Recent research reveals significant insights into sea level changes over the past 15 million years, shedding light on potential future scenarios, including predictions of rising sea levels that could inundate the U.S. coastline by 2050. Scientists suggest that a slowdown in ocean crust production during this ancient period may have contributed to a dramatic drop in sea levels, with estimates indicating a decrease of 26 to 32 meters.
Between 15 million and 6 million years ago, researchers identified a 35% reduction in crust production. This slowdown likely resulted in decreased volcanic emissions of greenhouse gases, leading to global cooling. The current rapid rise in sea levels, attributed primarily to climate change, is driven by the melting of ice sheets and glaciers, along with thermal expansion of seawater. However, the geological processes affecting sea levels over millions of years differ fundamentally from today’s accelerated changes.
Limited evidence exists regarding sea level fluctuations over the past 15 million years, primarily derived from coastal rock layers. The researchers' findings are consistent with existing sequence stratigraphy data collected from coastal New Jersey and offshore Nova Scotia. By analyzing these data sets, the team estimated that heat flowing into the ocean from the underlying hot mantle decreased by approximately 8% during this period.
The study highlights that hydrothermal flux near oceanic ridges also decreased by 35%, further supporting the hypothesis of an ancient seafloor spreading slowdown. If this decrease had occurred, it could have resulted in sea level falling by over 60 additional meters due to thermal contraction of seawater and increased water retention in continental ice sheets. Notably, the potential sea level change resulting from the melting of the East Antarctic Ice Sheet is comparable to the changes predicted from the ancient crust production slowdown.
The researchers considered various initial conditions related to ocean crust ages and destruction rates while employing sequence stratigraphy data to estimate past sea level variations. This study provides a finer resolution and greater statistical certainty than most previous analyses, thereby enhancing the understanding of long-term geological processes that reshape Earth’s ocean basins.
Sarah Stanley, an environmental microbiologist with a diverse background in science communication, emphasizes the importance of these findings. Understanding ancient sea level dynamics is crucial for predicting future trends and preparing for potential impacts on coastal communities.
