Azolla event

When Azolla event a proliferation of Süßwasserfarns Azolla in the Arctic Ocean during the middle Eocene, 49 million years ago is called. The plants declined after its death on the seabed of the then stagnant water and were deposited on the sea floor. It is believed that the resulting withdrawal of carbon dioxide led to to convert the Planet Earth from the former warm period in the still existing ice age.

Geological evidence for the event

In sediment layers that extend across the Arctic Basin, at least 8 m thick section can be seen in the siliceous, clastic layers alternating with millimeter- thick layers of fossilized material derived from Azolla. The siliceous layers provide the usual marine deposits at Hintergrundsedimentation by plankton, with organic material can also be detected in the form of a gamma-ray peak of activity, which could be observed in the entire Arctic basin. By measuring the gamma radiation can be compared with cores that are obtained at different locations.

By palynological tests and calibrations by means of high-resolution data on the geomagnetic field Umpolungsereignisse the duration of the event to 800,000 years was estimated. The event coincides exactly with a catastrophic drop in atmospheric carbon dioxide levels, which fell from 3500 ppm to 650 ppm in the early Eocene during the event.

Azolla

Azolla was classified as a "super plant" because it can bind a ton of nitrogen per acre per year ( 0.25 kg ∙ m ⁻ ² ∙ a ⁻ ¹ ); in parallel, it removes 6 tons per acre (1.5 kg ∙ m ⁻ ² ⁻ ¹ ∙ a ) carbon. Azollas ability to use atmospheric nitrogen for their metabolism, it means that its growth is limited mainly by the availability of phosphorus: carbon, nitrogen and sulfur are essential for protein synthesis, phosphorus is required for DNA, RNA and energy metabolism. The plant can grow rapidly under favorable conditions - even heat, and 20 hours of sunshine duration were present at the poles in the early Eocene - and double their biomass in such a climate, within two to three days.

The event favoring conditions

Because of the arrangement of the continents during the Eocene, the Arctic Ocean was almost completely isolated from the larger oceans. A mixing, as it takes place as the Gulf Stream by deep currents today, there was not so. This necessitated a stratified water column, similar to the modern Black Sea. High temperatures and winds led to excessive evaporation, which increased the density of the ocean. Through increased rains came through the leading- there flows to increased deposits in the Arctic Basin. Fresh water, which has a lower density, formed a floating on the dense seawater nepheloide layer. A only a few centimeters thick freshwater layer would have been sufficient for a settlement by Azolla; In addition, the river water was probably rich in minerals such as phosphorus. They came from mud and rocks with which the river water had interacted. The growth of the plant was also favored by high concentrations of carbon dioxide and freely available nitrogen. It is known that the atmospheric concentration of these elements at that time was high. The Blühereignisse alone are not sufficient to explain some geological influence; to sustainably withdraw the carbon dioxide cycle and thus trigger a climate change, the plants must be covered with sediments and ultimately petrifying.

Global Effects

In the course of 800,000 years, recurrent flowering periods in a 4 million square kilometers large basins were more than adequate to sufficiently buried on the deposition of plant material carbon to thereby alone the observed 80 % to explain cent drop in carbon dioxide concentration, even at a conservative estimate; it probably also other factors played a role. The concentration of waste managed the transition from former greenhouse climate in the still ongoing ice age; the Arctic cooled by an average temperature of 13 ° C from the existing temperature of -9 ° C today. ; the other regions of the world were subject to similar changes. For perhaps the first time in the history of the earth, the earth was covered with ice at both poles. A geological standards faster temperature decrease in the time before 49 and 47 million years ago, at the time of Azolla event, has been proven: Drop Stones - which are considered as evidence for the existence of glaciers - are younger in Arctic sediments widespread nowadays. This happened against the backdrop of a slow long-term cooling: By the time million 15 years ago, there is no evidence of a vast polar ice.

Alternative explanations

While a ergrünter Arctic Ocean is a viable working hypothesis suggests skeptical scientists to the possibility that Azolla colonies may have been washed in river deltas or freshwater lagoons by strong currents in the Arctic Ocean, which makes floating on the ocean freshwater layer unnecessary.

Economic considerations

Azolla deposits are currently the subject of great interest in the search for oil in Arctic regions. The deposition of large amounts of organic material provides the bedrock for petroleum dar. At a temperature corresponding to the trapped Azolla deposits may have been converted to oil or gas. In the Netherlands, a research center was set up, whose focus is the study of the Azolla event.