The melting of the immense ice sheets that once covered our planet profoundly altered ocean levels at the end of the last ice age, but scientists have just discovered that the relative importance of these different melting sources was very different from what they had imagined.
A study led by Tulane University and published in Nature Geoscience reveals that North American ice sheets played a much greater role than expected in global sea level rise approximately 8,000 to 9,000 years ago. These ice masses that covered most of Canada alone would have caused a sea level rise of more than 10 meters (33 feet), a contribution that far exceeds that of Antarctica during the same period. This discovery challenges decades of research that attributed a predominant role to Antarctic ice.
Pixabay illustration image
The reconstruction of these ancient events was made possible by a chance discovery in the Mississippi Delta, where deeply buried ancient marsh sediments were preserved. Carbon-14 dating of these samples allowed researchers to trace sea level evolution over more than 10,000 years. By combining this data with records from Europe and Southeast Asia, the team was able to establish global comparisons that revealed striking differences in sea level rise rates.
This massive melting of North American ice released enormous quantities of fresh water into the North Atlantic Ocean, a particularly sensitive region of the global climate system. This freshwater input could have affected ocean currents like the Gulf Stream, which plays a crucial role in regulating European climate. Yet, the data suggests that this system showed surprising resilience in the face of these drastic changes.
The researchers emphasize that this study demonstrates the importance of adopting a truly global perspective in climate studies. By expanding their field of investigation beyond North America and Europe to include quality data from Southeast Asia, they were able to obtain a more complete picture of the mechanisms that govern our climate system and its evolution over millennia.
The Gulf Stream and its climate sensitivity
The Gulf Stream is a major ocean current that transports warm water from the tropics to the North Atlantic, contributing to the temperate climate of Northwestern Europe. This current is part of a larger system called thermohaline circulation, which functions like a massive ocean conveyor belt.
This circulation depends on water density differences: the cold, salty waters of the North Atlantic sink to the depths, creating a pull that maintains the current. The massive arrival of less dense fresh water can slow or even interrupt this sinking process.
Historically, significant freshwater inflows have already disrupted this circulation, such as during past climate events that caused rapid cooling in Europe. These episodes show the potential fragility of this system in the face of environmental changes.
The resilience observed in this study shows that ocean circulation possesses unexpected regulatory mechanisms.