The causes and consequences of global climate warming that took place 56 million years ago studied

This image shows continental sediments in the Esplugafreda ravine, a small tributary of the Noguera Ribagorzana river, in the extreme west of the province of Lleida and close to the village of Aren (Huesca). -  UPV/EHU-University of the Basque Country
This image shows continental sediments in the Esplugafreda ravine, a small tributary of the Noguera Ribagorzana river, in the extreme west of the province of Lleida and close to the village of Aren (Huesca). – UPV/EHU-University of the Basque Country

The growing and justified concern about the current global warming process has kindled the interest of the scientific community in geological records as an archive of crucial information to understand the physical and ecological effects of ancient climate changes. A study by the UPV/EHU’s Palaeogene Study Group deals with the behaviour of the sea level during the Palaeocene-Eocene Thermal Maximum (PETM) 56 million years ago and has ruled out any connection. The study has been published in the journal Palaeogeography, Palaeoclimatology, Palaeoecology.

“The fall in sea level did not unleash the emission of greenhouse gases during the Palaeocene-Eocene Thermal Maximum (PETM),” pointed out Victoriano Pujalte, lecturer in the UPV/EHU’s Department of Stratigraphy and Palaeontology, and lead researcher of the study.

The Palaeocene-Eocene Thermal Maximum (PETM) was a brief interval (in geological terms, it “only” lasted about 200,000 years) of extremely high temperatures that took place 56 million years ago as a result of a massive emission of greenhouse gases into the atmosphere. The global temperature increase is reckoned to have been between 5º C and 9º C. It was recorded in geological successions worldwide and was responsible for a great ecological impact: the most striking from an anthropological point of view was its impact on mammals, but it also affected other organisms, including foraminifera and nannofossils (marine microorganisms that are at the base of the trophic chain) and plants.

However, what actually caused this warming remains a controversial issue. The most widely accepted hypothesis suggests that it was due to the destabilising of methane hydrates that remained frozen on ocean floors. “Some authors, like Higgins and Schrag (2006), for example, proposed that a fall in sea level could have caused or co-contributed towards the unleashing of the emission of methane or CO2,” pointed out Victoriano Pujalte, lecturer in the UPV/EHU’s Department of Stratigraphy and Palaeontology, and lead researcher in the study. According to this hypothesis, “the marine sediments that were submerged in the sea were exposed when the sea level fell, and were responsible for the CO2 emissions,” he added. That is what, to a certain extent, prompted this study. Others not only reject that possibility but also the fall in sea level itself. “We set out to try and establish the behaviour of the sea level during that time interval, the PETM,” said Pujalte.

There is no cause-effect relationship

The studies were carried out mainly in the Pyrenees between Huesca and Lérida, specifically in the Tremp-Graus Basin, and also in Zumaia (Gipuzkoa, Basque Country). The Palaeocene-Eocene rocks have outcropped extensively in both areas, in other words, exposed on the surface, and they represent a whole range of ancient atmospheres, both continental and marine. “They provide a unique opportunity to explore the effects of changes in sea level and to analyse their effects,” added Pujalte.

The most useful indicators are the stable oxygen and carbon isotopes. The oxygen ones provide information on palaeotemperatures, but any sign of them can only be retrieved in deep-sea sample cores. The carbon isotopes provide data on variations in CO2 content in the atmosphere and in the oceans, and they can also be retrieved in ancient rocks that have outcropped in above-ground plots of land. In general, the variations of both isotopes run parallel, given that an increase in the proportion of CO2 is coupled with an increase in temperature.

The results obtained indicate that the PETM was in fact preceded by a fall in sea level, the size of which is estimated to have been about 20 metres and the maximum descent of which probably occurred about 75 million years before the start of the PETM. “However, it is doubtful that the descent was the cause of the PETM, although it could have contributed towards it,” pointed out Victoriano Pujalte. “They occurred at the same time, but there is no cause-effect relationship.”

