Paleocene–Eocene Thermal Maximum

The Paleocene / Eocene Thermal Maximum ( PETM ) 55 million years ago was a brief period of a globally comprehensive strong warming, which was associated with an increased entry of greenhouse gases. The temperature rose during the PETM within approximately 20,000 years to 6 ° from about 18 ° C. in the late Paleocene to over 23 ° C. The annual rate of increase was during this period on average 0.0003 °.

The event is associated with a pronounced decrease in concentration of the stable carbon isotope 13C. This indicates that a large amount of 13C - depleted carbon was placed in the atmosphere and / or hydrosphere at the beginning and / or during the PETM. The authors of a published in 2013 found in the publication " Marlboro Clay " of the " Salisbury Embayment " a sedimentary sequence, which can Δ18O signature course close to a release of 3,000 gigatons of carbon in just 13 years. Along detailed environmental changes are partly well documented for low latitudes. A 2004 taken in the central Arctic sediment sample provides insights into the changing conditions in the high northern latitudes.

Geoscientists study the PETM in order to gain a better understanding of what the impact of the man currently introduced carbon dioxide probably over the course of millennia.

Temperature determination in the Arctic before the PETM

A 1970 carried out on a drifting ice island superficial bore brought from the Upper Cretaceous sediments derived from the Alpha Ridge ( submarine increase) out.

Using the verified relationship between the composition of membrane lipids of marine Crenarcheota and the annual average ocean surface temperatures ( TEX86 method), the average surface temperature in the Arctic Ocean was determined ( at about 80 ° N) at 15 ± 1 ° C for the early Maastrichtium. By comparison, the current annual mean surface air temperature at 80 ° N is about -15 ° C.

In this anyway warm earth, a temperature increase, the Paleocene / Eocene Thermal Maximum ( PETM ) superimposed. The PETM includes about 200,000 years. For low and mid latitudes ( φ <60 ° ), a temperature rise of the surface of the ocean and deep water by about 4-8 ° C and extensive changes in the terrestrial and marine biosphere are well documented.

Study of a sediment sample of the Arctic

The research mission IODP 302 ( Integrated Ocean Drilling Program Expedition ) promoted in 2004 a sediment sample from the Lomonosov Ridge in the central Arctic evident. This ridge represents a piece of the continental crust, which has split off during the Paleocene from the Eurasian continental shelf edge and dived in today's lows after the Paleocene. The sediments that are assigned to the upper Paleocene and lower Eocene, approximately 406-263 m of sediment depth are below the seafloor.

Before the PETM the subtropical dinoflagellate Apectodinium occurred only at low latitudes. The sudden appearance of this type in about 387 to 378.5 m depth of the studied sediment sample testifies to the considerable increase in the Arctic Ocean surface temperatures. The comparison of δ13C - isotope studies in the Arctic sediment sample with measurements for the PETM in other shallow-water areas based on the assumption that this interval is assigned to the PETM. The measurements with TEX86 method revealed that the ocean surface temperatures of about 18 ° C in the late Paleocene to over 23 ° C increased during the PETM, and then gradually sank back down to 17 ° C. Various measurements suggest that the investigated region was here near the coast and was heavily influenced by riverine inputs in the late Paleocene. During the PETM, however, strengthened the influence of marine conditions. This is attributed to an increase in sea level. The thermal expansion of sea water by about 5 m due to the increase in the deep-water temperatures by 5-8 ° C may be a reason for this.

Climate models that simulate the early Paleocene with an atmospheric CO2 concentration of 2000 ppm, underestimate the Arctic Ocean surface temperatures in the summer at least 15 ° C for the PETM. The equator -pole temperature gradient is significantly overestimated by the models. The high polar temperatures and the lower equator -pole gradient can not be explained only by higher concentrations of greenhouse gases. In addition, Model simulations show that higher atmospheric heat transport is unlikely to be the cause. Therefore, it is believed that so far not considered in the models physical processes are responsible, in conjunction with a high concentration of greenhouse gases. To a warming of the high latitudes and tropical cooling of polar stratospheric clouds, the increase or the increased ocean mixing may have contributed by hurricanes.

More knowledge about the conditions in the Arctic during the PETM give research on the water cycle. To hydrogen isotope measurements ( Δ18O ) were carried out by n- alkanes. In the transport of air parcels from the tropical and subtropical ocean in higher layers of the atmosphere and towards the poles takes place cooling and condensation. This causes a reduction of the deuterium content. The results of? D measurements in the sediment sample showed that the precipitation in the Arctic compared to present-day conditions had a significantly higher D component. The most likely cause of this is a reduced meridional and / or vertical temperature gradient, which leads to a reduced rainout of subtropical water vapor transport in high latitudes. Increased precipitation in the Arctic regions causes a decrease in salinity. For the assumed increased water intake during the PETM, therefore, is supported by the observation that has increased in this period, the proportion of Dinocysten of organisms that tolerate low salinity, as well as a high seasonal flow entry.

Relevance today

The occurred during the PETM, strong rise in atmospheric carbon dioxide concentration can explain only between one and 3.5 degrees of the observed temperature rise. According to a 2009 study published in Nature is assumed that other, as yet unknown causes or reinforcing feedback. The authors point out that the potential impact of these factors should also be taken into account in the assessment today of future climate change.

Summary

In summary, one can say that the Arctic is characterized during the PETM, including by very high surface temperatures, a decreased temperature gradient between the equator and the poles, high concentrations of greenhouse gases, increased sea levels, an increase in the water supply in very high latitudes and a lower salt content. Can about the reasons for this development thereby in part only be guessed at, so that further research in this area is necessary also to present-day global development to better understand and be able to classify.