Published in Nature Communications, The work resolves a paradox of Milanković’s theory and could enable more accurate predictions of future climate
Gianluca Marino, a researcher at the Marine Research Centre of the University of Vigo (CIM), is part of an international team of scientists who have discovered that a prolonged warm period in the North Atlantic caused the melting of Greenland, raising sea levels more than ten meters above the present level around 400,000 years ago. The study, published in the journal Nature Communications, resolves one of the enigmas of the ice age cycles of the last million years.
As early as the first half of the 20th century, Serbian mathematician Milutin Milanković postulated a theory to explain these cycles. He argued that they result from long-term changes in the solar radiation received during summer. Stronger summer solar radiation melts the large ice sheets formed in North America and Eurasia during a glacial period, causing warm climates similar to the present, where ice is only found in Greenland and Antarctica. But 400,000 years ago, most of Greenland’s ice had disappeared despite weak summer solar radiation, puzzling the scientific community and seemingly refuting Milanković’s theory.
Regarding this, the CIM researcher highlighted, “Understanding the causes of the warm interval that occurred 400,000 years ago, known as Marine Isotope Stage 11, is key to understanding the cycles of ice ages.” He added, “During Marine Isotope Stage 11, Milanković’s theory, in its strictest formulation, fails to explain why the climate warmed so much and Greenland’s ice almost completely disappeared when the solar radiation was so weak.”
International Collaboration
The scientific team, including Gianluca Marino, comprised top academic institutions from Asia, Europe, and Australia and was led by Dr. Hsun-Ming Hu, a postdoctoral researcher in Professor River Shen’s group at the National Taiwan University. They specialize in an analytical technique that dates paleoclimate records with unparalleled precision up to 600,000 years. They applied this technique to cave carbonates, known as speleothems, from northwest Italy, and found that the mid-latitudes warmed, albeit moderately, long before 400,000 years ago and transported heat to Greenland for 15,000 years through a system of ocean currents known as the Atlantic Meridional Overturning Circulation. This current system includes a warm water flow that transfers heat to high latitudes in the North Atlantic and operates today, keeping western Iberia and Galicia warmer than expected for their latitudes.
Gianluca Marino commented, “In this study, we found that the heat transport to the high latitudes of the North Atlantic by ocean currents maintained warm temperatures, slowly destabilizing Greenland’s ice sheet until it almost disappeared. This mechanism had been overlooked until now.”
The scientist explained that “it all started when the lead author, Dr. Hsun-Ming Hu, then a doctoral student in the Department of Earth Sciences at the National Taiwan University under the direction of Professor Chuan-Chou Shen, contacted me because he knew my work and wanted to use some statistical and interpretive methods used in the Palaeoclimatology Lab at CIM in his project focused on speleothems from the Bàsura cave in Liguria, northern Italy.”
Specifically, Gianluca Marino contributed his knowledge on the role of the ocean in (paleo) climate change and collaborated with Hsun-Ming Hu to decipher the sequence of events that melted Greenland’s ice 400,000 years ago. The CIM researcher clarified, “I mainly contributed a quantitative analysis of the data and shared the knowledge gained about ice age cycles from previous projects. The quantitative analysis of the data, along with cutting-edge analytical techniques, are key aspects of the work.”
An Advance for Predicting Future Climate
“The climate around 400,000 years ago was quite similar to our pre-industrial climate. Therefore, the near-complete melting of Greenland’s ice sheet that occurred then could definitely happen again,” affirmed Gianluca Marino. In this regard, the scientist emphasized, “This interval is crucial for the climate community for that reason. However, there is one aspect I consider even more relevant and that should interest the climate modeling community. If they manage to simulate the total melting of Greenland, including all the conditions and processes we highlighted in our study, then we can have greater confidence in how these same models predict the future climate.”
Gianluca Marino aims to continue the work done. “The idea is to closely examine these prominent episodes of climate change with the same level of detail, or even better, than achieved in this study. This will allow us to decipher the processes that control ice age cycles, as well as the role of solar radiation, ocean circulation, and the carbon cycle.”
The scientist emphasized, “We hope the modeling community begins to incorporate the mechanism we documented in our study into their climate models to investigate the causes of ice ages.”
The research activity of the CIM is co-financed by the Xunta de Galicia and the European Union, through the European Funds (FEDER).