Furthermore, the researchers observed that the rise in the sea level continued after the PETM, when the global temperature returned to normal levels. “Its origin was not only caused, therefore, by the thermal expansion of the oceans linked to the warming,” said Pujalte. “It is suggested that the most likely cause of it was the volcanic activity documented in the North Sea during the end of the Palaeocene and start of the Eocene; this activity was related to the expansion of the oceanic ridge in the North Atlantic,” he concluded.

The causes and consequences of global climate warming that took place 56 million years ago studied

This image shows continental sediments in the Esplugafreda ravine, a small tributary of the Noguera Ribagorzana river, in the extreme west of the province of Lleida and close to the village of Aren (Huesca). -  UPV/EHU-University of the Basque Country
This image shows continental sediments in the Esplugafreda ravine, a small tributary of the Noguera Ribagorzana river, in the extreme west of the province of Lleida and close to the village of Aren (Huesca). – UPV/EHU-University of the Basque Country

The growing and justified concern about the current global warming process has kindled the interest of the scientific community in geological records as an archive of crucial information to understand the physical and ecological effects of ancient climate changes. A study by the UPV/EHU’s Palaeogene Study Group deals with the behaviour of the sea level during the Palaeocene-Eocene Thermal Maximum (PETM) 56 million years ago and has ruled out any connection. The study has been published in the journal Palaeogeography, Palaeoclimatology, Palaeoecology.

“The fall in sea level did not unleash the emission of greenhouse gases during the Palaeocene-Eocene Thermal Maximum (PETM),” pointed out Victoriano Pujalte, lecturer in the UPV/EHU’s Department of Stratigraphy and Palaeontology, and lead researcher of the study.

The Palaeocene-Eocene Thermal Maximum (PETM) was a brief interval (in geological terms, it “only” lasted about 200,000 years) of extremely high temperatures that took place 56 million years ago as a result of a massive emission of greenhouse gases into the atmosphere. The global temperature increase is reckoned to have been between 5º C and 9º C. It was recorded in geological successions worldwide and was responsible for a great ecological impact: the most striking from an anthropological point of view was its impact on mammals, but it also affected other organisms, including foraminifera and nannofossils (marine microorganisms that are at the base of the trophic chain) and plants.

However, what actually caused this warming remains a controversial issue. The most widely accepted hypothesis suggests that it was due to the destabilising of methane hydrates that remained frozen on ocean floors. “Some authors, like Higgins and Schrag (2006), for example, proposed that a fall in sea level could have caused or co-contributed towards the unleashing of the emission of methane or CO2,” pointed out Victoriano Pujalte, lecturer in the UPV/EHU’s Department of Stratigraphy and Palaeontology, and lead researcher in the study. According to this hypothesis, “the marine sediments that were submerged in the sea were exposed when the sea level fell, and were responsible for the CO2 emissions,” he added. That is what, to a certain extent, prompted this study. Others not only reject that possibility but also the fall in sea level itself. “We set out to try and establish the behaviour of the sea level during that time interval, the PETM,” said Pujalte.

There is no cause-effect relationship

The studies were carried out mainly in the Pyrenees between Huesca and Lérida, specifically in the Tremp-Graus Basin, and also in Zumaia (Gipuzkoa, Basque Country). The Palaeocene-Eocene rocks have outcropped extensively in both areas, in other words, exposed on the surface, and they represent a whole range of ancient atmospheres, both continental and marine. “They provide a unique opportunity to explore the effects of changes in sea level and to analyse their effects,” added Pujalte.

The most useful indicators are the stable oxygen and carbon isotopes. The oxygen ones provide information on palaeotemperatures, but any sign of them can only be retrieved in deep-sea sample cores. The carbon isotopes provide data on variations in CO2 content in the atmosphere and in the oceans, and they can also be retrieved in ancient rocks that have outcropped in above-ground plots of land. In general, the variations of both isotopes run parallel, given that an increase in the proportion of CO2 is coupled with an increase in temperature.

