Azolla event

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The recent swimming fern Azolla filiculoides . The mass multiplication of related organisms could have ushered in the transition to the current Ice Age.

The Azolla event describes a mass reproduction of the freshwater fern Azolla in the Arctic Ocean over several hundred thousand years during the Lower Eocene , 49 million years ago. The plants were after her death at the bottom of the surface then heavily sweetened deposited body of water and then sedimented . There are a number of indications that the resulting withdrawal of atmospheric carbon dioxide made a significant contribution to gradually transferring planet Earth from the warm climate prevailing at the time to the ice age that still exists today .

Geological evidence for the event

History of Delta O-18 over the past 65 million years. The Azolla event marks the end of the Eocene Optimum and the beginning of a slow temperature decline.

In the stratifications at the bottom of the 4 million km² arctic basin, a section of at least 8 meters in thickness can be seen in which pebbly, clastic sediments alternate with millimeter-thick layers of petrified material that comes from Azolla . The silica-containing layers represent the background sedimentation caused by plankton , which is common in maritime deposits . The organic material can also be detected in the form of a gamma-ray activity peak that occurs in the entire arctic basin. With the metrological evidence of traces of this gamma radiation, drill cores can be compared that were obtained at different locations.

By palynological tests and calibrations using high-resolution data on Umpolungsereignisse the geomagnetic field , the duration of the event to about 800,000 years was limited. This led to a slow but steady and considerable decrease in the atmospheric carbon dioxide content and thus to a significant global cooling.

Properties of Azolla

The algae fern Azolla , which belongs to the swimming fern family, is considered a “super plant” because it can bind one ton of nitrogen per acre per year (0.25 kg ∙ m⁻² ∙ a⁻¹); At the same time, it removes 6 tons (1.5 kg ∙ m⁻² ∙ a⁻¹) of carbon per acre . Azolla's ability to incorporate atmospheric nitrogen into metabolism means that its growth depends primarily on the availability of phosphorus : carbon, nitrogen, and sulfur are essential for protein synthesis, and phosphorus is used for DNA (deoxyribonucleic acid) , RNA (ribonucleic acid), and in energy metabolism needed. The floating plant can grow very quickly under favorable conditions - moderate warmth and 20 hours of sunshine were present at the poles 49 million years ago in the course of the season - and under optimal climatic conditions, their biomass can double within two to three days.

The framework

Due to the arrangement of the continents during the Eocene, the Arctic Ocean was almost completely isolated from the world's oceans. Mixing, as is currently the case with deep currents such as the Gulf Stream, therefore did not take place. This resulted in a stratified water column, similar to today's Black Sea . Winds and relatively high temperatures in the range of 10 to 14 ° C resulted in high levels of evaporation, which increased the density of the ocean. Due to the presumably very intensive rainfall in the north polar region, the rivers flowing into the area led to increased flooding into the Arctic basin. The lower density fresh water formed a nepheloid layer floating on the sea surface. Investigations showed that a freshwater layer only a few centimeters thick was sufficient for Azolla to colonize it . In addition, there is a high probability that the rivers transported minerals such as phosphorus dissolved from the soil as nutrients into the ocean. Azolla's growth was also promoted by freely available nitrogen and high levels of carbon dioxide.

The flowering events alone would not have been significant for a significant climatic effect. In order to permanently and in large quantities withdraw carbon dioxide from the natural cycle and thus initiate climate change, the dead plant parts first had to be covered with sediments and then petrified.

Climate development after the Azolla event

Arathem system series Age
( mya )
K
ä
n
o
z
o
i
k
u
m 		quaternary Holocene 0
⬍
0.0117
Pleistocene 0.0117
⬍
2,588
Neogene Pliocene 2,588
⬍
5.333
Miocene 5.333
⬍
23.03
Paleogene Oligocene 23.03
⬍
33.9
Eocene 33.9
⬍
56
Paleocene 56
⬍
66
earlier earlier earlier

In the specialist literature of the last few decades there is a series of strongly diverging information on the carbon dioxide content during the Eocene optimum climate - i.e. for the time before the Azolla event . A study published in 2016, based on a newly developed precision measurement including the stable boron isotope δ 11 B (Delta-B-11), comes to the result of a probable CO 2 level of 1,400 ppm. This value decreased in the following millions of years up to the beginning of the Oligocene by about 50 percent, with the first significant decrease occurring immediately after the numerous Azolla blooming periods in the Arctic basin.

At about the same time, the main phase of the collision of the Indian continental plate with the Eurasian plate, which was initially accompanied by violent flood basalt volcanism , ended . In the course of the unfolding of the Himalayas into high mountains, erosion and weathering processes and the associated CO 2 reduction became a climatic factor that further intensified the cooling process that began.

Nevertheless, there was still a pronounced warm climate over large parts of the Eocene. With the increase in the meridional temperature gradient (the temperature difference between the equator and the polar regions), significant climate changes were initially limited to the higher latitudes. For the Antarctic, a stronger cooling phase is documented 41 million years ago, and in the arctic regions finds of dropstones indicate the intermittent existence of continental ice 38 to 30 million years ago. A sharp climatic change occurred at the Eocene-Oligocene transition 33.9 to 33.7 million years ago with the beginning of the Cenozoic Ice Age . During this period there was another rapid drop in the atmospheric CO 2 concentration, combined with global cooling, including the oceans, and the almost simultaneous formation of the Antarctic ice sheet .

