When the Earth climate changed radically a million years ago
A million years ago, the Earthʼs climate was brutally altered due unknown causes. The continental ice masses accumulated in polar regions, glacial cycles became longer and colder -the most intense ones in the history of the Quaternary-, and as a result, the global climate system was fully altered.
A million years ago, the Earthʼs climate was brutally altered due unknown causes. The continental ice masses accumulated in polar regions, glacial cycles became longer and colder -the most intense ones in the history of the Quaternary-, and as a result, the global climate system was fully altered.
A change in the intensity of the global ocean circulation could be the reason of this climate alteration -the mid-Pleistocene transition (MPT),- which unchained a series of extreme glaciations about a million years ago. This is stated in the study published in the journal Nature Geoscience, which counts on the participation of the experts Leopoldo Pena and Maria Jaume-Seguí, from the Consolidated Research Group (GRC) on Marine Geosciences, from the Faculty of Earth Sciences of the University of Barcelona.
The study, led by the expert Jesse Farmer, from the Lamont-Doherty Earth Observatory (Columbia University, USA), counts on the participation of the teams from the University of Edinburgh (Scotland), the University of London (United Kingdom), Princeton University (United States), and the Max Planck Institute (Germany).
When the climate changed radically a million years ago
The real nature of the mechanisms that changed the climate of the planet during that certain period has been a topic of debate in the international scientific community for decades. According to the study of the journal Nature Geoscience, a brutal decrease of the intensity of deep ocean circulation or thermohaline 950,000 years ago -a documented phenomenon by the oceanographers Leopoldo Pena and Steven Goldstein (Science, 2014)- promoted the storage of atmospheric carbon dioxide (CO2) in the ocean at a planet scale.
A result of this deceleration of the global ocean circulation, “a part of this CO2 was trapped in the ocean and it could have contributed to a dramatic climate change in the planet system”, note researchers Leopoldo Pena and Maria Jaume-Seguí, members from the Department of Earth and Ocean Dynamics of the UB.
The authors of the new study estimated that over the most extreme stages of this climate transition, the deep Atlantic Ocean could had stored about 50,000 million tons of additional carbon, compared to the less intense glacial cycles that occurred prior the million years.
With these large amounts of carbon in the depths of the ocean, the level of carbon dioxide declined in the atmosphere, global temperatures became colder and the ice caps expanded around the planet during this particular period of the Quaternary.
“The deep ocean has played and acts like a CO2 storage. When this gas accumulates during hundreds or thousands of years in the depths of the ocean, there is a CO2 decline in the atmosphere which has global climate consequences. However, the opposite mechanism can also occur”, warns Leopoldo Pena.
Foraminifera: fossils reconstructing the climate history of the oceans
In the ocean depths, marine sediments keep the climate records of this exceptional period which meant an inflection point in the Earthʼs climate. As part of this study, the experts analyzed the isotopic composition of the fossil remains of planktonic and benthic fosaminifera, unicellular organisms able to create a mineral shell of calcic carbon.
The study of these protozoans, which prevail in the fossil records of ocean sediments, is determining to know the features of the climate and the marine ecosystems of the past.
Climate change: from the planetʼs past to its future
Understanding the nature of climate changes in the past is essential to improve the predictions on the evolution of the climate in the future. Now, some of the big challenges in paleoclimatology and paleoceanography are about knowing and getting an insight of the mechanisms of the CO2 emissions in ocean ecosystems, identifying and determining the dimension of these reservoirs and knowing its response to changes in oceanic circulation.
The new study of the journal Nature Geoscience describes some of the climate mechanisms that contributed to the mid-Pleistocene transition, and provides new perspectives to create more precise and reliable future climate predictions. According to the experts, it will be necessary to find out many enigmas on the changes in the deep ocean circulation that marked this period.
“The Earthʼs climate system, as we know it, is not stuck. Our study shows there are mechanisms that control the climate of our planet, which we do not fully understand”, says Leopoldo Pena. “About a million years ago -he continues-, many elements of the Earthʼs climate system acted together to boost the global climate towards a state of extreme and lasting glaciations. Now, the rise of atmospheric concentrations of carbon dioxide by humans could lead the climate system towards a totally different state”.
At the moment, there is evidence of the ocean circulation going slower by 15 % since the mid-20th Century in the Atlantic Ocean. Apart from the causes that can provoke this phenomenon, “it is important not to point out simple parallelisms: we could be tempted to say that if we do not slow circulation, the atmosphere CO2 could decrease, and that would be a serious mistake”, warns Leopoldo Pena. “In this case, -he continues- the surface waters rich in CO2 would not be transported to the deep ocean, while in other regions such as the Antarctic, deep waters rich in CO2 would still reach the surface, and as a result, the atmospheric CO2 would increase”.