The results obtained indicate that the PETM was in fact preceded by a fall in sea level, the size of which is estimated to have been about 20 metres and the maximum descent of which probably occurred about 75 million years before the start of the PETM. “However, it is doubtful that the descent was the cause of the PETM, although it could have contributed towards it,” pointed out Victoriano Pujalte. “They occurred at the same time, but there is no cause-effect relationship.”

Furthermore, the researchers observed that the rise in the sea level continued after the PETM, when the global temperature returned to normal levels. “Its origin was not only caused, therefore, by the thermal expansion of the oceans linked to the warming,” said Pujalte. “It is suggested that the most likely cause of it was the volcanic activity documented in the North Sea during the end of the Palaeocene and start of the Eocene; this activity was related to the expansion of the oceanic ridge in the North Atlantic,” he concluded.

A new science project on the historical and natural heritage of the Pyrenees

Six Spanish and French institutions are working jointly to put into action “The Origins Route”, a scientific dissemination project to develop a quality sustainable model for tourism in the Pyrenees. Participating is also the Centre for the Studies of Archaeological and Prehistoric Heritage (CEPAP) of Universitat Autònoma de Barcelona (UAB). The initiative comprises a set of activities to inform society about the origins of the Pyrenees in fields related to astronomy, geology, palaeontology and human evolution.

In the next three years, the project will be promoting an innovative and experimental model of tourism, respectful with the environment and at the same time valuing the natural and historical heritage and related scientific knowledge.

To do so participating institutions will create permanent science-tourism cooperation structures. In addition to UAB, taking part in the project are two institutions from La Noguera County, the Montsec Consortium and La Noguera Historical Heritage Research and Dissemination Association, and three from the French Midi-Pyrénées region: the astronomy and space centres Cité de l’Espace (Toulouse) and À Ciel Ouvert (Fleurance), and the Museum of Natural History of Toulouse.

“The Origins Route” proposes to create the basic elements needed for routes through the Pyrenees Mountains, offering visitors different itineraries to help them discover and understand many of the questions formulated today by scientists concerning both the universe and the first inhabitants of the region. Each stage of the itinerary will focus on a specific period. Thus the full route will offer a global vision of its origins, from the Big Bang to the birth of humanity. Proposed activities will allow participants to experience different situations such as palaentological or archaeological digs, skywatching or studying the mountain’s biodiversity.

The project will also include an itinerant exhibition coordinated by la Cité de l’Space which will last approximately ten years and will be on display at each of the participating institution headquarters and in different cities and towns of the region. A website will also be created to disseminate and promote information and activities carried out under the project. Users will also be able to view an online exhibition of the full itinerary.

Universitat Autònoma de Barcelona not only is taking part in these joint initiatives. It will also be in charge of the museumification of the prehistoric archaeological site Roca dels Bous, located near the town of Sant Llorenç de Montgai (La Noguera), where CEPAP researchers have been studying the origins and evolution of Neanderthals in the eastern Pyrenees. Known as ArkeoTic, this project will be the first to use innovative museographies based on information and communication technologies (ICT) to display the archaeological findings uncovered. The site and its surroundings will be prepared for visiting school groups and the public in general and will include wireless connections to complement on-site visits and interactive itineraries. The facilities will be completed by the end of this summer.

CEPAP-UAB researchers participating in the project are Rafael Mora, director of the Centre, Paloma González, Jorge Martínez, Antoni Bardavio and Mònica López. According to Rafael Mora, “we intend to show the construction of science and at the same time bring it closer to the public. By being able to see how researchers work and establishing direct contact with them we aim to foster young people’s interest in science”.

The total cost of the project is ?2,606,897. Almost two-thirds of the funding (65%) came from the Operational Programme Spain-France-Andorra 2007-2013 (POCTEFA) belonging to the European Regional Development Fund. All other funding came from participating institutions.

The POCTEFA programme, coordinated by the Pyrenees Work Community (CTP), with headquarters in Jaca, Huesca, aims to strengthen the economic and social integration of the cross-border area between Spain, Andorra and France.