In the further course of the Oligocene and especially during the Miocene , the CO 2 concentration and the global climate were subject to relatively strong fluctuations. At the height of the Miocene climatic optimum (17 to 15 mya) the atmospheric carbon dioxide content rose briefly from 350 ppm at the beginning of the Miocene to 500 to 600 ppm. At the same time, the Antarctic glaciers of that time lost part of their mass, but the core areas of the East Antarctic Ice Sheet were apparently not affected. Under the influence of strong erosion and weathering processes, the CO 2 concentration fell again to around 400 ppm towards the end of the optimum 14.8 million years ago, coupled with a renewed increase in inland Antarctic freezing. Nevertheless, 14 to 12.8 million years ago, temperatures in this region were 25 to 30 ° C above current levels.

The Quaternary Cold Age periods as a subsection of the Cenozoic Ice Age began around 2.7 million years ago with extensive glaciations in the northern hemisphere and were often associated with the closure of the Isthmus of Panama . In the meantime, however, the scientific community is of the opinion that the increasing arctic glaciation is associated with a significant decrease in the global CO 2 concentration, which means that the summer months in particular are cooler. Some studies state a first cooling phase in the late Pliocene (3.2 mya) and a second after the beginning of the Pleistocene (2.4 mya), during which the CO 2 content fell from originally 375 to 425 ppm to 275 to 300 ppm, with a further decrease during the subsequent cold-time cycles. Probably for the first time during the 541 million year Phanerozoic Era , both poles were covered by ice.

Different scenarios

Although the assumption of a “greened” inland sea is a viable working hypothesis, it was also pointed out that Azolla colonies in river deltas or freshwater lagoons could have entered the Arctic Ocean through strong currents, which would make a freshwater layer floating on the surface superfluous.

In contrast, a study published in 2017 postulated that the Arctic Ocean in the period 56 to 36 million years ago had considerably more extensive freshwater areas than originally assumed due to its almost complete isolation. It was only after a transition phase of 4 to 5 million years as a brackish water lagoon that the Arctic Ocean was connected to the global ocean circulation in the early Oligocene (≈32 mya) with the influx of salty North Atlantic water .

Economic Perspectives

Azolla deposits are currently the subject of great interest in exploring for oil in arctic regions. The deposit of large amounts of organic matter is the bedrock for petroleum. At a suitable temperature, the enclosed Azolla deposits could have been converted into oil or gas. A research center has been set up in the Netherlands with a focus on studying the Azolla event.

