s oceanic basins and alter their total storage volume.
In a study in the February edition in Geochemistry, Geophysics, Geosystems, Colleen Dalton et al. They are concentrated in a period between 15 million and 6 million years ago, during which, as revealed by previous investigations, the ocean crust production decreased 35%.
This reduction, resulting above all of a global slowdown of the expansion of marine funds, provoked the deepening of ocean basins.
In the new work, the researchers considered several possible initial conditions for the area and ages of the oceanic crust, as well as crust destruction rates, estimating that the old slowdown of the spread of the seabed would have resulted in a Sea level drop of 26-32 meters.
This amount is comparable to the change in the level of the sea that would currently result if the entire ice cloak of the Eastern Antarctic (the largest ice cloak on Earth) melted, but in the opposite direction.
If the entire ice cloak of the eastern Antarctica – including the denman glacier, portrayed here – melted today, the level of the sea would rise about 36 meters. Between 15 million and 6 million years ago, the deepening of Earth’s oceanic basins may have caused a change in the level of the similar magnitude, but in the opposite direction
As the scientists also stressed that the heat flow from hot to ocean cloak would have decreased by 8% between 15 million and 6 million years ago, with an even larger drop (35%) in hydrothermal flow near oceanic ridges. Investigators suggest that this fall may have caused significant changes in ocean chemistry.
In previous work, some of the same investigators proposed that the 35% slowdown in crust production could have led to a decrease in the volcanic emissions of greenhouse gases and therefore to global cooling during the same period.
If this decrease had occurred, the sea level could have descended more than 60 meters, thanks to the thermal contraction of seawater and the retention of more water in the continental ice layers.
Coastal rock layers only provide limited evidence of sea level changes in the last 15 million years.
However, the new calculations are consistent with the interpretations of existing sequence stratigraphy data collected from the coast of New Jersey and off the New Scotland, the researchers say.
Although this is not the first study to estimate sea level changes in the past based on tectonic plates’ travel speeds, it covers a more recent period with a thinner and more certain statistical resolution than most previous studies, the researchers add.