See also

Individual evidence

  1. ↑ a b c Henk Brinkhuis, Stefan Schouten, Margaret E. Collinson, Appy Sluijs, Jaap S. Sinninghe Damsté, Gerald R. Dickens, Matthew Huber, Thomas M. Cronin, Jonaotaro Onodera, Kozo Takahashi, Jonathan P. Bujak, Ruediger Stein , Johan van der Burgh, James S. Eldrett, Ian C. Harding, André F. Lotter, Francesca Sangiorgi, Han van Konijnenburg-van Cittert, Jan W. de Leeuw, Jens Matthiessen, Jan Backman, Kathryn Moran: Episodic fresh surface waters in the Eocene Arctic Ocean . (PDF) In: Nature . 441, 2006, pp. 606-609. doi : 10.1038 / nature04692 . Retrieved May 25, 2017.
  2. ^ LM Waddell, TC Moore: Salinity of the Early and Middle Eocene Arctic Ocean From Oxygen Isotope Analysis of Fish Bone Carbonate . In: American Geophysical Union, Fall Meeting 2006, abstract # OS53B-1097 . 2006. Retrieved May 9, 2018.
  3. ↑ a b c Eleni Anagnostou, Eleanor H. John, Kirsty M. Edgar, Gavin L. Foster, Andy Ridgwell, Gordon N. Inglis, Richard D. Pancost, Daniel J. Lunt, Paul N. Pearson: Changing atmospheric CO 2 concentration was the primary driver of early Cenozoic climate . In: Nature . 533, May 2016, pp. 380-384. doi : 10.1038 / nature17423 .
  4. ↑ Belnap, J .: Nitrogen fixation in biological soil crusts from southeast Utah, USA . (PDF) In: Biology and Fertility of Soils . 35, No. 2, 2002, pp. 128-135. doi : 10.1007 / s00374-002-0452-x . Retrieved October 17, 2007.
  5. ↑ Stein, R .: The Paleocene-Eocene ("Greenhouse") Arctic Ocean paleoenvironment: Implications from organic-carbon and biomarker records (IODP-ACEX Expedition 302) . (abstract) In: Geophysical Research Abstracts . 8, 2006, p. 06718. Retrieved October 16, 2007.
  6. ↑ David R. Greenwood, James F. Basinger, Robin Y. Smith: How wet was the Arctic Eocene rainforest? Estimates of precipitation from Paleogene Arctic macrofloras . In: Geology . 38, No. 1, January 2010, pp. 15-18. doi : 10.1130 / G30218.1 .
  7. ^ Jan Backman, Kathryn Moran: Expanding the Cenozoic paleoceanographic record in the Central Arctic Ocean: IODP Expedition 302 . (PDF) In: Central European Journal of Geosciences . 1 (2), 2009, pp. 157-175. doi : 10.2478 / v10085-009-0015 .
  8. ^ Dennis V. Kent, Giovanni Muttoni: Equatorial convergence of India and Early Cenozoic climate trends . In: PNAS . 105, No. 42, October 2008, pp. 16065-16070. doi : 10.1073 / pnas.0805382105 .
  9. ↑ Linda C. Ivany, Kyger C. Lohmann, Franciszek Hasiuk, Daniel B. Blake, Alexander Glass, Richard B. Aronson, Ryan M. Moody: Eocene climate record of a high southern latitude continental shelf: Seymour Island, Antarctica . (PDF) In: The Geological Society of America (GSA) Bulletin . 120, No. 5/6, pp. 659-678. doi : 10.1130 / B26269.1 .
  10. ↑ James S. Eldrett, Ian C. Harding, Paul A. Wilson, Emily Butler, Andrew P. Roberts: Continental ice in Greenland during the Eocene and Oligocene . (PDF) In: Nature . 446, March 2007, pp. 176-179. doi : 10.1038 / nature05591 .
  11. ↑ Mark Pagani, Matthew Huber, Zhonghui Liu, Steven M. Bohaty, Jorijntje Henderiks, Willem Sijp, Srinath Krishnan, Robert M. DeConton: The Role of Carbon Dioxide During the Onset of Antarctic Glaciation . (PDF) In: Science . 334, No. 6060, December 2011, pp. 1261-1264. doi : 10.1126 / science.1203909 .
  12. ↑ Wolfram M. Kürschner, Zlatko Kvaček, David L. Dilcher: The impact of Miocene atmospheric carbon dioxide fluctuations on climate and the evolution of terrestrial ecosystems . In: pnas . 105, No. 2, 2007, pp. 449-453. doi : 10.1073 / pnas.0708588105 .
  13. ^ AR Lewis, DR Marchant, AC Ashworth, SR Hemming, ML Machlus: Major middle Miocene global climate change: Evidence from East Antarctica and the Transantarctic Mountains . (PDF) In: Geological Society of America Bulletin . 119, No. 11/12, pp. 1449-1461. doi : 10.1130 / 0016-7606 (2007) 119 [1449: MMMGCC] 2.0.CO; 2 .
  14. ↑ Aaron O'Dea, Harilaos A. Lessios, Anthony G. Coates, Ron I. Eytan, Sergio A. Restrepo-Moreno, Alberto L. Cione, Laurel S. Collins, Alan de Queiroz, David W. Farris, Richard D. Norris, Robert F. Stallard, Michael O. Woodburne, Orangel Aguilera, Marie-Pierre Aubry, William A. Berggren, Ann F. Budd, Mario A. Cozzuol, Simon E. Coppard, Herman Duque-Caro, Seth Finnegan, Germán M . Gasparini, Ethan L. Grossman, Kenneth G. Johnson, Lloyd D. Keigwin, Nancy Knowlton, Egbert G. Leigh, Jill S. Leonard-Pingel, Peter B. Marko, Nicholas D. Pyenson, Paola G. Rachello-Dolmen, Esteban Soibelzon, Leopoldo Soibelzon, Jonathan A. Todd, Geerat J. Vermeij, Jeremy BC Jackson: Formation of the Isthmus of Panama . In: Science Advances . 2, No. 8, August 2016. doi : 10.1126 / sciadv.1600883 .
  15. ↑ KT Lawrence, S. Sosdian, HE White, Y. Rosenthal: North Atlantic climate evolution through the Pliocene-Pleistocene climate transitions . (PDF) In: Earth and Planetary Science Letters . 300, No. 3-4, December 2010, pp. 329-342. doi : 10.1016 / j.epsl.2010.10.013 .
  16. ^ Matteo Willeit, Andrey Ganopolski, Reinhard Calov, Alexander Robinson, Mark Maslin: The role of CO 2 decline for the onset of Northern Hemisphere glaciation . (PDF) In: Quaternary Science Reviews . 119, July 2015, pp. 22–34. doi : 10.1016 / j.quascirev.2015.04.015 .
  17. ^ Tim Appenzeller: Great green north . In: National Geographic . May 2005.
  18. ↑ Michael Starkz, Wilfried Jokat, Gregor Knorr, Gerrit Lohmann: Threshold in North Atlantic-Arctic Ocean circulation controlled by the subsidence of the Greenland-Scotland Ridge . In: Nature Communications (online) . June 8, 2017. doi : 10.1038 / ncomms15681 .
  19. ^ Andrew C. Revkin: Under all that ice, maybe oil . In: New York Times , November 20, 2004. Retrieved October 17, 2007. 
  20. ^ The Azolla Research Team